Magnetic properties of MnBi1-xRx (R=rare earth) systems

MnBi crystallizes in a NiAs-type hexagonal crystal structure, exhibits a hi gh uniaxial anisotropy, and is potentially useful as a permanent magnet mat erial. We have examined the effect of partial substitution of Bi with rare earth elements on the magnetic properties of MnBi. MnBi1-xRx (R=Nd, Dy) wer e prepared by mechanically alloying powders of the constituent elements at liquid nitrogen temperature followed by heat treatment. X-ray diffraction a nd magnetic measurements were performed on powder samples to characterize t he samples. We found that in MnBi1-xNdx, coercivity (at room temperature) i ncreases from 0.7 kOe to 6.6 kOe for x=0.0 and 0.3, respectively. In MnBi1- xDyx the coercivity increases from 0.7 kOe to 7.9 kOe for x=0.0 and 0.3. Th e increase in coercivity may be in part due to the increase in the crystal field anisotropy as Nd or Dy is introduced and in part due to the finer par ticle size. A magnet made from MnBi shows coercivity of similar to 17 kOe. A very fine particle size is considered to be the reason for this high coer civity. (C) 2000 American Institute of Physics. [S0021-8979(00)79608-3].