RESUMO
The magnetic field dependence of the superconductivity in nanocrystalline boron doped diamond thin films is reported. Evidence of a superconducting glass state is presented, as demonstrated by the observation of a quasi de Almeida-Thouless line in the phase diagram and a logarithmic time dependence of the magnetism. The position of the phase boundary in the H-T plane is determined from electrical transport data by detailed fitting to quasi-zero-dimensional fluctuation conductivity theory. This allows determination of the boundary between resistive and non-resistive behaviour to be made with greater precision than the standard ad hoc onset/midpoint/offset criterion. We attribute the glassy superconductivity to the morphological granularity of the diamond films.
RESUMO
We report on the implementation of an induction based, low temperature, high frequency ac susceptometer capable of measuring at frequencies up to 3.5 MHz and at temperatures between 2 K and 300 K. Careful balancing of the detection coils and calibration allow a sample magnetic moment resolution of 5 × 10-10 Am2 at 1 MHz. We discuss the design and characterization of the susceptometer and explain the calibration process. We also include some example measurements on the spin ice material CdEr2S4 and iron oxide based nanoparticles to illustrate functionality.
RESUMO
We describe and demonstrate the automated operation of a novel cryostat design that is capable of maintaining an unloaded base temperature of less than 300 mK continuously, without the need to recycle the gases within the final cold head, as is the case for conventional single shot sorption pumped (3)He cooling systems. This closed dry system uses only 5 l of (3)He gas, making this an economical alternative to traditional systems where a long hold time is required. During testing, a temperature of 365 mK was maintained with a constant 20 µW load, simulating the cooling requirement of a far infrared camera.