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 4f~7 electrons and 21% of the 5d~1 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 Gd_2O_3 impurity, and the existence of the phase of antiferromagnefism in the nanocrystalline Gd. The curves of the magnetic susceptibility X which are dependent on the temperature T of the samples were steep in the vicinity of the phase-transition point T_c.It was determined to be a second-order phase transition by the linear relationship between the reciprocal of the magnetic susceptibility 1/X,and temperature T by the analysis of Landau's phase-transition theory.
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