Local and long-range realizations of a spin-reorientation surface phase transition

TL;DR

This paper investigates the spin reorientation transition in ultrathin Fe films on Ni/W(110), revealing both local and long-range magnetic behaviors and providing a comprehensive quantitative description of susceptibility measurements.

Contribution

It introduces a detailed analysis of local and long-range realizations of the spin reorientation transition, integrating both effects into a unified quantitative model.

Findings

Identification of two susceptibility peaks corresponding to local and long-range transitions

Demonstration that the transition occurs at a non-integer layer thickness for long-range order

Quantitative agreement between the model and experimental susceptibility data

Abstract

The spin reorientation transition of an ultrathin film from perpendicular to in-plane magnetization is driven by a competition between dipole and anisotropy energies. \textit{In situ} measurements of the magnetic susceptibility of Fe/2 ML Ni/W(110) films as a function of Fe coverage, made as the films are deposited at constant temperature, show two clear peaks; one at the long-range and one at the local realization of the transition. In the long-range realization, the susceptibility probes the striped domain pattern that is formed in response to the balance of energetics on a mesoscopic scale. Here the reorientation transition occurs at a non-integer layer thickness. In the local realization, the susceptibility probes the response of small islands with in-plane anisotropy in the 3rd atomic Fe layer that are grown on the 2nd atomic Fe layer, which has perpendicular anisotropy. It is a response to the local finite-size, metastable energetics due to discrete steps in thickness. An excellent quantitative description of the susceptibility data is obtained when both local and long-range aspects of the spin reorientation transition are included.