The Investigation Of Electromagnetic Properties And Thermal Conductivity Of Rare Earth Doped MnZn Ferrite

With the continuous development of MnZn ferrite power devices in the field of high-frequency applications,the heat dissipation problem of devices has attracted growing attention.For one,the introduction of additives to reduce high-frequency loss can solve the temperature rising problem.Nevertheless,there is still a lack of systematic understanding to the influence of rare earth additives.For another,the thermal conductivity of the MnZn ferrite also has a great impact on the heat dissipation property.Hence,investigating the thermal conductivity of the MnZn ferrite is of great significance to heat dissipationIn this paper,Sc-doped and Dy-doped MnZn ferrites were prepared by the solid-phase sintering method.The influences of Sc and Dy doping on the phase composition,microstructure and electromagnetic properties were investigated,which provides a reliable experimental basis for further researching on rare earth-doped MnZn ferrites.Besides,the thermal conductivity of MnZn ferrite was analyzed in detail.The results are shown as follows:1.For Mn_0.757Zn_0.107Sc_xFe_2.136-xO₄（x=0～0.07）ferrite material,as x increases from 0 to 0.07,both the average grain size and density first increase and then decrease.When x is 0.1,both the average grain size and density of sample show the maximum value of 4.50μm and 4.80 g/cm³ respectively.Meanwhile,the saturation magnetization（M_s）of sample show the maximum value of 92.7 A·m²/kg,the magnetocrystalline anisotropy constant（K₁）surges from 123.48 J/m³to 175.07 J/m³,which leads to the deterioration of soft magnetic performance.Additionally,the initial permeability（μ_i）decreases from 640 to 484,and the power loss increases from 107 k W/m³ to 220 k W/m³.2.For Dy-doped ferrite material,with the addition of Dy₂O₃ increasing from 0 wt%to 0.1 wt%,both the average grain size and density of samples first increase and then decrease.When the addition amount of Dy₂O₃ is 0.05 wt%,both the average grain size and density of sample show maximum value of 4.71μm and 4.82 g/cm³ respectively.Meanwhile,the sample exhibits relatively excellent soft magnetic properties,the value of M_s is 95.8 A·m²/kg,the value of H_c is 55.9 A/m,and the value of K₁ decreases from164.84 J/m³ to 143.75 J/m³.Additionally,theμ_i of the sample increases from 640 to845,and the power loss reduce from 736 k W/m³ to 586 k W/m³.3.Based on the effective medium theory（EMT）,the influences of grain and grain boundary,density and pore distribution on the thermal conductivity are quantitatively analyzed.When the grain thermal conductivity,the grain boundary thermal conductivity and the grain boundary thickness are 13.65 W/m·K,1.45 W/m·K,and12nm,respectively,the calculated thermal conductivity of MnZn ferrite is well consistent with the experiment result.Within the scope of investigation,the thermal conductivity of material increases about 10.4%～33.6%with 4 W/m·K increament of grain thermal conductivity.But the influence of grain size on thermal conductivity is relatively small.The thermal conductivity of material increases less than 3.7%with 3μm increament of average grain size.Meanwhile,the thermal conductivity of MnZn ferrite increases about 8.8%～29.5%,when the thermal conductivity of grain boundary increases by every 0.2 W/m·K.In addition,the influence of grain boundary thickness on thermal conductivity is relatively small,the thermal conductivity of material decreases less than 1%with 4 nm increament of grain boundary thickness.