Spin Glass and ferromagnetism in disordered Cerium compounds

TL;DR

This paper investigates the complex interplay between spin glass, ferromagnetism, and Kondo effects in disordered cerium compounds using a generalized model, revealing phase transitions and stable states that align with experimental observations.

Contribution

It introduces a generalized Mattis model for disordered cerium compounds, analyzing phase transitions between spin glass, ferromagnetic, and Kondo states using functional integral techniques.

Findings

Second order transition from paramagnetic to spin glass with decreasing temperature.

First order transition between spin glass and ferromagnetic-like states at lower temperatures.

Kondo state emerges at high Kondo coupling values.

Abstract

The competition between spin glass, ferromagnetism and Kondo effect is analysed here in a Kondo lattice model with an inter-site random coupling $J_{ij}$ between the localized magnetic moments given by a generalization of the Mattis model 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 giving $T/{J}$ {\it versus} $J_K/J$ where $T$ is the temperature, $J_{K}$ and ${J}$ are the strengths of the intrasite Kondo and the intersite random couplings, respectively. If $J_K/{J}$ is small, when temperature is decreased, there is a second order transition from a paramagnetic to a spin glass phase. For lower $T/{J}$, a first order transition appears between the spin glass phase and a region where there are Mattis states which are thermodynamically equivalent to the ferromagnetism. For very low ${T/{J}}$, the Mattis states become stable. On the other hand, it is found as solution a Kondo state for large $J_{K}/{J}$ values. These results can improve the theoretical description of the well known experimental phase diagram of $CeNi_{1-x}Cu_{x}$.