Colossal magnetic phase transition asymmetry in mesoscale FeRh stripes

TL;DR

This study reveals that mesoscale FeRh stripes exhibit a highly asymmetric first-order magnetic phase transition, with pronounced supercooling and abrupt changes upon cooling, driven by long-range exchange correlations.

Contribution

The paper demonstrates that mesoscale structuring dramatically enhances transition asymmetry in FeRh, highlighting the role of long-range correlations in magnetic phase transitions.

Findings

Strong supercooling observed in FeRh stripes

Abrupt ferromagnetic to antiferromagnetic transition upon cooling

Asymmetry is independent of magnetic field and involves large activation volumes

Abstract

Coupled order parameters in phase-transition materials can be controlled using various driving forces such as temperature, magnetic and electric field, strain, spin-polarized currents and optical pulses. Tuning the material properties to achieve efficient transitions would enable fast and low-power electronic devices. Here we show that the first-order metamagnetic phase transition in FeRh films becomes strongly asymmetric in mesoscale structures. In patterned FeRh stripes we observed pronounced supercooling and an avalanche-like abrupt transition from the ferromagnetic to the antiferromagnetic phase while the reverse transition remains nearly continuous over a broad temperature range. Although modest asymmetry signatures have been found in FeRh films, the effect is dramatically enhanced at the mesoscale. The asymmetry in the transitions is independent of applied magnetic fields and the activation volume of the antiferromagnetic phase is more than two orders of magnitude larger than typical magnetic heterogeneities observed in films. The collective behavior upon cooling results from the role of long-range ferromagnetic exchange correlations that become important at the mesoscale and should be a general property of first-order magnetic phase transitions.