Effect of a magnetic field on Ni-Pt alloys.

Abstract

Magnetic properties of ${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pt}}_{\mathit{x}}$ alloys were studied in both the disordered and ordered states for x=0.25, 0.35, 0.44, and 0.50. Different magnetic fields were applied in the range from 0 to 800 Oe for the disordered state and from 0 to 10 kOe for the ordered state under the zero-field cooling condition with the temperature range from 5 to 400 K. For x=0.25 and 0.35 alloys, a ferromagnetic moment was observed in both the disordered and ordered states for the whole magnetic-field range. In the ordered state, an unusual behavior of the magnetic moment was observed, which is independent of magnetic field. For the x=0.44 alloy, a ferromagnetic moment was observed in the disordered state, but peculiar results were observed in the ordered state. A weak ferromagnetic moment appeared at 0 and 10 Oe magnetic field but from 50 up to 1000 Oe magnetic field, an antiferromagnetic-type feature is seen, where the antiferromagnetic-paramagnetic transition temperature ${\mathit{T}}_{\mathit{N}}$ decreases monotonically with increasing magnetic field. Further, from 1200 Oe up to 10 kOe, the paramagnetism is evident. Hysteresis-loop data and the curve of the inverse of the magnetic susceptibility confirmed antiferromagnetism in the alloy. This is the first observation to our knowledge for such a change under an applied magnetic field in the binary alloys. For the x=0.50 alloy, a ferromagnetic moment in the disordered state and a clear paramagnetic moment in the ordered state were observed for the whole magnetic-field range.