Manipulating Ferrimagnets by Fields and Currents

TL;DR

This paper explores the dynamic properties of ferrimagnets manipulated by fields and currents, revealing how their behavior transitions between ferromagnetic and antiferromagnetic states and demonstrating potential for ultrafast, self-stabilized spin-torque oscillators.

Contribution

It provides a generic understanding of ferrimagnets with varying sublattice spin ratios and demonstrates their unique dynamical features and advantages over antiferromagnets in spin-torque applications.

Findings

Current-induced torques can induce terahertz oscillations in FIMs.

FIM-based spin-torque oscillators have lower threshold currents and are self-stabilized.

The dynamical modes connect ferromagnetic and antiferromagnetic behaviors.

Abstract

Ferrimagnets (FIMs) can function as high-frequency antiferromagnets while being easy to detect as ferromagnets, offering unique opportunities for ultrafast device applications. While the physical behavior of FIMs near the compensation point has been widely studied, there lacks a generic understanding of FIMs where the ratio of sublattice spins can vary freely between the ferromagnetic and antiferromagnetic limits. Here we investigate the physical properties of a model two-sublattice FIM manipulated by static magnetic fields and current-induced torques. By continuously varying the ratio of sublattice spins, we clarify how the dynamical chiral modes in an FIM are intrinsically connected to their ferro- and antiferromagnetic counterparts, which reveals unique features not visible near the compensation point. In particular, we find that current-induced torques can trigger spontaneous oscillation of the terahertz exchange mode. Compared with its realization in antiferromagnets, a spin-torque oscillator using FIMs not only has a reduced threshold current density but also can be self-stabilized, obviating the need for dynamic feedback.