Anomalies in the switching dynamics of C-type antiferromagnets and antiferromagnetic nanowires

TL;DR

This paper reveals unexpected switching behaviors in antiferromagnetic nanostructures, driven by dipolar interactions and damping effects, challenging conventional assumptions about AFM stability and resonance properties.

Contribution

It uncovers the role of dipolar interactions in AFM switching anomalies and introduces a damped non-linear pendulum model to explain these phenomena.

Findings

AFM order parameter switches away from easy-axis below a critical anisotropy.

Switching time varies non-monotonically with damping.

Resonance absorption peaks are shifted and have low quality factors near phase boundaries.

Abstract

Antiferromagnets (AFMs) are widely believed to be superior than ferromagnets in spintronics because of their high stability due to the vanishingly small stray field. It is thus expected that the order parameter of AFM should always align along the easy-axis of the crystalline anisotropy. In contrast to this conventional wisdom, we find that the AFM order parameter switches away from the easy-axis below a critical anisotropy strength when an AFM is properly tailored into a nano-structure. The switching time first decreases and then increases with the damping. Above the critical anisotropy, the AFM order parameter is stable and precesses under a microwave excitation. However, the absorption peak is not at resonance frequency even for magnetic damping as low as 0.01. To resolve these anomalies, we first ascertain the hidden role of dipolar interaction that reconstructs the energy landscape of the nano-system and propose a model of damped non-linear pendulum to explain the switching behavior. In this framework, the second anomaly appears when an AFM is close to the boundary between underdamped and overdamped phases, where the observed absorption lineshape has small quality factor and thus is not reliable any longer. Our results should be significant to extract the magnetic parameters through resonance techniques.