Structure and magnetic properties of nanocrystalline dysprosium powders

In this current study, nanocrystalline Dy powders were prepared by melt-spinning and subsequent high-energy ball-milling. The effect of ball-milling time on the structure and magnetic properties of the powders was studied. The crystal structure and microstructure of the melt-spun ribbons and ball-milled powders were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Magnetic measurement of all samples was performed with vibrating sample magnetometer (VSM). XRD results indicate that the average crystal grain size of the powders decreases from 90.09 nm of the ribbons to 10.42 nm of the 4-h ball-milled powders. Further TEM observation shows that the grains are fine and uniform. The Neel temperature (T-N) decreases from 182 K of the ribbons to 172 K of the powders, while the Curie temperature (T-C) increases from 100 to 130 K, demonstrating that the grain size has substantial influence on the magnetic transition process. Moreover, at 60 K, as the ball-milling time increases, the coercivity of the powders increases first, peaking at 0.48 T for 2-h milling, then drops again, while the remanence of the powders decreases monotonically. As a result, the powders milled for 2 h exhibit an optimal maximum energy product of 64.0 kJ center dot m(-3), demonstrating the good potential of these powders as a permanent magnet at low temperatures.