Name: scanning squid study of vortex manipulation by local contact
Uploaded: 2017-02-01T14:00:00
Description: Watch this Scientific Journal Video about Scanning SQUID Study of Vortex Manipulation by Local Contact at JoVE.com

We thank A. Sharoni from Bar-Ilan University for providing the superconducting films. This research was supported by European Research Council Grant ERC-2014-STG- 639792, Marie Curie Career Integration Grant FP7-PEOPLE-2012-CIG-333799, and Israel Science Foundation Grant ISF-1102/13.

1. Access to a Scanning SQUID System
<ol>
	<li>Use a scanning SQUID system that includes a SQUID sensor fabricated on a chip9,10, stick slip coarse motion stage, and a piezo-based scanner for fine motion. See Figure 1.</li>
	<li>Polish the SQUID chip into a corner around the pickup loop. The material of the chip needs to be removed all the way to the pickup loop.
	<ol>
		<li>Gently polish the SQUID, using a 5 to 0.5 &#181;m nonmagnetic polishin...

     

<ol>
	<li>Olson Reichhardt, C. J., Hastings, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Do+Vortices+Entangle?.">Do Vortices Entangle?.</a> Phys. Rev. Lett. 92, 157002 (2004).</li><li>Milo&#353;evi&#263;, M. V., Berdiyorov, G. R., Peeters, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluxonic+cellular+automata.">Fluxonic cellular automata.</a> Appl. Phys. Lett. 91, 212501 (2007).</li><li>Kalisky, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning+Probe+Manipulation+of+Magnetism+at+the+LaAlO3/SrTiO3+Heterointerface.">Scanning Probe Manipulation of Magnetism at the LaAlO3/SrTiO3 Heterointerface.</a> Nano Lett. 12, 4055-4059 (2012).</li><li>Silva, C. C. D. S., Van de Vondel, J., Morelle, M., Moshchalkov, V. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+multiple+reversals+of+a+ratchet+effect.">Controlled multiple reversals of a ratchet effect.</a> Nature. 440, 651-654 (2006).</li><li>Kalisky, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+single+vortices+in+grain+boundaries:+I-V+characteristics+on+the+femtovolt+scale.">Dynamics of single vortices in grain boundaries: I-V characteristics on the femtovolt scale.</a> Appl. Phys. Lett. 94, 202504 (2009).</li><li>Embon, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Probing+dynamics+and+pinning+of+single+vortices+in+superconductors+at+nanometer+scales.">Probing dynamics and pinning of single vortices in superconductors at nanometer scales.</a> Sci. Rep. 5, 7598 (2015).</li><li>Auslaender, O. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanics+of+individual+isolated+vortices+in+a+cuprate+superconductor.">Mechanics of individual isolated vortices in a cuprate superconductor.</a> Nature Phys. 5, 35-39 (2008).</li><li>Kalisky, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Behavior+of+vortices+near+twin+boundaries+in+underdoped+Ba(Fe1-xCox)2As2.">Behavior of vortices near twin boundaries in underdoped Ba(Fe1-xCox)2As2.</a> Phys. Rev. B. 83, 064511 (2011).</li><li>Huber, M. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gradiometric+micro-SQUID+susceptometer+for+scanning+measurements+of+mesoscopic+samples.">Gradiometric micro-SQUID susceptometer for scanning measurements of mesoscopic samples.</a> Rev. Sci. Instrum. 79, 053704 (2008).</li><li>Koshnick, N. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+terraced+scanning+super+conducting+quantum+interference+device+susceptometer+with+submicron+pickup+loops.">A terraced scanning super conducting quantum interference device susceptometer with submicron pickup loops.</a> Appl. Phys. Lett. 93, 243101 (2008).</li><li>Kremen, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+Control+of+Individual+Superconducting+Vortices.">Mechanical Control of Individual Superconducting Vortices.</a> Nano Lett. 16, 1626-1630 (2016).</li></ol>

Successful manipulation of vortices depends on several critical steps. It is important to align the sensor at an angle, such that the tip of the chip will be the first to make contact with the sample. Second, it is important to note that the force exerted on the sample is determined by the mechanical properties of the cantilever that the chip is mounted on. In the elastic regime, the force applied is proportional to the deflection, x, according to Hooke&#39;s law: 
F = -kx
Where k is the ...

Vortices are magnetic objects at the nanoscale, formed in type 2 superconductors in the presence of external magnetic field. In a defect free sample, vortices can move freely. However, different defects in the material result in regions of reduced superconductivity which are energetically favorable for vortices. Vortices tend to decorate these regions, also known as the pinning sites. In this case, the force required to move a vortex must be greater than the pinning force. Properties of vortices, such as vortex density, interaction strength and range, can be easily determined by external field, temperature, or geometry of the sample. The ability to control these properties makes them a good model system for condensed matter behavior that can be easily tuned, as well as suitable candidates for electronic applications1,2. Control of the location of individual vortices is essential for the design of such logical elements.
Mechanical control of magnetic nanoparticles had been achieved before. Kalisky et al. recently used scanning superconducting quantum interference device (SQUID) to study the influence of local mechanical stress on ferromagnetic patches in complex oxide interfaces3. They were able to change the orientation of the patch by scanning in contact, pressing the tip of the SQUID into the sample, applying a force of up to 1 &#181;N in the process. We have used a similar method in our protocol in order to move vortices.
In existing studies of vortex manipulation, motion was achieved by applying current to the sample, thus creating Lorentz force4,5,6. While this method is effective, it is not local, and in order to control a single vortex, additional fabrication is required. Vortices can also be manipulated by applying external magnetic field, for example with a magnetic force microscope (MFM) or with a SQUID field coil7,8. This method is effective and local, but the force applied by these tools is small, and can overcome the pinning force only at high temperatures, close to the critical temperature of the superconductor. Our protocol allows effective, local manipulation at low temperatures (4 K) without additional fabrication of the sample.
We image vortices using scanning SQUID microscopy. The sensor is fabricated on a silicon chip which is polished into a corner, and glued on a flexible cantilever. The cantilever is used for capacitive sensing of the surface. The chip is placed at an angle to the sample, so that the contact point is at the tip of the chip. We apply forces of up to 2 &#181;N by pushing the chip into the sample. We move the sample relative to the SQUID by piezo elements. We move the vortex by tapping the silicon tip next to a vortex, or by sweeping it, touching the vortex.

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			<td height="21" style="height:21px;width:299px;">piezo elements</td>
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			<td height="21" style="height:21px;width:299px;">dewar</td>
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			<td style="width:207px;">ICE oxford</td>
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			<td height="21" style="height:21px;width:299px;">vacuum cap</td>
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			<td height="21" style="height:21px;width:299px;">lapping film</td>
			<td style="width:207px;">3M</td>
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			<td height="21" style="height:21px;width:299px;">Nb target</td>
			<td style="width:207px;">Kurt J. Lesker</td>
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			<td height="21" style="height:21px;width:299px;">GE Varnish</td>
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			<td>for cryogenic heatsinking</td>
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			<td height="22" style="height:22px;width:299px;">Silver paste</td>
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scanning squid study of vortex manipulation by local contact

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the lattice, and with other magnetic objects. Here, we present a protocol for vortex manipulation in thin superconducting films by local contact, without applying current or magnetic field. Vortices are imaged using a scanning superconducting quantum interference device (SQUID), and vertical stress is applied to the sample by pushing the tip of a silicon chip into the sample, using a piezoelectric element. Vortices are moved by tapping the sample or sweeping it with the silicon tip. Our method allows for effective manipulation of individual vortices, without damaging the film or affecting its topography. We demonstrate how vortices were relocated to distances of up to 0.8 mm. The vortices remained stable at their new location up to five days. With this method, we can control vortices and move them to form complex configurations. This technique for vortex manipulation could also be implemented in applications such as vortex based logic devices.

Our protocol was successfully tested on thousands of individual, well separated vortices in two samples of Nb, and nine samples of NbN. We generate new vortices on the same sample by heating the sample above Tc, and cooling it back to 4.2 K in the presence of a magnetic field. We chose the external magnetic field to achieve the desired vortex density. We show here data from these experiments. These results have been described in detail by Kremen et al.11.<...

Watch this Scientific Journal Video about Scanning SQUID Study of Vortex Manipulation by Local Contact at JoVE.com

Scanning SQUID Study of Vortex Manipulation by Local Contact

We present a protocol for manipulation of individual vortices in thin superconducting films, using local mechanical contact. The method does not include applying current, magnetic field or additional fabrication steps.

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual ...

The overall goal of this procedure is to manipulate vortices in thin superconducting films by local vertical stress without applying current or magnetic field. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the material, and with other magnetic objects. The main advantage of this technique is that it is a local method which allows a very effective manipulation of an individual vortex with no additional fabrication steps.We first witnessed the effect of strain on submicro and ferro-magnetic objects when we used to SQUID to image and examine the way they change their orientation as a result of stress. Following this study, we wanted to investigate the effect of local stress on other nano-magnetic objects, and the first system we tested is the system of vortices in a superconductor. First, prepare a thin superconducting film sample.Then, obtain a SQUID sensor fabricated on a silicon chip. Gently polish the chip with nonmagnetic polishing paper to form a symmetrical point containing the sensing area. The material must be polished all the way down to expose the sensing area.Glue a flexible cantilever to a conducting plate with a dielectric layer. Then, glue the sensor chip to the cantilever. Mount the sample with varnish or silver paste.Then, attach it to the Z-Axis Piezo element. Set up two telescopes on translation stages, and connect the telescopes to a computer via a camera. Connect the stick slip course motion system controller.Direct the telescopes at the front and side of the chip to provide optical imaging. Using the Z-stick slip stage, move the sample to about one micrometer from the sensor so that the sensor is reflected in the sample. Do not allow the sample to contact the sensor.Check the angles between the chip and its reflection on both sides of the tip when viewed from the front. Then, move the sample about 0.5 to one millimeter away from the sensor to prevent damage to the SQUID. Rotate the alignment screws so that the angles between the chip and its reflection are equal on both sides of the tip when viewed from the front.Move the sample back to about one micrometer from the sensor, and check the angles again. Once the angles are equal, rotate the alignment screws until the angle between the chip and its reflection is at least four degrees when viewed from the side to ensure that the tip contacts the sample when moving the vortices. It is important to align the sensor at an angle so that only the sensor tip touches the sample.This way, a distinct point of contact can be determined. Load the scanning head of the SQUID system into a four Calvin cooling system. To generate vortices, cool the sample to 4.2 Calvins in the presence of a magnetic field based on the sample size and desired number of vortices.Turn off the magnetic field, and turn on the SQUID. Using the Z-stick slip, move the sample closer to the sensor chip. Apply voltage between the cantilever and the capacitance detection plate to bring the cantilever into the bridge circuit.Sweep the Z Piezo element from zero to 200 volts while monitoring the capacitance between the cantilever and the plate. When the sample contacts the sensor chip, a large change in capacitance will occur. Once the sample has successfully contacted the chip, repeat this process at several locations on the sample to define the plane of the sample relative to the sensor.To move the sample relative to the sensor, sweep the voltage on the X and Y Piezo elements. Once the plane is defined, use the Z Piezo element to move the sample so that the sensor scans at a constant height above the sample. Scan around one vortex to precisely determine the location of its center relative to the sensing area.Turn off the SQUID, and then apply a voltage greater than the touch-down voltage to the Z Piezo element. Either tap the sample next to the vortex center, or slowly drag the sensor while in contact with the sample to the desired new vortex location. Turn the SQUID back on, and scan the sample at a constant height to determine the new vortex location.Vortices were generated on a niobium thin film sample. Using this method, the vortices can be moved into defined patterns. A vortex may be moved multiple times.Even after moving this vortex 820 micrometers, the vortex remained stable at its new location. The magnetic signal is mapped by recording the flux through the SQUID as function of position. The signal is recorded through the SQUID's pickup loop.However, contact with the sample is made at the tip of the sensor chip. This distance must be compensated for when selecting a contact location for vortex manipulation. In this case, contact happens prior to recording the magnetic signal.If the sensor is turned on during a manipulation scan, the displacement event appears as a faint step in the signal. The vortex, imaged at its new position, appears intact. This technique can be applied to study the effect of local mechanical stress on other nano-magnetic objects.An effective and reproducible manipulation technique of nano-magnetic objects is essential to promote possible applications such as logic elements.

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