Grain-size-dependent Curie transition in nanocrystalline Gd: the influence of interface stress

The dependence of the Curie transition temperature T-C on the average crystallite size of a nanocrystalline material has been studied experimentally in nanostructured Gd prepared by the inert-gas condensation method. Measurements of heat capacity and AC magnetic susceptibility indicate that T-C shifts to lower temperatures and the Curie transition takes on an increasingly broadened and rounded appearance with decreasing crystallite size. Isothermal annealing steps resulted in controlled grain growth, thus permitting the functional dependence of the T-C shift on crystallite size to be determined. The latter was inconsistent with the finite-size effect observed in Gd films. Rather, the shift in Curie temperature could best be understood as a consequence of the significant internal pressure induced by the interface stress of high-angle grain boundaries in Gd. (C) 2002 Elsevier Science B.V. All rights reserved.