Magnetocapacitance on the transition fields in Ni²⁺ doped Y-type hexaferrite Ba_0.6Sr_1.4Co₂Fe₁₁AlO₂₂ obtained by high-energy ball milling

Y-type hexaferrites possess multiple magnetic phases that are temperature and magnetic-field dependent. Some of these phases are ferrimagnetic and also exhibit room temperature spin-driven ferroelectricity that corresponds to a type-II magnetoelectric. The temperature stability and the magnetic activation field of the multiferroic phases of Y-type hexaferrite can be tuned by substituting Co²⁺ sites with transition metal ions, such as Ni²⁺. The present work describes a simple method for obtaining Y-type hexaferrites using high-energy ball milling with heat treatment at relative low temperatures, compared with other methods, and evaluates the effect of nickel as dopant in Ba_0.6Sr_1.4Co_2-xNi_xFe₁₁AlO₂₂, with x varying from 0 to 2.0 (Δx = 0.5), on the magnetic, dielectric, and magnetodielectric properties. The results show successful synthesis of pure hexagonal Y-type hexaferrite (R-3 m) by an easy and economical method. In addition, it is observed that nickel doping produces a diminution in the specific magnetization, a change in the magnetic thresholds of the magnetic phases, and an increase in space charge polarization. In addition, the magnetodielectric measurements also show different positive magnetocapacitance behaviors linked to the effect of doping on the magnetic and electronic structure.