Magnetic transitions in Mn3O4and an anomaly at 38 K in magnetization and specific heat

Abstract

Mn${}_{3}$O${}_{4}$ is one of the archetypal examples of tetragonally distorted spinels. In this paper we reinvestigate its complex magnetic ordering process by using high-resolution magnetic and calorimetric measurements. The first-order transition to the ground state is found to exhibit a latent heat of $\ensuremath{\simeq}$4 J mol${}^{\ensuremath{-}1}$ and a thermal hysteresis of $\ensuremath{\simeq}$0.6 K. Moreover, the peculiar field-induced broadening observed at this transition is shown to be consistent with general predictions about incommensurate-to-commensurate transition. In addition to the known sequence of transitions at ${T}_{N}\ensuremath{\simeq}43$ K, ${T}_{1}\ensuremath{\simeq}40$ K, and ${T}_{2}\ensuremath{\simeq}34$ K, a new anomaly close to ${T}^{*}\ensuremath{\simeq}38$ K is observed in both magnetization and heat capacity data. A possible origin of this feature is discussed in terms of magnetic instability within the incommensurate spiral spin configuration.