Features of crystal and magnetic structures of solid solutions BaFe12-xDxO19 (D = Al3+, In3+; x=0.1) in a wide temperature range

摘要

The study of barium ferrites partially substituted by diamagnetic Al and In ions has been performed by the neutron diffraction method with high resolution. Both samples BaFe11.9D0.1O19 (D = Al and In) preserve a magnetoplumbit structure in a broad temperature range from 4.2K to 730 K. The Invar effect was found in the low-temperature region in both samples. This unusual behavior of the unit cell was explained by changes of the regime of mutual rotations and tilts of the oxygen octahedra. The magnetic structure described by the Gorter model is saved up to the ferrimagnetic and paramagnetic phase transition temperature, 705K and 695 K, for the Al- and In-substituted ions, respectively. The substitution of iron by aluminum or indium ions decreases the total magnetic moment of the investigated composition from 20 mu(B) (BaFe12O19) to 19 and 16.7 mu(B), respectively. A higher coercitivity was found H-c similar to 0.1T, for the In-substituted compositions, differently from H-c similar to 0.007 T of the Al-doped ones because of the frustration of the magnetic structure. The decrease of ambient temperature increases microstresses in crystallites because of the increasing influence of the magnetic subsystem.