Magnetic properties of hematite with large coercivity
نویسندگان
چکیده
The magnetic properties of hematite powders produced by a solid state nucleation-and-growth process are studied as a function of temperature T and applied field H. Independently of the temperature, there exists a soft magnetic contribution that is assigned to the canting of spins at the superficial shell of each particle and is not affected by the Morin transition. At 220 < T < TM a magnetic contribution with high coercivity is observed, due to spin–flop in the anti ferromagnetic state and above TM = 248 K the weakly ferromagnetic state has a coercivity that ranges from 6 kOe to 4 kOe when raising T up to room temperature. Different sub-grain structures were obtained by means of isochronal and isothermal annealing. Changes in the susceptibility are directly related to the sub-particle size. It is concluded that sub-boundaries are the defects responsible for the high coercivities observed in the weakly ferromagnetic state. PACS 75.47.Lx, 75.50.Tt, 91.25.F-, 91.60.Ed
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