Phase Boundary Exchange Coupling in the Mixed Magnetic Phase Regime of a Pd-doped FeRh Epilayer

TL;DR

This study investigates phase boundary exchange coupling in Pd-doped FeRh epilayers during the magnetic phase transition, revealing how antiferromagnetic regions influence ferromagnetic exchange stiffness and damping.

Contribution

It models the antiferromagnetic phase as a thin layer affecting exchange coupling, supported by spin-dynamics simulations and FMR measurements, providing new insights into phase boundary effects.

Findings

Exchange stiffness is suppressed by antiferromagnetic phase presence.

Exchange coupling develops across phase boundaries with thickness-dependent behavior.

Gilbert damping correlates with phase boundary development.

Abstract

Spin-wave resonance measurements were performed in the mixed magnetic phase regime of a Pd-doped FeRh epilayer that appears as the first-order ferromagnetic-antiferromagnetic phase transition takes place. It is seen that the measured value of the exchange stiffness is suppressed throughout the measurement range when compared to the expected value of the fully ferromagnetic regime, extracted via the independent means of a measurement of the Curie point, for only slight changes in the ferromagnetic volume fraction. This behavior is attributed to the influence of the antiferromagnetic phase: inspired by previous experiments that show ferromagnetism to be most persistent at the surfaces and interfaces of FeRh thin films, we modelled the antiferromagnetic phase as forming a thin layer in the middle of the epilayer through which the two ferromagnetic layers are coupled up to a certain critical thickness. The development of this exchange stiffness is then consistent with that expected from the development of an exchange coupling across the magnetic phase boundary, as a consequence of a thickness dependent phase transition taking place in the antiferromagnetic regions and is supported by complimentary computer simulations of atomistic spin-dynamics. The development of the Gilbert damping parameter extracted from the ferromagnetic resonance investigations is consistent with this picture.