Magnetic order and transport in a spin-fermion model on a superlattice

TL;DR

This paper investigates how RKKY interactions influence magnetic order and electrical conductivity in a spin-fermion superlattice, revealing oscillations between ferromagnetic and antiferromagnetic states and their impact on transport properties.

Contribution

It introduces a non-perturbative analysis of RKKY-driven magnetic phases and transport in a spin-fermion superlattice with classical spins, extending understanding beyond traditional perturbative approaches.

Findings

RKKY interaction induces various magnetic phases depending on system parameters.

Ground state oscillates between ferromagnetic and antiferromagnetic order as buffer size varies.

Conductivity, reflected in the Drude weight, oscillates with magnetic order, akin to giant magnetoresistance phenomena.

Abstract

We consider a spin-fermion model consisting of free electrons coupled to classical spins, where the latter are embedded in a quasi one-dimensional superlattice structure consisting of spin blocks separated by spinless buffers. Using a spiral ansatz for the spins, we study the effect of the electron mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction on the $T=0$ ground state of the system. We find that the RKKY interaction can lead to ferromagnetic, antiferromagnetic, or intermediate spiral phases for different system parameters. When the width is much larger than the length of the individual blocks, the spiral phases are suppressed, and the ground state oscillates between ferromagnetic and antiferromagnetic order as the size of the buffer regions is varied. This is accompanied by a corresponding oscillation in the Drude weight reflecting an increased conductivity in the ferromagnetic state compared to the antiferromagnetic one. These results are reminiscent of classic giant magnetoresistance phenomena observed in a similar geometry of thin, sandwiched magnetic and non-magnetic layers. Our analysis provides a robust framework for understanding the role of the RKKY interaction on the ground state order and corresponding transport properties of such systems, extending beyond the conventional perturbative regime.