# Electron states and magnetic phase diagrams of strongly correlated systems

## TL;DR

This paper analyzes various auxiliary-particle methods for electron correlations in many-electron models, applying them to copper-oxide systems and exploring magnetic phase diagrams within Hubbard and Kondo models.

## Contribution

It compares auxiliary-particle approaches and employs a generalized Hartree-Fock method to analyze magnetic phases and phase separation in correlated electron systems.

## Key findings

- Correct estimation of doubly occupied states improves phase energy calculations
- Magnetic phase diagrams depend on band filling and interaction parameters
- Slave-boson approach effectively captures correlations in Hubbard model

## Abstract

Various auxiliary-particle approaches to treat electron correlations in many-electron models are analyzed. Applications to copper-oxide layered systems are discussed. The ground-state magnetic phase diagrams are considered within the Hubbard and $s$-$d$ exchange (Kondo) models for square and simple cubic lattices vs. band filling and interaction parameter. A generalized Hartree-Fock approximation is employed to treat commensurate ferro-, antiferromagnetic, and incommensurate (spiral) magnetic phases, and also magnetic phase separation. The correlations are taken into account within the Hubbard model by using the slave-boson approach. The main advantage of this approach is correct estimating the contribution of doubly occupied states number and therefore the paramagnetic phase energy.