Magnetocaloric effect for the altermagnetic candidate MnTe

TL;DR

This work investigates magnetocaloric effects in MnTe, a candidate altermagnet, near a spin-polarized transition well below the Néel temperature. Isothermal magnetization measurements across $T=80$--$85$ K are analyzed with the Maxwell relation $\Delta S = \mu_0 \int_0^H (\partial M/\partial T)_H dH$ to obtain the entropy change. A narrow $|\Delta S|$ peak is observed at $T_c \approx 81$ K, accompanied by a sharp $M(T)$ jump, indicating a SOC-driven transition from the spin-polarized altermagnetic state to a conventional antiferromagnetic-like phase. The small magnitude of the effect highlights MnTe as a model system for altermagnetic MCE and motivates search for materials with larger magnetocaloric responses for potential refrigeration applications.

Abstract

We experimentally investigate magnetocaloric effect for single crystals of MnTe altermagnet at the transition to the state with spontaneous spin polarization, i.e. well below the Néel temperature of MnTe. The isothermal magnetic entropy change $ΔS$ is calculated from the experimental magnetization curves by using Maxwell relation. We observe well-defined magnetocaloric effect as a narrow $ΔS$ peak around the cricital temperature $T_c\approx 81$~K, which is accompanied by sharp magnetization jump. This behavior is unusual for standard ferromagnetic transitions, so it confirms the predicted spin-orbit-induced spin polarization in the MnTe altermagnetic state.

Figures (3)

• Figure 1: (Color online) Transition from antiferromagnetic to the ferromagnetic-like magnetization around 81 K for the 5.73 mg MnTe sample, see Refs. orlova_mnteorlova_mnte1 for details. (a) $M(H)$ magnetization curves above the transition, at 85 K temperature. There are nonlinear $M(H)$ branches in high magnetic fields, while $M(H)$ is strictly linear in low fields, as it is depicted in the inset. This $M(H)$ behavior is expected for the antiferromaghetic state (b) Nonlinear $M(H)$ branches are shifted vertically at low 78 K temperature, so a pronounced zero-field kink can be seen. The inset shows low-field $M(H)$ ferromagnetic-like hysteresis. (c) Appearence of spontaneous magnetization below 81 K as a sharp $M(T)$ jump. The red and the blue curves are obtained at 300 Oe magnetic field, for heating and cooling, respectively.
• Figure 2: (Color online) (a) $M(H,T=const)$ isothermal magnetization curves from 80 K to 84.4 K temperatures with 0.2 K step, with sharp $M(T)$ jump at the transition temperature $T_c\approx 81$ K. The initial sample state is obtained after ZFC from room temperature to 78 K. Between the curves, temperature is always stabilized at zero field. (b) The isothermal magnetic entropy change $\Delta S$ with narrow peak at the cricital temperature $T_c\approx 81$ K. The obtained $|\Delta S|$ values are much below the usual ones for standard ferromagnetic transitions around the Curie temperature CoSnS_coloric. The data are obtained for the 5.73 mg MnTe sample.
• Figure 3: (Color online) $M(H,T=const)$ isothermal magnetization curves (a) and $|\Delta S|$ values (b) for the 2.89 mg MnTe sample. The transition can be seen as sharp $M(T)$ jump at $T_c\approx 79.5$ K, which well corresponds to the position of the $|\Delta S|$ peak. The peak amplitude is diminished for this 2.89 mg MnTe sample in comparison with the 5.73 mg one in Fig. \ref{['fig2']} (b). The magnetization value does not scale with the sample mass for the ferromagnetic-like state in low fields orlova_mnteorlova_mnte1.