Coercivity and magnetic viscosity in mechanical milled nanocrystalline YCo5

High coercivity and magnetic viscosity in nanocrystalline YCo5 alloy were observed. The alloy was obtained by arc-melting the raw materials, mechanical milling for 4h with subsequent heat treatment for short times at 1103K and a final quenching in water. The x-ray diffraction pattern showed a single hexagonal 1:5 phase. The average crystallite size determined by transmission electron microscopy was 13nm. Magnetic measurements were carried out at 85K in a pulsed field magnetometer varying the field in the range 50–250kOe and keeping the pulse duration equal to 0.3s. A maximum coercivity of 50kOe was measured when applying a maximum magnetic field of 250kOe. The viscosity parameter was measured varying the dH/dt rate in the range 511–1113kOe∕s. The calculated activation volumes from viscosity data were smaller than the crystallite volume from transmission electron microscopy, consistent with their different physical meanings.