2013/01/07 by Roman Wölbing, Wölbing, Roman, Tobias Schwarz +11
Physics and Astronomy · #FOS: Physical sciences #Magnetic properties of thin films #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #Superconductivity (cond-mat.supr-con)
paper · pdf · doi:10.48550/arxiv.1301.1189
openalex publication_date 2013/01/07 · openalex created_date 2022/10/04 · openalex updated_date 2026/07/28
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 Sμ1/2=SΦ1/2/ϕμ of a few μ_\rmB/\rmHz1/2 (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 μ\rm B/\rmHz1/2 for optimized devices seems to be realistic.