title: 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 (DeltaT(M)) associated with the Morin transition and field dependence of the Morin temperature (T(M)) are observed in warming-cooling cycles (DeltaT(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.
authors.affiliation: CNR-Istituto di Struttura della Materia, via, Salaria km 29,300,00016 Monterotondo St, Roma, Italy. lorenza.suber@ism.cnr.it
authors.forename: L
authors.initials: L
authors.lastname: Suber
authors.forename: P
authors.initials: P
authors.lastname: Imperatori
authors.forename: A
authors.initials: A
authors.lastname: Mari
authors.forename: G
authors.initials: G
authors.lastname: Marchegiani
authors.forename: M Vasquez
authors.initials: MV
authors.lastname: Mansilla
authors.forename: D
authors.initials: D
authors.lastname: Fiorani
authors.forename: W R
authors.initials: WR
authors.lastname: Plunkett
authors.forename: D
authors.initials: D
authors.lastname: Rinaldi
authors.forename: C
authors.initials: C
authors.lastname: Cannas
authors.forename: G
authors.initials: G
authors.lastname: Ennas
authors.forename: D
authors.initials: D
authors.lastname: Peddis