Scanning superconducting quantum interference device susceptometry

Gardner, Brian W.; Wynn, Janice C.; Björnsson, Per G.; Straver, Eric W. J.; Moler, Kathryn A.; Kirtley, J. R.; Ketchen, M. B.

doi:10.1063/1.1364668

Cited by 72 publications

(70 citation statements)

References 9 publications

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“…We use scanning SQUID microscopy 20,21 to magnetically image many samples (Methods), primarily a series with varying LAO thickness. Figure 1a-d show representative examples of the magnetic landscapes for four thicknesses of the LAO layer.…”

Section: Magnetic Squid Imaging Of Samples With Varying Lao Thicknessmentioning

confidence: 99%

Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures

et al. 2012

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In LaAlo 3 /srTio 3 heterointerfaces, charge carriers migrate from the LaAlo 3 to the interface in an electronic reconstruction. magnetism has been observed in LaAlo 3 /srTio 3 , but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlo 3 thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.

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Section: Magnetic Squid Imaging Of Samples With Varying Lao Thicknessmentioning

confidence: 99%

Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures

et al. 2012

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“…[20]). We used a variable-T scanning SQUID susceptometer [37][38][39] with two field coil / pickup loop pairs in a gradiometer configuration. Figure 1a shows the sensing region 3 of the probe, which was polished to a corner to bring it as close as possible to the sample.…”

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confidence: 99%

Behavior of vortices near twin boundaries in underdoped Ba(Fe1−xCox)2As<

et al. 2011

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We use scanning SQUID microscopy to investigate the behavior of vortices in the presence of twin boundaries in the pnictide superconductor Ba(Fe 1-x Co x ) 2 As 2 . We show that the vortices avoid pinning on twin boundaries. Individual vortices move in a preferential way when manipulated with the SQUID: they tend to not cross a twin boundary, but rather to move parallel to it. This behavior can be explained by the observation of enhanced superfluid density on twin boundaries in Ba(Fe 1-x Co x ) 2 As 2 . The observed repulsion from twin boundaries may be a mechanism for enhanced critical currents observed in twinned samples in pnictides and other superconductors. 2Dissipation from moving vortices is a major limitation for the use of superconductors in high current density applications. Vortex motion in superconductors is controlled by competition between the Lorentz force in the presence of an applied current, thermal energy, the interactions between vortices, and their interaction with the local pinning landscape [1][2][3][4][5]. Sources of pinning locally reduce the free energy of a vortex that passes though them, resulting in improved critical current in samples with strong pinning [1,[6][7][8][9][10]. The various types of pinning sources, including oxygen vacancies, impurities, dislocations, extended columnar defects caused by irradiation, and others [1,[11][12][13][14][15], can be broadly categorized by the dimensionality of the pinning potentiality. One technologically important two-dimensional pinning source is grain boundaries, the boundaries between grains with different crystalline orientations [16]. If the angle between the two grains is low, dislocations are formed, separated by regions that are well lattice-matched. In this case, the lattice-matched area remains superconducting and the dislocations act as pinning sites. At high angles the misorientation is hard to accommodate, the superconductivity is reduced, and the grain boundary behaves like a Josephson junction. Twin boundaries are a particular kind of grain boundary formed in materials with orthorhombic symmetry by a nearly 90 degree rotation around the c-axis, or equivalently by an interchange between the a and b crystalline axes. Twin boundaries can be found in many of the relatively new family of pnictide superconductors [17,18]. The 122 pnictide compounds undergo a tetragonal to orthorhombic transition and twin formation occurs prior to entering the superconducting phase in the underdoped part of the superconducting dome [19][20][21]. We have previously reported enhanced superfluid density on twin boundaries in the Cobalt-doped 122 pnictide family [22,23], while bulk magnetization measurements show enhanced vortex pinning associated with the presence of twins [24].In the present work we wish to examine the effect of twin boundaries in pnictides on the vortices and their dynamics. We use scanning Superconducting QUantum Interference Device (SQUID) microscopy, which is local and sensitive enough to measure both individual vortices and the loc...

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“…The pickup loops have diameters down to ∼ 4 µm and are connected via well shielded superconducting thin film leads to the SQUID loop at typically ∼ 1 mm distance on the same chip 145 . This technology has also been used to realize a miniature vector magnetometer for SSM by using three SQUIDs with orthogonal pickup loops on a single chip 146 58,59 . Based on the original microsusceptometer design of Ketchen et al 44 , these devices contain two oppositely wound pickup coils, to cancel homogeneous applied fields.…”

Section: Nanosquids For Scanning Squid Microscopymentioning

confidence: 99%

“…This susceptometer was operated in a dilution refrigerator, and the output signal was measured in open-loop configuration and amplified by an rf SQUID preamplifier. Magnetic susceptibility measurements performed with this system will be reviewed in section IV C. Very similar devices based on Nb/Al-AlO x /Nb JJs with √ S Φ = 0.8 µΦ 0 / √ Hz at 4 K and 0.25 µΦ 0 / √ Hz below 0.5 K were adapted to the use in scanning SQUID microscopes 58,59 ; see section V. Broad-band SQUID microsusceptometers have been realized by locally modifying SQUID current sensors based on Nb/Al-AlO x /Nb JJ technology. Those sensors 60 come in two types: (i) high-input inductance (∼ 1 µH) sensors incorporate an intermediate transformer loop with gradiometric design; (ii) low-input inductance (2 nH) devices without intermediate loop; here the input signal is directly coupled to the SQUID via four single-turn gradiometric coils connected in parallel.…”

Section: µMmentioning

confidence: 99%

Sample Preparation for Inorganic Trace Element Analysis

Matusiewicz¹

2017

Physical Sciences Reviews

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Scanning superconducting quantum interference device susceptometry

Cited by 72 publications

References 9 publications

Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures

Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures

Behavior of vortices near twin boundaries in underdoped Ba(Fe1−xCox)2As<

Sample Preparation for Inorganic Trace Element Analysis

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