Spin glass and ferromagnetism in disordered Kondo lattice

Abstract

The competition among spin glass (SG), ferromagnetism and Kondo effect has been analysed in a Kondo lattice model, where the inter-site coupling J ij between the localized magnetic moments is given by a generalized Mattis model (D. J. Mattis, Phys. Lett. 56 A (1977) 421.) which represents an interpolation between ferromagnetism and a highly disordered spin glass. Functional integral techniques with Grassmann fields have been used to obtain the partition function. The static approximation and the replica symmetric ansatz have also been used. The solution of the problem is presented as a phase diagram temperature T versus J K (the strength of the intra-site interaction). If J K is small, for decreasing temperature there is a second-order transition from a paramagnetic to a spin glass phase. For lower temperatures, a first-order transition appears where solutions for the spin-glass-order parameter and the local magnetizations are simultaneously non-zero. For very low temperatures, the local magnetizations become thermodynamically stable. For high J K , the Kondo state is dominating. These results could be helpful to clarify the experimental situation of CeNi 1 - x Cu x .