The effects of indium doping on the electrical, magnetic, and magnetodielectric properties of M-type strontium hexaferrites

Abstract

A series of indium-doped hexaferrite ceremics with composition of SrInxFe12-xO19 (x = 0, 1.8, 2.4 and 3.0) were synthesized by a solid-state reaction method. The samples have a single-phase magneto-plumbite structure, and their lattice parameters a and c gradually decrease with the doping indium amount. The indium doping can reduce the ceramic pores. The dielectric constant, dielectric loss, saturation magentization and coercivity also decrease with the indium concentration. The dielectric change with temperature under different frequencies and magnetic fields reveals that the magnetic field has a certain manipulation on the dielectric parameter. Indium doping induces the non-collinear magnetic structure, causing a magnetodielectric effect. The influence of the magnetic field on the magnetodielectric coefficient shows that the magnetodielectric coefficient changes from positive to negative for SrInxFe12-xO19 with x = 0.0, 2.4 and 3.0, while keeps negative in the whole temperature range for SrIn1.8Fe10.2O19. At the same time, the positive and negative magnetodielectric transition temperature is different for the samples with different doping amounts. The transition temperature of SrFe12O19 is between 50 K and 75 K, while that of SrInxFe12-xO19 (x = 2.4–3.0) is between 25 and 50 K. In addition, SrIn2.4Fe9.6O19 enjoys the magnetodielectric effect with remarkable twisted-butterfly loop at room temperature, which is an intrinsic effect confirmed by the fact that the magnetodielectric coefficient is invariable with frequency. Our results provide a helpful research basis for the magnetodielectric materials.