Study On Magnetic Properties Of FeSiAl Soft Magnetic Composites Insulated And Coated With Layered Materials

FeSiAl magnetic powder core has many strengths including high saturation magnetization,high resistivity,and low cost,making it widely used in high-power inductance devices such as switching power transformers,power chokes,line filters,etc.With the development of electronic systems towards miniaturization and integration,electronic devices are expected to be smaller in size and can work at high frequency with low loss,which puts forward higher requirements for the electromagnetic performance of metal magnetic powder core.In this paper,aiming to diminish the magnetic loss of composite materials and optimize their magnetic properties,a thin,uniform,dense,and efficient inorganic coating with high resistivity,and good thermal stability is fabricated to reduce eddy current loss,and then transverse bias magnetic field is utilized to reduce the hysteresis loss of soft magnetic composite materials.This paper focuses on the research of FeSiAl magnetic powder,innovatively selects layered materials as the insulating coating material,and has prepared efficient inorganic-coated FeSiAl soft magnetic composite with high permeability,low loss,and high-quality factor,whose phase structure,microscopic morphology,coating thickness,saturation magnetization,permeability,magnetic loss,magnetic spectrum,DC bias performance,and high-frequency performance are systematically studied.A new phenomenon is observed,and some innovative research results are obtained.The main findings are as follows:1.Under the shear force and crushing force generated by high-speed ball milling,two-dimension（2-D）layered silicate material biotite mother sheet is peeled into nano-scale 2-D biotite thin sheet,which is attached to the surface of micro-scale FeSiAl particles to form an efficient,dense,uniform and thin inorganic coating layer.At 1 wt.%biotite content,the soft magnetic composite has high permeability（106）and a magnetic loss of 220 kW/m³（0.1 T,50 kHz）,which is superior to the magnetic properties reported in the relevant literature.A larger amount of biotite coating is not only conducive to improving the frequency stability and DC bias performance of FeSiAl/biotite soft magnetic composite but also conducive to reducing the relative magnetic loss of FeSiAl/biotite soft magnetic composite.2.2-D semiconductor material MoS₂ is innovatively selected as an insulating coating material.Under mechanical milling,MoS₂ is peeled into 2-D nanoflakes,which are used to fabricate efficient inorganic MoS_2-coated FeSiAl/MoS₂ composite material with low loss and high permeability.The magnetic property analysis results show that at 1 wt.%MoS₂ content,FeSiAl/MoS₂ composite has the best performance,whose magnetic loss is 454 kW/m³（0.1 T,0.1 MHz）,permeability is 109,and saturation magnetization is 127.4 emu/g.Compared with the results reported in the relevant literature,FeSiAl/MoS₂ composite has distinct advantages in saturation magnetization,permeability,magnetic loss,and other properties.As the MoS₂ content increases,the hysteresis loss of FeSiAl/MoS₂ composite gradually increases,the eddy current loss gradually decreases,and the cut-off frequency increases,indicating that it is suitable for high frequency and high power applications.3.Under the shear force generated by the cavitation effect of high-power ultrasonic wave,the layered semiconductor material WS₂ is peeled into a 2-D nano-WS₂ thin sheet.Then the low-loss,thin,and efficient inorganic WS₂ -coated FeSiAl soft magnetic composite is prepared by mixing a 2-D nano-WS₂ thin sheet and FeSiAl magnetic powder with an ultrasonic wave.The magnetic loss of FeSiAl/2.25wt%WS₂ composite is 431 kW/m³（0.1 T,0.1 MHz）,which is 30%lower than that of the present commercial FeSiAl soft magnetic composite.A new phenomenon has been found during loss separation.With the increase of WS₂ content,the hysteresis loss of FeSiAl/WS₂ composites prepared by ultrasound wave decreases,which is different from the trend of FeSiAl/biotite and FeSiAl/MoS₂ composites.In order to reduce the eddy current loss in the particles,the fine FeSiAl/2.25 wt.%WS₂ soft magnetic composite samples were fabricated.Results of the test at high-frequency show that its magnetic loss is merely 367 kW/m³（20 mT,1 MHz）,indicating that the material has a much better performance compared with the data reported in the literature.4.Besides coating FeSiAl with 2-D layered nanomaterials to reduce eddy current loss,a transverse bias magnetic field is also exploited to diminish the magnetic hysteresis loss of FeSiAl soft magnetic composite,aiming to reduce both eddy current loss and hysteresis loss.After applying a transverse bias magnetic field of 140 kA/m on the FeSiAl/WS₂ composite with good performance,the permeability decreases by about 9%and the magnetic loss decreases by about 47%（50 mT,10 kHz）.Through loss separation,it is found that the transverse bias magnetic field can reduce the hysteresis loss of FeSiAl/WS₂ soft magnetic composite,and the eddy current loss is unchanged.At 2.25 wt.%WS₂ content,the magnetic loss of the FeSiAl/WS₂ sample is about 356 kW/m³（100 kHz,0.1 T）,which is reduced to about 75%of the magnetic loss before the transverse bias field is applied and is about 40%lower than the magnetic loss of the same type of FeSiAl magnetic particle core of American Magnetic Corporation.After applying a 140 kA/m transverse bias magnetic field,the magnetic loss of the fine FeSiAl/2.25 wt.%WS₂ soft magnetic composite sample is only 234kW/m³（20 mT,1 MHz）.It shows that the sample has excellent low-loss performance at high frequencies and is suitable for high-frequency and high-power applications.5.By analyzing the data of three kinds of soft magnetic composites,FeSiAl/biotite,FeSiAl/MoS_2,and FeSiAl/WS₂ ,a new phenomenon that has not been reported in previous literature is found:with the increase of magnetic induction strength,the quality factor Q of soft magnetic composites first decreases and then increases,indicating that when the magnetic induction strength becomes relatively strong,despite the magnetic loss gradually increases,the relative magnetic loss is gradually decreasing.The reason is that with the increase of magnetic induction intensity,the hysteresis loop of the sample gradually changes from a"straight line"shape to an"S"shape.