The 229th Special CMSM seminar   

Modelling CPP GMR under homogeneous and inhomogeneous current

Dr. Bernard Dieny
SPINTEC, Université Grenoble Alpes / CEA / CNRS , Grenoble, France

Date & Time: 10:00 - 11:10, February 6th (Mon), 2017.
Place: 8F Medium Seminar Room(#811-812), Sengen.


  CPP-GMR is the object of a renewed interest in the context of magnetoresistive heads for hard disk drives. The first experimental CPP-GMR studies were performed in 1991 (1) on metallic pillars sandwiched between superconducting leads. Subsequently, different experimental approaches were used including the use of magnetic multilayers wires grown by electrodeposition (2), magnetic multilayers deposited on grooved substrates (3) and later nanopatterned multilayered pillars (4). On the theoretical side, the first approach to model the CPP-GMR in magnetic pillars was just assuming serial connection of the stacked layers in a two-current model neglecting spin-flip (1). Later, Valet and Fert introduced the concept of spin accumulation and pointed out the importance of spin diffusion length in CPP transport (5). Their model was developed for a uniform current. This concept was extended to any multilayered composition by N.Strelkov et al (6). Based on this extended theory, a software allowing to compute the CPP-GMR in any multilayered stack from the spin-dependent transport parameters of each individual layers (resistivity, scattering asymmetry, spin-diffusion length, interfacial resistance, interfacial scattering asymmetry) was developed at SPINTEC. This software will be presented during the talk. Later, the spin-dependent diffusion equations were generalized at 3D to be able to cover the case of non-uniform current in CPP geometry. These diffusion equations can be solved using a finite element solver such as COMSOL. Examples will be shown illustrating the cases of current crowding effect in CPP-GMR pillars (7) and of nanoconstricted spin-valves (8).

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2. L.Piraux, A.Fert, JMMM 200 (1999) 338
3. Oepts et al, APL66, (1995) 1939
4. Bass J et al, JMMM 200, 274 (1999) (review).
5. Valet T and Fert A, Phys.Rev.B48, 7099(1993)
6. N.Strelkov, A.Vedyaev, B.Dieny, Joun.Appl.Phys. 94, 3278 (2003).
7. Strelkov, N., Vedyayev, A., Gusakova, D., Buda-Prejbeanu, L.D., Chshiev, M., Amara, S., Vaysset, A., Dieny, B.; Magnetics Letters, IEEE, 1, 3000304 (2010).
8. Strelkov, N., A. Vedyaev, N. Ryzhanova, D. Gusakova, L.D. Buda-Prejbeanu, M. Chshiev, S. Amara, N. de Mestier, C. Baraduc and B. Dieny, Physical Review B 84 (2011) 024416