Fluctuations in Transition Metals
Fluctuation Phenomena in Transition Metal and Actinide Based Systems with Magnetic and Structural Instabilities
Tech Area / Field
- PHY-ANU/Atomic and Nuclear Physics/Physics
3 Approved without Funding
All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow
- All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar / State Center for Condensed Matter Physics of MINATOM, Russia, Moscow
- US Department of Commerce / NIST Center for Neutron Research, USA, MD, Gaithersburg\nIowa State University of Science and Technology / Ames Laboratory, USA, IA, Ames\nRuhr Universität Bochum / Institute für Theoretische Physic III, Germany, Bochum\nCNRS / Laboratoire de Magnétisme, France, Grenoble
The overall aim of the project is to analyze effects of strongly coupled spin and lattice fluctuations in transition and rare-earth metal and actinide based systems with magnetic and structural instabilities and to work out a theory for quantitative description of these systems.
Experimental evidence strongly suggests an important role of overdamped magnetic or spin fluctuations (SF) in metals with magnetic instabilities (itinerant electron magnets), which up to now remains one of the most fundamental problems of physics of magnetism. The conventional theory of SF  is based on the constraint of weak coupling of SF and essentially uses a perturbative approach. However, both experiments and theoretical estimates for transitional metal and actinide based systems reveal strong coupling (spin anharmonicity) of overdamped SF caused by quantum zero-point effects [2, 3]. In magnetic metals with structural instabilities SF may strongly affect lattice properties causing, e.g., anomalies in Invar alloys important for high technology applications . The basis for understanding the problem of strongly coupled SF in itinerant electron magnets was recently worked out jointly by the scientists of A.A. Bochvar Institute, SCP, Ruhr University, and Neel Laboratory in a series of papers [3, 5, 6] where a soft-mode (SM) theory of SF was formulated accounting for strong spin anharmonicity within a novel non-perturbative variational approach. There was also formulated a new approach to non-linear magnetic dynamics in terms of multi-mode scattering of overdamped SF [7, 8]. Essential efforts in the Ruhr University, Neel Laboratory, NIST and Ames Laboratory were also devoted to investigate Invar anomalies [9, 10], effects of magneto-volume instabilities [9, 11], frustration  and magnetic dynamics . Basing on the jointly established grounds the following fundamental problems with an emphasis to high technology applications will be solved:
- SF thermodynamics based on a novel variational approach will be worked out to account for strong spin anharmonicity within all main regimes of SF;
- non-linear magnetic dynamics in relaxational and non-relaxational regimes will be formulated with account of strong mode-mode coupling of SF.
In the frame of the project the following results are planned to be obtained:
A. Non-linear thermodynamics.
- with respect to spatial dispersion and quantum effects a novel classification scheme, including Fermi liquid (FL), soft-mode (SM), and localized moments (LM) regimes of SF will be introduced;
- analysis of thermal and zero-point SF effects for all SF regimes;
- analysis of SF effects near quantum critical points (FL vs. non-FL behavior, heavy fermion effects, etc.);
- analysis of a saturation of local magnetic moments and Curie-Weiss behavior with account of quantum SF effects;
- investigation of thermal expansion anomalies and Invar problem;
- analysis of the effects of strong magnetic fields and high pressure on magnetic transitions;
- analysis of the magnetovolume effect and spin and lattice fluctuation couplings in transition metal and actinide based systems.
B. Non-linear magnetic dynamics:
- microscopic analysis of non-linear magnetic dynamics;
- investigation of non-linear magnetic relaxation;
- analysis of multi-mode scattering of SF and new non-linear types of SF;
- analysis of SF damping of magnons.
1. T. Moriya. Spin fluctuations in itinerant electron magnetism (Springer, Berlin, 1985)
2. M. Shiga et.al. J. Phys. Soc. Jap. 62 (1993) 1329.
3. A. Solontsov and D. Wagner. Phys. Rev. 51B (1995) 12410.
4. E.Wassermann. In: Ferromagnetic materials, v.5, eds. K.H. Buschow and E.P. Wohlfarth (North-Holland, Amsterdam, 1990).
5. A. Solontsov and D. Wagner. J.Phys.: Condens. Matter 6 (11994) 7395.
6. C. Lacroix, A. Solontsov, and R. Ballou. Phys. Rev. 54B (1996) 15178.
7. A. Solontsov and A. Vasil'ev. Phys.Lett. 177A (1993) 362.
8. A. Solontsov, A. Vasil'ev, and D. Wagner. J. Phys.: Condens. Matter 7 (1995) 1855.
9. Th. Jechalik and D. Wagner, J. Magn. Magn. Mat. 131 (1994) 107
10. J. Lynn et.al. J. Appl. Phys. 75 (1994) 6806.
1l. C. Pinettes and C. Lacroix, J. Phys.: Condens. Mat. 6 (1994) 10093
12. V.P. Antropov, M.I. Katsnelson and B. Harmon, Phys. Rev. 54 В (1996) 1019
Potential role of foreign collaborators
A successful long-term cooperation between Theoretical Laboratory (A.A. Bochvar Institute), SCP with the Ruhr University (Bochum, Germany) and Neel Laboratory (CNRS, Grenoble, France), has already resulted in important findings published jointly. A cooperation with Ames Laboratory (Iowa, USA) is planned as an important part of the project. Dr. C. Lacroix (CNRS) is participating as a specialist in microscopic description of the ground state properties. The group of Prof. D. Wagner (Ruhr University) establishes a phenomenological basis for it. A cooperation with Prof. J. Lynn (NIST) is needed to compare theoretical results with his neutron scattering investigations of metallic magnets. A collaboration with the group of Dr. B. Harmon (Ames Laboratory) may essentially affect establishing a novel microscopic approach to non-linear magnetic dynamics.
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