A radio frequency-spin-polarized–scanning tunneling microscope for spin dynamics experiments

Spin dynamic processes of single atoms and magnetic nanostructures can take place on time scales as fast as femtoseconds. From the perspective of data storage technology, processes in the nano- and picosecond range are desirable, in order to compete with the existing technology. For magnetic nanostructures down to the size of single atoms, spin-polarized scanning tunneling microscopy is a powerful tool to investigate the magnetic properties of a system. However, due to the low tunnel currents, the use of a transimpedance amplifier is indispensable, which leads to a limited time resolution for the scanning tunneling microscope. This problem can be solved by using the pump-probe technique. For a purely electronically operated scanning tunneling microscope, this requires the application of a short voltage pulse to the tunnel barrier. In this work, a new experimental setup with a spin-polarized scanning tunneling microscope is presented. The microscope allows for the use of microwave technology with a limiting frequency beyond 20 GHz, at a temperature of 1.1 K and in a magnetic field of 3 T. The microscope and its wiring as well as the associated cryostat system were specially designed and manufactured for this purpose. For tip and sample preparation, an ultra-high vacuum system has been developed, which is equipped with self-made modular preparation platforms. Test measurements were performed on an Au(111) crystal and showed its herringbone reconstruction pattern and atomic lattice. Further measurements on the Fe/Ir(111) system revealed magnetic skyrmions with a corrugation of 10 pm. The measurement of the pump-probe cross-correlation showed a full-width-at-half-maximum of 103 ps. For the study of magnetization dynamics with the new experimental setup, the Pd/Fe/Ir(111) system was prepared. Magnetic skyrmions were imaged by utilizing the effect of non-collinear magnetoresistance. The tip induced hopping of skyrmions between energetically favorable positions at a pinning center was observed. The interaction of neighboring skyrmions, as influenced by the STM tip, was indirectly detected.