Crossover between Local-Moment Magnetism and Itinerant-Electron Magnetism in the t–J Model

Abstract

A Kondo-lattice theory is applied to the crossover between local-moment magnetism for almost half fillings of electrons and itinerant-electron magnetism away from the half filling. In clean systems with no disorder, the bandwidth W^* of quasiparticles is non-zero and of the order of |J| at T=0K even in the limit of the half filling, with J the superexchange interaction constant between nearest neighbors. The so called Gutzwiller's term also contributes to W^* away from the half filling; it is approximately proportional to doping concentrations measured from the half filling. Magnetism is enhanced by disorder because the renormalization of W^* by J is reduced by disorder. The asymmetry of disorder between electron-doped and hole-doped cuprate oxide superconductors must be, at least partly, responsible for that of antiferromagnetic phases between them. The so called Kumagai phase is characterized as an SDW state in a disordered system rather than a spin glass. The Neel temperature T_N about 300K of non-doped cuprate oxides can be explained by the reduction of T_N by critical thermal antiferromagnetic fluctuations in quasi-two dimensions.