Effect of Al–Cr doping on the structural, magnetic and dielectric properties of strontium hexaferrite nanomaterials

Nanosized strontium hexaferrite doped with a binary mixture of Al–Cr at the iron site is synthesized by the chemical co-precipitation method. The hexagonal phase and the nominal composition of the synthesized nanomaterials are confirmed by X-ray diffraction and energy dispersive X-ray fluorescence analyses. The crystallite size is found in the range of 14–30 nm, which is small enough to obtain a suitable signal-to-noise ratio in high density recording media. The average grain size of the material is found in the range of 40–85 nm as determined by scanning electron microscopy. The magnetic properties, such as saturation magnetization, remanence and coercivity, are calculated from hysteresis loop measurement, and the value of the magnetic moment is also calculated from the saturation magnetization data. All the magnetic properties are found to decrease with the increase in Al–Cr content, which is due to the occupation of the doped cations at the octahedral sites (12k and 2a) having spin of electrons in upward direction. The variation in the dielectric constant and dielectric loss factor with frequency is discussed on the basis of Wagner and Koop’s theory. It is found that the dielectric constant decreases with the increase in Al–Cr content, which suggests that the doped nanomaterials are suitable for applications in microwave devices.