INTAS Project No 01-0386

"Tunning of exchange coupling with hydrogen: playground for study of low-dimensional magnetism"

Periodic report

Project co-ordinator: Prof. Dr. H. Zabel
This report covers the activity during the period 01.06.02-01.06.03.

1. RESEARCH

1.1. Overview of Research Activities
Following work specified in the Work Programme has been carried out by the teams participating in the project:

- Growth of Fe/V multilayers with high epitaxial quality in which loading of the hydrogen into V spacer leads to the variation of exchange interaction between magnetic layers; Several Fe/Cr, Fe/V, Fe0.82Ni0.18/V multilayers were grown by CR1, CR7. The Cr/V multilayers with thick V layers were grown by CO.

- Investigation of chemical structures, magnetic structures, short range order and their evolution with hydrogen uptake, using different complimentary experimental methods. Different teams took part in this activity using different experimental methods: Polarized Neutron Reflectometry (CO, CR10), MOKE (CO, CR1), Mossbauer Spectroscopy (CR2, CR6), Magnetometer (CO,CR1,CR7), dc-magnetoresistive, micro-waves experiments (CR7) etc. Some experiments were performed by CO and CR1 with hydrogen loading. Interpretation of these experiments was performed on the basis of the theory developed in cooperation with CR6 team.

- New device for in situ study of surface and interface magnetic properties using Spin Polarised Secondary Electron Emission (SPSEE), Spin Polarised Auger Electron Spectroscopy (SPAES), was developed and tested by CR9 team. First results were obtained for V overlayers on FeNi3. In the interpretation of these data, which gave element specific information about magnetic moments on Fe, Ni and V atoms, took part CR4 and CR6.

- In the development of the theoretical approach, which includes modeling of the epitaxial growth and hydrogenation process with subsequent self-consistent calculations of magnetic structure on the basis of ab initio and model approaches took part CR3, CR6, CR7, CR8 teams. The code for modeling of intermixing and for calculations of magnetic structure was developed by CR6 team. Some calculations with this code were performed by CR6 and CR3 teams. Ab initio calculations were carry out by CR8 team in cooperation with CR6 team. CR6 team developed also the code for modeling of hydrogen loading in Fe/V superlattices with rough interfaces.

- quantitative interpretation of experimental data obtained using different methods on the basis of uniform theoretical approach were performed by CO, CR1, CR3, C6 teams; the theory which connects atomic-scale magnetic structure and the values observable in experiments was developed for interpretation of mossbauer (CR3 and CR6) and magnetometor experiments (CO, CR1 CR6); This theoretical approach as well as a new codes developed during the first year, will be used later for realistic description of experiments.

All research were carry out in accordance with the Work Programme
Next year we will continue experimental and theoretical work. We are not planning the deviations from the Work Programme for the future activity.

1.2. Scientific Results

The influence of interface alloying on the phase and strength of the short-range oscillations of the interlayer exchange coupling (IEC) in the Fe/Cr multilayers is analyzed on the basis of stochastic modeling of interdiffusion with subsequent self-consistent calculations of magnetic structure by Strasbourg (CR4) and St.Petersburg (CR6) teams. They explain the experimentally observed behavior of the IEC in the Fe/Cr/Fe trilayers grown on Fe whisker (PRB 66, 092408 (2002)). Experiments with artificially alloyed FeCr layer deposited at the top of the Cr spacer allow the determination of intermixing parameters for the Fe/Cr and for the Cr/Fe interfaces. It was shown that the same mechanism of intermixing is working for Fe/V and Cr/V heterostructures.

The experiments and calculations for the determination of magnetic moments for pristine and hydrogen loaded Fe/V superlattices were performed in cooperation by Bochum (CO), Uppsala (CR1) and St.Petersburg (CR6) teams. The experiments show that the average magnetic saturation moment decreases with decreasing Fe layer thickness and increases proportional to the hydrogen concentration in the V layer. The epitaxial growth and different degrees of interface mixing were modeled via algorithms simulating the deposition and exchange of atoms with atoms of the substrate. The electronic density of states and the distribution of magnetic moments in the Fe and V layers were determined within the periodic Anderson model including rough interfaces and various hydrogen concentrations. The parameters of the model were chosen such as to reproduce the main features of the electron DOS obtained by ab initio calculations for ideal systems. The periodic Anderson model can reproduce the main features of the experimental observations. The Fe magnetic moment is reduced as compared to the bulk value close to the Fe/V interface and decreases with increasing roughness. V exhibits a small and induced moment in the interface region polarized opposite to the Fe moment. With increasing hydrogen concentration the magnetic moment of the Fe layers increase, whereas the V moment remains essentially constant, resulting in an overall increase of the Fe/V saturation magnetization, in accordance with experimental results.

CR3 and CR7 teams performed the self-consistent calculations of magnetic moments distribution for the ordered and disordered Fe/V bulk bcc alloys and Fe/V(110) films with interface intermixing within the framework of Vector Periodic Anderson model. It was shown that magnetic structure depend essentially on the type of alloying at the interface. They have found collapse of the magnetic moments of both Fe and V atoms for the ordered FeV equiatomic compound evaporated on the V(110) substrate as well as for the isolated Fe islands on the top of V substrate.

Experiments performed by CR10 team using neutron reflectometry have shown that magnetic and nuclear profiles are not symmetrical in periodical Fe/V structure (JMMM 258-259, 332 (2003)). It is in accordance with models suggested by CR7, CR4, and CR5 for description of interface asymmetry in metallic multilayers. Decreasing of magnetization of iron layer which is in contact with thick vanadium layer and magnetization of iron layers of periodical structure are observed at transition from 7K to 3K in magnetic field 1500Ое and 4500Ое. It can be explained by proximity effects in Fe-V bi-layer and Fe/V periodical structures (CR10).

The high efficiency Spin Polarized Auger Electron Spectrometer (SPAES) was constructed and tested by CR9 team. For the design of setup they used compact classical electron home-made spin detector (Mott polarimeter). SPAES allows study the local magnetization of atoms on the surface of solids. The spectrometer was tested using an FeNi3(110) crystal because the concentration and magnetization values of its components are well-known. It was found that magnetic moment of V films is uncertain, if the nominal thickness of V is less than 2 monolayers (ML). For the thickness about 2 ML vanadium has antiferromagnetic coupling with the surface of FeNi3(110). The magnetization is in plane of the surface. According to our estimation the mean magnetic moment of such film is about 0.5mB. Then magnetic moment of V on the surface of the sample decrease versus film's thickness and became zero at thickness 4-5ML. The magnetization of Fe and Ni is degreasing slightly (less then 30%) for such thickness on V film.

Mossbauer study of Fe/V multilayers using specula and normal geometry of experiment (performed by CR6 team) has shown the existence of in plane anisotropy for hyperfine fields on Fe nuclei. It has to be taken into account for interpretation of other experiments with Fe/V structures.

The treatment of the EXAFS data on the Fe/V superlattices with hydrogen, performed by CR9 team, leads to the conclusion that the most suitable model for these samples is a model which considers the V layers as a mixture of 20 % of V_2H and 80 % of V.

Duisburg team (CR2) and St.Petersburg team (CR6) used floating algorithm for modeling of the epitaxial growth together with self-consistent calculations of magnetic moments on each atoms in different multilayer systems. They gave a new interpretation for mossbauer experiments with 57Fe and 119Sn probe layers in Fe/Cr, Fe/Cr/Sn, V/Cr/Sn, Fe/Ag systems. It leads to revision of traditional point of view on the role of interface and bulk scattering in magnetic superlattices, on the reasons of suppression of Cr magnetic moments in Fe/Cr/Sn, V/Cr/Sn , on interface structure in Fe/Ag multilayers.
First-principles calculations of Fe/Cr/Sn/Cr were performed by CR8 team in cooperation with CR6 team. The hyperfine field at Sn nuclei reflects qualitatively the behavior of the magnetic moment magnitude at the nearest Cr atoms. With decreasing the Cr film thickness, the Sn HFF and Cr magnetic moment decrease, though the magnitude and the character of the calculated change do not exactly correspond to the experimental data. An explanation of the experimental data requires additional mechanisms, such as interface alloying.

Analytical description of the surface spin-flop transition in antiferromagnetically coupled finite-size multilayers was considered by CR7 team given. Anisotropy induced multi-kink magnetic states are predicted.

Joint Publications of INTAS and NIS project teams
International journals:

1. V.M. Uzdin, C. Demangeat, Manipulation of short-wavelength interlayer exchange coupling in Fe/Cr multilayers via interface alloying, Phys. Rev. B, 66, 092408 (2002).
2. V.L. Aksenov, Yu.V. Nikitenko, V.V. Proglyado, M.A. Andreeva, B. Kalska, L. Haggstrom, R. Wappling, "Polarized neutron reflectometry studies of depth magnetization distribution in Fe/V layered structure", JMMM 258-259, 332 (2003).
3. V. Uzdin, K. Westerholt, H. Zabel, B. Hjorvarsson, Interface alloying and tunability of magnetic structure with hydrogen in Fe/V multilayersand, submitted to Phys. Rev. B
4. V.L. Aksenov, Y.V. Nikitenko, K.M. Jernenkov, E.A. Kravtsov, D. Tihonov, H. Zabel. Thickness distribution of magnetization in layered structures. - submitted to Physica B.
5. N. S. Yartseva, S. V. Yartsev, N. G. Bebenin, C. Demangeat. Magnetic properties of Fe/V nanostructures in preparation
6. V.M.Uzdin, W. Keune, Atomic scale interface structure in the metallic multilayers, submitted in Phys. Rev. B
7. N.S. Yartseva, S.V. Yartsev, N.G. Bebenin, C. Demangeat. Vector-simulated magnetism of Fe/V nanostructures. -Article to Proceedings of ICM2003, Rome, Italy (in preparation)

National journals:

1. V.M.Uzdin, M.V.Molchanova, C.Demangeat, Mechanisms of interface intermixing and magnetic ordering in metallic superlattices, Proceedings of International Meeting "Phase transitions in solid solutions and alloys", 4-7 September 2002, Big Sochi , Russia, p. 119-122 (in Russian).

Abstracts

1. V.M.Uzdin, W.Keune, Fe/Cr interface magnetism studied by CEMS, Books of Abstracts, International conference "Mossbauer spectroscopy and its applications", St.Petersburg, Russia, 08-12 July 2002.
2. V.M.Uzdin, K. Westerholt, H. Zabel, B. Hjorvarsson, and C. Demangeat, Tunability of exchange coupling with hydrogen: playgraund for study of low-dimensional magnetism, Abstracts of 12th General Conference of the European Physical Society EPS-12, Trends in Physics, Budapesht (Hungary), 26-30 August 2002, p.398
3. V.L. Aksenov, E.A. Kravtsov, Yu.V. Nikitenko, V.V. Ustinov, H. Zabel, Neutron optics of layered magnetic nanostructures, Abstracts of XXXIII National conference on low temperature physics, Ekaterinburg, June 2003, accepted.
4. V.L. Aksenov, K.N. Jernenkov, Yu.V. Nikitenko, A.V. Petrenko, E.A. Kravtsov, H. Zabel, Time-of-flight Neutron Reflectometry of Layered Structures, Abstracts of 3rd Europ. Conf. On Neutron scattering, Sept. 2003, Montpellier, accepted.
5. N.S. Yartseva, C. Demangeat, V.M. Uzdin, S.V. Yartsev, J.C. Parlebas. Noncollinear magnetism for various Cr surfaces. - Abstract to Low-Dimensional Magnetism, LDM03, satellite to ICM2003, Florence, Italy. (accepted).
6. N.S. Yartseva, N.G. Bebenin, S.V. Yartsev. Effect of order and disorder on the surface magnetism of Fe on V films. - Abstract to Low-Dimensional Magnetism, LDM03, satellite to ICM2003, Florence, Italy. (accepted).
7. N.S. Yartseva, S.V. Yartsev, N.G. Bebenin, C. Demangeat. Vector-simulated magnetism of Fe/V nanostructures. - Abstract to ICM2003, Rome, Italy. (accepted).

Publications without INTAS-NIS co-authorship of the project teams
International journals:

1. A.K. Arzhnikov, L.V. Dobysheva, D.V. Fedorov and V.M.Uzdin. Magnetic moments and hyperfine fields at Sn in Fe/Cr/Sn/Cr multilayers, accepted in Phys. Rev. B
2. A.K.Arzhnikov, L.V.Dobysheva and D.V.Fedorov Magnetism and hyperfine magnetic fields in Fe/Cr/Sn/Cr and Cr/Sn multilayers, submitted to JMMM
3. V.V.Ustinov, A.B.Rinkevich, M.A.Milyaev, L.N.Romashev, T.P.Krinitsina, I.K.Maksimova, N.N.Sidun. Magnetic properties and high-frequency magnetoresistance of Fe0.82Ni0.18/V multillayer. - Article, in preparation.
4. Rinkevich A.B., Romashev L.N., Ustinov V.V. Microwave Properties of Metallic Nanostructures with Giant Magnetoresistive Effect. - Proceedings of 15-th International Symposium "Thin Films in Optics and Electronics", pp. 189-204, April, 2003, Kharkov, Ukraina

National journals:

1. V.V.Panchuk, V.G.Semenov, V.M.Uzdin, CEMS: magnetic structure, hyperfine field and modeling of epitaxial growth of metallic multilayers, Proceedings of workshop "Rentgen Optics" , Niznij Novgorod, 11-14 March 2003, P. 424-430 (In Russian)

Abstracts in proceedings:

1. A.K.Arzhnikov and L.V.Dobysheva Hyperfine magnetic fields at nuclei in disordered and partly disordered metal -metalloid alloys. Abstracts of 12th General Conference of the European Physical Society EPS-12, Trends in Physics, Budapesht (Hungary), 26-30 August 2002, p.334
2. A.K.Arzhnikov, L.V.Dobysheva, and D.V.Fedorov, Magnetism and hyperfine magnetic fields in Fe/Cr/Sn/Cr and Cr/Sn/Cr multilayers. Abstract to ICM 2003 (Rome, Italy, 27.07.03.-01.08.03), accepted.
3. V.V. Ustinov. Anisotropy induced multi-kink magnetic states and surface spin-flop phase in finite-size antiferromagnetic superlattices. - Abstract to ICM2003, Rome, Italy, accepted.
4. V.V. Ustinov, L.N. Romashev, T.P. Krinitsina, M.A. Milyaev, E.A. Kravtsov et al. Crystallography and magnetic properties of (Fe/Cr)/(100), (110) and (211)MgO superlattices. - Abstract to ICM2003, Rome, Italy, accepted.

Books, monographs, internal reports, thesis, patents
Summarise the scientific output (number of papers, etc.) in the table below:

2. MANAGEMENT

2.1. Meetings and visits
During the first year 2 co-ordination meeting were organized in Bochum:

1. First INTAS meeting (20 November 2002) Participants: C. Demangeat (Strassbourg), W. Keune (Duisburg), E.Kravtsov (Ekaterinburg - Bochum), U. Mick (Dusseldorf), W. Park (Dusseldorf), T. Reich (Mainz), A. Remhof (Bochum), V. Uzdin (St. Petersburg) K. Westerholt (Bochum), H.Zabel (Bochum).
   Minutes of the meeting are attached in Annex
2. Second INTAS meeting (16-17 May 2003). Participants: Anatoly Arzhnikov, PTI-RAS, Izhevsk, Russia; Claude Demangeat, IPCMS, Strasbourg, France; Bjorgvin Hjovarsson, UU, Uppsala, Sweden; Kirill Jernenkov, FLNP, JINR, Dubna, Russia; Erhard Kisker, University Dusseldorf, Germany; Evgeny Kravtsov, RUB, Bochum, Germany; Eduardo Martinez, UV, Valladolid, Spain; Aleksei Nefedov, RUB, Bochum, Germany; Yuri Nikitenko, FLNP, JINR, Dubna, Russia ; Martin Parnaste, Uppsala University, Sweden; Arndt Remhof, RUB, Bochum, Germany; Anatoly Rinkevich, IMP-RAS, Ekaterinburg; Russia Kurt; Katharina Theis-Brohl, RUB, Bochum, Germany; Valery Uzdin, SPBSU, St. Petersburg, Russia; Kurt Westerholt, RUB, Bochum, Germany; Dieter Wolf, University Duisburg, Germany; Hartmut Zabel, RUB, Bochum, Germany; Ruslan Zigmatullin, University Duisburg, Germany.

Visits:

1. E. Kravtsov* (CO) visited Dubna in December 2002 to perform neutron reflectivity experiments and Ekaterinburg for sample characterization
2. H. Zabel** (CO) visited Uppsala (CR1) from June 2-5, 2002 to organize the joined activities.
3. E.A. Kravtsov ** (CO) visited Grenoble (ILL and ESRF), Juelich and Berlin for experiments on the Cr/V.
4. B. Hjorvarsson and M. Parnaste (CR1) visited Bochum 16-19 May 2003 to participate in the second INTAS-meeting.
5. C.Demangeat** (CR3) visited Duesseldorf and Bochum 19-22 November 2002 to participate in the first co-ordination meeting.
6. C.Demangeat (CR3) visited Bochum 16-19 May 2003 to participate in the second INTAS-meeting.
7. E. Martinez (CR3) visited Bochum 16-19 May 2003 to participate in the second INTAS-meeting.
8. T. Reich (CR5) visited Bochum 19 - 22 November 2002 to participate in the first co-ordination meeting.
9. T. Reich** (CR5) visited ESRF in Grenoble 22 - 25 April 2003. He discussed the experiments planned at the Rossendorf Beamline ROBL with the beam line scientists.
10. V.Uzdin* (CR6) visited Duesseldorf, Duisburg, Bochum 10-26 June 2002: coordination of work within the Project.
11. V.Uzdin* (CR6) visited Duesseldorf, Duisburg, Bochum 17.11-01.12 2002 common interpretation of experiments with CR3, CO teams, participation in the first co-ordination meeting.
12. V.Uzdin* (CR6) visited Duesseldorf, Duisburg, Bochum 01-21 May 2003 for discussion about results of calculations and experiments performed in St.Petersburg and for participation in the second INTAS-meeting
13. V.Uzdin** (CR6) visited Budapesht to take part in EPS-12 conference "Trends in Physics" with contribution about work performed within the framework of present Project.
14. M.Moltchanova (CR6) visited Duesseldorf , Duisburg 03.11-01.12 to organize the calculations using codes developed in St.Petersburg University
15. N.S.Yartseva** (CR7) visited St. Petersburg and Strasbourg (September 2002) for discussion of results of work with with CR6 and CR3 teams
16. A. Rinkevich (CR7) visited Bochum 11-19 May 2003 to participate in the second INTAS meeting.
17. A. Arzhnikov**(CR8) visited St.Petersburg 08-12 July 2002 to discuss common activity within the frame of the project with CR6
18. A. Arzhnikov**(CR8) visited Budapest to take part in EPS-12 conference "Trends in Physics" with contribution about work performed within the framework of present Project.
19. A. Arzhnikov (CR8) visited Bochum 16-19 May 2003 to participate in the second INTAS meeting
20. V. Petrov** (CR9) visited Strasbourg 03.08-01.09 2002 to discuss common activity within the frame of the project with CR3.
21. Yu.Nikitenko (CR10) and K. Jernenkov (CR10) visited Bochum 15-19 May 2003 to participate in the second INTAS meeting.

* visit was partially supported from other funds
**visit was totally supported from other funds