Structural and magnetic properties of BaFe_{12−2 x} Cu _x Mn _x O₁₉ hexaferrites

In this study, ball-milling method was adopted for the synthesis BaM-hexaferrites BaFe_{12−2 x} Cu _x Mn _x O₁₉ ( x   =  0.00, 0.25, 0.50, 0.75, and 1.00). The system shows pure BaM phase in the samples with x   =  0.0 and x   =  0.25. At higher substituent concentrations, Y-type hexaferrite phase developed. The evolution of the Y-type phase was confirmed by Rietveld refinement of the x-ray diffraction patterns, and the thermomagnetic measurements from which the Curie temperature of the existing phases was determined. The Curie temperature for the M-type phase decreased with increasing x , signaling the reduction of the superexchange interaction strength. The particle size of the pure sample was within the critical single-domain size, and the size increased with increasing x as determined by SEM imaging. These variations induced significant reduction in the coercivity as a consequence of the development of multi-domain particles with increasing x . The coercivity decreased from 3.4 kOe for the pure sample, down to 50 Oe for the sample with x   =  0.50, and then increased slightly at higher x values. The saturation magnetization ( M _s) decreased monotonically with increasing x , from 67.2 (emu g⁻¹) for pure sample, down to 43.0 emu g⁻¹ for the sample with x   =  1.0. The sample with x   =  0.25 exhibited magnetic properties suitable for high density magnetic recording, while the samples with higher x values exhibited magnetic softening, prohibiting the potential for such applications. (paper)