Magnetic transformation of Zn-substituted Mg-Co ferrite nanoparticles: Hard magnetism → soft magnetism

摘要

Zinc substituted magnesium-cobalt ferrite nanoparticles having the basic composition Mg_(0.2)Co_(0.8-x)_Zn_xFe_2O_4 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) were successfully synthesized using sol-gel auto combustion method. The results show that the doping amount of Zn~(2+) ions has a great influence on its structure and magnetic properties. X-ray diffraction (XRD) measurements show that Mg_(0.2)Co_(0.8-x)_Zn_xFe_2O_4 has a good phase formation, and all samples have single-phase cubic spinel structure. The average crystallite size is calculated from Scheller's formula to be between 49 and 54nm. And the lattice constant increases from 8.38 to 8.43 A with the increase of Zn~(2+) ions content. Fourier transform infrared (FTIR) measurements also confirm the formation of the cubic spinel structure of ferrite. The ferrite samples were observed by scanning electron microscopy (SEM) to be spherical nanoparticles. The magnetic properties of the samples have been determined at room temperature by vibrating sample magnetometer (VSM). The results show that the magnetic properties of Mg-Co ferrite are significantly affected by the doping amount of Zn~(2+) ions. For Zn-substituted Mg-Co ferrites, the magnetic properties decrease obviously with the increase of Zn content. This rapid decrease of magnetic properties reveals that the magnetic properties of Zn-substituted magnesium-cobalt ferrite have realized the transition from hard magnetic to soft magnetic. Meanwhile, the coercivity is He = 21.26 Oe, the saturation magnetization is 4.56 emu/g and the re-manent magnetization is 0.03 emu/g for Mg_(0.2)Zn_(0.8)Fe_2O_4 sample. This also indicates that the ferrite samples prepared have a transition from ferromagnetic behavior to superparamagnetic behavior. The smaller coercivity value confirms that soft ferrite has been obtained. Meanwhile, this transition from hard magnetism to soft magnetism can be used as a potential high frequency soft magnetic material.