Abstract
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<T M a magnetic contribution with high coercivity is observed, due to spin–flop in the anti ferromagnetic state and above T M =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.
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Bercoff, P.G., Bertorello, H.R. Magnetic properties of hematite with large coercivity. Appl. Phys. A 100, 1019–1027 (2010). https://doi.org/10.1007/s00339-010-5983-7
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DOI: https://doi.org/10.1007/s00339-010-5983-7