CPM Seminar

Magnetization Dependent Transport in Nanomagnets

Shaffique Adam

Cornell University

We examine two effects in small ferromagnets where the charge transport is coupled to the magnetization. The first of these is that a sufficiently large unpolarized current can cause a spin-wave instability in a nanomagnet with asymmetric contacts. The instability is a consequence of the Slonczewski spin-transfer torque that transfers angular momentum between normal-metal contacts and the thin ferromagnet. The dynamics beyond the instability is calculated analytically in the perturbative regime of small spinwave amplitudes, and numerically for larger currents. The second effect is “anisotropic magnetoresistance fluctuations” which is the ferromagnetic analog of the well-known Universal Conductance Fluctuations in metals. The conductance of a ferromagnetic particle depends on the relative orientation of the magnetization with respect to the direction of current flow. This phenomena is known as “anisotropic magnetoresistance” and has no counterpart in normal-metal conductors. We show that quantum interference leads to an additional, random yet (statistically) universal dependence of the conductance of a ferromagnet on the magnetization direction. The mechanism for these anisotropic magnetoresistance fluctuations is the interplay of spin-orbit scattering, random impurity scattering, and the ferromagnet's exchange field.

Current induced transverse spin-wave instability in thin ferromagnets: beyond linear stability analysis S. Adam, M.L. Polianski, and P.W. Brouwer, Phys. Rev. B 73, 024425 (2006)
Mesoscopic anisotropic magnetoconductance fluctuations in ferromagnets S. Adam, M. Kindermann, S. Rahav and P.W. Brouwer, Submitted to Phys. Rev. Lett. http://arxiv.org/abs/cond-mat/0512287