Magnetic response of FeRh to static and dynamic disorder

TL;DR

This study investigates how static and dynamic disorder, introduced by light ion-irradiation, affects the magnetic and structural properties of FeRh thin films, revealing disorder-induced ferromagnetism at room temperature.

Contribution

It provides new insights into the microscopic magnetic and structural changes in FeRh caused by disorder, highlighting the relationship between defects and magnetic phase transitions.

Findings

Ion irradiation induces ferromagnetism at room temperature.

Disorder broadens magnetic hysteresis and lowers transition temperature.

Microscopic analysis shows increased defects without changing chemical composition.

Abstract

Changes of the magnetic and crystal structure on the microscopic scale in 40 nm FeRh thin films have been applied to investigate the phenomena of a disorder induced ferromagnetism at room temperature initiated through light ion-irradiation with fluences up to 0.125 Ne$^+$/nm$^{-2}$. Magnetometry shows an increase of magnetic ordering at low temperatures and a decrease of the transition temperature combined with a broadening of the hysteresis with rising ion fluence. $^{57}$Fe M\"ossbauer spectroscopy reveals the occurrence of an additional magnetic contributions with an hyperfine splitting of 27.2 T - identical to that of ferromagnetic B2-FeRh. The appearance of an anti-site Fe-contribution can be assumed to be lower than 0.6 Fe-at%, indicating that no change of the chemical composition is evident. The investigation of the local structure shows an increase of the static mean square relative displacement determined by X-ray absorption fine structure spectroscopy, while an increase of the defect-concentration has been determined by positron annihilation spectroscopy. From the changes of the microscopic magnetic structure a similarity between the temperature induced and the structural disorder induced ferromagnetic phase can be observed. These findings emphasize the relationship between magnetic ordering and the microscopic defect structure in FeRh.