Imaging Spin Reorientation Transitions in Consecutive Atomic Co layers

TL;DR

This study uses SPLEEM to observe how the magnetic easy-axis of atomic-layer cobalt films on ruthenium changes orientation during deposition, revealing a reorientation at two monolayers due to strain and surface effects.

Contribution

It provides the first direct imaging of spin reorientation transitions in atomic-scale cobalt layers and links these transitions to strain and interface effects through relativistic calculations.

Findings

One- and three-monolayer films are magnetized in-plane.

Two-monolayer films are magnetized out-of-plane.

The out-of-plane magnetization at two monolayers is due to strain and surface effects.

Abstract

By means of spin-polarized low-energy electron microscopy (SPLEEM) we show that the magnetic easy-axis of one to three atomic-layer thick cobalt films on ruthenium crystals changes its orientation twice during deposition: one-monolayer and three-monolayer thick films are magnetized in-plane, while two-monolayer films are magnetized out-of-plane, with a Curie temperature well above room temperature. Fully-relativistic calculations based on the Screened Korringa-Kohn-Rostoker (SKKR) method demonstrate that only for two-monolayer cobalt films the interplay between strain, surface and interface effects leads to perpendicular magnetization.