Giant Self-Production of Spin Current and Self-Torque on Single GdFeCo Magnetic Layers*

Two-dimensional spin-textured materials or interfaces are expected to exhibit high efficiency for the interconversion of spin current into charge current¹. Magnetic materials possessing strong spin-orbit coupling such as GdFeCo can also efficiently generate spin currents of different symmetries, spin anomalous Hall effect SAHE-like, and spin Hall effect SHE-like. And one such symmetry, SHE-like, could produce what we have coined "self-torque"^2,3.

We studied ferrimagnetic FiM GdFeCo alloys in which the 5d band of Gd induces large spin-orbit couplings. We demonstrate the giant spin current emission (SAHE+SHE) by GdFeCo from the current-induced modulation of the ferromagnetic resonance linewidth of NiFe in GdFeCo/Cu/NiFe. Overall efficiency is 25 times more important in GdFeCo/Cu/NiFe than in Pt/Cu/NiFe.

The study of the self-torque is carried out by harmonic Hall voltage measurements in samples where the GdFeCo layer exhibits out-of-plane magnetization. We compare the self-torque in GdFeCo/Cu with torques induced by Pt or Ta in Pt/Cu/GdFeCo and Ta/Cu/GdFeCo². Taking advantage of the different characteristics temperatures in FiM^2-4, we show the features that differentiate self-torque from what we know so far, the "external" spin-orbit torque³.

These results pave the way for new architectures to achieve switching by self-SOT and skyrmions manipulation.

 Work performed with co-authors in Ref. 2,3.

1. Rojas-Sánchez, J. C. & Fert, A. Compared Efficiencies of Conversions between Charge and Spin Current by Spin-Orbit Interactions in Two- and Three-Dimensional Systems. Phys. Rev. Appl. 11, 054049 (2019).

2. Céspedes-Berrocal D., Damas H. et al. Current-Induced Spin Torques on Single GdFeCo Magnetic Layers. Adv. Materials 33, 2007047 (2021)

3. Damas H. et al. In preparation

4. Pham, TH et al, Thermal contribution to the spin-orbit torque in metallic-ferrimagnetic systems. Phys. Rev. Appl. 9, 064032 (2018).