Structural and magnetic properties of Ga-substituted Co2-W hexaferrites

Precursor powders of BaCo2Fe16-xGaxO27 with 0.0 <= x <= 0.8 were prepared using high-energy ball milling, and the effects of chemical composition on the structural and magnetic properties of the powders sintered at 1300 degrees C were investigated using x-ray diffractometer (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD patterns of all samples indicated crystallization of pure BaCo2-W (BaCo2Fe16O27) hexaferrite phase. SEM measurements revealed large step-like formations with hexagonal crystallites. The magnetic data revealed small fluctuations of the saturation magnetization below the value 72.56 emu/g corresponding to the unsubstituted sample. The coercive field H-c of all samples ranged between 70 Oe and 130 Oe, indicating soft magnetic phase. Curie temperature determined from the thermomagnetic curves of the samples decreased from 485 degrees C at x = 0.0 down to 451 degrees C at x = 0.6. Also, the thermomagnetic curves revealed the presence of a minority magnetic phase with enhanced superexchange interaction, and the occurrence of complex magnetic phase transitions associated with spin reorientation transitions above room temperature. (C) 2018 Korean Physical Society. Published by Elsevier B.V. All rights reserved.