Large Resistance Change Research Articles

Conjectured orbital ordering behavior of Nd0.5Sr0.5MnO3 under high pressures

We have synthesized Nd0.5Sr0.5MnO3 polycrystalline bulk samples by solid state reaction, which show ferromagnetic (FM), A-type antiferromagnetic (AF) and charge ordering charge exchange (CE)-type AF transitions on cooling from room temperature to 78K. We consider that the abundant magnetic structures are caused by phase segregation. We have investigated and conjectured the orbital ordering behavior under hydrostatic pressures up to 7.5GPa and found that low pressure favors the A-type AF phase with d(x2−y2) orbital ordering and the CE-type AF phase with d(3x2−r2)∕d(3y2−r2) orbital ordering, while suppressing the FM phase with disordered orbital ordering; however, high pressure favors the A-type phase and suppresses the CE-type AF phase. Transport property enhancement and large resistance changes under high pressures are observed.

Photoinduced resistivity changes in Bi0.4Ca0.6MnO3 thin films

We report charge-ordered Bi0.4Ca0.6MnO3 thin films with charge-ordering temperature near room temperature, and observation of large photoinduced resistivity changes in these films associated with melting of the charge ordering by visible light. Films grown under small compressive strain exhibit the largest photoinduced resistivity changes. The lifetime of the photoinduced low-resistance state is on the order of half a minute. These photoinduced resistivity changes in thin films of Bi0.4Ca0.6MnO3 make them very promising for photonic device application.

Connexins pave the way for vascular communication.

Coordinated behavior within arterioles is necessary for large resistance changes to occur and is reflected as a conduction of dilations/constrictions along arterioles. These responses arise from locally initiated hyper- or depolarizations that propagate via transmembrane channels formed by connexins (gap junctions). Mounting evidence indicates that gap-junctional communication contributes to the control of vascular tone.

Highly sensitive and selective room temperature NH 3 gas microsensor using an ionic conductor (CuBr) film

A new ammonia gas microsensor was developed, based on the large resistance change of an ionic conductor (CuBr) film when exposed to low NH 3 concentrations. The detection is based on specific interactions between ammonia molecules contained in the gas atmosphere and mobile copper ions in the copper(I) bromide layer. The sensor is operating at ambient temperature and allows highly sensitive and specific ammonia detection. The sensor works at ammonia concentrations between 1 and 500 ppm. There are no significant cross-effects to acetylene and carbon monoxide and only a weak cross-sensitivity to hydrogen sulfide gas (200 ppm). The selectivity was experimentally compared with commercial tin dioxide sensors (TGS 826). The sensor fabrication is a simple process, allowing low cost device production.

Electrical Characterization of NiTi Film on Silicon Substrate

Among the different methods of measuring the phase transformation temperature, electrical resistivity measurement is found to be an important probe in determining different phases in sputtered NiTi film. In the present investigation NiTi film deposited by DC magnetron sputtering, on Sih100i substrate from a hot target is studied. A four-point probe technique has been used to characterize the film. It is observed that there is a sharp and large change in the electrical resistivity whenever there is a phase change. This measurement is sufficiently sensitive to identify the presence of precipitates in the film. It is also observed that the transformation of austenite to rhombohedral produces a very sharp and large change in resistivity. The resistivity values obtained for martensite, austenite and rhombohedral phases agree well with those of bulk value. Results from DSC measurements are used to validate the resistivity measurements. However, the DSC measurements do not appear to be as sensitive.

Highly sensitive and selective room temperature NH3 gas microsensor using an ionic conductor (CuBr) film

A new ammonia gas microsensor was developed, based on the large resistance change of an ionic conductor (CuBr) film when exposed to low NH3 concentrations. The detection is based on specific interactions between ammonia molecules contained in the gas atmosphere and mobile copper ions in the copper(I) bromide layer. The sensor is operating at ambient temperature and allows highly sensitive and specific ammonia detection. The sensor works at ammonia concentrations between 1 and 500 ppm. There are no significant cross-effects to acetylene and carbon monoxide and only a weak cross-sensitivity to hydrogen sulfide gas (200 ppm). The selectivity was experimentally compared with commercial tin dioxide sensors (TGS 826). The sensor fabrication is a simple process, allowing low cost device production.

Magnetoresistance in nanocontacts induced by magnetostrictive effects

Nickel atomic contacts made with the break junction technique have been subject to a magnetic field while monitoring their resistance. Large resistance changes with the angle between the applied field and the contact direction can be explained by modifications of the contact geometry induced by magnetostriction.

Anomalous-filling-factor-dependent nuclear-spin polarization in a 2D electron system.

Spin-related electronic phase transitions in the fractional quantum Hall regime are accompanied by a large change in resistance. Combined with their sensitivity to spin orientation of nuclei residing in the same plane as the 2D electrons, they offer a convenient electrical probe to carry out nuclear magnetometry. Despite conditions which should allow both electronic and nuclear-spin subsystems to approach thermodynamic equilibrium, we uncover for the nuclei a remarkable and strongly electronic filling-factor-dependent deviation from the anticipated thermal nuclear-spin polarization.

Large negative magnetoresistance effects in Co 2Cr 0.6Fe 0.4Al

Materials, which display large changes in resistivity in response to an applied magnetic field (magnetoresistance) are currently of great interest due to their potential for applications in magnetic sensors, magnetic random access memories, and spintronics. Guided by striking features in the electronic structure of several magnetic compounds, we prepared the Heusler compound Co 2Cr 0.6Fe 0.4Al. Based on our band structure calculations, we have chosen this composition in order to obtain a half-metallic ferromagnet with a van Hove singularity in the vicinity of the Fermi energy in the majority spin channel and a gap in the minority spin channel. We find a magnetoresistive effect of 30% in a small magnetic field of 0.1 T at room temperature. This demonstrates the feasibility of a cheap and simple magnetic sensor based on polycrystalline, intermetallic material.

Two dimensionality aspects of HTSC

Based on transport and magnetic measurements on Gd(Ba2−xPrx)Cu3O7+δ, and some other properties of high temperature superconductors (HTSC), we have extracted similarities between superconductors, two-dimensional electron gas (2D-EG) i.e. MOSFETs and ultrathin films of conventional superconductors. These are based on properties such as superconductor–insulator transition in superconductors and metal–insulator transition (MIT) in 2D-EG with doping and magnetic field, localization in transport conduction, quantum unit of resistance at MIT, larger change in resistance from critical doping to the insulating side in comparison with change from critical doping to the metallic side and strong electron–electron coupling. These similarities could lead to a deeper understanding of HTSC and 2D-EG systems.

Evaluation of an EIT reconstruction algorithm using finite difference human thorax models as phantoms

A finite difference model of the human thorax with 113 400 control volumes (nodes) based on ECG gated MRI images was used to evaluate the Sheffield DAS-01P EIT system. Sixteen simulated electrode positions equally spaced around the thorax model at approximately the fourth intercostals space level were selected. Pairs of adjacent positions were excited sequentially by injecting current in a manner similar to that used by the Sheffield DAS-01 P EIT system. The resulting voltages on the non-excited electrode positions were calculated and used to reconstruct the image using the Sheffield filtered back projection algorithm. By changing the resistivities of the lungs, the ventricles and the atria over a range of 1% to 40%, the resulting changes in the images were quantified by measuring the average resistivity change over a region defined automatically by two thresholds, 40% or 80% of the average of the first four pixels with the largest change. The results show that the changes observed in the images are consistently less than the changes in the model, but changed in a nearly linear manner as a function of resistivity in the model. For 40% resistivity changes in the model for right lung, right ventricle and right atrium, the observed resistivity changes in the region of interest (ROI, defined by the 80% threshold) of the images are 32% for the right lung, 11% for the right ventricle and 5.5% for the right atrium, which suggests strong volume dependence of EIT imaging. The effect of structural (size) change between end diastole and end systole was also studied, which showed large resistivity changes caused in the heart region of the constructed image. The study demonstrates that the Sheffield DAS-01P EIT reconstruction algorithm tracks the change occurring in the lungs most closely and with proper scaling may be used to observe physiological changes.

Electromechanical properties of metallic, quasimetallic, and semiconducting carbon nanotubes under stretching.

An electromechanical system is constructed to explore the electrical properties of various types of suspended single-walled carbon nanotubes under the influence of tensile stretching. Small band-gap semiconducting (or quasimetallic) nanotubes exhibit the largest resistance changes and piezoresistive gauge factors ( approximately 600 to 1000) under axial strains. Metallic nanotubes exhibit much weaker but nonzero sensitivity. Comparison between experiments and theoretical predictions and potential applications of nanotube electromechanical systems for physical sensors (e.g., strain gauges, pressure sensors, etc.) are discussed.

1∕f noise in hydrogenated amorphous silicon–germanium alloys

Measurements were made of conductance noise of a-Si:H and a-Si1−xGex:H in two different geometries: one where the current flow is transverse to the surface and the other where it is longitudinal to the surface. Because of the large change in sample resistance between the two geometries, it was not possible to measure both geometries at the same temperature. For both geometries, alloying with up to 40% Ge reduces the noise magnitude by several orders of magnitude over that found in a-Si:H. The decrease is incompatible with several popular noise models. Extrapolating the temperature trends for each geometry shows that it is possible that the noise observed in the transverse samples has the same origin as the higher frequency part of the double power law spectra observed in the longitudinal samples.

Actuator characteristic and electrode of multilayer piezoelectric ceramics

AbstractThe topic of this research is the investigation of Ag‐Pd internal electrodes used to interconnect layers of multilayer actuator stacks. The layers are made of the piezoelectric ceramic material Pb(Zn1/3Nb2/3)0.125−Ti0.49Zr0.385O3 + MnO2 1.0 mass % + Al2O3 0.5 mass % (hereafter referred to as PZNTZ). It is found that when PZNTZ is added to the Ag‐Pd mixing powder in amounts greater than 0.1 mass %, the peeling strength of the electrodes is improved. The data reported here indicate that the addition of this material does not lead to large changes in the electrode resistance, and hence does not compromise its function. Two explanations are offered as to why the addition of PZNTZ produces this effect: first, it decreases the wetting of the electrode at the boundary between electrode and piezoelectric material; and second, it decreases the fluidity of the electrode material in the horizontal (surface) direction that accompanies shrinkage during sintering. When Ag‐Pd with PZNTZ added is used to make electrodes for the internal connections of a tuning fork consisting of multilayer piezoelectric ceramic material, and the tuning fork is driven under conditions that cause it to vibrate at the large amplitude of 25 µm, the tuning fork exhibits markedly superior linearity characteristics, including minimal changes in its resonance frequency. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(1): 36–46, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.1116

P2 purinoceptors regulate calcium-activated chloride and fluid transport in 31EG4 mammary epithelia.

It has been reported that secretory mammary epithelial cells (MEC) release ATP, UTP, and UDP upon mechanical stimulation. Here we examined the physiological changes caused by ATP/UTP in nontransformed, clonal mouse mammary epithelia (31EG4 cells). In control conditions, transepithelial potential (apical side negative) and resistance were -4.4 +/- 1.3 mV (mean +/- SD, n = 12) and 517.7 +/- 39.4 Omega. cm(2), respectively. The apical membrane potential was -43.9 +/- 1.7 mV, and the ratio of apical to basolateral membrane resistance (R(A)/R(B)) was 3.5 +/- 0.2. Addition of ATP or UTP to the apical or basolateral membranes caused large voltage and resistance changes with an EC(50) of approximately 24 microM (apical) and approximately 30 microM (basal). Apical ATP/UTP (100 microM) depolarized apical membrane potential by 17.6 +/- 0.8 mV (n = 7) and decreased R(A)/R(B) by a factor of approximately 3. The addition of adenosine to either side (100 microM) had no effect on any of these parameters. The ATP/UTP responses were partially inhibited by DIDS and suramin and mediated by a transient increase in free intracellular Ca(2+) concentration (427 +/- 206 nM; 15-25 microM ATP, apical; n = 6). This Ca(2+) increase was blocked by cyclopiazonic acid, by BAPTA, or by xestospongin C. 31EG4 MEC monolayers also secreted or absorbed fluid in the resting state, and ATP or UTP increased fluid secretion by 5.6 +/- 3 microl x cm(-2) x h(-1) (n = 10). Pharmacology experiments indicate that 31EG4 epithelia contain P2Y(2) purinoceptors on the apical and basolateral membranes, which upon activation stimulate apical Ca(2+)-dependent Cl channels and cause fluid secretion across the monolayer. This suggests that extracellular nucleotides could play a fundamental role in mammary gland paracrine signaling and the regulation of milk composition in vivo.

Large exchange bias in interdiffused NiFe/Mn bilayers

The effect of the annealing temperature a well as the antiferromagnetic (AF) and ferromagnetic (F) thickness on exchange coupling in Ni81Fe19/Mn single bilayers was systematically studied. We then show that a large exchange coupling is observed when the bilayers are annealed at 300 °C: it corresponds to an exchange field of about 290 Oe. This large exchange field is induced with a rather thick F layer of 46 nm. Both the exchange field Hex and coercive field Hc increase with Mn thickness reaching saturation around 100 nm of Mn. The exchange coupling is associated with interfacial diffusion at the NiFe/Mn interface. This result is confirmed by a large change in magnetization and resistivity before and after annealing. We show that the existence of the exchange field is associated with the clear evidence of a new FeMnNi phase in the x-ray spectrum.

Magnetic entropy change and magnetoresistance in the LaFe11.375Al1.625 compound

Large magnetic entropy change |ΔS| with a nearly temperature-independent magnitude over a wide temperature range (about 70 K span from ∼140 K to 210 K) was observed in an Fe-based NaZn13-type compound LaFe11.375Al1.625. Such a behavior of magnetic entropy change is ascribed to two closely spaced magnetic transitions. One at 181 K (TN) with second-order nature is from the paramagnetic to antiferromagnetic state; another at 140 K (TO) with first-order nature, temperature hysteresis ∼5 K, is from antiferromagnetic to ferromagnetic state. At the antiferromagnetic to ferromagnetic transition a large change of resistance was found, which can be induced as a function of temperature as well as field. The magnetoresistence under a field of 1 T reaches 3.4%.

Solid oxide fuel cells that enable the detection of CO in reformed gases

Solid oxide fuel cells (SOFCs) using Pd metal as the anode were fabricated for detection of CO in a flowing mixture of 0–4000 ppm CO, 50% H 2, 10% CO 2 and 6% H 2O vapor between 300 and 400 °C. When 20 mol% Sm 3+-doped CeO 2 (SDC) was used as the electrolyte, the Pd anode was subjected to a large and reversible change in the anodic-reaction resistance with the CO concentration. This behavior brought about an almost linear relationship between the electromotive force (EMF) generated from the cell or the short-circuit current through the cell and the logarithm of the CO concentration. In both signals, the minimum detectable CO concentration was 50 ppm, and the 90% response and 90% recovery times were about 60 s. However, the EMF of the cell at a CO concentration of 0 ppm significantly deviated from the theoretical value, which made it difficult to obtain reproducible data. In addition, the current signal of a few μA at a CO concentration of 4000 ppm was not large enough to monitor the CO concentration exactly. The improvement of these problems could be achieved by using 25 mol% Y 3+-doped BaCeO 3 (BCY25) with higher ionic conduction as the electrolyte: the EMF of the cell at a CO concentration of 0 ppm was near the theoretical value; the current signal reached 66 μA at a CO concentration of 4000 ppm.

High room temperature sensitivity of magnetoresistance in NiFe/CuAgAu/Co/CuAgAu multilayers

The magnetoresistive properties of sputtered [NiFe/Cu 0.85Ag 0.1Au 0.05/Co/Cu 0.85Ag 0.1Au 0.05] N multilayers are reported. It is shown that these structures exhibit large resistance changes within small magnetic field ranges resulting in sensitivities of up to 6.8%/Oe at room temperature. The observed magnetoresistance effect is anisotropic. The largest resistance changes have been observed for magnetic fields applied parallelly to the easy axis of permalloy layers.

Two-stage transformation of aluminum-containing NiTi

Measurements of electrical resistivity, ultrasonic velocity and attenuation for equiatomic NiTi and Ni 50Ti 49Al 1 were performed in order to characterize the thermoelastic martensitic transformation during cooling. The NiTi shows a one-stage transformation, essentially, because a premartensitic phenomenon is negligibly faint. The ultrasonic anomalies in NiTi appear near the temperature at a faint resistivity-peak, which correspond to lattice softening at the start temperature of martensitic transformation from the high-temperature phase to the low-temperature phase. The resistivity of Ni 50Ti 49Al 1 has a negative temperature coefficient over the wide temperature range from room temperature to154 K, and indicates a large peak. Such an anomaly in resistivity corresponds to an enhanced premartensitic phenomenon, where ultrasonic anomalies caused by a two-stage transformation are observed which accompany a large change in electrical resistivity. However, a resistivity peak in the aluminum-containing NiTi is formed at lower temperature than those at ultrasonic anomalies by over 40 K, and the temperature at the resistivity peak is not one characterizing the transformation behavior. It proved helpful to measure the ultrasonic properties in comparison with the electrical resistivity in order to characterize successive transformations in the temperature range of a premartensitic phenomenon of NiTi enhanced by addition of aluminum.