Gradiometric micro-SQUID susceptometer for scanning measurements of mesoscopic samples

Huber, M. E.; Koshnick, Nicholas C.; Bluhm, Hendrik; Archuleta, Leonard J.; Azua, Tommy; Björnsson, Per G.; Gardner, Brian W.; Halloran, Sean; Lucero, Erik; Moler, Kathryn A.

doi:10.1063/1.2932341

Cited by 158 publications

(143 citation statements)

References 26 publications

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“…At present, Hall-sensors and SQUID sensors are among the most sensitive magnetic field detectors. 4,5 Furthermore, a great deal of success has been achieved with magnetic resonance force microscopy, where the force between a magnetic tip and the magnetic moment under investigation is exploited to detect single electron-spins, achieving a resolution of a few cubic nanometers. [6][7][8] On the other hand, the very low temperatures that are required in such schemes represent a considerable drawback to imaging systems in many biological environments.…”

Section: Introductionmentioning

confidence: 99%

High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature

et al. 2015

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We demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy (NV) magnetometer and a target spin, the magnetometer sensitivity is increased dramatically. Specifically, using materials and techniques already experimentally available, we find that by taking advantage of the ferromagnetic resonance the minimum magnetic moment that can be measured is smaller by four orders of magnitude in comparison to current state-of-the-art magnetometers. As such, our proposed setup is sensitive enough to detect a single nuclear spin at a distance of 30 nm from the surface within less than one second of data acquisition at room temperature. Our proposal opens the door for nanoscale NMR on biological material under ambient conditions.

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Section: Introductionmentioning

confidence: 99%

High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature

et al. 2015

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“…Scanning micro-and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth 15,19 . The two main technological approaches to the fabrication of scanning SQUIDs are based on planar lithographic methods 21,26,[33][34][35][36] and on self-aligned SQUIDon-tip (SOT) deposition 22,24,37 .In the planar SQUID architecture, spatial resolution is limited but pickup and modulation coils can be integrated to allow operation of the SQUID at optimal flux bias conditions using a fluxlocked loop (FLL) feedback mechanism 15,18,19,21,33,38,39 . Because the magnetic field of the sample is not coupled to the SQUID loop directly, but rather through a pickup coil, integration of a modulation coil or an integrated current-carrying element 15,19,21,33,38,39 allows the total flux in the SQUID loop to be maintained at its optimal bias while the magnetic field of the sample is varied independently.…”

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Electrically Tunable Multiterminal SQUID-on-Tip

et al. 2016

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We present a new nanoscale superconducting quantum interference device (SQUID) whose interference pattern can be shifted electrically in-situ. The device consists of a nanoscale fourterminal/four-junction SQUID fabricated at the apex of a sharp pipette using a self-aligned threestep deposition of Pb. In contrast to conventional two-terminal/two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 µ B /Hz 1/2 over a continuous field range of 0 to 0.5 T, with promising applications for nanoscale scanning magnetic imaging.KEYWORDS: superconducting quantum interference device, SQUID on tip, nanoscale magnetic imaging, current-phase relations 2 In recent years, there has been a growing effort to develop and apply nanoscale magnetic imaging tools in order to address the rapidly evolving fields of nanomagnetism and spintronics.These include magnetic force microscopy (MFM) 1,2 , magnetic resonance force microscopy (MRFM) [3][4][5] , nitrogen vacancy (NV) centers sensors [6][7][8][9] , scanning Hall probe microscopy (SHPM) 10-12 , x-ray magnetic microscopy (XRM) 13 , and micro-or nano-superconducting quantum interference device (SQUID) [14][15][16][17][18][19][20] based scanning microscopy (SSM) [21][22][23][24][25][26][27][28][29][30][31][32] . Scanning micro-and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth 15,19 . The two main technological approaches to the fabrication of scanning SQUIDs are based on planar lithographic methods 21,26,[33][34][35][36] and on self-aligned SQUIDon-tip (SOT) deposition 22,24,37 .In the planar SQUID architecture, spatial resolution is limited but pickup and modulation coils can be integrated to allow operation of the SQUID at optimal flux bias conditions using a fluxlocked loop (FLL) feedback mechanism 15,18,19,21,33,38,39 . Because the magnetic field of the sample is not coupled to the SQUID loop directly, but rather through a pickup coil, integration of a modulation coil or an integrated current-carrying element 15,19,21,33,38,39 allows the total flux in the SQUID loop to be maintained at its optimal bias while the magnetic field of the sample is varied independently.SOTs, in contrast, have better spatial resolution due to their small size and close proximity to the sample, attain higher spin sensitivity, and can operate at high magnetic fields 24 . The nanoscale proximity of the SOT to the sample surface, which is its key advantage, dictates however that the flux in the SQUID loop is directly coupled to the local field of the sample and therefore cannot be modified independently. As a result, the FLL concept cannot be implemented in direct nanoscale magnetic imaging. This poses a significant drawback, since the high sensitivity of the SOT is achieved only at specific field va...

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“…Much effort has been devoted recently to the development of nanoSQUIDs, which have shown very promising flux sensitivity. [2][3][4][5][6][7][8] Most of these devices, however, are based on planar technology using lithographic or focused ion beam (FIB) patterning methods; 3-11 the large in-plane size of the devices precludes bringing the SQUID loop into sufficiently close proximity to the sample (due to alignment issues) to scan it with optimal sensitivity. Recently, a terraced SQUID susceptometer was developed that is based on a multilayered lithographic process combined with FIB etching.…”

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Self-Aligned Nanoscale SQUID on a Tip

et al. 2010

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A nanometer-size superconducting quantum interference device (nanoSQUID) is fabricated on the apex of a sharp quartz tip and integrated into a scanning SQUID microscope.A simple self-aligned fabrication method results in nanoSQUIDs with diameters down to 100 nm with no lithographic processing. An aluminum nanoSQUID with an effective area of 0.034 µm 2 displays flux sensitivity of 1.8 × 10 −6 Φ 0 / √ Hz and operates in fields as high as 0.6 T.With projected spin sensitivity of 65 µ B / √ Hz and high bandwidth, the SQUID on a tip is a highly promising probe for nanoscale magnetic imaging and spectroscopy.Imaging magnetic fields on a nanoscale is a major challenge in nanotechnology, physics, chemistry, and biology. One of the milestones in this endeavor will be the achievement of sensitivity sufficient for detection of the magnetic moment of a single electron. patterning methods; 3-11 the large in-plane size of the devices precludes bringing the SQUID loop into sufficiently close proximity to the sample (due to alignment issues) to scan it with optimal sensitivity. Recently, a terraced SQUID susceptometer was developed that is based on a multilayered lithographic process combined with FIB etching. This device includes a 600 nm pickup loop which can be scanned 300 nm above the sample surface. 12 Here we present a simple method for the self-aligned fabrication of a DC nanoSQUID on a tip with effective diameter as small as 100 nm that can be scanned just a few nm above the sample.We have fabricated several SQUID-on-tip (SOT) devices of various sizes. A quartz tube of 1 mm outside diameter is pulled to a sharp tip with apex diameter that can be controllably varied between 100 and 400 nm. The fabrication of the SOT consists of three "self-aligned" steps of thermal evaporation of Al, as shown schematically in Fig. 1a. In the first step, 25 nm of Al are deposited on the tip tilted at an angle of -100 • with respect to the line to the source. Then the tip is rotated to an angle of 100 • , followed by a second deposition of 25 nm. As a result, two leads on opposite sides of the quartz tube are formed, as shown in Fig. 1b. In the last step 17 nm of Al are evaporated at an angle of 0 • , coating the apex ring of the tip. The two areas where the leads contact the ring form "strong" superconducting regions, whereas the two parts of the ring in the gap between the leads, indicated by arrows in Fig. 1c, constitute two weak links, thus forming the SQUID. The resulting nanoSQUID requires no lithographic processing, its size is controlled by a conventional pulling procedure of a quartz tube, and it is located at the apex of a sharp tip that is ideal for scanning probe microscopy.The studies were carried out at 300 mK, well below the critical temperature T c ≈ 1.6 K of granular thin films of aluminum in our deposition system. Instead of the commonly used current 2 bias, the SOT was operated in a voltage bias mode, as shown schematically in the inset to Fig. 2. We use a low bias resistance R b of about 2 Ω and the SOT current...

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Gradiometric micro-SQUID susceptometer for scanning measurements of mesoscopic samples

Cited by 158 publications

References 26 publications

High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature

High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature

Electrically Tunable Multiterminal SQUID-on-Tip

Self-Aligned Nanoscale SQUID on a Tip

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