SKM 2023 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 23: Poster Magnetism I

MA 23.16: Poster

Dienstag, 28. März 2023, 17:00–19:00, P1

Suppression of magnetic fluctuations lead to a better reversibility in low-field entropy changes near triple point — •Tapas Samanta¹, Chris Taake¹, and Luana Caron^{1, 2} — ¹Faculty of Physics, Bielefeld University, PO Box 100131, D-33501 Bielefeld, Germany — ²Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 12489, Germany

We report the detailed study of the phase transitions in MnNi_1−xCo_xGe_0.97Al_0.03 (x=0.20, 0.25 0.30, 0.35, 0.37, 0.40 and 0.45) compounds. In the parent Al-free compound, the structural and magnetic phase transitions are decoupled. Small amounts of Al substitution for Ge can lower the structural phase transition temperature, resulting in a coupled first-order magnetostructural transition (MST) near room temperature for all reported compositions. An antiferromagnetic-type (AFM) to paramagnetic (PM) MST has been observed for lower Co concentrations. At x=0.37 the phase transition transforms to a ferromagnetic-type (FM) to PM MST after exhibiting a triple point (where AFM, FM and PM phase transitions coincide) in the close vicinity of x=0.36. Interestingly, a relatively large reversible low-field entropy change (ΔS=-6.9 J/kg K for ΔH=2 T) has been observed near the triple point for x=0.37, which is rather rare in this class of materials due to the large associated thermal hysteresis. The observed reversible ΔS reaches values of -17.2 and -24.5 J/kg K for ΔH=5 and 7 T, respectively, for x=0.30. Our observations further reveal that a sudden decrease of magnetic fluctuation results in larger reversible entropy change near triple point.