Spintronic phenomena in magnetic nanostructures with non-collinear spin configurations have been of major interest for scientists and engineers. Among the most important phenomena arising from non-collinearity of magnetic moments and which has tremendous impact on spintronics [1] is current induced magnetization switching caused by spin transfer torque [2] (STT). The latter continues to generate interest for spin electronic applications such as magnetic random access and domain wall racetrack memories, spin torque oscillators and detectors. Among the most favorable candidates for realization of STT devices are crystalline magnetic tunnel junctions (MTJ) where Bloch state symmetry based spin filtering may lead to extremely high TMR ratios [3] (MTJ).

 

The first part of this talk will include theory of non-equilibrium spin currents and the corresponding spin transfer torques in MTJs with non-collinear moments. Calculations are based on the Keldysh formalism in which the non-equilibrium Green functions are calculated within a tight-binding model and free electron models. The properties of spin transfer torque and spin currents as a function of applied bias, barrier thickness and distance from the interface in the free layer will be discussed [4].

 

The second part of the presentation will be devoted to phenomenon of interlayer exchange coupling which also results from equilibrium spin currents in non-collinear magnetic configurations. In particular, using ab-initio and tight-binding approaches, we will address the impact of interfacial oxidation conditions on amplitude of IEC in MTJs [5] as well as the importance of occupation numbers on period of IEC oscillation as a function of ferromagnetic electrode thickness [6] and dynamics of exchange coupled magnetic moments.

 

In conclusion, theory of voltage induced switching in magnetically frustrated bulk materials will be presented [7].

 

[1] A. Fert et al, Mat. Sci. Eng. B, 84, 1 (2001); S. A. Wolf, Science, 294, 1488 (2001).

[2] J. C. Slonczewski, J. Magn. Magn. Mat. 159, L1 (1996); L. Berger, Phys. Rev. B 54, 9353 (1996).

[3] W. H. Butler et al, Phys. Rev. B, 63, 054416 (2001); J. Mathon et al, Phys. Rev. B, 63, 220403(R) (2001).

[4] I. Theodonis et al, Phys. Rev. Lett. 97, 237205 (2006); M. Chshiev et al. IEEE Trans. Mag. 44 (11) (2008); A. Kalitsov et al, Phys. Rev. B 79, 174416 (2009); S.-C. Oh et al, Nature Physics 5, 898 (2009).

[5] H. X. Yang et al, Appl. Phys. Lett. 96, 262509 (2010).

[6] L. E. Nistor et al, Phys. Rev B 81, 220407 (2010).

[7] A. Kalitsov et al, Phys. Rev. B 82, 094420 (2010).