Non-saturating Behavior Research Articles

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 O2 gas flow ratio RO2), 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.

Non-saturating upper critical field of organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl

The layered superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl in the magnetic field applied strictly parallel to the superconducting plane shows the upper critical field exhibiting non-saturating behavior toward 0 K. The relation to the spatially modulated order-parameter state predicted by Fulde–Ferrell and Larkin–Ovchinnikov is argued.

Explanation of the non-saturating behavior of the hysteresis loop based on the relaxation current

The hysteresis loop of ferroelectric thin film capacitors, shows sometimes non-saturation effects, i.e. the high electric field parts of the hysteresis loop do not close and the apparent remanent polarization increases with the amplitude of the measurement signal. Several models attributed this effect to the presence of leakage current, but the very high current levels predicted have not been always confirmed by the direct measurements of the DC leakage. Here, we show that the relaxation current, rather than the true DC leakage current can, in these cases, explains the non-saturating behavior. This effect would than not be caused by the movement of free charges, but rather to of the localized ones.

Superconductivity and magnetoresistance in a single-crystal LaNiSn

Superconductivity in LaNiSn has been found below the transition temperature T c=0.59 K by measurements of the electrical resistivity and the a.c. magnetic susceptibility on a single-crystalline sample. The upper critical magnetic field was determined by the field dependence of the transition temperature. The non-saturating behavior in the magnetoresistance for transverse configurations suggests that LaNiSn is a compensated metal with no open orbits along the principal axes of the orthorhombic structure.

Structure and magnetic properties of Fe/EuO granular films

AbtractWe produced Fe/EuO granular films by reactive co-evaporation, and measured their structural and magnetic properties using X-ray diffraction (XRD), transmission electron microscopy, and a superconducting quantum interference device magnetometer. The XRD patterns of Fe/EuO films deposited at substrate temperatures up to 200 °C show only weak peaks due to Fe, while films deposited at 400 °C show diffraction peaks due to Fe and EuO, indicating that an Fe/EuO granular film was formed. Magnetic measurements of the Fe/EuO granular films revealed the following: (i) the magnetization at 300 K shows typical ferromagnetic behavior, while that measured at 5 K shows non-saturating behavior with the magnetization above 15 kOe exceeding the saturation value at 300 K; (ii) the magnetization at a magnetic field of 10 kOe increases gradually with increasing temperature up to about 200 K, followed by a constant value, while that at 50 kOe shows an initial large value, which decreases to the constant value at around 200 K. These results indicate that the coupling between the magnetic moments of Fe and those of EuO is non-collinear, and that the moments gradually align themselves with an externally applied magnetic field.

Modeling pentode-like characteristics of recessed-gate static induction transistor

A new analytical model is described for the pentode-like region of the characteristics of recessed-gate SIT structures. The model allows one to investigate the transition from saturating characteristics of long channel JFET's to nonsaturating behavior of SIT devices, taking into account realistic device geometry. >

Effects of process parameter distributions and ion strike locations on SEU cross-section data (CMOS SRAMs)

The effect of statistical parameter distributions and stochastic ion strike locations in hardened memory arrays on observed SEU (single event upset) cross-section data is discussed. Application of numerical analysis to the parasitic bipolar gain distributions in SIMOX (separation by implantation of oxygen) SRAMs (static random-access memories) and the introduction of an effective critical charge based on sensitivities to ion strike locations explain the nonsaturating behavior of measured cross-section curves in SOI (silicon-on-insulator) and other hardened memories. A direct, analytical relationship between the measured cross-section curves seen in contemporary SOI CMOS SRAMs and the distribution of the parasitic bipolar beta values controlling each cell critical charge is presented. Results of this technique clearly indicate that distributed processing parameters and random ion strike locations lead to nonideal cross-section curves. The results also indicate that if the distribution for a critical parameter is known, the LET (linear energy transfer) threshold and shape of the upset cross-section curves can be anticipated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigations of evaporated silicon p-n junctions and their application to junction field-effect transistors

p-n junctions formed by vacuum evaporation of silicon on crystalline silicon have been investigated. The junctions were formed by ion implantation of 49BF+2 in the evaporated silicon films. Subsequently, an isochronal heat treatment in the range of 600–850 °C was performed and its influence on the doping distributions and corresponding diode behavior was studied. Secondary-ion mass spectrometry was used to investigate the resulting boron distributions. A sharp decrease in the boron concentration was found at the interface for the sample annealed at 850 °C.The fabricated p-n junctions were evaluated by measuring the current-voltage characteristics. Comparisons were made to ordinary diffused p-n junctions in bulk silicon. Using the current-voltage measurements, the leakage current and the ideality factor of the diodes were extracted. The reverse currents were also measured and show a nonsaturating behavior. The resistivity of the films were investigated as a function of anneal temperature, and it was found that the boron in the films is effectively activated for heat treatments &amp;gt;700 °C. An estimation of the hole mobility in the films was made from the measured resistivity and doping distributions. The annealed structure was investigated with transmission electron microscopy. The heat treated films were found to be polycrystalline with very small grains (&amp;lt;250 Å). To demonstrate the usefulness of this technology, a junction field-effect transistor with evaporated gate diode was fabricated. The performance of this transistor is also demonstrated.

V-I characteristics of a plane disc probe in collisionless streaming plasmas

Expansion of high-temperature high-density plasmas produced by focussing high-power lasers on solid targets gives rise to collisionless streaming plasmas with flow velocity U such that Ci ≪U≲Ce, where Ce and Ci are electron and ion thermal velocities, respectively. Dimensionless V-I characteristics of a plane disc probe in such streaming plasmas are obtained. The characteristics show a nonsaturation behavior of the probe current in the electron attracting region of the probe operation. It is observed that in the electron repelling region, the slope of the V-I characteristics increases with the decrease in the probe potential.

Effects of unequal pump intensity in resonantly enhanced degenerate four-wave mixing

Experiments performed in SF 6 using a CO 2 laser show the effect of unequal pump intensity in resonantly enhanced degenerate four-wave mixing (DFWM). A two-level saturable absorber model was extended to include the effects of unequal pump intensity and the results show significant departure from typical nonsaturating behavior. The experimental results and theory show qualitative agreement.

A study of the conduction properties of a rectifying nGaAs- n(Ga, Al)As heterojunction

The I– V characteristics of a rectifying nGaAs- nAl x Ga 1- xAs heterojunction ( x ≈ 0.28) have been measured over a temperature range of 145–300°K and compared with theory. The non-saturating behavior of the reverse current can be explained by using the graded gap model for the heterojunction. The conduction band-edge step at the interface, determined from these measurements, is 280 meV, in good agreement with existing evidence. This model however fails to account for the forward current, which exhibits an anamolous “pseudo-saturation” behavior. The forward characteristics are qualitatively explained by including in the model deep-level states near the interface, which become negatively charged under forward bias.

Effect of group relaxation response training on blood pressure in essential hypertension: Sallee J. Cabeen, University of Illinois, College of Nursing, 123 Southwest Glendale, Peoria, Illinois 61605; Felissa L. Cohen

We report the magnetic and magnetocaloric properties of rapidly solidified Ni0.895Cr0.105MnGe1.05 melt-spun ribbons studied by both direct (adiabatic temperature change) and indirect (isothermal magnetic entropy change) methods in intermediate and high magnetic fields up to 10 T. The maximum values of the adiabatic temperature changes (ΔTad) and magnetic entropy changes (ΔSM) were found to be ∼2.6 K (µoH = 10 T) and 4.4 J kg−1 K−1 (µoΔH = 5 T), respectively, near the Curie temperature (TC). The ΔTad curves and magnetization isotherms were found to be completely reversible, which indicates the high degree of reversibility of the MCEs in this system. A large temperature span (of about 61 K) and a non-saturating behavior of ΔTad were observed at magnetic fields up to 10 T. The adiabatic temperature change was found to be a linear function of (µoH)2/3 near TC, in accordance with the Landau theory of phase transitions.

Temperature and Field Dependence of Magnetization of Amorphous (Fe, Mn)-P-C Alloys

Amorphous quasibinary alloys having the composition (Fe1−xMnx)0.75P0.15C0.10, where 0.0≤x≤1.0, were synthesized by rapid quenching from the liquid state. Their magnetic behavior was characterized by measurements of the magnetization as a function of temperature in the range 4.2°–300°K, and in fields ranging from 1 to 8.5 kOe. The iron-rich alloys with 0.0≤x≤0.4 are ferromagnetic: the magnetic moment at 0°K decreases linearly from 2.07 μB/Fe atom in Fe0.75P0.15C0.10 to 0.22 μB/(Fe, Mn) atom in (Fe0.6-Mn0.4)0.75P0.15C0.10. Judging from the large values of the parameter qc/qs, where qc and qs are the number per mole of magnetic carriers in the paramagnetic and ferromagnetic states, respectively, and also from the nonsaturating behavior of magnetization with field at 4.2°K, it appears that the ferromagnetism in these alloys may be of the itinerant kind. Alloys having 0.5≤x≤1.0 possess considerably more complex magnetic structures. They are characterized by a peak in the magnetization curve at temperatures between 15° and 40°K, and a ferrimagnetic-type curvature in the Curie-Weiss plots. This kind of magnetic behavior may be ascribed to ferrimagnetism existing in conjunction with parastic antiferromagnetism over some local regions in the amorphous structure.