Narrow Results

The aging behavior of the random n-vector model with long-range interaction decaying as r^-(d+σ) (where d is the dimensionality), is investigated by the theoretic renormalization-group approach. The system initially disordered at a high temperature is firstly quenched to the critical temperature T_c and then released to an evolution with model A dynamics. The aging properties are studied by the short-time expansions. The scaling behavior of two-time response and correlation functions are obtained in a frame of the expansion in ∊ = 2σ-d. In dimensions d < 2σ, the long-time limit of the critical fluctuation dissipation ratio X^∞ is calculated up to one-loop order. The simulation of X^∞ is discussed.

A series of Y₂O₃ nanoparticles of average particle size 19–37 nm are synthesized by a glycine-nitrate method. Room temperature ferromagnetism is observed in all samples. The magnetization of these samples decreases with increasing annealing temperature, showing a size-dependent ferromagnetism. Vacuum-heating effect on the ferromagnetism is also investigated, which indicates that the observed ferromagnetism is possibly associated with oxygen defects. Interestingly, an aging behavior of the ferromagnetism is observed when the sample is exposed to air or immersed in ethanol. These results further support the oxygen-vacancy-mediated ferromagnetism mechanism.