Effects of CoFe₂O₄ substitution on magnetic properties of NiFe₂O₄ spinel ferrite

Abstract

Functional magnetic materials of composition Ni1 − xCoxFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were prepared using NiFe2O4 (soft) and CoFe2O4 (semi-hard) nanomaterials following solid state synthesis technique. Magnetic properties of synthesized samples were studied employing XRD, FESEM, VSM and DSC techniques. Curie temperature, Tc of all the samples were determined from the temperature dependence of permeability and compared with the peak temperature of DSC thermograph. Tc is found to decrease with increasing CoFe2O4 substitution which has been ascribed due to weakening of JAB super-exchange interaction between tetrahedral and octahedral sites. The detail hysteresis parameters such as Ms, Mr, Hc have been determined from M-H loop measured at 80, 200 and 300K. Saturation magnetization, Ms measured at 80K was found much higher compared with data at 300K. Ms is found to increase with decreasing temperature and attained a maximum value corresponding to CoFe2O4 at any measurement temperature which may be attributed to higher magnetic moment of CoFe2O4 compared with NiFe2O4. A gradual magnetic hardening was observed to increase with increasing CoFe2O4 content with a maximum value of Hc at x = 0.8. Initial permeability as a function of frequency has been measured by an impedance analyzer. Phase transition temperature determined from DSC measurements and temperature dependence of initial permeability was found to display a good correlation. In addition, magnetic hardening of soft NiFe2O4 with increasing amount of CoFe2O4 substitution is also explained based on the existing theories of magnetism.