| People can’t live without materials,and the application of ferrite is gradually increasing because of its advantages,such as simple preparation,low cost and good performance.Especially for hexagonal ferrite Ba/Sr Fe12O19,it has been widely used as a hard magnetic phase.However,single hard magnetic materials cannot meet the demand for high performance,so the research of composite materials is becoming a trend.In this paper,the electromagnetic properties of composites were improved by the composition between hard and soft magnetic phase,which can be explained by the exchange-coupling mechanism.The phase formation,microstructure,magnetic properties and microwave absorbing properties were investigated.The main content is as follows:1.xSrFe12O19/(1-x)Co Fe2O4 composite,were prepared at 1230℃ for 4 h.The grains have uniform distribution.Typical magnetic hysteresis loops are observed.The saturation magnetization of composite increases from 45.25A·m2·kg-1 to 64.84A·m2·kg-1 with the increase of Co Fe2O4 phase.Meanwhile,remanent magnetization and coercivity were enhanced markedly too.For 0.7Sr Fe12O19/0.3Co Fe2O4 composite,the coercivity value decreases with the increase of sintering temperature.Both single Sr Fe12O19 and Co Fe2O4 ferrites have the best microwave absorbing properties with the thickness of 2mm.Compared with single-phase Co Fe2O4,the hexagonal ferrite Sr Fe12O19 has Stronger microwave absorption peaks.In the range of 11-18 GHz,with the increase of Sr Fe12O19 content,the absorbing peak moves towards low frequency direction,which has large peak bandwidth and the minimum reflectance.When x is 0.3,the composite has best absorbing performance(14.8GHz,-40 d B)with the peak bandwidth of 1.2GHz.2.xSrFe12O19/(1-x)Ni Fe2O4 composite sintered at 1230 oC for 3h was prepared by traditional solid state route,which have uniform grain size distribution.The relative density is up to 93.81%,.Except for 0.3Sr Fe12O19/0.7Ni Fe2O4 composite,the magnetic hysteresis loops of other samples show single phase magnetic behavior.The Saturation magnetization,remanence,coercivity of xSrFe12O19 /(1-x)Ni Fe2O4 composites increase initially,and then decease,which has the maximum values of 42.1A·m2·kg-1,17.2A·m2·kg-1,78.7k A·m-1 separately.When x is 0.3,the composite exhibit a typical “been waist” hysteresis loop.The remanence and coercivity of composite increase and then show a reduction tendency with the increase of temperature.Ni Fe2O4 ferrites has the smallest reflection loss of-18.3d B with the thickness of 2mm.Meanwhile,Sr Fe12O19 ferrites has the smallest reflection loss of-12.5d B with the thickness of 2.5mm.In addition,the peaks of composites shift towards to lower frequency compared with single Sr Fe12O19.The microwave absorbing properties was improved,especially for the mole ratio of 9:1 and 3:7.3.Ba Fe12O19/Ni0.5Zn0.5Fe2 Cr O4/Ni Fe2O4 composites,which have high uniform grain size distribution,were prepared at 1280℃ for 3h.The X-ray diffraction patterns for Ni0.5Zn0.5Fe2 Cr O4/Ni Fe2O4 is lower with the increase of Ba Fe12O19 content.In the composite,Ba Fe12O19 particle boundary is clear and the average particle size is 1um.The doping of Cr3+ decreases the particle size of Ni0.5Zn0.5Fe2 Cr O4.The particle boundary of Ni0.5Zn0.5Fe2 Cr O4/Ni Fe2O4 become clear gradually from the shape of smooth ball for the mass ratio of 5:5.The magnetic hysteresis loops of Ni0.5Zn0.5Fe2 Cr O4/Ni Fe2O4 and Ba Fe12O19 have the properties of hard and soft magnetic materials.The saturation magnetization,remanent magnetization and coercivity of composite decrease with the increase of temperature.The saturation magnetization increases,and the remanent magnetism increases initially and then decreases.While the coercivity decreases from 10.8k A·m-1 to 5.3k A·m-1.Ba Fe12O19 and Ni0.5Zn0.5Fe2 Cr O4/Ni Fe2O4 ferrites have three absorption peaks in the frequency range of 6-18 GHz.Single Ba Fe12O19 and Ni0.5Zn0.5Fe2 Cr O4/Ni Fe2O4 have the minimum reflection loss value of 16.3GHz,-36.4d B and 14.1GHz,-16.2d B separately.In addition,obvious microwave absorption peak occurs in the frequency range of 10-18 GHz.When x is 0.3,the composite has the maximum reflection loss value of-27.2d B with bandwidth of 1.1GHz. |
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