Ultrathin ferrimagnetic GdFeCo films with very low damping

Spin-Hall nano oscillators (SHNOs) [1] have recently emerged as an alternative for microwave signal generation and bio-inspired oscillatory computing [2]. Due to their ultrafast magnetization dynamics with a ferromagnet-like spin-orbit-torque (SOT) behavior, there is a lot of interest in compensated ferrimagnets. For use in SHNOs, it is however important to ensure that such films retain their ferrimagnetic behavior also in ultrathin films. In this work, ferrimagnetic Gd_x(FeCo)_1-x thin films were grown on high resistance (HR) Si (100) substrates, and their magneto-dynamics was studied using ferromagnetic resonance measurements at room temperature. By tuning the stoichiometry, a nearly compensated behavior is for the first time demonstrated in 2 nm thin films. Values for the effective magnetization and effective Gilbert damping constant (α) of 0.02 Tesla and 0.0078 comparable to the lowest values obtained in thick films. In search of high-frequency auto-oscillations in SHNOs, constrictions with 50-300 nm widths were also prepared using Gd_x(FeCo)_1-x (2-10nm)/Pt(5nm) based stacks and Brillouin Light Scattering show SOT controllable ferromagnetic modes in these devices.

1. T. Chen et al, Proc. IEEE 104, 1919 (2016)

2. M. Zahedinejad et al., Nat. Nano. 15, 47–52 (2020).