Superparamagnetic response of Fe-coated W tips in spin-polarized scanning tunneling microscopy

TL;DR

This study investigates the superparamagnetic behavior of Fe-coated W tips in spin-polarized STM, revealing how temperature affects magnetic response and identifying the nano-apex composition as a key factor.

Contribution

It provides a quantitative analysis of superparamagnetic effects in Fe-coated W tips using a Langevin function model, linking tip composition to magnetic response.

Findings

Temperature increases reduce the differential conductance slope.

Superparamagnetic behavior is well described by a Langevin function.

Fe nano-apex composed of 220-300 Fe atoms influences tip magnetism.

Abstract

We performed spin-polarized scanning tunneling spectroscopy on biatomic-layer-high Co nanoislands grown on Cu(111) in magnetic fields oriented normal to the sample surface, with Fe-coated W tips. Increasing the temperature from 10 to 30 K, we observe a reduced slope of the differential conductance around zero field. A quantitative analysis of the field- and temperature-dependent differential conductance data in the framework of superparamagnetism as described by a Langevin function gives an excellent description of the experimental results. The analysis suggests that a Fe nano-apex at the W tip, which is composed of 220-300 Fe atoms, determines the magnetic response of the tip.