Preparation Of Spinel Ferrite Materials And Their Magnetic,Electrical And Gas Sensing Properties

Spinel ferrite material MFe₂O₄?M=Zn,Co,Ni and other metal elements?is a ferromagnetic metal oxide,where M is generally a divalent metal ion.MFe₂O₄ferrite materials have good magnetic properties and dielectric properties.It has a wide range of applications in medical diagnostics,microwave absorption,magnetic memory and other fields.In addition,as a gas sensing material,MFe₂O₄ ferrite materials have better stability and gas selectivity,which further broadens the application range of ferrite materials.Although ferrite materials have multifunctional characteristics,ferrite materials still have shortcomings in some aspect,such as low saturation magnetic moment,poor temperature/frequency stability of dielectric constant,and poor sensitivity to gas sensing performance and so on.It has been found that the doping and sintering conditions of the sample have a great influence on the microstructure of the ferrite,which further affects the magnetic,electrical and gas sensing properties.Therefore,in this paper,MnFe₂O₄ and NiFe₂O₄ ferrites were doped with different cations to optimize the preparation and sintering conditions of the design samples,and the materials were modified to improve the performance.A series of excellent performances were obtained.Ferrite materials,the main research work and results are as follows:Mn_1-xZn_xFe₂O₄?x=0.2-0.8?ferrite samples were successfully prepared by the sol-gel method.X-ray diffraction study reveals that single cubic spinel phase is formed in most Mn_1-xZn_xFe₂O₄ samples.The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺doping concentration and sintering temperature while the grain size grow up to 9.48?m for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100^oC.Further,the dielectric and magnetic measurements indicated that both Zn²⁺doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner.The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100^oC for 8 h is found to show the largest M_s value?77.30 emu/g?in this work.These results indicate that Zn²⁺doping or sintering temperature can adjust the microstructures,dielectric and magnetic properties of Mn_1-xZn_xFe₂O₄ ferrites.Cu_xNi_1-xFe₂O₄ powders were prepared by the sol-gel method and the corresponding temperature dependence of microstructure,magnetic and dielectric properties of different Cu_xNi_1-xFe₂O₄ samples have been investigated.Results of XRD and SEM indicate that the Cu²⁺concentration played an important role in both crystal phase and particle distribution of Cu_xNi_1-xFe₂O₄.The measurement of magnetic properties shows that both Cu²⁺doping and sintering conditions could change the saturation magnetization and remnant magnetization in a noticeable manner,and even the magnetic material type.The Cu_0.2Ni_0.8Fe₂O₄ sample sintered at 900^oC had the largest M_s?34.61 emu/g?,M_r?17.85 emu/g?and the lowest H_c?0.17 kOe?.The dielectric measurements show strong frequency dependence for all the samples.The peak observed in frequency dependence of dielectric loss measurements shifts to higher frequency with the increasing Cu²⁺concentration and sintering temperature.The above results indicate that the doping of Cu²⁺has a significant influence on the microstructure and magnetic and electrical properties of NiFe₂O₄.Ni_xCo_1-xFe₂O₄ and Mg_xZn_1-xFe₂O₄ powders were prepared by the sol-gel method.X-ray diffraction?XRD??scanning electronic microscope?SEM??vibrating sample magnetometer?VSM?and Gas sensing Analysis System?CGS-8?were used to characterize the Ni_xCo_1-xFe₂O₄ and Mg_xZn_1-xFe₂O₄powders.Results of XRD and SEM indicate that the Ni²⁺concentration played an important role in both crystal phase and particle distribution of Ni_xCo_1-xFe₂O₄.The VSM revealed that both Ni²⁺doping and sintering temperature could change the saturation magnetization and remnant magnetization in a noticeable manner.The CoFe₂O₄ sample sintered at 750^oC had the largest M_s?139.73 emu/g?,M_r?66.95 emu/g?and H_c?1185.59 Oe?.At the prime working temperature of 210^oC,Ni_0.6Co_0.4Fe₂O₄ showed a high selectivity towards ethanol,the sensor showed the highest gas response of 3.38 towards 100 ppm ethanol.Results of XRD and SEM indicate that the Mg²⁺concentration played an important role in both crystal phase and particle distribution of Mg_xZn_1-xFe₂O₄.The VSM revealed that both Mg²⁺doping and sintering temperature could change the saturation magnetization?M_s?and remnant magnetization?M_r?in a noticeable manner.The Mg_0.8Zn_0.2Fe₂O₄ sample sintered at 750^oC had the largest M_s?93.59 emu/g?,the largest M_r?23.36 emu/g?and the H_c did not change too much with temperature.At the prime working temperature of 230^oC,Mg_0.8Zn_0.2Fe₂O₄ showed a high selectivity towards ethanol,the sensor showed gas response of 4.29 towards 100ppm ethanol.Mg_0.8Zn_0.2Fe₂O₄ has a better selectivity for acetone than ethanol.