Tuning exchange interactions in antiferromagnetic Fe/W(001) by 4d transition-metal overlayers

TL;DR

This study uses first-principles calculations to explore how 4d transition-metal overlayers modify the magnetic exchange interactions and ground states of Fe/W(001), revealing transitions from antiferromagnetic to ferromagnetic states and potential for complex spin structures.

Contribution

It provides a detailed first-principles analysis of how 4d overlayers influence magnetic interactions and ground states in Fe/W(001), including the role of spin spirals and spin-orbit effects.

Findings

4d overlayers reduce ferromagnetic exchange and enhance next-nearest interactions.

The magnetic ground state transitions from antiferromagnetic to ferromagnetic across the 4d series.

Significant Dzyaloshinskii-Moriya interactions suggest potential for non-collinear spin textures.

Abstract

We use first-principles calculations based on density functional theory to study how the magnetic properties of an Fe monolayer on a W(001) surface -- exhibiting a $c(2 \times 2)$ antiferromagnetic ground state -- can be modified by an additional 4d transition-metal overlayer. To obtain an overview of how the 4d-band filling influences the exchange interactions in the Fe layer we have calculated the energy dispersion of spin spirals for 4d/Fe/2W unsupported quadlayers, in which the W(001)substrate is represented by only two atomic layers. Hybridization with the overlayer leads to a reduced ferromagnetic nearest-neighbor exchange interaction and the next-nearest neighbor exchange gains in strength. Surprisingly, we find that the $c(2 \times 2)$ antiferromagnetic state is unfavorable for all systems with a 4d overlayer. For 4d overlayers from the beginning (Nb) or end (Pd) of the series we find a ferromagnetic ground state. As one moves to the center of the series there is a transition via a spin spiral (Mo, Rh) to a $p (2 \times 1)$ antiferromagnetic ground state (Tc, Ru). We have studied the Mo, Ru, and Pd overlayer on Fe/W(001) representing the surface by a sufficiently large number of W layers to obtain bulk like properties in its center. The energy dispersion of spin spirals show qualitatively the same results as those from the 4\textit{d}/Fe/2W quadlayers. The Dzyaloshinskii-Moriya interaction calculated upon including spin-orbit coupling shows significant strength and considerable frustration effects. The calculated magnetocrystalline anisotropy energy is large as well. All 4d/Fe/W(001) films are potential candidates for complex non-collinear spin structures.