【摘要】 应用么正变换微扰论和平均场近似研究了一维Ｈｕｂｂａｒｄ－Ｈｉｒｓｃｈ模型的铁磁性，无论单中心积分常数Ｕ多大，只有双中心的交换积分常数Ｊ″＞０，才可能有铁磁性．掺杂结果不利于铁磁性，使铁磁相的区域比无掺杂的半满情况减少．更多还原

【Abstract】 By using a perturbative canonical transformation and mean field theory, the parameter regimes that give rise to ferromagnetism are determined in the one-dimensional Hubbad-Hirsch model. The model decribes a tight-binding band with on-site repulsion U. nearest-neighbor Coulomb exchange matrix element J" and doping parameter δ.Ferromagnetism only occurs for J">0. with the required value of J" decreasing as U increases and increasing as δ increases. The ferromagnetism regions are always smaller than that for half-filling for a fixed J".更多还原