Magnetic properties and Mossbauer study of gallium doped M-type barium hexaferrites

Ga-substituted (0 < x < 1.2) ceramics samples of the M-type Ba-hexaferrites (BaFe12O19) were obtained via solid state reactions. The features of crystal structure were studied by XRD. It has been observed that with x increase the unit cell parameters linearly and slightly decrease. The very small reduction of the unit cell parameters and, of the resulting unit cell volume is caused by the very small difference of ionic radiuses of Ga3+ (0.62 A) and Fe3+ (0.64 A) cations. Raman spectroscopy investigations and Mossbauer studies were performed. The distribution of Ga3+ in different non-equivalent oxygen coordination (octahedral, tetrahedral and bipiramidal position) is not statistical. It has been established that in BaFe1.2-xGaxO19 (0 < x < 1.2) solid solutions magnetic properties critically depend on the Ga3+ cations distribution by different oxygen coordination. At a low level of diamagnetic substitution (x < 0.3) Ga3+ cations are preferably distributed in 2b position. At a higher level of diamagnetic substitution (x < 0.9) Ga3+ cations are preferably distributed in 12k position. Experimental data of Mossbauer studies are in good agreement with theoretical data which were obtained using the first principles total energy calculations (based on density functional theory).