Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles

TL;DR

This study investigates electron tunneling through discrete energy levels in ferromagnetic cobalt nanoparticles, revealing magnetic anisotropy effects and complex spectra possibly involving spin-wave excitations.

Contribution

It provides the first detailed measurement of tunneling via individual electronic states in ferromagnetic nanoparticles with magnetic anisotropy effects.

Findings

Energy levels shift with magnetic field orientation

Both spin-increasing and decreasing tunneling observed

Denser spectrum than predicted, indicating spin-wave excitations

Abstract

We measure electron tunneling via discrete energy levels in ferromagnetic cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. Due to magnetic anisotropy, the energy of each tunneling resonance shifts as an applied magnetic field rotates the particle's magnetic moment. We see both spin-increasing and decreasing tunneling transitions, but we do not observe the spin degeneracy at small magnetic fields seen previously in non-magnetic materials. The tunneling spectrum is denser than predicted for independent electrons, possibly due to spin-wave excitations.