Local-magnetic-field generation with a scanning tunneling microscope

We report on the manipulation of magnetic ultrathin structures of small lateral size by applying a local magnetic field generated with a ferromagnetic scanning tunneling microscope (STM) tip. The range and strength of the stray field of a ferromagnetic tip depends largely on the curvature at the tip’s apex and on the cone angle. The ability to vary these parameters renders it possible to produce tailored ferromagnetic STM tips for the experiment. The technique is applied to the ferromagnetic system of Fe epitaxially grown on Cu(001). At room temperature, 1.8 monolayers (ML) to 2.9 ML Fe films show a perpendicular magnetic anisotropy. The local magnetic field was applied to particles of Fe∕Cu(001) with lateral size in the order of a few micrometers, after which magnetic switching was observed. Theoretical studies based on experimental data of ferromagnetic STM tips reveal that the magnitude of the stray field is in the order of the bulk magnetization M of the used ferromagnetic tip material. Furthermore, the spatial range of the stray field is in the order of the tip’s apex radius.