Using a hybrid superconducting-ferromagnetic tip as a magnetic scanning tunneling microscope

TL;DR

This paper introduces a hybrid superconducting-ferromagnetic tip for a magnetic scanning tunneling microscope (MSTM) that can simultaneously measure surface topography and spin polarization at the Fermi level, enhancing magnetic imaging capabilities.

Contribution

The work presents a novel hybrid tip design combining superconducting and ferromagnetic materials to enable spin-sensitive tunneling measurements in STM.

Findings

The hybrid tip can distinguish between spin-insensitive and spin-sensitive tunneling currents.

Optimization of tip geometry improves the sensitivity of the MSTM.

The device allows for simultaneous topographical and magnetic surface imaging.

Abstract

Approaching a two-component tip made of a superconductor (S) and a ferromagnet (F) from a magnetic sample allows for two distinct tunneling processes between the ferromagnets, through S: i) Charge and spin are conserved; ii) Charge and spin are reversed, e.g. a Cooper pair flows from S, one electron going into F, the other into the sample. At subgap voltages, this allows two currents to flow from the tip : one is insensitive to the spin polarizations and allows for surface topography, the other directly tracks the relative spin polarizations of F and the sample. The whole device acts as a STM sensitive to the spin polarization at the Fermi level (MSTM). Its sensitivity is studied and optimized with respect to the tip geometry.