Study On The Effect Of Insulating Material Doping On Magnetic Properties And Resistivity Of NdFeB Magnets

When the NdFeB rare earth permanent magnetic materials used in high frequencyalternating electric field will create the induced electromotive force, because theNdFeB permanent magnetic materials have less resistivity （about230μ·cm）, theinduction electromotive force cause large induction current, the magnet surface is easyto produce strong swirl and make the magnet itself heating. The raise of magnetstemperature leads to the magnetic properties decline, shorten the service life andrestrict the fields of ues. A solution envisaged for this problem what produce on therare earth magnet in use is to improve the resistivity of itself to reduce the eddy currentloss.The purpose of this study is to find out a suitable way to prepare NdFeBpermanent magnetic with high resistivity and keep the magnetic properties on a certainlevel. The experiments adopt three methods to prepare the composite NdFeB magnetwith high resistivity: chemical coating、high resistivity powder doping and polymermaterial cladding.Chemical coating prepared with NdFeB/SiO₂composite magnets, the resistivityincreased with the SiO₂coating thickness adding. When the SiO₂coating thicknesswas closed to64nm,the resistivity of composite magnets increased to260μ·cm butthe maximum magnetic energy product （BH）maxdecreased to30.7MGOe, theinfluence of SiO₂coatings with different thickness on magnetic properties wasdifferent, this may be due to the atomic diffusion during hot deformation.High resistivity powder doping method prepared NdFeB/Al₂O₃compositemagnets, the affect of magnetic properties by nano-Al₂O₃doping amount is great, themagnetic energy product and the intrinsic coercivity decreases linearly with theincrease of Al₂O₃content. The resistivity increases by13%reached to260μ·cm whenthe nano-Al₂O₃mass fraction is1.5wt%.NdFeB/Epoxy resin bonded composite magnets by polymer material cladding,the resistivity reached as high as4.5×1010μ·cm when the additive amount of epoxyresin was10wt%, then the remanence and energy product was significantly reducedand little effect on coercivity. Composite NdFeB magnets with high resistivity were prepared by this threedifferent methods, though the added of non-magnetic material to some extent reducesthe magnetic properties, the affect of resistivity and magnetic properties were differentof magnets type and quantity of insulating material.