Faculty

Condensed matter physics; mesoscopic magnetic systems;

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Research Electrical transport in magnetically layered structures has produced some exciting phenomena; amongst them is the unusually large change in the resistance as the magnetic configuration is realigned from an antiferromagnetic or random in zero field to ferromagnetic at saturation. Known as giant magnetoresistance [GMR] for metallic multilayers and junction magnetoresistance [JMR] for magnetic tunnel junctions, we have been studying the mechanisms that produce this effect. We have adapted extant theories of electrical transport, such as, Kubo's linear response, the Boltzmann equation, and the Landauer approach, to the layered geometries that display this effect. The role of the spin dependent scattering at the interfaces between magnetic and nonmagnetic metals has been identified as the primary source of the GMR in metallic multilayers, while for magnetic tunnel junctions it's the spin dependent density of states at the interface between the magnetic electrode and the insulating barrier. Analytic solutions of the resistivity are found for realistic models of the band structure in the magnetic multilayers. Also, we use the results of ab-initio calculations of the electronic structure that use the coherent potential approximation to account for the effects of the defect scattering to determine the electrical resistivity and GMR of layered structures.

Currently, we are studying transport across noncollinear magnetic multilayers and determining the role of spin accumulation in switching the magnetization. The possibility of current induced switching by using polarized currents is an attractive way of resetting magnetic memories.

Publications Jianwei Zhang and Peter M Levy, Layer by layer approach to transport in noncollinear magnetic structures, Physical Review B 71, 184426 (2005).

Jianwei Zhang and Peter M Levy, Time dependent spin diffusion in noncollinear magnetic multilayers, Physical Review B 71, 184417 (2005).

Jianwei Zhang and Peter M Levy, Different steady states for spin currents in noncollinear multilayers, J.Phys.: Condens. Matter 16, S5601 (2004).

Jianwei Zhang and Peter M Levy, The steady state in noncollinear magnetic multilayers, Physical Review B 70, 184442 (2004).

Peter M Levy and Jianwei Zhang, Current induced spin flip scattering at interfaces in noncollinear magnetic multilayers, Physical Review B 70, 132406 (2004).

Jianwei Zhang, Peter M Levy, Shufeng Zhang and Vladimir Antropov, Identification of transverse spin currents in noncollinear magnetic structures, Physical Review Letters 93, 256602 (2004).

S. Gallego, P. Weinberger, L. Syunyogh, C. Sommers, and Peter M Levy, Ab inition description of domain walls in Permalloy: Energy of formation and resistivities, Physical Review B 68, 054406 (2003).

Asya Shpiro, Peter M Levy, and Shufeng Zhang, A self consistent treatment of non-equilibrium spin torques in magnetic multilayers, Physical Review B 67, 104430 (2003).

Kuising Wang, Shufeng Zhang, Laszlo Szunyogh (co-authors), On the calculation of magnetoresistance of tunnel junctions with parallel paths of conduction, Philosophical Magazine 83, 1255-1286 (2003).

Shufeng Zhang and Peter M. Levy, "Time dependence of spin accumulation and magnetoresistance in magnetic multilayers", Physical Review B 65, 052409 (2002).

Peter Weinberger, Claudia Blaas, Andreas Vernes, Peter Mohn, Laszlo Szunyogh Peter M. Levy and Charles Sommers , "Magnetic properties, interlayer exchange coupling and electrical transport in Fe/Cr/Fe trilayers", Philosophical Magazine B 82, 85-104 (2002).

Christoph Uiberacker and Peter M. Levy, "Role of symmetry on interface states in magnetic tunnel junctions", Physical Review B 64, 193404 (2001).

Claudia Blass, Laszlo Szunyogh, Peter Weinberger, Charles Sommers and Peter M. Levy,"Electrical transport of bulk NicFe1-c alloys and related spin-valve systems", Physical Review B 63, 224408 (2001).

Christoph Uiberacker, Kuising Wang, Carsten Heide and Peter M. Levy, "Ab-initio non equilibrium calculation of magnetic tunnel junctions", Journal of Applied Physics, 89, 7561 (2001).

Asya Shpiro and Peter M. Levy, "Resistance across an interface and that measured far from it", Physical Review B 63, 14 419 (2001).

Horacio Camblong and Peter M. Levy, "Electrical resistivity of a thin metallic film", Physical Review B 60, to appear (1999).

C. Blaas, P. Weinberger, L. Szunyogh, P.M. Levy and C.B. Sommers, "Ab-Initio Calculations of Magnetoresistance for Magnetic Multilayers", Physical Review B 60, 492-501 (1999).

Shufeng Zhang and Peter M. Levy, "Models for Magnetoresistance in Tunnel Junctions" , European Physical Journal B10, 599-606 (1999).

Peter M. Levy and Shufeng Zhang, "Spin Dependent Tunneling", Current Opinion in Solid State & Materials Science vol 4, 231-236 (1999).

C. Blaas, P. Weinberger, L. Szunyogh, J. Kudrnovsky, V. Drchal, P.M. Levy and C.B. Sommers, "On the orientational dependence of giant magnetoresistance", European Physical Journal B 9, 245-250 (1999).

Shufeng Zhang and Peter M. Levy, "Magnetoresistance of magnetic tunnel junctions in the presence of a non-magnetic layer", Physical Review Letters 81, 5660-5663 (1998).

Kuising Wang, Shufeng Zhang, Peter M. Levy, Laszlo Szunyogh and Peter Weinberger, "Role of Electronic Structure in Magnetic Tunneling", Journal of Magnetism and Magnetic Materials 189, L131-L135 (1998).

C. Blaas, P. Weinberger, L. Szunyogh, P.M. Levy, C.B. Sommers and I. Mertig, "Giant magnetoresistance of repeated multilayers of Cu(3)Ni(3) embedded in Cu(100)" , Philosophical Magazine B 78, 549 -555(1998).

P.M. Levy, S. Maekawa and P. Bruno, "Range Dependence of Interlayer Exchange Coupling", Physical Review B58, 5588-5593 (1998).

S. Zhang and P.M. Levy, "Interplay of the Specular and Diffuse Scattering at Interfaces of Magnetic Multilayers", Physical Review B57, 5336-5339(1998).

P.M. Levy and S. Zhang, "Resistivity due to Domain Wall Scattering", Physical Review Letters 79, 5110-5113 (1997).

S. Zhang, P.M. Levy, A.C. Marley and S.S.P. Parkin, "Quenching of Magnetoresistance by Hot Electrons in Magnetic Tunnel Junctions", Physical Review Letters 79, 3744-3747 (1997).

P.M. Levy, "Theory of Giant Magnetoresistance of Magnetic Multilayers", chapter in Aspects of Modern Magnetism, edited by F. C. Pu, Y. J. Wang and C.H. Shang, World Scientific, Singapore; 1996) 148-163.

K. Wang, S. Zhang and P.M. Levy, "Angular Dependence of Giant Magnetoresistance in a Superlattice", Physical Review B 54,11965-11968 (1996).

P.M. Levy and C. Sommers, "Quantum Well States in Metallic Superlattices", J. de Physique I France 6, 1461-1467 (1996).

P.M. Levy and S. Zhang, "Current Status of Our Understanding of Magnetotransport in Magnetic Multilayers", Journal of Magnetism and Magnetic Materials 164, 284-292 (1996).

P. Weinberger, P.M. Levy, J. Banhart, L. Szunyogh and B. Ujfalussy, "Band Structure and Electrical Conductivity of Disordered Semi-infinite Systems", J. Physics: Condensed Matter 8, 7677 - 7688(1996).

S. Zhang and P.M. Levy, "Enhanced Spin Dependent Scattering at Interfaces", Physical Review Letters 77, 916-919 (1996).

P.M. Levy, S. Zhang, T. Ono, and T. Shinjo, "Electrical Transport in Corrugated Multilayered Structures", Physical Review B 52, 16049-16054 (1995).

H.E.Camblong, P.M.Levy and S.Zhang, "Electron transport in magnetic inhomogeneous media", Phys. Rev.B 51,16052-16072 (1995).

P. M. Levy, "Antiferromagnetic Superexchange in Interlayer Magnetic Coupling", Journal of Magnetism and Magnetic Materials 140-144, 513-514 (1995).

P. M. Levy, "Current Understanding and Open Questions on Giant Magnetoresistance", Journal of Magnetism and Magnetic Materials 140-144, 485-487 (1995).

P.M.Levy and S. Zhang, "Spin-Transport Theory of Magnetically Inhomogeneous Systems", Materials Science and Engineering B 31, 157-162 (1995).

P.M. Levy and S. Zhang, "Our Current Understanding of Giant Magnetoresistance in Transition-Metal Multilayers", Journal of Magnetism and Magnetic Materials 151, 315-323 (1995).

P.M.Levy, "Giant magnetoresistance in magnetic layered and granular materials", Chapter in SOLID STATE PHYSICS Vol.47, edited by H.Ehrenreich and D.Turnbull (Academic Press, Cambridge MA, 1994)367-462.

H. E. Camblong, P.M.Levy and S. Zhang, "Theory of Transport in Inhomogeneous Magnetic Structures", Journal of Applied Physics 75, 6906-6908 (1994).

H. E. Camblong, S. Zhang and P.M.Levy, "Effective Internal Fields and Magnetization Buildup for Magnetotransport in Magnetic Multilayered Structures", Journal of Applied Physics 75, 7076-7078 (1994).

Z. P. Shi, P.M.Levy and J. L. Fry, "Interlayer Magnetic Coupling in Metallic Multilayered Structures", Physical Review B 49, 15159-15178 (1994).

S. Zhang, and P.M.Levy, "Effects of Domains on Giant Magnetoresistance", Physical Review B 50, 6089-6093 (1994).

Z. P. Shi, P.M.Levy and J. L. Fry, "Antiferromagnetic Bias in the Interlayer Magnetic Coupling", Europhysics Letters 26, 473-479 (1994).