Three-Junction SQUID-on-Tip with Tunable In-Plane and Out-of-Plane Magnetic Field Sensitivity

Abstract

Nanoscale superconducting quantum interference devices (SQUIDs) demonstrate record sensitivities to small magnetic moments but are typically sensitive only to the field component that is normal to the plane of the SQUID and out-of-plane with respect to the scanned surface. We report on a nanoscale three-junction Pb SQUID, which is fabricated on the apex of a sharp tip. Because of its three-dimensional structure, it exhibits a unique tunable sensitivity to both in-plane and out-of-plane fields. We analyze the two-dimensional interference pattern from both numerical and experimental points of view. This device is integrated into a scanning microscope, and its ability to independently measure the different components of the magnetic field with outstanding spin sensitivity better than 5 μB/Hz(1/2) is demonstrated. This highlights its potential as a local probe of nanoscale magnetic structures.

Superconducting Quantum Interferometers for Nondestructive Evaluation

“…A scanning SQUID microscope (SSM) is a powerful noninvasive tool for fundamental and applied research (see for example [2,46,47] and references therein). The high-T c DC SQUID microscope developed at FZJ for studies of room temperature objects is based on a high-T c DC SQUID with a magnetic flux antenna and was described in detail in our previous publications [48,49,50] (see Figure 6).…”

“…Low-T c DC SQUIDs with sizes of below 1 µm (“nanoSQUIDs”) have been fabricated on sharp tips of pulled quartz tubes and have demonstrated unprecedented spin sensitivities of ~0.38 μ B /√Hz [58] with spatial resolutions of ~20 nm [2]. The implementation of an electrically tunable multi-terminal SQUID configuration [59] provided optimal flux bias conditions by the direct injection of flux modulation and feedback current into the SQUID loop, thereby avoiding the need for the application of bias fields as high as ~0.4 T in the case of a 40-nm loop of a nanoSQUID.…”

“…Superconducting quantum interference devices (SQUIDs) provide unprecedented sensitivity down to the sub-fT/√Hz range, a broad frequency range of >1 MHz and a dynamic range of up to ~120 dB [1]. SQUID-based NDE systems have been developed for the investigation of objects that have dimensions of nanometers (nanoSQUID microscopes [2]) to kilometers (nondestructive archeology or geomagnetic evaluation [3,4]). Related scanning methods vary from 3D piezo stages to airborne systems transported by planes or helicopters.…”

Electrically Tunable Multiterminal SQUID-on-Tip

“…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.…”

Sample Preparation for Inorganic Trace Element Analysis

“…A device able of distinguishing in-plane and out-ofplane magnetic signals was also reported 160 . This is achieved by using a pipette with θ-shaped cross section to form a three JJ SQUID (3JSOT).…”