Characterizing the Nonequilibrium Response of FeRh Thin Films using Time-Domain Thermoreflectance (TDTR)

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Abstract
Two-tint Time-Domain Thermoreflectance (TDTR) characterization of FeRh throughout its first order antiferromagnetic (AF) to ferromagnetic (FM) transition shows that the transient reflectance, $\Delta$R(t)/R, strongly depends on the magnetic order of the sample. Using a probe wavelength of approximately 783 nm, we have found that the $\Delta$R(t)/R of the AF phase exhibits a large negative response, while the response of the FM phase is positive. This magnetic phase sensitivity has allowed us to study the transient response of both the AF and FM phase to the pump pulse excitation as well as the mixed phase of the material. We have found that the AF phase exhibits a strong transient signal which is not observed in the FM phase. A model using linear system techniques was able to represent and analyze the behavior of the system in each phase. The thermalization time of the electrons in the AF phase occurred on a timescale at least twice as long as that in the FM phase. These results indicate that the two-tint TDTR can be used to study the transient properties of the AF and FM phase of FeRh as well as the mixed phase.

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