Reading and Writing Single-Atom Magnets

TL;DR

This paper demonstrates the ability to read and write magnetic information in individual holmium atoms on magnesium oxide surfaces, showing potential for atomic-scale data storage with long-term stability and electrical control.

Contribution

It introduces a method for independently reading and writing single-atom magnetic states using STM and EPR, advancing atomic-scale magnetic memory technology.

Findings

Single Ho atoms retain magnetic states for hours.

Magnetic states are read via tunnel magnetoresistance.

Four states are written and read in a two-atom structure.

Abstract

The highest-density magnetic storage media will code data in single-atom bits. To date, the smallest individually addressable bistable magnetic bits on surfaces consist of 5-12 atoms. Long magnetic relaxation times were demonstrated in molecular magnets containing one lanthanide atom, and recently in ensembles of single holmium (Ho) atoms supported on magnesium oxide (MgO). Those experiments indicated the possibility for data storage at the fundamental limit, but it remained unclear how to access the individual magnetic centers. Here we demonstrate the reading and writing of individual Ho atoms on MgO, and show that they independently retain their magnetic information over many hours. We read the Ho states by tunnel magnetoresistance and write with current pulses using a scanning tunneling microscope. The magnetic origin of the long-lived states is confirmed by single-atom electron paramagnetic resonance (EPR) on a nearby Fe sensor atom, which shows that Ho has a large out-of-plane moment of $(10.1 \pm 0.1)$ $\mu_{\rm B}$ on this surface. In order to demonstrate independent reading and writing, we built an atomic scale structure with two Ho bits to which we write the four possible states and which we read out remotely by EPR. The high magnetic stability combined with electrical reading and writing shows that single-atom magnetic memory is possible.