Effects of Substitution in Barium hexaferrites BaFe_(12-x)X_xO_(19)(X=Co,Ti; Sc)

摘要

The short and long-range atomic and magnetic order in BaFe_(12-x)Co_xTi_xO_(19) (x=0.4, 0.7, 0.8) and BaFe_(10.4)Sc_(1.6)O_(19) prepared by soft chemistry routes were studied and compared with parent BaFe_(12)O_(19) prepared by solid-state reaction. For BaFe_(10.3)Co_(0.85)Ti_(0.85)O_(19) neutron diffraction and magnetic measurements revealed that (Co~(2+) , Ti~(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_(12)O_(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 10 K a block-type conical magnetic structure sets in. For BaFe_(10.4)Sc_(1.6)O_(19), combined neutron diffraction, field-dependent ~(57)Fe Mossbauer studies and magnetic measurements show that the collinear block-type structure remains effective at 300 K and below it down to about 190 K. In the 190 - 1.6 K range we observe a temperature dependent incommensurate complex block-type conical structure.