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Pronounced noise signatures enabling one to discriminate metastable resistivity states in La0.86Ca0.14MnO3 single crystals have been observed. The normalized noise spectra for metastable resisitivity differ both in shape and magnitude, indicating that the metastable state is associated with transition of the electronic system into another local minimum of the potential landscape. Such scenario is consistent with freezing of the electronic system into a Coulomb glass state. [ABSTRACT FROM AUTHOR]

Magnetic properties of CaMn1-xWxO3 (0 ≤ x ≤ 0.1) have been investigated, and the research was focused on the exchange bias (EB) phenomenon in CaMn0.93W0.07O3. Magnetic ground state was found to be dependent on tungsten doping level and the following states were distinguished: (i) G-type antiferromagnetic (AFM) state with a weak ferromagnetic (FM) component at x=0 and 0.04; (ii) mostly orbitally ordered C-type AFM at x=0.07 and 0.1. For the studied manganites, spontaneous magnetization increases sharply with increasing doping level reaching M0 ≈ 9.5 emu/g at T=10K for x=0.04, and then decreases rapidly reaching zero for x=0.1. Exchange bias effect, manifested by vertical and horizontal shifts in the hysteresis loop for field cooled sample, has been observed in CaMn0.93W0.07O3. Exchange bias field, coercivity, remanence asymmetry, and magnetic coercivity depend strongly on temperature, cooling field, and maximal measuring field. Horizontal and vertical shifts of magnetization loop sharply decrease with increasing temperature and vanish above 70K, whereas coercivity and magnetic coercivity disappear only above 100K (temperature of transition to the G-type AFM state). The exchange bias field HEB increases with increasing cooling field Hcool and goes through a broad maximum at 40 kOe, while the remanence asymmetry increases monotonously in the entire investigated cooling field range, up to 50 kOe. For the compound with x=0.07, the size of the FM regions 2 nm was estimated from the dependence of exchange bias field HEB upon Hcool. It is suggested that the exchange bias originates from interface exchange coupling between small FM clusters and the G-type AFM phase inside the primary C-type orbitally ordered AFM phase. [ABSTRACT FROM AUTHOR]

Magnetic properties of compacted Sm0.1Ca0.9MnO3 particles with 25 and 60 nm average sizes have been investigated. Particular attention has been paid to Griffiths-like features at temperatures above magnetic transition temperature TC and to the system glassiness at low temperatures. Griffiths-like features in inverse magnetic susceptibility of Sm0.1Ca0.9MnO3 nanoparticles have been linked to the presence of short range ferromagnetically correlated spin clusters above TC. Glassy behavior has been revealed in temperature and frequency dependence of ac-susceptibility, temperature and field dependence of thermoremanent and isothermoremanent magnetization, and time decay of the remanent magnetization. Experiments revealed the major impact of the glassy component on magnetic properties of investigated nanoparticles. The magnetic relaxation associated with glassy features was found to be much more pronounced in smaller particles, where a formation of collective state in an ensemble of phase separated nanoparticles may take place. Thermomagnetic irreversibility found in Sm0.1Ca0.9MnO3 nanoparticles has been linked to martensitic strain effects. [ABSTRACT FROM AUTHOR]

High temperature X-ray powder diffraction technique was employed to study the orthorhombic to rhombohedral (O-R) structural transition (ST) in single crystal and ceramics of La0.7Ca0.3MnO3. The data obtained evidence that such ST in both samples occurs in the vicinity of temperature T ∼ 700 K and demonstrates O and R phases coexistence within the T-intervals of about 20 K in crystal and ∼60 K in ceramics. This first order transition is hysteretic on heating and cooling procedures and it is shifted on ΔT ∼ 10 K to higher temperatures in crystal as compared to the ceramics of the same composition. We have described these features in the terms of the difference between 'technologically driven' chemical disorder characteristic for considered samples. Thus, it seems that spatial (up to the micron size scale) fluctuations of the Ca-dopant content in crystal and 'mesoscopic scale disorder' within grain boundary regions in ceramics are responsible for both: above noted difference of ST parameters and reported earlier difference in magnetic ordering of these samples. [ABSTRACT FROM AUTHOR]

A highly crystalline single- or few-layered 2D-MoS2 induces a high dark current, due to which an extremely small photocurrent generated by a few photons can be veiled or distorted. In this report, we show that suppression in the dark current with the enhancement in the photocurrent of a 2D-based photodetector, which is a prerequisite for photoresponse enhancement, can be achieved by constructing an ideal p‐n junction based on functionalizing n-type 2D-MoS2 with p-type quantum dots (QDs). Highly crystalline solution-processed manganese oxide QDs (MnO QDs) are synthesized via the pulsed femtosecond laser ablation technique in ethanol. The ablated MnO QDs are spray-coated on an exfoliated 2D-MoS2 substrate with interdigitated Au electrodes through N2-assisted spraying. In the resulting MnO QD-decorated 2D-MoS2 photodetector with a heterojunction, dark current is reduced and is accompanied by photocurrent enhancement, thereby markedly improving the photoresponsivity and detectivity of MoS2-based devices. To elucidate the underlying mechanisms contributing to this enhancement, power- and wavelength-dependent photoresponses, along with material characterizations based on spectroscopic, chemical, morphological measurements, and analyses, are discussed. [ABSTRACT FROM AUTHOR]

Magnetic properties of compacted Sm0.1Ca0.9MnO3 nanoparticles with average particle size of 25 and 60 nm have been investigated. It was found that the relative volume of the ferromagnetic phase decreases with decreasing particle size. Magnetization curves measured in field cooled and zero field cooled mode separate near the transition temperature TC and remain different even in magnetic field of 15 kOe. AC-susceptibility is strongly frequency dependent below TC, although the temperature of the maximum depends on frequency only slightly. Magnetization hysteresis loops exhibit horizontal and vertical shifts, relatively small in 60 nm and much larger in 25 nm particles, due to size-dependent exchange bias effect. The exchange bias field and the coercive field depend in a non-monotonic way on cooling magnetic field, while the asymmetry of remanence magnetization and magnetic coercivity increase monotonously with the increase of cooling field. Applied pressure enhances Curie temperature TC of nanoparticles with a pressure coefficient dTC/dP ≈ 0.6 K kbar-1, close to that of the bulk, suggesting that magnetic state of the core is similar to the bulk state. The thermoremanance and isothermoremanance curves provide fingerprints of irreversible magnetization originating from the presence of glassy component. We have ascribed the magnetic behavior of the nanoparticles to a core-shell scenario with phase separated core containing ferromagnetic clusters embedded in an antiferromagnetic matrix and partially disordered antiferromagnetic or paramagnetic shell. The suppression of the ferromagnetic phase in the core with decreasing particle size may account for the enhancement of the exchange bias effect seen in smaller particles. [ABSTRACT FROM AUTHOR]

X-band electron magnetic resonance and dc/ac magnetic measurements have been employed to study the effects of chemical disorder on magnetic ordering in bulk and nanometer-sized single crystals and bulk ceramics of optimally-doped La0.7Ca0.3MnO3 manganite. The magnetic ground state of bulk samples appeared to be ferromagnetic with the lower Curie temperature and higher magnetic homogeneity in the vicinity of the ferromagnetic-paramagnetic phase transition in the crystal, as compared with those characteristics in the ceramics. The influence of technological driven 'macroscopic' fluctuations of Ca-dopant level in crystal and 'mesoscopic' disorder within grain boundary regions in ceramics was proposed to be responsible for these effects. Surface spin disorder together with pronounced inter-particle interactions within agglomerated nano-sample results in well defined core/shell spin configuration in La0.7Ca0.3MnO3 nano-crystals. The analysis of the electron paramagnetic resonance data enlightened the reasons for the observed difference in the magnetic order. Lattice effects dominate the first-order nature of magnetic phase transition in bulk samples. However, mesoscale chemical disorder seems to be responsible for the appearance of small ferromagnetic polarons in the paramagnetic state of bulk ceramics. The experimental results and their analysis indicate that a chemical/magnetic disorder has a strong impact on the magnetic state even in the case of mostly stable optimally hole-doped manganites. [ABSTRACT FROM AUTHOR]

The oxygen content and the local oxygen arrangement of laser processed YBa2Cu3O7-δ (YBCO) thin films grown on LaAlO3 substrates have been probed by micro-Raman spectroscopy On these films, channels for easy vortex motion have been laser written (LW) into the bridge constrictions by heat-induced, partial depletion of oxygen from the laser-illuminated areas of these films. Raman microscopy has been used to investigate and characterize the oxygen content and structure of the laser written channels. Direct evidence for local micro-structural changes in the film during the LW process is presented and the heat affected zone, surrounding the channel borders, has been mapped. [ABSTRACT FROM AUTHOR]

Anisotropic magnetoresistance (AMR) in La0.79Ca0.21MnO3 single crystals has been investigated. In contrast with previous studies, in our experiments AMR increases with decreasing temperature, reaches the maximum below TC and decreases with further temperature decrease. Variations of MR while rotating the sample around the [110] crystalline direction may be associated with uniaxial magnetocrystalline anisotropy. The unusual enhancement of AMR below TC is ascribed to changes in the magnetic domain structure revealed by magneto-optical techniques. [ABSTRACT FROM AUTHOR]

Magnetic and transport properties of 100 nm thick La0.9MnO3-δ self-doped manganite films have been investigated in the temperature range 5–300 K. The films exhibit a paramagnetic to ferromagnetic transition at TC=194 K. The temperature dependence of the resistivity shows a metal-insulator transition at 204 K and a strong resistivity increase below 160 K. The magnetoresistance was always negative and slightly bias dependent. Variations in resistivity with magnetic field and current are nonhysteretic, while the temperature dependence of the resistivity exhibits unusual inverse thermal hysteresis. The magnetic field independent inverse thermal hysteresis is strongly influenced by a thermal history of the sample. The data suggest that nonlinear low temperature transport is dominated by inelastic tunneling through intrinsic tunnel junctions formed by phase-separated ferromagnetic metallic domains and insulating antiferromagnetic matrix. [ABSTRACT FROM AUTHOR]

Electric properties of YBa2Cu3O7-δ (YBCO) superconducting thin-film bridges with artificial 5-μm-wide channels for easy motion of Abrikosov vortices have been investigated. Vortex channels have been laser written into the bridge constrictions by means of heat-induced, partial depletion of oxygen from the laser-illuminated areas. Insertion of the channel into a bridge structure increases its resistivity in the normal state, broadens the superconducting transition, and dramatically reduces the critical current density. Experimentally observed features have been ascribed to the vortex channeling mechanism, which reduces the pinning efficiency of the extended growth defects in YBCO. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the relation between random telegraphy noise and 1/f-type background voltage fluctuations in current biased high-T films. Information on elementary and macroscopic two-level fluctuators; Experimental procedure; Results of the study.

Deals with a study which investigated excess low-frequency noise extending to MHz frequencies in de current biased granular high T[subc] thin films. Observations on lifetimes of the low- and high-voltage states of the fluctuating system; Method used to get an insight into physical mechanism causing the fluctuations.

Despite the recent growing interest in 2D-MoS2 nanostructures for versatile platforms of sensor applications, robust and practical 2D-MoS2 nanostructures have rarely been reported to date due to the absence of a facile, scalable, and repeatable nanofabrication method. Herein, we show the fabrication of periodically aligned 2D-MoS2 nanoribbon (MNR) array with an area of 2.25 cm2 via direct metal transfer. The MNR width is scalable from 463 nm to 135 nm at 650 nm pitch, and the smallest width is approximately 80 nm. The robust and stable material characteristics are analyzed via various spectroscopic analyses and application sensor devices. [ABSTRACT FROM AUTHOR]

ac and dc magnetic measurements have been employed to probe and compare magnetic ordering in bulk and nanometer-sized La0.9Ca0.1MnO3 single crystals. About the same cationic content was determined in both types of the samples. However, the magnetic ground state of the bulk crystal is characterized by a complex mixture of antiferromagnetically and ferromagnetically ordered phases, while the ground state of the nanosample seems to be ferromagnetic and coexisting with the superparamagnetic state at T<240 K. The results are discussed in terms of the different randomness of indirect ferromagnetic exchange interactions mediated by the bound holes. [ABSTRACT FROM AUTHOR]

Transport properties of Pr1-xSrxMnO3 single crystals doped close to the percolation threshold have been investigated. It was found that the resistivity of x=0.22 crystal obeys the Arrhenius law above TC. Below TC, the dynamic resistance starts to depend strongly on bias current and a drop of the activation energy points to a change in the conduction mechanism. The results resemble closely features of the previously investigated La1-xCaxMnO3 manganites. [ABSTRACT FROM AUTHOR]

Magnetic properties of self-doped LaMn1-xO3 manganites (0<=x<=0.06) under hydrostatic pressure up to 12 kbar have been investigated. Samples with x=0 and 0.02 are antiferromagnetic insulators with a Néel temperature TN=138 K and 124 K, respectively. Materials with x=0.04 and 0.06 are ferromagnetic with a Curie temperature TC close to 110 K. With increasing self-doping, the ferromagnetic moment at T=5 K increases significantly while the pressure coefficient of TN decreases significantly. Pressure dependences of TC and of spontaneous magnetization are markedly different. For x=0.04, both quantities increase under increasing pressure. However, for x=0.06 transition temperature becomes pressure independent while magnetization markedly decreases with increasing pressure. Suppression of the ferromagnetism under pressure is tentatively attributed to the development of antiferromagnetic domains capable of competing with the ferromagnetic order under pressure. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Experimental manifestations of current enforced metastable conductivity in La[sub 0.82]Ca[sub 0.18]MnO[sub 3] single crystals are discussed. Metastable conductivity manifests itself by complex current dependence, a pronounced bias dependent structure, resistance hysteresis, enhanced noise with non-Gaussian components, and long relaxation times. Spin polarized tunneling through intrinsic tunnel junctions associated with a network of twin boundaries has been tentatively associated with the phenomena observed. [ABSTRACT FROM AUTHOR]

Exchange bias effect in CaMn1-xRexO3 (x ≤ 0.1) has been investigated. The effect is very small in the samples doped at x = 0.02 and 0.04, but increases monotonously with further increase in Re doping. For x = 0.1, both vertical and horizontal shifts in hysteresis loop of field cooled sample decrease monotonously with increasing temperature and vanish above 70 K, while coercivity disappears only above 90 K upon approaching the Néel temperature.Exchange bias field, coercivity, and remanence asymmetry depend sensitively on temperature and maximal measuring field. Magnetic training effect has been studied for x = 0.06, 0.08, 0.1 samples and analyzed using a spin relaxation model. The observed exchange bias is attributed to the low-temperature phase separation into ferromagnetic clusters and the G-type and/or C-type antiferromagnetic matrix. [ABSTRACT FROM AUTHOR]

Examines the spectral properties of radio frequency radiation from intrinsic Josephson junctions in high T[subc] Y-Ba-Cu-O thin film. Determination of synchronization conditions by direct current and external magnetic field bias; Observation of the frequency locking of radiation to external resonant circuit; Distinction of spectral line narrowing due to resonant lock from the coherence-induced narrowing by different tuning properties of the emission line.

In this paper, the electrical discharge characteristics of plasmas generated in coaxial cylindrical electrodes capacitively powered by a radio-frequency power supply at atmospheric pressure are investigated with respect to helium and argon gases. The electrical discharge parameters, voltage (V), current (I), and power (P), are measured for both helium and argon plasmas, and the electron temperatures and electron densities for them are evaluated by means of the equivalent circuit model and the power balance equation. By comparison of the discharge characteristics of the helium and argon plasmas, it is found that the discrepant macroscopic characteristics of helium and argon plasma, viz., current and voltage characteristics and current and power characteristics, are owed to their own intrinsic microscopic parameters of the helium and argon atoms, such as the first excited energy, the ionization energy, the total cross section, and the atom mass. Furthermore, the influences of the additive gas, oxygen gas, on the electrical discharge characteristics are also investigated in the helium and argon plasmas, which are closely related to the electron temperature of plasmas. [ABSTRACT FROM AUTHOR]

The electrical breakdown characteristics of the rf capacitive plasma source are investigated theoretically and experimentally. The plasma source is the electrode type consisting of the concentric cylinders for generating nonequilibrium plasma at atmospheric pressure. The theoretical model based on the diffusion-controlled breakdown mechanism is proposed to analyze the electrical breakdown phenomenon in this rf capacitive plasma source of the coaxial cylinders. The electron temperature at the electrical breakdown is calculated from the theoretical model, thereby evaluating the electrical breakdown voltages. The experimental data of the electrical breakdown voltage are measured with respect to the variation of the geometric parameters of plasma source, the gas temperature, and the concentration of the foreign reactive gases (oxygen and nitrogen) mixed in the helium gas. The theoretical results of the electrical breakdown voltage agree remarkably well with experimental data. This indicates that not only the electron temperature is important in determining the electrical breakdown voltage, but also the geometric variables, the gas temperature, and the scattering cross sections of molecules play significant roles. [ABSTRACT FROM AUTHOR]

Ultrahigh frequency rf-SQUID magnetometer employing a cryogenic preamplifier and a commercially available thin film rf-SQUID sensor have been designed, manufactured, and tested. The system has been operated at 316 MHz, which is the maximum pump frequency accepted by the thin film sensor. The cryogenic preamplifier has been built around a microwave high-electron-mobility transistor which was made unconditionally stable at ultrahigh frequency band by means of an appropriate circuit design, namely, a cascode configuration. The total flux noise of the magnetometer has been found to be 8.4 × 10-6[uppercase_phi_synonym]0/[Square_Root]Hz at 4.2 K and 5.8× 10-6[uppercase_phi_synonym]0/[Square_Root]Hz at 1.4 K. The temperature dependence of the fractional step rise α of the current-voltage rf characteristic has been measured to be proportional to the 2/3 power of the SQUID sensor temperature. The noise performance of the system at 4.2 K has been limited by the intrinsic SQUID noise only, in good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]