Suppression of low-temperature magnetic states in Mn3O4 nanoparticles

We have investigated the low-temperature magnetic properties of Mn3O4 nanoparticles using thermodynamic and magnetic measurements. While bulk Mn3O4 exhibits three magnetic transitions close to 42, 40 and 34 K, the two lower temperature transitions appear to be absent above 15 K in Mn3O4 nanoparticles. The magnetization and spin entropy associated with the ferrimagnetic transition at 42 K is smaller in the Mn3O4 nanoparticles than bulk Mn3O4, which is consistent with roughly 30–50% of the spins not contributing to the magnetic order. We tentatively attribute this suppression of the lower temperature transitions to a combination of finite size effects and effects arising from amorphous surface spins on the nanoparticles.