Skyrmion Lattice Detection, Tuning Fork Implementation
microscopy has been achieved for the fi rst time to the best of our knowledge in a dry cryostat.
Figure 8: (a) Quartz-crystal tuning fork with tungsten tip (1) and Akiyama probe (2). Bar = 0.2 mm. (b) Shear-force mode noise scan; we measured 2 nm rms noise (bandwidth 200 Hz).
Discussion T e ultra-low vibration environment in our dry cryostat enables immediate application of SPM techniques. Contact-mode AFM measurements inside the dry cryostat resolved atomic steps of 0.39 nm height in a SrTiO 3 sample, owing to a relative tip-sample vibration amplitude of less than 65 pm. T is level of noise allowed measurement of the skyrmion-lattice phase in Fe 0.5 Co 0.5 Si by magnetic force microscopy. T is had only been achieved quite recently in state-of-the-art liquid cryostat systems [ 2 ]. Furthermore, quartz-crystal tuning fork shear-force
We studied the absolute vibrational noise in the sample space using a true inertial technique, measuring residual vibrations in the low nm range. We have also shown that these small displace- ments at very low frequencies do not infl uence the operation of the microscope and still enable measurements with high sensitivity. Our microscope is top-loaded in the cryostat and does not require being spring-suspended for further vibration isolation. T is stiff architecture of the microscope head is of particular advantage when combining SPM with high-resolution confocal light microscopy where free-space
optics is incompatible with spring mounting. T e system as described allows a turnover of up to three experimental sessions per nine-hour working day. Beyond this work we hope to enable the implementation of further high-resolution imaging methods in dry cryostats and novel instances of magnetic force microscopy, such as scanning diamond magnetometry [ 13 ].
Conclusion A closed-cycle dry cryostat capable of maintaining
temp eratures as low as 4 K was used as a platform for magnetic force microscopy measurements. T is instrument provided images of nanoscale spin textures in chiral magnets such as magnetic skyrmions. Tuning-fork shear- force microscopy measurements in a dry cryostat are shown here for the fi rst time. T e stiff architecture of the system allows for the combination of SPM with light optical imaging, by achieving vibrations as low as 65 pm.
Acknowledgments
Two of us (F. P. Q. and J. P.) acknowledge fi nancial support from Q-NET, a Marie Curie Initial Training Network funded by the European Commission (project number 264034). C. P. acknowledges fi nancial support by the European Research Council (ERC AdG 291079, TOPFIT) and the German Science Foundation (TRR80, From Electronic Correlation to Functionality). A. B. acknowledges fi nancial support through the TUM Graduate School.
References [1] K Nowack et al ., Nature Materials 12 ( 2013 ) 787 – 91 .
Figure 9 : Quartz-crystal tuning fork AFM scans of SiO 2 20 ± 2 nm high patterns on Si, performed in our dry cryostat at T = 4 K. 200 scan lines at 500 nm/s. (a) 5 × 5 μ m 2 tapping mode scan with Akiyama probe (test grating pitch 2 μ m). B = 2 μ m. (b) 9 × 9 μ m 2 shear-force mode scan with quartz-tuning-fork-tungsten-tip confi guration (test grating pitch 4 μ m). Bar in (d) = 4 μ m. Cross sections relative to each scan are shown.
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[2] P Milde et al ., Science 340 ( 2013 ) 1076 – 80 .
[3] D Rugar et al ., Nature 430 ( 2004 ) 329 – 32 .
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