Optimizing the spin sensitivity of grain boundary junction nanoSQUIDs—towards detection of small spin systems with single-spin resolution

Abstract

We present an optimization study of the spin sensitivity of nanoSQUIDs based on resistively shunted grain boundary Josephson junctions. In addition the dc SQUIDs contain a narrow constriction onto which a small magnetic particle can be placed (with its magnetic moment in the plane of the SQUID loop and perpendicular to the grain boundary) for efficient coupling of its stray magnetic field to the SQUID loop. The separation of the location of optimum coupling from the junctions allows for an independent optimization of the coupling factor φµ and junction properties. We present different methods for calculating φµ (for a magnetic nanoparticle placed 10 nm above the constriction) as a function of device geometry and show that those yield consistent results. Furthermore, by numerical simulations we obtain a general expression for the dependence of the SQUID inductance on geometrical parameters of our devices, which allows to estimate their impact on the spectral density of flux noise SΦ of the SQUIDs in the thermal white noise regime. Our analysis of the dependence of SΦ and φµ on the geometric parameters of the SQUID layout yields a spin sensitivity S 1/2 µ = S 1/2 Φ /φµ of a few µB/Hz 1/2 (µB is the Bohr magneton) for optimized parameters, respecting technological constraints. However, by comparison with experimentally realized devices we find significantly larger values for the measured white flux noise, as compared to our theoretical predictions. Still, a spin sensitivity on the order of 10 µB/Hz 1/2 for optimized devices seems to be realistic.

Electrically Tunable Multiterminal SQUID-on-Tip

“…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 .…”

Meissner effect measurement of single indium particle using a customized on-chip nano-scale superconducting quantum interference device system

“…3(b). For N = 10 4 , the white flux noise determined by measuring P sw reached 28 μФ 0 /Hz 1/2 , with a corresponding sensitivity in magnetic moments of approximately 4.6 × 10 −17  emu/Hz 1/2  82728. Compared with the value for a commercial MPMS system (Quantum Design MPMS-3) of 1.0 × 10 −8  emu/Hz 1/2 , our on-chip SQUID measurement system showed an improvement of 9 orders of magnitude.…”

Ultradense Tailored Vortex Pinning Arrays in Superconducting YBa2Cu3O7−δThin Films Created by Focused He Ion Beam Irradiation for Fluxonics Applications

“…On the other hand, thin films of YBCO have an in-plane λ L,ab (0) ∼ 250 nm, [18][19][20][21] and edge and screw dislocations, as one important type of intrinsic defects in YBCO films, have typical distances of about 300 nm. 22 Since intrinsic defects compete with the artificially created pinning landscape, it is important to fabricate and investigate pinning arrays with lattice spacings significantly below these two characteristic lengths.…”