Electrical resistivity and magnetoresistance in monodispersed oxide-coated Fe cluster assemblies

We systematically studied electrical resistivity and magnetoresistance (MR) of size-monodispersed oxide-coated Fe cluster assemblies with the mean cluster sizes of d = 9-17 nm prepared by a plasma-gas-condensation-type cluster beam deposition system. The electrical resistivity and magnetoresistance strongly depend on the temperature, surface oxidization degree of the clusters (namely O-2 gas flow ratio R-O2), Fe cluster size d, and magnetic field. The oxide-coated Fe cluster assemblies exhibit a large negative MR effect which is further enhanced at low temperatures due to the dominant contribution of the spin-dependent tunneling process between the Fe cores through the oxide shell layers. It has been found that the magnetic field dependence of the MR ratio at all temperatures shows no saturation tendency up to a maximum field H = 50 kOe and completely disagrees with the magnetization curves which indicate a saturation tendency. These results have been interpreted by consideration of the magnetic state of the Fe-oxide shell layers, spin-dependent tunneling mechanism, and intercluster magnetic correlation. The high-field nonsaturation behavior in the magnetoresistance effect is attributed to the spin-disordered structure, which is frozen in a spin-glass-like state at low temperatures, in the surface of the Fe-oxide shell crystallites or the whole thinner Fe-oxide shell layers

Crystal structure of Fe-N clusters prepared by plasma-gas-condensation

Fe-N clusters were prepared by a plasma-gas-condensation cluster deposition apparatus at various nitrogen gas flow rate R-N2, and their crystal structures were investigated by transmission electron microscopy. For R-N2 > 2.2 x 10(-7) mol/s, fcc single-phase FeN clusters are obtained and their lattice parameter is a = 0.428 nm, being close to that (a = 0.433 nm) of ZnS-type FeN films. When R-N2 greater than or equal to 7.5 x 10(-7) mol/s, almost all clusters are of a tetrahedron shape with cluster sizes of d = 8-25 nm. This reveals that the tetrahedron shape of FeN compound clusters is stable in such small sizes, implying a low (111) surface energy and/or high elastic strain energy and twin boundary energy compared with pure metal clusters with fcc structure

Heavy Fermion Behaviors of Amorphous Ce_9Cu_<91> Alloy in High Magnetic Fields(Transport and Fermiology)

Heavy fermion behaviors observed in the amorphous(a-) Ce_9Cu_ alloy are markedly suppressed by applying high magnetic fields, H. The electronic specific heat coefficient, which is extremely large at H=0 Oe becomes smaller for H>100 kOe. With increasing H, the magnetization curve increases nonlinearly, where the magnetic susceptibility estimated for H>100 kOe is one order smaller than that for H<10 kOe. At 4.2 K, the magnetoresistance is negative and its absolute value is very small owing to the disorder scattering. These features indicate that a dense Kondo behavior is strongly suppressed in a high magnetic field

Thermal Infrared Imaging Experiments of C-Type Asteroid 162173 Ryugu on Hayabusa2

The thermal infrared imager TIR onboard Hayabusa2 has been developed to investigate thermo-physical properties of C-type, near-Earth asteroid 162173 Ryugu. TIR is one of the remote science instruments on Hayabusa2 designed to understand the nature of a volatile-rich solar system small body, but it also has significant mission objectives to provide information on surface physical properties and conditions for sampling site selection as well as the assessment of safe landing operations. TIR is based on a two-dimensional uncooled micro-bolometer array inherited from the Longwave Infrared Camera LIR on Akatsuki (Fukuhara et al., 2011). TIR takes images of thermal infrared emission in 8 to 12 μm with a field of view of 16×12∘ and a spatial resolution of 0.05∘ per pixel. TIR covers the temperature range from 150 to 460 K, including the well calibrated range from 230 to 420 K. Temperature accuracy is within 2 K or better for summed images, and the relative accuracy or noise equivalent temperature difference (NETD) at each of pixels is 0.4 K or lower for the well-calibrated temperature range. TIR takes a couple of images with shutter open and closed, the corresponding dark frame, and provides a true thermal image by dark frame subtraction. Data processing involves summation of multiple images, image processing including the StarPixel compression (Hihara et al., 2014), and transfer to the data recorder in the spacecraft digital electronics (DE). We report the scientific and mission objectives of TIR, the requirements and constraints for the instrument specifications, the designed instrumentation and the pre-flight and in-flight performances of TIR, as well as its observation plan during the Hayabusa2 mission