Broadband magnetic and dielectric properties of U-type hexaferrite Sr4CoZnFe36O60

Abstract

Sr4CoZnFe36O60 ceramics with U-type hexaferrite crystal structure were for the first time prepared and their structural, dielectric, magnetic and magnetoelectric properties were characterized. Broadband dielectric spectra (1 Hz −1 GHz) showed giant permittivity due to two Maxwell-Wagner dielectric relaxations whose frequencies follow the Arrhenius law. These relaxations are caused by inhomogeneous conductivity in the ceramic grains and their boundaries. Temperature and magnetic field dependences of magnetization revealed ferrimagnetic phase transition at Tc1 = 635 K and other two magnetic phase transitions at Tc2 = 305 K and Tc3 = 145 K. Magnetoelectric measurement at 10 K revealed only small polarization 35 nC/m2 which has probably extrinsic origin, so the sample is probably not multiferroic. The observed magnetocapacitance effect (-0.8 %) was attributed to the magnetoresistance (-4 %) caused by non-homogeneous conductivity of the ceramics. High-frequency magnetic permeability measured up to 1.8 GHz evidences the Curie-Weiss behavior above Tc2 and Tc3 and two magnetic field-dependent excitations which exhibit anomalies at magnetic phase transitions. We attributed these excitations to the magnetic domain wall dynamics.