Effect of Ni substitution on Y -type barium ferrite

Here, we have investigated the crystal structure and magnetic properties of Ni-substituted Y-type barium ferrite. The single-phased Ba2Co2−xNixFe12O22 (x = 0.0, 0.5, 1.0) samples were synthesized by solid-state reaction method. The crystal structure of samples was determined to be rhombohedral with R-3 m. The Rietveld refinement showed that the unit cell volume (Vu) of the samples decreased with increasing Ni contents because the ionic radius of the Ni2+ is smaller than that of Co2+. Saturation magnetization (Ms) and coercivity (Hc) of Ba2Co2−xNixFe12O22 were also decreased with Ni concentration. The temperature dependence of the magnetization curve of Ba2CoNiFe12O22 under 100 Oe showed the magnetic structure transitions from helimagnet to ferrimagnet around 204 K and from ferrimagnet to paramagnet around 720 K. While the spin transition temperature (TS) of the samples decreased with Ni substitution, the Curie temperature (TC) increased with increasing Ni contents. The Mössbauer spectra analysis showed the coexistence of Fe ions at six sub-lattices with different occupancy ratio. Also, from temperature dependence of isomer shift value and magnetic hyperfine field (Hhf), we determined that Fe ions were at high spin Fe3+ state. In addition, we have observed an abrupt change in Hhf around 204 K, corresponding to the helimagnet to ferrimagnet phase transition shown in zero-field-cooled curve. Also, the experimentally observed increase in Hhf with Ni contents can be attributed to the change in the super-exchange interaction.