Surface spin-flop transition in a uniaxial antiferromagnetic Fe/Cr superlattice induced by a magnetic field of arbitrary direction

TL;DR

This study investigates the surface spin-flop transition in a uniaxial Fe/Cr superlattice under magnetic fields of arbitrary direction, combining experimental magnetometry, neutron reflectivity, and micromagnetic modeling to understand the transition's nature.

Contribution

The paper presents a combined experimental and theoretical analysis of the surface spin-flop transition in Fe/Cr superlattices for arbitrary magnetic field orientations, revealing the transition's first-order and continuous regimes.

Findings

Magnetometry shows a finite jump in magnetization for small angles, indicating a first-order transition.

The phase diagram indicates a critical angle (~4.75°) separating first-order and continuous transitions.

Micromagnetic calculations agree with experimental observations of the transition behavior.

Abstract

We studied the transition between the antiferromagnetic and the surface spin-flop phases of a uniaxial antiferromagnetic [Fe(14 \AA)/Cr(11 \AA]$_{\rm x20}$ superlattice. For external fields applied parallel to the in-plane easy axis, the layer-by-layer configuration, calculated in the framework of a mean-field one-dimensional model, was benchmarked against published polarized neutron reflectivity data. For an in-plane field $H$ applied at an angle $\psi \ne 0$ with the easy axis, magnetometry shows that the magnetization $M$ vanishes at H=0, then increases slowly with increasing $H$. At a critical value of $H$, a finite jump in $M(H)$ is observed for $\psi<5^{\rm o}$, while a smooth increase of $M$ $vs$ $H$ is found for $\psi>5^{\rm o}$. A dramatic increase in the full width at half maximum of the magnetic susceptibility is observed for $\psi \ge 5^{\rm o}$. The phase diagram obtained from micromagnetic calculations displays a first-order transition to a surface spin-flop phase for low $\psi$ values, while the transition becomes continuous for $\psi$ greater than a critical angle, $\psi_{\rm max} \approx 4.75^{\rm o}$. This is in fair agreement with the experimentally observed results.