Magnetic and Thermal Properties of FeMn2O4 Single Crystals

We have investigated the magnetic and thermal properties of single-crystalline FeMn$_{\mathrm{2}}$O$_{\mathrm{4}}$, which forms an inverse spinel structure. Specific heat and thermal conductivity reveal smooth but unusual temperature dependence below 400 K. Quantitative data analysis suggests that these quantities contain large magnetic contributions, reflected by the T$^{\mathrm{3/2}}$ dependence of specific heat at low temperatures and the speedy drop of thermal conductivity below 75 K. Correspondingly, there is a sharp decrease of magnetization at T$_{\mathrm{N1}}\approx $ 75 K. Further investigation of neutron powder diffraction indicates that the system undergoes two magnetic transitions on cooling: one from paramagnetic to a collinear ferrimagnetic (FI) order at T$_{\mathrm{N2}}\approx $ 420 K, followed by another transition to a non-collinear FI order at T$_{\mathrm{N1}}\approx $ 75 K. The magnetic structure-property relationship will be discussed.