Effects of Substitution in Barium hexaferrites BaFe{sub}(12-x)X{sub}xO{sub}19 (X=Co,Ti; Sc)

摘要

The short and long-range atomic and magnetic order in BaFe{sub}(12-x)Co{sub}xTi{sub}xO{sub}19 (x=0.4, 0.7, 0.8) and BaFe{sub}10.4Sc{sub}1.6O{sub}19 prepared by soft chemistry routes were studied and compared with parent BaFe{sub}12O{sub}19 prepared by solid-state reaction. For BaFe{sub}10.3Co{sub}0.85Ti{sub}0.85O{sub}19 neutron diffraction and magnetic measurements revealed that (Co{sup}(2+), Ti{sup}(4+)) substitution causes significant distortions in the local oxygen surrounding of ferric cation sites, while the grain-size effect on the structural parameters is considerably smaller. The thermal expansion coefficient exhibits a strong anisotropy. The refined magnetic moments for x=0.45 and 0.7 based on the five-cation sublattice block-type collinear ferrimagnetic structure of uniaxial type known as Gorter type for BaFe{sub}12O{sub}19, are considerably lower than the theoretical spin only moments, especially for the 4e and 12k sites, indicating for x=0.7 a local noncollinearity with short-range ordering. For x=0.85, at 10K a block-type conical magnetic structure sets in. For BaFe{sub}10.4Sc{sub}1.6O{sub}19, combined neutron diffraction, field-dependent 57{sup left}Fe Mossbauer studies and magnetic measurements show that the collinear block-type structure remains effective at 300K and below it down to about 190K. In the 190-1.6K range we observe a temperature dependent incommensurate complex block-type conical structure