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 Co(2)Z-type Ba ferrite Ba3Co2Fe24O41 (Ba(3)Z) and those with Sr2+ substitution for Ba2+, i.e., Ba1.5Sr1.5Co2Fe24O41 (Ba(1.5)Sr(1.5)Z) and Sr3Co2Fe24O41 (Sr(3)Z) 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 Sr(3)Z 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 Ba(3)Z and Ba(1.5)Sr(1.5)Z lie in the c plane, but that those in Sr(3)Z 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 moment directions of magnetic ions. Magnetic moments in Ba(3)Z and Ba(1.5)Sr(1.5)Z turn to the c axis when temperature rises from 523 to 573 K. However, the moments in Sr(3)Z turn to the c axis at the lower temperature of 50 K. These results were consistent with the present measurements on permeability, XRD, and magnetization. The change in moment direction caused by temperature rise must be attributed to the disappearance of effective moments of cobalt ions in these temperature regions. (c) 2006 American Institute of Physics.