Magnetic and magnetoelectric properties of M-type substitution hexaferrites TSc$_x$Fe$_{12-x}$O$_{19}$ (T = Ba, Sr)

Single crystals of M-type substitution hexaferrites BaSc$_x$Fe$_{12-x}$O$_{19}$ and SrSc$_x$Fe$_{12-x}$O$_{19}$ ($x=1.3$–$1.7$) have been grown. Their anisotropic magnetic and magnetoelectric properties have been studied at temperatures of $2$–$360$ K in magnetic fields up to $200$ kOe. In all compounds under study, a spontaneous transition from the collinear ferrimagnetic uniaxial phase to a conical structure has been detected with a decrease in the temperature at a temperature increasing with the concentration of Sc up to room temperature. In magnetic fields both parallel and perpendicular to the $c$ axis, the conical phase is suppressed and the transition to the collinear ferrimagnetic structure occurs. Phase diagrams have been plotted in $H$-$T$ coordinates. In conical magnetic structures, a magnetic-field-induced electric polarization (higher than $40$ $\mu$C/m$^2$ at $4$ K) has been detected in the geometry corresponding to the inverse Dzyaloshinskii–Moriya interaction mechanism (spin current). A higher stability of the polar state with respect to magnetic fields (higher than $50$ kOe) and temperatures (up to $100$ K) has been revealed as compared to previous studies of the Ba system. Various possibilities of controlling the chirality of the conical structure determining the sign of the polarization, which is important for applications, have been demonstrated.