Preparation and physical properties of M-type hexaferrite SrCo₂Ti₂Fe₈O₁₉

ABSTRACT: Measurements of Raman spectra, dielectric constant and magnetization were performed on M-type hexaferrite SrCo₂Ti₂Fe₈O₁₉ single crystal, which was grown by travelling solvent method in an optical furnace. The Raman spectra measurements at room temperature revealed that main Raman modes, which are associated with the bipyramid FeO₅, octahedra Fe⁽⁴⁾O₆ and Fe⁽⁵⁾O₆ as well with mixed octahedral vibration all with A_{1 g} symmetry, shift monotonously to higher wave numbers. In the low-frequency region (<10 kHz), permittivity rapidly decreases with increasing frequency, exhibiting a typical characteristic of Maxwell-Wagner type relaxation. The relaxation peak in dielectric losses centred on 100 kHz can be attributed to ionic relaxation processes caused by multiple valence states of iron ion (Fe²⁺ and Fe³⁺). M-type hexaferrite SrCo₂Ti₂Fe₈O₁₉ orders magnetically at 768 K and undergoes order-to-order magnetic phase transition at 380 K. Magnetic properties are almost isotropic around room temperatures with very low hysteresis having coercive field with induction lower than 3×10⁻³ T and with remnant magnetization lower than 0.17 μ_B/f.u. for magnetic fields applied along main crystallographic directions.