Single crystal synthesis and magnetic properties of Co2+-substituted and non-substituted magnetoplumbite-type Na-La ferrite

Single crystals of magnetoplumbite-type Na-La ferrite with and without Co doping were grown by the flux method. Wave length dispersive X-ray analysis reveals that Na and La are present in the ratio of Na/La = 0.25-0.41, and Co is successfully substituted for Fe. Magnetization measurements using single crystals indicate uniaxial magnetic anisotropy in these materials. A metamagnetic transition for the hard-axis magnetization was observed in non Co2+-substituted samples at around 7 kOe due to the magnetic free energy double minima originating from the Fe2+ ion. The successful introduction of Co2+ enhances the uniaxial magnetic anisotropy favorable for permanent magnets.