Structural and magnetic properties of 3d transition metal oxide chains on the (001) surfaces of Ir and Pt

TL;DR

This study investigates the structural and magnetic properties of transition metal oxide chains on Ir(001) and Pt(001) surfaces, revealing diverse magnetic behaviors including antiferromagnetic coupling and spin spirals through advanced STM techniques.

Contribution

It provides the first experimental confirmation of predicted magnetic structures in transition metal oxide chains on noble metal surfaces using spin-polarized STM.

Findings

FeO2 chains on Ir(001) exhibit ferromagnetic inter-chain coupling.

MnO2 chains on Ir(001) show a non-collinear 120° spin spiral.

MnO2 chains on Pt(001) display a long-wavelength spin rotation.

Abstract

We present a survey of the structural and magnetic properties of submonolayer transition metal dioxides on the (001) surfaces of the heavy face-centered cubic (fcc) noble metals Ir and Pt performed by spin-averaged scanning tunneling microscopy (STM) and spin-polarized (SP-)STM. Our STM results confirm that deposition of Co, Fe, Mn, and Cr on the (2 {\times} 1) oxygen-reconstructed Ir(001) surface leads to the formation of quasi one-dimensional chains with a (3 {\times} 1) unit cell. As recently predicted by density functional theory [Ferstl et al., Phys. Rev. Lett. 117, 046101 (2016)], our SP-STM images of FeO2 and MnO2 on Ir(001) show a two-fold periodicity along the chains which is characteristic for an antiferromagnetic coupling along the chains. In addition, these two materials also exhibit spontaneous, permanent, and long-range magnetic coupling across the chains. Whereas we find a ferromagnetic inter-chain coupling for FeO2/Ir(001), the magnetic coupling of MnO2 on Ir(001) appears to be a non-collinear 120{\deg} spin spiral, resulting in a (9 {\times} 2) magnetic unit cell. On Pt(001) patches of (3 {\times} 1)-reconstructed oxide chains could only be prepared by transition metal (Co, Fe, and Mn) deposition onto the cold substrate and subsequent annealing in an oxygen atmosphere. Again SP-STM on MnO2/Pt(001) reveals a very large, (15 {\times} 2) magnetic unit cell which can tentatively be explained by a commensurate 72{\deg} spin spiral. Large scale SP-STM images reveal a long wavelength spin rotation along the MnO2 chain.