Thermal hysteresis of Morin transition in hematite particles

Abstract

Rhombohedral shaped, single crystal hematite particles with narrow size distribution (〈D_TEM〉 = 93 ± 2 nm) were prepared by hydrolysis of iron chloride and polymerisation in water. The results of field dependent magnetization measurements at different warming–cooling rates and ac susceptibility measurements at varying frequencies are reported and discussed. Thermal hysteresis (ΔT_M) associated with the Morin transition and field dependence of the Morin temperature (T_M) are observed in warming–cooling cycles (ΔT_M = 25 and 13 K for H = 0.1 and 3 T, respectively) due to the first order phase transition. A frequency dependence of ac susceptibility is observed above T_M, as a result of the relaxation of the magnetic moment of hematite particles in the weak-ferromagnetic phase.