Local magnetic probes of superconductors

Electrically Tunable Multiterminal SQUID-on-Tip

“…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.…”

“…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.…”

Laser scanning microscopy of guided vortex flow in microstructured high-Tc films

“…2 Imaging technologies are powerful tools to visualize and understand vortex motion in patterned superconductors. The low-temperature versions of scanning tunneling microscopy ͑STM͒, 3 magnetic force microscopy ͑MFM͒, scanning Hall probe microscopy, 4 laser scanning microscopy ͑LSM͒, 5 and magneto-optic 6 ͑MO͒ microscopy are complementary technologies for the visualization of vortices in superconductors. For instance, high resolution MFM and MO imaging are sensitive on the scale of the London penetration depth L , whereas STM is sensitive to the variations of the order parameter .…”

Demonstration of magnetoelectric scanning probe microscopy

“…Magnetic force microscopy ͑MFM͒, for instance, has spatial resolution as high as 10 nm at room temperature. 1,2 However, it measures field gradients instead of actual fields, and its typical reported field sensitivity is 10 −4 T. 2 Recently, scanning Hall probe microscopes have shown spatial resolutions as high as 50 nm with field sensitivities down to 10 −8 T. 2,3 Superconducting quantum interference devices ͑SQUIDs͒ are known to be the highest sensitivity magnetometers, capable of detecting single flux quanta, and have been incorporated in scanning microscopes. For low temperature scanning SQUID microscopes using Nb-based SQUIDs, the maximum demonstrated field sensitivity is 2 ϫ 10 −14 T/Hz 1/2 .…”

“…The best demonstrated sensitivity for these systems is 10 −14 T/Hz 1/2 . 2 However, the distance between the sample and the sensor limits the spatial resolution to 20 m. 2,4 Recently, tunneling magnetoresistance sensors have been incorporated in probe microscopes with spatial resolutions as high as 0.1 m and a demonstrated field sensitivity of 10 −9 T. 5 Magnetoelectric ͑ME͒ materials are material systems that simultaneously display ferromagnetism and ferroelectricity. Laminated magnetoelectrics, a subclass of magnetoelectric materials, have gained significant attention in the past few years due to their ability to sense very small magnetic fields.…”