Preparation And Magnetic Properties Of Spinel Zinc Ferrite Obtained By A Hydrothermal Method

Theoretically,zinc ferrite（ZnFe₂O₄）is a unique spinel structure of zero magnetic moment.It was found that its magnetic properties can be tailored by means of modulating the ion occupancy of spinel ferrite through ion substitution.Therefore,it has great academic value to study the relationship between ion occupancy and magnetic properties of zinc ferrite with zero magnetic moment by ion substitution.In this thesis,the hydrothermal method was used to prepare single-phase ZnFe₂O₄ferrites,and the optimal preparation conditions were studied.In order to investigate the origin of magnetism in ZnFe₂O₄ obtained via a hydrothermal method,their magnetic properties were compared with those of ZnFe₂O₄ obtained via a ceramic method.In addition,Cr³⁺and Co²⁺ions were used to substitute Fe³⁺in B sites and Zn²⁺in A sites in ZnFe₂O₄,respectively,and their structural and magnetic properties were studied systematically.It was found that the optimal conditions of preparing the single-phase ZnFe₂O₄ferrites via a hydrothermal method were the Zn/Fe atomic molar ratio is 1:2 and the temperature condition was 200℃×6h.The morphology of ZnFe₂O₄ exhibited an ellipsoidal structure of about 7 nm in size.The maximum magnetization at the external magnetic fields of 1600 k A/m was 21.10 emu/g.Compared with the magnetic properties in ZnFe₂O₄obtained via a ceramic method,the origin of magnetic properties should be ascribed to the different Fe³⁺ion occupancy due to the Zn loss in the hydrothermal process.For ZnFe_2-xCr_xO₄ zinc ferrites substituted by Cr³⁺,it can be found that the typical single-phase spinel structure can be obtained after substitution of Fe³⁺by Cr³⁺in B sites.With the increase of Cr³⁺content,the average grain size and the maximum magnetization at the external magnetic fields of 1600 k A/m exhibited a decreasing and an increasing tendency,repaectivley.In order to further study the magnetic properties of ion substitution,sigle-phase Zn_1-xCo_xFe_1.9Cr_0.1O₄ ferrites were obtained by using Co²⁺ions to substitute Zn²⁺in A sites.Compared with the ZnFe_2-xCr_xO₄ ferrites,the satutation magnetization（M_s）of Cr³⁺-Co²⁺co-substituted Zn_1-xCo_xFe_1.9Cr_0.1O₄ ferrites was enhanced obviously,and the maximum value of M_s increased from 16.36 to 45.87 emu/g.In addition,the M_s increased with the increasing Co content.