Entropy change and kinetic effects at the magnetostructural phase transition of MnBi

• At the α-β transition of MnBi we find Δs = 17.6 J kg−1 K−1, (1/μ0)dT/dH = 2.6 KT−1.
• The temperature hysteresis is 19 K and the maximum predicted ΔTad is 37 K.
• The transition upon cooling has a two step behavior.
• The first step is characterized by kinetics effects dT/dln (dT/dt) = −3.8 K.
• We interpret the kinetics as an order-disorder effects in the NiAs-type structure.

In this paper we investigate the entropy change and the kinetics at the magneto-structural transition (at 628 K) of polycrystalline MnBi. Samples were prepared by rapid quenching and annealing and exhibit 86 wt% of the hexagonal MnBi phase. The entropy change at the transition is found to be Δs = 17.6 J kg−1 K−1 and the magnetic field shifts the transition temperature at a rate of 2.6 K T−1. The temperature hysteresis, of 19 K, is quite large for magneto-thermal application. The transition shows kinetics effects upon cooling in which the transition temperature is found to depend approximately to the logarithm of the temperature rate with coefficient −3.8 K.