Uni Hamburg Fachbereich Physik
Logo STM/sts, SPM-Group, Institute of Applied Physics, Hamburg

Recent Results

Spin polarized scanning tunneling microscopy on Fe islands

Fig. 1: Spin polarized in-plane contrast of Fe-islands of different thickness deposited on W(110); since the W(110) is covered with a monolayer of Fe, also the area between the islands exhibits a contrast.

In order to study ferromagnet/semiconductor interfaces at a later time, we first investigated magnetic properties of ferromagnetic islands, which will later be deposited on a semiconductor. For the sake of simplicity we deposited them on W(110) and studied them by spin polarized scanning tunneling microscopy (link to Bode) using tips covered with Cr. Depending on the thickness of the islands, we found either monodomain or multidomain states both magnetized in-plane (Fig.1). Interestingly, the multidomain state exhibits a flux closure configuration as indicated by the arrows in the left image of Fig. 2.

Fig. 2: Left: in-plane contrast of a single island of 8 nm height with tentative orientation of the domains indicated; Right: inner area of an island measured with in-plane (upper) and out-of-plane (lower) sensitive tip.

This configuration requires a magnetic vortex in the center of the island. Theory already perdicted in 1965 that the vortex core will be avoided by turning the spins out-of plane. Indeed we found this out-of-plane area by preparing two different types of tips, which are either in-plane or out-of-plane sensitive. The upper right image in Fig.2 shows the in-plane contrast in the center of an island, while the lower right-image shows the out-of-plane contrast. Obviously, there is an out-of-plane magnetization in the center. Its shape has been compared to theory under different magnetic fields and perfectly agreed with the micromagnetic simulations as displayed in Fig. 3.

Fig. 3: Distance dependence of out-of-plane intensity measured from the vortex core at different magnetic fields (lines); the result of a micromagnetic calculation is shown for comparison (dots).

Related Publications

A. Wachowiak, J. Wiebe, M. Bode, O. Pietzsch, M. Morgenstern, and R. Wiesendanger, Science 298, 577 (2002):
Internal Spin-Structure of Magnetic Vortex Cores observed by Spin-Polarized Scanning Tunneling Microscopy.