Poster De Conférence Année : 2023

Laser-Assisted Antiferromagnetic-Ferromagnetic Transition in FeRh

Catherine Gourdon

Résumé

Among magnetic materials near equiatomic FeRh alloys, with their temperature driven antiferromagnetic (AF) to ferromagnetic (FM) hysteretic transition near room temperature were studied long ago in bulk form. In the recent years they have aroused a renewed interest as thin films with particular focus on their AF nature at room temperature, the electrical detection of their magnetic state, and their giant magneto-caloric effect (MCE) [1]. FeRh is also a good candidate to investigate laser-assisted transient or irreversible phase transition. Most experiments have used ultrashort excitation/detection schemes either all optical [2], or with optical pump and X-rays or photoemission probe [3]. However, at short time scale electron, spin and phonon dynamics are entangled whereas at much longer timescale (µs range) only thermal effects are at play. We investigate the AF-FM transition using a modulated reflectance experiment [4], taking advantage of the 4% reflectivity difference between the AF anf FM phases. In the optical microscopy setup the pump beam (532 nm laser with square modulation at 100 kHz) and the probe beam (488 nm laser) are focused on the same spot. Two components (at f0=0 (CW) and f1=100 kHz) of the reflected probe are detected while the temperature is scanned across the transition. The f0 reflectance shows the modification of the hysteresis cycle with increasing pump power. The average transition temperature shifts by 2.2°C per mW of pump power, consistently with the thermal conductivities of the two phases, which are determined in this work, while the hysteresis shape is strongly affected. Under pump heating the nucleation of the FM phase occurs at lower temperature whereas the FM-to-AF transition is hardly affected. At about 4 mW of pump power the hysteresis loop closes, which is not the result of irreversible damage since removing the pump restores the initial cycle. This on-demand closing of the hysteresis while maintaining the AF and FM reflectance (hence the magnetization in the FM phase) might be of great use for magneto-calorics. The f1 signal varies linearly with pump power in the in the pure FM and AF phases where it can be ascribed to thermoreflectance only. In the mixed AF-FM phase it shows a strongly non-linear behavior with pump power. We show that it is consistent with breathing FM domains at the modulation frequency. The AF-FM domain wall velocity, smaller than 1 m/s, can then be estimated, which opens new insight for the yet little investigated AF-FM interfaces.
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Dates et versions

hal-04934105 , version 1 (07-02-2025)

Identifiants

  • HAL Id : hal-04934105 , version 1

Citer

Catherine Gourdon, Kévin Alhada-Lahbabi, Giovanni Olivetti, Vojtěch Uhlíř, Jon Ander Arregi, et al.. Laser-Assisted Antiferromagnetic-Ferromagnetic Transition in FeRh. Joint European Magnetic Symposia (JEMS2023), Aug 2023, Madrid, Spain. ⟨hal-04934105⟩
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