Effect of Nd on structure and magnetic properties of CoPt alloys

The effects of Nd on the microstructure and magnetic properties of NdxCo50−xPt50 alloys (x = 0, 0.5, 1.0, 1.5) were investigated. The XRD results indicated that all the alloys that were homogenized at 1000 °C mainly contain the A1 (fcc) phase, while the alloys that were annealed at 675–750 °C consist of the hard magnetic face-centered-tetragonal (fct) phase and magnetically soft fcc phase. In any case, a few amount of NdPt5 phase exists in alloys when x > 1.0. The (1 1 1) reflection belonging to fct phase shifts to a higher angle and the c/a ratio increases as the Nd content increases, which leads to the decrease in degree of ordering S. As a function of annealing time, both maximum values of the coercivity Hc and remanence ratio mr were reached in Nd0.5Co49.5Pt50 alloys annealed at 675 °C for 40 and 60 min, respectively. For the series of NdxCo50−xPt50 alloys annealed at 675 °C for 60 min, the Hc decreases monotonically with the increase in Nd concentration but the value of mr is enhanced at first and then weakened, showing the highest value of 0.84 at x = 0.5.