The first-principles study of thermodynamical properties of random magnetic overlayers on fcc-Cu(001) substrate

TL;DR

This study uses first-principles calculations and Monte Carlo simulations to analyze the thermodynamical properties and magnetic behavior of iron-cobalt overlayers on Cu(001), revealing insights into Curie temperatures and disorder effects.

Contribution

It introduces a combined theoretical approach using first-principles, Monte Carlo, and RPA methods to study magnetic overlayers, highlighting the limitations of simplified models at low coverage.

Findings

Weak maximum of Curie temperature as a function of composition

Good agreement between RPA-VCA and MC for full monolayer

RPA-VCA fails at low coverage due to magnetic percolation

Abstract

We present the theoretical study of thermodynamical properties of fcc-Cu(001) substrate covered by iron-cobalt monolayer as well as by incomplete iron layer. The effective two-dimensional Heisenberg Hamiltonian is constructed from first principles and properties of exchange interactions are investigated. The Curie temperatures are estimated using the Monte-Carlo (MC) simulations and compared with a simplified approach using the random-phase approximation (RPA) in connection with the virtual-crystal approach (VCA) to treat randomness in exchange integrals. Calculations indicate a weak maximum of the Curie temperature as a function of composition of the iron-cobalt overlayer. While a good quantitative agreement between RPA-VCA and MC was found for iron-cobalt monolayer, the RPA-VCA approach fails quantitatively for low coverage due to the magnetic percolation effect. We also present the study of the effect of alloy disorder on the shape of magnon spectra of random overlayers.