Magnetic phase transition in Y0.97Dy0.03

Abstract

Neutron diffraction has been used to study the long-range helical magnetic order in a single crystal of the dilute alloy Y0.97Dy0.03. In zero applied magnetic field, the propagation vector is along the c axis and of magnitude 0.28(2π/c), with the magnetic moments lying in the basal plane of the hexagonal lattice. The Dy develops the full free-ion moment and exhibits a temperature dependence similar to that of the Brillouin function for J=15/2. At T=6 K, a magnetic field applied in the basal plane causes almost no shift in the value of the modulation wave vector and as the magnetic field is increased, the peak scattered intensity of the magnetic satellite drops continuously, with the helical phase being completely suppressed in a field of 3 T. On reducing the field, there is hysteresis in the peak intensity, with only 79% of the original intensity being recovered at H=0. This residual intensity grows slowly with time, increasing to approximately 82% of the original value over a period of 1 h. This behavior differs from that of the Y(Gd) system, which shows no hysteresis and displays a sharp transition between helical and sinusoidal phases, the difference presumably being due to the presence of crystal field anisotropy in the case of Dy.