We have performed superconducting quantum interference device and -Hall local magnetization measurements on Nb thin films of different thicknesses (120 nmрdр1200 nm) and widths (95 mрwр900 m) in order to characterize the effects due to thermomagnetic instabilities ͑TMI's͒ and their geometry dependence. We show that the second magnetization peak which occurs at fields H SM P (T)ӶH c2 (T) depends on the sample dimensions and discuss it in terms of the classical theory of TMI's. Local magnetization measurements reveal a domelike flux profile at low fields which is not due to edge barriers. The Bean-like flux distribution is recovered at applied fields HуH SM P (T). ͓S0163-1829͑99͒04138-7͔
W e report the use of an ultralow noise nano-superconducting quantum interference device nanoSQUID_ to measure the hysteretic magnetization behavior of a single FePt nanobead at a temperature of around 7 K in a magnetic field of only 10 mT. W e also show that the nanobead can be accurately positioned with respect to the SQUID loop and then removed without affecting SQUID performance. This system is capable of further development with wide applications in nanomagnetism.
We have realized an improved resistance calibration setup based on a cryogenic
current comparator (CCC). The comparator, with 18 windings and 4647
turns in total, is well-suited for all the necessary comparisons with a 100
Ω
standard resistor with the quantum Hall effect and inside the range of standard resistance values from
1 Ω
to 1 MΩ. The new state-of-the-art setup is equipped with a low-noise dc SQUID (superconducting
quantum interference device) and a digital double current source. Proper damping of the
CCC resonance, careful electronics design (‘box-in-box’) and application of internal
wideband feedback to the SQUID sensor improve the dynamic stability considerably and
lower the overall measurement time as compared against our previous setup.
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