NEPCO effect and the influence of pressure on the Curie temperature of spinel-type FeV₂O₄ and TiFe₂O₄

Abstract

The magnetic permeability of ferrimagnetic normal-spinel-type FeV₂O₄ and inverse-spinet-type TiFe₂O₄ at high pressures has been measured in a piston-cylinder apparatus. The Curie temperature and the Hopkinson temperature of FeV₂O₄ increase with increasing pressure at rates of 4·8 ± 0·4 to 3·4 ± 0·2K GPa⁻¹ and 1·9 ± 0·1 to 1·1 ± 0·1 K GPa⁻¹ respectively, and those of TiFe₂O₄ increase with pressure at rates of 3·7 ± 0·7 to 4·8 ± 0·1 K GPa⁻¹ and 2·2 ± 0·3 to 3·3 ± 0·3 K GPa ⁻¹ respectively. A condition for the occurrence of the NEPCO effect (i.e. a negative pressure derivative of the Curie temperature for magnetic oxides) in the samples studied to date is full Co²⁺ occupancy of the tetrahedral site.