Phase transitions in K2Mn2(SO4)3 studied by ESR and specific heat

Originally, K 2 Mn 2 (SO 4 ) 3 (KMS) was reported to undergo one phase transition, cubic(P2 1 3) to orthorhombic(P2 1 2 1 2 1 ) at 201K. However, recent x-ray diffraction, specific heat measurement and thermal expansion experiment showed indication that KMS undergoes, at least two transitions. The different results seem to originate from sample dependence. We have grown new KMS crystals, and examined the phase transitions by Mn 2+ ESR and AC calorimetry. In this paper, we found that not only the linewidth but also the g-value is good indication of phase transition. It was found that the unstable crystals give several transitions, mainly having the largest anomaly at 171K. The anomalies can be changed by low temperature heat-treatment. However, the heat-treatment at 250°C produced very stable crystals which have transition temperature at 195K.