"Magnetism of low-dimensional metallic structures Fe/Cr and FeNi3/g-Fe interfaces: spin density wave materials with ferromagnetic interfaces"

1. TITLE, REFERENCE NUMBER

INTAS Project No. 96-0531

Project co-ordinator: Prof. C. Demangeat
This report covers the activity during the period 01.09.1997-29.02.2000.

2. RESEARCH

2.1. Scientific Objectives

1. To investigate, using a wide range of experimental methods, the electronic and magnetic structures of Fe/Cr and FeNi₃/ g-Fe interfaces in multilayer systems. To clarify the role of spin density wave (SDW) structure of a bulk material (bcc Cr, fcc Fe) in the formation of noncollinear moment ordering near the interface as well as in the biquadratic interlayer coupling in the multilayers.
2. To develop the theory within a model Hamiltonian approach for self-consistent calculations of magnetic structure for the systems under consideration, taking into account interface (including surface) roughness and interdiffusion. To develop the theory and to generate the computational schemes for description of noncollinear distribution of magnetic moments. To perform the calculation within an ab-initio approach for a set of ideal systems for determination of phenomenological parameters used in model Hamiltonians. To calculate the noncollinear magnetic structure around defects, such as steps, embedded clusters and pinholes, in low dimensional magnetic systems.
3. To use up-to-date theory for the interpretation of experimental data, obtained by a range of complementary experimental methods on the same (or closely similar) samples. To coordinate the information which can be obtained using various experimental methods. To reveal the influence of non-ideality and structural defects on the observed magnetic properties.

2.2. Research Activities

The research was in accordance with the Work Program.

The series of multilayer samples Al₂O₃/[⁵⁷Fe(t_Fe)/Cr(t_Cr)]_n and MgO/[⁵⁷Fe(t_Fe)/Cr(t_Cr)]_n with different thicknesses t_Fe of Fe and t_Cr of Cr layers were grown by MBE method in Ekaterinburg (Institute of Metal Physics, participant 7) . Investigations of magnetic properties of these samples over the temperature range from the liquid helium to the room temperature were performed using vibrating sample and SQUID magnetometers at the Institute of Metal Physics (Ekaterinburg) and Polarised neutron reflectometer D-17 at the Institute of Laue-Langevin (Grenoble). The measurements of the magnetoresistance were made with four-probe standard technique over the same temperature range. During the last year the activity of Ekaterinburg group was devoted mainly to the study of the microscopic origin and the macroscopic manifestations of the non-collinear ordering in Fe/Cr magnetic multilayers. The team started the study of the influence of the conditions of the growth on the interface structure and magnetic properties. A new series of ⁵⁷Fe/Cr multilayers were grown by MBE, with the substrate temperature being varied from 300K to 510K for different samples in the series. The sample quality was controlled in-situ with Reflection High Energy Electron Diffraction (RHEED) and ex-situ with X-ray Diffraction and Transmission Electron Microscopy. Combined structural investigations including Mossbauer Spectroscopy, Polarised Neutron Reflectometry and Electron Diffraction showed that at the Fe-Cr interfaces there are mixed regions of 5-10 angstroms in thickness having complex atomic and magnetic structures. The magnetisation is distributed non-uniformly within the mixed interface region, and in very specific cases the magnetic moments are in out-of-plane direction.

The Fe/Cr multilayers consisting of continuous Cr layers and discontinuous clustered Fe layers were studied with polarized neutron reflectometry. The extra off-specular neutron scattering due to in-plane atomic and magnetic inhomogeneities within the Fe layers was revealed.

The magnetic field dependence of the ferromagnetic resonance frequencies in Fe/Cr multilayers was investigated experimentally. For the multilayers with strong biquadratic interlayer exchange coupling (IEC) new optical modes of ferromagnetic resonance was discovered.

Spin wave frequencies were calculated for a superlattices with non-collinear magnetic ordering. It was shown that the microwave measurement is an effective method to investigate transport in magnetic multilayers. It was established theoretically that there is a strong correlation between giant magnetoresistance effect and electromagnetic wave losses in magnetic multilayers. Experimental research revealed a microwave analogy of static giant magnetoresistance effect in Fe/Cr multilayers. Investigations of Ekaterinburg group have shown that essential information about magnetic structure can be obtained magneto-acoustic measurements.

The theoretical calculations of non-collinear magnetic ordering in Fe/Cr multilayers were performed through collaborations between Ekaterinburg, St. Petersburg (St. Petersburg State University, participant 5) and Strasbourg (IPCMS, participant 1) groups. A new method based on the Periodic Anderson Model (PAM) is developed for a vector description of the magnetic moments near rough Fe/Cr interfaces. The method allows to perform self-consistent calculations of local magnetic moments and d-electron numbers on a given atomic site for different orientations of the moment relative to the quantization axis. The self-consistent solution with a minimal energy on each site under consideration is used to perform the calculation for the next step. In this approach the noncollinear magnetic structure for stepped Fe/Cr superlattices is obtained. The ground state is always noncollinear and the angle between the magnetic moments of the Fe layers depends on the thickness of the Cr and Fe layers. During the last year self-consistent calculations were performed for superlattices with different step's width at the interface. It was shown that due to frustration in the interface region the ground state corresponds to non-collinear orientation of magnetic moments near steps. This non-collinear ordering penetrates on a large distance from the interface in both Fe and Cr layers and leads to the non-collinear magnetic coupling between Fe layers through the Cr spacer. Angle between magnetic moments of the Fe slabs depends strongly not only on the thickness of the Cr spacer but on the interface structure at atomic scale.

The Mott polarimeter with new fast electronics was completed in St. Petersburg Technical University (participant 6). The new electron energy analyser was tested and calibrated. Final assembly of apparatus was performed. The Mott detector , electron energy analyser, manipulator with a FeNi₃ crystal were mounted on the apparatus sites appropriate to them.

The dependence of the MOKE-signal on the temperature of this crystal was investigated. It was found that this dependence corresponds to similar dependence of bulk magnetisation of the crystal measured using standard magnetometer. The Curie temperature of near- surface area of FeNi₃ corresponds to its bulk value.

Investigations of the magnetisation at the FeNi₃ (110) surface were carried out by Spin Polarised Secondary Electron Emission (SPSEE). It was established, that there is an antiferromagnetic coupling between surface and volume. It was found that such ordering remains only in weak magnetic fields. A transition toward ferromagnetic configuration is obtained with an increase of the magnetic field.

Theoretical calculations allowing to calibrate high voltage conventional detectors of polarisation of electron beam have been performed within small angle scattering approximation which is valid for high energies of electron scattering. This calculations are used for the investigations of surface magnetism by SPSEE method . It was ascertained that adsorption of nonmagnetic substances (oxygen, nitrogen, carbon oxide) on the surface of FeNi₃ destroyed the antiferromagnetic coupling between the surface and the bulk crystal. This may be connected with the structural reconstructions of the surface which leads to the change of magnetic properties. The Angle Resolved Spin Polarized Inverse Photoemission techniques was used for study of the spin splitting of the unoccupied electron states in FeNi₃ for different angles of incidence of the electron beam. On the base of these measurements the dispersion dependencies for the surface states of FeNi₃ (110) were derived.

V. Uzdin (St. Petersburg State University) and C.Demangeat (IPCMS, Strasbourg) performed a relativistic calculations of the X-ray magnetic circular dichroism (XMCD) for the Fe and Ni L_2,3 absorption spectra in ordered FeNi₃ alloy within Full Potential Linear Muffin Tin Orbital (FPLMTO) method. These calculations are ready for the interpretation of dichroism experiments.

Daresbury Laboratory, Synchrotron Radiation Department (participant 3) has developed the off-line facilities available for performing spin polarised photoemission experiments using synchrotron radiation.. These comprise a UHV chamber equiped with turbomolecular-, titanium sublimation- and ion-pumps, LEED optics, an argon ion gun, an electron gun, evaporators suitable for transition metals and a microMott polarimeter mounted at the exit aperture of a hemispherical electron energy analyser. In addition, a suitable sample holder with liquid nitrogen cooling and sample exchange capabilities has been built. These facilities allow us to grow ultrathin transition metal films and to characterise them using spin polarised secondary electron spectroscopy and spin polarised Auger electron spectroscopy.

Group from Regensburg University (participant 4) has focussed their studies on in-situ-magnetometry (AGM) measurements of epitaxial Fe/Cr/Fe trilayer systems with varying surface topography. Structural investigations have been performed with RHEED and STM. A new experimental setup allows both quantitative magnetic and structural characterization simultaneously during film growth.

The evolution of the integral magnetic moment during Cr deposition at room temperature on Fe(001) was investigated for samples with different surface structure: smooth surfaces are related to a strong decrease of the integral moment by 5.2 m_B / 2D unit cell for a 5ML Cr film, whereas rough surfaces show no change of integral moment at all. Intermediate values of 1.1 .. 1.8 m_B are observed in most cases, when surface structure is good, but not ideal. According to STM data these samples show a surface step density of 1 atomic step per 5 lateral atomic distances. Tight binding calculations (Strasbourg group) of the local spin configuration for Cr on vicinal Fe surfaces with similar step densities (e.g. Fe(109) ) show substantial magnetic frustration effects near step edges and a reduction of the average magnetic moment per atom. However, for a quantitative comparison of the experimental values with the theoretical case, interdiffusion at the Fe/Cr interface has to be taken into account.

In-situ-magnetometry studies were performed for Fe grow on top of stepped Cr /Fe films as well. For the initial Fe growth, no change of magnetic moment or shape of the hysteresis curve is observed. Only after 4 .. 6 ML a decrease of remanence is observed which is due to AF coupling to the bottom Fe layer at Cr thickness of e.g. 10 A. This behaviour is attributed to a multi domain configuration in the initial Fe layer, caused by the alternating step heights of the underlying Cr and the strong coupling of the Fe moments to the Cr spins. Such a behaviour was predicted before in real space tight binding calculations by Strasbourg and Saint-Petersburg groups. Depending on the specific topography of the Cr surface a transition to a single domain configuration is observed for 4..6 ML Fe thickness.

It is now well known that magnetic and structural properties of thin magnetic films are very sensitive to the sample preparation conditions. Consequently, for systematic investigation of these systems it is necessary to control the process of the epitaxial growth of Fe (FeNi alloy) on different substrates and to clarify in particular the magnetic behavior of very thin Fe films, because the initial stage of the growth can determine the properties of the sample. Such investigations of single crystal Fe films grown on InAs(100) by molecular beam epitaxy, evolution of the ferromagnetic phase of ultrathin Fe films grown on GaAs(100), micromagnetic structures and microscopic magnetization-reversal processes in epitaxial Fe/GaAs(001) were performed in the Thin Film Magnetism group led by Dr. J.A.C Bland in Cambridge, UK (participant 2). During last year this investigations were continued by group of prof. Bayreuther from Regensburg. They investigated the morphology, magnetic moment and in-plane magnetic anisotropy of ultrathin bcc Fe(001) films deposited at room temperature by MBE on ZnSe epilayers grown on GaAs (001) single crystal. The growth mode and structure have been determined in situ by means of RHEED and Auger electron spectroscopy (AES). The magnetic properties were characterized ex situ by AGM, SQUID magnetometry and conversion Mossbauer spectrometry (CEMS). It was shown that the Fe growth is epitaxial, three-dimensional and the coalescence of the islands occurs around 7 monolayers (ML). In agreement with SQUID results, CEMS measurements indicate no reduction of the Fe magnetic moment compared to the bulk value even for the first Fe MLs. Determination of in-plane anisotropy constant as function of the Fe thickness shows a strong interface-induced uniaxial in-plane magnetic anisotropy which leads to a continuous evolution from pure uniaxial anisotropy _ magnetic easy axis along [110] direction – for thickness below 10 ML to the pure bulk cubic Fe anisotropy above 40 ML.

The magnetic interactions at the interface and the effects of the ferromagnetic substrate on the magnetic ordering of submonolayer coverages of magnetic overlayers was investigated in Mn/fcc Co(001)/Cu(001) during last year by Cambridge group. This system represents an ideal comparison for studies of FM/AF interaction effects. They found a striking sensistivity of the surface structure and magnetic properties of the interface structure and magnetic properties in ultrathin fcc Co/Cu(001) structures to the deposition of submonolayers of Mn. The magnetic properties correlate directly with the stabilisation of a two-dimensional c(2x2) MnCo surface alloy. Corresponding to the two structural regions defined by the absence and stabilisation of the surface alloy respectively, two magnetic phases of Mn overlayers were identified; a ferromagnetic phase due to interfacial coupling up to a monolayer of Mn, and a nonmagnetic phase above 1 ML of Mn. It was concluded that the Kerr signal, magnetic anisotropy strengh and coercivity are correlated with the stabilisation of the MnCo surface alloy and growth conditions.

Parallel to the above study the group of Dr. J.A.C. Bland from Cambridge investigated the dynamic of magnetisation reversal in thin polycrystalline Ni₈₀Fe₂₀ films. They have demonstrated the dimension (thickness)-invariance of the dynamic scaling behaviour. According to the theory this invariance reveals that the dynamic magnetisation reversal mechanism is identical independently of thickness.

The group from Saint-Petersburg State University (Dr. V. Uzdin) in co-operation with scientists from Ekaterinburg (Dr. N.Yartseva) and Strasbourg (Dr. C.Demangeat)) worked towards the theoretical description of magnetic structure of low-dimensional magnetic systems and interpretation of different experimental results. A new approach for the interpretation of spin-resolved photoemission and magnetic dichroismspectra is developed. It includes a special algorithm for modelling epitaxial growth of overlayers with different roughness together with self-consistent calculations of the magnetic moment distribution within a Periodic Anderson Model (PAM). Then the magnetic signature of the photoemission signal is expressed in terms of a weighted averages of the individual magnetic moments. This approach was used for the interpretation of the experimental data obtained on Fe/Cr/Fe trilayers using synchrotron facilities in Daresbury.

A method of self-consistent calculation of the magnetic ordering in low-dimensional metallic structures in the presence of external magnetic field was developed on the basis of PAM in Hartree-Fock approximation with real space recursion. Multiple self-consistent solutions for the magnetic moment distribution at the interface region leads to the hysteresis-like dependence of average magnetic moment on the value of the applied field. It is shown that in dependence on the structure of interface region the shape of the hysteresis loop calculated separately for Fe and for Cr atoms essentially changes.

A mechanism, responsible for the non-Poisson growth of islands of metals on metal substrate (in particular Cr on Fe) was suggested. It is connected with the confinement of the electrons with one spin projection inside the quantum wells (QW) formed by islands. Oscillations of the energy of these electrons with the width of the wells lead to the suppression of the formation of islands with definite thickness. This effect is especially important for the submonolayer coverage and for the initial phase of the epitaxial process. Analogy between QW-theory for the oscillations of exchange coupling in metallic magnetic multilayers and the theory of non-Poisson islands formation was found.

The origin of the phase shifts in the oscillatory behaviour of IEC of FM/NM/FM trilayers with addition of Ag impurities into the FM layer is explained within the framework of a quantum well (QW) model. It is shown that Ag impurities induce shift of the Fermi level relative to the bottom of the band and allow the observation of short-range oscillations of the IEC. This is in contrast to studies involving the increase of the layer thickness where only the long-range period is observed due to “aliasing” effect. On the basis of the simplified infinite QW-theory the difference between phase shift in symmetrical and asymmetrical trilayers have been analysed.

Group of Dr. V. Uzdin (St. Petersburg State University) performed the calculations of distribution of d-electron magnetic moments within the PAM for Fe/Cr superlattices with various interface roughness. Special random algorithms were developed for the modelling of stepped interfaces with different average size of the steps as well as for the modelling of interface alloying. Self-consistent calculations of magnetic moment distribution for alloyed interfaces show strong correlation with hyperfine fields on Fe nuclei, measured by the Mossbauer spectroscopy. It allows to connect the hyperfine field with specific environment of the interfacial Fe atoms and leads to the essential correction of the empirical approach for the interpretation of CEMS spectra. New criterion for the testing of smothness of the interface using Mossbauer data is suggested.

The group of Strasbourg is involved in the determination of the electronic and magnetic structure of low-dimensional magnetic systems such as metallic surfaces, thin overlayers, films and superlattices. Theoretical description of these systems was performed within the framework of model Hamiltonians and ab-initio codes. Ab-initio codes are presently restricted to systems presenting a few number of in equivalent atoms whereas the influence of space defects - steps at the surface and interface, roughness and embedded clusters near interfaces, pinhole defects - on the magnetic structure of Low Dimensional Magnetic Systems (LDMS) was investigated through Hubbard model (HM).

In the first publication on Fe/Cr dated back 1990 a two-layers period of the oscillatory behavior of the interlayer exchange coupling between Fe slabs separated by a Cr spacer was obtained within HM. This calculation was performed by assuming a perfect (abrupt) interface between Fe and Cr. Later on it was shown that "experimentally" the interface is not ideal and that interdiffusion and roughness should be taken into account. As an example, M. Freyss (PhD student) has discussed the effect of alloying on the interlayer exchange coupling and the stability of the non-collinear configurations within Hubbard model. In 1994 a collaboration between V. Uzdin and C. Demangeat on Fe/Cr has started and some of the results concerning the Project were mentioned above.

C. Demangeat at Strasbourg has determined the electronic and magnetic structure of the surface of the ordered B2 FeCr alloy within Tight-Binding Linear-Muffin-Tin-Orbital (TB-LMTO) ab-initio method. This alloy is ferromagnetic in the bulk but presents magnetic reconstruction at the surface. Because the local density approximation (LDA) does not give the real ground state of bcc Fe and leads to a paramagnetic ground state for Cr he used the TB-LMTO version with gradient corrections (GGA). 2 versions of GGA have been tested (Langreth-Mehl-Hu and Perdew-Wang). The GGA-Langreth-Mehl-Hu has given reasonable results for bulk Cr so that this version of the GGA was choosen. He investigated the (001) and (111) crystallographic surfaces. The (011) has not really converged up to now so that for a communication to the EMMA'98 conference at Zaragoza he have restricted to (001) and (111). Magnetic reconstruction is always present at the surfaces. For the (001) surface the c(2x2) magnetic configuration is found to be the ground state. For the (111) surface the ground state is found to be an antiferromagnetic coupling between surface and subsurface atoms. At this (111) surface only in-plane "frustrated" antiferromagnetic configurations are present within a fully constrained collinear approach. It is therefore pertinent to determine the ground state within a fully unconstrained approach as developed by V. Uzdin for the case of Fe/Cr multilayers.

The question of the stability of the compact Cr trimer has appeared in the case of Cr at the (111) surface of the B2 FeCr alloy. In this case, in a constrained collinear configuration the antiferromagnetic configurations are frustrated. H. Cheng and L.S. Wang (Phys. Rev. Lett. 77 (1996) 51) have shown that the solution obtained presents a very strange behavior as compared to unconstrained solutions obtained within an Heisenberg like Hamiltonian (see for example H. Kawamura, J. Phys. Condens. Matter 10 (1998) 4707): the ground state is found to be a canted ordered state. Very recently, T. Oda et al (Phys. Rev. Lett. 80 (1998) 3622) using a fully unconstrained approach have shown that the ground state of the small free standing Fe clusters is slightly non-collinear.

From all that it appears necessary to consider a fully unconstrained approach for the determination of free Cr trimers and supported Cr trimers. S. Uzdin, V. Uzdin, C. Demangeat have determined the ground state of the Cr-trimers supported on nonmagnetic metal substrate by recursion method within Anderson model. The values of the moments are enhanced relatively to bulk bcc Cr due to the reduction of the coordination number. Angles between the moments depend on the relations between hopping parameters V_ij, determined by the interatomic distance in the cluster. Systematic calculations of the ground state for different values of parameters V₁₂=V₁₃ and V₂₃ were performed. For V₁₂<<V₂₃ ground state corresponds to moments on the atoms 2 and 3 with opposite direction , whereas the moment on atom 1 is perpendicular to them. For V₁₂=V₂₃ the angle between each pair of moments equals 2p/3 and the total moment of the trimer is zero. A decrease of V₂₃ versus V₁₂ leads to collinear state with a moment on the atom 1 antiparallel to the moments on second and third. Calculation in external magnetic field reveals the co-existence of two self-consistent states with essentially different total magnetic moments. In weak field these solutions are very close in energy whereas with the increase of the field the state with larger moment is stabilized. For the Fe trimer another dependence versus hoping parameters of the angles between magnetic moments was obtained. Now the calculations performed for other 3d-trimers. This work was possible due to the visit of a student from St. Petersburg group to Strasbourg, where in cooperation with Dr. C. Demangeat he developed the code and performed the calculations during the summer 1999.

Another problem investigated by the group from St. Petersburg State University in cooperation with IPCMS group during visit of Dr. V.Uzdin in Strasbourg is the ab initio calculations of Fe/V superlattices under hydrogenation. Electronic and magnetic structures of Fe/V superlattices with and without hydrogen in the vanadium spacer were investigated using a relativistic full-potential linear muffin-tin orbital method. Short-range induced spin polarization in V as well as reduced Fe polarization at the Fe/V interface were obtained. The value of the magnetic moment induced on the V atoms depends strongly on the distortion caused by the lattice mismatch and hydrogen loading whereas the total moment of the Fe and V interface layers remains almost unchanged. Hydrogenation of the V spacer leads to the decrease of the interface magnetic moment on the V atoms and to a reduction of the density of states (DOS) at the Fermi level. A low DOS could be one of the reason for the increase of the resistivity of the sample under hydrogen loading and leads to the disappearance of the antiferromagnetic exchange coupling in the Fe/(VH) superlattices for large hydrogen concentration. Doping the V film by a gold monolayer increases the DOS at the Fermi level and could recover the antiferromagnetic coupling.

2.3. Scientific Results

Scientific papers and presentations which have been resulted directly from this project are listed below.

List of scientific papers

1. J.Reinmuth, F.Passek, V.N.Petrov, M.Donath, V.Popesscu and H.Ebert Spin-dependent local density of empty electronic states in FeNi₃Phys. Rev. B 56 (1997) 12893.
2. Y. B. Xu, E. T. M. Kernohan, M. Tselepi , J. A. C. Bland, and S. Holmes Single crystal Fe films grown on InAs(100) by molecular beam epitaxy, Appl.Phys.Lett. 73 (1998) 399.
3. Y. B. Xu, E. T. M. Kernohan, D. J. Freeland, M. Tselepi, and J. A. C. Bland, Evolution of the ferromagnetic phase of ultrathin Fe films grown on GaAs(100)-4? 6, Phys.Rev.B. 58 (1998) 890.
4. J. A. C. Bland, C.Daboo, M.Patel, T.Fujimoto, J.Penfold, Interface selective magnetometry of FeNi/Cu/Co trilayer spin-valve structures, Phys. Rev.B. 79 (1998) 5290
5. E.Gu, E.Ahmad, J.A.C.Bland, L.M.Brown, M.Ruhrig, A.J.McGibbon, J.N.Chapman Micromagnetic structures and microscopic magnetization-reversal processes in epitaxial Fe/GaAs(001) elements, Phys. Rev. B 57 (1998) 7814.
6. B.-Ch. Choi, P.J. Bode, and J.A.C. Bland, Formation of a two-dimensional c(2? 2) Mn-Co(001) ferromagnetic surface alloy on Cu(001), Phys. Rev. B 58 (1998) 5166.
7. L.Pizzagalli, M. Freyss,G. Moraitis, D. Stoeffler, C. Demangeat, H. Dreysse, A. Vega, S.Miethaner, G. Bayreuther, Spin Polarization at Fe/Cr Interfaces, J. Appl. Phys. 81 (1997) 4347.
8. V.N.Petrov, M. Landolt, M.S.Galactionov, Yu.A. Mamaev, A new Mott polarimetr for spin polarized electron spectroscopy, Proceedings of Low Energy Polarized Electron Workshop , St.Petersburg, September 2-5, 1998, p. 148-151.
9. V.V.Ustinov, A.B.Rinkevich, L.N.Romashev, Microwave current-perpendicular-to-plane giant magnetoresistance of Fe/Cr superlattices, J. Magn. Phys. Soc.Jap., 23 (1999) 114.
10. V.V.Ustinov, A.B.Rinkevich, L.N.Romashev, Microwave magnetoresistance of Fe/Cr multilayers in current-perpendicular-to-plane geometry, JMMM, 198-199 (1999) 82.
11. V.I.Okulov, E.A.Pamyatnykh, V.V.Slovikovskaya, V.V.Ustinov, Theory of acoustic magnetic resonance in the surface elastic wave absorption by metal multilayers, JMMM, 198-199 (1999) 608.
12. V.M.Uzdin, A.Mokrani, C.Demangeat, N.S.Yartseva, Noncollinear magnetic structure of Fe/Cr interfaces, JMMM, 198-199 (1999) 471. download full text (82 Kb)
13. V.M.Uzdin, D. Knabben, F.U. Hillebrecht, and E. Kisker Structure of Cr overlayers on Fe surfaces. A new approach for interpretation of spin-resolved photoemission and magnetic dichroism spectra. JMMM, 198-199 (1999) 680. download full text (90 Kb)
14. V.M.Uzdin, N.S.Yartseva, L.A.Adamowicz, Phase shift of exchange coupling oscillations in magnetic multilayers, JMMM, 203 (1999) 283. download full text (110 Kb)
15. V.M.Uzdin, N.S.Yartseva, Fe/Cr interface magnetism in the external magnetic field, JMMM, 203 (1999) 280. download full text (118 Kb)
16. V.M.Uzdin, D. Knabben, F.U. Hillebrecht, and E. Kisker Magnetic dichroism and spin-resolved photoemission from rough interfaces. Phys. Rev. B59 (1999) 1214. download full text (0,2 Mb)
17. V.M.Uzdin, N.S.Yartseva, S.V.Yartsev, Non-collinear magnetism of Fe/Cr films and multilayers, JMMM, 196-197 (1999) 70.download full text (80 Kb)
18. V.M. Uzdin, Quantum well states in magnetic multilayers and non-Poisson island formation during epitaxial growth. JMMM, 196-197 (1999) 85. download full text (75 Kb)
19. M. Freyss, D. Stoeffler, S. Miethaner, G. Bayreuther, H. Dreysse Interfacial Interdiffusion and Magnetic Properties of Transition Metal Based Materials, in: "Current Problems in Condensed Matter: Theory and Experiment", edited by Moran-Lopez. Plenum Press, New York, 1998. P. 209
20. F. Amalou, M. Benakki, A. Mokrani and C. Demangeat Surface dependence of the magnetic configurations of the ordered B2 FeCr alloy , Eur. Journal B9 (1999) 49.
21. T.P. Krinitsina, E.A. Kravtsov, V.V. Lauter-Passiouk, H.J. Lauter, V.V.Popov, L.N. Romashev, V.A. Tsurin A.M. Burchanov and V.V. Ustinov, Morphology of crystallites and magnetic structure of non-collinear Fe/Cr multilayers, JMMM 203 (1999) 181.
22. S.Uzdin, V.Uzdin, C.Demangeat, Magnetic trimer on non-magnetic substrate: From frustration towards non-collinearity, Europhys. Lett., 47 (1999) 556.download full text (175 Kb)
23. A.B. Drovosekov, O.V. Jotikova, N.M. Kreines, V.F. Meshcheryakov, M.A. Milyaev, L.N. Romashev, V.V. Ustinov, D.I. Kholin, The FMR inhomogeneous modes in [Fe/Cr]_n superlattices with non-collinear magnetic ordering, JETP, 116 (1999) 1817
24. S.Ostanin, V.M.Uzdin, C.Demangeat, J. Wills, M.Alouani and H. Dreysse, Effect of hydrogen on the interlayer exchange coupling in Fe/V superlattices, Phys. Rev. B 61 (2000) 4870.download full text (0,3 Mb)
25. A.B. Rinkevich, L.N. Romashev, V.V. Ustinov, Microwave magnetoresistance of Fe/Cr multilayers, JETP, in press.
26. N.S. Yartseva , S.V. Yartsev , V.M. Uzdin , C.Demangeat, Interface defects and formation of noncollinear magnetic ordering in Fe/Cr multilayers, accepted to Comp. Mat. Sci.
27. V.M. Uzdin, Distribution of magnetic moments and hyperfine fields for Fe/Cr multilayers with different interface roughness, accepted to Comp. Mat. Sci.
28. S.Uzdin, V.Uzdin, C.Demangeat, Non-collinear structure of Cr trimer on the surface of non-magnetic metals, accepted to Comp. Mat. Sci.
29. N.G. Bebenin, V.V. Ustinov, Spin wave frequencies in magnetic superlattice with biquadratic exchange, accepted to Phys.Met.Metallogr. (in Russian)
30. E.Reiger, G.Garreau, E. Vogl, M.Ernst, M.Zolfl, F.Bensch, S.Bauer, H.Preis, G.Bayreuther, Magnetic moments and anisotropy in ultrathin epitaxial Fe films on ZnSe(001), accepted to J. Appl. Phys.
31. V.M.Uzdin, W. Keune and H. Schrцr, Fe /Cr Interface Magnetism: Correlation between Hyperfine Fields and Magnetic Moments, submitted to Phys. Rev. B
32. V.N.Petrov, M.S.Galaktionov, K.N.Komlev, Y.A.Mamaev, AFM and FM coupling on the surface of FeNi₃, submitted to "Physica tverdogo tela" (in Russian)
33. V.I. Okulov, E.A. Pamyatnykh, V.V. Slovikovskaya and V.V. Ustinov, Theory of imperfect electron acoustic absorption in the magnetic layers and multilayers with interfaces, in preparation.

List of abstracts

1. V.N.Petrov, M.Landolt, M.S.Galaktionov, Yu.A.Mamaev, New method of calibration of ”conventional” Mott polarimeters. Abstract Book of the 17^th European conference on Surface Science, (ECOSS 17), (September 16-17), Enschede, The Netherlants, 1997
2. V.N.Petrov, M.S.Galaktionov, New Compact 60 kV Mott Polarimeter. - Abstract Book of the 3^rd International Symposium on Metallic Multilayers held jointly with the EMRS Symposium on Magnetic Ultrathin Films and Ultrathin Film Nanostructures (MML’98), (June14-19, 1998) Vancouver, British Columbia, Canada, 1998, p.277.
3. F.Schedin, L.Hewitt, P.Morrall, G.Thornton, V.N.Petrov, Exchange splitting of surface states on FeNi₃ alloy. Abstract Book of the 3^rd International Symposium on Metallic Multilayers held jointly with the EMRS Symposium on Magnetic Ultrathin Films and Ultrathin Film Nanostructures (MML’98), (June14-19, 1998) Vancouver, British Columbia, Canada, 1998, p.363
4. V.V.Ustinov, A.B.Rinkevich, L.N.Romashev, Microwave magnetoresistance of Fe/Cr multilayers in current-perpendicular-to-plane geometry. - Abstract Book of the 3^rd International Symposium on Metallic Multilayers held jointly with the EMRS Symposium on Magnetic Ultrathin Films and Ultrathin Film Nanostructures (MML’98), (June14-19, 1998) Vancouver, British Columbia, Canada, 1998, p.51.
5. V.M.Uzdin, A.Mokrani, C.Demangeat, N.S.Yartseva, Noncollinear magnetic structure of Fe/Cr interfaces. - Abstract Book of the 3^rd International Symposium on Metallic Multilayers held jointly with the EMRS Symposium on Magnetic Ultrathin Films and Ultrathin Film Nanostructures (MML’98), (June14-19, 1998) Vancouver, British Columbia, Canada, 1998, p.192.
6. V.M.Uzdin, D. Knabben, F.U. Hillebrecht, and E. Kisker Structure of Cr overlayers on Fe surfaces. A new approach for interpretation of spin-resolved photoemission and magnetic dichroism spectra. - Abstract Book of the 3^rd International Symposium on Metallic Multilayers held jointly with the EMRS Symposium on Magnetic Ultrathin Films and Ultrathin Film Nanostructures (MML’98), (June14-19, 1998) Vancouver, British Columbia, Canada, 1998, p.279.
7. V.V.Ustinov, A.B.Rinkevich, L.N.Romashev, High-frequency analog of giant magnetoresistance effect in Fe/Cr multilayers. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NМMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p.18.
8. V.A.Tsurin, L.N.Romashev, V.V.Ustinov, Mossbauer study of atomic environment and orientations of Fe atomic magnetic moments in interface regions of non-collinear Fe/Cr multilayers. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NМMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p.31.
9. L.N.Romashev, A.M.Burchanov, V.V.Ustinov, A.A.Yuvchenko, Magnetic Fe/Cr superlattices as new materials for magnetic field sensors. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NМMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p..32.
10. A.V.Semerikov, T.P.Krinitsina, V.V.Popov, A.M.Burchanov, M.B.Mitberg, Structure of Fe/Cr superlattices grown on single crystal Al₂O₃ and MgO substrates. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NМMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p.33-34.
11. V.V.Ovchinnicov, L.N.Romashev, Monte-Carlo calculation of configurations of ⁵⁷Fe atomic local environment and interface concentration in ⁵⁷Fe/Cr multilayers. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NМMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p..35-36.
12. V.V.Lauter-Passiouk, H.J.Lauter, E.A.Kravtsov, M.A.Milyaev, L.N.Romashev, V.V.Ustinov, Magnetic ordering in Fe/Cr multilayers from low angle polarized neutron diffraction. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NМMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p.37.
13. V.M.Uzdin, N.S.Yartseva, Magnetic structure of interfaces in Fe/Cr multilayers. - Abstract Book of the XVI International Symposium ”New magnetic materials for magnetoelectronics (NMMM’98)”, (June 23-26, 1998), Moscow University, Russia, 1998, p.38-39.
14. V.M.Uzdin, N.S.Yartseva, Fe/Cr interface magnetism in the external magnetic field. – Abstract Book of the Magnetism of Nanostructured Phases Conference (MNP), San Sebastian, Spain, (4-6 September 1998), p. 174.
15. V.M.Uzdin, N.S.Yartseva, L.A.Adamowicz, Phase shift of exchange coupling oscillations in magnetic multilayers. – Abstract Book of the Magnetism of Nanostructured Phases Conference (MNP), San Sebastian, Spain, (4-6 September 1998), p.148.
16. T.P. Krinitsina, V.V. Lauter-Passiouk, H.J. Lauter, L.N. Romashev, V.A. Tsurin and V.V. Ustinov, Morphology of crystallites and magnetic structure of non- collinear Fe/Cr multilayers. - Abstract Book of the Magnetism of Nanostructured Phases Conference (MNP), San Sebastian, Spain, (4-6 September 1998), p. 98.
17. F.Amalou, M. Benakki, A. Mokrani, C. Demangeat and G. Moraitis Non ferromagnetic solutions at the surface of B2 FeCr alloy Abstract Book of the European Magnetic Materials and Applications Conference (EMMA’98), Zaragoza (SPAIN), (9-12 September 1998), p.37
18. V.M.Uzdin, N.S.Yartseva, S.V.Yartsev, Non-collinear magnetism of Fe/Cr films and multilayers. - Abstract Book of the European Magnetic Materials and Applications Conference (EMMA’98), Zaragoza (SPAIN), (9-12 September 1998), p. 52
19. V.M. Uzdin, Quantum well states in magnetic multilayers and non-Poisson island formation during epitaxial growth. Abstract Book of the European Magnetic Materials and Applications Conference (EMMA’98), Zaragoza (SPAIN), (9-12 September 1998), p.58
20. V.N.Petrov, M.Landolt, M.S.Galaktionov, Yu.A.Mamaev, A new high-energy Mott polarimeter for spin polarized electron spectroscopy. Abstract Book of the Low Energy Polarized Electron Workshop (LE’98), ), satellite meeting of 13^th International Symposium on High Energy Spin Physics (SPIN’98), (September 2-5), St. Petersburg, Russia, 1998.
21. Yu.P.Yashin, Yu.A.Mamaev, A.Ambrazhei, Polarised Electron Photocatody research at SPES Laboratory. Abstract Book of the Low Energy Polarized Electron Workshop (LE’98), satellite meeting of 13^th International Symposium on High Energy Spin Physics (SPIN’98), ), satellite meeting of(September 2-5), St. Petersburg, Russia, 1998.
22. V.V. Ustinov, Nanostructure and non-collinear magnetism in Fe/Cr superlattices. - Abstract Book of the VIII International Seminar Dislocation Structure and Mechanical Properties of Metals and Alloys (DSP NM-99), Ekaterinburg, Russia, (16-20 March 1999), p. 10.
23. A.B. Drovosekov, O.V. Jotikova, N.M. Kreines, D.I.Kholin, V.F.Meshcheryakov, M.A. Milyaev, L.N. Romashev and V.V. Ustinov, The FMR inhomogeneous modes in [Fe/Cr]_n superlattices with non-collinear magnetic ordering. - Abstract Book of the Moscow International Symposium on Magnetism, Moscow, Russia, (20-24 June 1999), p. 106.
24. V.V. Ustinov, I.D. Lobov, V.M. Maevskii and L.N. Romashev, Magnetooptical intensity effect in Fe/Cr superlattices. - Abstract Book of the Moscow International Symposium on Magnetism, Moscow, Russia, (20-24 June 1999) p. 108.
25. V.N. Petrov, M.S. Galaktionov, K.N. Komlev, Yu.A. Mamaev, "FM - AFM transition on the surface of FeNi3", Book of Abstracts of the 18-th European Conference on Surface Science, (ECOSS 18), Vienna, Austria, 1999, Th-P-166.
26. N.V. Kourtina, E.A. Kravtsov, M.A. Milyaev, A.V. Semerikov, V.V. Ustinov Definition of structure Fe/Cr superlattices with x-ray reflectometry, The IV International scientific Conference of Young Scientists and Specialists, Dubna, Russia, February 2000.
27. V. Lauter-Passiouk, H.J. Lauter, B. Toperverg, O. Nikonov, E. Kravtsov, M.A. Milyaev, L. Romashev, V. Ustinov, Interface formation and magnetic ordering in hybrid multilayers Fe/Cr, International Workshop "Polarized Neutrons for Condensed Matter Investigations" Gatchina, St.Petersburg, Russia, June 20-25, 2000.
28. V.V. Ustinov, A.B. Rinkevich, L.N. Romashev, High-frequency analogues of giant magnetoresistance in magnetic superlattices, 8^th European Magnetic Materials and Applications Conference (ЕММА-2000), Kiev, Ukraine, June 2000.
29. L.N. Romashev, A.V. Semerikov, M.A. Milyaev, E.A. Kravtsov, N.V. Kourtina, A.M. Burkhanov, T.P. Krinitsina, V.V. Popov, Influence of growth temperature on fine structure, magnetic, and magnetoresistive properties of Fe/Cr multilayers, 8^th European Magnetic Materials and Applications Conference (ЕММА-2000), Kiev, Ukraine, June 2000.
30. V. Lauter-Passiouk, H.J. Lauter, B. Toperverg, O. Nikonov, E. Kravtsov, T. Krinitsina, M. Milayev, V. Popov, L. Romashev, V. Ustinov, Influence of fine structure on magnetic off-specular neutron scattering in Fe/Cr multilayers, 8^th European Magnetic Materials and Applications Conference (ЕММА-2000), Kiev, Ukraine, June 2000.
31. V.V. Ustinov, M.A. Milyaev, L.N. Romashev, T.P. Krinitsina, E.A. Kravtsov, V.V. Lauter-Passiouk, H.J. Lauter, Magnetization in-plane anisotropy of biquadratic exchange coupled Fe/Cr superlattices, International Conference on Magnetism (ICM 2000), Recife, Brazil, August 2000.

2.4 Applications

New experimental equipment and computer codes developed within the frame of the Project will be used in future for investigation of other low-dimensional magnetic systems. Theoretical calculations provided new information, which can be used for the control of the interface quality and for fabrication of nanostructures with required properties.

3. MANAGEMENT

3.1 Meetings and visits

The number of scientists and the number of person days, which were supported directly from INTAS-project, are shown in the brackets.

1. V.Ustinov*, E. Kravtsov * (Ekaterinburg) and V. Uzdin* (St.Petersburg) visited Institute Laue-Langevin (Grenoble) to perform polarised neutron experiments on Fe/Cr multilayers with French and German collaborators (experiment No. 5-51-82, 6-11 November, 1997)
2. V.Uzdin visited IPCMS (Strasbourg) for discussion about the code for the calculation of Noncollinear structure of Fe/Cr interface ( 11-23 November, 1997)
3. V.Uzdin, C. Demangeat* visited Regensburg University for presentation of preliminary results of collaboration (11-15 December 1997).
4. G.Bayreuther*, J. A.C. Bland*, V.Ustinov*, and V.Uzdin* visited Vancouver, British Columbia, Canada for presentation of results of investigations on MML-98 conference and for common discussion about future activity. V. Uzdin also presented the results obtained by second St. Petersburg group (V.Petrov) (14-24 June 1998)
5. V.Ustinov* (Ekaterinburg) visited St. Petersburg to discuss the plan of collaboration 10-20 August, 1997)
6. V.Uzdin*, V.Ustinov*, T.Krinisina*, N.Yartseva* visited San-Sebastian (Spain) for presentation of results of investigations on MNP-98 conference and for common discussion about future activity (04-06 September 1998).
7. C. Demangeat*, J. A.C. Bland*, and V.Uzdin*, N.Yartseva*, N.Bebenin* visited Zaragoza (Spain) for presentation of results of investigations on EMMA-98 conference and for common discussion about future activity (09-13 September 1998).
8. V. Uzdin visited IPCMS, Strasbourg (01-14 October) for discussion about calculation of magnetic structures using FP LMTO code.
9. G.Baureuther*, C.Demangeat*, J.A.C. Bland, V.Uzdin, V.Ustinov, V.Petrov took part in the meeting in Regensburg (16-18 October 1998) which was devoted to the scientific results of the first year activity within the frame of INTAS-project.
10. C.Demangeat, V.Uzdin* took part in the international workshop “Magnetism and Electronic structure” 17-18 December 1998, where results of investigations were reported.
11. V.Uzdin* visited IPCMS, Strasbourg (February-August 1999) for common with C.Demangeat calculations of low-dimensional magnetic structures within semi-empirical tight-binding and ab-initio FP LMTO methods.
12. V. Petrov* visited Ekaterinburg (16-28 March) for discussion about experimental equipment.
13. N.Yartseva* visited Strasbourg for presentation of results of investigations on EMRS-99 conference and for common discussion about future activity (03-06 June 1999).
14. S. Uzdin visited IPCMS, Strasbourg (June-August 1999) for calculations of non-collinear structures of small Fe and Cr clusters supported on the surface of non-magnetic metals.
15. All groups took part in the second INTAS-workshop "Magnetic nanostructures: intimate correlation between electronic, magnetic and optical properties and their growth" in St. Petersburg, 29 .09.99 - 02.10.99. List of participants and scientific program are attached.
16. V. Petrov visited Zurich University (Switzerland) for testing of Mott-detector developed within the frame of the project. (02-15 October 1999)

* - visit was supported from other funds.

3.2. Time Schedule.

The time planning was in accordance with the work program.