Magnetic phase transitions in Ba_0.5Sr_1.5Zn₂Fe_11.92Al_0.08O₂₂ hexaferrites

We report studies on the effect of substituting the magnetic Fe³⁺ cations with nonmagnetic Al³⁺ cations in Y-type hexaferrite Ba_0.5Sr_1.5Zn₂Fe_11.92Al_0.08O₂₂ powders on their magnetic properties and especially on the magnetic phase transitions responsible for observing the magnetoelectric effect. In this research, the Y-type hexaferrite powders were synthesized by citric acid sol-gel auto-combustion. After the auto-combustion process, the precursor powders were annealed at 1170 °C in air to obtain the Y-type hexaferrite materials. The effects of Al substitution on the structural, microstructural properties and phase content were investigated in detail using X-ray powder diffraction and scanning electron microscopy. Hysteresis measurements were performed by a physical-property-measurement-system (PPMS) (Quantum Design) at 4.2 K and at room temperature. Dc-magnetic measurements of the temperature dependence of the magnetization at magnetic fields of 50 Oe, 100 Oe and 500 Oe were used to determine the effect of applying a magnetic field on the temperature of magnetic-phase transitions. We demonstrated that the helical spin state can be modified further by varying the magnetic field.