Coexistence of charge and ferromagnetic order in fcc Fe

TL;DR

This study demonstrates the coexistence of charge order and ferromagnetic states in a simple Fe monolayer on Rh(001), revealing complex phase interactions in a minimal system through microscopy and theoretical modeling.

Contribution

It provides the first evidence of charge and magnetic order coexistence in a single-element monolayer, expanding understanding of phase coexistence beyond complex compounds.

Findings

Charge order stripes observed below 130 K.

Superimposed ferromagnetic domains near liquid helium temperature.

Temperature-dependent cross-talk between charge and spin order modeled by Landau theory.

Abstract

Phase coexistence phenomena have been intensively studied in strongly correlated materials where several ordered states simultaneously occur or compete. Material properties critically depend on external parameters and boundary conditions, where tiny changes result in qualitatively different ground states. However, up to date, phase coexistence phenomena have exclusively been reported for complex compounds composed of multiple elements. Here we show that charge- and magnetically ordered states coexist in double-layer Fe on Rh(001). Scanning tunneling microscopy and spectroscopy measurements reveal periodic charge order stripes below a temperature of 130 K. Close to liquid helium temperature, they are superimposed by ferromagnetic domains as observed by spin-polarized scanning tunneling microscopy. Temperature-dependent measurements reveal a pronounced cross-talk between charge and spin order at the ferromagnetic ordering temperature about 70 K, which is successfully modeled within an effective Landau theory including sixth-order terms. Our results show that subtle balance between structural modifications can lead to competing ordering phenomena.