Magnetic properties of the bulk CoFe2O4 polycrystalline under the pressure

Abstract

Ground state magnetic properties of bulk polycrystalline CoFe2O4 (CFO) were determined based on the competition among inter-grain magnetic dipolar interaction (MDI), exchange coupling (EC), and anisotropy. The present study aims to investigate effects of pressure on magnetic interactions and macroscopic magnetic properties in CFO. Results of zero-field cooling magnetization MZFC measured under different pressures and applied magnetic field of 100 Oe indicated that: (1) pressure effect is temperature-dependent. In low temperature region below 179 K, strong MDI determines the reversal of magnetic moments of particles, and moments are frozen in the direction of random anisotropy. The pressure leads to an increase in magnetization M (ΔM > 0) in low (high) temperature region below (above) 179 K, while reduces M (ΔM < 0) in the intermediate temperature region at around 179 K. The value of ΔM in high temperature region is greater than that in low temperature region. ΔM increases significantly as the pressure increases to 2.21 GPa with ΔM > 0 in the whole temperature range due to pressure-enhanced EC; its value decreases monotonously with increasing temperature. (2) For P = 0 and 0.28 GPa, MZFC changes from positive to negative at 38 and 20 K, respectively. Changes of the anisotropy were caused by magnetic moment freezing, sign conversion of MZFC, and competition of magnetic interactions. (3) For P = 0.12 GPa, remanence ratio increases from 0.73 (P = 0) to 0.80. Moreover, experimental evidence of enhanced EC by pressure was also provided.