Study of the laser-induced modulated
Antiferromagnetic-Ferromagnetic phase transition in
FeRh Films

Alexis Pecheux, Morgan Almanza, Catherine Gourdon, Laura Thevenard, Daniele Fournier, Jon Ander, Vojtěch Uhlíř, Martino Lobue

► To cite this version:

Alexis Pecheux, Morgan Almanza, Catherine Gourdon, Laura Thevenard, Daniele Fournier, et al. Study of the laser-induced modulated Antiferromagnetic-Ferromagnetic phase transition in FeRh Films. 2025 IEEE Advances in Magnetics, Feb 2025, Bressanone, Italy. hal-05022106

HAL Id: hal-05022106

https://hal.science/hal-05022106v1

Submitted on 5 Apr 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Study of the laser-induced modulated Antiferromagnetic-
Ferromagnetic phase transition in FeRh Films

Alexis Pecheux(a), Morgan Almanza(a), Catherine Gourdon(b), Laura Thevenard(b), Daniele Fournier(b), Jon Ander Arregi(c), Vojtěch Uhlíř(c,d), Martino Lo Bue(a)

<sup>a</sup> Université Paris-Saclay, ENS Paris-Saclay, CNRS, SATIE, 91190 Gif-sur-Yvette, France

<sup>b</sup> Institut des Nanosciences de Paris, Sorbonne-Université, CNRS, 4 Place Jussieu, F75005 Paris, France

<sup>c</sup> CEITEC BUT, Brno University of Technology, Purkyňova 123, 612 00 Brno, Czech Republic

<sup>d</sup> Institute of Physical Engineering, Brno University of Technology, Technicka 2, 61669 Brno, Czech Republic

Near equiatomic FeRh alloy exhibits an Antiferromagnetic (AF) to Ferromagnetic (FM) first-order phase transition near 360 K [1] accompanied by lattice expansion, and by several physical properties changes, such as electrical resistivity, and optical reflectivity. This makes FeRh a prototypical multifunctional material promising for technologies as different as magnetic cooling, and spintronics [1]. Understanding the mechanisms underlying the phase change and the associated thermal hysteresis is the key for harnessing its functional properties. In this study we use the remarkable change in optical reflectance between the AF and FM phase (≈4%) [2] to probe phase-coexistence in a temperature driven hysteretic phase transition. A modulated thermoreflectance setup [3], where a pump and a probe laser (532 nm modulated at 500 Hz and 488 nm, respectively) are focused on a 4 µm radius spot, is used on a 195 nm thick FeRh film grown over a MgO (001) substrate. The pump induces a fast (≈10 K/µs), and periodic (square modulated at 500 Hz) temperature pulse ΔT on the sample surface while the probe measures the reflectance (Voltage on Figure 1a,1b). Starting from the pure AF phase the pump laser power is set in order to get temperature pulses ΔT, over the spot, reaching the onset of the quasi-static phase-coexistence region as shown in Figure 1c. The consequent modulation of the FM phase fraction shows a random behavior. The FM fraction doesn't systematically follow the temperature modulation. The statistic of the modulated FM phase (i.e. relative frequency, amplitude, and time delay of the FM bursts with respect to the temperature pulses) is studied, and its relationship with hysteresis is discussed.

<figure><img src="image_2.png" /><figcaption>Figure 1. (a): Time-dependent reflectance (orange line) illustrating the transition randomness under modulated pump (blue line in zoomed plot). (b): zoom on the figure 1a. (b): Schematic quasi-static cycle acquired without pump where ΔT is the temperature pulse induced by the laser.</figcaption></figure>

[1] L H Lewis et al 2016, J. Phys. D: Appl. Phys. 49 323002

[2] V Saidl et al 2016, New J. Phys. 18 083017
[3] D Fournier et al 2020, J. Appl. Phys. 128, 241101