Development of Nd-Fe-B Sintered Magnets with high magnetizing ability

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Purpose : Nd-Fe-B sintered magnets exhibit high coercivity, remanence and the maximum energy products. However, high applied field over 1.2 MA/m, was needed to obtain good magnetic properties. Then Nd-Fe-B sintered magnets with good magnetizing ability, which show higher magnetic properties with lower magnetizing field, have been strongly demanded in order to make a small multipole magnets. In this study, the effects of the microstructure (alignment of Nd_2Fe_<14>B particles and the amount of non-magnetic phases) and magnetizing temperature on the magnetizing ability were investigated.Experimental Procedures : The compositions of studied alloys were Nd_<15>Fe_<77>B_8 and Nd_<14.4>Fe_<79.6>B_<6.0>. These alloy powders were prepared by the conventional powder metallurgy method or the powder mixing method utilizing hydrogen decrepitation. These fine powders were pressed into the compacts in a magnetic field of 0.98MAm^<-1> at a pressure of 100Pa. Magnetic properties were measured by BH looptracer and vibrating sample magnetometer (VSM). The magnetizing ability were evaluated by the ratio of the magnetic properties with every applied field to those after applying pulsed field of 4.0MAm^<-1>. The microstructures were observed using a optical microscope and a scanning electromicroscopy.Results : The magnetizing ability improved with decreasing the amount of non-magnetic phases and increasing alignment of Nd_2Fe_<14>B particles. The main facter affecting magnetizing ability is the demagnetization field breaking out around the Nd_2Fe_<14>B particles. It is found that magnetizing at high temperature is useful method for increasing magnetizing ability. Because the demagnetization field is closely related to the saturate magnetization of Nd_2Fe_<14>B particles and it decreases with increasing temperature.