Structural and magnetic properties of Ni-substituted Ba0.5Sr1.5-based Y-type hexaferrite

The Ni-doped Y-type hexaferrites Ba0.5Sr1.5Zn2-xNixFe12O22 have been prepared using the solid-state technique. The X-ray diffraction patterns indicate that the lattice constant is increased as the Ni content raises, which can be ascribed to the different ionic radius of Zn2+ and Ni2+. All samples are polycrystalline with clear grain interface by means of scanning electron microscopy. The grain size is found to increase with an increase of Ni concentration. The magnetic properties of all samples show different Ni-substitution dependence and strongly depend on Ni content. The results indicate that the value of saturation magnetization increases to a maximum of 41.5 emu/g at x = 0.8, and then decreases with increasing Ni content. For low-doped Ni-substitution (x <= 0.8) specimens, the magnetic transition temperature associated with a screw to ferrimagnetic state increases, suggesting that magnetically induced ferroelectric polarization will be observed at high temperature even room temperature. Especially for x = 1.2 specimen, the stabilization of the ferroelectricity phase at a low magnetic field is expected in terms of the disappearance of phase boundary from the screw to intermediate-I. At the same time, the ferroelectric polarization can be maintained in a wide range of magnetic fields for Ni-doped samples. These results confirm that Ba0.5Sr1.5-based Y-type hexaferrite with different Ni-doped content have a great application prospect in magnetoelectric devices at high temperature and under low magnetic fields.