Room Temperature In Magnetic Fields Research Articles

Near IR and Visible Photoluminescence Studies of Porous Silicon

ABSTRACTWe report photoluminescence emission and photoluminescence excitation studies of porous silicon obtained from p-type Si(111) wafers over the range of 0.9–13.0 eV (∼400–1400 nm). Strong IR emission above and below the bulk silicon band gap at ∼1.09 eV (1135 nm) at 300 K was observed. This luminescence due to intrinsic band-to-band recombination, was found to be enhanced by two orders of magnitude or more over the IR spectrum from an unanodized wafer. The visible luminescence peak that has been attributed to quantum confinement effects in porous silicon was located at ∼1.8 eV (689 nm). We studied the high intensity IR and visible PL in detail as a function of temperature (4–700 K), laser excitation energy (1.96–3.80 eV), and laser power (0.1–1000 mW). The measured shift in the bulk silicon band gap was approximately linear from 300–700 K (∼−0.22 meV/K), while the visible peak red-shifted by ∼− 1.24 meV/K over the same range. Below 300 K they both had comparable temperature dependences. The visible PL was investigated at room temperature in magnetic fields up to 15 T; no discernible shift in the peak position or change in the peak intensity was observed.

Magnetic moment and high-field susceptibility of amorphous FeB Invar-type alloys

The saturation magnetization and high-field susceptibility of amorphous Fe 100− x B x (11 ⩽ x ⩽ 22) alloys have been measured at 4.2 K, 77 K and room temperature in magnetic fields up to 100 kOe. The concentration dependence of the saturation moment per iron atom shows a maximum around 14% boron, while the high-field susceptibility increases remarkably with decreasing boron content. The features are similar to those of crystalline FeNi Invar alloys.

Temperature and magnetic field dependences of the resistivity of amorphous alloys

High-resolution resistivity measurements on a wise variety of amorphous alloys are reported for the temperature range from 0.5K to room temperature in magnetic fields up to 45 kOe. The resistivities are large. At the lower temperatures, below 20K, the resistivity is dominated by a -In(T2+ Delta 2) term with Delta approximately 0.5K. This term is unaffected by magnetic fields ruling out magnetic scattering in favour of scattering from the disordered structure. Successive thermal annealing of selected samples has no effect on the resistivity until the onset of crystallisation, after which the residual resistivity decreases and the low-temperature anomaly all but disappears.

Magnetic Susceptibility in the Technical Saturation Region and the Internal Stress in Invar Alloys

The differential susceptibility of high purity Fe–Ni alloys with 33∼50 at.%Ni was measured at room temperature in magnetic fields of up to 11 kOe. The data were analysed in terms of the law of the approach to magnetic saturation and the internal stresses in the alloys were evaluated. The internal stresses increase with decreasing Ni-concentration and their values are scarcely changed with the period of annealing at 1000°C.

The Magneto‐Seebeck Coefficient of Bismuth Single Crystals

AbstractThe magneto‐Seebeck Coefficients α11 (B3) and α33 (B1) have been measured for pure bismuth crystals between about 20 K and room temperature in magnetic fields of up to 5.5 T. The observed behaviour has been compared with a theory due to Korenblit. It appears that a phonon‐drag component of the Seebeck coefficient at very high fields persists up to well above liquid nitrogen temperature. However, some features of the results are not in accordance with theory.

A comparison of thermomagnetic materials for use at room temperature

A novel experimental technique based upon the hybrid DC thermoelectric-thermomagnetic transformer has been developed to carry out a comparison of the properties of some promising thermomagnetic materials, namely Bi, Bi-Sb, Bi-Ag, InSb-NiSb and Cd3As2-NiAs. The factors that determine the performance of various devices have been studied at room temperature in magnetic fields up to 1·5 T. Of the materials examined, InSb-NiSb is the best for use in a heat-flow meter while Cd3As2-NiAs is superior for the other applications.

Induced Anisotropy in Iron-Deficient Ni-Co Ferrites at Low Temperatures

The anisotropy Ku at -183°C in iron-deficient Ni-Co ferrites cooled down from room temperature in magnetic field is observed. It increases rapidly with decreasing contents of Fe 2 O 3 and seems to attain a saturation value at a certain value of Fe 2 O 3 contents. It also increases approximately in proportion to Co concentration. The activation energy for this process is about 0.25 to 0.4 eV. This anisotropy has been explained in terms of the preferential occupation of Co 3+ ions in the four kinds of 16d sites arising from electron migration between Co 2+ and Co 3+ ions. The anisotropy Ku is not observed in iron deficient Mg-, Mn-, and Cu- ferrites containing a small amount of Co.

Hall effect, resistivity and superconductivity of some metastable uranium-rich alloys

The Hall effect and electrical resistivity of metastable γ-phase (b.c.c.) binary alloys of uranium containing 11.6, 21.7 and 30.5 atomic percent molybdenum and 22.2 atomic percent niobium have been studied between ∼ 1°K and room temperature in magnetic fields up to 30 kG. The Hall coefficients of the latter three alloys were positive and only weakly temperature-dependent, while the Hall coefficient of the 11.6 atomic percent molybdenum alloy was strongly dependent upon both temperature and magnetic field. All samples exhibited superconductivity below ∼ 2°K and were characterized by weak negative temperature coefficients of resistivity between the transition temperatures and room temperature. Magnetic fields of ∼ 30 kG were required to restore the normal resistivity at 1.2°K. The bearing of the results of this investigation on an understanding of the electronic structure of the γ-phase is discussed.

Hall Coefficient and Thermoelectric Power of Thorium Metal

The Hall coefficient of two samples of thorium metal was measured at room temperature in magnetic fields on the order of 4000 gauss, and an average value of -1.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ volt-cm/abampere gauss obtained. The voltage of a thorium-platinum thermocouple in the temperature range 400\ifmmode^\circ\else\textdegree\fi{}C to 1100\ifmmode^\circ\else\textdegree\fi{}C is also reported.