Sensitivity and spatial resolution of square loop SQUID magnetometers

We calculate the flux threading the pick-up coil of a square SQUID magnetometer in the presence of a current dipole source. The result reproduces that of a circle coil magnetometer calculated by Wikswo with only small differences. However it has a simpler form so that it is possible to derive from it closed form expressions for the current dipole sensitivity and the spatial resolution. The results are useful to assess the overall performance of the device and to compare different designs

Thin-film microsusceptometer with integrated nanoloop

Trabajo presentado al 14th International Superconductive Electronics Conference (ISEC), celebrado en Cambridge, Massachusetts (EE. UU.) del 7 al 11 de julio de 2013.-- et al.We report the design and performance of thin-film microsusceptometers intended for magnetic measurements on samples at variable temperature down to the low mK range and excitation frequencies of up to about 1 MHz. The devices are realized as first-order gradiometers with two circular loops of 60 μm or 30 μm average diameter resulting in a total inductance of 360 pH or 250 pH, respectively. An integrated excitation coil generates a magnetic field with a sensitivity of 0.1 T/A at the sample position, whereas the Josephson junctions are located in a field-reduced area. The susceptometers are fabricated by a conventional Nb/AlOx/Nb trilayer process. In order to enhance the sensitivity to the level required for the measurement of sub-μm samples, an extra detection loop of about 450 nm inner diameter was integrated into one of the pickup loops by using a focused ion beam (FIB). We show that this device is able of detecting signals from very small permalloy samples. An improved susceptometer design for equipment with integrated nanoloops is also presented, for which a total inductance of 50 pH is predicted.This work was partly funded by the European Microkelvin Collaboration within the 7th Framework Programme of the European Commission (Grant number 228464), by the Spanish Ministry of Economy and Competitiveness (Grant MAT2012-38318-C03), and by the EMRP (EMRP: European Metrology Research Programme) project MetNEMS NEW08. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.Peer reviewe

Ac magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a microSQUID sensor

We report the controlled integration, via Dip Pen Nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 100, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.Comment: 4 pages 3 figure

Characterization of low temperature metallic magnetic calorimeters having gold absorbers with implanted 163^{163}Ho ions

For the first time we have investigated the behavior of fully micro-fabricated low temperature metallic magnetic calorimeters (MMCs) after undergoing an ion-implantation process. This experiment had the aim to show the possibility to perform a high precision calorimetric measurement of the energy spectrum following the electron capture of $^{163}$Ho using MMCs having the radioactive $^{163}$Ho ions implanted in the absorber. The implantation of $^{163}$Ho ions was performed at ISOLDE-CERN. The performance of a detector that underwent an ion-implantation process is compared to the one of a detector without implanted ions. The results show that the implantation dose of ions used in this experiment does not compromise the properties of the detector. In addition an optimized detector design for future $^{163}$Ho experiments is presented

First Results from the AMoRE-Pilot neutrinoless double beta decay experiment

The Advanced Molybdenum-based Rare process Experiment (AMoRE) aims to search for neutrinoless double beta decay (0$\nu\beta\beta$) of $^{100}$Mo with $\sim$100 kg of $^{100}$Mo-enriched molybdenum embedded in cryogenic detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from $^{48}$Ca-depleted calcium and $^{100}$Mo-enriched molybdenum ($^{48\textrm{depl}}$Ca$^{100}$MoO$_4$). The simultaneous detection of heat(phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot $0\nu\beta\beta$ search with a 111 kg$\cdot$d live exposure of $^{48\textrm{depl}}$Ca$^{100}$MoO$_4$ crystals. No evidence for $0\nu\beta\beta$ decay of $^{100}$Mo is found, and a upper limit is set for the half-life of 0$\nu\beta\beta$ of $^{100}$Mo of $T^{0\nu}_{1/2} > 9.5\times10^{22}$ y at 90% C.L.. This limit corresponds to an effective Majorana neutrino mass limit in the range $\langle m_{\beta\beta}\rangle\le(1.2-2.1)$ eV

Enhancing the sensitivity of magnetic sensors by 3D metamaterial shells

Magnetic sensors are key elements in our interconnected smart society. Their sensitivity becomes essential for many applications in fields such as biomedicine, computer memories, geophysics, or space exploration. Here we present a universal way of increasing the sensitivity of magnetic sensors by surrounding them with a spherical metamaterial shell with specially designed anisotropic magnetic properties. We analytically demonstrate that the magnetic field in the sensing area is enhanced by our metamaterial shell by a known factor that depends on the shell radii ratio. When the applied field is non-uniform, as for dipolar magnetic field sources, field gradient is increased as well. A proof-of-concept experimental realization confirms the theoretical predictions. The metamaterial shell is also shown to concentrate time-dependent magnetic fields upto frequencies of 100 kHz

[email protected]; phone +31 30 2535710; fax +31 30 2540860, www.sron.nl Space Telescopes and Instrumentation

ABSTRACT The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 x 5 pixel array of TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing (FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogenfree cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs, fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital electronics, etc. Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray energy resolution of 1.58 eV at 250 eV and 2.5 eV @ 5.9 keV for the read-out of one TES-pixel only. Next step is deployment of FDM to read-out the full array. Full performance demonstration is expected mid 2009