Abstract
Electron paramagnetic resonance (EPR) performed with a scanning tunneling microscope (STM) allows for probing the spin excitation of single atomic species with MHz energy resolution. One of the basic applications of conventional EPR is the precise determination of magnetic moments. However, in an STM, the local magnetic fields of the spin-polarized tip can introduce systematic errors in the measurement of the magnetic moments by EPR. We propose to solve this issue by finding tip-sample distances at which the EPR resonance shift caused by the magnetic field of the tip is minimized. To this end, we measure the dependence of the resonance field on the tip-sample distance at different radiofrequencies and identify specific distances for which the true magnetic moment is found. Additionally, we show that the tip's influence can be averaged out by using magnetically bistable tips, which provides a complementary method to accurately measure the magnetic moment of surface atoms using EPR STM.
Highlights
Electron paramagnetic resonance (EPR) [1] allows for the precise determination of the electronic and magnetic properties of paramagnetic species by measuring their magnetic moment with high accuracy
The EPR scanning tunneling microscope (STM) spectra were acquired by sweeping Bext at constant radiofrequency and recording the change in tunneling current that is caused by the radiofrequency signal generated by an antenna placed next to the STM tip
We introduced two methods to measure the magnetic moment of a surface atom with increased precision using EPR STM based on NOTIN EPR and bistable magnetic tips
Summary
Electron paramagnetic resonance (EPR) [1] allows for the precise determination of the electronic and magnetic properties of paramagnetic species by measuring their magnetic moment with high accuracy. In typical experiments performed in resonant cavities, the magnetic moment can be measured with an accuracy of up to a few parts per million [2], often limited by the accuracy of measuring the magnetic field or the applicable radiofrequency [3]. The recent implementation of EPR into a scanning tunneling microscope (STM) enabled the study of magnetic properties and interactions of single surface atoms with MHz resolution, which is orders of magnitude below the thermal limit in typical low-temperature STMs [9,10,11,12].
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