Stabilization of room temperature spin driven ferroelectric phases in Ni²⁺ doped Y- type BaSrCo_2-xNi_xFe₁₁AlO₂₂

Type II multiferroics possess the highest magnetoelectric coupling among single phase multiferroics due to the relation between the spin order and the ferroelectric polarization. However, these materials tend to exhibit magnetoelectric coupling at temperatures lower than room temperature which limits their applications. In recent years the Y-type hexaferrites have been studied due to the tunability of its magnetic structure which enables to stabilize its magnetoelectric phases up to room temperature. In the present work, the effects of Ni²⁺ doping in BaSrCo_2-xNi_xFe₁₁AlO_22, with x varying from 0 to 1.5, Δx = 0.5, are studied. Temperature scan of the magnetic properties and hysteresis loops confirm that Ni²⁺ concentration reduces magnetization and, stabilizes the spin driven ferroelectric phases. Magnetic behavior and magnetodielectric measurements allow identifying that the samples with x of 1.0 and 1.5 mol of Ni²⁺ exhibit room temperature spin driven electric polarization. In addition, XRD Rietveld refinement shows a reduction of the a/b and c cell parameters while the T-S boundary through the Fe8–O9 bond is stretched, which may be attributed to the stability of the spin driven ferroelectric phases.