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ETH Zürich - D-PHYS - Solid State Physics - Microstructure Research - Projects - Local magnetic field

Local magnetic field

Selected Article

Nat. Comm 7, 13611 (2016)
Critical exponents and scaling invariance in the absence of a critical point
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Proc. R. Soc. A 472, 2195 (2016)
Thirty per cent contrast in secondary-electron imaging by scanning field-emission microscopy
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Phys. Rev. B 89, 014429 (2014)
Domain-wall free energy in Heisenberg ferromagnets
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Phys. Rev. B 87, 115436 (2013)
Scale invariance of a diodelike tunnel junction
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Figure 1: In situ SEMPA and SEM experiment. UHV SEM,60 kV Mott detector and STM
The experimental set-up and the mode of operation of the SEMPA-STM is illustrated by this slide. With SEMPA we can measure two directions of spin-polarisation of the secondary electrons emitted by the sample. One in plane and the out of plane polarisation. As SEMPA detects only the low energy secondary electrons emitted by the sample it was necessary to move the STM-scanner away from the sample surface while performing SEMPA measurements. Otherwise the slow electrons would be deflected by the scanner and wouldn't reach the Mott-detector. But the detector of the SEM detects the whole energy-range of the secondary electrons. Therefore STM and SEM could be done in parallel.
Figure 2: Images of Co STM-tip (a) SEM image of a tip holder with m-coil and tip. (b) SEM image of a tip while tunnelling above Co dot. (c) SEM image of tip end. (d) and (e) SEMPA images.
Figure 2 shows a typical procedure for magnetic manipulation with STM. On Image (a) one sees a tip holder with the tip on the left hand side. In the background one can see the sample surface. With help of the SEM we guide the tip to every desired spot of the sample. Once we have found the spot of interest on the sample, the tip can be approached. On the right hand side of image (b) we see a Co tip while tunnelling above a Co island. The cross which is visible on the sample consist of evaporated silver wire and is used in another experiment. Image (c) is the topograph of the headmost part of the Co tip. The tip has a diameter of less than 50 nm at this end. Fundamentally for STM induced magnetisation is the knowledge about the magnetic properties of the used Co-tips. The SEMPA images (d) and (e) show the remnant magnetisation of a Co tip. The headmost part of the tip is divided into several micron large domains. Their magnetic orientation is indicated by arrows.
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