Effect of Nd on structure and magnetic properties of CoPt alloys

The effects of Nd on the microstructure and magnetic properties of Nd x Co 50− x Pt 50 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 NdPt 5 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 H c and remanence ratio m r were reached in Nd 0.5Co 49.5Pt 50 alloys annealed at 675 °C for 40 and 60 min, respectively. For the series of Nd x Co 50− x Pt 50 alloys annealed at 675 °C for 60 min, the H c decreases monotonically with the increase in Nd concentration but the value of m r is enhanced at first and then weakened, showing the highest value of 0.84 at x = 0.5.