Spin Glass and ferromagnetism in disordered Kondo lattice

TL;DR

This paper investigates the complex interplay between spin glass, ferromagnetism, and Kondo effects in a disordered Kondo lattice model using functional integral techniques, revealing phase transitions and phase diagrams relevant to experimental systems.

Contribution

It introduces a generalized Mattis model to interpolate between ferromagnetic and spin glass behavior in a Kondo lattice, providing a detailed phase diagram analysis.

Findings

Second order transition from paramagnetic to spin glass phase at low J_K

First order transition with coexisting spin glass and magnetization at lower temperatures

Dominance of Kondo state at high J_K

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 \cite{Mattis} which represents an interpolation between ferromagnetism and a highly disordered spin glass. Functional integral techniques with of Grassmann fields has been used to obtain the partition function. The static approximation and the replica symmetric ansatz has also been used. The solution of the problem is presented as a phase diagram temperature $T$ {\it 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 becomes thermodinamically stables. For high $J_K$, the Kondo state is dominating. These results could be helpful to clarify the experimental situation of $CeNi_{1-x}Cu_{x}$.