In situ growth and magnetic characterization of Cr Chloride monolayers

TL;DR

This study demonstrates the in situ growth and magnetic characterization of Cr chloride monolayers on various substrates, revealing distinct magnetic behaviors and coexistence of different valence compounds with superparamagnetic properties.

Contribution

It introduces a method for growing and analyzing Cr chloride monolayers on different substrates, showing how substrate chemistry influences valence states and magnetic properties.

Findings

CrCl3 and CrCl2 monolayers exhibit distinct magnetic properties.

Substrate chemistry affects the formation of different valence compounds.

Coexistence of CrCl3 and CrCl2 with superparamagnetic behavior was observed.

Abstract

Monolayer Chromium Dihalides and Trihalides materials can be grown on a variety of substrates by molecular beam epitaxy regardless of the lattice mismatch thanks to the van der Waals epitaxy. In this work, we studied the magnetic nature of Cr Chloride monolayers grown on Au(111), Ni(111) and graphene-passivated Ni(111) from the evaporation in ultra-high vacuum of the same halide precursor. Structural, morphological and magnetic characterizations were conducted in situ by low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and X-ray magnetic circular dichroism (XMCD). Owing to opposite chemical behaviour, Au(111) and Ni(111) promote the formation of two different valence compounds, i.e. CrCl$_3$ and CrCl$_2$, showing distinct magnetic properties at 4 K. When graphene is used to passivate the Ni(111) surface, the formation of CrCl$_3$ becomes allowed also on this substrate. The coexistence of CrCl$_3$ and CrCl$_2$, both showing few nm lateral size and super-paramagnetic properties, is demonstrated by XMCD spectra displaying two dichroic peaks at the characteristic Cr$^{3+}$ and Cr$^{2+}$ energies. Site-selective magnetization measurements performed with the photon energy tuned on the two absorption edges show reversed magnetization of some of the CrCl$_2$ islands with respect to the CrCl3 domains, which is interpreted in terms of magnetic frustration.