Influence of thermomagnetic treatments on the magnetic properties of Co-Pt 50-50 alloy

A Co-Pt 50-50 single crystal annealed at 950°C was quenched very rapidly and subsequently annealed in the range 200-750°C in the presence of a magnetic field. For annealing temperatures below the Curie temperature, an analysis of the induced magnetic anisotropy detects both directional ordering and the onset of long range ordering. If the magnetic field is directed along one of the fourfold axes of the initially disordered crystal, a uniaxial anisotropy is detected due to a preferential development of the ordered regions having their tetragonal axis parallel to the direction of the magnetic field. Although this effect is weak below the Curie temperature due to the low diffusion rate, it is sufficient to determine the later development of order at higher temperatures. After such a heat treatment up to 750°C, the analysis of the magnetization curves and a study of the neutron diffraction pattern show that the entire specimen consists of practically one single-ordered region having its tetragonal axis in the direction of the applied magnetic field.