Magnetic properties of Sr0.5Ba0.5HoxFe12-xO19 (x ≤ 0.10) nanohexaferrites

The Ho3+ ion-substituted SrBa nanohexaferrites, Sr0.5Ba0.5Fe12-xHoxO19 (x & LE; 0.1) (Ho & RARR; SrBa NHFs), were fabricated via ultrasonic-assisted sol-gel route. The hexagonal structure and plate-like morphology were confirmed by X-ray powder pattern (XRD), transmittance electron microscope (TEM), scanning electron microscope (SEM), and high-resolution transmittance electron microscope (HR-TEM). It has been found out that the crystallite size (D-XRD) was within 45-74 nm range. Both elemental mapping and energy-dispersive X-ray spectroscopy (EDX) analyses provided the purity and expected chemical composition of the products. Using the M-H hysteresis loops (at 300 and 10 K), magnetic properties of Ho & RARR; SrBa NHFs are analyzed. Upon a sudden fall at x = 0.02, as soon as Ho ions are added, the magnetization is improved with the Ho substitution and prominently enhanced with decreasing temperature. However, the coercivity H-c is decreased with the Ho substitution. The Ho-doped samples represent a magnetically soft material at both high and low temperatures, which is also confirmed through M-T measurements. Their squareness ratio is found to be less than 0.5, suggesting the generation of multi-magnetic domains. The unsubstituted HFs and the samples with x = 0.02 and 0.06 show usual M-T variations with typical field-cooling (FC) and zero-field-cooling (ZFC) branches. However, the other samples (with x = 0.04, 0.08, and 0.10) exhibit unusual behavior with anomalies in their M-T plots. From Fe-57 Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting, and hyperfine magnetic field values on Ho3+ substitution have been determined. Mossbauer spectra show that Ho3+ ions located at generally octahedral 12 k site. The s-electron density of around Fe3+ ions has not influenced doped content.