Yukio Takada

Crystal and magnetic structures and their temperature dependence of Co2Z-type hexaferrite (Ba,Sr)3Co2Fe24O41 by high-temperature neutron diffraction

We have prepared nonoriented and magnetically oriented specimens of Co2Z-type Ba ferrite Ba3Co2Fe24O41 (Ba3Z) and those with Sr2+ substitution for Ba2+, i.e., Ba1.5Sr1.5Co2Fe24O41 (Ba1.5Sr1.5Z) and Sr3Co2Fe24O41 (Sr3Z) with the conventional solid-state reaction method. Permeability measurements of nonoriented specimens have shown that this substitution improves the frequency characteristic of permeability, though the permeability in Sr3Z significantly decreases. X-ray diffraction (XRD) and magnetization measurements of magnetically oriented specimens have shown that the magnetic moments of iron and cobalt ions in Ba3Z and Ba1.5Sr1.5Z lie in the c plane, but that those in Sr3Z deviate from the c plane. We have studied the substitution effect of Sr2+ for Ba2+ on the crystal structures and the effective sizes and directions of magnetic moments and their temperature dependences with high-temperature neutron diffraction technique. This substitution induces the change in the distribution of cobalt ions and mome...

Anomalous X-ray Scattering Study on Site Preference of Co and Fe Ions in Hexagonal Z-Type Barium Ferrite

Anomalous X-ray scattering experiments were performed at Fe-K edge with hexagonal Z-type barium ferrite samples Ba3Co2-xFe24+xO41 (x=0, 0.2 and 0.4) in order to study distributions of iron and cobalt atoms over ten crystallographically different sites in the structure. The results were consistent with those determined by the neutron diffraction technique combined with the Rietveld analysis and with those by extended X-ray absorption fine structure (EAXFS) analyses.

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

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.

Correlation between Magnetic Property and Cation Distribution in Z-type Hexagonal Barium-Ferrite (Ba 3 Co 2- x Fe 24+ x O 41 ) by Neutron Diffraction

Abstract : Z-type hexagonal ferrite samples in which cobalt is partially substituted with iron, Ba3Co(2-x)Fe(24+x)O41 (x=0, 0.2, 0.4, 0.6), were prepared by the ceramic process under a sintering oxygen partial pressure, P(O2)=21.3 or 101.3 kPa, at 1573K. The influence of the substitution ratio and oxygen partial pressure on the complex permeability was investigated by examining the cobalt distribution over various cation sites in the Z-type structure with the neutron powder diffraction analysis performed at 294 K (neutron wave length was 1.006 Angstrom). The neutron diffraction pattern was studied with the Rietveld method. A significant difference in the preferential occupation of cobalt on various kind of cation sites was observed between the samples obtained under P(O2)=21.3 and 101.3 kPa. Almost all cobalt atoms are on the 12k octahedral site at the boundary between S- and R-blocks in the sample of x=0, P(O2) 21.3 kPa. On the other hand, in the sample of x=0, P(O2)=101.3 kPa, cobalt atoms are as well on other sites, the 12k octahedral site at the boundary between S- and T-blocks, the 4e tetrahedral site in S-block, the 2a octahedral site in T-block and the 2d five fold (trigonal bypiramid) site in T-block.