Thermal hysteresis of Morin transition in hematite particles

SUBER, LORENZA; IMPERATORI, PATRIZIA; MARI, ALESSANDRA; MARCHEGIANI, G; VASQUEZ MANSILLA, MARCELO; FIORANI, DINO; PLUNKETT W. R; RINALDI, DANIELLE; CANNAS, C; ENNAS, G; PEDDIS, DAVIDE

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2010 vol. 12 p. 6984 - 6989

1463-9076

Rhombohedral shaped, single crystal hematite particles with narrow size distribution (〈DTEM〉 = 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 (ΔTM) associated with the Morin transition and field dependence of the Morin temperature (TM) are observed in warming–cooling cycles (ΔTM = 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 TM, as a result of the relaxation of the magnetic moment of hematite particles in the weak-ferromagnetic phase.