The structures,grain sizes and magnetism were analyzed and computed for three typical samples:the stock of polycrystalline metal Gd(sample 1),the bulk nanocrystalline Gd prepared by spark plasma sintering(SPS) technique and subjected to the annealing process of 623 K for 0.5 h(sample 2) and the bulk nanocrystalline Gd prepared by the SPS technique at 573 K(sample 3).The computation results indicated that the sample 3 had the efficiency of space filling up to 99.38%.The computation results of magnetization indicated that the ferromagnetism was contributed by the 4f7 electrons and 21% of the 5d1 itinerant electrons in the metal Gd.The ferromagnetism of the nanocrystalline Gd decreased significantly compared with the stock of the polycrystalline Gd.The possible reasons are:the existence of a small quantity of the Gd2O3 impurity,and the existence of the phase of antiferromagnetism in the nanocrystalline Gd.The curves of the magnetic susceptibility χ which are dependent on the temperature T of the samples were steep in the vicinity of the phase-transition point Tc.It was determined to be a second-order phase transition by the linear relationship between the reciprocal of the magnetic susceptibility 1/χ and temperature T by the analysis of Landau's phase-transition theory.
