Towards Laterally Resolved Ferromagnetic Resonance with Spin-Polarized Scanning Tunneling Microscopy.

Marie Hervé,Moritz Peter,Wulf Wulfhekel,Timofey Balashov

doi:10.3390/nano9060827

Abstract

We used a homodyne detection to investigate the gyration of magnetic vortex cores in Fe islands on W(110) with spin-polarized scanning tunneling microscopy at liquid helium temperatures. The technique aims at local detection of the spin precession as a function of frequency using a radio-frequency (rf) modulation of the tunneling bias voltage. The gyration was excited by the resulting spin-polarized rf current in the tunneling junction. A theoretical analysis of different contributions to the frequency-dependent signals expected in this technique is given. These include, besides the ferromagnetic resonance signal, also signals caused by the non-linearity of the characteristics. The vortex gyration was modeled with micromagnetic finite element methods using realistic parameters for the tunneling current, its spin polarization, and the island shape, and simulations were compared with the experimental results. The observed signals are presented and critically analyzed.

Highlights

Spin-polarized scanning tunneling microscopy (SP-STM) is a powerful technique to study the local magnetic structure of surfaces [1,2]
We used a homodyne detection to investigate the gyration of magnetic vortex cores in Fe islands on W(110) with spin-polarized scanning tunneling microscopy at liquid helium temperatures
The vortex gyration was modeled with micromagnetic finite element methods using realistic parameters for the tunneling current, its spin polarization, and the island shape, and simulations were compared with the experimental results

Summary

Introduction

Spin-polarized scanning tunneling microscopy (SP-STM) is a powerful technique to study the local magnetic structure of surfaces [1,2]. Their work stimulated the area of time-resolved STM, so that other groups reported on the development of all-electronic pump probe experiments allowing even higher time resolution down to 120 ps [7] Another approach to study the Larmor precession of single atoms on surfaces in the frequency domain has been proposed by Manassen et al [8,9]. The high frequency part of the tunneling current was separated from the DC part by a high-pass-low-pass network and was detected with a spectrum analyzer This technique was called electron spin noise STM (ESN-STM). In some of the presented measurements, only 0.5% of the spectra show a single data point spike above the noise background [11] As this approach is based on a stochastic excitation and not on a continuous spin precession, the detection of the small signals is challenging. The main hurdles of this technique are, on the one hand, the low signal-to-noise ratio of the rf currents in the pA/nA range and, on the other hand, the lack of a coherent excitation to maintain spin-precession over the measurement time

Methods

Results

Conclusion