Direct measurements of the magnetocaloric effect of Fe₄₉Rh₅₁ using the mirage effect

The magnetocaloric effect in the Fe₄₉Rh₅₁ alloy was systematically studied using three different approaches: in-field differential scanning calorimetry, standard direct measurement of the adiabatic temperature change, and a non-contact method based on a thermo-optical phenomenon, the mirage effect, which was able to directly test the magnetocaloric response induced by a fast magnetic field variation. The metamagnetic phase transition of Fe₄₉Rh₅₁ was studied in the temperature range of 290–330 K at magnetic fields up to 1.8 T through magnetic and calorimetric measurements. The estimated parameters of phase transition were comparable with the literature data. The values of adiabatic temperature change obtained with the three methods (calorimetry, standard direct measurement, and mirage-based technique), which explore three different time scales of the field variation (static field, 1 T s⁻¹, 770 T s⁻¹), were consistent, proving the absence of dynamic constraints in the first-order magnetostructural transition at the maximum field sweep rate.