Terahertz-frequency magnetization oscillations in an uncompensated ferrimagnet under a spin-transfer torque*

Current of spin-polarized electrons can interact with materials exhibiting a long-range magnetic order via a spin-transfer torque (STT). An STT of a sufficient magnitude may compensate damping and the spins come into a self-sustained precession [1]. In ferromagnetic materials the precession frequency is limited to tens of GHz by the value of the external magnetic field. In materials with more than one magnetic sublattice, the strong exchange interaction speeds up the precession frequency up to several THz [2], but due to magnetic compensation, in antiferromagnetic materials the THz frequency output power is small [3]. In our simulations we show that in easy-plane unbiased nearly compensated GdFeCo thin layers: (i) the precession frequency can be in over of THz and controlled by current, (ii) the precession of the Neel vector is conical, where the cone angle is defined by the non-compensation of the sublattices. The conical precession excites an AC spin-current, which can be converted to AC voltage by inverse spin-Hall effect.

[1] Slavin, Tiberkevich IEEE Trans. on Magn. 45, 1875 (2009).
[2] Gomonay, Loktev Low Temp. Phys. 40, 17 (2014).
[3] Khymyn el at S. Rep. 7, 43705 (2017).