Study On Phase Structure And Magnetic Properties Of MnBiM(M=C?Fe?Zr)Permanent Magnet Alloy

In recent years,MnBi alloy has received extensive attention as a new type of rare earth-free permanent magnet material.MnBi alloy is a potential substitute for rare earth permanent magnets in medium and high temperature environments because it not only has high coercivity and good saturation magnetization and magnetic energy product,but also has a positive coercivity temperature coefficient within a certain range.During the peritectic reaction,when the LTP MnBi phase solidifies,the Mn and MnBi liquid phase are easily separated,and it is difficult to obtain a pure MnBi alloy.Therefore,there is still a big gap between the experimental results and the theoretical performance of MnBi.Element doping is considered to be a method to improve magnetic properties,and the phase structure and magnetic properties of the MnBi alloy can be affected by the alloying method.In order to obtain better performance samples,LTP MnBi alloy was prepared by arc melting method,rapid quenching method and heat treatment process.The influence of doping the third element on the phase structure and magnetic properties of MnBi alloy was studied systematically in order to obtain high performance.MnBi permanent magnet alloy material.It mainly includes the following aspects:1.Effect of process conditions on magnetic properties of MnBi alloyThe MnBi alloy is prepared by a rapid quenching and heat treatment process.The MnBi alloy ribbons with different properties were obtained by setting different copper roller speeds and subsequent vacuum annealing processes.The effects of process parameters on the magnetic properties of MnBi alloys were studied and the process conditions were optimized.It is concluded that the optimum process parameters for preparing MnBi permanent magnet alloy ribbon are copper roller linear velocity 30m/s,vacuum heat treatment condition 523 K,and rapid cooling after 10min insulation.2.Effect of alloying on phase structure and magnetic properties of MnBi alloyBased on the pre-optimized process conditions,three different types of elements,C(non-metal small atom),Fe(transition metal atom)and Zr(metal small atom),were selected as doping elements of MnBi alloy.The effect of three elements on the phase structure and magnetic properties of MnBi permanent magnet alloys.The specific research results are as follows:(1)The magnetic properties of the MnBi strip doped at 2 at%C atoms are optimal,and the coercive force and saturation magnetization are improved.(2)The Fe element can suppress the segregation of the Mn atom,promote the formation of the LTP MnBi phase,and improve the saturation magnetization of the MnBi alloy.However,there is no effect on the phase transition temperature.(3)With the addition of Zr element,the LTP MnBi phase content of the annealed sample increased from 10%in the Zr-free sample to 65%in the sample of1 at%Zr atom,and the _maximum value of Ms reached 40emu/g.However,the LTP MnBi phase in the sample of 3 at%?5 at%Zr atoms gradually decreased,and Ms gradually decreased.With the addition of Zr element,the coercive force of MnBi alloy decreases first and then increases.(4)In the three sets of experiments,the effect of doping with Fe and Zr is better than C,and the properties of MnBi Fe and MnBiZr series alloys are similar,and the squareness of the hysteresis loop of the MnBiZr series alloy is better.3.Magnetization behavior of MnBiZr permanent magnet alloyThe coercivity mechanism of MnBiZr permanent magnet alloy was analyzed by Kronmüller-Plot fitting,and the exchange coupling effect of the alloy was analyzed by first-order inversion curve(FORC)and henkel-plot(?M)curve.Studies have shown that both undoped and Zr-doped MnBi alloys are magnetic domain nucleation reversal mechanisms.The exchange coupling effect of MnBi alloy is enhanced after1at%Zr atom doping.When the doping content of Zr element is more than 3at%,the effect on the coercivity of MnBi alloy is mainly the effect of grain refinement.The microstructure shows that the addition of Zr is beneficial to refine the grains,and the finer grain size leads to the crystal field.The increase in the anisotropy greatly increases the coercive force of MnBi.Therefore,as the Zr element increases,the coercive force first decreases and then increases.The thermomagnetic curve shows that the Tc of the Mn₅₅Bi_45-xZr_x(x=0,1,5)alloy decreases from 620 K to 600 K when the Zr concentration increases from x=0to x=5.