Growth and characterization of ultrathin cobalt ferrite films on Pt(111)

TL;DR

This study reports the growth, annealing, and detailed characterization of ultrathin cobalt ferrite films on Pt(111), revealing effects on grain size, magnetic order, and cation distribution through various in-situ techniques.

Contribution

It provides new insights into how annealing conditions influence the structural and magnetic properties of cobalt ferrite thin films.

Findings

Annealing increases grain size and induces magnetic order at room temperature.

Cobalt segregation occurs on the surface of thicker films after annealing.

Cationic distribution varies with annealing atmosphere, approaching an inverse spinel structure in oxygen.

Abstract

CoFe2O4 thin films (5 nm and 20 nm thick) were grown by oxygen assisted molecular beam epitaxy on Pt(111) at 523~K and subsequently annealed at 773 K in vacuum or oxygen. They were characterized in-situ using Auger Electron Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy and Conversion Electron M\"ossbauer Spectroscopy. The as-grown films were composed of small, nanometric grains. Annealing of the films produced an increase in the grain size and gave rise to magnetic order at room temperature, although with a fraction of the films remaining in the paramagnetic state. Annealing also induced cobalt segregation to the surface of the thicker films. The measured M\"ossbauer spectra at low temperature were indicative of cobalt ferrite, the both films showing very similar hyperfine patterns. Annealing in oxygen or vacuum affected the cationic distribution, which was closer to that expected for an inverse spinel in the case of annealing in an oxygen atmosphere.