Exchange scattering as the driving force for ultrafast all-optical and bias-controlled reversal in ferrimagnetic metallic structures

Experimentally observed ultrafast all-optical magnetization reversal in ferrimagnetic metals and heterostructures based on antiferromagnetically coupled ferromagnetic $d-$ and $f-$metallic layers relies on intricate energy and angular momentum flow between electrons, phonons and spins. Here we treat the problem of angular momentum transfer in the course of ultrafast laser-induced dynamics in a ferrimagnetic metallic system using microscopical approach based on the system of rate equations. We show that the magnetization reversal is supported by a coupling of $d-$ and $f-$ subsystems to delocalized $s-$ or $p-$ electrons. The latter can transfer spin between the two subsystems in an incoherent way owing to the $(s;p)-(d;f)$ exchange scattering. Since the effect of the external excitation in this process is reduced to the transient heating of the mobile electron subsystem, we also discuss possibility to trigger the magnetization reversal by applying a voltage bias pulse to antiferromagnetically coupled metallic ferromagnetic layers embedded in point contact or tunneling structures. We argue that such devices allow controlling reversal with high accuracy. We also suggest to use the anomalous Hall effect to register the reversal, thus playing a role of reading probes.