Large enhancement of magnetostriction due to compaction hydrostatic pressure and magnetic annealing in CoFe2O4

Polycrystalline CoFe2O4 was produced by a ceramic method. The heat-treated powder was pressed, varying the hydrostatic pressure between 87 and 278 MPa, and was heat-treated again at 1350 degrees C for 24 h. All magnetic parameters showed a clear dependence on this hydrostatic pressure. The saturation magnetization showed a minimum, and the coercivity, the anisotropy, and the magnetostriction showed a maximum at compaction pressures around 150 MPa. This pressure dependence of the magnetic parameters can be explained by a cation redistribution due to the hydrostatic pressure and heat treatment. Additionally, all samples were field-annealed in an external field of 10 T (at 300 degrees C for 3 h). The field-annealing process causes an induced uniaxial anisotropy, which results in a reduction of the coercivity (in the easy axis) as well as a dramatic increase in the magnitude of the magnetostriction along the hard axis. Maximum magnetostriction value of -400X10(-6) was obtained. Additionally, d lambda/dH is increased within a factor of three with magnetic heat treatment. (C) 2012 American Institute of Physics. [doi:10.1063/1.3675489]