Cr-substituted Ni-Zn ferrites via oxalate decomposition. Structural, electrical and magnetic properties

摘要

A series of Cr-substituted Ni-Zn ferrites; Ni_(0.8)Zn_(0.2)Cr_xFe_(2-x)O_4 (x=0.0-1.0) were prepared via oxalate decomposition route to characterize the effect of Cr-substitution on structural, magnetic and electrical properties. The prepared powders were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and transmission electron microscopy (TEM). XRD indicated single-phase cubic ferrites. The lattice parameters (a_(Exp)) exhibited a gradual decrease with increasing chromium, attributed to the smaller ionic radii of Cr~(3+) substituent. According to the obtained structural data, an appropriate cation distribution was suggested and fortified through FT-IR spectroscopy besides magnetic and electrical measurements. TEM image showed agglomerated cubic crystals with an average size of about 20 nm. Vibrating sample magnetometer (VSM) measurements indicated minimal hysteresis characteristic for soft magnetic material. The decrease in saturation magnetization (M_s) with Cr-substitution was discussed in view of Neel's two sub-lattice model. The change in the coercivity with Cr-content was discussed in view of estimated cation distribution and magnetization values. The obvious fall in the Curie temperature, estimated from molar susceptibility measurements, with increasing Cr-concentrations was assigned to the gradual replacement of Fe~(3+) ions on the octahedral sites by paramagnetic Cr~(3+) ions. ac-con-ductivity as a function of both frequency and absolute temperature exhibited a semi-conducting behavior. The decrease in conductivity with increasing Cr-content was attributed to the preferential occupation of Cr~(3+) ions by octahedral sites which replacing Fe~(3+) ions and limiting Fe~(2+)-Fe~(3+) conduction.