Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

Abstract

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spinflop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.

Selective damping modulation in a synthetic antiferromagnet induced by spin–orbit torque

“…9,10) Although the magnetization dynamics in the SyAFM have been intensively studied, [11][12][13][14][15] the dynamics are not understood in several states. Further, the effect of the spin-orbit torque (SOT) driven by spin Hall effect on the SyAFM, [16][17][18][19][20][21][22][23][24][25] which is one of the most important phenomena in spintronics, is unclear. It is possible to effectively control the dynamics using the several magnetization states and both the acoustic and optical modes.…”

“…As the two magnetizations are antiferromagnetically coupled to each other, there are two resonance conditions for the detected signal, the so-called acoustic (in-phase) and optical (out-of-phase) modes. 10,11,15,19,30) Therefore, we need two combinations of Lorentzian and their derivatives to analyze the detected ST-FMR signal V mix 26,27) as exhibited in Eq. (…”

“…This leads to the injection of ac spin current from one FM to another FM, and vice versa, the so-called mutual spin pumping. 10,15,19,[32][33][34][35][36] Consequently, the magnetizations are damped owing to the pumping effect. In the same spin-flop state in the optical mode, the precessional motions between two magnetizations are at out-of-phase.…”