'Theory for the enhanced induced magnetization in coupled magnetic trilayers in the presence of spin fluctuations'

TL;DR

This paper presents a theoretical study on how spin fluctuations enhance induced magnetization in coupled magnetic trilayers, revealing significant effects not explained by mean field models, with implications for layered magnetic systems.

Contribution

The study introduces a Green's function approach combined with a Heisenberg Hamiltonian to account for magnetic fluctuations, explaining experimental observations of induced magnetization.

Findings

Magnetization in Ni film is strongly enhanced near its Curie temperature due to interlayer coupling.

Resonance-like peaks in Ni susceptibility shift with interlayer exchange strength.

Magnetic fluctuations significantly influence the magnetic properties of layered systems.

Abstract

Motivated by recent experiments, the effect of the interlayer exchange interaction $J_{inter}$ on the magnetic properties of coupled Co/Cu/Ni trilayers is studied theoretically. Here the Ni film has a lower Curie temperature $T_{C,\rm Ni}$ than the Co film in case of decoupled layers. We show that by taking into account magnetic fluctuations the interlayer coupling induces a strong magnetization for $T\gtsim T_{C,\rm Ni}$ in the Ni film. For an increasing $J_{inter}$ the resonance-like peak of the longitudinal Ni susceptibility is shifted to larger temperatures, whereas its maximum value decreases strongly. A decreasing Ni film thickness enhances the induced Ni magnetization for $T\gtsim T_{C,\rm Ni}$. The measurements cannot be explained properly by a mean field estimate, which yields a ten times smaller effect. Thus, the observed magnetic properties indicate the strong effect of 2D magnetic fluctuations in these layered magnetic systems. The calculations are performed with the help of a Heisenberg Hamiltonian and a Green's function approach.