Temperature Dependence of Magnetic Moment Orientation in Co2Z-Type Hexaferrite Estimated by High-Temperature Neutron Diffraction

Abstract

We investigated the correlation between the thermomagnetic curve of Co2Z-type hexagonal barium ferrite and its magnetic moment direction. We measured the thermomagnetic curve of Ba3Co1.8Fe24.2O41, prepared using the conventional solid-state reaction method, in the temperature range from 294 to 773 K with a vibrating sample magnetometer under 70 Oe. The curve shows two significant magnetization slumps at 540 K and 680 K. High-temperature XRD patterns show that no crystal transformation occurs in the temperature region from 294 to 773 K. High-temperature neutron diffraction experiments were performed to investigate the magnetic moment orientation at elevated temperatures. The Rietveld analyses of the neutron diffraction patterns indicate that the temperature rise from 523 to 573 K makes the magnetic moments turn to the c-axis from a direction parallel to the c-plane most significantly. The slump in magnetization at 540 K may be attributed to the change in easy magnetization direction from the c-plane to the c-axis. The change in average orientation of the magnetic moments must be induced by the disappearance of the contribution of cobalt to magnetism in this temperature range.