Quantum well states in Fe/Nb(001) multilayers: First principles study

TL;DR

This study uses first-principles calculations to analyze interlayer exchange coupling in Fe/Nb multilayers, revealing oscillatory behavior explained better by the quantum well model than the RKKY model, with implications for magnetic multilayer design.

Contribution

It provides a detailed first-principles comparison of RKKY and quantum well models in explaining exchange coupling oscillations in Fe/Nb multilayers.

Findings

Exchange coupling oscillates with short and long periodicities.

Quantum well model better describes the oscillatory behavior.

Majority-spin bands significantly contribute to quantum well states.

Abstract

We present a first-principles study to understand the phenomena of interlayer exchange coupling in Fe/Nb multilayers using the linearized-muffin-tin-orbitals method within the generalized gradient approximation. We find that the exchange coupling oscillates with both short and long periodicities, which have been examined in terms of the Ruderman-Kittel-Kasuya-Yosida (RKKY) model as well as the quantum well (QW) model. We have investigated the behavior of the exchange coupling by artificially varying moments of Fe atoms in ferromagnetic layers. For a small moment of Fe, the coupling shows bilinearity in the magnetic moments, implying its RKKY character. However, at higher moments close to that of bulk Fe, the saturation of long-period oscillations is in accordance with the QW model. Quantum well dispersions around the Fermi level demonstrate that the majority-spin bands contribute largely to the formation of quantum well states, which we analyze quantitatively by making use of the phase accumulation model. Our analysis indicates that the quantum well model gives a better description of the oscillatory behavior of the exchange coupling in Fe/Nb multilayers.