The Spin Glass,Magnetocaloric Effect And Critical Behavior Of NiCuZn Ferrites

In today's world,energy efficiency and sustainability are increasing the subject of research,and the demand for high efficiency,no pollution,high energy and miniaturization materials and devices is increasing.NiCuZn ferrites have attracted much attention due to its low price,low loss and wide Curie temperature range.In this paper,we have prepared Ni_xCu_0.2Zn_0.8-xFe₂O₄?0?x?0.28?ferrites by solid phase reaction method and investigated the microstructure,morphology,spin glass,magnetocaloric effect and critical behavior.The relationship between composition and magnetic properties are also studied.The main content are as follows:1.Ni_xCu_0.2Zn_0.8-xFe₂O₄?0?x?0.28?samples are prepared by solid phase reaction method.As the concentration of Ni²⁺ions increase,X-ray diffraction?XRD?suggests the lattice constant decreases,while scanning electron microscope?SEM?shows that the crystallite size increases.Furthermore,energy dispersive X-ray?EDX?spectra are recorded for all samples to check the element composition.2.The effect of Ni substituted on the magnetic properties of Ni_xCu_0.2Zn_0.8-xFe₂O₄?0?x?0.28?is systematically studied.Antiferromagnetic interaction is dominant in the competition between antiferromagnetic interaction and ferromagnetic interaction for x=0.As the substitution of Ni for Zn increase,the interaction of ferromagnetic interaction gradually is equivalent to the antiferromagnetic interaction and dominant,while the M_S and T_C increase which is due to the enhancement of the super-exchange interaction J_AB.For 0.12?x?0.28,all samples show typical re-entrant spin glass state.For x=0.12,it is verified to be in spin glass state at low temperature by measuring the ac susceptibility and magnetic time relaxation.The spin glass state at low temperature is the result of ferromagnetic interaction and antiferromagnetic interaction.3.The magnetocaloric effect of Ni_0.2Cu_0.2Zn_0.6Fe₂O₄ is studied.According to the isothermal magnetization curves of the sample,the slope of Arrott graph is positive,which indicates it has a second-order phase transition near T_C.According to Curie-weiss law fitting,the Curie temperature is 337 K.In addition,the maximum magnetic entropy change becomes0.77 J/kg K and relative cooling power?RCP?is 31.9 J/kg for H=25 kOe.4.The critical behavior of Ni_0.2Cu_0.2Zn_0.6Fe₂O₄ near the second-order ferromagnetic to paramagnetic transition is analyzed.According to the different method,the deduced critical exponents are very close to those of the mean-field model,suggesting that a long-range ferrimagnetic order is dominant.Furthermore,the exchange distance is estimated as J?r?^r-4.6,which also indicates long-range ferromagnetic coupling plays the dominant role in the system...