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The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composite using in conductometric gas sensors and can restrict application of nanocomposites in these devices. Technology features of composite synthesis and device fabrication, which should be taken into account while designing and fabricating sensors based on metal oxide composites, are considered. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

In this work it was studied the influence of cross-interference effects between hydrogen and ozone on the performances of the SnO 2 -based thin film gas sensors. The SnO 2 films with different thickness were deposited by spray pyrolysis. It was shown that the interference of gases was not a simple arithmetic addition of two effects related to the influence of individual gases on the sensor parameters. Interference of gases depends on many factors, including the concentration of the interacting gases, the film structure and the surface properties of the gas-sensitive material. Therefore it is difficult to predict this effect basing on the results obtained during the sensor testing to individual gases. It was also found that the air ozonization could be used to optimize the sensor parameters, i.e. to increase sensitivity and decrease the time constants of response and recovery. In addition, we have proposed temperature conditions, providing an improvement of the sensor selectivity when detecting hydrogen and ozone.

This article describes in detail the SnO2 and In2O3 metal oxides as materials for designing solid state conductometric ozone sensors. The main focus of this article is on the description of the SnO2 and In2O3 films' structural parameters important for gas sensor design and on the establishment of the main regularities of the film parameters influence on the sensor characteristics. Advantages and disadvantages of approaches used for optimization of ozone sensor parameters are also analyzed. In particular, surface modification, bulk doping of SnO2 and In2O3, and the use of 1D structures and hybrid materials are considered. The main factors, controlling parameters of SnO2- and In2O3-based ozone sensors, are determined, and recommendations for the process of the SnO2 and In2O3 films deposition, facilitating the search of the film parameters and the fabrication technologies that optimize the ozone sensor performance, are formulated.

We report the increase of the optical output power of InGaN/GaN multiple quantum well (MQW) flip-chip blue light-emitting diodes (LEDs) using cobalt–iron (CoFe) ferromagnetic layers. The CoFe alloy layer is deposited on a p-ohmic reflector of the flip-chip LEDs to apply a magnetic field in the MQWs. The optical output power of LEDs with a CoFe layer after magnetization is increased by 23% at an injection current of 20 mA compared with LEDs that have a CoFe layer before magnetization. The time-resolved photoluminescence spectra and magnetic field simulations indicated that the improvement of the optical output power of the LEDs is attributed to an enhanced radiative recombination rate in the MQWs by the additional drift of carriers in the MQWs due to the gradients of the magnetic field of the CoFe ferromagnetic layer.

Engineering approaches designed to improve parameters of conductometric gas sensors are being considered in this survey. In particular, in this paper we have analyzed engineering approaches used both for improvement of sensor stability and reliability, and for decrease of power dissipated by conductometric gas sensors. Analysis has shown that those engineering approaches can eliminate some genetic disadvantages of conductometric gas sensors, provide a significant improvement of their exploitation parameters, and expand their application in various fields.

Present paper is devoted to analysis of both cathodoluminescence (CL) and gas sensing properties of the SnO2-based materials. For those purposes SnO2 doped by Pt and Pd (0.01–10 wt%) during powders synthesis, and the SnO2 films doped by Fe, Co, and Cu (0–16 at%) during spray pyrolysis deposition have been used. It is shown that there is correlation between cathodoluminescence and gas sensing properties of the SnO2-based devices, in particular, between the CL intensity and magnitude of sensor response. It was concluded that while analyzing both the CL spectra and CL intensity, one can receive additional information on structural parameters of doped SnO2 which could be used for better understanding of gas sensing effects. It is shown that heavily doped SnO2 films had considerable structural disordering and reduced both sensor response and the CL intensity. It was also concluded that for achievement maximum response of doped SnO2:(Pd, Pt, Co, Cu)-based sensors, concentration of additives during bulk doping should provide their full incorporation in the SnO2 lattice without forming clusters at the SnO2 grain surface, i.e. doping concentration should be less than the limiting solubility of dopants in the metal oxide.

Engineering approaches designed to improve the parameters of conductometric gas sensors, are considered in this short survey. In particular, in the first part of the paper we analyze the engineering approaches used for the improvement of sensor sensitivity and selectivity. Analysis has shown that engineering approaches in a number of cases can eliminate some intrinsic disadvantages of conductometric gas sensors, can give significant improvement of gas sensors performances and expand their application in various fields.

Effect of doping by cobalt on gas sensing, electrophysical and structural properties of the SnO2 films was studied. Undoped and doped SnO2 films were deposited by spray pyrolysis method on alumina, silicon and quartz substrates kept at 410–450 °C. The film structure was controlled by XRD and SEM methods. Ozone and hydrogen were used as tested gases. It was found that the influence of doping by cobalt on the SnO2-based gas sensor parameters depends on the concentration of doping additives and could be accompanied by either improvement of sensor parameters at low level of doping (CCo

The influence of Se doping on the operating characteristics of In 2 O 3 -based gas sensors was studied. Here, In 2 O 3 -based ceramic beads were prepared by sol–gel technology. The Se concentration in the solution used for the synthesis of In 2 O 3 powders was varied in the range 0–10 wt.%. O 3 (∼1 ppm), CO (2000 ppm) and H 2 (1000 ppm) were used as the test gases. The addition of selenium into the In 2 O 3 matrix was found to be effective in increasing sensor response to the oxidizing gas, ozone. It was posited that this improvement is connected to optimization of the In 2 O 3 ceramic structure.

The paper considers SnO2and In2O3thin films as materials for the design of solid-state conductometric ozone sensors in depth. In particular, the present review covers the analysis of the fundamentals of SnO2- and In2O3-based conductometric ozone sensor operation. The main focus is on the description of mechanisms of ozone interaction with metal oxides, the influence of air humidity on sensor response, and processes that control the kinetics of sensor response to ozone.

The potential for successive ionic layer deposition (SILD) technology to be used in the surface modification of SnO2 films using Ag nanoclusters was analyzed in this paper. It was found that the surface modification by SILD of Ag nanoclusters can be used to improve both the sensitivity and response rate of SnO2-based gas sensors to CO and H2. Models showing the promotional role of Ag additives were then discussed. It was also established that the presence of Ag clusters on the surface of SnO2 depresses the sensor response to ozone. This effect can be used to improve the selectivity of sensors of reducing gases aimed for operation in atmosphere containing oxidizing gases.

Short description of methods of ozone detection and sensing materials acceptable for those applications is presented in this paper. Advantages and disadvantages of SnO 2 application for design of conductometric ozone sensors are discussed as well. For those purposes detailed characterization of the SnO 2 -based ozone sensors and comparative analysis of ozone sensors designed on the base of undoped SnO 2 and In 2 O 3 films deposited by spray pyrolysis was conducted. It was concluded that long recovery process and high chemical stability could be referred to the main disadvantages of the SnO 2 -based ozone sensors in comparison with the In 2 O 3 -based devices.

In the present brief review modern views on the reasons of time instability of gas sensors parameters, as well as approaches, which could be used for the improvement of this important sensor's parameter, are summarized. In particular, the influence of factors such as structure transformation, phase transformation, poisoning, degradation of contacts and heaters, bulk diffusion, errors in design, change of humidity, fluctuations of temperature in the surrounding atmosphere, and interference effect was analyzed. It was shown that while designing devices such as solid-state gas sensors, there are no secondary issues or tasks—all are important. Sensors work in extreme temperatures in the presence of active gases, and therefore every element of the sensor could be responsible for its long-term stability. The conclusions, regarding the efficiency of approaches such as optimization of technological processes and optimization of exploitation processes used for improvement of stability of conductometric metal oxide gas sensors, were made as well.

This review is devoted to the analysis of the problems related to fabrication of the Si porous layers. The review was motivated by a great interest to Si-based porous materials from nano- to macro-scale for various applications in electronics, optoelectronics, photonics, chemical sensors, biosensors, etc. The peculiarities of the silicon porosification and the principles of preparing porous layers are considered in the present article. Various methods used for Si porosification such as chemical stain etching, chemical vapor etching, laser-induced etching, metal-assisted etching, spark processing and reactive ion (plasma) etching were analyzed. However, the main attention was focused on electrochemical porosification of Si. The review discusses in detail the influence of parameters such as electrolyte composition and pH, current density, etching time, temperature, wafer doping and orientation, lighting, magnetic field, and ultrasonic agitation on the process of Si porosification. It was shown that the stru...

A systematic experimental study of the spectral and transient characteristics of the photoconductivity near the fundamental optical absorption edge of both nanocrystalline and epitaxial In2O3 thin films was carried out. Transient characteristics of conductivity under step changes of oxidizing conditions caused by surrounding atmosphere changing (air ↔ N2) and (air ↔ O3) have been analyzed and the main regularities were identified. Experiments were performed at operation temperatures from 150 to 400 °C, which correspond to the reproducible conductivity responses to oxidizing and reducing atmospheres. During step changing of the oxidizing properties of surrounding atmosphere, kinetic experiments revealed practically identical transient patterns in both photoconductivity and dark conductivity. An anomalous large magnitude of photocurrent within mm-scale length In2O3 samples was found. Spectral dependencies of photocurrent have revealed some features near photon energy 2.9 eV that is about 0.5 eV smaller than the fundamental optical band gap of In2O3. The appearance of a peak near 2.9 eV under ozone exposure, and subsequent disappearance of this peak under hydrogen exposure were noted. The mechanism of photoconductivity in nanoscale In2O3 films and the role of chemisorbed oxygen in analyzed effects were discussed and semi-quantitative model was proposed.

The present review article is devoted to the analysis of the problems related to the design of gas sensors based on porous semiconductors (PS). The peculiarities of the semiconductor porosification by anodic etching and the principles of gas sensor design based on porous semiconductors, including gas sensor construction and main operating characteristics, are considered in the article. It is shown that the influence of the surrounding atmosphere on such parameters of porous semiconductors as refractive index, the intensity of photoluminescence, electroconductivity, dielectric constant, and surface potential might be used for gas sensor design. Based on the conducted analysis it is concluded that porous semiconductors have a great potential for the above-mentioned applications. However, the realization of those opportunities is restrained by such factors as bad reproducibility, increased temporal drift of characteristics, low selectivity, and an unsatisfactory level of understanding of the operating mechan...

The influence of the thickness of SnO2 films deposited by a spray pyrolysis method on the operating characteristics of gas sensors is analyzed in this paper. It outlines how the thickness of metal oxides is an important parameter for gas sensors in determining the main operating parameters, such as the magnitude and rate of the sensor response and the optimal operating temperature. It is also shown that the optimal film thickness of a gas sensing layer depends on the required sensor parameters.

The influence of the SnO2 surface modification by the SnO2–Au nanocomposites on conductivity response to such reducing gases as CO and H2 has been analyzed in the present paper. Both initial SnO2 films, subjected for surface modification, and SnO2–Au nanocomposites were deposited by Successive Ionic Layer Deposition (SILD) method. The SnO2–Au nanocomposites with Au/Sn ratio ∼1 were synthesized using HAuCl4 and SnCl2 precursors. The thickness of the Au-SnO2 nanolayers varied from 0.7–1.0 nm to 10–15 nm. It was established that the increase in the thickness of the SnO2–Au nanocomposite layer formed on the surface of the SnO2 films was accompanied by both the improvement of sensor response and the decrease in response and recovery times. An explanation of the observed effects has been proposed.

We consider the influence of surface modification by SnO2–Au nanocomposites on the conductivity response of SnO2 films to ozone. SnO2–Au nanocomposites with an Au/Sn ratio ∼1 were synthesized by the Successive Ionic Layer Deposition (SILD) method. The thickness of the Au–SnO2 nanocomposites deposited on the surface of the SnO2 films was controlled through a change of the number of deposition cycles. It was established that the indicated modification promotes optimization of sensor parameters. It was shown that sensors with a modified surface had a higher sensitivity to ozone and a shorter recovery time. An explanation of the observed effects is given.

Based on the experimental results, obtained by studying both structural and gas-sensing properties of the SnO2 and In2O3 films deposited by the spray pyrolysis method, we analyzed the influence of crystallite size on the parameters of the SnO2- and In2O3-based thin film solid-state gas sensors. For comparison, the behavior of ceramic-type gas sensors was considered as well. In particular, we examined the correlation between the grain size and parameters of conductometric-type gas sensors such as the magnitude of sensor signal, the rate of sensor response, thermal stability, and the sensitivity of sensor signal to air humidity. Findings confirmed that that grain size is one of the most important parameters of metal oxides, controlling almost all operating characteristics of the solid state gas sensors fabricated using both the ceramic and thin film technologies. However, it was shown that there is no single universal requirement for the grain size, because changes in grain size could either improve, or wor...

The current-induced domain-wall depinning in ferromagnetic nanowires with perpendicular magnetic anisotropy is investigated. The nanowire patterns with 500-nm width are fabricated from 8-nm-thick Co-Re-Pt alloy films on 1-nm-thick Ta underlayer. By injecting the current into the nanowire, the domain wall motion via depinning from extrinsic structural pinning sites is observed. The depinning time ranging over 1 mus-1 s is found to be exponentially dependent on the current density. Based on generalized Neel-Brown formula, the slope of the exponential dependence is analyzed to estimate the depinning energy barrier as a function of the current density under a constant bias magnetic field.

We investigated the out-of-plane anisotropy of Co50Fe50/Tb multilayer film with changing the thickness of Tb layer and applying an inplane filed of 200 Oe during film deposition. A strong out-of-plane anisotropy was found only for the multilayer with small thickness of Tb layer (tTb = 1 nm) and was suppressed significantly by the application of an inplane magnetic field of 200 Oe during deposition, resulting in an inplane anisotropy. It was also found that the application of the magnetic field caused the enhanced intermixing between CoFe and Tb layers to form Co-Tb and Fe-Tb alloys at the interface of the layers. While the origin of the out-of-plane anisotropy and the change of the out-of-plane to inplane anisotropy with the application of inplane field of 200 Oe are not understood completely, it seems that there is a strong correlation between the out-of-plane anisotropy and the formation of the alloys and the stress at the interface.

Polyoxometalate anion PMo 12 O 40 3− (POM) is chemically impregnated into a Pt-supported carbon nanotubes (Pt/CNTs) catalyst that is prepared via a colloidal method. The POM-impregnated Pt/CNTs catalyst system (Pt/CNTs-POM) shows at least 50% higher catalytic mass activity with improved stability for the electrooxidation of methanol than Pt/CNTs or POM-impregnated Pt/C (Pt/C-POM) catalyst systems. The enhancement in electrochemical performance of the Pt/CNTs-POM catalyst system can be attributed to the combined beneficial effects of improved electrical conductivity due to the CNTs support, highly dispersed Pt nanoparticles on the CNTs, and increased oxidation power of the polyoxometalate that can assist oxidative removal of reaction intermediates adsorbed on the Pt catalyst surface.

11 B Pulsed nuclear magnetic resonance (NMR) measurements have been performed on a single crystal of YNi 2 B 2 C superconductor to investigate the vortex structure and dynamical behavior. Spectrum, line width and transverse relaxation rate of 11 B NMR are measured at 1.8 and 3.0 T. The spectrum below 4 K exhibits a typical local field distribution for a square lattice at 3.0 T parallel to the c -axis. However, the shape of the spectrum at higher temperature changes to a symmetric narrow line, which indicates significant motion of vortices. Furthermore, thermal hysteresis of the saddle-point field, motional narrowing of line width, and enhancement of transverse relaxation rate also confirm substantial distortion and fluctuation of vortices in this low T c and nearly isotropic 3D superconductor.

Magnetostriction and magnetoresistance of single-crystalline HoNi 2 B 2 C have been measured at ambient pressure. A large anisotropy was found in the field dependence of these properties. The magnetoresistance was also measured at high pressure up to 2 GPa at low temperature below the superconducting transition temperature (9 K). Several anomalies were found due to the metamagnetic transitions, in which the transition fields increased with increasing pressure. These results will be discussed from a thermodynamical point of view and compared with the anisotropy in the lattice compression.

The Ce8Pd24M compounds, with an ordered structure derived from CePd3, have been synthesized for various group 13 and 14 p-block elements. The electrical resistivities of the group 13 compounds have features that can be attributed to strong Kondo interactions while the group 14 compounds show typical metallic behavior. The thermopowers, or Seebeck coefficients, for each compound were measured at both 297 and 78 K, and are much smaller (|S

Temperature-dependent specific heat, magnetic susceptibility, and resistance measurements have been carried out to study the electronic state of Yb ion in Yb 2 Ni 12 (P,As) 7 . All the measurements identify a valence fluctuating state for the Yb in both compounds. The electronic contributions to the specific heat, γ , are enhanced compared to those of the corresponding Yttrium compounds. The γ is temperature dependent (increasing with lowering temperature) for Yb 2 Ni 12 P 7 and temperature independent for Yb 2 Ni 12 As 7 . The parameters of valence fluctuation for the Yb ion are calculated from magnetic susceptibility using the ICF model and were found to be T sf ≈68 K, E ex ≈278 K and T sf ≈204 K, E ex ≈1709 K, resulting in the Yb valence of 2.21 and 2.79, for Yb 2 Ni 12 (P,As) 7 , respectively.

The magnetic properties of the RNi 2 B 2 C (R=Gd, Tb, Dy, Ho, Er, Tm) compounds are presented and studied in terms of the crystalline electric field effect (CEF). All of the compounds containing the magnetic rare earths R=Tb, Dy, Ho, Er, and Tm exhibit a strong temperature-dependent highly anisotropic magnetic behavior while isotropic for R=Gd. From the magnetization measurements, the R +3 magnetic moments in the Tb, Dy, and Ho compounds are found to have an easy-plane anisotropy, with the easy plane being the a b (RC) plane, whereas the Tm moments in the R=Tm compound are found to have an easy axis anisotropy with the easy axis along the c axis. The Er compound shows intermediate behavior. These anisotropies, together with the isotropy for R=Gd, are discussed and found to be in good agreement with point-charge CEF prediction. The intermediate anisotropy in R=Er compound is found to be due to the small value of Steven's coefficient B 2 0 .

Magnetic tunnel junctions (MTJs) were fabricated using nitrogen-mixed oxygen plasma (O/sub 2/:N/sub 2/=10:1). From the measurements of time-dependent dielectric breakdown (TDDB) under a constant voltage stress, the reliability of MTJs with an oxy-nitride barrier was investigated and compared with that of MTJs fabricated using pure oxygen plasma. The reliability of MTJs with an oxy-nitride barrier is much improved with the incorporation of nitrogen to oxidation process. In addition, the reliability of the oxy-nitride barrier is gradually enhanced with increasing oxy-nitridation time even after the time exceeds the optimal value. It is believed that the enhancement is due to the bonding of nitrogen to electron traps both in the oxide barriers and at the bottom interface. The characteristics of the bonding were examined by XPS measurements, which reveal a nitrogen 1s peak in Al-N bond. The lifetime of the two barriers was also estimated for comparison.

We have performed 11B nuclear magnetic resonance (NMR) measurements to look for microscopic evidence of the ferromagnetic state in several CaB6 single crystals. A number of 11B NMR resonance peaks are observed with the frequency and intensity of those peaks distinctively changing depending on the angle between the crystalline axis and a magnetic field. Analyzing this behavior, we find that the electric field gradient tensor at the boron has its principal axis perpendicular to the six cubic faces with a quadrupole resonance frequency ν Q ≈ 600 kHz . However, the satellite resonances are found to be made of two peaks. Detailed analysis of the four composite satellite peaks confirms that there are two different boron sites with slightly different ν Q 's. This suggests that the boron octahedron cages are locally distorted. However, this distortion is not directly related to ferromagnetism. Even though the magnetization data highlight the ferromagnetic hysteresis, 11B NMR linewidth and shift data show no clear microscopic evidence of the ferromagnetic state in several different compositions of CaB6 single crystals.

We have performed 11B nuclear magnetic resonance (NMR) measurements to investigate vortex dynamics in the polycrystalline MgB 2 superconductor. 11B NMR spectrum, shift and transverse relaxation rate 1 / T 2 were measured down to 4.3 K at ∼ 1.8 T . The spectrum below T c exhibits a typical local field distribution for a vortex lattice under magnetic field. The peak point of the spectrum shifts toward low magnetic field due to incomplete field penetration. Below the irreversibility temperature T irr , 1 / T 2 data, probing the slow motion of vortices, shows a single peak with a small change of the rate, contrary to the results of nickel borocarbides. Also, the relaxation profile changes from Lorentzian decay below T c to Gaussian decay at lower temperature. It strongly suggests that thermal fluctuation of vortices is reduced at low temperature and the vortex motion is much weaker compared with nickel borocarbides.

Previous investigations have shown that SrPd2Ge2, a compound isostructural with "122" iron pnictides but iron- and pnictogen-free, is a conventional superconductor with a single s-wave energy gap and a strongly three-dimensional electronic structure. In this work we reveal the Abrikosov vortex lattice formed in SrPd2Ge2 when exposed to magnetic field by means of scanning tunneling microscopy and spectroscopy. Moreover, by examining the differential conductance spectra across a vortex and estimating the upper and lower critical magnetic fields by tunneling spectroscopy and local magnetization measurements, we show that SrPd2Ge2 is a strong type II superconductor with ��>> sqrt(2). Also, we compare the differential conductance spectra in various magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit type II superconductor in the gapless region. This way we demonstrate that the type II superconductivity is induced by the sample being in the dirty limit, while in the clean limit it would be a type I superconductor with �� << sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B 85, (2012))., 9 pages, 4 figures

Detailed measurements of the field H and temperature T dependent, anisotropic magnetization M ( T , H ) on single crystal ErNi 2 B 2 C indicate that there is a phase transition to a magnetically ordered ground state that has a weak ferromagnetic component of 0.33 μ B /Er for T 2 B 2 C, but, unlike TbNi 2 B 2 C, the ferromagnetic component exists in ErNi 2 B 2 C for temperatures and fields that are well below the T c and H c2 . Therefore, in ErNi 2 B 2 C there appears to be the coexistence of superconductivity and weak ferromagnetism for T H

The electrical resistance of a single crystal of the magnetic superconductor HoNi 2 B 2 C has been measured as a function of temperature ( T ) and magnetic field ( H ) under high pressure ( P ). It is found that the superconducting transition temperature T c decreases with increasing pressure with d T c /d P = −0.05 K/kbar and the antiferromagnetic transition temperature T N increases with d T N /d P = 0.07 K/kbar. As T c approaches T N , the interplay between these two transitions manifests itself as an increased broadening of the superconducting transition.

Single crystals of GdNi 2 B 2 C have been grown out of Ni 2 B flux at high temperatures. Temperature and field dependent magnetization measurements on these crystals show that in low fields (1 kG) there are two phase transitions: at 20 K there is a paramagnetic to antiferromagnetic phase transition and at 14 K there is another transition which we infer to be a spin reorientation transition. The lower temperature transition manifests itself clearly in the anisotropic magnetization data, but is effectively averaged out in measurements of a powdered sample as well as in the polycrystalline average of the anisotropic magnetization data. Both of these transitions are also conspicuous in the temperature dependent electrical resistivity. GdB 2 C 2 single crystals were also grown out of Ni 2 B flux. This compound has an antiferromagnetic phase transition at 47 K and is very likely an impurity phase responsible for the earlier, spurious, report of a 45 K phase transition in GdNi 2 B 2 C.

Tunneling spectra of a single crystalline YNi 2 B 2 C ( T c = 15.4 K) and LuNi 2 B 2 C ( T c = 15.7 K) have been measured by a point-contact spectroscopy using a low-temperature scanning tunneling microscope. The conductance curve of these materials shows a smeared gap structure with an almost linear density of states inside of the gap region as well as a sizable zero-bias conductance. The linear conductance inside the gap region has been explained by a proximity-induced energy gap in the degraded surface normal layer. The resulting energy gap at 4.2 K is 3.2 meV and 3.3 meV for YNi 2 B 2 C and LuNi 2 B 2 C, respectively. A simple analysis using a smeared BCS density of states, on the other hand, yields energy gap of 2.55 meV and 2.65 meV. Temperature dependence of the energy gap in LuNi 2 B 2 C shows a reasonable agreement with the BCS type temperature dependence except a slight deviation near T c .

Neutron diffraction techniques have been used to study the magnetic structure of powder samples of the superconducting HoNi2B2C. In addition to the modulation of the moments along c ∗ reported previously, we observe in the vicinity of 5 K, where the compound exhibits reentrant behavior, a modulation of the moments along a ∗ . We demonstrate that all presently available experimental data on single crystals as well as powder samples contain unambiguous evidence for a modulation of the moments along a ∗ with a wave vector, qa, of approximately 0.585 a ∗ . We conclude that this modulation of the moments along a ∗ is characteristic of the magnetic structure of HoNi2B2C.

Neutron diffraction techniques have been used to study the magnetic structure of DyNi2B2C. The measurements, performed on single crystals of this compound depleted in the neutron absorbing B10 nuclei, show that below approximately 10 K the compound is a simple collinear antiferromagnet. The moments are aligned ferromagnetically in each rare-earth carbon layer perpendicular to the c-axis with the magnetic moments of two consecutive layers aligned in opposite directions. In contrast to the case of both HoNi2B2C and ErNi2B2C no modulation along the a∗ direction was observed in this compound.

Measurements of the superconducting transition temperature T c under hydrostatically applied pressure have been carried out on single-crystalline RNi 2 B 2 C (R = Y, Ho, Er, Tm) superconductors. YNi 2 B 2 C exhibit peaks in T c ( P ) centered at ≈0.52 GPa and ≈0.94 GPa with initial slopes of d T c /d P ≈+0.03 K/GPa and d T c /d P ≈+0.17 K/GPa, respectively. T c (P) of HoNi 2 B 2 C and TmNi 2 B 2 C decreases in a nearly linear fashion with d T c /d P ≈−0.25 K/GPa and −0.45 K/GPa, respectively. The discussion of the T c (P) results focuses on the shape of the density of states near the Fermi level. The strong negative d T c /d P value (as well as the low T c ( P = 0)) of TmNi 2 B 2 C is attributed to the existence of magnetic correlations above T c .

The magnetization of single-crystal HoNi 2 B 2 C has been measured as a function of applied field ( H ) and temperature in order to probe the interplay between superconductivity and magnetism in this complex layered system. The normal-state magnetic susceptibility of HoNi 2 B 2 C is highly anisotropic with a Curie-Weiss-like temperature dependence for H applied perpendicular to the c -axis and with a much weaker temperature dependence for H applied parallel to the c -axis, indicating that the Ho +3 magnetic moments lie predominately in the tetragonal a − b plane below 20 K. High-field magnetization (2000 Oe), low-field magnetization (20 Oe) and zero-field specific heat all give an antiferromagnetic ordering temperature of T N =5.0 K. Remarkably, in 20 Oe applied field both superconductivity ( T c =8.0 K) and antiferromagnetism ( T N =5.0 K) clearly make themselves manifest in the magnetization data. From these magnetization data a phase diagram in the H − T plane was constructed for both directions of applied field. This phase diagram shows a non-monotonic temperature dependence of H c2 with a deep minimum at T N =5 K. The high-field magnetization data for H applied perpendicular to the c -axis also reveal a cascade of three phase transitions for T H H versus T phase diagram for HoNi 2 B 2 C at low temperatures.

We have measured the specific heat of single crystals of superconducting YNi 2 B 2 C and TmNi 2 B 2 C. Analysis of YNi 2 B 2 C data in zero and 5 T magnetic fields indicates modestly strong electron-phonon coupling and a superconducting energy gap Δ ( O ) = 29 K . Superconductivity coexists with antiferromagnetic order below 1.5 K in TmNi 2 B 2 C. An interpretation of very low temperature specific heat indicates substantial magnetic anisotropy, with ferromagnetic planes weakly coupled antiferromagnetically to each other. Two-dimensional ferromagnetic spin waves produce a large linear-in-temperature contribution to the specific heat. We find no compelling evidence for an unconventional pairing mechanism in these systems.

Single crystals of YNi 2 B 2 C have been grown via high-temperature flux growth, using Ni 2 B as a solvent. Magnetization measurements have been carried out over a large portion of the magnetic field-temperature plane on a single crystal of YNi 2 B 2 C for field applied parallel to the c -axis in order to determine the range of thermodynamic reversibility and the critical magnetic fields. The magnetization is thermodynamically reversible within 2% of the magnetization for fields above 0.5 T and temperatures above 3 K. Near T c , the upper critical field has a slope of -0.32 T/K. The zero-temperature Ginzburg-Landau parameter κ is 13≈15, the penetration depth λ ab is about 150 nm, and the coherence distance λ ab is about 10 nm. The irreversibility line H irr ( T ) obeys H irr ( T ) = H irr (0) (1- T / T c ) 1.16 . The magnetization data below T c closely follow a logarithmic dependence on applied field, in the intermediate region, as predicted by the London model. The magnetization versus temperature curves shift uniformly to lower temperature as the field increases. Based on these measurements, YNi 2 B 2 C seems more similar to conventional low- T c superconductors than to high- T c superconductors.

A new and simple method for the fabrication of densely packed magnetic nanodot arrays was developed using conventional sputtering deposition at room temperature. An anodized alumina template was employed for the formation of nanodot assemblies, consisting of carbon nanotubes (CNTs) and magnetic nanodot arrays. Each nanodot was formed exactly on top of a CNT and was arranged with a well-ordered structure in a wide range of area. It was also found that the size of dots and the distance between dots can be tailored by changing the length of CNTs, inducing a change of strength of dipolar interaction between nanodots.

11 B NMR measurements have been performed on single crystals of LuNi2B2C superconductor to investigate vortex lattice structure and dynamical behavior. The spectrum in the superconducting state is significantly broadened by local field inhomogeneity due to the vortex lattice and the peak point of the spectrum shifts toward low magnetic field due to the imperfect field penetration. The linewidth of the spectrum reflecting local field variation is much smaller than expected for conventional vortex lattices and shows a peculiar increase at low temperature. Furthermore, the transverse relaxation rate, 1/T2, probing slow motion of vortices, exhibits a peak as temperature decreases. These results highlight significant fluctuation of vortices even for this low Tc and nearly isotropic 3D superconductor.

The electrical resistivity of single crystalline ErNi2B2C has been measured at high pressures up to 2.2 GPa and magnetic fields up to 5 T in order to make clear the relation between antiferromagnetism and superconductivity. It is found that the superconducting transition temperature Tc is almost independent of pressure, while the upper critical field Hc2 for H⊥c decreases with increasing pressure. The Neel temperature TN increases with increasing pressure. The present results are compared with those of other borocarbides and discussed taking into account the interplay between the superconductivity and the antiferromagnetism.

The characteristics of domain wall (DW) pinning at a notch in a spin-valve nanowire were investigated when a DW was created by a current, flowing into a spin-valve nanowire. It was found that DW pinning at a notch is quite sensitive to the magnitude of the current and its polarity. The current-polarity dependence of DW pinning is likely due to the spin structure in the core of the DW, which is determined by an Oersted field from the current in a Cu layer. This indicates that the control of DW pinning at a notch in a nanowire can be achieved by a current acting on its own, which is an important advantage of this method, compared with field-induced DW control.

The electrical resistivity of single crystalline TmNi 2 B 2 C has been measured at high pressures up to 2 GPa and magnetic fields up to 5 T. It is found that the superconducting transition temperature T c and the upper critical field H c2 decrease with increasing pressure, ∂T c / ∂P =−0.50 K/GPa and ∂H c2 / ∂P =−0.38 T/GPa. The present results are compared with those of other borocarbides and discussed by taking into account the interplay between the superconductivity and the antiferromagnetism.

Superconducting single crystals of SmFeAsO$_{1-x}$ without fluorine doping were grown at a pressure of 3.3 GPa and a temperature of 1350-1450 $^\circ$C by using the self-flux method. Plate-like single crystals of a few-150 $\mu$m in their lateral size were obtained. Single crystals showed the superconducting transition at about 53.5 K with a narrow transition width of 0.5 K. The synchrotron-irradiated x-ray diffractometry patterns and high-angle-annular-dark-field scanning transmission electron microscopy images point to the high quality of the crystals with a well-defined layered tetragonal structure. The chemical compositions of the crystals were estimated by using the electron-probe x-ray microanalysis., Comment: 12 pages, 3 figures

The paramagnetic susceptibility of YNi 2 B 2 C single crystal in a high magnetic field is found to be about 2×10 −5 cm 3 /mol, which is one order of magnitude smaller than the previous reports. The paramagnetic behavior is caused by the sample impurity, not by the intrinsic magnetism of the YNi 2 B 2 C superconductor and shows simple Curie–Weiss behavior. In this case, an upper critical field of the YNi 2 B 2 C can be easily obtained by extracting the paramagnetic contribution. The upper critical field shows an anomalous behavior, the steep rising at the low temperature region.