Electro-mechanical heat switch for cryogenic applications

DOEpatents

van den Berg, Marcel L.; Batteux, Jan D.; Labov, Simon E.

2003-01-01

A heat switch includes two symmetric jaws. Each jaw is comprised of a link connected at a translatable joint to a flexible arm. Each arm rotates about a fixed pivot, and has an articulated end including a thermal contact pad connected to a heat sink. The links are joined together at a translatable main joint. To close the heat switch, a closing solenoid is actuated and forces the main joint to an over-center position. This movement rotates the arms about their pivots, respectively, forces each of them into a stressed configuration, and forces the thermal contact pads towards each other and into compressive contact with a cold finger. The closing solenoid is then deactivated. The heat switch remains closed due to a restoring force generated by the stressed configuration of each arm, until actuation of an opening solenoid returns the main joint to its starting open-switch position.

Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers

PubMed Central

Stamopoulos, D.; Aristomenopoulou, E.

2015-01-01

Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent ‘on’ and ‘off’, thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis. PMID:26306543

Coupled qubits as a quantum heat switch

NASA Astrophysics Data System (ADS)

Karimi, B.; Pekola, J. P.; Campisi, M.; Fazio, R.

2017-12-01

We present a quantum heat switch based on coupled superconducting qubits, connected to two LC resonators that are terminated by resistors providing two heat baths. To describe the system, we use a standard second order master equation with respect to coupling to the baths. We find that this system can act as an efficient heat switch controlled by the applied magnetic flux. The flux influences the energy level separations of the system, and under some conditions, the finite coupling of the qubits enhances the transmitted power between the two baths, by an order of magnitude under realistic conditions. At the same time, the bandwidth at maximum power of the switch formed of the coupled qubits is narrowed.

Anisotropic magnetoresistance and tunneling magnetoresistance of conducting filaments in NiO with different resistance states

NASA Astrophysics Data System (ADS)

Zhao, Diyang; Qiao, Shuang; Luo, Yuxiang; Chen, Aitian; Zhang, Pengfei; Zheng, Ping; Sun, Zhong; Guo, Minghua; Chiang, F.-K.; Wu, Jian; Luo, Jianlin; Li, Jianqi; Wang, Yayu; Zhao, Yonggang; Tsinghua University Team; Chinese Academy of Sciences Collaboration

Resistive switching (RS) effect in conductor/insulator/conductor thin-film stacks has attracted much attention due to its interesting physics and potentials for applications. NiO is one of the most representative systems and its RS effect has been generally explained by the formation and rupture of Ni related conducting filaments, which are very unique since they are formed by electric forming process. We study the MR behaviors in NiO RS films with different resistance states. Rich and interesting MR behaviors were observed, including the normal and anomalous anisotropic magnetoresistance (AMR) and tunneling magnetoresistance (TMR), etc., which provide new insights into the nature of the filaments and their evolution in the resistive switching process. First-principles calculation reveals the essential role of oxygen migration into the filaments during the RESET process and can account for the experimental results. Our work provides a new avenue for the exploration of the conducting filaments in RS materials, and is significant for understanding the RS mechanism as well as multifunctional device design.

Integrated Heat Switch/Oxide Sorption Compressor

NASA Technical Reports Server (NTRS)

Bard, Steven

1989-01-01

Thermally-driven, nonmechanical compressor uses container filled with compressed praseodymium cerium oxide powder (PrCeOx) to provide high-pressure flow of oxygen gas for driving closed-cycle Joule-Thomson-expansion refrigeration unit. Integrated heat switch/oxide sorption compressor has no moving parts except check valves, which control flow of oxygen gas between compressor and closed-cycle Joule-Thomson refrigeration system. Oxygen expelled from sorbent at high pressure by evacuating heat-switch gap and turning on heater.

Heat Switches Providing Low-Activation Power and Quick-Switching Time for Use in Adiabatic Demagnetization Refrigerators

NASA Technical Reports Server (NTRS)

Kimball, Mark O.; Shirron, Peter J.

2011-01-01

An adiabatic demagnetization refrigerator (ADR) is a solid-state cooler capable of achieving sub-Kelvin temperatures. It neither requires moving parts nor a density gradient in a working fluid making it ideal for use in space-based instruments. The flow of energy through the cooler is controlled by heat switches that allow heat transfer when on and isolate portions of the cooler when off. One type of switch uses helium gas as the switching medium. In the off state the gas is adsorbed in a getter thus breaking the thermal path through the switch. To activate the switch, the getter is heated to release helium into the switch body allowing it to complete the thermal path. A getter that has a small heat capacity and low thermal conductance to the body of the switch requires low-activation power. The cooler benefits from this in two ways: shorter recycle times and higher efficiency. We describe such a design here.

Heat Switches Providing Low-Activation Power and Quick-Switching Time for Use in Cryogenic Multi-Stage Refrigerators

NASA Technical Reports Server (NTRS)

Kimball, Mark O.; Shirron, Peter J.

2011-01-01

An adiabatic demagnetization refrigerator (ADR) is a solid-state cooler capable of achieving sub-Kelvin temperatures. It neither requires moving parts nor a density gradient in a working fluid making it ideal for use in space-based instruments. The flow of energy through the cooler is controlled by heat switches that allow heat transfer when on and isolate portions of the cooler when off. One type of switch uses helium gas as the switching medium. In the off state the gas is adsorbed in a getter thus breaking the thermal path through the switch. To activate the switch, the getter is heated to release helium into the switch body allowing it to complete the thermal path. A getter that has a small heat capacity and low thermal conductance to the body of the switch requires low-activation power. The cooler benefits from this in two ways: shorter recycle times and higher efficiency. We describe such a design here.

A lightweight thermal heat switch for redundant cryocooling on satellites

NASA Astrophysics Data System (ADS)

Dietrich, M.; Euler, A.; Thummes, G.

2017-04-01

A previously designed cryogenic thermal heat switch for space applications has been optimized for low mass, high structural stability, and reliability. The heat switch makes use of the large linear thermal expansion coefficient (CTE) of the thermoplastic UHMW-PE for actuation. A structure model, which includes the temperature dependent properties of the actuator, is derived to be able to predict the contact pressure between the switch parts. This pressure was used in a thermal model in order to predict the switch performance under different heat loads and operating temperatures. The two models were used to optimize the mass and stability of the switch. Its reliability was proven by cyclic actuation of the switch and by shaker tests.

Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi

2014-05-28

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

Giant magnetoresistance in perpendicularly magnetized synthetic antiferromagnetic coupling with Ir spacer

NASA Astrophysics Data System (ADS)

Fukushima, A.; Taniguchi, T.; Sugihara, A.; Yakushiji, K.; Kubota, H.; Yuasa, S.

2018-05-01

Perpendicularly magnetized magnetic tunnel junction (p-MTJ) is a key element for developing high-density spin-transfer torque switching magnetoresistive random access memory. Recently, a large exchange coupling (IEC) in the synthetic antiferromagnetic reference layer with Ir interlayer was observed in p-MTJs. The evaluation of the IEC is, however, difficult due to the electrostatic breakdown of MTJs. This study demonstrates the evaluation of the IEC with Ir interlayer in giant magnetoresistive (GMR) nanopillar. We fabricated three kinds of perpendicularly magnetized GMR elements; bottom-free structures with Cu or Ir spacer, and top-free structure with Ir spacer. The magnetoresistance (RH) loops of all samples show sharp changes of the magnetoresistance at the magnetic fields over ±10 kOe, indicating the existence of the large IECs. In particular, a sharp change of the magnetoresistance at the field over ±20 kOe was found for the element with Cu of 2 nm thickness.

Large magnetoresistance of nickel-silicide nanowires: non-equilibrium heating of magnetically-coupled dangling bonds.

PubMed

Kim, T; Chamberlin, R V; Bird, J P

2013-03-13

We demonstrate large (>100%) time-dependent magnetoresistance in nickel-silicide nanowires and develop a thermodynamic model for this behavior. The model describes nonequilibrium heating of localized spins in an increasing magnetic field. We find a strong interaction between spins but no long-range magnetic order. The spins likely come from unpaired dangling bonds in the interfacial layers of the nanowires. The model indicates that although these bonds couple weakly to a thermal bath, they dominate the nanowire resistance.

Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures

NASA Astrophysics Data System (ADS)

Kally, James; Lv, Yang; Zhang, Delin; Lee, Joon Sue; Samarth, Nitin; Wang, Jian-Ping; Department of Electrical; Computer Engineering, University of Minnesota, Minneapolis Collaboration; Department of Physics, Pennsylvania State University Collaboration

The surface states of topological insulators offer a potentially very efficient way to generate spins and spin-orbit torques to magnetic moments in proximity. The switching by spin-orbit torque itself only requires two terminals so that a charge current can be applied. However, a third terminal with additional magnetic tunneling junction structure is needed to sense the magnetization state if such devices are used for memory and logic applications. The recent discovery of unidirectional spin Hall magnetoresistance in heavy metal/ferromagnetic and topological insulator/magnetically doped topological insulator systems offers an alternative way to sense magnetization while still keeping the number of terminals to minimal two. The unidirectional spin Hall magnetoresistance in topological insulator/strong ferromagnetic layer heterostructure system has yet not been reported. In this work, we report our experimental observations of such magnetoresistance. It is found to be present and comparable to the best result of the previous reported Ta/Co systems in terms of magnetoresistance per current density per total resistance.

Compact flat-panel gas-gap heat switch operating at 295 K

NASA Astrophysics Data System (ADS)

Krielaart, M. A. R.; Vermeer, C. H.; Vanapalli, S.

2015-11-01

Heat switches are devices that can change from a thermally conducting (on-) state to an insulating (off-) state whenever the need arises. They enable adaptive thermal management strategies in which cooling rates are altered either spatially or temporally, leading to a substantial reduction in the energy and mass budget of a large range of systems. State-of-the-art heat switches are only rarely employed in thermal system architectures, since they are rather bulky and have a limited thermal performance (expressed as the heat transfer ratio between the on- and off-state heat conductance). Using selective laser melting additive manufacturing technology, also known as 3D printing, we developed a compact flat-panel gas-gap heat switch that offers superior thermal performance, is simpler and more economic to produce and assemble, contains no moving parts, and is more reliable because it lacks welded joints. The manufactured rectangular panel heat switch has frontal device dimensions of 10 cm by 10 cm, thickness of 3.2 mm and weighs just 121 g. An off heat conductance of 0.2 W/K and on-off heat conductance ratio of 38 is observed at 295 K.

Enhanced Thermo-Optical Switching of Paraffin-Wax Composite Spots under Laser Heating

PubMed Central

Said, Asmaa; Salah, Abeer; Abdel Fattah, Gamal

2017-01-01

Thermo-optical switches are of particular significance in communications networks where increasingly high switching speeds are required. Phase change materials (PCMs), in particular those based on paraffin wax, provide wealth of exciting applications with unusual thermally-induced switching properties, only limited by paraffin’s rather low thermal conductivity. In this paper, the use of different carbon fillers as thermal conductivity enhancers for paraffin has been investigated, and a novel structure based on spot of paraffin wax as a thermo-optic switch is presented. Thermo-optical switching parameters are enhanced with the addition of graphite and graphene, due to the extreme thermal conductivity of the carbon fillers. Differential Scanning Calorimetry (DSC) and Scanning electron microscope (SEM) are performed on paraffin wax composites, and specific heat capacities are calculated based on DSC measurements. Thermo-optical switching based on transmission is measured as a function of the host concentration under conventional electric heating and laser heating of paraffin-carbon fillers composites. Further enhancements in thermo-optical switching parameters are studied under Nd:YAG laser heating. This novel structure can be used in future networks with huge bandwidth requirements and electric noise free remote aerial laser switching applications. PMID:28772884

Enhanced Thermo-Optical Switching of Paraffin-Wax Composite Spots under Laser Heating.

PubMed

Said, Asmaa; Salah, Abeer; Fattah, Gamal Abdel

2017-05-12

Thermo-optical switches are of particular significance in communications networks where increasingly high switching speeds are required. Phase change materials (PCMs), in particular those based on paraffin wax, provide wealth of exciting applications with unusual thermally-induced switching properties, only limited by paraffin's rather low thermal conductivity. In this paper, the use of different carbon fillers as thermal conductivity enhancers for paraffin has been investigated, and a novel structure based on spot of paraffin wax as a thermo-optic switch is presented. Thermo-optical switching parameters are enhanced with the addition of graphite and graphene, due to the extreme thermal conductivity of the carbon fillers. Differential Scanning Calorimetry (DSC) and Scanning electron microscope (SEM) are performed on paraffin wax composites, and specific heat capacities are calculated based on DSC measurements. Thermo-optical switching based on transmission is measured as a function of the host concentration under conventional electric heating and laser heating of paraffin-carbon fillers composites. Further enhancements in thermo-optical switching parameters are studied under Nd:YAG laser heating. This novel structure can be used in future networks with huge bandwidth requirements and electric noise free remote aerial laser switching applications.

Observation of a thermally enhanced magnetoresistance in NiFe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Y.; Feng, C., E-mail: fengchun@ustb.edu.cn, E-mail: ghyu@mater.ustb.edu.cn; Liu, D. X.

2016-04-15

A thermally enhanced magnetoresistance (ThMR) was designed and obtained by simultaneously applying charge and heat currents to a NiFe thin film. From the measurement we observed that the magnetoresistance value was as high as -22600% when the input charge current and applied temperature gradient was 0.966 μA and 2.5 °C/mm, respectively. This ThMR can be controllable by adjusting the relative values of the input charge and heat currents. On increasing the input charge current from 0.85 to 1.05 μA by fixing the temperature gradient at 2.5 °C/mm, the ThMR first increased from 9% to 183% and then decreased from -259%more » to -13%, at intervals of ∼0.96 μA. This can be explained by the spin-dependent transport phenomenon i.e., scattering induced sign difference between magnetoresistance and magnetothermopower in NiFe.« less

Note: Cryogenic heat switch with stepper motor actuator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melcher, B. S., E-mail: bsmelche@syr.edu; Timbie, P. T., E-mail: pttimbie@wisc.edu

2015-12-15

A mechanical cryogenic heat switch has been developed using a commercially available stepper motor and control electronics. The motor requires 4 leads, each carrying a maximum, pulsed current of 0.5 A. With slight modifications of the stepper motor, the switch functions reliably in vacuum at temperatures between 300 K and 4 K. The switch generates a clamping force of 262 N at room temperature. At 4 K it achieves an “on state” thermal conductance of 5.04 mW/K and no conductance in the “off state.” The switch is optimized for cycling an adiabatic demagnetization refrigerator.

Novel specific heat and magnetoresistance behavior of Tb0.5Ho0.5Mn2Si2

NASA Astrophysics Data System (ADS)

Pandey, Swati; Siruguri, V.; Rawat, R.

2018-04-01

In this report, we study temperature dependent heat capacity and electrical resistance of Tb1-xHoxMn2Si2 (x = 0.5). Two successive low temperature magnetic transitions T1 (˜15 K) and T2 (˜25 K) are observed from both measurements. Anomalous rise in heat capacity at low temperatures is ascribed to the nuclear Schottky effect. Sommerfeld coefficient (γ), Debye temperature (θD) and density of states at Fermi level N(EF) is calculated from the zero field specific heat data. We observe 4f contribution to heat capacity from T1 to 100K, which is attributed to crystal field effect. In the electrical transport study, application of the magnetic field shows a substantial change around the ordering temperature of rare earth moment resulting in large positive magnetoresistance of about 20% with field change of 6T.

Design and Test of Passively Operated Heat Switches for 0.2 to 15 K

NASA Technical Reports Server (NTRS)

DiPirro, M. J.; Shirron, P. J.; Canavan, E. R.; Francis, J. J.; Tuttle, J. G.

2003-01-01

Heat switches have many uses in cryogenics, from regulating heat flow between refrigeration stages to thermally isolating components once they have cooled to low temperature. Among the techniques one can use for thermal switching, the gas-gap technique has the advantages of wide operating temperature range, high switching ratio, and no moving parts. The traditional gas-gap switch uses copper conductors separated by a small gap and an external getter. The switch is activated by heating and cooling the getter by moving gas into and out of the gap, turning the switch on and off. We have designed, built and tested heat switches that use an internal getter to passively turn off at temperatures between 0.2 and 15 K. The getter is thermally anchored to one side of the switch, and when that side of the switch cools through a transition region, gas adsorbs onto the getter and the switch turns off. The challenges are to make the transition region very narrow and tailorable to a wide range of applications, and to achieve high gas conductance when the switch is on. We have made switches using He-3, He-4, hydrogen, and neon gas, and have used charcoal and various metal substrates as getters. Switching ratios range from 1000 to over 10,000. Design and performance of these switches will be discussed in detail.

Tunnelling anisotropic magnetoresistance at La{sub 0.67}Sr{sub 0.33}MnO{sub 3}-graphene interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, L. C., E-mail: lee.phillips@cantab.net; Yan, W.; Kar-Narayan, S.

2016-03-14

Using ferromagnetic La{sub 0.67}Sr{sub 0.33}MnO{sub 3} electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ∼32–35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La{sub 0.67}Sr{sub 0.33}MnO{sub 3}-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

Quick-Response Thermal Actuator for Use as a Heat Switch

NASA Technical Reports Server (NTRS)

Cepeda-Rizo, Juan

2010-01-01

This work improves the performance of a heat switch, or a thermal actuator, by delivering heat to the actuator in a more efficient manner. The method uses a heat pipe as the plunger or plug instead of just using a solid piece of metal. The heat pipe could be one tailored for fast transient thermal response.

Passive Gas-Gap Heat Switches for Use in Low-Temperature Cryogenic Systems

NASA Technical Reports Server (NTRS)

Kimball, M. O.; Shirron, P. J.; Canavan, E. R.; Tuttle, J. G.; Jahromi, A. E.; Dipirro, M. J.; James, B. L.; Sampson, M. A.; Letmate, R. V.

2017-01-01

We present the current state of development in passive gas-gap heat switches. This type of switch does not require a separate heater to activate heat transfer but, instead, relies upon the warming of one end due to an intrinsic step in a thermodynamic cycle to raise a getter above a threshold temperature. Above this temperature sequestered gas is released to couple both sides of the switch. This enhances the thermodynamic efficiency of the system and reduces the complexity of the control system. Various gas mixtures and getter configurations will be presented.

Coexistence of non-volatile bi-polar resistive switching and tunneling magnetoresistance in spatially confined La0.3Pr0.4Ca0.3MnO3 films

NASA Astrophysics Data System (ADS)

Jeon, J.; Jung, J.; Chow, K. H.

2017-12-01

We report the coexistence of non-volatile bi-polar resistive switching (RS) and tunneling magnetoresistance (TMR) in spatially confined La0.3Pr0.4Ca0.3MnO3 films grown on LaAlO3 substrates. At certain temperatures, the arrangement of electronic phase domains in these narrow systems mimics those found in heterostructured metal-insulator-metal devices. The relative spin orientations between adjacent ferromagnetic metallic phase domains enable the TMR effect, while the creation/annihilation of conduction filaments between the metallic phase domains produces the RS effect.

Assessment of Zr-Fe-V getter alloy for gas-gap heat switches

NASA Technical Reports Server (NTRS)

Prina, M.; Kulleck, J. G.; Bowman, R. C., Jr.

2000-01-01

A commercial Zr-V-Fe alloy (i.e., SAES Getters trade name alloy St-172) has been assessed as reversible hydrogen storage material for use in actuators of gas gap heat switches. Two prototype actuators containing the SAES St-172 material were built and operated for several thousand cycles to evaluate performance of the metal hydride system under conditions simulating heat switch operation.

Improved heat switch for gas sorption compressor

NASA Technical Reports Server (NTRS)

Chan, C. K.

1985-01-01

Thermal conductivities of the charcoal bed and the copper matrix for the gas adsorption compressor were measured by the concentric-cylinder method. The presence of the copper matrix in the charcoal bed enhanced the bed conductance by at least an order of magnitude. Thermal capacities of the adsorbent cell and the heat leaks to two compressor designs were measured by the transient method. The new gas adsorption compressor had a heat switch that could transfer eight times more heat than the previous one. The cycle time for the new prototype compressor is also improved by a factor of eight to within the minute range.

High density submicron magnetoresistive random access memory (invited)

NASA Astrophysics Data System (ADS)

Tehrani, S.; Chen, E.; Durlam, M.; DeHerrera, M.; Slaughter, J. M.; Shi, J.; Kerszykowski, G.

1999-04-01

Various giant magnetoresistance material structures were patterned and studied for their potential as memory elements. The preferred memory element, based on pseudo-spin valve structures, was designed with two magnetic stacks (NiFeCo/CoFe) of different thickness with Cu as an interlayer. The difference in thickness results in dissimilar switching fields due to the shape anisotropy at deep submicron dimensions. It was found that a lower switching current can be achieved when the bits have a word line that wraps around the bit 1.5 times. Submicron memory elements integrated with complementary metal-oxide-semiconductor (CMOS) transistors maintained their characteristics and no degradation to the CMOS devices was observed. Selectivity between memory elements in high-density arrays was demonstrated.

Passive Gas-Gap Heat Switches for Use in Adiabatic Demagnetization Refrigerators

NASA Technical Reports Server (NTRS)

Shirron, P. J.; Canavan, E. R.; DiPirro, M. J.; Jackson, M.; Panek, J.; Tuttle, J. G.; Krebs, Carolyn (Technical Monitor)

2001-01-01

We have designed, built, and tested a gas gap heat switch that works passively, without the need for a separate, thermally activated getter. This switch uses He-3 condensed as a thin film on alternating plates of copper. The switch is thermally conductive at temperatures above about 0.2 K, and is insulating if either end of the switch is below about 0.15 K. The "on" conductance (7 mW/K at 0.25K) is limited by the surface area and gap between the copper leaves, the saturated vapor pressure of the He-3, and the Kapitza boundary resistance between the He-3 and the copper. The "off" conductance is determined by the helium containment shell which physically supports the two conductive ends. We have also designed and are building passive gas gap heat switches which will passively turn off near 1 K and 4 K. For these switches we rely on the rapidly changing vapor pressure of He-4 above neon or copper substrates, respectively, when the coverage is less than one monolayer. The different binding energies of the He-4 to the neon or copper give rise to the different temperatures where the switches transition between the on and off states.

Magnetization reversal and inverted magnetoresistance of exchange-biased spin valves with a gadolinium layer

NASA Astrophysics Data System (ADS)

Milyaev, M.; Naumova, L.; Chernyshova, T.; Proglyado, V.; Kamensky, I.; Krinitsina, T.; Ryabukhina, M.; Ustinov, V.

2017-03-01

FeMn-based spin valves with a gadolinium layer have been fabricated by magnetron sputtering. The magnetoresistive properties of the spin valves have been investigated at temperatures of 80-293 K. Temperature-induced switching between low- and high-resistance magnetic states has been revealed. Realization of the low- or high-resistance states depends on which magnetic moment dominates in the exchange-coupled Gd/CoFe, of Gd or CoFe. It has been shown that the switching temperature depends on the thickness of the gadolinium layer.

Power Supply for Variable Frequency Induction Heating Using MERS Soft-Switching High Frequency Inverter

NASA Astrophysics Data System (ADS)

Isobe, Takanori; Kitahara, Tadayuki; Fukutani, Kazuhiko; Shimada, Ryuichi

Variable frequency induction heating has great potential for industrial heating applications due to the possibility of achieving heating distribution control; however, large-scale induction heating with variable frequency has not yet been introduced for practical use. This paper proposes a high frequency soft-switching inverter for induction heating that can achieve variable frequency operation. One challenge of variable frequency induction heating is increasing power electronics ratings. This paper indicates that its current source type dc-link configuration and soft-switching characteristics can make it possible to build a large-scale system with variable frequency capability. A 90-kVA 150-1000Hz variable frequency experimental power supply for steel strip induction heating was developed. Experiments confirmed the feasibility of variable frequency induction heating with proposed converter and the advantages of variable frequency operation.

Evaluation of Magnetoresistive RAM for Space Applications

NASA Technical Reports Server (NTRS)

Heidecker, Jason

2014-01-01

Magnetoresistive random-access memory (MRAM) is a non-volatile memory that exploits electronic spin, rather than charge, to store data. Instead of moving charge on and off a floating gate to alter the threshold voltage of a CMOS transistor (creating different bit states), MRAM uses magnetic fields to flip the polarization of a ferromagnetic material thus switching its resistance and bit state. These polarized states are immune to radiation-induced upset, thus making MRAM very attractive for space application. These magnetic memory elements also have infinite data retention and erase/program endurance. Presented here are results of reliability testing of two space-qualified MRAM products from Aeroflex and Honeywell.

Switching effects and spin-valley Andreev resonant peak shifting in silicene superconductor

NASA Astrophysics Data System (ADS)

Soodchomshom, Bumned; Niyomsoot, Kittipong; Pattrawutthiwong, Eakkarat

2018-03-01

The magnetoresistance and spin-valley transport properties in a silicene-based NM/FB/SC junction are investigated, where NM, FB and SC are normal, ferromagnetic and s-wave superconducting silicene, respectively. In the FB region, perpendicular electric and staggered exchange fields are applied. The quasiparticles may be described by Dirac Bogoliubov-de Gennes equation due to Cooper pairs formed by spin-valley massive fermions. The spin-valley conductances are calculated based on the modified Blonder-Tinkham-Klapwijk formalism. We find the spin-valley dependent Andreev resonant peaks in the junction shifted by applying exchange field. Perfect conductance switch generated by interplay of intrinsic spin orbit interaction and superconducting gap has been predicted. Spin and valley polarizations are almost linearly dependent on biased voltage near zero bias and then turn into perfect switch at biased voltage approaching the superconducting gap. The perfect switching of large magnetoresistance has been also predicted at biased energy near the superconducting gap. These switching effects may be due to the presence of spin-valley Andreev resonant peak near the superconducting gap. Our work reveals potential of silicene as applications of electronic switching devices and linear control of spin and valley polarizations.

Magnetization and Magnetoresistance in Iron Intercalated Transition Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Choe, Jesse

The understanding of magnetism in strongly correlated electronic systems is a vital area of research. Not only is it linked to other phenomena like high temperature superconductivity in the cuprates and iron pnictides, but magnetic materials have been used in electronics since before the computer. As it becomes harder to prop up Moore's law by increasing the density of transistors, mankind must look towards new methods to improve technology or risk stagnation. Research into alternative materials for technology, such as transition metal dichalcogenides, is a promising direction of research to maintain the rate of technological improvement. Our work focuses on the effect of iron intercalation in TiS2. Single crystals of FexTiS 2 (0 ≤ x ≤ 1) were grown using vapor transport. Anisotropic susceptibility and magnetization measurements of the samples were measured, showing ferromagnetism and sharp switching behavior in the magnetization. Finally electrical transport measurements were taken, both with and without field. Measurements of magnetoresistance for x = 0.2 and 0.3 show large magnetoresistance (up to ˜ 60%) and an atypical 'bowtie' shape.

Fast Magnetoresistive Random-Access Memory

NASA Technical Reports Server (NTRS)

Wu, Jiin-Chuan; Stadler, Henry L.; Katti, Romney R.

1991-01-01

Magnetoresistive binary digital memories of proposed new type expected to feature high speed, nonvolatility, ability to withstand ionizing radiation, high density, and low power. In memory cell, magnetoresistive effect exploited more efficiently by use of ferromagnetic material to store datum and adjacent magnetoresistive material to sense datum for readout. Because relative change in sensed resistance between "zero" and "one" states greater, shorter sampling and readout access times achievable.

Superconducting spin switch with infinite magnetoresistance induced by an internal exchange field.

PubMed

Li, Bin; Roschewsky, Niklas; Assaf, Badih A; Eich, Marius; Epstein-Martin, Marguerite; Heiman, Don; Münzenberg, Markus; Moodera, Jagadeesh S

2013-03-01

A theoretical prediction by de Gennes suggests that the resistance in a FI/S/FI (where FI is a ferromagnetic insulator, and S is a superconductor) structure will depend on the magnetization direction of the two FI layers. We report a magnetotransport measurement in a EuS/Al/EuS structure, showing that an infinite magnetoresistance can be produced by tuning the internal exchange field at the FI/S interface. This proximity effect at the interface can be suppressed by an Al(2)O(3) barrier as thin as 0.3 nm, showing the extreme confinement of the interaction to the interface giving rise to the demonstrated phenomena.

Memristive switching of MgO based magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Krzysteczko, Patryk; Reiss, Günter; Thomas, Andy

2009-09-01

Here we demonstrate that both, tunnel magnetoresistance (TMR) and resistive switching (RS), can be observed simultaneously in nanoscale magnetic tunnel junctions. The devices show bipolar RS of 6% and TMR ratios of about 100%. For each magnetic state, multiple resistive states are created depending on the bias history, which provides a method for multibit data storage and logic. The electronic transport measurements are discussed in the framework of a memristive system. Differently prepared MgO barriers are compared to gain insight into the switching mechanism.

Mutual influence between current-induced giant magnetoresistance and radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs 2DES

DOE PAGES

Samaraweera, R. L.; Liu, H. -C.; Wang, Z.; ...

2017-07-11

Radiation-induced magnetoresistance oscillations are examined in the GaAs/AlGaAs 2D system in the regime where an observed concurrent giant magnetoresistance is systematically varied with a supplementary dc-current, I dc . The I dc tuned giant magnetoresistance is subsequently separated from the photo-excited oscillatory resistance using a multi-conduction model in order to examine the interplay between the two effects. The results show that the invoked multiconduction model describes the observed giant magnetoresistance effect even in the presence of radiation-induced magnetoresistance oscillations, the magnetoresistance oscillations do not modify the giant magnetoresistance, and the magnetoresistance oscillatory extrema, i.e., maxima and minima, disappear rather asymmetricallymore » with increasing I dc. Lastly, the results suggest the interpretation that the I dc serves to suppress scattering between states near the Fermi level in a strong magnetic field limit.« less

Magnetoresistance in relativistic hydrodynamics without anomalies

DOE PAGES

Baumgartner, Andrew; Karch, Andreas; Lucas, Andrew

2017-06-12

We present expressions for the magnetoconductivity and the magnetoresistance of a strongly interacting metal in 3 + 1 dimensions, derivable from relativistic hydrodynamics. Such an approach is suitable for ultraclean metals with emergent Lorentz invariance. When this relativistic fluid contains chiral anomalies, it is known to exhibit longitudinal negative magnetoresistance. We show that similar effects can arise in non-anomalous relativistic fluids due to the distinctive gradient expansion. In contrast with a Galilean-invariant fluid, the resistivity tensor of a dirty relativistic fluid exhibits similar angular dependence to negative magnetoresistance, even when the constitutive relations and momentum relaxation rate are isotropic. Wemore » further account for the effect of magnetic field-dependent corrections to the gradient expansion and the effects of long-wavelength impurities on magnetoresistance. We note that the holographic D3/D7 system exhibits negative magnetoresistance.« less

Magnetoresistance in relativistic hydrodynamics without anomalies

NASA Astrophysics Data System (ADS)

Baumgartner, Andrew; Karch, Andreas; Lucas, Andrew

2017-06-01

We present expressions for the magnetoconductivity and the magnetoresistance of a strongly interacting metal in 3 + 1 dimensions, derivable from relativistic hydrodynamics. Such an approach is suitable for ultraclean metals with emergent Lorentz invariance. When this relativistic fluid contains chiral anomalies, it is known to exhibit longitudinal negative magnetoresistance. We show that similar effects can arise in non-anomalous relativistic fluids due to the distinctive gradient expansion. In contrast with a Galilean-invariant fluid, the resistivity tensor of a dirty relativistic fluid exhibits similar angular dependence to negative magnetoresistance, even when the constitutive relations and momentum relaxation rate are isotropic. We further account for the effect of magnetic field-dependent corrections to the gradient expansion and the effects of long-wavelength impurities on magnetoresistance. We note that the holographic D3/D7 system exhibits negative magnetoresistance.

Enhancement of switching stability of tunneling magnetoresistance system with artificial ferrimagnet

NASA Astrophysics Data System (ADS)

You, Chun-Yeol; Bader, Sam. D.; Scheinfein, M. R.

2002-03-01

In the study of spin dependent magnetic tunneling junctions, the switching stability of the magnetically hard layer is a crucial issue in magnetic random access memory applications[1]. After repeated cycling of the soft layer, the magnetization of the hard layer is demagnetized by the stray field from the domain wall created during the switching[2]. The magnitude of the stray field from the soft layer is large enough to switch a domain in the hard layer. Therefore, reducing this stray field is necessary to increase the switching stability. In this study, we explore an artificial ferrimagnet to replace the usual soft layer in order to reduce stray field. The ferrimagnet consists of an antiferromagnetically coupled trilayer that has two ferromagnetic layers of unequal thickness and opposite magnetization orientation. Since the sign of stray field of the two ferromagnetic layers is opposed, the total stray field is greatly reduced. [Supported by the US DOE, BES-MS, under Contract W-31-109-ENG-38.] [1] S. Gider et al. Science 281, 797 (1998). [2] L. Thomas et al. Phys. Rev. Lett. 84, 1816 (2000).

Viscous magnetoresistance of correlated electron liquids

NASA Astrophysics Data System (ADS)

Levchenko, Alex; Xie, Hong-Yi; Andreev, A. V.

2017-03-01

We develop a theory of magnetoresistance of two-dimensional electron systems in a smooth disorder potential in the hydrodynamic regime. Our theory applies to two-dimensional semiconductor structures with strongly correlated carriers when the mean free path due to electron-electron collisions is sufficiently short. The dominant contribution to magnetoresistance arises from the modification of the flow pattern by the Lorentz force, rather than the magnetic field dependence of the kinetic coefficients of the electron liquid. The resulting magnetoresistance is positive and quadratic at weak fields. Although the resistivity is governed by both the viscosity and thermal conductivity of the electron fluid, the magnetoresistance is controlled by the viscosity only. This enables the extraction of viscosity of the electron liquid from magnetotransport measurements.

Tunneling anisotropic magnetoresistance driven by magnetic phase transition.

PubMed

Chen, X Z; Feng, J F; Wang, Z C; Zhang, J; Zhong, X Y; Song, C; Jin, L; Zhang, B; Li, F; Jiang, M; Tan, Y Z; Zhou, X J; Shi, G Y; Zhou, X F; Han, X D; Mao, S C; Chen, Y H; Han, X F; Pan, F

2017-09-06

The independent control of two magnetic electrodes and spin-coherent transport in magnetic tunnel junctions are strictly required for tunneling magnetoresistance, while junctions with only one ferromagnetic electrode exhibit tunneling anisotropic magnetoresistance dependent on the anisotropic density of states with no room temperature performance so far. Here, we report an alternative approach to obtaining tunneling anisotropic magnetoresistance in α'-FeRh-based junctions driven by the magnetic phase transition of α'-FeRh and resultantly large variation of the density of states in the vicinity of MgO tunneling barrier, referred to as phase transition tunneling anisotropic magnetoresistance. The junctions with only one α'-FeRh magnetic electrode show a magnetoresistance ratio up to 20% at room temperature. Both the polarity and magnitude of the phase transition tunneling anisotropic magnetoresistance can be modulated by interfacial engineering at the α'-FeRh/MgO interface. Besides the fundamental significance, our finding might add a different dimension to magnetic random access memory and antiferromagnet spintronics.Tunneling anisotropic magnetoresistance is promising for next generation memory devices but limited by the low efficiency and functioning temperature. Here the authors achieved 20% tunneling anisotropic magnetoresistance at room temperature in magnetic tunnel junctions with one α'-FeRh magnetic electrode.

Large magnetoresistance in non-magnetic silver chalcogenides and new class of magnetoresistive compounds

DOEpatents

Saboungi, Marie-Louis; Price, David C. L.; Rosenbaum, Thomas F.; Xu, Rong; Husmann, Anke

2001-01-01

The heavily-doped silver chalcogenides, Ag.sub.2+.delta. Se and Ag.sub.2+.delta. Te, show magnetoresistance effects on a scale comparable to the "colossal" magnetoresistance (CMR) compounds. Hall coefficient, magnetoconductivity, and hydrostatic pressure experiments establish that elements of narrow-gap semiconductor physics apply, but both the size of the effects at room temperature and the linear field dependence down to fields of a few Oersteds are surprising new features.

Magnetoresistance enhancement in Gd- Y bilayers

NASA Astrophysics Data System (ADS)

Freitas, P. P.; From, M.; Melo, L. V.; Plaskett, T. S.

1991-02-01

Gd-Y-Gd bilayers were prepared that show a magnetoresistance enhancement when the non-magnetic Y layer separations is 11 or 32 Å. This oscillatory behavior of the magnetoresistance versus Y thickness is tentatively related to oscillations in the interlayer coupling.

Operation of an ADR using helium exchange gas as a substitute for a failed heat switch

NASA Astrophysics Data System (ADS)

Shirron, P.; DiPirro, M.; Kimball, M.; Sneiderman, G.; Porter, F. S.; Kilbourne, C.; Kelley, R.; Fujimoto, R.; Yoshida, S.; Takei, Y.; Mitsuda, K.

2014-11-01

The Soft X-ray Spectrometer (SXS) is one of four instruments on the Japanese Astro-H mission, which is currently planned for launch in late 2015. The SXS will perform imaging spectroscopy in the soft X-ray band (0.3-12 keV) using a 6 × 6 pixel array of microcalorimeters cooled to 50 mK. The detectors are cooled by a 3-stage adiabatic demagnetization refrigerator (ADR) that rejects heat to either a superfluid helium tank (at 1.2 K) or to a 4.5 K Joule-Thomson (JT) cryocooler. Four gas-gap heat switches are used in the assembly to manage heat flow between the ADR stages and the heat sinks. The engineering model (EM) ADR was assembled and performance tested at NASA/GSFC in November 2011, and subsequently installed in the EM dewar at Sumitomo Heavy Industries, Japan. During the first cooldown in July 2012, a failure of the heat switch that linked the two colder stages of the ADR to the helium tank was observed. Operation of the ADR requires some mechanism for thermally linking the salt pills to the heat sink, and then thermally isolating them. With the failed heat switch unable to perform this function, an alternate plan was devised which used carefully controlled amounts of exchange gas in the dewar's guard vacuum to facilitate heat exchange. The process was successfully demonstrated in November 2012, allowing the ADR to cool the detectors to 50 mK for hold times in excess of 10 h. This paper describes the exchange-gas-assisted recycling process, and the strategies used to avoid helium contamination of the detectors at low temperature.

Operation of an ADR Using Helium Exchange Gas as a Substitute for a Failed Heat Switch

NASA Technical Reports Server (NTRS)

Shirron, P.; DiPirro, M.; Kimball, M.; Sneiderman, G.; Porter, F. S.; Kilbourne, C.; Kelley, R.; Fujimoto, R.; Yoshida, S.; Takei, Y.;

Fabrication and local laser heating of freestanding Ni{sub 80}Fe{sub 20} bridges with Pt contacts displaying anisotropic magnetoresistance and anomalous Nernst effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brandl, F.; Grundler, D., E-mail: grundler@ph.tum.de

2014-04-28

In spin caloritronics, ferromagnetic samples subject to relatively large in-plane temperature gradients ∇T have turned out to be extremely interesting. We report on a preparation technique that allows us to create freely suspended permalloy/Pt hybrid structures where a scanning laser induces ∇T on the order of a few K/μm. We observe both the anisotropic magnetoresistance at room temperature and the magnetic field dependent anomalous Nernst effect under laser heating. The technique is promising for the realization of device concepts considered in spin caloritronics based on suspended ferromagnetic nanostructures with electrical contacts.

Large magnetoresistance by Pauli blockade in hydrogenated graphene

NASA Astrophysics Data System (ADS)

Guillemette, J.; Hemsworth, N.; Vlasov, A.; Kirman, J.; Mahvash, F.; Lévesque, P. L.; Siaj, M.; Martel, R.; Gervais, G.; Studenikin, S.; Sachrajda, A.; Szkopek, T.

2018-04-01

We report the observation of a giant positive magnetoresistance in millimeter-scale hydrogenated graphene with the magnetic field oriented in the plane of the graphene sheet. A positive magnetoresistance in excess of 200% at a temperature of 300 mK was observed in this configuration, reverting to negative magnetoresistance with the magnetic field oriented normal to the graphene plane. We attribute the observed positive in-plane magnetoresistance to a Pauli blockade of hopping conduction induced by spin polarization. Our Rapid Communication shows that spin polarization in concert with electron-electron interaction can play a dominant role in magnetotransport within an atomic monolayer.

Giant magnetoresistance and anomalous transport in phosphorene-based multilayers with noncollinear magnetization

NASA Astrophysics Data System (ADS)

Zare, Moslem; Majidi, Leyla; Asgari, Reza

2017-03-01

We theoretically investigate the unusual features of the magnetotransport in a monolayer phosphorene ferromagnetic/normal/ferromagnetic (F/N/F) hybrid structure. We find that the charge conductance can feature a minimum at parallel (P) configuration and a maximum near the antiparallel (AP) configuration of magnetization in the F/N/F structure with n -doped F and p -doped N regions and also a finite conductance in the AP configuration with the N region of n -type doping. In particular, the proposed structure exhibits giant magnetoresistance, which can be tuned to unity. This perfect switching is found to show strong robustness with respect to increasing the contact length and tuning the chemical potential of the N region with a gate voltage. We also explore the oscillatory behavior of the charge conductance or magnetoresistance in terms of the size of the N region. We further demonstrate the penetration of the spin-transfer torque into the right F region and show that, unlike graphene structure, the spin-transfer torque is very sensitive to the chemical potential of the N region as well as the exchange field of the F region.

Design and Development of a Series Switch for High Voltage in RF Heating

NASA Astrophysics Data System (ADS)

Patel, Himanshu K.; Shah, Deep; Thacker, Mauli; Shah, Atman

2013-02-01

Plasma is the fourth state of matter. To sustain plasma in its ionic form very high temperature is essential. RF heating systems are used to provide the required temperature. Arching phenomenon in these systems can cause enormous damage to the RF tube. Heavy current flows across the anode-cathode junction, which need to be suppressed in minimal time for its protection. Fast-switching circuit breakers are used to cut-off the load from the supply in cases of arching. The crowbar interrupts the connection between the high voltage power supply (HVPS) and the RF tube for a temporary period between which the series switch has to open. The crowbar shunts the current across the load but in the process leads to short circuiting the HVPS. Thus, to protect the load as well as the HVPS a series switch is necessary. This paper presents the design and development of high voltage Series Switch for the high power switching applications. Fiber optic based Optimum triggering scheme is designed and tested to restrict the time delay well within the stipulated limits. The design is well supported with the experimental results for the whole set-up along with the series switch at various voltage level before its approval for operation at 5.2 kV.

Systematic study of doping dependence on linear magnetoresistance in p-PbTe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneider, J. M.; Chitta, V. A.; Oliveira, N. F.

2014-10-20

We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF{sub 2} exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30 T. The linear magnetoresistance slope ΔR/ΔB is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linearmore » magnetoresistance response has a maximum for small BaF{sub 2} doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.« less

Structure-dependent magnetoresistance and spin-transfer torque in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions

NASA Astrophysics Data System (ADS)

Jia, Xingtao; Tang, Huimin; Wang, Shizhuo; Qin, Minghui

2017-02-01

We predict large magnetoresistance (MR) and spin transfer torque (STT) in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions based on first-principles scattering theory. MR as large as ˜100 % is found in one junction. Magnetic dynamic simulations show that STT acting on the antiferromagnetic order parameter dominates the spin dynamics, and an electronic bias of order 10-1mV and current density of order 105Acm-2 can switches a junction of three-layer MgO, they are about one order smaller than that in Fe |MgO |Fe junction with the same barrier thickness, respectively. The multiple scattering in the antiferromagnetic region is considered to be responsible for the enhanced spin torque and smaller switching current density.

Support of NASA ADR/ Cross-Enterprise NRA Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling from 10K to 50mK, Development of a Heat Switch

NASA Technical Reports Server (NTRS)

Richards, Paul L.

2005-01-01

Mechanical heat switches are used in conjunction with sorption refrigerators, adiabatic demagnetization refrigerators and for other cryogenic tasks including the pre-cooling cryogenic systems. They use a mechanical actuator which closes Au plated Cu jaws on an Au plated Cu bar. The thermal conductance in the closed position is essentially independent of the area of the jaws and proportional to the force applied. It varies linearly with T. It is approximately 10mW/K for 200 N at 1.5K. In some applications, the heat switch can be driven from outside the cryostat by a rotating rod and a screw. Such heat switches are available commercially from several sources. In other applications, including systems for space, it is desirable to drive the switch using a cold linear motor, or solenoid. Superconducting windings are used at temperatures s 4.2K to minimize power dissipation, but are not appropriate for pre-cooling a system at higher temperatures. This project was intended to improve the design of solenoid activated mechanical heat switches and to provide such switches as required to support the development of Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling from 10 K to 50 mK at GSFC. By the time funding began in 5/1/01, the immediate need for mechanical heat switches at GSFC had subsided but, at the same time, the opportunity had arisen to improve the design of mechanical heat switching by incorporating a "latching solenoid". In this device, the solenoid current is required only for changing the state of the switch and not during the whole time that the switch is closed.

Origin of nonsaturating linear magnetoresistivity

NASA Astrophysics Data System (ADS)

Kisslinger, Ferdinand; Ott, Christian; Weber, Heiko B.

2017-01-01

The observation of nonsaturating classical linear magnetoresistivity has been an enigmatic phenomenon in solid-state physics. We present a study of a two-dimensional ohmic conductor, including local Hall effect and a self-consistent consideration of the environment. An equivalent-circuit scheme delivers a simple and convincing argument why the magnetoresistivity is linear in strong magnetic field, provided that current and biasing electric field are misaligned by a nonlocal mechanism. A finite-element model of a two-dimensional conductor is suited to display the situations that create such deviating currents. Besides edge effects next to electrodes, charge carrier density fluctuations are efficiently generating this effect. However, mobility fluctuations that have frequently been related to linear magnetoresistivity are barely relevant. Despite its rare observation, linear magnetoresitivity is rather the rule than the exception in a regime of low charge carrier densities, misaligned current pathways and strong magnetic field.

Heating of metallic implants and instruments induced by gradient switching in a 1.5-Tesla whole-body unit.

PubMed

Graf, Hansjörg; Steidle, Günter; Schick, Fritz

2007-11-01

To examine gradient switching-induced heating of metallic parts. Copper and titanium frames and sheets ( approximately 50 x 50 mm(2), 1.5 mm thick, frame width = 3 mm) surrounded by air were positioned in the scanner perpendicular to the static field horizontally 20 cm off-center. During the execution of a sequence (three-dimensional [3D] true fast imaging with steady precession [True-FISP], TR = 6.4 msec) exploiting the gradient capabilities (maximum gradient = 40 mT/m, maximum slew rate = 200 T/m/second), heating was measured with an infrared camera. Radio frequency (RF) amplitude was set to zero volts. Heating of a copper frame with a narrowing to 1 mm over 20 mm at one side was examined in air and in addition surrounded by several liters of gelled saline using fiber-optic thermography. Further heating studies were performed using an artificial hip made of titanium, and an aluminum replica of the hip prosthesis with the same geometry. For the copper specimens, considerable heating (>10 degrees C) in air and in gelled saline (>1.2 degrees C) could be observed. Heating of the titanium specimens was markedly less ( approximately 1 degrees C in air). For the titanium artificial hip no heating could be detected, while the rise in temperature for the aluminum replica was approximately 2.2 degrees C. Heating of more than 10 degrees C solely due to gradient switching without any RF irradiation was demonstrated in isolated copper wire frames. Under specific conditions (high gradient duty cycle, metallic loop of sufficient inductance and low resistance, power matching) gradient switching-induced heating of conductive specimens must be considered.

Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide

NASA Astrophysics Data System (ADS)

Niu, Q.; Yu, W. C.; Yip, K. Y.; Lim, Z. L.; Kotegawa, H.; Matsuoka, E.; Sugawara, H.; Tou, H.; Yanase, Y.; Goh, Swee K.

2017-06-01

In conventional metals, modification of electron trajectories under magnetic field gives rise to a magnetoresistance that varies quadratically at low field, followed by a saturation at high field for closed orbits on the Fermi surface. Deviations from the conventional behaviour, for example, the observation of a linear magnetoresistance, or a non-saturating magnetoresistance, have been attributed to exotic electron scattering mechanisms. Recently, linear magnetoresistance has been observed in many Dirac materials, in which the electron-electron correlation is relatively weak. The strongly correlated helimagnet CrAs undergoes a quantum phase transition to a nonmagnetic superconductor under pressure. Here we observe, near the magnetic instability, a large and non-saturating quasilinear magnetoresistance from the upper critical field to 14 T at low temperatures. We show that the quasilinear magnetoresistance may arise from an intricate interplay between a nontrivial band crossing protected by nonsymmorphic crystal symmetry and strong magnetic fluctuations.

Angle-Dependent Magnetoresistance in Organic Metals

NASA Astrophysics Data System (ADS)

Blundell, Stephen J.; Singleton, John

1996-12-01

Recent experimental studies of the angle-dependent magnetoresistance in various organic metals have been remarkably successful in elucidating the nature of the low-temperature ground state and providing information about the Fermi surface shape which is hard or impossible to obtain using other techniques. We review various theoretical approaches to describe angel-dependent magnetoresistance and a number of important experimental results which have been obtained.

Recent Developments of Magnetoresistive Sensors for Industrial Applications

PubMed Central

Jogschies, Lisa; Klaas, Daniel; Kruppe, Rahel; Rittinger, Johannes; Taptimthong, Piriya; Wienecke, Anja; Rissing, Lutz; Wurz, Marc Christopher

2015-01-01

The research and development in the field of magnetoresistive sensors has played an important role in the last few decades. Here, the authors give an introduction to the fundamentals of the anisotropic magnetoresistive (AMR) and the giant magnetoresistive (GMR) effect as well as an overview of various types of sensors in industrial applications. In addition, the authors present their recent work in this field, ranging from sensor systems fabricated on traditional substrate materials like silicon (Si), over new fabrication techniques for magnetoresistive sensors on flexible substrates for special applications, e.g., a flexible write head for component integrated data storage, micro-stamping of sensors on arbitrary surfaces or three dimensional sensing under extreme conditions (restricted mounting space in motor air gap, high temperatures during geothermal drilling). PMID:26569263

A Josephson Junction based SPDT switch

NASA Astrophysics Data System (ADS)

Zhang, Helin; Earnest, Nathan; Lu, Yao; Ma, Ruichao; Chakram, Srivatsan; Schuster, David

RF microwave switches are useful tools in cryogenic experiments, allowing for multiple experiments to be connected to a single cryogenic measurement chain. However, these switches dissipate a substantial amount of heat, preventing fast switching. Josephson junction (JJ) are a promising avenue for realizing millikelvin microwave switching. We present a JJ based single-pole-double throw (SPDT) switch that has fast switching time, no heat dissipation, large on/off contrast, and works over a wide bandwidth. The switch can be used for real-time switching between experiments, routing single photons, or even generating entanglement. We will describe the design of the switch and present experimental characterization of its performance.

Antidamping-Torque-Induced Switching in Biaxial Antiferromagnetic Insulators

NASA Astrophysics Data System (ADS)

Chen, X. Z.; Zarzuela, R.; Zhang, J.; Song, C.; Zhou, X. F.; Shi, G. Y.; Li, F.; Zhou, H. A.; Jiang, W. J.; Pan, F.; Tserkovnyak, Y.

2018-05-01

We investigate the current-induced switching of the Néel order in NiO (001 )/Pt heterostructures, which is manifested electrically via the spin Hall magnetoresistance. Significant reversible changes in the longitudinal and transverse resistances are found at room temperature for a current threshold lying in the range of 1 07 A /cm2 . The order-parameter switching is ascribed to the antiferromagnetic dynamics triggered by the (current-induced) antidamping torque, which orients the Néel order towards the direction of the writing current. This is in stark contrast to the case of antiferromagnets such as Mn2Au and CuMnAs, where fieldlike torques induced by the Edelstein effect drive the Néel switching, therefore resulting in an orthogonal alignment between the Néel order and the writing current. Our findings can be readily generalized to other biaxial antiferromagnets, providing broad opportunities for all-electrical writing and readout in antiferromagnetic spintronics.

Enhancement of Spin-transfer torque switching via resonant tunneling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterji, Niladri; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran

We propose the use of resonant tunneling as a route to enhance the spin-transfer torque switching characteristics of magnetic tunnel junctions. The proposed device structure is a resonant tunneling magnetic tunnel junction based on a MgO-semiconductor heterostructure sandwiched between a fixed magnet and a free magnet. Using the non-equilibrium Green's function formalism coupled self consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation, we demonstrate enhanced tunnel magneto-resistance characteristics as well as lower switching voltages in comparison with traditional trilayer devices. Two device designs based on MgO based heterostructures are presented, where the physics of resonant tunneling leads to an enhanced spin transfer torquemore » thereby reducing the critical switching voltage by up to 44%. It is envisioned that the proof-of-concept presented here may lead to practical device designs via rigorous materials and interface studies.« less

Positive magnetoresistance effect in rare earth cobaltites

NASA Astrophysics Data System (ADS)

Troyanchuk, I. O.; Bushinskii, M. V.; Karpinsky, D. V.; Dobryanskii, V. M.; Sikolenko, V. V.; Balagurov, A. M.

2009-06-01

The structure, magnetic, and magnetotransport properties of the Pr0.5Sr0.5Co1 - x Fe x O3 system have been studied. The ferromagnet-spin glass ( x = 0.5)- G-type antiferromagnet ( x = 0.7) transitions and the metal—insulator transitions ( x = 0.25) have been revealed. It has been established that the magnetoresistance of the metallic ferromagnetic cobaltites changes sign from positive to negative as the external magnetic field increases. The positive component increases and the negative component decreases with decreasing temperature. The negative magnetoresistance increases sharply in the insulating spinglass phase. Possible causes of the low-magnetic-field positive magnetoresistance in the rare earth metallic cobaltites are discussed.

Effect of quantum tunneling on spin Hall magnetoresistance

NASA Astrophysics Data System (ADS)

Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

2017-02-01

We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

Origin of the extremely large magnetoresistance in topological semimetal PtS n4

NASA Astrophysics Data System (ADS)

Luo, X.; Xiao, R. C.; Chen, F. C.; Yan, J.; Pei, Q. L.; Sun, Y.; Lu, W. J.; Tong, P.; Sheng, Z. G.; Zhu, X. B.; Song, W. H.; Sun, Y. P.

2018-05-01

PtS n4 with extremely large magnetoresistance (XMR), a fascinating topological material platform, hosts a novel topological structure and Dirac node arcs, in which the Dirac nodes form closed loops in the momentum space. Here we performed the angular dependent magnetoresistivity (AMR), Hall effect, heat capacity measurements, and first-principles calculations to study the electronic properties of topological semimetal PtS n4 . There are some interesting observations on PtS n4 . (1) In the different experimental probes, we observed the anomalies around T ˜55 K . Significant changes of the transport results and the heat capacity have been observed, indicating successive Fermi surface reconstruction induced by the temperature. It means there is Lifshitz transition (LT) induced by the temperature in PtS n4 . (2) The perfect compensation between the electron and hole has been found around T ˜30 K , where the XMR appears, which is confirmed by the Hall effect measurements and the first-principles calculations. The XMR effect in PtS n4 is suggested to originate from the combination of the electron-hole compensation and a particular orbital texture on the electron pocket. Meanwhile, we also found that LT seems to serve as a knob for the novel topological properties in two-dimensional (2D) topological semimetals (TSMs).

Studies of current-perpendicular-to-plane magnetoresistance (CPP-MR) and current-induced magnetization switching (CIMS)

NASA Astrophysics Data System (ADS)

Kurt, Huseyin

2005-08-01

We present two CPP-MR studies of spin-valves based upon ferromagnetic/nonmagnetic/ferromagnetic (F/N/F) trilayers. We measure the spin-diffusion lengths of N = Pd, Pt, and Au at 4.2K, and both the specific resistances (sample area A times resistance R) and spin-memory-loss of N/Cu interfaces. Pd, Pt and Au are of special device interest because they give perpendicular anisotropy when sandwiching very thin Co layers. Comparing our spin-memory-loss data at Pd/Cu and Pt/Cu interfaces with older data for Nb/Cu and W/Cu gives insight into the importance of spin-orbit coupling in producing such loss. We reproduce and extend prior studies by Eid of 'magnetic activity' at the interface of Co and N-metals (or combinations of N-metals), when the other side of the N-metal contacts a superconductor (S). Our data suggest that magnetic activity may require strong spin-flipping at the N/S interface. We present five studies of a new phenomenon, CIMS, in F1/N/F2 trilayers, with F1 a thick 'polarizing' layer and F2 a thin 'switching' layer. In all prior studies of CIMS, positive current caused the magnetization of F2 to switch from parallel (P) to anti-parallel (AP) to that of F1- 'normal' switching. By judicious addition of impurities to F-metals, we are able to controllably produce both 'normal' and 'inverse' switching- where positive current switches the magnetization of F2 from AP to P to that of F1. In the samples studied, whether the switching is normal or inverse is set by the 'net polarization' produced by F1 and is independent of the properties of F2. As scattering in the bulk of F1 and F2 is essential to producing our results, these results cannot be described by ballistic models, which allow scattering only at interfaces. Most CIMS experiments use Cu as the N-layer due to its low resistivity and long spin-diffusion length. We show that Ag and Au have low enough resistivities and long enough spin-diffusion lengths to be useful alternatives to Cu for some devices. While

Spin-controlled negative magnetoresistance resulting from exchange interactions

NASA Astrophysics Data System (ADS)

Agrinskaya, N. V.; Kozub, V. I.; Mikhailin, N. Yu.; Shamshur, D. V.

2017-04-01

We studied conductivity of AlGaAs-GaAs quantum well structures (where centers of the wells were doped by Be) at temperatures higher than 4 K in magnetic fields up 10 T. Throughout all the temperature region considered the conductivity demonstrated activated behavior. At moderate magnetic fields 0.1 T < H < 1 T, we observed negative isotropic magnetoresistance, which was linear in magnetic field while for magnetic field normal with respect to the plane of the wells the magnetoresistance was positive at H > 2T. To the best of our knowledge, it was the first observation of linear negative magnetoresistance, which would be isotropic with respect to the direction of magnetic field. While the isotropic character of magnetoresistance apparently evidences role of spins, the existing theoretical considerations concerning spin effects in conductance fail to explain our experimental results. We believe that such a behavior can be attributed to spin effects supported by exchange interactions between localized states.

Magnetoresistance in Permalloy Connected Brickwork Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Park, Jungsik; Le, Brian; Chern, Gia-Wei; Watts, Justin; Leighton, Chris; Schiffer, Peter

Artificial spin ice refers to a two-dimensional array of elongated ferromagnetic elements in which frustrated lattice geometry induces novel magnetic behavior. Here we examine room-temperature magnetoresistance properties of connected permalloy (Ni81Fe19) brickwork artificial spin ice. Both the longitudinal and transverse magnetoresistance of the nanostructure demonstrate an angular sensitivity that has not been previously observed. The observed magnetoresistance behavior can be explained from micromagnetic modelling using an anisotropic magnetoresistance model (AMR). As part of this study, we find that the ground state of the connected brickwork artificial spin ice can be reproducibly created by a simple field sweep in a narrow range of angles, and manifests in the magnetotransport with a distinct signal. Supported by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Grant Number DE-SC0010778. Work at the University of Minnesota was supported by the NSF MRSEC under award DMR-1420013, and DMR-1507048.

The Anomalous Magnetoresistance of Graphite at High Magnetic Fields,

DTIC Science & Technology

1983-05-01

magnetoresistance anomaly. In the present work, the unusual properties of this fine structure (which is periodic in magnetic field H ) is examined in more detail...structure associated with the magnetoresistance anomly is (AH/ H ) - 0.1 T/25 T or about 0.4 Z. Thus, for typical magnetic field sweep rates (10 T in 10...magnetoresistance above 12 T have been associated by lye at al.2 with a linear increase in carrier concentration with increasing H .1 The anomalous increase

Organic magnetoresistance based on hopping theory

NASA Astrophysics Data System (ADS)

Yang, Fu-Jiang; Xie, Shi-Jie

2014-09-01

For the organic magnetoresistance (OMAR) effect, we suggest a spin-related hopping of carriers (polarons) based on Marcus theory. The mobility of polarons is calculated with the master equation (ME) and then the magnetoresistance (MR) is obtained. The theoretical results are consistent with the experimental observation. Especially, the sign inversion of the MR under different driving bias voltages found in the experiment is predicted. Besides, the effects of molecule disorder, hyperfine interaction (HFI), polaron localization, and temperature on the MR are investigated.

A miniature continuous adiabatic demagnetization refrigerator with compact shielded superconducting magnets

NASA Astrophysics Data System (ADS)

Duval, Jean-Marc; Cain, Benjamin M.; Timbie, Peter T.

2004-10-01

Cryogenic detectors for astrophysics depend on cryocoolers capable of achieving temperatures below ~ 100 mK. In order to provide continuous cooling at 50 mK for space or laboratory applications, we are designing a miniature adiabatic demagnetization refrigerator (MADR) anchored at a reservoir at 5 K. Continuous cooling is obtained by the use of several paramagnetic pills placed in series with heat switches. All operations are fully electronic and this technology can be adapted fairly easily for a wide range of temperatures and cooling powers. We are focusing on reducing the size and mass of the cooler. For that purpose we have developed and tested magnetoresistive heat switches based on single crystals of tungsten. Several superconducting magnets are required for this cooler and we have designed and manufactured compact magnets. A special focus has been put on the reduction of parasitic magnetic fields in the cold stage, while minimizing the mass of the shields. A prototype continuous MADR, using magnetoresistive heat switches, small paramagnetic pills and compact magnets has been tested. A design of MADR that will provide ~ 5 uW of continuous cooling down to 50 mK is described.

Extremely large magnetoresistance and Kohler's rule in PdSn 4 : A complete study of thermodynamic, transport, and band-structure properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jo, Na Hyun; Wu, Yun; Wang, Lin-Lin

The recently discovered material PtSn 4 is known to exhibit extremely large magnetoresistance (XMR) that also manifests Dirac arc nodes on the surface. PdSn 4 is isostructural to PtSn 4 with the same electron count. Here, we report on the physical properties of high-quality single crystals of PdSn 4 including specific heat, temperature- and magnetic-field-dependent resistivity and magnetization, and electronic band-structure properties obtained from angle-resolved photoemission spectroscopy (ARPES). We observe that PdSn 4 has physical properties that are qualitatively similar to those of PtSn 4 , but find also pronounced differences. Importantly, the Dirac arc node surface state of PtSnmore » 4 is gapped out for PdSn 4. By comparing these similar compounds, we address the origin of the extremely large magnetoresistance in PdSn 4 and PtSn 4; based on detailed analysis of the magnetoresistivity ρ ( H , T ) , we conclude that neither the carrier compensation nor the Dirac arc node surface state are the primary reason for the extremely large magnetoresistance. On the other hand, we also find that, surprisingly, Kohler's rule scaling of the magnetoresistance, which describes a self-similarity of the field-induced orbital electronic motion across different length scales and is derived for a simple electronic response of metals to an applied magnetic field is obeyed over the full range of temperatures and field strengths that we explore.« less

Extremely large magnetoresistance and Kohler's rule in PdSn 4 : A complete study of thermodynamic, transport, and band-structure properties

DOE PAGES

Jo, Na Hyun; Wu, Yun; Wang, Lin-Lin; ...

2017-10-27

The recently discovered material PtSn 4 is known to exhibit extremely large magnetoresistance (XMR) that also manifests Dirac arc nodes on the surface. PdSn 4 is isostructural to PtSn 4 with the same electron count. Here, we report on the physical properties of high-quality single crystals of PdSn 4 including specific heat, temperature- and magnetic-field-dependent resistivity and magnetization, and electronic band-structure properties obtained from angle-resolved photoemission spectroscopy (ARPES). We observe that PdSn 4 has physical properties that are qualitatively similar to those of PtSn 4 , but find also pronounced differences. Importantly, the Dirac arc node surface state of PtSnmore » 4 is gapped out for PdSn 4. By comparing these similar compounds, we address the origin of the extremely large magnetoresistance in PdSn 4 and PtSn 4; based on detailed analysis of the magnetoresistivity ρ ( H , T ) , we conclude that neither the carrier compensation nor the Dirac arc node surface state are the primary reason for the extremely large magnetoresistance. On the other hand, we also find that, surprisingly, Kohler's rule scaling of the magnetoresistance, which describes a self-similarity of the field-induced orbital electronic motion across different length scales and is derived for a simple electronic response of metals to an applied magnetic field is obeyed over the full range of temperatures and field strengths that we explore.« less

Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts.

PubMed

Schöneberg, J; Otte, F; Néel, N; Weismann, A; Mokrousov, Y; Kröger, J; Berndt, R; Heinze, S

2016-02-10

Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin-orbit coupling. This work shows that engineering the AMR at the single atom level is feasible.

Optically Tunable Magnetoresistance Effect: From Mechanism to Novel Device Application.

PubMed

Liu, Pan; Lin, Xiaoyang; Xu, Yong; Zhang, Boyu; Si, Zhizhong; Cao, Kaihua; Wei, Jiaqi; Zhao, Weisheng

2017-12-28

The magnetoresistance effect in sandwiched structure describes the appreciable magnetoresistance effect of a device with a stacking of two ferromagnetic layers separated by a non-magnetic layer (i.e., a sandwiched structure). The development of this effect has led to the revolution of memory applications during the past decades. In this review, we revisited the magnetoresistance effect and the interlayer exchange coupling (IEC) effect in magnetic sandwiched structures with a spacer layer of non-magnetic metal, semiconductor or organic thin film. We then discussed the optical modulation of this effect via different methods. Finally, we discuss various applications of these effects and present a perspective to realize ultralow-power, high-speed data writing and inter-chip connection based on this tunable magnetoresistance effect.

Mechanical Signature of Heat Generated in a Current-Driven Ferromagnetic Resonance System

NASA Astrophysics Data System (ADS)

Cho, Sung Un; Jo, Myunglae; Park, Seondo; Lee, Jae-Hyun; Yang, Chanuk; Kang, Seokwon; Park, Yun Daniel

2017-07-01

In a current-driven ferromagnetic resonance (FMR) system, heat generated by time-dependent magnetoresistance effects, caused by magnetization precession, cannot be overlooked. Here, we describe the generated heat by magnetization motion under electric current in a freestanding nanoelectromechanical resonator fashioned from a permalloy (Py )/Pt bilayer. By piezoresistive transduction of Pt, the mechanical mode is electrically detected at room temperature and the internal heat in Py excluding thermoelectric effects is quantified as a shift of the mechanical resonance. We find that the measured spectral shifts correspond to the FMR, which is further verified from the spin-torque FMR measurement. Furthermore, the angular dependence of the mechanical reaction on an applied magnetic field reveals that the full accounting of FMR heat dissipation requires the time-dependent magnetoresistance effect.

Antiferromagnetic exchange and magnetoresistance enhancement in Co-Re superlattices

NASA Astrophysics Data System (ADS)

Freitas, P. P.; Melo, L. V.; Trindade, I.; From, M.; Ferreira, J.; Monteiro, P.

1992-02-01

Co-Re superlattices were prepared that show either antiferromagnetic or ferromagnetic coupling between the Co layers depending on the Re spacer thickness. Enhanced saturation magnetoresistance occurs for antiferromagnetically coupled layers. The saturation magnetoresistance decays exponentially with Re thickness but does not depend critically on the Co thickness.

Magnetoresistance effect in (La, Sr)MnO3 bicrystalline films.

PubMed

Alejandro, G; Steren, L B; Pastoriza, H; Vega, D; Granada, M; Sánchez, J C Rojas; Sirena, M; Alascio, B

2010-09-01

The angular dependence of the magnetoresistance effect has been measured on bicrystalline La(0.75)Sr(0.25)MnO(3) films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.

Anomalous negative magnetoresistance of two-dimensional electrons

NASA Astrophysics Data System (ADS)

Kanter, Jesse; Vitkalov, Sergey; Bykov, A. A.

2018-05-01

Effects of temperature T (6-18 K) and variable in situ static disorder on dissipative resistance of two-dimensional electrons are investigated in GaAs quantum wells placed in a perpendicular magnetic-field B⊥. Quantum contributions to the magnetoresistance, leading to quantum positive magnetoresistance (QPMR), are separated by application of an in-plane magnetic field. QPMR decreases considerably with both the temperature and the static disorder and is in good quantitative agreement with theory. The remaining resistance R decreases with the magnetic field exhibiting an anomalous polynomial dependence on B⊥:[R (B⊥) -R (0 ) ] =A (T ,τq) B⊥η where the power is η ≈1.5 ±0.1 in a broad range of temperatures and disorder. The disorder is characterized by electron quantum lifetime τq. The scaling factor A (T ,τq) ˜[κ(τq) +β (τq) T2] -1 depends significantly on both τq and T where the first term κ ˜τq-1/2 decreases with τq. The second term is proportional to the square of the temperature and diverges with increasing static disorder. Above a critical disorder the anomalous magnetoresistance is absent, and only a positive magnetoresistance, exhibiting no distinct polynomial behavior with the magnetic field, is observed. The presented model accounts memory effects and yields η = 3/2.

Magnetoresistance in two-dimensional array of Ge/Si quantum dots

NASA Astrophysics Data System (ADS)

Stepina, N. P.; Koptev, E. S.; Pogosov, A. G.; Dvurechenskii, A. V.; Nikiforov, A. I.; Zhdanov, E. Yu

2012-07-01

Magnetoresistance in two-dimensional array of Ge/Si was studied for a wide range of the conductance, where the transport regime changes from hopping to diffusive one. The behavior of magnetoresistance is similar for all samples; it is negative in weak fields and becomes positive with increasing of magnetic field. Negative magnetoresistance can be described in the frame of weak localization approach with suggestion that quantum interference contribution to the conductance is restricted not only by the phase breaking length but also by the localization length.

Magnetoresistance behavior in nanobulk assembled Bi2Se3 topological insulator

NASA Astrophysics Data System (ADS)

Bera, Sumit; Behera, P.; Mishra, A. K.; Krishnan, M.; Patidar, Manju Mishra; Singh, Durgesh; Venkatesh, R.; Phase, D. M.; Ganesan, V.

2018-05-01

Temperature and magnetic field dependent magnetoresistance (MR) including structural, morphological studies of Bi2Se3 nanoflower like structure synthesized by microwave assisted solvothermal method has been investigated. Powder X-ray diffraction (XRD) has confirmed the formation of single phase. Morphology of the material shows nanoflower kind of structures with edge to edge size of around 4 µm and such occurrences are quite high. The temperature dependent resistance invokes a metallic behavior up to a certain lower temperature, below which it follows -ln(T) behavior that has been elucidated in literature using electron-electron interaction and weak anti-localization effects. High temperature magnetoresistance is consistent with parabolic field dependence indicating a classical magnetoresistance in metals as a result of Lorenz force. In low temperature regime magnetoresistance as a function of magnetic field at different temperatures obeys power law near low field which indicates a three dimensional weak-antilocalization. A linear magnetoresistance at low temperature and high magnetic field shows the domination of surface state conduction.

Giant oscillating magnetoresistance in silicene-based structures

NASA Astrophysics Data System (ADS)

Oubram, O.; Navarro, O.; Rodríguez-Vargas, I.; Guzman, E. J.; Cisneros-Villalobos, L.; Velásquez-Aguilar, J. G.

2018-02-01

Ballistic electron transport in a silicene structure, composed of a pair of magnetic gates, in the ferromagnetic and an-tiferromagnetic configuration is studied. This theoretical study has been done using the matrix transfer method to calculate the transmission, the conductance for parallel and antiparallel magnetic alignment and the magnetoresistance. Results show that conductance and magnetoresistance oscillate as a function of the length between the two magnetic domains. The forbidden transmission region also increases as a function of the barrier separation distance.

Reflective HTS switch

DOEpatents

Martens, Jon S.; Hietala, Vincent M.; Hohenwarter, Gert K. G.

1994-01-01

A HTS switch includes a HTS conductor for providing a superconducting path for an electrical signal and an serpentine wire actuator for controllably heating a portion of the conductor sufficiently to cause that portion to have normal, and not superconducting, resistivity. Mass of the portion is reduced to decrease switching time.

Ultra-Sensitive Magnetoresistive Displacement Sensing Device

NASA Technical Reports Server (NTRS)

Olivas, John D. (Inventor); Lairson, Bruce M. (Inventor); Ramesham, Rajeshuni (Inventor)

2003-01-01

An ultrasensitive displacement sensing device for use in accelerometers, pressure gauges, temperature transducers, and the like, comprises a sputter deposited, multilayer, magnetoresistive field sensor with a variable electrical resistance based on an imposed magnetic field. The device detects displacement by sensing changes in the local magnetic field about the magnetoresistive field sensor caused by the displacement of a hard magnetic film on a movable microstructure. The microstructure, which may be a cantilever, membrane, bridge, or other microelement, moves under the influence of an acceleration a known displacement predicted by the configuration and materials selected, and the resulting change in the electrical resistance of the MR sensor can be used to calculate the displacement. Using a micromachining approach, very thin silicon and silicon nitride membranes are fabricated in one preferred embodiment by means of anisotropic etching of silicon wafers. Other approaches include reactive ion etching of silicon on insulator (SOI), or Low Pressure Chemical Vapor Deposition of silicon nitride films over silicon substrates. The device is found to be improved with the use of giant magnetoresistive elements to detect changes in the local magnetic field.

Oxygen Impurities Link Bistability and Magnetoresistance in Organic Spin Valves.

PubMed

Bergenti, Ilaria; Borgatti, Francesco; Calbucci, Marco; Riminucci, Alberto; Cecchini, Raimondo; Graziosi, Patrizio; MacLaren, Donald A; Giglia, Angelo; Rueff, Jean Pascal; Céolin, Denis; Pasquali, Luca; Dediu, Valentin

2018-03-07

Vertical crossbar devices based on manganite and cobalt injecting electrodes and a metal-quinoline molecular transport layer are known to manifest both magnetoresistance (MR) and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the MR and magnetic modulation of bistability. To explain the device functionality, we identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with the chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrate under voltage application, resulting in a modification of the electronic properties of the organic material and of the oxidation state of the interfacial layer with the ferromagnetic contacts. Variable oxygen doping of the organic molecules represents the key element for correlating bistability and MR, and our measurements provide the first experimental evidence in favor of the impurity-driven model describing the spin transport in organic semiconductors in similar devices.

Study of magnetoresistance in the supercooled state of Dy-Y alloys

NASA Astrophysics Data System (ADS)

Jena, Rudra Prasad; Lakhani, Archana

2018-02-01

We report the magnetoresistance studies on Dy1-xYx (x ≤ 0.05) alloys across the first order helimagnetic to ferromagnetic phase transition. These alloys exhibit multiple magnetic phases on varying the temperature and magnetic field. The magnetoresistance studies in the hysteresis region shows irreversibility in forward and reverse field cycles. The resistivity values at zero field for these alloys after zero field cooling to the measurement temperatures, are different in both forward and reverse field cycles. The path dependence of magnetoresistance suggests the presence of helimagnetic phase as the supercooled metastable state which transforms to the stable ferromagnetic state on increasing the field. At high magnetic fields negative magnetoresistance following a linear dependence with field is observed which is attributed to the magnon scattering.

Large magnetoresistance induced by crystallographic defects in FexTaS2 single crystals

NASA Astrophysics Data System (ADS)

Chen, Chih-Wei; Morosan, Emilia; Morosan's Group Team

The search for the materials that show large magnetoresistance and the mechanisms that induce it remains challenging in both experimental and theoretical aspects. The giant magnetoresistance in one class of materials, ferromagnetic conductors, is generally attributed to the misalignments of magnetic moments, which cause spin disorder scattering. Recently, very large magnetoresistance (>60 %) was discovered in the ferromagnetic Fe-intercalated transition metal dichalcogenide, Fe0.28TaS2 [Phys. Rev. B 91, 054426(2015)]. The mechanism that led to this large magnetoresistance was suggested to be due to the deviation of Fe concentration from commensurate values (1/4 or 1/3), which caused magnetic moments' misalignments. Here we report a study of FexTaS2 crystals with x close to the commensurate values. Our results qualitatively demonstrate that crystallographic defects significantly affect magnetoresistance in FexTaS2. This provides a way to search for large magnetoresistance in more intercalated transition metal dichalcogenides. This work is supported by the Department of Defense PECASE.

Spin-transfer torque switched magnetic tunnel junctions in magnetic random access memory

NASA Astrophysics Data System (ADS)

Sun, Jonathan Z.

2016-10-01

Spin-transfer torque (or spin-torque, or STT) based magnetic tunnel junction (MTJ) is at the heart of a new generation of magnetism-based solid-state memory, the so-called spin-transfer-torque magnetic random access memory, or STT-MRAM. Over the past decades, STT-based switchable magnetic tunnel junction has seen progress on many fronts, including the discovery of (001) MgO as the most favored tunnel barrier, which together with (bcc) Fe or FeCo alloy are yielding best demonstrated tunnel magneto-resistance (TMR); the development of perpendicularly magnetized ultrathin CoFeB-type of thin films sufficient to support high density memories with junction sizes demonstrated down to 11nm in diameter; and record-low spin-torque switching threshold current, giving best reported switching efficiency over 5 kBT/μA. Here we review the basic device properties focusing on the perpendicularly magnetized MTJs, both in terms of switching efficiency as measured by sub-threshold, quasi-static methods, and of switching speed at super-threshold, forced switching. We focus on device behaviors important for memory applications that are rooted in fundamental device physics, which highlights the trade-off of device parameters for best suitable system integration.

Stripe domains and magnetoresistance in thermally deposited nickel films

NASA Astrophysics Data System (ADS)

Sparks, P. D.; Stern, N. P.; Snowden, D. S.; Kappus, B. A.; Checkelsky, J. G.; Harberger, S. S.; Fusello, A. M.; Eckert, J. C.

2004-05-01

We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.21+/-0.02 up to 120nm thickness. There is a negative magnetoresistance for fields out of the plane.

Millimeter-scale liquid metal droplet thermal switch

NASA Astrophysics Data System (ADS)

Yang, Tianyu; Kwon, Beomjin; Weisensee, Patricia B.; Kang, Jin Gu; Li, Xuejiao; Braun, Paul; Miljkovic, Nenad; King, William P.

2018-02-01

Devices capable of actively controlling heat flow have been desired by the thermal management community for decades. The need for thermal control has become particularly urgent with power densification resulting in devices with localized heat fluxes as high as 1 kW/cm2. Thermal switches, capable of modulating between high and low thermal conductances, enable the partitioning and active control of heat flow pathways. This paper reports a millimeter-scale thermal switch with a switching ratio >70, at heat fluxes near 10 W/cm2. The device consists of a silicone channel filled with a reducing liquid or vapor and an immersed liquid metal Galinstan slug. Galinstan has a relatively high thermal conductivity (≈16.5 W/mK at room temperature), and its position can be manipulated within the fluid channel, using either hydrostatic pressure or electric fields. When Galinstan bridges the hot and cold reservoirs (the "ON" state), heat flows across the channel. When the hot and cold reservoirs are instead filled with the encapsulating liquid or vapor (the "OFF" state), the cross-channel heat flow significantly reduces due to the lower thermal conductivity of the solution (≈0.03-0.6 W/mK). We demonstrate switching ratios as high as 15.6 for liquid filled channels and 71.3 for vapor filled channels. This work provides a framework for the development of millimeter-scale thermal switches and diodes capable of spatial and temporal control of heat flows.

Giant magnetoresistive sensor

DOEpatents

Stearns, Daniel G.; Vernon, Stephen P.; Ceglio, Natale M.; Hawryluk, Andrew M.

1999-01-01

A magnetoresistive sensor element with a three-dimensional micro-architecture is capable of significantly improved sensitivity and highly localized measurement of magnetic fields. The sensor is formed of a multilayer film of alternately magnetic and nonmagnetic materials. The sensor is optimally operated in a current perpendicular to plane mode. The sensor is useful in magnetic read/write heads, for high density magnetic information storage and retrieval.

Data center coolant switch

DOEpatents

Iyengar, Madhusudan K.; Parida, Pritish R.; Schultz, Mark D.

2015-10-06

A data center cooling system is operated in a first mode; it has an indoor portion wherein heat is absorbed from components in the data center, and an outdoor heat exchanger portion wherein outside air is used to cool a first heat transfer fluid (e.g., water) present in at least the outdoor heat exchanger portion of the cooling system during the first mode. The first heat transfer fluid is a relatively high performance heat transfer fluid (as compared to the second fluid), and has a first heat transfer fluid freezing point. A determination is made that an appropriate time has been reached to switch from the first mode to a second mode. Based on this determination, the outdoor heat exchanger portion of the data cooling system is switched to a second heat transfer fluid, which is a relatively low performance heat transfer fluid, as compared to the first heat transfer fluid. It has a second heat transfer fluid freezing point lower than the first heat transfer fluid freezing point, and the second heat transfer fluid freezing point is sufficiently low to operate without freezing when the outdoor air temperature drops below a first predetermined relationship with the first heat transfer fluid freezing point.

Reflective HTS switch

DOEpatents

Martens, J.S.; Hietala, V.M.; Hohenwarter, G.K.G.

1994-09-27

A HTS (High Temperature Superconductor) switch includes a HTS conductor for providing a superconducting path for an electrical signal and an serpentine wire actuator for controllably heating a portion of the conductor sufficiently to cause that portion to have normal, and not superconducting, resistivity. Mass of the portion is reduced to decrease switching time. 6 figs.

Electric field control of magnetoresistance in InP nanowires with ferromagnetic contacts.

PubMed

Zwanenburg, F A; van der Mast, D W; Heersche, H B; Kouwenhoven, L P; Bakkers, E P A M

2009-07-01

We demonstrate electric field control of sign and magnitude of the magnetoresistance in InP nanowires with ferromagnetic contacts. The sign change in the magnetoresistance is directly correlated with a sign change in the transconductance. Additionally, the magnetoresistance is shown to persist at such a high bias that Coulomb blockade has been lifted. We also observe the magnetoresistance when one of the ferromagnets is replaced by a nonmagnetic metal. We conclude that it must be induced by a single ferromagnetic contact, and that spin transport can be ruled out as the origin. Our results emphasize the importance of a systematic investigation of spin-valve devices in order to discriminate between ambiguous interpretations.

Negative and positive magnetoresistance in GaInNAs/GaAs modulation-doped quantum well structures

NASA Astrophysics Data System (ADS)

Nutku, Ferhat; Donmez, Omer; Sarcan, Fahrettin; Erol, Ayşe; Puustinen, Janne; Arıkan, Mehmet Çetin; Guina, Mircea

2015-03-01

In this work, magnetoresistance of as-grown and annealed n- and p-type modulation-doped Ga0.68In0.32NyAs1-y/GaAs single quantum well structures with various nitrogen concentrations has been studied. At low temperatures and low magnetic fields, in n-type samples negative and in p-type samples positive, magnetoresistance has been observed. The observed negative magnetoresistance in n-type samples is an indication of enhanced backscattering of electrons due to the weak localization of the electrons as an effect of the N-induced defects. Nitrogen concentration and thermal annealing dependence of the magnetoresistance have been studied for both n- and p-type samples. The observed decrease in the negative magnetoresistance in n-type and enhanced positive magnetoresistance in p-type samples following thermal annealing have been explained by considering thermal annealing-induced improvement of mobility and the crystal quality in N-containing samples. After thermal annealing, the magnitude of negative magnetoresistance decreases and the breaking of the weak localization is achieved at lower magnetic fields in n-type samples. It is observed that as the mobility of the sample increases, critical magnetic field of negative to positive magnetoresistance transition becomes lower.

High-temperature interlayer magnetoresistance in La5Mo4O16

NASA Astrophysics Data System (ADS)

Kobayashi, K.; Katsufuji, T.

2011-03-01

We found that La5Mo4O16 with Mo4+ and Mo5+ ions (S=1 and S=1/2 spins) on a quasisquare lattice exhibits a distinct magnetoresistance for the current perpendicular to the square-lattice layers below the antiferromagnetic ordering temperature TAF=190 K. This magnetoresistance occurs well below 1 T, and can be attributed to a metamagnetic transition from antiferromagnetically aligned moments between the layers to ferromagnetically aligned ones. The magnetoresistance changes its characteristic with the change of the magnetic state below TF=70 K, where spontaneous magnetization appears.

Stability of standing spin wave in permalloy thin film studied by anisotropic magnetoresistance effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamanoi, K.; Yokotani, Y.; Cui, X.

2015-12-21

We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of themore » standing spin wave is an important advantage for the high power operation of the spin-wave device.« less

Anomalous electronic structure and magnetoresistance in TaAs2

NASA Astrophysics Data System (ADS)

Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

2016-06-01

The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.

Anomalous electronic structure and magnetoresistance in TaAs2

PubMed Central

Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

2016-01-01

The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions. PMID:27271852

Infrared spectra of magnetoresistive ferromagnets in magnetic fields

NASA Astrophysics Data System (ADS)

Telegin, A. V.; Bessonova, V. A.; Sukhorukov, Yu. P.

2018-05-01

The influence of a magnetic field on reflection and transmission spectra of ferromagnetic manganites possessed the colossal magnetoresistance effect has been in the infrared range studied. It was shown that observed magnetotransmission and magnetoreflection of unpolarized light are an optical response to the colossal magnetoresistance in optimally doped manganites. Compared to crystals and multilayers the effects are the most pronounced and reach the magnitude of up to few tens of percent in single-layer thin films near the Curie temperature. A new low-temperature mechanism of magnetotransmission connected with the tunnel magnetoresistance was revealed far below the Curie point in Ba-doped manganite films with a variant structure. The observed magneto-optical effects in manganites can be described in the framework of the magnetorefractive effect theory. The observed effects are one or two orders of magnitude greater than the conventional IR magnetooptical phenomena in manganites. Being quite large, magnetoreflection and magnetotransmission effects in manganites structures could be successfully used in optoelectronics.

Magnetoresistive magnetometer for space science applications

NASA Astrophysics Data System (ADS)

Brown, P.; Beek, T.; Carr, C.; O'Brien, H.; Cupido, E.; Oddy, T.; Horbury, T. S.

2012-02-01

Measurement of the in situ dc magnetic field on space science missions is most commonly achieved using instruments based on fluxgate sensors. Fluxgates are robust, reliable and have considerable space heritage; however, their mass and volume are not optimized for deployment on nano or picosats. We describe a new magnetometer design demonstrating science measurement capability featuring significantly lower mass, volume and to a lesser extent power than a typical fluxgate. The instrument employs a sensor based on anisotropic magnetoresistance (AMR) achieving a noise floor of less than 50 pT Hz-1/2 above 1 Hz on a 5 V bridge bias. The instrument range is scalable up to ±50 000 nT and the three-axis sensor mass and volume are less than 10 g and 10 cm3, respectively. The ability to switch the polarization of the sensor's easy axis and apply magnetic feedback is used to build a driven first harmonic closed loop system featuring improved linearity, gain stability and compensation of the sensor offset. A number of potential geospace applications based on the initial instrument results are discussed including attitude control systems and scientific measurement of waves and structures in the terrestrial magnetosphere. A flight version of the AMR magnetometer will fly on the TRIO-CINEMA mission due to be launched in 2012.

Quantized magnetoresistance in atomic-size contacts.

PubMed

Sokolov, Andrei; Zhang, Chunjuan; Tsymbal, Evgeny Y; Redepenning, Jody; Doudin, Bernard

2007-03-01

When the dimensions of a metallic conductor are reduced so that they become comparable to the de Broglie wavelengths of the conduction electrons, the absence of scattering results in ballistic electron transport and the conductance becomes quantized. In ferromagnetic metals, the spin angular momentum of the electrons results in spin-dependent conductance quantization and various unusual magnetoresistive phenomena. Theorists have predicted a related phenomenon known as ballistic anisotropic magnetoresistance (BAMR). Here we report the first experimental evidence for BAMR by observing a stepwise variation in the ballistic conductance of cobalt nanocontacts as the direction of an applied magnetic field is varied. Our results show that BAMR can be positive and negative, and exhibits symmetric and asymmetric angular dependences, consistent with theoretical predictions.

Electronic structure basis for the extraordinary magnetoresistance in WTe 2

DOE PAGES

Pletikosić, I.; Ali, Mazhar N.; Fedorov, A. V.; ...

2014-11-19

The electronic structure basis of the extremely large magnetoresistance in layered non-magnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at the Fermi level, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic, quasi one-dimensional Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. As a result, a change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior ofmore » the magnetoresistance in WTe₂ was identified.« less

Impact of Tunnel-Barrier Strength on Magnetoresistance in Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Morgan, Caitlin; Misiorny, Maciej; Metten, Dominik; Heedt, Sebastian; Schäpers, Thomas; Schneider, Claus M.; Meyer, Carola

2016-05-01

We investigate magnetoresistance in spin valves involving CoPd-contacted carbon nanotubes. Both the temperature and bias-voltage dependence clearly indicate tunneling magnetoresistance as the origin. We show that this effect is significantly affected by the tunnel-barrier strength, which appears to be one reason for the variation between devices previously detected in similar structures. Modeling the data by means of the scattering matrix approach, we find a nontrivial dependence of the magnetoresistance on the barrier strength. Furthermore, an analysis of the spin precession observed in a nonlocal Hanle measurement yields a spin lifetime of τs=1.1 ns , a value comparable with those found in silicon- or graphene-based spin-valve devices.

Switching from usual brand cigarettes to a tobacco-heating cigarette or snus: Part 2. Biomarkers of exposure.

PubMed

Ogden, Michael W; Marano, Kristin M; Jones, Bobbette A; Morgan, Walter T; Stiles, Mitchell F

2015-01-01

A randomized, multi-center study of adult cigarette smokers switched to tobacco-heating cigarettes, snus or ultra-low machine yield tobacco-burning cigarettes (50/group) was conducted, and subjects' experience with the products was followed for 24 weeks. Differences in biomarkers of tobacco exposure between smokers and never smokers at baseline and among groups relative to each other and over time were assessed. Results indicated reduced exposure to many potentially harmful constituents found in cigarette smoke following product switching. Findings support differences in exposure from the use of various tobacco products and are relevant to the understanding of a risk continuum among tobacco products (ClinicalTrials.gov Identifier: NCT02061917).

Theory of unidirectional magnetoresistance in magnetic heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Steven S.-L.; Vignale, Giovanni

2017-09-01

We present a general drift-diffusion theory beyond linear response to explain the unidirectional magnetoresistance (UMR) observed in recent experiments in various magnetic heterostructures. In general, such nonlinear magnetoresistance may originate from the concerted action of current-induced spin accumulation and spin asymmetry in electron mobility. As a case study, we calculate the UMR in a bilayer system consisting of a heavy-metal (HM) and a ferromagnetic metal (FM), where the spin accumulation is induced via the spin Hall effect in the bulk of the HM layer. Our previous formulation [cf. PRB 94, 140411(R) (2016)] is generalized to include the interface resistance and spin memory loss, which allows us to analyze in details their effects on the UMR. We found that the UMR turns out to be independent of the spin asymmetry of the interfacial resistance, at variance with the linear giant-magnetoresistance (GMR) effect. A linear relation between the UMR and the conductivity-spin asymmetry is revealed, which provides an alternative way to control the sign and magnitude of the UMR and hence may serve as an experimental signature of our proposed mechanism.

Anomalous electronic structure and magnetoresistance in TaAs 2

DOE PAGES

Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; ...

2016-01-01

We report that the change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs 2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. In conclusion, density functional calculations find that TaAs 2 is a new topological semimetal [Z 2more » invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.« less

Magnetoresistance manipulation and sign reversal in Mn-doped ZnO nanowires

DOE PAGES

Sapkota, Keshab R.; Chen, Weimin; Maloney, F. Scott; ...

2016-10-14

We report magnetoresistance (MR) manipulation and sign reversal induced by carrier concentration modulation in Mn-doped ZnO nanowires. At low temperatures positive magnetoresistance was initially observed. When the carrier concentration was increased through the application of a gate voltage, the magnetoresistance also increased and reached a maximum value. However, further increasing the carrier concentration caused the MR to decrease, and eventually an MR sign reversal from positive to negative was observed. An MR change from a maximum positive value of 25% to a minimum negative value of 7% was observed at 5 K and 50 KOe. The observed MR behavior wasmore » modeled by considering combined effects of quantum correction to carrier conductivity and bound magnetic polarons. Finally, this work could provide important insights into the mechanisms that govern magnetotransport in dilute magnetic oxides, and it also demonstrated an effective approach to manipulating magnetoresistance in these materials that have important spintronic applications.« less

Reusable fast opening switch

DOEpatents

Van Devender, John P.; Emin, David

1986-01-01

A reusable fast opening switch for transferring energy, in the form of a high power pulse, from an electromagnetic storage device such as an inductor into a load. The switch is efficient, compact, fast and reusable. The switch comprises a ferromagnetic semiconductor which undergoes a fast transition between conductive and insulating states at a critical temperature and which undergoes the transition without a phase change in its crystal structure. A semiconductor such as europium rich europhous oxide, which undergoes a conductor to insulator transition when it is joule heated from its conductor state, can be used to form the switch.

Reusable fast opening switch

DOEpatents

Van Devender, J.P.; Emin, D.

1983-12-21

A reusable fast opening switch for transferring energy, in the form of a high power pulse, from an electromagnetic storage device such as an inductor into a load. The switch is efficient, compact, fast and reusable. The switch comprises a ferromagnetic semiconductor which undergoes a fast transition between conductive and metallic states at a critical temperature and which undergoes the transition without a phase change in its crystal structure. A semiconductor such as europium rich europhous oxide, which undergoes a conductor to insulator transition when it is joule heated from its conductor state, can be used to form the switch.

Spin-orbit torque magnetization switching of a three-terminal perpendicular magnetic tunnel junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cubukcu, Murat; Boulle, Olivier; Drouard, Marc

2014-01-27

We report on the current-induced magnetization switching of a three-terminal perpendicular magnetic tunnel junction by spin-orbit torque and its read-out using the tunnelling magnetoresistance (TMR) effect. The device is composed of a perpendicular Ta/FeCoB/MgO/FeCoB stack on top of a Ta current line. The magnetization of the bottom FeCoB layer can be switched reproducibly by the injection of current pulses with density 5 × 10{sup 11} A/m{sup 2} in the Ta layer in the presence of an in-plane bias magnetic field, leading to the full-scale change of the TMR signal. Our work demonstrates the proof of concept of a perpendicular spin-orbit torque magnetic memorymore » cell.« less

The tunneling magnetoresistance current dependence on cross sectional area, angle and temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Z. H., E-mail: zhaohui@physics.umanitoba.ca; Bai, Lihui; Hu, C.-M.

2015-03-15

The magnetoresistance of a MgO-based magnetic tunnel junction (MTJ) was studied experimentally. The magnetoresistance as a function of current was measured systematically on MTJs for various MgO cross sectional areas and at various temperatures from 7.5 to 290.1 K. The resistance current dependence of the MTJ was also measured for different angles between the two ferromagnetic layers. By considering particle and angular momentum conservation of transport electrons, the current dependence of magnetoresistance can be explained by the changing of spin polarization in the free magnetic layer of the MTJ. The changing of spin polarization is related to the magnetoresistance, itsmore » angular dependence and the threshold current where TMR ratio equals zero. A phenomenological model is used which avoid the complicated barrier details and also describes the data.« less

Quantum and Classical Magnetoresistance in Ambipolar Topological Insulator Transistors with Gate-tunable Bulk and Surface Conduction

PubMed Central

Tian, Jifa; Chang, Cuizu; Cao, Helin; He, Ke; Ma, Xucun; Xue, Qikun; Chen, Yong P.

2014-01-01

Weak antilocalization (WAL) and linear magnetoresistance (LMR) are two most commonly observed magnetoresistance (MR) phenomena in topological insulators (TIs) and often attributed to the Dirac topological surface states (TSS). However, ambiguities exist because these phenomena could also come from bulk states (often carrying significant conduction in many TIs) and are observable even in non-TI materials. Here, we demonstrate back-gated ambipolar TI field-effect transistors in (Bi0.04Sb0.96)2Te3 thin films grown by molecular beam epitaxy on SrTiO3(111), exhibiting a large carrier density tunability (by nearly 2 orders of magnitude) and a metal-insulator transition in the bulk (allowing switching off the bulk conduction). Tuning the Fermi level from bulk band to TSS strongly enhances both the WAL (increasing the number of quantum coherent channels from one to peak around two) and LMR (increasing its slope by up to 10 times). The SS-enhanced LMR is accompanied by a strongly nonlinear Hall effect, suggesting important roles of charge inhomogeneity (and a related classical LMR), although existing models of LMR cannot capture all aspects of our data. Our systematic gate and temperature dependent magnetotransport studies provide deeper insights into the nature of both MR phenomena and reveal differences between bulk and TSS transport in TI related materials. PMID:24810663

Anomalous spin Hall magnetoresistance in Pt/Co bilayers

NASA Astrophysics Data System (ADS)

Kawaguchi, Masashi; Towa, Daiki; Lau, Yong-Chang; Takahashi, Saburo; Hayashi, Masamitsu

2018-05-01

We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance within the plane transverse to the current flow, of Pt/Co bilayers. We find that the SMR increases with increasing Co thickness: the effective spin Hall angle for bilayers with thick Co exceeds the reported values of Pt when a conventional drift-diffusion model is used. An extended model including spin transport within the Co layer cannot account for the large SMR. To identify its origin, contributions from other sources are studied. For most bilayers, the SMR increases with decreasing temperature and increasing magnetic field, indicating that magnon-related effects in the Co layer play little role. Without the Pt layer, we do not observe the large SMR found for the Pt/Co bilayers with thick Co. Implementing the effect of the so-called interface magnetoresistance and the textured induced anisotropic scattering cannot account for the Co thickness dependent SMR. Since the large SMR is present for W/Co but its magnitude reduces in W/CoFeB, we infer that its origin is associated with a particular property of Co.

Quantum linear magnetoresistance in NbTe2

NASA Astrophysics Data System (ADS)

Chen, Hongxiang; Li, Zhilin; Fan, Xiao; Guo, Liwei; Chen, Xiaolong

2018-07-01

NbTe2 is a quasi-2D layered semimetal with charge density wave ground state showing a distorted-1T structure at room temperature. Here we report the anisotropic magneto-transport properties of NbTe2. An anomalous linear magnetoresistance up to 30% at 3 K in 9 T was observed, which can be well explained by a quantum linear magnetoresistance model. Our results reveal that a large quasi-2D Fermi surface and small Fermi pockets with linearly dispersive bands coexist in NbTe2. The comparison with the isostructural TaTe2 provides more information about the band structure evolution with charge density wave transitions in NbTe2 and TaTe2.

Switching from usual brand cigarettes to a tobacco-heating cigarette or snus: Part 2. Biomarkers of exposure

PubMed Central

Ogden, Michael W.; Marano, Kristin M.; Jones, Bobbette A.; Morgan, Walter T.; Stiles, Mitchell F.

2015-01-01

Abstract A randomized, multi-center study of adult cigarette smokers switched to tobacco-heating cigarettes, snus or ultra-low machine yield tobacco-burning cigarettes (50/group) was conducted, and subjects’ experience with the products was followed for 24 weeks. Differences in biomarkers of tobacco exposure between smokers and never smokers at baseline and among groups relative to each other and over time were assessed. Results indicated reduced exposure to many potentially harmful constituents found in cigarette smoke following product switching. Findings support differences in exposure from the use of various tobacco products and are relevant to the understanding of a risk continuum among tobacco products (ClinicalTrials.gov Identifier: NCT02061917). PMID:26554277

Enhanced spin-valve giant magneto-resistance in non-exchange biased sandwich films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, M; Cerjan, C; Law, B

2000-02-17

A large giant magnetoresistance (GMR) value of 7.5% has been measured in simple NiFeCo(1)/Cu/NiFeCo(2) sandwich films grown on a 30 {angstrom} Cr seed layer. This spin-valve GMR effect is consistent with the differential switching of the two NiFeCo layers due to an enhanced coercivity of the NiFeCo(1) layer grown on the Cr seed layer. A change in growth texture of the NiFeCo(1) layer from fcc (111) to bcc (110) crystallographic orientation leads to an increase in magnetic anisotropy and an enhancement in coercivity. The GMR value increases to 8.7% when a thin CoFe interfacial enhancing layer is incorporated. Further enhancementmore » in GMR values up to 14% is seen in the sandwich films by nano-oxide layer formation. The specular reflection at oxide/magnetic layer interface further extends the mean free path of spin-polarized electrons.« less

Domain wall magnetoresistance in BiFeO3 thin films measured by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Domingo, N.; Farokhipoor, S.; Santiso, J.; Noheda, B.; Catalan, G.

2017-08-01

We measure the magnetotransport properties of individual 71° domain walls in multiferroic BiFeO3 by means of conductive—atomic force microscopy (C-AFM) in the presence of magnetic fields up to one Tesla. The results suggest anisotropic magnetoresistance at room temperature, with the sign of the magnetoresistance depending on the relative orientation between the magnetic field and the domain wall plane. A consequence of this finding is that macroscopically averaged magnetoresistance measurements for domain wall bunches are likely to underestimate the magnetoresistance of each individual domain wall.

Dirac State in Giant Magnetoresistive Materials

NASA Astrophysics Data System (ADS)

Wu, Y.; Jo, N. H.; Ochi, M.; Huang, L.; Mou, D.; Kong, T.; Mun, E.; Wang, L.; Lee, Y.; Bud'Ko, S. L.; Canfield, P. C.; Trivedi, N.; Arito, R.; Kaminski, A.

We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of materials that recently were discovered to display titanic magnetoresistance. We find that that several of these materials have Dirac-like features in their band structure. In some materials those features are ``ordinary'' Dirac cones, while in others the linear Dirac dispersion of two crossing bands forms a linear object in 3D momentum space. Our observation poses an important question about the role of Dirac dispersion in the unusually high, non-saturating magnetoresistance of these materials. Research was supported by the US DOE, Office of Basic Energy Sciences under Contract No. DE-AC02-07CH11358; Gordon and Betty Moore Foundation EPiQS Initiative (Grant No. GBMF4411); CEM, a NSF MRSEC, under Grant No. DMR-1420451.

Thermal diodes, regulators, and switches: Physical mechanisms and potential applications

NASA Astrophysics Data System (ADS)

Wehmeyer, Geoff; Yabuki, Tomohide; Monachon, Christian; Wu, Junqiao; Dames, Chris

2017-12-01

Interest in new thermal diodes, regulators, and switches has been rapidly growing because these components have the potential for rich transport phenomena that cannot be achieved using traditional thermal resistors and capacitors. Each of these thermal components has a signature functionality: Thermal diodes can rectify heat currents, thermal regulators can maintain a desired temperature, and thermal switches can actively control the heat transfer. Here, we review the fundamental physical mechanisms of switchable and nonlinear heat transfer which have been harnessed to make thermal diodes, switches, and regulators. The review focuses on experimental demonstrations, mainly near room temperature, and spans the fields of heat conduction, convection, and radiation. We emphasize the changes in thermal properties across phase transitions and thermal switching using electric and magnetic fields. After surveying fundamental mechanisms, we present various nonlinear and active thermal circuits that are based on analogies with well-known electrical circuits, and analyze potential applications in solid-state refrigeration and waste heat scavenging.

Large linear magnetoresistance in topological crystalline insulator Pb{sub 0.6}Sn{sub 0.4}Te

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roychowdhury, Subhajit; Ghara, Somnath; Guin, Satya N.

2016-01-15

Classical magnetoresistance generally follows the quadratic dependence of the magnetic field at lower field and finally saturates when field is larger. Here, we report the large positive non-saturating linear magnetoresistance in topological crystalline insulator, Pb{sub 0.6}Sn{sub 0.4}Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. Magnetoresistance value as high as ∼200% was achieved at 3 K at magnetic field of 9 T. Linear magnetoresistance observed in Pb{sub 0.6}Sn{sub 0.4}Te is mainly governed by the spatial fluctuation carrier mobility due to distortions in the current paths in inhomogeneous conductor. - Graphical abstract: Largemore » non-saturating linear magnetoresistance has been evidenced in topological crystalline insulator, Pb{sub 0.6}Sn{sub 0.4}Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. - Highlights: • Large non-saturating linear magnetoresistance was achieved in the topological crystalline insulator, Pb{sub 0.6}Sn{sub 0.4}Te. • Highest magnetoresistance value as high as ~200% was achieved at 3 K at magnetic field of 9 T. • Linear magnetoresistance in Pb{sub 0.6}Sn{sub 0.4}Te is mainly governed by the spatial fluctuation of the carrier mobility.« less

Dynamic control of Hsf1 during heat shock by a chaperone switch and phosphorylation

PubMed Central

Zheng, Xu; Krakowiak, Joanna; Patel, Nikit; Beyzavi, Ali; Ezike, Jideofor; Khalil, Ahmad S; Pincus, David

2016-01-01

Heat shock factor (Hsf1) regulates the expression of molecular chaperones to maintain protein homeostasis. Despite its central role in stress resistance, disease and aging, the mechanisms that control Hsf1 activity remain unresolved. Here we show that in budding yeast, Hsf1 basally associates with the chaperone Hsp70 and this association is transiently disrupted by heat shock, providing the first evidence that a chaperone repressor directly regulates Hsf1 activity. We develop and experimentally validate a mathematical model of Hsf1 activation by heat shock in which unfolded proteins compete with Hsf1 for binding to Hsp70. Surprisingly, we find that Hsf1 phosphorylation, previously thought to be required for activation, in fact only positively tunes Hsf1 and does so without affecting Hsp70 binding. Our work reveals two uncoupled forms of regulation - an ON/OFF chaperone switch and a tunable phosphorylation gain - that allow Hsf1 to flexibly integrate signals from the proteostasis network and cell signaling pathways. DOI: http://dx.doi.org/10.7554/eLife.18638.001 PMID:27831465

Co/Cu multilayers with reduced magnetoresistive hysteresis

NASA Astrophysics Data System (ADS)

Kubinski, D. J.; Holloway, H.

1997-01-01

Practical applications of Co/Cu multilayers (MLs) require copper thicknesses either ≈ 9 Å or ≈ 20 Å corresponding to the first or second antiferromagnetic maximum (AFM). The first AFM has much smaller magnetoresistive hysteresis than the second, but also has lower sensitivity. We discuss application of these MLs when low hysteresis is required. For the first AFM we may improve the sensitivity while retaining low hysteresis by increasing the cobalt thickness to 30-40 Å. At the second AFM we can reduce the magnetoresistive hysteresis by reducing the cobalt thickness to ˜ 3 Å. A particularly attractive combination of high sensitivity and low hysteresis is obtained at the second AFM by alternating such very thin Co layers with 15 Å thick Co layers.

Magnetoresistance of a nanostep junction based on topological insulators

NASA Astrophysics Data System (ADS)

Hu, Wei; Hong, Jin-Bin; Zhai, Feng

2018-06-01

We investigate ballistic transport of helical electrons in a three-dimensional topological insulator traversing a nanostep junction. We find that a magnetic field perpendicular to its side surface shrinks the phase space for transmission, leading to magnetoresistance for the Fermi energy close to the Dirac point of the top surface. We also find transmission resonances and suppression of the Fano factor due to Landau-level-related quasibound states. The transmission blockade in the off-resonance case can result in a huge magnetoresistance for Fermi energy higher than the Dirac point of the side surface.

Active control of magnetoresistance of organic spin valves using ferroelectricity

PubMed Central

Sun, Dali; Fang, Mei; Xu, Xiaoshan; Jiang, Lu; Guo, Hangwen; Wang, Yanmei; Yang, Wenting; Yin, Lifeng; Snijders, Paul C.; Ward, T. Z.; Gai, Zheng; Zhang, X.-G.; Lee, Ho Nyung; Shen, Jian

2014-01-01

Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage, which is correlated with the polarization of the ferroelectric layer; the magnetoresistance even changes sign when the electric polarization of the ferroelectric layer is reversed. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves. PMID:25008155

Multiplex giant magnetoresistive biosensor microarrays identify interferon-associated autoantibodies in systemic lupus erythematosus

NASA Astrophysics Data System (ADS)

Lee, Jung-Rok; Haddon, D. James; Wand, Hannah E.; Price, Jordan V.; Diep, Vivian K.; Hall, Drew A.; Petri, Michelle; Baechler, Emily C.; Balboni, Imelda M.; Utz, Paul J.; Wang, Shan X.

2016-06-01

High titer, class-switched autoantibodies are a hallmark of systemic lupus erythematosus (SLE). Dysregulation of the interferon (IFN) pathway is observed in individuals with active SLE, although the association of specific autoantibodies with chemokine score, a combined measurement of three IFN-regulated chemokines, is not known. To identify autoantibodies associated with chemokine score, we developed giant magnetoresistive (GMR) biosensor microarrays, which allow the parallel measurement of multiple serum antibodies to autoantigens and peptides. We used the microarrays to analyze serum samples from SLE patients and found individuals with high chemokine scores had significantly greater reactivity to 13 autoantigens than individuals with low chemokine scores. Our findings demonstrate that multiple autoantibodies, including antibodies to U1-70K and modified histone H2B tails, are associated with IFN dysregulation in SLE. Further, they show the microarrays are capable of identifying autoantibodies associated with relevant clinical manifestations of SLE, with potential for use as biomarkers in clinical practice.

Advances in Explosively Formed Fuse Opening Switches

DTIC Science & Technology

1987-06-01

ADVANCES IN EXPLOSIVELY FORMED FUSE OPENING SWITCHES* J. H. Goforth, R. S. Caird, A. E. Greene, I. R. Lindemuth, S. P. Marsh, H. Oona, and R. E...conductor into a series of thin sections. Augmented by an undetermined amount of heating due to the extrusion process, Joule heating in the thin...with initial field fed directly into the generator by a capacitor bank. As described in Ref. 2, these tests demonstrated that the switch would

Lateral electric-field control of giant magnetoresistance in Co/Cu/Fe/BaTiO{sub 3} multiferroic heterostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Savitha Pillai, S.; Kojima, H.; Itoh, M.

2015-08-17

We report lateral electric-field-driven sizable changes in the magnetoresistance of Co/Cu/Fe tri-layered wires on BaTiO{sub 3} single crystal. While the observed change is marginal in the tetragonal phase of BaTiO{sub 3}, it reaches over 40% in the orthorhombic and rhombohedral phases with an electric field of 66 kV/cm. We attribute it to possible electric-field-induced variations of the spin-dependent electronic structures, i.e., spin polarization, of the Fe via interfacial strain transfer from BaTiO{sub 3}. The contrasting results for the different phases of BaTiO{sub 3} are discussed, associated with the distinct aspects of the ferroelectric polarization switching processes in each phase.

EDITORIAL: Molecular switches at surfaces Molecular switches at surfaces

NASA Astrophysics Data System (ADS)

Weinelt, Martin; von Oppen, Felix

2012-10-01

In nature, molecules exploit interaction with their environment to realize complex functionalities on the nanometer length scale. Physical, chemical and/or biological specificity is frequently achieved by the switching of molecules between microscopically different states. Paradigmatic examples are the energy production in proton pumps of bacteria or the signal conversion in human vision, which rely on switching molecules between different configurations or conformations by external stimuli. The remarkable reproducibility and unparalleled fatigue resistance of these natural processes makes it highly desirable to emulate nature and develop artificial systems with molecular functionalities. A promising avenue towards this goal is to anchor the molecular switches at surfaces, offering new pathways to control their functional properties, to apply electrical contacts, or to integrate switches into larger systems. Anchoring at surfaces allows one to access the full range from individual molecular switches to self-assembled monolayers of well-defined geometry and to customize the coupling between molecules and substrate or between adsorbed molecules. Progress in this field requires both synthesis and preparation of appropriate molecular systems and control over suitable external stimuli, such as light, heat, or electrical currents. To optimize switching and generate function, it is essential to unravel the geometric structure, the electronic properties and the dynamic interactions of the molecular switches on surfaces. This special section, Molecular Switches at Surfaces, collects 17 contributions describing different aspects of this research field. They analyze elementary processes, both in single molecules and in ensembles of molecules, which involve molecular switching and concomitant changes of optical, electronic, or magnetic properties. Two topical reviews summarize the current status, including both challenges and achievements in the field of molecular switches on

Tunnelling magnetoresistance and 1/f noise in phase-separated manganites

NASA Astrophysics Data System (ADS)

Sboychakov, A. O.; Rakhmanov, A. L.; Kugel, K. I.; Kagan, M. Yu; Brodsky, I. V.

2003-03-01

The magnetoresistance and the noise power of non-metallic phase-separated manganites are studied. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in an insulating matrix. The concentration of metallic phase is assumed to be far from the percolation threshold. The electron tunnelling between ferrons causes the charge transfer in such a system. The magnetoresistance is determined both by the increase in the volume of the metallic phase and by the change in the electron hopping probability. In the framework of such a model, the low-field magnetoresistance is proportional to H2 and decreases with temperature as T-n, where n can vary from 1 to 5, depending on the parameters of the system. In the high-field limit, the tunnelling magnetoresistance grows exponentially. Different mechanisms of the voltage fluctuations in the system are analysed. The noise spectrum generated by the fluctuations of the number of droplets with extra electrons has a 1/f form over a wide frequency range. In the case of strong magnetic anisotropy, the 1/f noise can also arise due to fluctuations of the magnetic moments of ferrons. The 1/f noise power depends only slightly on the magnetic field in the low field range whereas it can increase as H6 in the high-field limit.

Analysis of the Distribution of Magnetic Fluid inside Tumors by a Giant Magnetoresistance Probe

PubMed Central

Gooneratne, Chinthaka P.; Kurnicki, Adam; Yamada, Sotoshi; Mukhopadhyay, Subhas C.; Kosel, Jürgen

2013-01-01

Magnetic fluid hyperthermia (MFH) therapy uses the magnetic component of electromagnetic fields in the radiofrequency spectrum to couple energy to magnetic nanoparticles inside tumors. In MFH therapy, magnetic fluid is injected into tumors and an alternating current (AC) magnetic flux is applied to heat the magnetic fluid- filled tumor. If the temperature can be maintained at the therapeutic threshold of 42°C for 30 minutes or more, the tumor cells can be destroyed. Analyzing the distribution of the magnetic fluid injected into tumors prior to the heating step in MFH therapy is an essential criterion for homogenous heating of tumors, since a decision can then be taken on the strength and localization of the applied external AC magnetic flux density needed to destroy the tumor without affecting healthy cells. This paper proposes a methodology for analyzing the distribution of magnetic fluid in a tumor by a specifically designed giant magnetoresistance (GMR) probe prior to MFH heat treatment. Experimental results analyzing the distribution of magnetic fluid suggest that different magnetic fluid weight densities could be estimated inside a single tumor by the GMR probe. PMID:24312280

Selenium bond decreases ON resistance of light-activated switch

NASA Technical Reports Server (NTRS)

1965-01-01

Vitrified amorphous selenium bond decreases the ON resistance of a gallium arsenide-silicon light-activated, low-level switch. The switch is used under a pulse condition to prolong switch life and minimize errors due to heating, devitrification, and overdrawing.

Model for large magnetoresistance effect in p–n junctions

NASA Astrophysics Data System (ADS)

Cao, Yang; Yang, Dezheng; Si, Mingsu; Shi, Huigang; Xue, Desheng

2018-06-01

We present a simple model based on the classic Shockley model to explain the magnetotransport in nonmagnetic p–n junctions. Under a magnetic field, the evaluation of the carrier to compensate Lorentz force establishes the necessary space-charge region distribution. The calculated current–voltage (I–V) characteristics under various magnetic fields demonstrate that the conventional nonmagnetic p–n junction can exhibit an extremely large magnetoresistance effect, which is even larger than that in magnetic materials. Because the large magnetoresistance effect that we discussed is based on the conventional p–n junction device, our model provides new insight into the development of semiconductor magnetoelectronics.

Spin-orbit torque induced magnetization switching in Ta/Co{sub 20}Fe{sub 60}B{sub 20}/MgO structures under small in-plane magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Jiangwei, E-mail: caojw@lzu.edu.cn; Zheng, Yuqiang; Su, Xianpeng

2016-04-25

Spin-orbit torque (SOT)-induced magnetization switching under small in-plane magnetic fields in as-deposited and annealed Ta/CoFeB/MgO structures is studied. For the as-deposited samples, partial SOT-induced switching behavior is observed under an in-plane field of less than 100 Oe. Conversely, for the annealed samples, an in-plane field of 10 Oe is large enough to achieve full deterministic magnetization switching. The Dzyaloshinskii-Moriya interaction at the Ta/CoFeB interface is believed to be the main reason for the discrepancy of the requisite in-plane magnetic fields for switching in the as-deposited and annealed samples. In addition, asymmetric field dependence behavior of SOT-induced magnetization switching is observed in themore » annealed samples. Deterministic magnetization switching in the absence of an external magnetic field is obtained in the annealed samples, which is extremely important to develop SOT-based magnetoresistive random access memory.« less

Tunneling magnetoresistance sensor with pT level 1/f magnetic noise

NASA Astrophysics Data System (ADS)

Deak, James G.; Zhou, Zhimin; Shen, Weifeng

2017-05-01

Magnetoresistive devices are important components in a large number of commercial electronic products in a wide range of applications including industrial position sensors, automotive sensors, hard disk read heads, cell phone compasses, and solid state memories. These devices are commonly based on anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), but over the past few years tunneling magnetoresistance (TMR) has been emerging in more applications. Here we focus on recent work that has enabled the development of TMR magnetic field sensors with 1/f noise of less than 100 pT/rtHz at 1 Hz. Of the commercially available sensors, the lowest noise devices have typically been AMR, but they generally have the largest die size. Based on this observation and modeling of experimental data size and geometry dependence, we find that there is an optimal design rule that produces minimum 1/f noise. This design rule requires maximizing the areal coverage of an on-chip flux concentrator, providing it with a minimum possible total gap width, and tightly packing the gaps with MTJ elements, which increases the effective volume and decreases the saturation field of the MTJ freelayers. When properly optimized using this rule, these sensors have noise below 60 pT/rtHz, and could possibly replace fluxgate magnetometers in some applications.

Nonmonotonic magnetoresistance of a two-dimensional viscous electron-hole fluid in a confined geometry

NASA Astrophysics Data System (ADS)

Alekseev, P. S.; Dmitriev, A. P.; Gornyi, I. V.; Kachorovskii, V. Yu.; Narozhny, B. N.; Titov, M.

2018-02-01

Ultrapure conductors may exhibit hydrodynamic transport where the collective motion of charge carriers resembles the flow of a viscous fluid. In a confined geometry (e.g., in ultra-high-quality nanostructures), the electronic fluid assumes a Poiseuille-type flow. Applying an external magnetic field tends to diminish viscous effects leading to large negative magnetoresistance. In two-component systems near charge neutrality, the hydrodynamic flow of charge carriers is strongly affected by the mutual friction between the two constituents. At low fields, the magnetoresistance is negative, however, at high fields the interplay between electron-hole scattering, recombination, and viscosity results in a dramatic change of the flow profile: the magnetoresistance changes its sign and eventually becomes linear in very high fields. This nonmonotonic magnetoresistance can be used as a fingerprint to detect viscous flow in two-component conducting systems.

Comparative study of microwave radiation-induced magnetoresistive oscillations induced by circularly- and linearly- polarized photo-excitation

PubMed Central

Ye, Tianyu; Liu, Han-Chun; Wang, Zhuo; Wegscheider, W.; Mani, Ramesh G.

2015-01-01

A comparative study of the radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs heterostructure two dimensional electron system (2DES) under linearly- and circularly- polarized microwave excitation indicates a profound difference in the response observed upon rotating the microwave launcher for the two cases, although circularly polarized microwave radiation induced magnetoresistance oscillations observed at low magnetic fields are similar to the oscillations observed with linearly polarized radiation. For the linearly polarized radiation, the magnetoresistive response is a strong sinusoidal function of the launcher rotation (or linear polarization) angle, θ. For circularly polarized radiation, the oscillatory magnetoresistive response is hardly sensitive to θ. PMID:26450679

Comparative study of microwave radiation-induced magnetoresistive oscillations induced by circularly- and linearly- polarized photo-excitation.

PubMed

Ye, Tianyu; Liu, Han-Chun; Wang, Zhuo; Wegscheider, W; Mani, Ramesh G

2015-10-09

A comparative study of the radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs heterostructure two dimensional electron system (2DES) under linearly- and circularly- polarized microwave excitation indicates a profound difference in the response observed upon rotating the microwave launcher for the two cases, although circularly polarized microwave radiation induced magnetoresistance oscillations observed at low magnetic fields are similar to the oscillations observed with linearly polarized radiation. For the linearly polarized radiation, the magnetoresistive response is a strong sinusoidal function of the launcher rotation (or linear polarization) angle, θ. For circularly polarized radiation, the oscillatory magnetoresistive response is hardly sensitive to θ.

Detection of magnetic resonance signals using a magnetoresistive sensor

DOEpatents

Budker, Dmitry; Pines, Alexander; Xu, Shoujun; Hilty, Christian; Ledbetter, Micah P; Bouchard, Louis S

2013-10-01

A method and apparatus are described wherein a micro sample of a fluidic material may be assayed without sample contamination using NMR techniques, in combination with magnetoresistive sensors. The fluidic material to be assayed is first subject to pre-polarization, in one embodiment, by passage through a magnetic field. The magnetization of the fluidic material is then subject to an encoding process, in one embodiment an rf-induced inversion by passage through an adiabatic fast-passage module. Thereafter, the changes in magnetization are detected by a pair of solid-state magnetoresistive sensors arranged in gradiometer mode. Miniaturization is afforded by the close spacing of the various modules.

Giant anisotropic magnetoresistance and planar Hall effect in the Dirac semimetal Cd3As2

NASA Astrophysics Data System (ADS)

Li, Hui; Wang, Huan-Wen; He, Hongtao; Wang, Jiannong; Shen, Shun-Qing

2018-05-01

Anisotropic magnetoresistance is the change tendency of resistance of a material on the mutual orientation of the electric current and the external magnetic field. Here, we report experimental observations in the Dirac semimetal Cd3As2 of giant anisotropic magnetoresistance and its transverse version, called the planar Hall effect. The relative anisotropic magnetoresistance is negative and up to -68% at 2 K and 10 T. The high anisotropy and the minus sign in this isotropic and nonmagnetic material are attributed to a field-dependent current along the magnetic field, which may be induced by the Berry curvature of the band structure. This observation not only reveals unusual physical phenomena in Weyl and Dirac semimetals, but also finds additional transport signatures of Weyl and Dirac fermions other than negative magnetoresistance.

Comparative study of microwave radiation-induced magnetoresistive oscillations induced by circularly- and linearly- polarized photo-excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Tianyu; Liu, Han -Chun; Wang, Zhuo

A comparative study of the radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs heterostructure two dimensional electron system (2DES) under linearly- and circularly- polarized microwave excitation indicates a profound difference in the response observed upon rotating the microwave launcher for the two cases, although circularly polarized microwave radiation induced magnetoresistance oscillations observed at low magnetic fields are similar to the oscillations observed with linearly polarized radiation. For the linearly polarized radiation, the magnetoresistive response is a strong sinusoidal function of the launcher rotation (or linear polarization) angle, θ. As a result, for circularly polarized radiation, the oscillatory magnetoresistive response ismore » hardly sensitive to θ.« less

Comparative study of microwave radiation-induced magnetoresistive oscillations induced by circularly- and linearly- polarized photo-excitation

DOE PAGES

Ye, Tianyu; Liu, Han -Chun; Wang, Zhuo; ...

2015-10-09

A comparative study of the radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs heterostructure two dimensional electron system (2DES) under linearly- and circularly- polarized microwave excitation indicates a profound difference in the response observed upon rotating the microwave launcher for the two cases, although circularly polarized microwave radiation induced magnetoresistance oscillations observed at low magnetic fields are similar to the oscillations observed with linearly polarized radiation. For the linearly polarized radiation, the magnetoresistive response is a strong sinusoidal function of the launcher rotation (or linear polarization) angle, θ. As a result, for circularly polarized radiation, the oscillatory magnetoresistive response ismore » hardly sensitive to θ.« less

Large negative magnetoresistance of a nearly Dirac material: Layered antimonide EuMnS b2

NASA Astrophysics Data System (ADS)

Yi, Changjiang; Yang, Shuai; Yang, Meng; Wang, Le; Matsushita, Yoshitaka; Miao, Shanshan; Jiao, Yuanyuan; Cheng, Jinguang; Li, Yongqing; Yamaura, Kazunari; Shi, Youguo; Luo, Jianlin

2017-11-01

Single crystals of EuMnS b2 were successfully grown and their structural and electronic properties were investigated systematically. The material crystallizes in an orthorhombic-layered structure (space group: Pnma, No. 62) comprising a periodic sequence of -MnSb/Eu/Sb/Eu/- layers (˜1 nm in thickness), and massless fermions are expected to emerge in the Sb layer, by analogy of the candidate Dirac materials EuMnB i2 and A Mn P n2 (A =Ca or Sr or Ba, P n =Sb or Bi). The magnetic and specific heat measurements of EuMnS b2 suggest an antiferromagnetic ordering of Eu moments near 20 K. A characteristic hump appears in the temperature-dependent electrical resistivity curve at ˜25 K . A spin-flop transition of Eu moments with an onset magnetic field of ˜15 kOe (at 2 K) was observed. Interestingly, EuMnS b2 shows a negative magnetoresistance (up to -95 % ) in contrast to the positive magnetoresistances observed for EuMnB i2 and A Mn P n2 (A =Ca or Sr or Ba, P n =Sb or Bi), providing a unique opportunity to study the correlation between electronic and magnetic properties in this class of materials.

Complementary resistive switching in BaTiO3/NiO bilayer with opposite switching polarities

NASA Astrophysics Data System (ADS)

Li, Shuo; Wei, Xianhua; Lei, Yao; Yuan, Xincai; Zeng, Huizhong

2016-12-01

Resistive switching behaviors have been investigated in the Au/BaTiO3/NiO/Pt structure by stacking the two elements with different switching types. The conducting atomic force microscope measurements on BaTiO3 thin films and NiO thin films suggest that with the same active resistive switching region, the switching polarities in the two semiconductors are opposite to each other. It is in agreement with the bipolar hysteresis I-V curves with opposite switching polarities for single-layer devices. The bilayer devices show complementary resistive switching (CRS) without electroforming and unipolar resistive switching (URS) after electroforming. The coexistence of CRS and URS is mainly ascribed to the co-effect of electric field and Joule heating mechanisms, indicating that changeable of resistance in this device is dominated by the redistribution of oxygen vacancies in BaTiO3 and the formation, disruption, restoration of conducting filaments in NiO. CRS in bilayer with opposite switching polarities is effective to solve the sneak current without the introduction of any selector elements or an additional metal electrode.

The origin of dispersion of magnetoresistance of a domain wall spin valve

NASA Astrophysics Data System (ADS)

Sato, Jun; Matsushita, Katsuyoshi; Imamura, Hiroshi

2010-01-01

We theoretically study the current-perpendicular-to-plane magnetoresistance of a domain wall confined in a nanocontact which is experimentally fabricated as current-confined-path (CCP) structure in a nano-oxide-layer (NOL). We solve the non-collinear spin diffusion equation by using the finite element method and calculate the MR ratio by evaluating the additional voltage drop due to the spin accumulation. We investigate the origin of dispersion of magnetoresistance by considering the effect of randomness of the size and distribution of the nanocontacts in the NOL. It is observed that the effect of randomness of the contact size is much larger than that of the contact distribution. Our results suggest that the origin of dispersion of magnetoresistance observed in the experiments is the randomness of the size of the nanocontacts in the NOL.

Anomalies of magnetoresistance of compounds with atomic clusters RB{sub 12} (R = Ho, Er, Tm, Lu)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sluchanko, N. E., E-mail: nes@lt.gpi.ru; Bogach, A. V.; Glushkov, V. V.

2009-04-15

The magnetoresistance and magnetization of single-crystal samples of rare-earth dodecaborides RB{sub 12} (R = Ho, Er, Tm, Lu) have been measured at low temperatures (1.8-35 K) in a magnetic field of up to 70 kOe. The effect of positive magnetoresistance that obeys the Kohler's rule {delta}{rho}/{rho} = f({rho}(0, 300 K)H/{rho}(0, T)) is observed for the nonmagnetic metal LuB{sub 12}. In the magnetic dodecaborides HoB{sub 12}, ErB{sub 12}, and TmB{sub 12}, three characteristic regimes of the magnetoresistance behavior have been revealed: the positive magnetoresistance effect similar to the case of LuB{sub 12} is observed at T > 25 K; in themore » range T{sub N} {<=} T {<=} 15 K, the magnetoresistance becomes negative and depends quadratically on the external magnetic field; and, finally, upon the transition to the antiferromagnetic phase (T < T{sub N}), the positive magnetoresistance is again observed and its amplitude reaches 150% for HoB{sub 12}. It has been shown that the observed anomalies of negative magnetoresistance in the paramagnetic phase can be explained within the Yosida model of conduction electron scattering by localized magnetic moments. The performed analysis confirms the formation of spin-polaron states in the 5d band in the vicinity of rare-earth ions in paramagnetic and magnetically ordered phases of RB{sub 12} and makes it possible to reveal a number of specific features in the transformation of the magnetic structure of the compounds under investigation.« less

Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS.

PubMed

Ali, Mazhar N; Schoop, Leslie M; Garg, Chirag; Lippmann, Judith M; Lara, Erik; Lotsch, Bettina; Parkin, Stuart S P

2016-12-01

Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual "butterfly"-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 10 5 percent at 9 T and 2 K at a 45° angle between the applied current ( I || a ) and the applied field (90° is H || c ). Approaching 90°, a "dip" is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states.

Tuning spin transport properties and molecular magnetoresistance through contact geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulman, Kanchan; Narasimhan, Shobhana; Sheikh Saqr Laboratory, ICMS, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064

2014-01-28

Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips thanmore » to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its “closed” and “open” conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of ∼5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by ∼400%.« less

Tuning spin transport properties and molecular magnetoresistance through contact geometry

NASA Astrophysics Data System (ADS)

Ulman, Kanchan; Narasimhan, Shobhana; Delin, Anna

2014-01-01

Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips than to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its "closed" and "open" conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of ˜5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by ˜400%.

Magneto-Resistance in thin film boron carbides

NASA Astrophysics Data System (ADS)

Echeverria, Elena; Luo, Guangfu; Liu, J.; Mei, Wai-Ning; Pasquale, F. L.; Colon Santanta, J.; Dowben, P. A.; Zhang, Le; Kelber, J. A.

2013-03-01

Chromium doped semiconducting boron carbide devices were fabricated based on a carborane icosahedra (B10C2H12) precursor via plasma enhanced chemical vapor deposition, and the transition metal atoms found to dope pairwise on adjacent icosahedra site locations. Models spin-polarized electronic structure calculations of the doped semiconducting boron carbides indicate that some transition metal (such as Cr) doped semiconducting boron carbides may act as excellent spin filters when used as the dielectric barrier in a magnetic tunnel junction structure. In the case of chromium doping, there may be considerable enhancements in the magneto-resistance of the heterostructure. To this end, current to voltage curves and magneto-transport measurements were performed in various semiconducting boron carbide both in and out plane. The I-V curves as a function of external magnetic field exhibit strong magnetoresistive effects which are enhanced at liquid Nitrogen temperatures. The mechanism for these effects will be discussed in the context of theoretical calculations.

Enhancement of magnetoresistance by hydrogen ion treatment for current-perpendicular-to-plane giant magnetoresistive films with a current-confined-path nano-oxide layer

NASA Astrophysics Data System (ADS)

Yuasa, H.; Hara, M.; Murakami, S.; Fuji, Y.; Fukuzawa, H.; Zhang, K.; Li, M.; Schreck, E.; Wang, P.; Chen, M.

2010-09-01

We have enhanced magnetoresistance (MR) for current-perpendicular-to-plane giant-magnetoresistive (CPP-GMR) films with a current-confined-path nano-oxide layer (CCP-NOL). In order to realize higher purity in Cu for CCPs, hydrogen ion treatment (HIT) was applied as the CuOx reduction process. By applying the HIT process, an MR ratio was increased to 27.4% even in the case of using conventional FeCo magnetic layer, from 13.0% for a reference without the HIT process. Atom probe tomography data confirmed oxygen reduction by the HIT process in the CCP-NOL. The relationship between oxygen counts and MR ratio indicates that further oxygen reduction would realize an MR ratio greater than 50%.

Current-driven thermo-magnetic switching in magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Kravets, A. F.; Polishchuk, D. M.; Pashchenko, V. A.; Tovstolytkin, A. I.; Korenivski, V.

2017-12-01

We investigate switching of magnetic tunnel junctions (MTJs) driven by the thermal effect of the transport current through the junctions. The switching occurs in a specially designed composite free layer, which acts as one of the MTJ electrodes, and is due to a current-driven ferro-to-paramagnetic Curie transition with the associated exchange decoupling within the free layer leading to magnetic reversal. We simulate the current and heat propagation through the device and show how heat focusing can be used to improve the power efficiency. The Curie-switch MTJ demonstrated in this work has the advantage of being highly tunable in terms of its operating temperature range, conveniently to or just above room temperature, which can be of technological significance and competitive with the known switching methods using spin-transfer torques.

Switching dynamics of TaOx-based threshold switching devices

NASA Astrophysics Data System (ADS)

Goodwill, Jonathan M.; Gala, Darshil K.; Bain, James A.; Skowronski, Marek

2018-03-01

Bi-stable volatile switching devices are being used as access devices in solid-state memory arrays and as the active part of compact oscillators. Such structures exhibit two stable states of resistance and switch between them at a critical value of voltage or current. A typical resistance transient under a constant amplitude voltage pulse starts with a slow decrease followed by a rapid drop and leveling off at a low steady state value. This behavior prompted the interpretation of initial delay and fast transition as due to two different processes. Here, we show that the entire transient including incubation time, transition time, and the final resistance values in TaOx-based switching can be explained by one process, namely, Joule heating with the rapid transition due to the thermal runaway. The time, which is required for the device in the conducting state to relax back to the stable high resistance one, is also consistent with the proposed mechanism.

Automatic thermal control switches. [for use in Space Shuttle borne Get Away Special container

NASA Technical Reports Server (NTRS)

Wing, L. D.

1982-01-01

Two automatic, flexible connection thermal control switches have been designed and tested in a thermal vacuum facility and in the Get Away Special (GAS) container flown on the third Shuttle flight. The switches are complementary in that one switch passes heat when the plate on which it is mounted exceeds some selected temperature and the other switch will pass heat only when the mounting plate temperature is below the selected value. Both switches are driven and controlled by phase-change capsule motors and require no other power source or thermal sensors.

Active Radiative Thermal Switching with Graphene Plasmon Resonators.

PubMed

Ilic, Ognjen; Thomas, Nathan H; Christensen, Thomas; Sherrott, Michelle C; Soljačić, Marin; Minnich, Austin J; Miller, Owen D; Atwater, Harry A

2018-03-27

We theoretically demonstrate a near-field radiative thermal switch based on thermally excited surface plasmons in graphene resonators. The high tunability of graphene enables substantial modulation of near-field radiative heat transfer, which, when combined with the use of resonant structures, overcomes the intrinsically broadband nature of thermal radiation. In canonical geometries, we use nonlinear optimization to show that stacked graphene sheets offer improved heat conductance contrast between "ON" and "OFF" switching states and that a >10× higher modulation is achieved between isolated graphene resonators than for parallel graphene sheets. In all cases, we find that carrier mobility is a crucial parameter for the performance of a radiative thermal switch. Furthermore, we derive shape-agnostic analytical approximations for the resonant heat transfer that provide general scaling laws and allow for direct comparison between different resonator geometries dominated by a single mode. The presented scheme is relevant for active thermal management and energy harvesting as well as probing excited-state dynamics at the nanoscale.

A Magnetoresistive Tactile Sensor for Harsh Environment Applications

PubMed Central

Alfadhel, Ahmed; Khan, Mohammed Asadullah; Cardoso, Susana; Leitao, Diana; Kosel, Jürgen

2016-01-01

A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature. PMID:27164113

Magnetoresistance in organic semiconductors: Including pair correlations in the kinetic equations for hopping transport

NASA Astrophysics Data System (ADS)

Shumilin, A. V.; Kabanov, V. V.; Dediu, V. I.

2018-03-01

We derive kinetic equations for polaron hopping in organic materials that explicitly take into account the double occupation possibility and pair intersite correlations. The equations include simplified phenomenological spin dynamics and provide a self-consistent framework for the description of the bipolaron mechanism of the organic magnetoresistance. At low applied voltages, the equations can be reduced to those for an effective resistor network that generalizes the Miller-Abrahams network and includes the effect of spin relaxation on the system resistivity. Our theory discloses the close relationship between the organic magnetoresistance and the intersite correlations. Moreover, in the absence of correlations, as in an ordered system with zero Hubbard energy, the magnetoresistance vanishes.

Multilevel resistance switching effect in Au/La2/3Ba1/3MnO3/Pt heterostructure manipulated by external fields

NASA Astrophysics Data System (ADS)

Wen, Jiahong; Zhao, Xiaoyu; Li, Qian; Zhang, Sheng; Wang, Dunhui; Du, Youwei

2018-04-01

Multilevel resistance switching (RS) effect has attracted more and more attention due to its promising potential for the increase of storage density in memory devices. In this work, the transport properties are investigated in an Au/La2/3Ba1/3MnO3 (LBMO)/Pt heterostructure. Taking advantage of the strong interplay among the spin, charge, orbital and lattice of LBMO, the Au/LBMO/Pt device can exhibit bipolar RS effect and magnetoresistance effect simultaneously. Under the coaction of electric field and magnetic field, four different resistance states are achieved in this device. These resistance states show excellent repeatability and retentivity and can be switched between any two states, which suggest the potential applications in the multilevel RS memory devices with enhanced storage density.

Intelligent switches of integrated lightwave circuits with core telecommunication functions

NASA Astrophysics Data System (ADS)

Izhaky, Nahum; Duer, Reuven; Berns, Neil; Tal, Eran; Vinikman, Shirly; Schoenwald, Jeffrey S.; Shani, Yosi

2001-05-01

We present a brief overview of a promising switching technology based on Silica on Silicon thermo-optic integrated circuits. This is basically a 2D solid-state optical device capable of non-blocking switching operation. Except of its excellent performance (insertion loss<5dB, switching time<2ms...), the switch enables additional important build-in functionalities. It enables single-to- single channel switching and single-to-multiple channel multicasting/broadcasting. In addition, it has the capability of channel weighting and variable output power control (attenuation), for instance, to equalize signal levels and compensate for unbalanced different optical input powers, or to equalize unbalanced EDFA gain curve. We examine the market segments appropriate for the switch size and technology, followed by a discussion of the basic features of the technology. The discussion is focused on important requirements from the switch and the technology (e.g., insertion loss, power consumption, channel isolation, extinction ratio, switching time, and heat dissipation). The mechanical design is also considered. It must take into account integration of optical fiber, optical planar wafer, analog electronics and digital microprocessor controls, embedded software, and heating power dissipation. The Lynx Photon.8x8 switch is compared to competing technologies, in terms of typical market performance requirements.

Magnetoresistance of oxygen concentration-modulated Co-Ti-O films

NASA Astrophysics Data System (ADS)

Nakano, Masatoshi; Wan, Fuxing; Wang, Jian; Sannomiya, Takumi; Muraishi, Shinji; Harumoto, Takashi; Nakamura, Yoshio; Shi, Ji

2018-06-01

Co-Ti-O films have been prepared by a sputtering method in an Ar- and O2-mixed atmosphere. The O2 flow rate was modulated during the deposition to optimize the oxygen concentration and the microstructure of the films. For the as-deposited film, negligible magnetization and magnetoresistance (MR) were observed. The structure of the layers with lower O2 flow rate is basically amorphous alloy with Ti-O and Co-Ti bonds. On the other hand, in the layers with high O2 flow rate, both Ti and Co are oxidized. Upon thermal annealing in a vacuum, significant enhancements in both magnetization and MR in Co-Ti-O films were observed. It is found that granular structure of Co particles embedded in insulating TiO2 matrix is formed due to the oxygen diffusion and further oxidization of Ti as a result of the heat treatment. The significantly enhanced magnetization and MR ratio have been ascribed to the formation of nano-sized Co particles and the tunneling conduction between these Co particles across the TiO2 interlayers, respectively.

Evaluation of Biomarkers of Exposure in Smokers Switching to a Carbon-Heated Tobacco Product: A Controlled, Randomized, Open-Label 5-Day Exposure Study

PubMed Central

Haziza, Christelle; Weitkunat, Rolf; Magnette, John

2016-01-01

Introduction: Tobacco harm reduction aims to provide reduced risk alternatives to adult smokers who would otherwise continue smoking combustible cigarettes (CCs). This randomized, open-label, three-arm, parallel-group, single-center, short-term confinement study aimed to investigate the effects of exposure to selected harmful and potentially harmful constituents (HPHCs) of cigarette smoke in adult smokers who switched to a carbon-heated tobacco product (CHTP) compared with adult smokers who continued to smoke CCs and those who abstained from smoking for 5 days. Methods: Biomarkers of exposure to HPHCs, including nicotine and urinary excretion of mutagenic material, were measured in 24-hour urine and blood samples in 112 male and female Caucasian smokers switching from CCs to the CHTP ad libitum use. Puffing topography was assessed during product use. Results: Switching to the CHTP or smoking abstinence (SA) resulted in marked decreases from baseline to Day 5 in all biomarkers of exposure measured, including carboxyhemoglobin (43% and 55% decrease in the CHTP and SA groups, respectively). The urinary excretion of mutagenic material was also markedly decreased on Day 5 compared with baseline (89% and 87% decrease in the CHTP and SA groups, respectively). No changes in biomarkers of exposure to HPHCs or urinary mutagenic material were observed between baseline and Day 5 in the CC group. Conclusions: Our results provide clear evidence supporting a reduction in the level of exposure to HPHCs of tobacco smoke in smokers who switch to CHTP under controlled conditions, similar to that observed in SA. Implications: The reductions observed in biomarkers of exposure to HPHCs of tobacco smoke in this short-term study could potentially also reduce the incidence of cancer, cardiovascular and respiratory diseases in those smokers who switch to a heated tobacco product. PMID:26817490

Fast and low power Michelson interferometer thermo-optical switch on SOI.

PubMed

Song, Junfeng; Fang, Q; Tao, S H; Liow, T Y; Yu, M B; Lo, G Q; Kwong, D L

2008-09-29

We designed and fabricated silicon-on-insulator based Michelson interferometer (MI) thermo-optical switches with deep etched trenches for heat-isolation. Switch power was reduced approximately 20% for the switch with deep etched trenches, and the MI saved approximately 50% power than that of the Mach-Zehnder interferometer. 10.6 mW switch power, approximately 42 micros switch time for the MI with deep trenches, 13.14 mW switch power and approximately 34 micros switch time for the MI without deep trenches were achieved.

Angular Magnetoresistance and Hall Measurements in New Dirac Material, ZrSiS

NASA Astrophysics Data System (ADS)

Ali, Mazhar; Schoop, Leslie; Lotsch, Bettina; Parkin, Stuart

Dirac and Weyl materials have shot to the forefront of condensed matter research in the last few years. Recently, the square-net material, ZrSiS, was theorized and experimentally shown (via ARPES) to host several highly dispersive Dirac cones, including the first Dirac cone demanded by non-symmorphic symmetry in a Si square net. Here we report the magnetoresistance and Hall Effect measurements in this compound. ZrSiS samples with RRR = 40 were found to have MR values up to 6000% at 2 K, be predominantly p-type with a carrier concentration of ~8 x 1019 cm-3 and mobility ~8500 cm2/Vs. Angular magnetoresistance measurements reveal a peculiar behavior with multiple local maxima, depending on field strength, indicating of a sensitive and sensitive Fermi surface. SdH oscillations analysis confirms Hall and angular magnetoresistance measurements. These results, in the context of the theoretical and ARPES results, will be discussed.

Magnetization reversal in exchange biased Co/CoO probed with anisotropic magnetoresistance

NASA Astrophysics Data System (ADS)

Gredig, Thomas; Krivorotov, Ilya N.; Dahlberg, E. Dan

2002-05-01

The magnetization reversal in exchange coupled polycrystalline Co/CoO bilayers has been investigated as a function of CoO thickness using anisotropic magnetoresistance as a probe. The anisotropic magnetoresistance (AMR) was measured during the magnetization reversal and it was used to determine the orientation of the magnetization. For thin CoO layers large training effects were present; ergo the first hysteresis loop after field cooling was not the same as the second. The magnitude of the observed training was found to decrease with increasing CoO thickness. In the samples where substantial training was observed, the first magnetization reversal was dominated by nucleation of reversed domains. For the reversal from the antiparallel state back to the parallel direction, the AMR is consistent with a rotation process. In thicker CoO films where the training was less, the asymmetry was drastically reduced. A simple model that couples the antiferromagnetic grains to the ferromagnetic layer simulates qualitatively the observed magnetoresistance.

Fractional Modeling of the AC Large-Signal Frequency Response in Magnetoresistive Current Sensors

PubMed Central

Arias, Sergio Iván Ravello; Muñoz, Diego Ramírez; Moreno, Jaime Sánchez; Cardoso, Susana; Ferreira, Ricardo; de Freitas, Paulo Jorge Peixeiro

2013-01-01

Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function Zt(if) is obtained considering it as the relationship between sensor output voltage and input sensing current, Zt(jf)=Vo,sensor(jf)/Isensor(jf). The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), spin-valve (GMR-SV) and tunnel magnetoresistance (TMR). The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications. PMID:24351648

Switching dynamics of doped CoFeB trilayers and a comparison to the quasistatic approximation

NASA Astrophysics Data System (ADS)

Forrester, Michael; Kusmartsev, Feodor; Kovács, Endre

2013-05-01

The investigation of the switching times of the magnetization reversal of two interacting CoFeB nanomagnets, with dimensions small enough to maintain a single-domain structure, has been carried out. A quasistatic approximation is shown to give valid results and to compare well to the damped dynamical solutions of the Landau-Lifshitz-Gilbert equations. The characteristics of the switching are shown in the associated hysteresis loops and we build a complete phase diagram of the various parallel, antiparallel, and scissoring states of the magnetization in terms of the coupling energy between the nanomagnets, magnetic anisotropy, and the interaction with an applied magnetic field. The phase diagram summarizes the different kinds of hysteresis associated with the magnetization reversal phenomena. The switching fields and times are estimated and the vulnerabilities of the magnetic phases to thermally induced magnetic field variations are examined. The stability of the phases is a fine balance between intrinsic and extrinsic magnetism and we examine its precarious nature. Our work identifies the structures that have the most robust magnetization states and hence a design ethic for creating nanomagnetic heterostructures with outstanding magnetoresistance properties based upon the two magnetic elements.

Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS

PubMed Central

Ali, Mazhar N.; Schoop, Leslie M.; Garg, Chirag; Lippmann, Judith M.; Lara, Erik; Lotsch, Bettina; Parkin, Stuart S. P.

2016-01-01

Magnetoresistance (MR), the change of a material’s electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual “butterfly”-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 105 percent at 9 T and 2 K at a 45° angle between the applied current (I || a) and the applied field (90° is H || c). Approaching 90°, a “dip” is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states. PMID:28028541

Current-induced switching in a magnetic insulator

NASA Astrophysics Data System (ADS)

Avci, Can Onur; Quindeau, Andy; Pai, Chi-Feng; Mann, Maxwell; Caretta, Lucas; Tang, Astera S.; Onbasli, Mehmet C.; Ross, Caroline A.; Beach, Geoffrey S. D.

2017-03-01

The spin Hall effect in heavy metals converts charge current into pure spin current, which can be injected into an adjacent ferromagnet to exert a torque. This spin-orbit torque (SOT) has been widely used to manipulate the magnetization in metallic ferromagnets. In the case of magnetic insulators (MIs), although charge currents cannot flow, spin currents can propagate, but current-induced control of the magnetization in a MI has so far remained elusive. Here we demonstrate spin-current-induced switching of a perpendicularly magnetized thulium iron garnet film driven by charge current in a Pt overlayer. We estimate a relatively large spin-mixing conductance and damping-like SOT through spin Hall magnetoresistance and harmonic Hall measurements, respectively, indicating considerable spin transparency at the Pt/MI interface. We show that spin currents injected across this interface lead to deterministic magnetization reversal at low current densities, paving the road towards ultralow-dissipation spintronic devices based on MIs.

Method of making active magnetic refrigerant, colossal magnetostriction and giant magnetoresistive materials based on Gd-Si-Ge alloys

DOEpatents

Gschneidner, Jr., Karl A.; Pecharsky, Alexandra O.; Pecharsky, Vitalij K.

2003-07-08

Method of making an active magnetic refrigerant represented by Gd.sub.5 (Si.sub.x Ge.sub.1-x).sub.4 alloy for 0.ltoreq.x.ltoreq.1.0 comprising placing amounts of the commercially pure Gd, Si, and Ge charge components in a crucible, heating the charge contents under subambient pressure to a melting temperature of the alloy for a time sufficient to homogenize the alloy and oxidize carbon with oxygen present in the Gd charge component to reduce carbon, rapidly solidifying the alloy in the crucible, and heat treating the solidified alloy at a temperature below the melting temperature for a time effective to homogenize a microstructure of the solidified material, and then cooling sufficiently fast to prevent the eutectoid decomposition and improve magnetocaloric and/or the magnetostrictive and/or the magnetoresistive properties thereof.

Magneto-hydrodynamic modeling of gas discharge switches

NASA Astrophysics Data System (ADS)

Doiphode, P.; Sakthivel, N.; Sarkar, P.; Chaturvedi, S.

2002-12-01

We have performed one-dimensional, time-dependent magneto-hydrodynamic modeling of fast gas-discharge switches. The model has been applied to both high- and low-pressure switches, involving a cylindrical argon-filled cavity. It is assumed that the discharge is initiated in a small channel near the axis of the cylinder. Joule heating in this channel rapidly raises its temperature and pressure. This drives a radial shock wave that heats and ionizes the surrounding low-temperature region, resulting in progressive expansion of the current channel. Our model is able to reproduce this expansion. However, significant difference of detail is observed, as compared with a simple model reported in the literature. In this paper, we present details of our simulations, a comparison with results from the simple model, and a physical interpretation for these differences. This is a first step towards development of a detailed 2-D model for such switches.

Shape-Memory Wires Switch Rotary Actuator

NASA Technical Reports Server (NTRS)

Brudnicki, Myron J.

1992-01-01

Thermomechanical rotary actuator based on shape-memory property of alloy composed of equal parts of titanium and nickel. If alloy stretched while below transition temperature, it reverts to original length when heated above transition temperature. Two capstans on same shaft wrapped with shape-memory wires. As one wire heated, it contracts and stretches opposite wire. Wires heated in alternation so they switch shaft between two extreme angular positions; "on" and "off" positions of rotary valve.

Origin of the extremely large magnetoresistance in the semimetal YSb

DOE PAGES

Xu, J.; Ghimire, N. J.; Jiang, J. S.; ...

2017-08-29

Extremely large magnetoresistance (XMR) was recently discovered in YSb but its origin, along with that of many other XMR materials, is an active subject of debate. Here we demonstrate that YSb, with a cubic crystalline lattice and anisotropic bulk electron Fermi pockets, can be an excellent candidate for revealing the origin of XMR. We carried out angle dependent Shubnikov – de Haas quantum oscillation measurements to determine the volume and shape of the Fermi pockets. In addition, by investigating both Hall and longitudinal magnetoresistivities, we reveal that the origin of XMR in YSb lies in its carrier high mobility withmore » a diminishing Hall factor that is obtained from the ratio of the Hall and longitudinal magentoresistivities. The high mobility leads to a strong magnetic field dependence of the longitudinal magnetoconductivity while a diminishing Hall factor reveals the latent XMR hidden in the longitudinal magnetoconductivity whose inverse has a nearly quadratic magnetic-field dependence. The Hall factor highlights the deviation of the measured magnetoresistivity from its full potential value and provides a general formulation to reveal the origin of XMR behavior in high mobility materials and of nonsaturating MR behavior as a whole. Our approach can be readily applied to other XMR materials.« less

Predicition and Discovery of High Tunneling Magnetoresistance in Magnetic Tunnel Junctions with Crystalline Barriers

NASA Astrophysics Data System (ADS)

Butler, William

2005-03-01

Tunneling magnetoresistance in excess of 200% has recently been observed in magnetic tunnel junctions using bcc Fe or bcc CoFe electrodes with crystalline MgO tunnel barriers[1,2]. These results demonstrate that tunneling magnetoresistance depends on more than the ``electrode polarization''. This talk will describe the calculations that predicted high TMR in these and other systems[3,4,5]. These calculations helped us to understand certain principles that may lead to high TMR through coherent electron tunneling. They can be briefly summarized as follows: (1) If the symmetry of a Bloch state can be preserved as electrons cross the interfaces between the electrode and the tunnel barrier, this be used to advantage for spin filtering. (2) Evanescent states of different symmetries decay at different rates in the barrier. (3) Interfacial bonding can be very important in determining the probability that an electron can traverse the interface. (4) Electrons of disallowed symmetry cannot propagate in an electrode. Once these simple principles are understood, simple band codes can be used to screen and to develop heterostructures with the proper symmetries to obtain high TMR. [1] S. S. P. Parkin, C. Kaiser, A. Panchula, P. M. Rice, B. Hughes, M. Samant AND S.-H. Yang, ``Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers,'' Nature Materials, Advance Online Publication [2] S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, K. Ando, ``Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions,'' Nature Materials, Advance Online Publication [3] W. H. Butler, X.-G. Zhang, T. C. Schulthess, and J. M. MacLaren, ``Spin-dependent tunneling conductance of Fe | MgO | Fe sandwiches'' Phys. Rev. B 63, 054416 (2001) [4] J. Mathon, A. Umerski, ``Theory of tunneling magnetoresistance of an epitaxial Fe/MgO/Fe(001) junction,'' Phys. Rev. B 63, 220403(R) (2001). [5] X.-G. Zhang, and W. H. Butler, ``Large magnetoresistance in

Recent observations of negative longitudinal magnetoresistance in semimetal

NASA Astrophysics Data System (ADS)

Xu, Xi-Tong; Jia, Shuang

2016-11-01

The discovery of Dirac semimetal and Weyl semimetal has motivated a growing passion for investigating the unique magneto-transport properties in the topological materials. A Weyl semimetal can host Weyl fermions as its low-energy quasi-particle excitations, and therefore perform exotic features analogous to those in high-energy physics, such as the violation of the chiral charge conservation known as the chiral anomaly. One of the electrical transport signatures of the chiral anomaly is the Adler-Bell-Jackiw (ABJ) anomaly which presents as a negative magnetoresistance when the magnetic field and the current are parallel. Very recently, numerous experiments reported negative longitudinal magnetoresistance (NLMR) in topological materials, but the details of the measurement results are various. Here the materials and the corresponding experiment results are briefly reviewed. Besides the plausible explanation of the ABJ anomaly, some other origins of the NLMR are also discussed. Project supported by the National Basic Research Program of China (Grant Nos. 2013CB921901 and 2014CB239302).

Temperature dependence of magnetoresistance in copper single crystals

NASA Astrophysics Data System (ADS)

Bian, Q.; Niewczas, M.

2018-03-01

Transverse magnetoresistance of copper single crystals has been measured in the orientation of open-orbit from 2 K to 20 K for fields up to 9 T. The experimental Kohler's plots display deviation between individual curves below 16 K and overlap in the range of 16 K-20 K. The violation of the Kohler's rule below 16 K indicates that the magnetotransport can not be described by the classical theory of electron transport on spherical Fermi surface with a single relaxation time. A theoretical model incorporating two energy bands, spherical and cylindrical, with different relaxation times has been developed to describe the magnetoresistance data. The calculations show that the electron-phonon scattering rates at belly and neck regions of the Fermi surface have different temperature dependencies, and in general, they do not follow T3 law. The ratio of the relaxation times in belly and neck regions decreases parabolically with temperature as A - CT2 , with A and C being constants.

NiFeCo/Cu superlattices with high magnetoresistive sensitivity and weak hysteresis

NASA Astrophysics Data System (ADS)

Bannikova, N. S.; Milyaev, M. A.; Naumova, L. I.; Krinitsina, T. P.; Patrakov, E. I.; Proglyado, V. V.; Chernyshova, T. A.; Ustinov, V. V.

2016-10-01

The microstructure and the magetoresistive characteristics of [NiFeCo/Cu]8 superlattices prepared by magnetron sputtering with various thickness of the buffer NiFeCr layer and exhibiting a giant magnetoresistive effect have been studied. It has been found that these nanostructures are formed with a strong or weak hysteresis depending on the structure (bcc or fcc) formed in the NiFeCr buffer layer. The method of the substantial decrease in the hysteresis loop width of the magnetoresistance by using the composite Ta/NiFeCr buffer layer has been suggested.

Observation of linear-polarization-sensitivity in the microwave-radiation-induced magnetoresistance oscillations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mani, R. G.; Ramanayaka, A. N.; Wegscheider, W.

2013-12-04

We examine the linear polarization sensitivity of the radiation- induced magneto-resistance oscillations by investigating the effect of rotating in-situ the electric field of linearly polarized microwaves relative to the current, in the GaAs/AlGaAs system. We find that the frequency and the phase of the photo-excited magneto-resistance oscillations are insensitive to the polarization. On the other hand, the amplitude of the resistance oscillations are strongly sensitive to the relative orientation between the microwave antenna and the current-axis in the specimen.

Temperature- and Bias-Dependence of Magnetoresistance in Doped Manganite Thin Film Trilayer Junctions

NASA Astrophysics Data System (ADS)

Sun, J. Z.; Xiao, Gang

1998-03-01

Large low-field magnetoresistance, up to a factor of five change in resistance, was observed in trilayer junctions formed by epitaxial thin films of La_0.67Sr_0.33 MnO3 - SrTiO3 - La_0.67Sr_0.33MnO3 at 4.2K and 100 Oe. Such magnetoresistance decreases with increasing sample temperature, and disappears for temperatures above 150K. The magnetoresistance also decreases upon increasing bias voltage across the junction. We present systematic experimental studies of both temperature and bias-dependence. These results in manganite trilayer junctions at low temperatures are similar to what has been observed in metallic trilayer magnetic tunneling valves, and are qualitatively consistent with the interface magnon excitation model proposed by Zhang et al.(S. Zhang, P. M. Levy, A. C. Marley and S. S. P. Parkin, Phys. Rev. Lett. 79), 3744 (1997).

Synthesis and characterization of Copper/Cobalt/Copper/Iron nanostructurated films with magnetoresistive properties

NASA Astrophysics Data System (ADS)

Ciupinǎ, Victor; Prioteasa, Iulian; Ilie, Daniela; Manu, Radu; Petrǎşescu, Lucian; Tutun, Ştefan Gabriel; Dincǎ, Paul; MustaÅ£ǎ, Ion; Lungu, Cristian Petricǎ; Jepu, IonuÅ£; Vasile, Eugeniu; Nicolescu, Virginia; Vladoiu, Rodica

2017-02-01

Copper/Cobalt/Copper/Iron thin films were synthesized in order to obtain nanostructured materials with special magnetoresistive properties. The multilayer films were deposited on silicon substrates. In this respect we used Thermionic Vacuum Arc Discharge Method (TVA). The benefit of this deposition technique is the ability to have a controlled range of thicknesses starting from few nanometers to hundreds of nanometers. The purity of the thin films was insured by a high vacuum pressure and a lack of any kind of buffer gas inside the coating chamber. The morphology and structure of the thin films were analyzed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) Techniques and Energy Dispersive X-ray Spectroscopy (EDXS). Magnetoresistive measurement results depict that thin films possess Giant Magneto-Resistance Effect (GMR). Magneto-Optic-Kerr Effect (MOKE) studies were performed to characterize the magnetic properties of these thin films.

Detection and characterization of multi-filament evolution during resistive switching

DOE PAGES

Mickel, Patrick R.; Lohn, Andrew J.; Marinella, Matthew J.

2014-08-05

We present resistive switching data in TaO x memristors displaying signatures of multi-filament switching modes, and develop a geometrically defined equivalent circuit to separate the individual resistances and powers dissipated in each filament. Using these resolved values, we compare the individual switching curves of each filament and demonstrate that the switching data of each filament collapse onto a single switching curve determined by the analytical steady-state resistive switching solution for filamentary switching. Analyzing our results in terms of this solution, we determine the switching temperature, heat flow, conductivity, and time evolving areas of each filament during resistive switching. Finally, wemore » discuss operational modes which may limit the formation of additional conducting filaments, potentially leading to increased device endurance.« less

Cr doping induced negative transverse magnetoresistance in C d3A s2 thin films

NASA Astrophysics Data System (ADS)

Liu, Yanwen; Tiwari, Rajarshi; Narayan, Awadhesh; Jin, Zhao; Yuan, Xiang; Zhang, Cheng; Chen, Feng; Li, Liang; Xia, Zhengcai; Sanvito, Stefano; Zhou, Peng; Xiu, Faxian

2018-02-01

The magnetoresistance of a material conveys various dynamic information about charge and spin carriers, inspiring both fundamental studies in physics and practical applications such as magnetic sensors, data storage, and spintronic devices. Magnetic impurities play a crucial role in the magnetoresistance as they induce exotic states of matter such as the quantum anomalous Hall effect in topological insulators and tunable ferromagnetic phases in dilute magnetic semiconductors. However, magnetically doped topological Dirac semimetals are hitherto lacking. Here, we report a systematic study of Cr-doped C d3A s2 thin films grown by molecular-beam epitaxy. With the Cr doping, C d3A s2 thin films exhibit unexpected negative transverse magnetoresistance and strong quantum oscillations, bearing a trivial Berry's phase and an enhanced effective mass. More importantly, with ionic gating the magnetoresistance of Cr-doped C d3A s2 thin films can be drastically tuned from negative to positive, demonstrating the strong correlation between electrons and the localized spins of the Cr impurities, which we interpret through the formation of magnetic polarons. Such a negative magnetoresistance under perpendicular magnetic field and its gate tunability have not been observed previously in the Dirac semimetal C d3A s2 . The Cr-induced topological phase transition and the formation of magnetic polarons in C d3A s2 provide insights into the magnetic interaction in Dirac semimetals as well as their potential applications in spintronics.

Allicat magnetoresistive head design and performance

NASA Astrophysics Data System (ADS)

Hannon, David; Krounbi, Mohamed; Christner, Jodie

1994-03-01

The general design features of the magnetoresistive (MR) merged head are described and compared to the earlier MR piggy-back head called Corsair. Examples of static, magnetic, and error rate testing are given. Dual track profiles show the read-narrow feature of the MR head. Stability of the signal with write disturbance shows the effectiveness of the hard-bias longitudinal biasing. Error rate versus off-track position indicates the robustness of the file design.

Tunnel magnetoresistance of ferrocene molecules

NASA Astrophysics Data System (ADS)

Matsuura, Yukihito

2018-01-01

The spin transport in ferrocene molecules has been examined by using the nonequilibrium Green's function formalism with density functional theory. The ferrocene molecules were sandwiched between the two nickel electrodes in a parallel magnetic configuration, which enhanced the current in comparison with that in an antiparallel spin state and resulting in tunnel magnetoresistance (TMR). The current, having an opposite spin state to that of the ferromagnetic electrode, was the main channel for electron transport. In addition, it became clear that ferrocenylene molecules, having a fulvalene structure with an extended π-conjugation, enhanced the TMR effect.

Modeling of CMOS compatible ring resonator switch with intermediate vanadium oxide as the switching element

NASA Astrophysics Data System (ADS)

Singh, Mandeep; Datta, Arnab

2018-05-01

In this paper, silicon based dual ring resonator with hybrid plasmonic bus waveguides (Cu-SiO2-Si-SiO2-Cu) is investigated for achieving switching in the telecommunication C-band (λ = 1.54-1.553µm). The switch element uses vanadium oxide (VO2) as the switching medium when inserted between the rings in order to tailor transmission from one ring to the other through heating induced phase transition. In this manner, the proposed switch element uses one vanadium oxide medium instead of refractive index tailoring of the whole ring as in the prior reported works and achieves switching response. From two-dimensional finite element analysis we have found that, the proposed switch can achieve maximum extinction ratio of 2.72 dB at λ = 1.5434µm, exclusively by tailoring VO2 phase. Furthermore, impact of aperture width, and gap (separation between the bus waveguide and rings) are investigated to gain insight on the improvement of extinction ratio. From our numerical simulations, we find that free spectral range (FSR) and figure of merit (Q) for OFF and ON states are (173.36 nm, 92.63), and (173.58 nm, 65.39), respectively.

FAST ACTING CURRENT SWITCH

DOEpatents

Batzer, T.H.; Cummings, D.B.; Ryan, J.F.

1962-05-22

A high-current, fast-acting switch is designed for utilization as a crowbar switch in a high-current circuit such as used to generate the magnetic confinement field of a plasma-confining and heat device, e.g., Pyrotron. The device particularly comprises a cylindrical housing containing two stationary, cylindrical contacts between which a movable contact is bridged to close the switch. The movable contact is actuated by a differential-pressure, airdriven piston assembly also within the housing. To absorb the acceleration (and the shock imparted to the device by the rapidly driven, movable contact), an adjustable air buffer assembly is provided, integrally connected to the movable contact and piston assembly. Various safety locks and circuit-synchronizing means are also provided to permit proper cooperation of the invention and the high-current circuit in which it is installed. (AEC)

Ternary NiFeX as soft biasing film in a magnetoresistive sensor

NASA Astrophysics Data System (ADS)

Chen, Mao-Min; Gharsallah, Neila; Gorman, Grace L.; Latimer, Jacquie

1991-04-01

The properties of NiFeX ternary films (X being Al, Au, Nb, Pd, Pt, Si, and Zr) have been studied for soft-film biasing of the magnetoresistive (MR) trilayer sensor. In general, the addition of the element X into the NiFe alloy film decreases the saturation magnetization Bs and magnetoresistance coefficient of the film, while increasing the film's electrical resistivity ρ. One of the desirable properties of a soft film for biasing is high sheet resistance for minimum current flow. A figure of merit Bsρ that takes into account both the rate of increase in Bs and the rate of decrease in ρ when adding X element was derived to compare the effectiveness of various X elements in reducing the current shunting through the soft-film layer. Using this criterion, NiFeNb and NiFeZr emerge as good soft-film materials having a maximum sheet resistance relative to the MR layer. Other critical properties such as magnetoresistance coefficient, magnetostriction, coercivity, and anisotropy field were also examined and are discussed in this paper.

Changes in Biomarkers of Exposure on Switching From a Conventional Cigarette to Tobacco Heating Products: A Randomized, Controlled Study in Healthy Japanese Subjects.

PubMed

Gale, Nathan; McEwan, Mike; Eldridge, Alison C; Fearon, Ian M; Sherwood, Neil; Bowen, Edward; McDermott, Simon; Holmes, Emma; Hedge, Andrew; Hossack, Stuart; Wakenshaw, Louise; Glew, James; Camacho, Oscar M; Errington, Graham; McAughey, John; Murphy, James; Liu, Chuan; Proctor, Christopher J

2018-06-15

Smoking is a leading cause of numerous human disorders including pulmonary disease, cardiovascular disease, and cancer. Disease development is primarily caused by exposure to cigarette smoke constituents, many of which are known toxicants. Switching smokers to modified risk tobacco products (MRTPs) has been suggested as a potential means to reduce the risks of tobacco use, by reducing such exposure. This randomized, controlled study investigated whether biomarkers of toxicant exposure (BoE) were reduced when smokers switched from smoking combustible cigarettes to using a novel (glo™/THP1.0) or in-market comparator (iQOS/THS) tobacco heating product (THP). One hundred eighty Japanese smokers smoked combustible cigarettes during a 2-day baseline period, followed by randomization to either continue smoking cigarettes, switch to using mentholated or non-mentholated variants of glo™, switch to using a non-mentholated variant of iQOS, or quit nicotine and tobacco product use completely for 5 days. Baseline and post-randomization 24-h urine samples were collected for BoE analysis. Carbon monoxide was measured daily in exhaled breath (eCO). On day 5 after switching, urinary BoE (excluding for nicotine) and eCO levels were significantly (p < .05) reduced by medians between 20.9% and 92.1% compared with baseline in all groups either using glo™ or iQOS or quitting tobacco use. Between-group comparisons revealed that the reductions in the glo™ groups were similar (p > .05) to quitting in many cases. glo™ or iQOS use for 5 days reduced exposure to smoke toxicants in a manner comparable to quitting tobacco use. THPs are reduced exposure tobacco products with the potential to be MRTPs. This clinical study demonstrates that when smokers switched from smoking combustible cigarettes to using tobacco heating products their exposure to smoke toxicants was significantly decreased. In many cases, this was to the same extent as that seen when they quit smoking completely. This

Better Gas-Gap Thermal Switches For Sorption Compressors

NASA Technical Reports Server (NTRS)

Bhandari, Pradeep; Rodriguez, Jose

1995-01-01

Gas-gap thermal switches associated with sorption compressors of some heat pumps and cryogenic systems designed for higher performance, according to proposal, by introducing controlled turbulent flows into gas gaps. Utilizes convection in turbulent flow to transfer heat at greater rate. Design takes advantage of flow of working fluid. Working fluid also serve as heat transfer medium in gas gap.

Magnetoresistive flux focusing eddy current flaw detection

NASA Technical Reports Server (NTRS)

Wincheski, Russell A. (Inventor); Simpson, John W. (Inventor); Namkung, Min (Inventor)

2005-01-01

A giant magnetoresistive flux focusing eddy current device effectively detects deep flaws in thick multilayer conductive materials. The probe uses an excitation coil to induce eddy currents in conducting material perpendicularly oriented to the coil's longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded by the excitation coil, is used to detect generated fields. Between the excitation coil and GMR sensor is a highly permeable flux focusing lens which magnetically separates the GMR sensor and excitation coil and produces high flux density at the outer edge of the GMR sensor. The use of feedback inside the flux focusing lens enables complete cancellation of the leakage fields at the GMR sensor location and biasing of the GMR sensor to a location of high magnetic field sensitivity. In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR sensor to accomplish the biasing. Experimental results have demonstrated identification of flaws up to 1 cm deep in aluminum alloy structures. To detect deep flaws about circular fasteners or inhomogeneities in thick multilayer conductive materials, the device is mounted in a hand-held rotating probe assembly that is connected to a computer for system control, data acquisition, processing and storage.

Magnetoresistive Flux Focusing Eddy Current Flaw Detection

NASA Technical Reports Server (NTRS)

Wincheski, Russell A. (Inventor); Namkung, Min (Inventor); Simpson, John W. (Inventor)

2005-01-01

A giant magnetoresistive flux focusing eddy current device effectively detects deep flaws in thick multilayer conductive materials. The probe uses an excitation coil to induce eddy currents in conducting material perpendicularly oriented to the coil s longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded by the excitation coil, is used to detect generated fields. Between the excitation coil and GMR sensor is a highly permeable flux focusing lens which magnetically separates the GMR sensor and excitation coil and produces high flux density at the outer edge of the GMR sensor. The use of feedback inside the flux focusing lens enables complete cancellation of the leakage fields at the GMR sensor location and biasing of the GMR sensor to a location of high magnetic field sensitivity. In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR sensor to accomplish the biasing. Experimental results have demonstrated identification of flaws up to 1 cm deep in aluminum alloy structures. To detect deep flaws about circular fasteners or inhomogeneities in thick multi-layer conductive materials, the device is mounted in a hand-held rotating probe assembly that is connected to a computer for system control, data acquisition, processing and storage.

Self-consistent study of local and nonlocal magnetoresistance in a YIG/Pt bilayer

NASA Astrophysics Data System (ADS)

Wang, Xi-guang; Zhou, Zhen-wei; Nie, Yao-zhuang; Xia, Qing-lin; Guo, Guang-hua

2018-03-01

We present a self-consistent study of the local spin Hall magnetoresistance (SMR) and nonlocal magnon-mediated magnetoresistance (MMR) in a heavy-metal/magnetic-insulator heterostructure at finite temperature. We find that the thermal fluctuation of magnetization significantly affects the SMR. It appears unidirectional with respect to the direction of electrical current (or magnetization). The unidirectionality of SMR originates from the asymmetry of creation or annihilation of thermal magnons induced by the spin Hall torque. Also, a self-consistent model can well describe the features of MMR.

Magnetostatic effects on switching in small magnetic tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bapna, Mukund; Piotrowski, Stephan K.; Oberdick, Samuel D.

Perpendicular CoFeB/MgO/CoFeB magnetic tunnel junctions with diameters under 100 nm are investigated by conductive atomic force microscopy. Minor loops of the tunnel magnetoresistance as a function of applied magnetic field reveal the hysteresis of the soft layer and an offset due to the magnetostatic field of the hard layer. Within the hysteretic region, telegraph noise is observed in the tunnel current. Simulations show that in this range, the net magnetic field in the soft layer is spatially inhomogeneous, and that antiparallel to parallel switching tends to start near the edge, while parallel to antiparallel reversal favors nucleation in the interior ofmore » the soft layer. As the diameter of the tunnel junction is decreased, the average magnitude of the magnetostatic field increases, but the spatial inhomogeneity across the soft layer is reduced.« less

Metal vapor arc switch electromagnetic accelerator technology

NASA Technical Reports Server (NTRS)

Mongeau, P. P.

1984-01-01

A multielectrode device housed in an insulator vacuum vessel, the metal vapor vacuum switch has high power capability and can hold off voltages up to the 100 kilovolt level. Such switches can be electronically triggered and can interrupt or commutate at a zero current crossing. The physics of arc initiation, arc conduction, and interruption are examined, including material considerations; inefficiencies; arc modes; magnetic field effects; passive and forced extinction; and voltage recovery. Heating, electrode lifetime, device configuration, and external circuit configuration are discussed. The metal vapor vacuum switch is compared with SCRs, GTOs, spark gaps, ignitrons, and mechanical breakers.

Magnetoresistive sensors based on the elasticity of domain walls.

PubMed

Zhang, Xueying; Vernier, Nicolas; Cao, Zhiqiang; Leng, Qunwen; Cao, Anni; Ravelosona, Dafine; Zhao, Weisheng

2018-06-19

Magnetic sensors based on the magnetoresistance effects have a promising application prospect due to their excellent sensitivity and advantages in terms of the integration. However, competition between higher sensitivity and larger measuring range remains a problem. Here, we propose a novel mechanism for the design of magnetoresistive sensors: probing the perpendicular field by detecting the expansion of the elastic magnetic Domain Wall (DW) in the free layer of a spin valve or a magnetic tunnel junction. Performances of devices based on this mechanism, such as the sensitivity and the measuring range can be tuned by manipulating the geometry of the device, without changing the intrinsic properties of the material, thus promising a higher integration level and a better performance. The mechanism is theoretically explained based on the experimental results. Two examples are proposed and their functionality and performances are verified via micromagnetic simulation. © 2018 IOP Publishing Ltd.

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field.

PubMed

Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

2017-02-23

Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 10 6  A·cm -2 , or about 1 × 10 25 electrons s -1 cm -2 . This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 10 13 electrons per cm 2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions.

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field

PubMed Central

Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

2017-01-01

Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 106 A·cm−2, or about 1 × 1025 electrons s−1 cm−2. This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 1013 electrons per cm2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions. PMID:28230054

Non-volatile, solid state bistable electrical switch

NASA Technical Reports Server (NTRS)

Williams, Roger M. (Inventor)

1994-01-01

A bistable switching element is made of a material whose electrical resistance reversibly decreases in response to intercalation by positive ions. Flow of positive ions between the bistable switching element and a positive ion source is controlled by means of an electrical potential applied across a thermal switching element. The material of the thermal switching element generates heat in response to electrical current flow therethrough, which in turn causes the material to undergo a thermal phase transition from a high electrical resistance state to a low electrical resistance state as the temperature increases above a predetermined value. Application of the electrical potential in one direction renders the thermal switching element conductive to pass electron current out of the ion source. This causes positive ions to flow from the source into the bistable switching element and intercalate the same to produce a non-volatile, low resistance logic state. Application of the electrical potential in the opposite direction causes reverse current flow which de-intercalates the bistable logic switching element and produces a high resistance logic state.

High peak and high average radiofrequency power transmit/receive switch for thermal magnetic resonance.

PubMed

Ji, Yiyi; Hoffmann, Werner; Pham, Michal; Dunn, Alexander E; Han, Haopeng; Özerdem, Celal; Waiczies, Helmar; Rohloff, Michael; Endemann, Beate; Boyer, Cyrille; Lim, May; Niendorf, Thoralf; Winter, Lukas

2018-04-01

To study the role of temperature in biological systems, diagnostic contrasts and thermal therapies, RF pulses for MR spin excitation can be deliberately used to apply a thermal stimulus. This application requires dedicated transmit/receive (Tx/Rx) switches that support high peak powers for MRI and high average powers for RF heating. To meet this goal, we propose a high-performance Tx/Rx switch based on positive-intrinsic-negative diodes and quarter-wavelength (λ/4) stubs. The λ/4 stubs in the proposed Tx/Rx switch design route the transmitted RF signal directly to the RF coil/antenna without passing through any electronic components (e.g., positive-intrinsic-negative diodes). Bench measurements, MRI, MR thermometry, and RF heating experiments were performed at f = 297 MHz (B 0  = 7 T) to examine the characteristics and applicability of the switch. The proposed design provided an isolation of -35.7dB/-41.5dB during transmission/reception. The insertion loss was -0.41dB/-0.27dB during transmission/reception. The switch supports high peak (3.9 kW) and high average (120 W) RF powers for MRI and RF heating at f = 297 MHz. High-resolution MRI of the wrist yielded image quality competitive with that obtained with a conventional Tx/Rx switch. Radiofrequency heating in phantom monitored by MR thermometry demonstrated the switch applicability for thermal modulation. Upon these findings, thermally activated release of a model drug attached to thermoresponsive polymers was demonstrated. The high-power Tx/Rx switch enables thermal MR applications at 7 T, contributing to the study of the role of temperature in biological systems and diseases. All design files of the switch will be made available open source at www.opensourceimaging.org. © 2018 International Society for Magnetic Resonance in Medicine.

Distinctive uniaxial magnetic anisotropy and positive magnetoresistance in (110)-oriented Fe3O4 films

NASA Astrophysics Data System (ADS)

Dho, Joonghoe; Kim, Byeong-geon; Ki, Sanghoon

2015-04-01

Magnetite (Fe3O4) films were synthesized on (110)-oriented MgO, MgAl2O4, and SrTiO3 substrates for comparative studies of the substrates' effects on magnetic and magnetoresistance properties of the films. For the [-110] direction, the hysteresis loops of the Fe3O4 film on MgAl2O4 exhibited a good squareness with the largest coercivity of ˜1090 Oe, and the ratio of remanent magnetization to saturation magnetization was ˜0.995. For the [001] direction, positive magnetoresistance in weak magnetic fields was most distinct for the (110) SrTiO3 substrate with the largest lattice mismatch. Positive magnetoresistance in the (110) Fe3O4 films was presumably affected by imperfect atomic arrangements at anti-phase boundaries.

Room temperature giant and linear magnetoresistance in topological insulator Bi2Te3 nanosheets.

PubMed

Wang, Xiaolin; Du, Yi; Dou, Shixue; Zhang, Chao

2012-06-29

Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi(2)Te(3) topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

Lab-on-Chip Cytometry Based on Magnetoresistive Sensors for Bacteria Detection in Milk

PubMed Central

Fernandes, Ana C.; Duarte, Carla M.; Cardoso, Filipe A.; Bexiga, Ricardo.; Cardoso, Susana.; Freitas, Paulo P.

2014-01-01

Flow cytometers have been optimized for use in portable platforms, where cell separation, identification and counting can be achieved in a compact and modular format. This feature can be combined with magnetic detection, where magnetoresistive sensors can be integrated within microfluidic channels to detect magnetically labelled cells. This work describes a platform for in-flow detection of magnetically labelled cells with a magneto-resistive based cell cytometer. In particular, we present an example for the validation of the platform as a magnetic counter that identifies and quantifies Streptococcus agalactiae in milk. PMID:25196163

Lab-on-chip cytometry based on magnetoresistive sensors for bacteria detection in milk.

PubMed

Fernandes, Ana C; Duarte, Carla M; Cardoso, Filipe A; Bexiga, Ricardo; Cardoso, Susana; Freitas, Paulo P

2014-08-21

Flow cytometers have been optimized for use in portable platforms, where cell separation, identification and counting can be achieved in a compact and modular format. This feature can be combined with magnetic detection, where magnetoresistive sensors can be integrated within microfluidic channels to detect magnetically labelled cells. This work describes a platform for in-flow detection of magnetically labelled cells with a magneto-resistive based cell cytometer. In particular, we present an example for the validation of the platform as a magnetic counter that identifies and quantifies Streptococcus agalactiae in milk.

Magnetotransport and Heat Capacity in Ternary Compounds U3M2M‧3‧, M=Al, Ga; M=Si, Ge

NASA Astrophysics Data System (ADS)

Troć, R.; Rogl, P.; Tran, V. H.; Czopnik, A.

2001-05-01

We report detailed studies of magnetization, electrical resistivity, magnetoresistivity, and heat capacity performed on the novel family of intermetallic compounds U3M2M‧3, (M=Al, Ga, and M‧=Si, Ge). The present measurements support the earlier conclusions about the ferrimagnetic properties of silicides and ferromagnetic properties of germanides. The resistivity for both compounds U3{Al,Ga}2Si3 exhibits below TC a pronounced maximum observed for the first time in an actinoid-ferrimagnet, probably caused by (a) the reduction of the number of effective conduction carriers or (b) a SDW-type of spin-disorder scattering of electrons. Both low-temperature resistivity (except for U3Ga2Si3) and heat capacity may be described by a T-dependence involving a small gap Δ on the order of 30-50 K in the magnon dispersion. The Cp/T values at 2 K are enhanced and point to a medium-heavy fermion character of all these ternaries. Magnetoresistance for ferrimagnetic U3{Al,Ga}2Si3 is rather small but positive in correspondence of antiferromagnetic interactions. In correspondence to the ferromagnetic materials, negative magnetoresistance is encountered for U3{Al,Ga}2Ge3. Specific features in the temperature dependence of magnetoresistivity Δρ/ρ at various fields confirm the sinusoidal modulation of the magnetic structure for U3Al2Ge3 between 40 and 60 K. Also, such data for U3Ga2Ge3 present strong indications for a similar magnetic modulation between 63 and 93 K, yet to be discovered by neutron diffraction experiments. In addition, the transition at 63 K is furthermore well resolved in the specific heat data of U3Ga2Ge3.

An all-optical switch based on a surface plasmon polariton resonator

NASA Astrophysics Data System (ADS)

Pan, Zijuan; Lang, Peilin; Duan, Gaoyan

2018-04-01

All-optical switch is one of the key parts of optical circuit. We employ a temperature-sensitive resonator to form an optical switch. The resonator deforms under the applied light and adjusts the transmittance of the structure. To our knowledge, this is the first design of an all-optical surface plasmon polariton (SPP) switch based on the heat deformation effect.

Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons.

PubMed

Alekseev, P S

2016-10-14

At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.

Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons

NASA Astrophysics Data System (ADS)

Alekseev, P. S.

2016-10-01

At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.

Large magnetoresistance in Fe3O4/molecule nanoparticles

NASA Astrophysics Data System (ADS)

Wang, S.; Yue, F. J.; Lin, L.; Shi, Y. J.; Wu, D.

2010-08-01

In this work, we successfully fabricate Fe3O4 nanoparticles self-assembled with molecules to explore a new approach of studying the molecular spintronics. Fourier transform infrared spectroscopy measurements indicate that one monolayer molecules chemically bonds to the Fe3O4 nanoparticles and the physically absorbed molecules do not exist in the samples. The magnetoresistance (MR) of molecule fully coated ~10 nm size nanoparticles is up to 7.3% at room temperature and 17.5% at 115 K under a field of 5.8 kOe. And the MR ratio is more than two times larger than that of pure Fe3O4 nanoparticles. This enhanced MR is likely arising from weak spin scattering while carriers transport through the molecules. Moreover, a very large low field magnetoresistance is also observed with ~500nm ferromagnetic Fe3O4 nanoparticles coated with acetic acid molecules. Those features open a door for the development of future spin-based molecular electronics.

Large magnetoresistance in the type-II Weyl semimetal WP 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Aifeng; Graf, D.; Liu, Yu

In this paper, we report a magnetotransport study on type-II Weyl semimetal WP 2 single crystals. Magnetoresistance exhibits a nonsaturating H n field dependence (14 300% at 2 K and 9 T), whereas systematic violation of Kohler's rule was observed. Quantum oscillations reveal a complex multiband electronic structure. The cyclotron effective mass close to the mass of free electron m e was observed in quantum oscillations along the b axis, while a reduced effective mass of about 0.5 m e was observed in α-axis quantum oscillations, suggesting Fermi surface anisotropy. The temperature dependence of the resistivity shows a large upturnmore » that cannot be explained by the multiband magnetoresistance of conventional metals. Finally, even though the crystal structure of WP 2 is not layered as in transition-metal dichalcogenides, quantum oscillations suggest partial two-dimensional character.« less

Large magnetoresistance in the type-II Weyl semimetal WP 2

DOE PAGES

Wang, Aifeng; Graf, D.; Liu, Yu; ...

2017-09-11

In this paper, we report a magnetotransport study on type-II Weyl semimetal WP 2 single crystals. Magnetoresistance exhibits a nonsaturating H n field dependence (14 300% at 2 K and 9 T), whereas systematic violation of Kohler's rule was observed. Quantum oscillations reveal a complex multiband electronic structure. The cyclotron effective mass close to the mass of free electron m e was observed in quantum oscillations along the b axis, while a reduced effective mass of about 0.5 m e was observed in α-axis quantum oscillations, suggesting Fermi surface anisotropy. The temperature dependence of the resistivity shows a large upturnmore » that cannot be explained by the multiband magnetoresistance of conventional metals. Finally, even though the crystal structure of WP 2 is not layered as in transition-metal dichalcogenides, quantum oscillations suggest partial two-dimensional character.« less

Ultrafast carrier dynamics in the large-magnetoresistance material WTe 2

DOE PAGES

Dai, Y. M.; Bowlan, J.; Li, H.; ...

2015-10-07

In this study, ultrafast optical pump-probe spectroscopy is used to track carrier dynamics in the large-magnetoresistance material WTe 2. Our experiments reveal a fast relaxation process occurring on a subpicosecond time scale that is caused by electron-phonon thermalization, allowing us to extract the electron-phonon coupling constant. An additional slower relaxation process, occurring on a time scale of ~5–15 ps, is attributed to phonon-assisted electron-hole recombination. As the temperature decreases from 300 K, the time scale governing this process increases due to the reduction of the phonon population. However, below ~50 K, an unusual decrease of the recombination time sets in,more » most likely due to a change in the electronic structure that has been linked to the large magnetoresistance observed in this material.« less

Study of polytropic exponent based on high pressure switching expansion reduction

NASA Astrophysics Data System (ADS)

Wang, Xuanyin; Luo, Yuxi; Xu, Zhipeng

2011-10-01

Switching expansion reduction (SER) uses a switch valve to substitute the throttle valve to reduce pressure for high pressure pneumatics. The experiments indicate that the simulation model well predicts the actual characteristics. The heat transfers and polytropic exponents of the air in expansion tank and supply tanks of SER have been studied on the basis of the experiments and the simulation model. Through the mathematical reasoning in this paper, the polytropic exponent can be calculated by the air mass, heat, and work exchanges of the pneumatic container. For the air in a constant volume tank, when the heat-absorption is large enough to raise air temperature in discharging process, the polytropic exponent is less than 1; when the air is experiencing a discharging and heat-releasing process, the polytropic exponent exceeds the specific heat ratio (the value of 1.4).

Effect of CoFeB electrode compositions on low frequency magnetic noise in tunneling magnetoresistance sensors

NASA Astrophysics Data System (ADS)

Wisniowski, P.; Dabek, M.; Wrona, J.; Cardoso, S.; Freitas, P. P.

2017-12-01

We study the effect of CoFeB electrode compositions on frequency dependent magnetic noise in tunneling magnetoresistance sensors with variable field sensitivity. We use the relationship between the normalized 1/f noise parameter (αt) and the magnetoresistance sensitivity product (MSP) to compare the magnetic noise of sensors with Co40Fe40B20, Co60Fe20B20, and Co20Fe60B20 electrodes. We observed the lowest slope of the αt vs. MSP curve of 9.1 × 10-13 μm3 T and a 1/f noise corner as low as 300 Hz for the sensors with Co60Fe20B20 electrodes. Furthermore, all sensors at a specific value of the magnetoresistance sensitivity product showed a deviation from the linear relationship between αt and MSP. The results show that in the design of high sensitivity CoFeB-MgO-CoFeB based tunneling magnetoresistance sensors for low field detection, selection of CoFeB electrodes is important and can be used to significantly improve the low frequency field detection limit.

Transient current interruption mechanism in a magnetically delayed vacuum switch

NASA Technical Reports Server (NTRS)

Morris, Gibson, Jr.; Dougal, Roger A.

1993-01-01

The capacity of a magnetically delayed vacuum switch to conduct current depends on the density of plasma injected into the switch. Exceeding the current capacity results in the switch entering a lossy mode of operation characterized by a transient interruption of the main current (opening behavior) and a rapid increase of voltage across the vacuum gap. Streak and framing photographs of the discharge indicate that a decrease of luminosity near the middle of the gap preceeds the transition to the opening phase. The zone of low luminosity propagates toward the cathode. This evidence suggests that the mechanism causing the opening phase is erosion of the background plasma in a manner similar to that in a plasma-opening switch. The resulting ion depletion forces a space-charge-limited conduction mode. The switch inductance maintains a high discharge current even during the space-charge-limited conduction phase, thus producing high internal fields. The high accelerating voltage, in turn, produces electron and ion beams that heat the electrode surfaces. As a result of the heating, jets of electrode vapor issue from the electrodes, either cathode or anode, depending on the selection of electrode materials.

Switching-type regulator circuit has increased efficiency

NASA Technical Reports Server (NTRS)

Clapp, W. M.

1967-01-01

Switching series regulator circuit uses an inductive network to feed most of the current applied to the control circuit to the load. This circuit eliminates resistive losses and the need for heat sinks.

Resistivity and magnetoresistivity of amorphous rare-earth alloys

NASA Astrophysics Data System (ADS)

Borchi, E.; Poli, M.; De Gennaro, S.

1982-05-01

The resistivity and magnetoresistivity of amorphous rare-earth alloys are studied starting from the general approach of Van Peski-Tinbergen and Dekker. The random axial crystal-field and the magnetic correlations between the rare-earth ions are consistently taken into account. The characteristic features of the available experimental data are explained both of the case of random ferromagnetic and antiferromagnetic order.

Theoretical Modeling of the Plasma Erosion Opening Switch for Inductive Storage Applications.

DTIC Science & Technology

1983-10-27

instantaneous and depends on the switch and load characteristics. In general T is finite and T >T >0. Thus energy will be lost to switch heatings s op - as...Top, then the switch opening time is the dominant factor and T T Clearly T must be small compared with the decay time of the load S op 5 current, T_

The magnetic ordering in high magnetoresistance Mn-doped ZnO thin films

DOE PAGES

Venkatesh, S.; Baras, A.; Lee, J. -S.; ...

2016-03-24

Here, we studied the nature of magnetic ordering in Mn-doped ZnO thin films that exhibited ferromagnetism at 300 K and superparamagnetism at 5 K. We directly inter-related the magnetisation and magnetoresistance by invoking the polaronpercolation theory and variable range of hopping conduction below the metal-to-insulator transition. By obtaining a qualitative agreement between these two models, we attribute the ferromagnetism to the s-d exchange-induced spin splitting that was indicated by large positive magnetoresistance (~40 %). Low temperature superparamagnetism was attributed to the localization of carriers and non-interacting polaron clusters. This analysis can assist in understanding the presence or absence of ferromagnetismmore » in doped/un-doped ZnO.« less

Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

DOE PAGES

Song, Tiancheng; Cai, Xinghan; Tu, Matisse Wei-Yuan; ...

2018-05-03

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI 3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI 3. In conclusion, ourmore » work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI 3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.« less

Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Tiancheng; Cai, Xinghan; Tu, Matisse Wei-Yuan

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI 3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI 3. In conclusion, ourmore » work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI 3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.« less

Preliminary study, analysis and design for a power switch for digital engine actuators

NASA Technical Reports Server (NTRS)

Beattie, E. C.; Zickwolf, H. C., Jr.

1979-01-01

Innovative control configurations using high temperature switches to operate actuator driving solenoids were studied. The impact on engine control system life cycle costs and reliability of electronic control and (ECU) heat dissipation due to power conditioning and interface drivers were addressed. Various power supply and actuation schemes were investigated, including optical signal transmission and electronics on the actuator, engine driven alternator, and inside the ECU. The use of a switching shunt power conditioner results in the most significant decrease in heat dissipation within the ECU. No overall control system reliability improvement is projected by the use of remote high temperature switches for solenoid drivers.

Extraordinary Hall resistance and unconventional magnetoresistance in Pt/LaCoO 3 hybrids

NASA Astrophysics Data System (ADS)

Shang, T.; Zhan, Q. F.; Yang, H. L.; Zuo, Z. H.; Xie, Y. L.; Zhang, Y.; Liu, L. P.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2015-10-01

We report an investigation of transverse Hall resistance and longitudinal resistance on Pt thin films sputtered on epitaxial LaCoO3 (LCO) ferromagnetic insulator films. The LaCoO3 films were deposited on several single crystalline substrates [LaAlO3,(La,Sr)(Al,Ta)O3, and SrTiO3] with (001) orientation. The physical properties of LaCoO3 films were characterized by the measurements of magnetic and transport properties. The LaCoO3 films undergo a paramagnetic to ferromagnetic (FM) transition at Curie temperatures ranging from 40 to 85 K, below which the Pt/LCO hybrids exhibit significant extraordinary Hall resistance up to 50 m Ω and unconventional magnetoresistance ratio Δ ρ /ρ0 about 1.2 ×10-4 , accompanied by the conventional magnetoresistance. The observed spin transport properties share some common features as well as some unique characteristics when compared with well-studied Y3Fe5O12 -based Pt thin films. Our findings call for new theories since the extraordinary Hall resistance and magnetoresistance cannot be consistently explained by the existing theories.

Gas gap heat switch for a cryogen-free magnet system

NASA Astrophysics Data System (ADS)

Barreto, J.; Borges de Sousa, P.; Martins, D.; Kar, S.; Bonfait, G.; Catarino, I.

2015-12-01

Cryogen-free superconducting magnet systems (CFMS) have become popular over the last two decades for the simple reason that the use of liquid helium is rather cumbersome and that helium is a scarce resource. Some available CFMS use a mechanical cryocooler as the magnet's cold source. However, the variable temperature insert (VTI) for some existing CFMS are not strictly cryogen-free as they are still based on helium gas circulation through the sample space. We designed a prototype of a gas gap heat switch (GGHS) that allows a thermal management of a completely cryogen-free magnet system, with no helium losses. The idea relies on a parallel cooling path to a variable temperature insert (VTI) of a magnetic properties measurement system under development at Inter-University Accelerator Centre. A Gifford-McMahon cryocooler (1.5 W @ 4.2 K) would serve primarily as the cold source of the superconducting magnet, dedicating 1 W to this cooling, under quite conservative safety factors. The remaining cooling power (0.5 W) is to be diverted towards a VTI through a controlled GGHS that was designed and built with a 80 μm gap width. The built GGHS thermal performance was measured at 4 K, using helium as the exchange gas, and its conductance is compared both with a previously developed analytical model and a finite element method. Lessons learned lead to a new and more functional prototype yet to be reported.

High-efficiency thermal switch based on topological Josephson junctions

NASA Astrophysics Data System (ADS)

Sothmann, Björn; Giazotto, Francesco; Hankiewicz, Ewelina M.

2017-02-01

We propose theoretically a thermal switch operating by the magnetic-flux controlled diffraction of phase-coherent heat currents in a thermally biased Josephson junction based on a two-dimensional topological insulator. For short junctions, the system shows a sharp switching behavior while for long junctions the switching is smooth. Physically, the switching arises from the Doppler shift of the superconducting condensate due to screening currents induced by a magnetic flux. We suggest a possible experimental realization that exhibits a relative temperature change of 40% between the on and off state for realistic parameters. This is a factor of two larger than in recently realized thermal modulators based on conventional superconducting tunnel junctions.

Interplanar coupling-dependent magnetoresistivity in high-purity layered metals

DOE PAGES

Kikugawa, N.; Goswami, P.; Kiswandhi, A.; ...

2016-03-29

The magnetic field-induced changes in the conductivity of metals are the subject of intense interest, both for revealing new phenomena and as a valuable tool for determining their Fermi surface. Here we report a hitherto unobserved magnetoresistive effect in ultra-clean layered metals, namely a negative longitudinal magnetoresistance that is capable of overcoming their very pronounced orbital one. This effect is correlated with the interlayer coupling disappearing for fields applied along the so-called Yamaji angles where the interlayer coupling vanishes. Therefore, it is intrinsically associated with the Fermi points in the field-induced quasi-one-dimensional electronic dispersion, implying that it results from themore » axial anomaly among these Fermi points. In its original formulation, the anomaly is predicted to violate separate number conservation laws for left- and right-handed chiral (for example, Weyl) fermions. Furthermore, its observation in PdCoO 2, PtCoO 2 and Sr 2RuO 4 suggests that the anomaly affects the transport of clean conductors, in particular near the quantum limit.« less

Superconducting Switch for Fast On-Chip Routing of Quantum Microwave Fields

NASA Astrophysics Data System (ADS)

Pechal, M.; Besse, J.-C.; Mondal, M.; Oppliger, M.; Gasparinetti, S.; Wallraff, A.

2016-08-01

A switch capable of routing microwave signals at cryogenic temperatures is a desirable component for state-of-the-art experiments in many fields of applied physics, including but not limited to quantum-information processing, communication, and basic research in engineered quantum systems. Conventional mechanical switches provide low insertion loss but disturb operation of dilution cryostats and the associated experiments by heat dissipation. Switches based on semiconductors or microelectromechanical systems have a lower thermal budget but are not readily integrated with current superconducting circuits. Here we design and test an on-chip switch built by combining tunable transmission-line resonators with microwave beam splitters. The device is superconducting and as such dissipates a negligible amount of heat. It is compatible with current superconducting circuit fabrication techniques, operates with a bandwidth exceeding 100 MHz, is capable of handling photon fluxes on the order of 1 05 μ s-1 , equivalent to powers exceeding -90 dBm , and can be switched within approximately 6-8 ns. We successfully demonstrate operation of the device in the quantum regime by integrating it on a chip with a single-photon source and using it to route nonclassical itinerant microwave fields at the single-photon level.

Negative tunnel magnetoresistance and differential conductance in transport through double quantum dots

NASA Astrophysics Data System (ADS)

Trocha, Piotr; Weymann, Ireneusz; Barnaś, Józef

2009-10-01

Spin-dependent transport through two coupled single-level quantum dots weakly connected to ferromagnetic leads with collinear magnetizations is considered theoretically. Transport characteristics, including the current, linear and nonlinear conductances, and tunnel magnetoresistance are calculated using the real-time diagrammatic technique in the parallel, serial, and intermediate geometries. The effects due to virtual tunneling processes between the two dots via the leads, associated with off-diagonal coupling matrix elements, are also considered. Negative differential conductance and negative tunnel magnetoresistance have been found in the case of serial and intermediate geometries, while no such behavior has been observed for double quantum dots coupled in parallel. It is also shown that transport characteristics strongly depend on the magnitude of the off-diagonal coupling matrix elements.

Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications

PubMed Central

Ennen, Inga; Kappe, Daniel; Rempel, Thomas; Glenske, Claudia; Hütten, Andreas

2016-01-01

The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors. PMID:27322277

A-site cationic disorder induced significantly large magnetoresistance in polycrystalline La0.2Gd0.5Ba0.3MnO3 compound

NASA Astrophysics Data System (ADS)

Saha, Suvayan; Das, Kalipada; Bandyopadhyay, Sudipta; Das, I.

2017-11-01

The observation of significantly large magnetoresistance at the liquid nitrogen temperature range in the polycrystalline La0.2Gd0.5Ba0.3MnO3 (LGBMO) compound has been addressed in the present manuscript. The motivation of considering LGBMO sample is the average 'A' site ionic radius 〈rA 〉 and tolerance factor (t), almost same as that of La0.7Sr0.3MnO3 (LSMO), which is a well studied colossal magnetoresistive material. Magnetoresistance of the LGBMO compound has been compared with the LSMO as well as parent compound La0.7Ba0.3MnO3(LBMO) to show the enhancement of magnetoresistance in LGBMO compound. This observed nature has been elucidated considering the disorder induced short range magnetic interaction due to the enhance size disorder parameter (σ2). Our study revels that, size disorder parameter plays the crucial role for enhancing the colossal magnetoresistance.

Strong spin-orbit coupling and Zeeman spin splitting in angle dependent magnetoresistance of Bi{sub 2}Te{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Rik, E-mail: rikdey@utexas.edu; Pramanik, Tanmoy; Roy, Anupam

We have studied angle dependent magnetoresistance of Bi{sub 2}Te{sub 3} thin film with field up to 9 T over 2–20 K temperatures. The perpendicular field magnetoresistance has been explained by the Hikami-Larkin-Nagaoka theory alone in a system with strong spin-orbit coupling, from which we have estimated the mean free path, the phase coherence length, and the spin-orbit relaxation time. We have obtained the out-of-plane spin-orbit relaxation time to be small and the in-plane spin-orbit relaxation time to be comparable to the momentum relaxation time. The estimation of these charge and spin transport parameters are useful for spintronics applications. For parallel field magnetoresistance,more » we have confirmed the presence of Zeeman effect which is otherwise suppressed in perpendicular field magnetoresistance due to strong spin-orbit coupling. The parallel field data have been explained using both the contributions from the Maekawa-Fukuyama localization theory for non-interacting electrons and Lee-Ramakrishnan theory of electron-electron interactions. The estimated Zeeman g-factor and the strength of Coulomb screening parameter agree well with the theory. Finally, the anisotropy in magnetoresistance with respect to angle has been described by the Hikami-Larkin-Nagaoka theory. This anisotropy can be used in anisotropic magnetic sensor applications.« less

Diluted magnetic semiconductor nanowires exhibiting magnetoresistance

DOEpatents

Yang, Peidong [El Cerrito, CA; Choi, Heonjin [Seoul, KR; Lee, Sangkwon [Daejeon, KR; He, Rongrui [Albany, CA; Zhang, Yanfeng [El Cerrito, CA; Kuykendal, Tevye [Berkeley, CA; Pauzauskie, Peter [Berkeley, CA

2011-08-23

A method for is disclosed for fabricating diluted magnetic semiconductor (DMS) nanowires by providing a catalyst-coated substrate and subjecting at least a portion of the substrate to a semiconductor, and dopant via chloride-based vapor transport to synthesize the nanowires. Using this novel chloride-based chemical vapor transport process, single crystalline diluted magnetic semiconductor nanowires Ga.sub.1-xMn.sub.xN (x=0.07) were synthesized. The nanowires, which have diameters of .about.10 nm to 100 nm and lengths of up to tens of micrometers, show ferromagnetism with Curie temperature above room temperature, and magnetoresistance up to 250 Kelvin.

Antiferromagnetic exchange and magnetoresistance enhancement in ultrathin Co-Re sandwiches

NASA Astrophysics Data System (ADS)

Freitas, P. P.; Melo, L. V.; Trindade, I.; From, M.

1992-10-01

Co-Re ultrathin sandwiches were prepared that show antiferromagnetic coupling and enhanced saturation magnetoresistance for Re spacer thicknesses below 9 Å. A field of 2.5 kOe is needed to saturate the antiferromagnetically coupled Co layers. These results are similar to those found in Co-Re superlattices.

Effect of annealing on magnetoresistance and microstructure of multilayered CoFe/Cu systems with different buffer layer

NASA Astrophysics Data System (ADS)

Bannikova, N. S.; Milyaev, M. A.; Naumova, L. I.; Proglyado, V. V.; Krinitsina, T. P.; Chernyshova, T. A.; Ustinov, V. V.

2015-02-01

The effects of annealing on the structure, magnetic hysteresis, and magnetoresistance of [Co90Fe10(15 Å)/Cu(23 Å)] n superlattices with Cr and Co90Fe10 buffer layers of different thicknesses have been studied. The optimum temperature and time of annealing that increase the magnetoresistance were shown to depend on the buffer layer thickness. The coefficients of effective interlayer diffusion due to the annealing have been determined.

Large linear magnetoresistance in a new Dirac material BaMnBi2

NASA Astrophysics Data System (ADS)

Wang, Yi-Yan; Yu, Qiao-He; Xia, Tian-Long

2016-10-01

Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles. Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials. In this paper, we report the synthesis of high quality single crystals of BaMnBi2 and investigate the transport properties of the samples. BaMnBi2 is a metal with an antiferromagnetic transition at T N = 288 K. The temperature dependence of magnetization displays different behavior from CaMnBi2 and SrMnBi2, which suggests the possible different magnetic structure of BaMnBi2. The Hall data reveals electron-type carriers and a mobility μ(5 K) = 1500 cm2/V·s. Angle-dependent magnetoresistance reveals the quasi-two-dimensional (2D) Fermi surface in BaMnBi2. A crossover from semiclassical MR ˜ H 2 dependence in low field to MR ˜ H dependence in high field, which is attributed to the quantum limit of Dirac fermions, has been observed in magnetoresistance. Our results indicate the existence of Dirac fermions in BaMnBi2. Project supported by the National Natural Science Foundation of China (Grant No. 11574391), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant No. 14XNLQ07).

Variable-range-hopping magnetoresistance

NASA Astrophysics Data System (ADS)

Azbel, Mark Ya

1991-03-01

The hopping magnetoresistance R of a two-dimensional insulator with metallic impurities is considered. In sufficiently weak magnetic fields it increases or decreases depending on the impurity density n: It decreases if n is low and increases if n is high. In high magnetic fields B, it always exponentially increases with √B . Such fields yield a one-dimensional temperature dependence: lnR~1/ √T . The calculation provides an accurate leading approximation for small impurities with one eigenstate in their potential well. In the limit of infinitesimally small impurities, an impurity potential is described by a generalized function. This function, similar to a δ function, is localized at a point, but, contrary to a δ function in the dimensionality above 1, it has finite eigenenergies. Such functions may be helpful in the study of scattering and localization of any waves.

Magnetic switching in granular FePt layers promoted by near-field laser enhancement

DOE PAGES

Granitzka, Patrick W.; Jal, Emmanuelle; Le Guyader, Loic; ...

2017-03-08

Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order ofmore » magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between “up” and “down” magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. Furthermore, the fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.« less

Heat-Assisted Multiferroic Solid-State Memory

PubMed Central

2017-01-01

A heat-assisted multiferroic solid-state memory design is proposed and analysed, based on a PbNbZrSnTiO3 antiferroelectric layer and Ni81Fe19 magnetic free layer. Information is stored as magnetisation direction in the free layer of a magnetic tunnel junction element. The bit writing process is contactless and relies on triggering thermally activated magnetisation switching of the free layer towards a strain-induced anisotropy easy axis. A stress is generated using the antiferroelectric layer by voltage-induced antiferroelectric to ferroelectric phase change, and this is transmitted to the magnetic free layer by strain-mediated coupling. The thermally activated strain-induced magnetisation switching is analysed here using a three-dimensional, temperature-dependent magnetisation dynamics model, based on simultaneous evaluation of the stochastic Landau-Lifshitz-Bloch equation and heat flow equation, together with stochastic thermal fields and magnetoelastic contributions. The magnetisation switching probability is calculated as a function of stress magnitude and maximum heat pulse temperature. An operating region is identified, where magnetisation switching always occurs, with stress values ranging from 80 to 180 MPa, and maximum temperatures normalised to the Curie temperature ranging from 0.65 to 0.99. PMID:28841185

Heat-Assisted Multiferroic Solid-State Memory.

PubMed

Lepadatu, Serban; Vopson, Melvin M

2017-08-25

A heat-assisted multiferroic solid-state memory design is proposed and analysed, based on a PbNbZrSnTiO₃ antiferroelectric layer and Ni 81 Fe 19 magnetic free layer. Information is stored as magnetisation direction in the free layer of a magnetic tunnel junction element. The bit writing process is contactless and relies on triggering thermally activated magnetisation switching of the free layer towards a strain-induced anisotropy easy axis. A stress is generated using the antiferroelectric layer by voltage-induced antiferroelectric to ferroelectric phase change, and this is transmitted to the magnetic free layer by strain-mediated coupling. The thermally activated strain-induced magnetisation switching is analysed here using a three-dimensional, temperature-dependent magnetisation dynamics model, based on simultaneous evaluation of the stochastic Landau-Lifshitz-Bloch equation and heat flow equation, together with stochastic thermal fields and magnetoelastic contributions. The magnetisation switching probability is calculated as a function of stress magnitude and maximum heat pulse temperature. An operating region is identified, where magnetisation switching always occurs, with stress values ranging from 80 to 180 MPa, and maximum temperatures normalised to the Curie temperature ranging from 0.65 to 0.99.

Peculiar behavior of magnetoresistance in HgSe single crystal with low electron concentration

NASA Astrophysics Data System (ADS)

Lonchakov, A. T.; Bobin, S. B.; Deryushkin, V. V.; Okulov, V. I.; Govorkova, T. E.; Neverov, V. N.

2018-02-01

Magnetoresistive properties of the single crystal of HgSe with a low electron concentration were studied in a wide range of temperatures and magnetic fields. Some fundamental parameters of the spectrum and scattering of electrons were experimentally determined. Two important features of magnetic transport were found—strong transverse magnetoresistance (MR) and negative longitudinal MR, which can indicate the existence of the topological phase of the Weyl semimetal (WSM) in HgSe. Taking this hypothesis into account, we suggest a modified band diagram of mercury selenide at low electron energies. The obtained results are essential for the deeper understanding of both physics of gapless semiconductors and WSMs—promising materials for various applications in electronics, spintronics, computer, and laser technologies.

Designing lateral spintronic devices with giant tunnel magnetoresistance and perfect spin injection efficiency based on transition metal dichalcogenides.

PubMed

Zhao, Pei; Li, Jianwei; Jin, Hao; Yu, Lin; Huang, Baibiao; Ying, Dai

2018-04-18

Giant tunnel magnetoresistance (TMR) and perfect spin-injection efficiency (SIE) are extremely significant for modern spintronic devices. Quantum transport properties in a two-dimensional (2D) VS2/MoS2/VS2 magnetic tunneling junction (MTJ) are investigated theoretically within the framework of density functional theory combining with the non-equilibrium Green's functions (DFT-NEGF) method. Our results indicate that the designed MTJ exhibits a TMR with a value up to 4 × 103, which can be used as a switch of spin-electron devices. And due to the huge barrier for spin-down transport, the spin-down electrons could hardly cross the central scattering region, thus achieving a perfect SIE. Furthermore, we also explore for the effect of bias voltage on the TMR and SIE. We find that the TMR increases with the increasing bias voltage, and the SIE is robust against either bias or gate voltage in MTJs, which can serve as effective spin filter devices. Our results can not only give fresh impetus to the research community to build MTJs but also provide potential materials for spintronic devices.

A CMOS Front-End With Integrated Magnetoresistive Sensors for Biomolecular Recognition Detection Applications.

PubMed

Costa, Tiago; Cardoso, Filipe A; Germano, Jose; Freitas, Paulo P; Piedade, Moises S

2017-10-01

The development of giant magnetoresistive (GMR) sensors has demonstrated significant advantages in nanomedicine, particularly for ultrasensitive point-of-care diagnostics. To this end, the detection system is required to be compact, portable, and low power consuming at the same time that a maximum signal to noise ratio is maintained. This paper reports a CMOS front-end with integrated magnetoresistive sensors for biomolecular recognition detection applications. Based on the characterization of the GMR sensor's signal and noise, CMOS building blocks (i.e., current source, multiplexers, and preamplifier) were designed targeting a negligible noise when compared with the GMR sensor's noise and a low power consumption. The CMOS front-end was fabricated using AMS [Formula: see text] technology and the magnetoresistive sensors were post-fabricated on top of the CMOS chip with high yield ( [Formula: see text]). Due to its low circuit noise (16 [Formula: see text]) and overall equivalent magnetic noise ([Formula: see text]), the full system was able to detect 250 nm magnetic nanoparticles with a circuit imposed signal-to-noise ratio degradation of only -1.4 dB. Furthermore, the low power consumption (6.5 mW) and small dimensions ([Formula: see text] ) of the presented solution guarantees the portability of the detection system allowing its usage at the point-of-care.

Three-dimensional fully-coupled electrical and thermal transport model of dynamic switching in oxide memristors

DOE PAGES

Gao, Xujiao; Mamaluy, Denis; Mickel, Patrick R.; ...

2015-09-08

In this paper, we present a fully-coupled electrical and thermal transport model for oxide memristors that solves simultaneously the time-dependent continuity equations for all relevant carriers, together with the time-dependent heat equation including Joule heating sources. The model captures all the important processes that drive memristive switching and is applicable to simulate switching behavior in a wide range of oxide memristors. The model is applied to simulate the ON switching in a 3D filamentary TaOx memristor. Simulation results show that, for uniform vacancy density in the OFF state, vacancies fill in the conduction filament till saturation, and then fill outmore » a gap formed in the Ta electrode during ON switching; furthermore, ON-switching time strongly depends on applied voltage and the ON-to-OFF current ratio is sensitive to the filament vacancy density in the OFF state.« less

Magnetization and magnetoresistance of common alloy wires used in cryogenic instrumentation.

PubMed

Abrecht, M; Adare, A; Ekin, J W

2007-04-01

We present magnetization and magnetoresistance data at liquid-helium and liquid-nitrogen temperatures for wire materials commonly used for instrumentation wiring of specimens, sensors, and heaters in cryogenic probes. The magnetic susceptibilities in Systeme International units at 4.2 K were found to be: Manganin 1.25x10(-2), Nichrome 5.6x10(-3), and phosphor bronze -3.3x10(-5), indicating that phosphor bronze is the most suitable for high-field applications. We also show the ferromagnetic hysteresis loop of Constantan wire at liquid-helium temperature. The magnetoresistance of these four wires was relatively small: the changes in resistance at 4 K due to a 10 T transverse magnetic field are -2.56% for Constantan, -2.83% for Manganin, +0.69% for Nichrome, and +4.5% for phosphor bronze, compared to about +188% for a typical copper wire under the same conditions.

Magnetization and magnetoresistance of common alloy wires used in cryogenic instrumentation

NASA Astrophysics Data System (ADS)

Abrecht, M.; Adare, A.; Ekin, J. W.

2007-04-01

We present magnetization and magnetoresistance data at liquid-helium and liquid-nitrogen temperatures for wire materials commonly used for instrumentation wiring of specimens, sensors, and heaters in cryogenic probes. The magnetic susceptibilities in Systeme International units at 4.2 K were found to be: Manganin 1.25×10-2, Nichrome 5.6×10-3, and phosphor bronze -3.3×10-5, indicating that phosphor bronze is the most suitable for high-field applications. We also show the ferromagnetic hysteresis loop of Constantan wire at liquid-helium temperature. The magnetoresistance of these four wires was relatively small: the changes in resistance at 4 K due to a 10 T transverse magnetic field are -2.56% for Constantan, -2.83% for Manganin, +0.69% for Nichrome, and +4.5% for phosphor bronze, compared to about +188% for a typical copper wire under the same conditions.

Development and Testing of a Variable Conductance Thermal Acquisition, Transport, and Switching System

NASA Technical Reports Server (NTRS)

Bugby, D. C.; Farmer, J. T.; Stouffer, C. J.

2013-01-01

This paper describes the development and testing of a scalable thermal control architecture for instruments, subsystems, or systems that must operate in severe space environments with wide variations in sink temperature. The architecture is comprised by linking one or more hot-side variable conductance heat pipes (VCHPs) in series with one or more cold-side loop heat pipes (LHPs). The VCHPs provide wide area heat acquisition, limited distance thermal transport, modest against gravity pumping, concentrated LHP startup heating, and high switching ratio variable conductance operation. The LHPs provide localized heat acquisition, long distance thermal transport, significant against gravity pumping, and high switching ratio variable conductance operation. Combining two variable conductance devices in series ensures very high switching ratio isolation from severe environments like the Earth's moon, where each lunar day spans 15 Earth days (270 K sink, with a surface-shielded/space viewing radiator) and each lunar night spans 15 Earth days (80-100 K radiative sink, depending on location). The single VCHP-single LHP system described herein was developed to maintain thermal control of International Lunar Network (ILN) anchor node lander electronics, but it is also applicable to other variable heat rejection space missions in severe environments. The LHPVCHP system utilizes a stainless steel wire mesh wick ammonia VCHP, a Teflon wick propylene LHP, a pair of one-third square meter high ? radiators (one capillary-pumped horizontal radiator and a second gravity-fed vertical radiator), a half-meter of transport distance, and a wick-bearing co-located flow regulator (CLFR) to allow operation with a hot (deactivated) radiator. The VCHP was designed with a small reservoir formed by extending the length of its stainless steel heat pipe tubing. The system was able to provide end-to-end switching ratios of 300-500 during thermal vacuum testing at ATK, including 3-5 W/K ON conductance

Development and Testing of a Variable Conductance Thermal Acquisition, Transport, and Switching System

NASA Technical Reports Server (NTRS)

Bugby, David C.; Farmer, Jeffery T.; Stouffer, Charles J.

2013-01-01

This paper describes the development and testing of a scalable thermal management architecture for instruments, subsystems, or systems that must operate in severe space environments with wide variations in sink temperature. The architecture involves a serial linkage of one or more hot-side variable conductance heat pipes (VCHPs) to one or more cold-side loop heat pipes (LHPs). The VCHPs provide wide area heat acquisition, limited distance thermal transport, modest against gravity pumping, concentrated LHP startup heating, and high switching ratio variable conductance operation. The LHPs provide localized heat acquisition, long distance thermal transport, significant against gravity pumping, and high switching ratio variable conductance operation. The single-VCHP, single-LHP system described herein was developed to maintain thermal control of a small robotic lunar lander throughout the lunar day-night thermal cycle. It is also applicable to other variable heat rejection space missions in severe environments. Operationally, despite a 60-70% gas blocked VCHP condenser during ON testing, the system was still able to provide 2-4 W/K ON conductance, 0.01 W/K OFF conductance, and an end-to-end switching ratio of 200-400. The paper provides a detailed analysis of VCHP condenser performance, which quantified the gas blockage situation. Future multi-VCHP/multi-LHP thermal management system concepts that provide power/transport length scalability are also discussed.

A wideband magnetoresistive sensor for monitoring dynamic fault slip in laboratory fault friction experiments

USGS Publications Warehouse

Kilgore, Brian D.

2017-01-01

A non-contact, wideband method of sensing dynamic fault slip in laboratory geophysical experiments employs an inexpensive magnetoresistive sensor, a small neodymium rare earth magnet, and user built application-specific wideband signal conditioning. The magnetoresistive sensor generates a voltage proportional to the changing angles of magnetic flux lines, generated by differential motion or rotation of the near-by magnet, through the sensor. The performance of an array of these sensors compares favorably to other conventional position sensing methods employed at multiple locations along a 2 m long × 0.4 m deep laboratory strike-slip fault. For these magnetoresistive sensors, the lack of resonance signals commonly encountered with cantilever-type position sensor mounting, the wide band response (DC to ≈ 100 kHz) that exceeds the capabilities of many traditional position sensors, and the small space required on the sample, make them attractive options for capturing high speed fault slip measurements in these laboratory experiments. An unanticipated observation of this study is the apparent sensitivity of this sensor to high frequency electomagnetic signals associated with fault rupture and (or) rupture propagation, which may offer new insights into the physics of earthquake faulting.

Switching from usual brand cigarettes to a tobacco-heating cigarette or snus: Part 3. Biomarkers of biological effect

PubMed Central

Ogden, Michael W.; Marano, Kristin M.; Jones, Bobbette A.; Morgan, Walter T.; Stiles, Mitchell F.

2015-01-01

Abstract A randomized, multi-center study of adult cigarette smokers switched to tobacco-heating cigarettes, snus or ultra-low machine yield tobacco-burning cigarettes (50/group) for 24 weeks was conducted. Evaluation of biomarkers of biological effect (e.g. inflammation, lipids, hypercoaguable state) indicated that the majority of consistent and statistically significant improvements over time within each group were observed in markers of inflammation. Consistent and statistically significant differences in pairwise comparisons between product groups were not observed. These findings are relevant to the understanding of biomarkers of biological effect related to cigarette smoking as well as the risk continuum across various tobacco products (ClinicalTrials.gov Identifier: NCT02061917). PMID:26525962

Giant magnetoresistance due to magnetoelectric currents in Sr{sub 3}Co{sub 2}Fe{sub 24}O{sub 41} hexaferrites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xian; School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074; Su, Zhijuan

2014-09-15

The giant magnetoresistance and magnetoelectric (ME) effects of Z-type hexaferrite Sr{sub 3}Co{sub 2}Fe{sub 24}O{sub 41} were investigated. The present experiments indicated that an induced magnetoelectric current in a transverse conical spin structure not only presented a nonlinear behavior with magnetic field and electric field but also depended upon a sweep rate of the applied magnetic field. More interestingly, the ME current induced magnetoresistance was measured, yielding a giant room temperature magnetoresistance of 32.2% measured at low magnetic fields (∼125 Oe). These results reveal great potential for emerging applications of multifunctional magnetoelectric ferrite materials.

Model for multishot all-thermal all-optical switching in ferromagnets

NASA Astrophysics Data System (ADS)

Gorchon, J.; Yang, Y.; Bokor, J.

2016-07-01

All-optical magnetic switching (AOS) is a recently observed rich and puzzling phenomenon that offers promising technological applications. However, a fundamental understanding of the underlying mechanisms remains elusive. Here we present a model for multishot helicity-dependent AOS in ferromagnetic materials based on a purely heat-driven mechanism in the presence of magnetic circular dichroism (MCD). We predict that AOS should be possible with as little as 0.5% of MCD, after a minimum number of laser shots heat the sample close to the Curie temperature. Finally, we qualitatively reproduce the all-optically switched domain patterns observed experimentally by numerically simulating the result of multiple laser shots on an FePtC granular ferromagnetic film.

Giant Tunnel Magnetoresistance with a Single Magnetic Phase-Transition Electrode

NASA Astrophysics Data System (ADS)

Zhang, Jia; Chen, X. Z.; Song, C.; Feng, J. F.; Wei, H. X.; Lü, Jing-Tao

2018-04-01

The magnetic phase-transition tunnel-magnetoresistance (MPT-TMR) effect with a single magnetic electrode is investigated by first-principles calculations. The calculations show that the MPT-TMR of an α'-FeRh /MgO /Cu tunnel junction can be as high as hundreds of percent when the magnetic structure of α'-FeRh changes from G -type antiferromagnetic (G -AFM ) to ferromagnetic order. This type of MPT-TMR may be superior to the tunnel anisotropic magnetoresistance because of its huge magnetoresistance effect and similar structural simplicity. The main mechanism for the giant MPT-TMR can be attributed to the formation of interface resonant states at the G -AFM FeRh /MgO interface. A direct FeRh /MgO interface is found to be necessary for achieving a high MPT-TMR experimentally. Moreover, we find the α'-FeRh /MgO interface with FeRh in the ferromagnetic phase has nearly full spin polarization due to the negligible majority transmission and significantly different Fermi surface of two spin channels. Thus, it may act as a highly efficient and tunable spin injector. In addition, the electric-field-driven MPT of FeRh-based heteromagnetic nanostructures can be utilized to design various energy-efficient tunnel-junction structures and the corresponding lower-power-consumption devices. We also discuss the consequence of various junction defects on MPT-TMR. The interface oxygen layer is found to be detrimental to MPT-TMR. The sign of MPT-TMR is reversed with Rh termination due to the lack of contribution from the interface resonance states. However, the MPT-TMR may be robust against the oxygen vacancy inside of MgO and the shift of the Fermi energy. Our results will stimulate further experimental investigations of MPT-TMR and other fascinating phenomenon of FeRh-based tunnel junctions that may be promising in antiferromagnetic spintronics.

Rapid detection of Escherichia coli O157:H7 using tunneling magnetoresistance biosensor

NASA Astrophysics Data System (ADS)

Wu, Yuanzhao; Liu, Yiwei; Zhan, Qingfeng; Liu, J. Ping; Li, Run-Wei

2017-05-01

A rapid method for the sensitive detection of bacteria using magnetic immunoassay, which are measured with a tunneling magnetoresistance (TMR) sensor, is described. For the measurement of Escherichia coli O157:H7 (E. coli O157:H7) bacteria, the target was labeled by magnetic beads through magnetic immunoassay. The magnetic beads produce a weak magnetic fringe field when external field is applied, thus induce the magnetoresistance change of TMR sensor. A detection limit of 100 CFU/mL E. coli O157:H7 bacteria in 5 hours was obtained. With its high sensitive and rapid detection scheme based on the TMR biosensor, the detection system is an excellent candidate suitable and promising for food safety and biomedical detection.

Colossal positive magnetoresistance in surface-passivated oxygen-deficient strontium titanite.

PubMed

David, Adrian; Tian, Yufeng; Yang, Ping; Gao, Xingyu; Lin, Weinan; Shah, Amish B; Zuo, Jian-Min; Prellier, Wilfrid; Wu, Tom

2015-05-15

Modulation of resistance by an external magnetic field, i.e. magnetoresistance effect, has been a long-lived theme of research due to both fundamental science and device applications. Here we report colossal positive magnetoresistance (CPMR) (>30,000% at a temperature of 2 K and a magnetic field of 9 T) discovered in degenerate semiconducting strontium titanite (SrTiO3) single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers. The low-pressure high-temperature homoepitaxial growth of several unit cells of SrTiO3 introduces oxygen vacancies and high-mobility carriers in the bulk SrTiO3, and the three-unit-cell LaAlO3 capping layer passivates the surface and improves carrier mobility by suppressing surface-defect-related scattering. The coexistence of multiple types of carriers and inhomogeneous transport lead to the emergence of CPMR. This unit-cell-level surface engineering approach is promising to be generalized to others oxides, and to realize devices with high-mobility carriers and interesting magnetoelectronic properties.

Flux concentration and modulation based magnetoresistive sensor with integrated planar compensation coils

NASA Astrophysics Data System (ADS)

Tian, Wugang; Hu, Jiafei; Pan, Mengchun; Chen, Dixiang; Zhao, Jianqiang

2013-03-01

1/f noise is one of the main noise sources of magnetoresistive (MR) sensors, which can cause intrinsic detection limit at low frequency. To suppress this noise, the solution of flux concentration and vertical motion modulation (VMM) has been proposed. Magnetic hysteresis in MR sensors is another problem, which degrades their response linearity and detection ability. To reduce this impact, the method of pulse magnetization and magnetic compensation field with integrated planar coils has been introduced. A flux concentration and VMM based magnetoresistive prototype sensor with integrated planar coils was fabricated using microelectromechanical-system technology. The response linearity of the prototype sensors is improved from 0.8% to 0.12%. The noise level is reduced near to the thermal noise level, and the low-frequency detection ability of the prototype sensor is enhanced with a factor of more than 80.

Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

NASA Astrophysics Data System (ADS)

Althammer, Matthias; Mishra, Rohan; Borisevich, Albina J.; Singh, Amit Vikam; Keshavarz, Sahar; Yurtisigi, Mehmet Kenan; Leclair, Patrick; Gupta, Arunava

We experimentally investigate the structural, magnetic and electrical transport properties of La0.67Sr0.33MnO3 based magnetic tunnel junctions with a SrSnO3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier the observed tunnel magnetoresistance is comparable to tunnel junctions with a better lattice matched SrTiO3 barrier, reaching values of up to 350 % at T = 5 K . Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease of the TMR with increasing bias voltage. Our results suggest that by reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future. We gratefully acknowledge financial support via NSF-ECCS Grant No. 1509875.

Negative magnetoresistance of ultra-narrow superconducting nanowires in the resistive state

NASA Astrophysics Data System (ADS)

Arutyunov, K. Yu.

2008-02-01

We present a phenomenological model that qualitatively explains negative magnetoresistance in quasi-one-dimensional superconducting channels in the resistive state. The model is based on the assumption that fluctuations of the order parameter (phase slips) are responsible for the finite effective resistance of a narrow superconducting wire sufficiently close to the critical temperature. Each fluctuation is accompanied by an instantaneous formation of a quasi-normal region, of the order of the non-equilibrium quasiparticle relaxation length, ‘pinned’ to the core of the phase slip. The effective time-averaged voltage measured in experiments is a sum of two terms. The first is the conventional contribution associated with the rate of the fluctuations via the Josephson relation. The second term is the Ohmic contribution of this quasi-normal region. Depending on the material properties of the wire, there might be a range of magnetic fields where the first term is not significantly affected, while the second term is effectively suppressed, contributing to the experimentally observed negative magnetoresistance.

Unusual negative magnetoresistance in Bi2Se3-ySy topological insulator under perpendicular magnetic field

NASA Astrophysics Data System (ADS)

Singh, Rahul; Gangwar, Vinod K.; Daga, D. D.; Singh, Abhishek; Ghosh, A. K.; Kumar, Manoranjan; Lakhani, A.; Singh, Rajeev; Chatterjee, Sandip

2018-03-01

The magneto-transport properties of Bi2Se3-ySy were investigated. Magnetoresistance (MR) decreases with an increase in the S content, and finally, for 7% (i.e., y = 0.21) S doping, the magnetoresistance becomes negative. This negative MR is unusual as it is observed when a magnetic field is applied in the perpendicular direction to the plane of the sample. The magneto-transport behavior shows the Shubnikov-de Haas (SdH) oscillation, indicating the coexistence of surface and bulk states. The negative MR has been attributed to the non-trivial bulk conduction.

Spin-glass and variable range hopping quantum interference magnetoresistance in FeSr2Y1.3Ce0.7Cu2O10-x

NASA Astrophysics Data System (ADS)

Sambale, S.; Williams, G. V. M.; Stephen, J.; Chong, S. V.

2014-12-01

Electronic transport and magnetic measurements have been made on FeSr2Y1.3Ce0.7Cu2O10-x. We observe a spin-glass at ˜23 K and a magnetoresistance that reaches -22% at 8 T. The magnetoresistance is due to variable range hopping quantum interference where at low temperatures each hop is over a large number of scatterers. This magnetoresistance is negative at and above 5 K and can be described by the Nguen, Spivak, and Shklovskii (NSS) model. However, there is an increasingly positive contribution to the magnetoresistance for temperatures below 5 K that may be due to scattering from localized free spins during each hop that is not accounted for in the NSS model.

AEA Cell-Bypass-Switch Activation: An Update

NASA Technical Reports Server (NTRS)

Keys, Denney; Rao, Gopalakrishna M.; Wannemacher, Harry

2002-01-01

The objectives of this project included the following: (1) verify the performance of AEA cell bypass protection device (CBPD) under simulated EOS-Aqua/Aura flight hardware configuration; (2) assess the safety of the hardware under an inadvertent firing of CBPD switch, as well as the closing of CBPD; and (3) confirm that the mode of operation of CBPD switch is the formation of a continuous low impedance path (a homogeneous low melting point alloy). The nominal performance of AEA CBPD under flight operating conditions (vacuum except zero-G, and high impedance cell) has been demonstrated. There is no evidence of cell rupture or excessive heat production during or after CBPD switch activation under simulated high cell impedance (open-circuit cell failure mode). The formation of a continuous low impedance path (a homogeneous low melting point alloy) has been confirmed.

Relation of Giant Thermo-EMF, Magnetothermo-EMF, Magnetoresistance, and Magnetization to Magnetic Impurity States in Manganites Nd(1- x)Sr x MnO3 and Sm(1- x)Sr x MnO3

NASA Astrophysics Data System (ADS)

Koroleva, L. I.; Batashev, I. K.; Morozov, A. S.; Balbashov, A. M.; Szymczak, H.; Slawska-Waniew, A.

2018-02-01

Thermo-EMF, magnetothermo-EMF, magnetoresistance, and magnetization of single-crystal samples of Nd(1- x)Sr x MnO3 and Sm(1- x)Sr x MnO3 with 0 ≤ x ≤ 0.3 have been studied experimentally. A sharp increase in the thermo-EMF and giant magnetothermo-EMF and magnetoresistance has been observed near the Curie point T C in compounds with 0.15 ≤ x ≤ 0.3. At the same time, no peculiarities have been found in compositions with x = 0. Since compounds with x > 0 consist of ferromagnetic clusters of the ferron type that reside in an antiferromagnetic A-type matrix, this means that the sharp increase in the thermo-EMF near T C is caused by ferrons. Indeed, the disappearance of ferrons due to a magnetic field or heating above T C leads to an abrupt decrease in the thermo-EMF. Therefore, thermo-EMF in alloyed magnetic semiconductors has been determined by the impurity concentration and the sample volume.

Neutron activated switch

DOEpatents

Barton, David M.

1991-01-01

A switch for reacting quickly to a neutron emission. A rod consisting of fissionable material is located inside a vacuum tight body. An adjustable contact is located coaxially at an adjustable distance from one end of the rod. Electrical leads are connected to the rod and to the adjustable contact. With a vacuum drawn inside the body, a neutron bombardment striking the rod causes it to heat and expand longitudinally until it comes into contact with the adjustable contact. This circuit closing occurs within a period of a few microseconds.

In-Plane Angular Effect of Magnetoresistance of Quasi-One-Dimensional Organic Metals, (DMET) 2AuBr 2 and (TMTSF) 2ClO 4

NASA Astrophysics Data System (ADS)

Yoshino, Harukazu; Saito, Kazuya; Nishikawa, Hiroyuki; Kikuchi, Koichi; Kobayashi, Keiji; Ikemoto, Isao

1997-08-01

Comparative study is presented for the in-plane angular effect of magnetoresistance of quasi-one-dimensional organic conductors, (DMET)2AuBr2 and (TMTSF)2ClO4. The magnetoresistance for the magnetic and electrical fields parallel and perpendicular to the most conducting plane, respectively, was measured at 4.2 K and up to 7.0 T. (DMET)2AuBr2 shows an anomalous hump in the field-orientation dependence of the magnetoresistance for the magnetic field nearly parallel to the most conducting axis and this is very similar to what previously reported for (DMET)2I3. Weak anomaly was detected for the magnetoresistance of (TMTSF)2ClO4 in the Relaxed state, while no anomaly was observed in the SDW phase in the Quenched state. By comparing the numerical angular derivatives of the magnetoresistance, it is shown that the anomaly in the in-plane angular effect continuously develops from zero magnetic field and is closely related to the quasi-one-dimensional Fermi surface. A simple method is proposed to estimate the anisotropy of the transfer integral from the width of the hump anomaly.

Current-induced SQUID behavior of superconducting Nb nano-rings

NASA Astrophysics Data System (ADS)

Sharon, Omri J.; Shaulov, Avner; Berger, Jorge; Sharoni, Amos; Yeshurun, Yosef

2016-06-01

The critical temperature in a superconducting ring changes periodically with the magnetic flux threading it, giving rise to the well-known Little-Parks magnetoresistance oscillations. Periodic changes of the critical current in a superconducting quantum interference device (SQUID), consisting of two Josephson junctions in a ring, lead to a different type of magnetoresistance oscillations utilized in detecting extremely small changes in magnetic fields. Here we demonstrate current-induced switching between Little-Parks and SQUID magnetoresistance oscillations in a superconducting nano-ring without Josephson junctions. Our measurements in Nb nano-rings show that as the bias current increases, the parabolic Little-Parks magnetoresistance oscillations become sinusoidal and eventually transform into oscillations typical of a SQUID. We associate this phenomenon with the flux-induced non-uniformity of the order parameter along a superconducting nano-ring, arising from the superconducting leads (‘arms’) attached to it. Current enhanced phase slip rates at the points with minimal order parameter create effective Josephson junctions in the ring, switching it into a SQUID.

Electrically tunable tunneling rectification magnetoresistance in magnetic tunneling junctions with asymmetric barriers.

PubMed

Wang, Jing; Huang, Qikun; Shi, Peng; Zhang, Kun; Tian, Yufeng; Yan, Shishen; Chen, Yanxue; Liu, Guolei; Kang, Shishou; Mei, Liangmo

2017-10-26

The development of multifunctional spintronic devices requires simultaneous control of multiple degrees of freedom of electrons, such as charge, spin and orbit, and especially a new physical functionality can be realized by combining two or more different physical mechanisms in one specific device. Here, we report the realization of novel tunneling rectification magnetoresistance (TRMR), where the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated in Co/CoO-ZnO/Co magnetic tunneling junctions with asymmetric tunneling barriers. Moreover, by simultaneously applying direct current and alternating current to the devices, the TRMR has been remarkably tuned in the range from -300% to 2200% at low temperature. This proof-of-concept investigation provides an unexplored avenue towards electrical and magnetic control of charge and spin, which may apply to other heterojunctions to give rise to more fascinating emergent functionalities for future spintronics applications.

Phonon-Mediated Colossal Magnetoresistance in Graphene/Black Phosphorus Heterostructures.

PubMed

Liu, Yanpeng; Yudhistira, Indra; Yang, Ming; Laksono, Evan; Luo, Yong Zheng; Chen, Jianyi; Lu, Junpeng; Feng, Yuan Ping; Adam, Shaffique; Loh, Kian Ping

2018-06-13

There is a huge demand for magnetoresistance (MR) sensors with high sensitivity, low energy consumption, and room temperature operation. It is well-known that spatial charge inhomogeneity due to impurities or defects introduces mobility fluctuations in monolayer graphene and gives rise to MR in the presence of an externally applied magnetic field. However, to realize a MR sensor based on this effect is hampered by the difficulty in controlling the spatial distribution of impurities and the weak magnetoresistance effect at the monolayer regime. Here, we fabricate a highly stable monolayer graphene-on-black phosphorus (G/BP) heterostructure device that exhibits a giant MR of 775% at 9 T magnetic field and 300 K, exceeding by far the MR effects from devices made from either monolayer graphene or few-layer BP alone. The positive MR of the G/BP device decreases when the temperature is lowered, indicating a phonon-mediated process in addition to scattering by charge impurities. Moreover, a nonlocal MR of >10 000% is achieved for the G/BP device at room temperature due to an enhanced flavor Hall effect induced by the BP channel. Our results show that electron-phonon coupling between 2D material and a suitable substrate can be exploited to create giant MR effects in Dirac semimetals.

Investigation of Non-Linear Optical Behavior of Semiconductors for Optical Switching. Volume 1.

DTIC Science & Technology

1987-09-30

a ’ 0.001 0.0014 0.0018 0.00 2 0.0026 0.003 0.0034. Figure 36 Plot of average grain size versus heat treatment temperature . i .1...linearity. This NLO behavior. switches on and off in sub-picosecond times. However, the switching time, the NLO coefficient and the operating temperature are...in sub-picosecond times. However, the switching time, the . 9NLO coefficient and the operating temperature are affected by the microstruc- ture of the

Strong influence of polaron-polaron interaction on the magnetoresistance effect in La0.7A0.3MnO3 thin films

NASA Astrophysics Data System (ADS)

Zhang, Haijuan; Wang, Kuidong; Zhang, Yuanyuan; Dong, Wenxia; Chen, Long; Tang, Xiaodong; Chen, Jie

2017-11-01

The colossal magnetoresistance effect endows La0.7A0.3MnO3 manganites distinctive fascination. Both theoretical and experimental studies demonstrated that the interplay among polarons could significantly influence magnetoresistance. However, the underlying microscopic mechanism of the influence remains elusive due to the lack of experimental evidences. Utilizing ultrafast optical spectroscopy to track the polaron dynamics around Curie temperatures, we observed a diverse two-step recovery process in three sibling manganite thin films with various magnetoresistance effects and Curie temperatures, while the slow step was proposed to be the formation evolution of correlated polarons through the polaron-polaron interaction. Polarons in La0.7Ca0.3MnO3 equilibrate much faster than those in La0.7(Ca0.58Sr0.42)0.3MnO3 and La0.7Sr0.3MnO3, indicating a comparatively tighter interaction between polarons and subsequently a stronger magnetoresistance effect.

A novel multi-actuation CMOS RF MEMS switch

NASA Astrophysics Data System (ADS)

Lee, Chiung-I.; Ko, Chih-Hsiang; Huang, Tsun-Che

2008-12-01

This paper demonstrates a capacitive shunt type RF MEMS switch, which is actuated by electro-thermal actuator and electrostatic actuator at the same time, and than latching the switching status by electrostatic force only. Since thermal actuators need relative low voltage compare to electrostatic actuators, and electrostatic force needs almost no power to maintain the switching status, the benefits of the mechanism are very low actuation voltage and low power consumption. Moreover, the RF MEMS switch has considered issues for integrated circuit compatible in design phase. So the switch is fabricated by a standard 0.35um 2P4M CMOS process and uses wet etching and dry etching technologies for postprocess. This compatible ability is important because the RF characteristics are not only related to the device itself. If a packaged RF switch and a packaged IC wired together, the parasitic capacitance will cause the problem for optimization. The structure of the switch consists of a set of CPW transmission lines and a suspended membrane. The CPW lines and the membrane are in metal layers of CMOS process. Besides, the electro-thermal actuators are designed by polysilicon layer of the CMOS process. So the RF switch is only CMOS process layers needed for both electro-thermal and electrostatic actuations in switch. The thermal actuator is composed of a three-dimensional membrane and two heaters. The membrane is a stacked step structure including two metal layers in CMOS process, and heat is generated by poly silicon resistors near the anchors of membrane. Measured results show that the actuation voltage of the switch is under 7V for electro-thermal added electrostatic actuation.

Spark gap switch system with condensable dielectric gas

DOEpatents

Thayer, III, William J.

1991-01-01

A spark gap switch system is disclosed which is capable of operating at a high pulse rate comprising an insulated switch housing having a purging gas entrance port and a gas exit port, a pair of spaced apart electrodes each having one end thereof within the housing and defining a spark gap therebetween, an easily condensable and preferably low molecular weight insulating gas flowing through the switch housing from the housing, a heat exchanger/condenser for condensing the insulating gas after it exits from the housing, a pump for recirculating the condensed insulating gas as a liquid back to the housing, and a heater exchanger/evaporator to vaporize at least a portion of the condensed insulating gas back into a vapor prior to flowing the insulating gas back into the housing.

Electric-field driven insulator-metal transition and tunable magnetoresistance in ZnO thin film

NASA Astrophysics Data System (ADS)

Zhang, Le; Chen, Shanshan; Chen, Xiangyang; Ye, Zhizhen; Zhu, Liping

2018-04-01

Electrical control of the multistate phase in semiconductors offers the promise of nonvolatile functionality in the future semiconductor spintronics. Here, by applying an external electric field, we have observed a gate-induced insulator-metal transition (MIT) with the temperature dependence of resistivity in ZnO thin films. Due to a high-density carrier accumulation, we have shown the ability to inverse change magnetoresistance in ZnO by ionic liquid gating from 10% to -2.5%. The evolution of photoluminescence under gate voltage was also consistent with the MIT, which is due to the reduction of dislocation. Our in-situ gate-controlled photoluminescence, insulator-metal transition, and the conversion of magnetoresistance open up opportunities in searching for quantum materials and ZnO based photoelectric devices.

Positive magnetoresistance of La0.7Sr0.3MnO3/C composites

NASA Astrophysics Data System (ADS)

Kabirov, Yu. V.; Gavrilyachenko, V. G.; Bogatin, A. S.

2016-07-01

The perovskite manganite La0.7Sr0.3MnO3 compound is used as a component in ceramic (1-x)(La0.7Sr0.3MnO3)-xC composites at x = 0.15-0.85. It is found that every studied specimen is characterized by the linear dependence of the positive magnetoresistance (PMR) on the magnetic field strength at room temperature. The 0.6(La0.7Sr0.3MnO3)-0.4C composite has the largest magnetoresistance value (15%) at room temperature and intensity of magnetic field H=15kOe. A possible mechanism for the PMR of (1-x)(La0.7Sr0.3MnO3)-xC composites is discussed.

Exchange bias and bistable magneto-resistance states in amorphous TbFeCo thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiaopu, E-mail: xl6ba@virginia.edu; Ma, Chung T.; Poon, S. Joseph, E-mail: sjp9x@virginia.edu

2016-01-04

Amorphous TbFeCo thin films sputter deposited at room temperature on thermally oxidized Si substrate are found to exhibit strong perpendicular magnetic anisotropy. Atom probe tomography, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy mapping have revealed two nanoscale amorphous phases with different Tb atomic percentages distributed within the amorphous film. Exchange bias accompanied by bistable magneto-resistance states has been uncovered near room temperature by magnetization and magneto-transport measurements. The exchange anisotropy originates from the exchange interaction between the ferrimagnetic and ferromagnetic components corresponding to the two amorphous phases. This study provides a platform for exchange bias and magneto-resistance switchingmore » using single-layer amorphous ferrimagnetic thin films that require no epitaxial growth.« less

Magnetoresistive Current Sensors for High Accuracy, High Bandwidth Current Measurement in Spacecraft Power Electronics

NASA Astrophysics Data System (ADS)

Slatter, Rolf; Goffin, Benoit

2014-08-01

The usage of magnetoresistive (MR) current sensors is increasing steadily in the field of power electronics. Current sensors must not only be accurate and dynamic, but must also be compact and robust. The MR effect is the basis for current sensors with a unique combination of precision and bandwidth in a compact package. A space-qualifiable magnetoresistive current sensor with high accuracy and high bandwidth is being jointly developed by the sensor manufacturer Sensitec and the spacecraft power electronics supplier Thales Alenia Space (T AS) Belgium. Test results for breadboards incorporating commercial-off-the-shelf (COTS) sensors are presented as well as an application example in the electronic control and power unit for the thrust vector actuators of the Ariane5-ME launcher.

Colossal Terahertz Magnetoresistance at Room Temperature in Epitaxial La0.7Sr0.3MnO3 Nanocomposites and Single-Phase Thin Films.

PubMed

Lloyd-Hughes, J; Mosley, C D W; Jones, S P P; Lees, M R; Chen, A; Jia, Q X; Choi, E-M; MacManus-Driscoll, J L

2017-04-12

Colossal magnetoresistance (CMR) is demonstrated at terahertz (THz) frequencies by using terahertz time-domain magnetospectroscopy to examine vertically aligned nanocomposites (VANs) and planar thin films of La 0.7 Sr 0.3 MnO 3 . At the Curie temperature (room temperature), the THz conductivity of the VAN was dramatically enhanced by over 2 orders of magnitude under the application of a magnetic field with a non-Drude THz conductivity that increased with frequency. The direct current (dc) CMR of the VAN is controlled by extrinsic magnetotransport mechanisms such as spin-polarized tunneling between nanograins. In contrast, we find that THz CMR is dominated by intrinsic, intragrain transport: the mean free path was smaller than the nanocolumn size, and the planar thin-film exhibited similar THz CMR to the VAN. Surprisingly, the observed colossal THz magnetoresistance suggests that the magnetoresistance can be large for alternating current motion on nanometer length scales, even when the magnetoresistance is negligible on the macroscopic length scales probed by dc transport. This suggests that colossal magnetoresistance at THz frequencies may find use in nanoelectronics and in THz optical components controlled by magnetic fields. The VAN can be scaled in thickness while retaining a high structural quality and offers a larger THz CMR at room temperature than the planar film.

Influence of nonmagnetic Al ions on magnetoresistance of double-perovskite Sr2Fe1-xAlxMoO6 (0<=x<=0.30)

NASA Astrophysics Data System (ADS)

Sui, Yu; Wang, Xianjie; Cheng, Jinguang; Liu, Zhiguo; Miao, Jipeng; Huang, Xiqiang; Lu, Zhe; Qian, Zhengnan; Su, Wenhui; Tang, Jinke; Ong, C. K.

2005-09-01

The structural, magnetic, and magnetoresistance properties of the double-perovskite series Sr2Fe1-xAlxMoO6 (0<=x<=0.30) were systematically investigated in order to clarify the influence of nonmagnetic Al ions on the magnetoresistance. The structural refinements of these samples show that the degree of cationic order increases gradually from 88.5% for x=0 to 92% for x=0.30 without any change in the crystal structure. The magnetization measurements reveal that the substitution of nonmagnetic Al ion for Fe ion enhances the magnetic moment per Fe ion significantly. In addition, the magnetic-field dependence of magnetization and magnetoresistance of these Sr2Fe1-xAlxMoO6 samples were all fitted excellently by taking into account the contributions from ferromagnetic-coupled Fe-O-Mo region and nonferromagnetic-coupled regions. The fitting results indicate that the low-field magnetoresistance can be greatly enhanced due to the separation of the cationic-ordered Fe-O-Mo regions by the paramagnetic Mo-O-Al-O-Mo chains introduced through Al doping. Furthermore, doping nonmagnetic Al ions also suppress the formation of antiferromagnetic Fe-O-Fe antiphase boundaries, and then lead to the improvement of cation ordering and the reduction of magnetoresistance under high field.

Pure spin-Hall magnetoresistance in Rh/Y3Fe5O12 hybrid

NASA Astrophysics Data System (ADS)

Shang, T.; Zhan, Q. F.; Ma, L.; Yang, H. L.; Zuo, Z. H.; Xie, Y. L.; Li, H. H.; Liu, L. P.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2015-12-01

We report an investigation of anisotropic magnetoresistance (AMR) and anomalous Hall resistance (AHR) of Rh and Pt thin films sputtered on epitaxial Y3Fe5O12 (YIG) ferromagnetic insulator films. For the Pt/YIG hybrid, large spin-Hall magne toresistance (SMR) along with a sizable conventional anisotropic magnetoresistance (CAMR) and a nontrivial temperature dependence of AHR were observed in the temperature range of 5-300 K. In contrast, a reduced SMR with negligible CAMR and AHR was found in Rh/YIG hybrid. Since CAMR and AHR are characteristics for all ferromagnetic metals, our results suggest that the Pt is likely magnetized by YIG due to the magnetic proximity effect (MPE) while Rh remains free of MPE. Thus the Rh/YIG hybrid could be an ideal model system to explore physics and devices associated with pure spin current.

Using granular C0-AI2O3 spacer for optimization of functional parameters of the FeMn/Fe20Ni80 magnetoresistive films

NASA Astrophysics Data System (ADS)

Gorkovenko, A. N.; Lepalovskij, V. N.; Adanakova, O. A.; Vas'kovskiy, V. O.

2016-03-01

In this paper we studied the possibility of tailoring the functional properties of the multilayer magnetoresistive medium with unidirectional anisotropy and the anisotropic magnetoresistance effect (AMR). Objects of the research were composite Co-Al2O3 films and Ta/Fe20Ni80/Fe50Mn50/Fe20Ni80/Co-Al2O3/Fe20Ni80/Ta multilayers structures obtained by magnetron sputtering and selectively subjected vacuum annealing. Structure, magnetic and magnetoresistive properties of the films in the temperature range 77÷440 K were investigated.

Tunable heat transfer with smart nanofluids.

PubMed

Bernardin, Michele; Comitani, Federico; Vailati, Alberto

2012-06-01

Strongly thermophilic nanofluids are able to transfer either small or large quantities of heat when subjected to a stable temperature difference. We investigate the bistability diagram of the heat transferred by this class of nanofluids. We show that bistability can be exploited to obtain a controlled switching between a conductive and a convective regime of heat transfer, so as to achieve a controlled modulation of the heat flux.

Integration of planar transformer and/or planar inductor with power switches in power converter

DOEpatents

Chen, Kanghua; Ahmed, Sayeed; Zhu, Lizhi

2007-10-30

A power converter integrates at least one planar transformer comprising a multi-layer transformer substrate and/or at least one planar inductor comprising a multi-layer inductor substrate with a number of power semiconductor switches physically and thermally coupled to a heat sink via one or more multi-layer switch substrates.

Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

DOE PAGES

Althammer, Matthias; Bavarian Academy of Sciences and Humanities; Vikam Singh, Amit; ...

2016-12-16

In this paper, we experimentally investigate the structural, magnetic, and electrical transport properties of La 0.67 Sr 0.33MnO 3 based magnetic tunnel junctions with a SrSnO 3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier, due to the large lattice mismatch, the observed tunnel magnetoresistance (TMR) is comparable to tunnel junctions with a better lattice matched SrTiO 3 barrier, reaching values of up to 350% at T = 5K. Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease ofmore » the TMR with increasing bias voltage. In addition, the observed TMR vanishes for T > 200K. Finally, our results suggest that by employing a better lattice matched ferromagnetic electrode, and thus reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future.« less

Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Althammer, Matthias; Bavarian Academy of Sciences and Humanities; Vikam Singh, Amit

In this paper, we experimentally investigate the structural, magnetic, and electrical transport properties of La 0.67 Sr 0.33MnO 3 based magnetic tunnel junctions with a SrSnO 3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier, due to the large lattice mismatch, the observed tunnel magnetoresistance (TMR) is comparable to tunnel junctions with a better lattice matched SrTiO 3 barrier, reaching values of up to 350% at T = 5K. Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease ofmore » the TMR with increasing bias voltage. In addition, the observed TMR vanishes for T > 200K. Finally, our results suggest that by employing a better lattice matched ferromagnetic electrode, and thus reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future.« less

Extremely Large Magnetoresistance in a Topological Semimetal Candidate Pyrite PtBi2

NASA Astrophysics Data System (ADS)

Gao, Wenshuai; Hao, Ningning; Zheng, Fa-Wei; Ning, Wei; Wu, Min; Zhu, Xiangde; Zheng, Guolin; Zhang, Jinglei; Lu, Jianwei; Zhang, Hongwei; Xi, Chuanying; Yang, Jiyong; Du, Haifeng; Zhang, Ping; Zhang, Yuheng; Tian, Mingliang

2017-06-01

While pyrite-type PtBi2 with a face-centered cubic structure has been predicted to be a three-dimensional (3D) Dirac semimetal, experimental study of its physical properties remains absent. Here we report the angular-dependent magnetoresistance measurements of a PtBi2 single crystal under high magnetic fields. We observed extremely large unsaturated magnetoresistance (XMR) up to (11.2 ×106)% at T =1.8 K in a magnetic field of 33 T, which is comparable to the previously reported Dirac materials, such as WTe2 , LaSb, and NbP. The crystals exhibit an ultrahigh mobility and significant Shubnikov-de Hass quantum oscillations with a nontrivial Berry phase. The analysis of Hall resistivity indicates that the XMR can be ascribed to the nearly compensated electron and hole. Our experimental results associated with the ab initio calculations suggest that pyrite PtBi2 is a topological semimetal candidate that might provide a platform for exploring topological materials with XMR in noble metal alloys.

Co layer fragmentation effect on magnetoresistive and structural properties of nanogranular Co/Cu multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spizzo, F.; Ronconi, F.; Ferrero, C.

We deposited nanogranular Co/Cu multilayers made of thin fragmented Co layers separated by thicker Cu layers to study how the structure and the microstructure of magnetic nanogranular samples change as the average particle size is reduced and how these changes affect the giant magnetoresistive response of the samples. Indeed, thanks to the vertical periodicity of the structure, namely, to the fact that Co/Cu interfaces display an ordered stacking and are not randomly distributed within the samples as in conventional granular materials, their self-correlation and cross correlation can be investigated. In this way, the characteristic length scale of the Co/Cu interfacialmore » roughness that is strictly related to the giant magnetoresistive response of the samples and the universality class of the growth mechanism that affects the systems structure can be both accessed. The Co/Cu nanogranular multilayers were characterized using different x-ray techniques, from specular reflectivity, which allows to probe the multilayer development in the vertical direction, to grazing incidence small angle diffuse scattering, which provides information on the self-correlation and cross correlation of the Co/Cu interfaces. Furthermore, diffraction measurements indicate that the degree of structural disorder increases by decreasing the thickness of the Co layers. Magnetoresistive and magnetization measurements are as well presented and discussed with the results of the structural characterization.« less

Study of magnetization switching in coupled magnetic nanostructured systems

NASA Astrophysics Data System (ADS)

Radu, Cosmin

A study of magnetization dynamics experiments in nanostructured materials using the rf susceptibility tunnel diode oscillator (TDO) method is presented along with a extensive theoretical analysis. An original, computer controlled experimental setup that measures the change in susceptibility with the variation in external magnetic field and sample temperature was constructed. The TDO-based experiment design and construction is explained in detail, showing all the elements of originality. This experimental technique has proven reliable for characterizing samples with uncoupled magnetic structure and various magnetic anisotropies like: CrO2, FeCo/IrMn and Co/SiO2 thin films. The TDO was subsequently used to explore the magnetization switching in coupled magnetic systems, like synthetic antiferromagnet (SAF) structures. Magnetoresistive random access memory (MRAM) is an important example of devices where the use of SAF structure is essential. To support the understanding of the SAF magnetic behavior, its configuration and application are reviewed and more details are provided in an appendix. Current problems in increasing the scalability and decreasing the error rate of MRAM devices are closely connected to the switching properties of the SAF structures. Several theoretical studies that were devoted to the understanding of the concepts of SAF critical curve are reviewed. As one can notice, there was no experimental determination of SAF critical curve, due to the difficulties in characterizing a magnetic coupled structure. Depending of the coupling strength between the two ferromagnetic layers, on the SAF critical curve one distinguishes several new features, inexistent in the case of uncoupled systems. Knowing the configuration of the SAF critical curve is of great importance in order to control its switching characteristics. For the first time a method of experimentally recording the critical curve for SAF is proposed in this work. In order to overcome technological

Morphological analysis of GeTe in inline phase change switches

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, Matthew R., E-mail: matthew.king2@ngc.com; Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695; El-Hinnawy, Nabil

2015-09-07

Crystallization and amorphization phenomena in indirectly heated phase change material-based devices were investigated. Scanning transmission electron microscopy was utilized to explore GeTe phase transition processes in the context of the unique inline phase change switch (IPCS) architecture. A monolithically integrated thin film heating element successfully converted GeTe to ON and OFF states. Device cycling prompted the formation of an active area which sustains the majority of structural changes during pulsing. A transition region on both sides of the active area consisting of polycrystalline GeTe and small nuclei (<15 nm) in an amorphous matrix was also observed. The switching mechanism, determined bymore » variations in pulsing parameters, was shown to be predominantly growth-driven. A preliminary model for crystallization and amorphization in IPCS devices is presented.« less

Cold-Rolled Strip Steel Stress Detection Technology Based on a Magnetoresistance Sensor and the Magnetoelastic Effect.

PubMed

Guan, Ben; Zang, Yong; Han, Xiaohui; Zheng, Kailun

2018-05-21

Driven by the demands for contactless stress detection, technologies are being used for shape control when producing cold-rolled strips. This paper presents a novel contactless stress detection technology based on a magnetoresistance sensor and the magnetoelastic effect, enabling the detection of internal stress in manufactured cold-rolled strips. An experimental device was designed and produced. Characteristics of this detection technology were investigated through experiments assisted by theoretical analysis. Theoretically, a linear correlation exists between the internal stress of strip steel and the voltage output of a magneto-resistive sensor. Therefore, for this stress detection system, the sensitivity of the stress detection was adjusted by adjusting the supply voltage of the magnetoresistance sensor, detection distance, and other relevant parameters. The stress detection experimental results showed that this detection system has good repeatability and linearity. The detection error was controlled within 1.5%. Moreover, the intrinsic factors of the detected strip steel, including thickness, carbon percentage, and crystal orientation, also affected the sensitivity of the detection system. The detection technology proposed in this research enables online contactless detection and meets the requirements for cold-rolled steel strips.

Cold-Rolled Strip Steel Stress Detection Technology Based on a Magnetoresistance Sensor and the Magnetoelastic Effect

PubMed Central

Guan, Ben; Zang, Yong; Han, Xiaohui; Zheng, Kailun

2018-01-01

Driven by the demands for contactless stress detection, technologies are being used for shape control when producing cold-rolled strips. This paper presents a novel contactless stress detection technology based on a magnetoresistance sensor and the magnetoelastic effect, enabling the detection of internal stress in manufactured cold-rolled strips. An experimental device was designed and produced. Characteristics of this detection technology were investigated through experiments assisted by theoretical analysis. Theoretically, a linear correlation exists between the internal stress of strip steel and the voltage output of a magneto-resistive sensor. Therefore, for this stress detection system, the sensitivity of the stress detection was adjusted by adjusting the supply voltage of the magnetoresistance sensor, detection distance, and other relevant parameters. The stress detection experimental results showed that this detection system has good repeatability and linearity. The detection error was controlled within 1.5%. Moreover, the intrinsic factors of the detected strip steel, including thickness, carbon percentage, and crystal orientation, also affected the sensitivity of the detection system. The detection technology proposed in this research enables online contactless detection and meets the requirements for cold-rolled steel strips. PMID:29883387

Negative Magnetoresistance in Amorphous Indium Oxide Wires

PubMed Central

Mitra, Sreemanta; Tewari, Girish C; Mahalu, Diana; Shahar, Dan

2016-01-01

We study magneto-transport properties of several amorphous Indium oxide nanowires of different widths. The wires show superconducting transition at zero magnetic field, but, there exist a finite resistance at the lowest temperature. The R(T) broadening was explained by available phase slip models. At low field, and far below the superconducting critical temperature, the wires with diameter equal to or less than 100 nm, show negative magnetoresistance (nMR). The magnitude of nMR and the crossover field are found to be dependent on both temperature and the cross-sectional area. We find that this intriguing behavior originates from the interplay between two field dependent contributions. PMID:27876859

Optical switches and switching methods

DOEpatents

Doty, Michael

2008-03-04

A device and method for collecting subject responses, particularly during magnetic imaging experiments and testing using a method such as functional MRI. The device comprises a non-metallic input device which is coupled via fiber optic cables to a computer or other data collection device. One or more optical switches transmit the subject's responses. The input device keeps the subject's fingers comfortably aligned with the switches by partially immobilizing the forearm, wrist, and/or hand of the subject. Also a robust nonmetallic switch, particularly for use with the input device and methods for optical switching.

Temperature Dependent Magnetoresistance of CeCu2Si2 up to 60 T [Proposal: P14728

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stritzinger, Laurel Elaine Winter; Lai, Y.; Mcdonald, Ross David

2017-03-23

We recently investigated the chemical substitution series CeCu2Si2-xPx, for x = 0, 0.01, and 0.14, using a contactless tunnel diode oscillator technique. These measurements revealed previously unreported Shubnikov-de Haas oscillations above 45 T with an unusual temperature dependence that could potentially be explained by a high magnetic field transition. To investigate this possible transition, magnetoresistance measurements were desired. However, initial magnetoresistance measurements on CeCu2Si2 showed poor signal-to-noise due to the small value of the sample's resistivity. To overcome this obstacle, we performed micro-structuring of a single crystal specimen to increase the sample's resistance.

Switch wear leveling

DOEpatents

Wu, Hunter; Sealy, Kylee; Gilchrist, Aaron

2015-09-01

An apparatus for switch wear leveling includes a switching module that controls switching for two or more pairs of switches in a switching power converter. The switching module controls switches based on a duty cycle control technique and closes and opens each switch in a switching sequence. The pairs of switches connect to a positive and negative terminal of a DC voltage source. For a first switching sequence a first switch of a pair of switches has a higher switching power loss than a second switch of the pair of switches. The apparatus includes a switch rotation module that changes the switching sequence of the two or more pairs of switches from the first switching sequence to a second switching sequence. The second switch of a pair of switches has a higher switching power loss than the first switch of the pair of switches during the second switching sequence.

A mechanically driven switch for decoupling cryocoolers

NASA Astrophysics Data System (ADS)

van der Laan, M. T. G.; Tax, R.; Ten Kate, H. H. J.; van de Klundert, L. J. M.

A superconductive magnet system solely cooled by thermal conduction and two Gifford-McMahon cryocoolers has been developed. One cooler is redundant to obtain reliable and serviceable operation. The magnet operates at a temperature of 12 K. In order to reduce the heat flux into the system when one cooler is out of service, two thermal switches were developed with the following features. In both cases, thermal contact is made by pressing two or more pieces of metal against each other. The first switch is a lathe-chuck type and consists of three metal pieces symmetrically arranged around a metal bar. They are simultaneously pushed in a radial direction thus making mechanical and thermal contact. The second is a bench-vise type. A metal bar is clamped between two metal jaws by means of the action of a screw driven by an external torque. In both cases, relatively fast switching is possible. The thermal resistance obtained in the on-state was better than 0.5 W/K, and in the off-state at least a factor of 1000 less. Thermal and mechanical cycling appeared to have no large influence on the switch performance.

Switch Transcripts in Immunoglobulin Class Switching

NASA Astrophysics Data System (ADS)

Lorenz, Matthias; Jung, Steffen; Radbruch, Andreas

1995-03-01

B cells can exchange gene segments for the constant region of the immunoglobulin heavy chain, altering the class and effector function of the antibodies that they produce. Class switching is directed to distinct classes by cytokines, which induce transcription of the targeted DNA sequences. These transcripts are processed, resulting in spliced "switch" transcripts. Switch recombination can be directed to immunoglobulin G1 (IgG1) by the heterologous human metallothionein II_A promoter in mutant mice. Induction of the structurally conserved, spliced switch transcripts is sufficient to target switch recombination to IgG1, whereas transcription alone is not.

Realisation of all 16 Boolean logic functions in a single magnetoresistance memory cell

NASA Astrophysics Data System (ADS)

Gao, Shuang; Yang, Guang; Cui, Bin; Wang, Shouguo; Zeng, Fei; Song, Cheng; Pan, Feng

2016-06-01

Stateful logic circuits based on next-generation nonvolatile memories, such as magnetoresistance random access memory (MRAM), promise to break the long-standing von Neumann bottleneck in state-of-the-art data processing devices. For the successful commercialisation of stateful logic circuits, a critical step is realizing the best use of a single memory cell to perform logic functions. In this work, we propose a method for implementing all 16 Boolean logic functions in a single MRAM cell, namely a magnetoresistance (MR) unit. Based on our experimental results, we conclude that this method is applicable to any MR unit with a double-hump-like hysteresis loop, especially pseudo-spin-valve magnetic tunnel junctions with a high MR ratio. Moreover, after simply reversing the correspondence between voltage signals and output logic values, this method could also be applicable to any MR unit with a double-pit-like hysteresis loop. These results may provide a helpful solution for the final commercialisation of MRAM-based stateful logic circuits in the near future.Stateful logic circuits based on next-generation nonvolatile memories, such as magnetoresistance random access memory (MRAM), promise to break the long-standing von Neumann bottleneck in state-of-the-art data processing devices. For the successful commercialisation of stateful logic circuits, a critical step is realizing the best use of a single memory cell to perform logic functions. In this work, we propose a method for implementing all 16 Boolean logic functions in a single MRAM cell, namely a magnetoresistance (MR) unit. Based on our experimental results, we conclude that this method is applicable to any MR unit with a double-hump-like hysteresis loop, especially pseudo-spin-valve magnetic tunnel junctions with a high MR ratio. Moreover, after simply reversing the correspondence between voltage signals and output logic values, this method could also be applicable to any MR unit with a double-pit-like hysteresis

Large room-temperature tunneling anisotropic magnetoresistance and electroresistance in single ferromagnet/Nb:SrTiO3 Schottky devices.

PubMed

Kamerbeek, Alexander M; Ruiter, Roald; Banerjee, Tamalika

2018-01-22

There is a large effort in research and development to realize electronic devices capable of storing information in new ways - for instance devices which simultaneously exhibit electro and magnetoresistance. However it remains a challenge to create devices in which both effects coexist. In this work we show that the well-known electroresistance in noble metal-Nb:SrTiO 3 Schottky junctions can be augmented by a magnetoresistance effect in the same junction. This is realized by replacing the noble metal electrode with ferromagnetic Co. This magnetoresistance manifests as a room temperature tunneling anisotropic magnetoresistance (TAMR). The maximum room temperature TAMR (1.6%) is significantly larger and robuster with bias than observed earlier, not using Nb:SrTiO 3 . In a different set of devices, a thin amorphous AlO x interlayer inserted between Co and Nb:SrTiO 3 , reduces the TAMR by more than 2 orders of magnitude. This points to the importance of intimate contact between the Co and Nb:SrTiO 3 for the TAMR effect. This is explained by electric field enhanced spin-orbit coupling of the interfacial Co layer in contact with Nb:SrTiO 3 . We propose that the large TAMR likely has its origin in the 3d orbital derived conduction band and large relative permittivity of Nb:SrTiO 3 and discuss ways to further enhance the TAMR.

Geothermal switch heater installation, testing and monitoring : phases 1 & 2.

DOT National Transportation Integrated Search

2016-07-01

Transportation Technology Center, Inc. (TTCI), Norfolk Southern (NS), and John A. Volpe National Transportation Systems Center (Volpe) completed Phases 1 and 2 of a project on a working prototype geothermal switch heating system designed to test the ...

Development and Application of Wide Bandwidth Magneto-Resistive Sensor Based Eddy Current Probe

NASA Technical Reports Server (NTRS)

Wincheski, Russell A.; Simpson, John

2010-01-01

The integration of magneto-resistive sensors into eddy current probes can significantly expand the capabilities of conventional eddy current nondestructive evaluation techniques. The room temperature solid-state sensors have typical bandwidths in the megahertz range and resolutions of tens of microgauss. The low frequency sensitivity of magneto-resistive sensors has been capitalized upon in previous research to fabricate very low frequency eddy current sensors for deep flaw detection in multilayer conductors. In this work a modified probe design is presented to expand the capabilities of the device. The new probe design incorporates a dual induction source enabling operation from low frequency deep flaw detection to high frequency high resolution near surface material characterization. Applications of the probe for the detection of localized near surface conductivity anomalies are presented. Finite element modeling of the probe is shown to be in good agreement with experimental measurements.

A Wireless Magnetoresistive Sensing System for an Intraoral Tongue-Computer Interface

PubMed Central

Park, Hangue; Kiani, Mehdi; Lee, Hyung-Min; Kim, Jeonghee; Block, Jacob; Gosselin, Benoit; Ghovanloo, Maysam

2015-01-01

Tongue drive system (TDS) is a tongue-operated, minimally invasive, unobtrusive, and wireless assistive technology (AT) that infers users’ intentions by detecting their voluntary tongue motion and translating them into user-defined commands. Here we present the new intraoral version of the TDS (iTDS), which has been implemented in the form of a dental retainer. The iTDS system-on-a-chip (SoC) features a configurable analog front-end (AFE) that reads the magnetic field variations inside the mouth from four 3-axial magnetoresistive sensors located at four corners of the iTDS printed circuit board (PCB). A dual-band transmitter (Tx) on the same chip operates at 27 and 432 MHz in the Industrial/Scientific/Medical (ISM) band to allow users to switch in the presence of external interference. The Tx streams the digitized samples to a custom-designed TDS universal interface, built from commercial off-the-shelf (COTS) components, which delivers the iTDS data to other devices such as smartphones, personal computers (PC), and powered wheelchairs (PWC). Another key block on the iTDS SoC is the power management integrated circuit (PMIC), which provides individually regulated and duty-cycled 1.8 V supplies for sensors, AFE, Tx, and digital control blocks. The PMIC also charges a 50 mAh Li-ion battery with constant current up to 4.2 V, and recovers data and clock to update its configuration register through a 13.56 MHz inductive link. The iTDS SoC has been implemented in a 0.5-μm standard CMOS process and consumes 3.7 mW on average. PMID:23853258

High magnetic field magnetoresistance anomalies in the charge density wave state of the quasi-two dimensional bronze KMo6O{17}

NASA Astrophysics Data System (ADS)

Guyot, H.; Dumas, J.; Marcus, J.; Schlenker, C.; Vignolles, D.

2005-12-01

We report high magnetic field magnetoresistance measurements performed in pulsed fields up to 55 T on the quasi-two dimensional charge density wave conductor KMo{6}O{17}. Magnetoresistance curves show several anomalies below 28 T. First order transitions to smaller gap states take place at low temperature above 30 T. A phase diagram T(B) has been obtained. The angular dependence of the anomalies is reported.

Colossal terahertz magnetoresistance at room temperature in epitaxial La 0.7Sr 0.3MnO 3 nanocomposites and single-phase thin films

DOE PAGES

Lloyd-Hughes, James; Mosley, C. D. W.; Jones, S. P. P.; ...

2017-03-13

Colossal magnetoresistance (CMR) is demonstrated at terahertz (THz) frequencies by using terahertz time-domain magnetospectroscopy to examine vertically aligned nanocomposites (VANs) and planar thin films of La 0.7Sr 0.3MnO 3. At the Curie temperature (room temperature), the THz conductivity of the VAN was dramatically enhanced by over 2 orders of magnitude under the application of a magnetic field with a non-Drude THz conductivity that increased with frequency. The direct current (dc) CMR of the VAN is controlled by extrinsic magnetotransport mechanisms such as spin-polarized tunneling between nanograins. In contrast, we find that THz CMR is dominated by intrinsic, intragrain transport: themore » mean free path was smaller than the nanocolumn size, and the planar thin-film exhibited similar THz CMR to the VAN. Surprisingly, the observed colossal THz magnetoresistance suggests that the magnetoresistance can be large for alternating current motion on nanometer length scales, even when the magnetoresistance is negligible on the macroscopic length scales probed by dc transport. This suggests that colossal magnetoresistance at THz frequencies may find use in nanoelectronics and in THz optical components controlled by magnetic fields. As a result, the VAN can be scaled in thickness while retaining a high structural quality and offers a larger THz CMR at room temperature than the planar film.« less

Switching behaviour of individual Ag-TCNQ nanowires: an in situ transmission electron microscopy study

NASA Astrophysics Data System (ADS)

Ran, Ke; Rösner, Benedikt; Butz, Benjamin; Fink, Rainer H.; Spiecker, Erdmann

2016-10-01

The organic semiconductor silver-tetracyanoquinodimethane (Ag-TCNQ) exhibits electrical switching and memory characteristics. Employing a scanning tunnelling microscopy setup inside a transmission electron microscope, the switching behaviour of individual Ag-TCNQ nanowires (NWs) is investigated in detail. For a large number of NWs, the switching between a high (OFF) and a low (ON) resistance state was successfully stimulated by negative bias sweeps. Fitting the experimental I-V curves with a Schottky emission function makes the switching features prominent and thus enables a direct evaluation of the switching process. A memory cycle including writing, reading and erasing features is demonstrated at an individual NW. Moreover, electronic failure mechanisms due to Joule heating are discussed. These findings have a significant impact on our understanding of the switching behaviour of Ag-TCNQ.

Degradation of the Giant Magnetoresistance in Fe/Cr Multilayers Due to Ar-Ion Beam Mixing

NASA Astrophysics Data System (ADS)

Kopcewicz, M.; Stobiecki, F.; Jagielski, J.; Szymański, B.; Schmidt, M.; Kalinowska, J.

2002-12-01

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in the Fe/Cr multilayer system exhibiting the giant magnetoresistance effect (GMR) is studied by conversion electron Mössbauer spectroscopy (CEMS), VSM hysteresis loops, magnetoresistivity and electric resistivity measurements and supplemented by the small-angle X-ray diffraction (SAXRD). The increase of Ar ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step-sites detected by CEMS as a result of which the GMR gradually decreases and vanishes at doses exceeding 1×1014 Ar/cm2. A degradation of GMR with increasing Ar-ion dose is related to the formation of pinholes between Fe layers and the decrease of the antiferromagnetically coupled fraction.

Template-switching during DNA synthesis by Thermus aquaticus DNA polymerase I.

PubMed Central

Odelberg, S J; Weiss, R B; Hata, A; White, R

1995-01-01

Recombinant DNA molecules are often generated during the polymerase chain reaction (PCR) when partially homologous templates are available [e.g., see Pääbo et al. (1990) J. Biol. Chem. 265, 4718-4721]. It has been suggested that these recombinant molecules are a consequence of truncated extension products annealing to partially homologous templates on subsequent PCR cycles. However, we demonstrate here that recombinants can be generated during a single round of primer extension in the absence of subsequent heat denaturation, indicating that template-switching produces some of these recombinant molecules. Two types of template-switches were observed: (i) switches to pre-existing templates and (ii) switches to the complementary nascent strand. Recombination is reduced several fold when the complementary template strands are physically separated by attachment to streptavidin magnetic beads. This result supports the hypothesis that either the polymerase or at least one of the two extending strands switches templates during DNA synthesis and that interaction between the complementary template strands is necessary for efficient template-switching. Images PMID:7596836

Interfacial exchange, magnetic coupling and magnetoresistance in ultra-thin GdN/NbN/GdN tri-layers

NASA Astrophysics Data System (ADS)

Takamura, Yota; Goncalves, Rafael S.; Cascales, Juan Pedro; Altinkok, Atilgan; de Araujo, Clodoaldo I. L.; Lauter, Valeria; Moodera, Jagadeesh S.; MIT Team

Superconducting spin-valve structures with a superconductive (SC) spacer sandwiched between ferromagnetic (FM) insulating layers [Li PRL 2013, Senapati APL 2013, Zhu Nat. Mat. 2016.] are attractive since the SC and FM characteristics can mutually be controlled by the proximity effect. We investigated reactively sputtered GdN/NbN/GdN tri-layer structures with various (SC) NbN spacer thicknesses (dNbN) from superconducting to normal layers. Magnetoresistive behavior similar to GMR in metallic magnetic multilayers was observed in the tri-layers with dNbN between 5-10 monolayers (ML), where thinner NbN layers did not show superconductivity down to 4.2 K. The occurrence of GMR signal indicates the presence of a ML of FM metallic layers at the GdN/NbN interfaces. Susceptibility and transport measurements in these samples revealed that the interface layers (ILs) are ferromagnetically coupled with adjacent GdN layers. The thickness of each of the IL is deduced to be about 1.25 ML, and as a result for dNbN <2.5-ML the two FM layers in the tri-layer were magnetically coupled and switched simultaneously. These findings and interfacial characterization by various techniques will be presented. Work supported by NSF and ONR Grants.

Dual source heat pump

DOEpatents

Ecker, Amir L.; Pietsch, Joseph A.

1982-01-01

What is disclosed is a heat pump apparatus for conditioning a fluid characterized by a fluid handler and path for circulating the fluid in heat exchange relationship with a refrigerant fluid; at least two refrigerant heat exchangers, one for effecting heat exchange with the fluid and a second for effecting heat exchange between refrigerant and a heat exchange fluid and the ambient air; a compressor for efficiently compressing the refrigerant; at least one throttling valve for throttling liquid refrigerant; a refrigerant circuit; refrigerant; a source of heat exchange fluid; heat exchange fluid circulating device and heat exchange fluid circuit for circulating the heat exchange fluid in heat exchange relationship with the refrigerant; and valves or switches for selecting the heat exchangers and direction of flow of the refrigerant therethrough for selecting a particular mode of operation. The heat exchange fluid provides energy for defrosting the second heat exchanger when operating in the air source mode and also provides a alternate source of heat.

Tunnel magnetoresistance and linear conductance of double quantum dots strongly coupled to ferromagnetic leads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weymann, Ireneusz, E-mail: weymann@amu.edu.pl

2015-05-07

We analyze the spin-dependent linear-response transport properties of double quantum dots strongly coupled to external ferromagnetic leads. By using the numerical renormalization group method, we determine the dependence of the linear conductance and tunnel magnetoresistance on the degree of spin polarization of the leads and the position of the double dot levels. We focus on the transport regime where the system exhibits the SU(4) Kondo effect. It is shown that the presence of ferromagnets generally leads the suppression of the linear conductance due to the presence of an exchange field. Moreover, the exchange field gives rise to a transition frommore » the SU(4) to the orbital SU(2) Kondo effect. We also analyze the dependence of the tunnel magnetoresistance on the double dot levels' positions and show that it exhibits a very nontrivial behavior.« less

Positive magnetoresistance in Fe3Se4 nanowires

NASA Astrophysics Data System (ADS)

Li, D.; Jiang, J. J.; Liu, W.; Zhang, Z. D.

2011-04-01

We report the magnetotransport properties of Fe3Se4 nanowire arrays in anodic aluminum oxide (AAO) porous membrane. The temperature dependence of resistance of Fe3Se4 nanowires at a zero field shows thermal activated behavior below 295 K. The exponential relationship in resistance is consistent with the model of strong localization with variable-range hopping (VRH) for a finite one-dimensional wire. Resistance versus magnetic field curves below 100 K show small positive magnetoresistance (MR). The field dependencies of log[R(H)/R(0)] explain the positive MR as the effect of magnetic field on the VRH conduction.

Tunneling magnetoresistance tuned by a vertical electric field in an AA-stacked graphene bilayer with double magnetic barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Dali, E-mail: wangdali@mail.ahnu.edu.cn; National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093; Jin, Guojun, E-mail: gjin@nju.edu.cn

2013-12-21

We investigate the effect of a vertical electric field on the electron tunneling and magnetoresistance in an AA-stacked graphene bilayer modulated by the double magnetic barriers with parallel or antiparallel configuration. The results show that the electronic transmission properties in the system are sensitive to the magnetic-barrier configuration and the bias voltage between the graphene layers. In particular, it is found that for the antiparallel configuration, within the low energy region, the blocking effect is more obvious compared with the case for the parallel configuration, and even there may exist a transmission spectrum gap which can be arbitrarily tuned bymore » the field-induced interlayer bias voltage. We also demonstrate that the significant discrepancy between the conductance for both parallel and antiparallel configurations would result in a giant tunneling magnetoresistance ratio, and further the maximal magnetoresistance ratio can be strongly modified by the interlayer bias voltage. This leads to the possible realization of high-quality magnetic sensors controlled by a vertical electric field in the AA-stacked graphene bilayer.« less

Solid-state switch increases switching speed

NASA Technical Reports Server (NTRS)

Mcgowan, G. F.

1966-01-01

Solid state switch for commutating capacitors in an RC commutated network increases switching speed and extends the filtering or commutating frequency spectrum well into the kilocycle region. The switch is equivalent to the standard double- pole double-throw /DPDT/ relay and is driven from digital micrologic circuits.

Negative to positive crossover of the magnetoresistance in layered WS{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yangwei; Ning, Honglie; Li, Yanan

2016-04-11

The discovery of graphene ignited intensive investigation of two-dimensional materials. A typical two-dimensional material, transition metal dichalcogenide (TMDC), attracts much attention because of its excellent performance in field effect transistor measurements and applications. Particularly, when TMDC reaches the dimension of a few layers, a wide range of electronic and optical properties can be detected that are in striking contrast to bulk samples. In this letter, we synthesized WS{sub 2} single-crystal nanoflakes using physical vapor deposition and carried out a series of measurements of the contact resistance and magnetoresistance. Focused ion beam (FIB) technology was applied to deposit Pt electrodes onmore » the WS{sub 2} flakes, and the FIB-deposited contacts exhibited linear electrical characteristics. Resistance versus temperature measurements showed similar Mott variable range hopping behavior in different magnetic fields. Additionally, a temperature-modulated negative-to-positive magnetoresistance transition was observed. Our work reveals the magnetotransport characteristics of WS{sub 2} flakes, which may stimulate further studies of the properties of TMDC and its corresponding electronic and optoelectronic applications.« less

Electronic structure and low temperature magnetoresistance of polycrystalline TlMQ2 (M = Sc, Bi, Q = Se, Te)

NASA Astrophysics Data System (ADS)

Aswathy, Vijayakumar Sajitha; Varma, Manoj Raama; Sankar, Cheriyedath Raj

2018-05-01

Thallium based ternary chalcogenide TlBiSe2 having α-NaFeO2 structure type is a candidate of 3D topological insulator family with very large positive linear magnetoresistance. Herein, we report the magnetoresistance studies along with the electronic structure of TlScQ2 (Q = Se, Te) system of the same structure type. Our calculations predict selenide to be a narrow indirect band-gap semiconductor whereas telluride is metallic with intriguing band dispersion characteristics. We observed huge positive MR for the polycrystalline TlBiSe2 and comparatively low MR for TlScQ2 which limits their chance to possess nontrivial surface states.

Multiple source heat pump

DOEpatents

Ecker, Amir L.

1983-01-01

A heat pump apparatus for conditioning a fluid characterized by a fluid handler and path for circulating a fluid in heat exchange relationship with a refrigerant fluid, at least three refrigerant heat exchangers, one for effecting heat exchange with the fluid, a second for effecting heat exchange with a heat exchange fluid, and a third for effecting heat exchange with ambient air; a compressor for compressing the refrigerant; at least one throttling valve connected at the inlet side of a heat exchanger in which liquid refrigerant is vaporized; a refrigerant circuit; refrigerant; a source of heat exchange fluid; heat exchange fluid circuit and pump for circulating the heat exchange fluid in heat exchange relationship with the refrigerant; and valves or switches for selecting the heat exchangers and directional flow of refrigerant therethrough for selecting a particular mode of operation. Also disclosed are a variety of embodiments, modes of operation, and schematics therefor.

Low-field magnetoresistance up to 400 K in double perovskite Sr{sub 2}FeMoO{sub 6} synthesized by a citrate route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harnagea, L., E-mail: harnagealuminita@gmail.com; Jurca, B.; Physical Chemistry Department, University of Bucharest, 4-12 Bd. Elisabeta, 030018 Bucharest

2014-03-15

A wet-chemistry technique, namely the citrate route, has been used to prepare high-quality polycrystalline samples of double perovskite Sr{sub 2}FeMoO{sub 6}. We report on the evolution of magnetic and magnetoresistive properties of the synthesized samples as a function of three parameters (i) the pH of the starting solution, (ii) the decomposition temperature of the citrate precursors and (iii) the sintering conditions. The low-field magnetoresistance (LFMR) value of our best samples is as high as 5% at room temperature for an applied magnetic field of 1 kOe. Additionally, the distinguishing feature of these samples is the persistence of LFMR, with amore » reasonably large value, up to 400 K which is a crucial parameter for any practical application. Our study indicates that the enhancement of LFMR observed is due to a good compromise between the grain size distribution and their magnetic polarization. -- Graphical abstract: The microstructure (left panel) and corresponding low-field magnetoresistance of one of the Sr{sub 2}FeMoO{sub 6} samples synthesized in the course of this work. Highlights: • Samples of Sr{sub 2}FeMoO{sub 6} are prepared using a citrate route under varying conditions. • Magnetoresistive properties are improved and optimized. • Low-field magnetoresitence values as large as 5% at 300 K/1 kOe are reported. • Persistence of low-field magnetoresistance up to 400 K.« less

Large magnetoresistance ratio of 10% by Fe50Co50 layers for current-confined-path current-perpendicular-to-plane giant magnetoresistance spin-valve films

NASA Astrophysics Data System (ADS)

Fukuzawa, Hideaki; Yuasa, Hiromi; Hashimoto, Susumu; Iwasaki, Hitoshi; Tanaka, Yoichiro

2005-08-01

We have realized a large magnetoresistance (MR) ratio of 10.2% by current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin-valve films having current-confined-path (CCP) structure formed by AlCu-NOL (nano-oxide-layer). CPP-GMR with conventional Co90Fe10 pinned and free layers showed an MR ratio and a ΔRA (the change of resistance area product) were 4% and 20mΩμm2, respectively, at a small RA (resistance area product) of 500mΩμm2. By replacing the Co90Fe10 layers by Fe50Co50 layers both for pinned and free layers, we have successfully realized a MR ratio and a ΔRA of 7.5% and 37.5mΩμm2, respectively, at a small RA of 500mΩμm2. Moreover, a large MR ratio of 10.2% and a large ΔRA of 418mΩμm2 were realized at a relatively large RA of 4100mΩμm2. This large MR ratio by using Fe50Co50 layers was due to a larger spin-dependent interface scattering factor γ of 0.72 for the interface between Fe50Co50 and Cu, which was improved from a γ of 0.62 for the interface between Co90Fe10 and Cu.

High-sensitivity two-terminal magnetoresistance devices using InGaAs/AlGaAs two-dimensional channel on GaAs substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Di-Cheng; Pan, You-Wei; Lin, Shih-Wei

2016-04-25

We demonstrate experimentally the two-terminal magnetic sensors exhibiting an extraordinary magneto-resistance effect by using an InGaAs quantum well channel with a metal-shunting structure. A high magneto-resistance of 17.3% and a sensitivity of 488.1 Ω/T have been obtained at 1 T and room temperature with our geometrical design. The two-contact configuration and the high-mobility electron transistor-compatible epitaxy structure make the devices promising for high-sensitivity magnetic sensing integration and applications.

The rotating heat pipe - Implementation as a uniform-temperature heat source

NASA Astrophysics Data System (ADS)

Limoges, R. F.

1981-11-01

A wickless rotating heat pipe, if properly controlled, is a uniform heat source. The data presented are based on work done with 12.7 cm diameter x 76 cm long rotating heat pipes operating between 120 and 140 C. The major areas reviewed are: materials of fabrication, working fluids, sealing, temperature control, heaters, and safety. The optimum rotating heat pipe defined by these studies is fabricated of type 304 stainless steel, uses water as the working fluid, is sealed with welded joints, and utilizes a pressure switch and a fast-response quartz lamp for temperature control. Surface-temperature control of + or - 0.15 C and temperature uniformity within 0.8 C are obtained. Results of experiments designed to study the effects of hydrogen in the enclosed volume of the heat pipe are presented.

Water-heating dehumidifier

DOEpatents

Tomlinson, John J.

2006-04-18

A water-heating dehumidifier includes a refrigerant loop including a compressor, at least one condenser, an expansion device and an evaporator including an evaporator fan. The condenser includes a water inlet and a water outlet for flowing water therethrough or proximate thereto, or is affixed to the tank or immersed into the tank to effect water heating without flowing water. The immersed condenser design includes a self-insulated capillary tube expansion device for simplicity and high efficiency. In a water heating mode air is drawn by the evaporator fan across the evaporator to produce cooled and dehumidified air and heat taken from the air is absorbed by the refrigerant at the evaporator and is pumped to the condenser, where water is heated. When the tank of water heater is full of hot water or a humidistat set point is reached, the water-heating dehumidifier can switch to run as a dehumidifier.

Towards a magnetoresistive platform for neural signal recording

NASA Astrophysics Data System (ADS)

Sharma, P. P.; Gervasoni, G.; Albisetti, E.; D'Ercoli, F.; Monticelli, M.; Moretti, D.; Forte, N.; Rocchi, A.; Ferrari, G.; Baldelli, P.; Sampietro, M.; Benfenati, F.; Bertacco, R.; Petti, D.

2017-05-01

A promising strategy to get deeper insight on brain functionalities relies on the investigation of neural activities at the cellular and sub-cellular level. In this framework, methods for recording neuron electrical activity have gained interest over the years. Main technological challenges are associated to finding highly sensitive detection schemes, providing considerable spatial and temporal resolution. Moreover, the possibility to perform non-invasive assays would constitute a noteworthy benefit. In this work, we present a magnetoresistive platform for the detection of the action potential propagation in neural cells. Such platform allows, in perspective, the in vitro recording of neural signals arising from single neurons, neural networks and brain slices.

Tunneling magnetoresistance sensors with different coupled free layers

NASA Astrophysics Data System (ADS)

Liu, Yen-Fu; Yin, Xiaolu; Yang, Yi; Ewing, Dan; De Rego, Paul J.; Liou, Sy-Hwang

2017-05-01

Large differences of magnetic coercivity (HC), exchange coupling field (HE), and tunneling magnetoresistance ratio (TMR) in magnetic tunnel junctions with different coupled free layers are discussed. We demonstrate that the magnetization behavior of the free layer is not only dominated by the interfacial barrier layer but also affected largely by the magnetic or non-magnetic coupled free layers. All these parameters are sensitively controlled by the magnetic nanostructure, which can be tuned also by the magnetic annealing process. The optimized sensors exhibit a large field sensitivity of up to 261%/mT in the region of the reversal synthetic ferrimagnet at the pinned layers.

Pho dynamically interacts with Spt5 to facilitate transcriptional switches at the hsp70 locus.

PubMed

Pereira, Allwyn; Paro, Renato

2017-12-06

Numerous target genes of the Polycomb group (PcG) are transiently activated by a stimulus and subsequently repressed. However, mechanisms by which PcG proteins regulate such target genes remain elusive. We employed the heat shock-responsive hsp70 locus in Drosophila to study the chromatin dynamics of PRC1 and its interplay with known regulators of the locus before, during and after heat shock. We detected mutually exclusive binding patterns for HSF and PRC1 at the hsp70 locus. We found that Pleiohomeotic (Pho), a DNA-binding PcG member, dynamically interacts with Spt5, an elongation factor. The dynamic interaction switch between Pho and Spt5 is triggered by the recruitment of HSF to chromatin. Mutation in the protein-protein interaction domain (REPO domain) of Pho interferes with the dynamics of its interaction with Spt5. The transcriptional kinetics of the heat shock response is negatively affected by a mutation in the REPO domain of Pho. We propose that a dynamic interaction switch between PcG proteins and an elongation factor enables stress-inducible genes to efficiently switch between ON/OFF states in the presence/absence of the activating stimulus.

Low temperature resistivity plateau and non-saturating magnetoresistance in Type-II Weyl semimetal WP2

NASA Astrophysics Data System (ADS)

Nagpal, V.; Kumar, P.; Sudesh, Patnaik, S.

2018-04-01

We have studied the resistivity and magnetoresistance (MR) properties of the recently predicted type-II Weyl semimetal WP2. Polycrystalline WP2 is synthesized using solid state reaction and crystallizes in an orthorhombic structure with the Cmc21 spacegroup. The temperature dependent resistivity is enhanced with the application of magnetic field and a resistivity plateau is observed at low temperatures. We find a small dip in resistivity around 30K at 5T field suggesting that there might be a metal-insulator-like transition at higher magnetic fields. A non-saturating magnetoresistance is observed at low temperatures with maximum MR ˜ 94% at 2K and 6T. The value of MR decreases with the increase in temperature. We see a deviation from Kohler's power law which implies that the system comprises of two types of charge carriers.

Temporal switching jitter in photoconductive switches

DOE Office of Scientific and Technical Information (OSTI.GOV)

GAUDET,JOHN A.; SKIPPER,MICHAEL C.; ABDALLA,MICHAEL D.

This paper reports on a recent comparison made between the Air Force Research Laboratory (AFRL) gallium arsenide, optically-triggered switch test configuration and the Sandia National Laboratories (SNL) gallium arsenide, optically-triggered switch test configuration. The purpose of these measurements was to compare the temporal switch jitter times. It is found that the optical trigger laser characteristics are dominant in determining the PCSS jitter.

Magnetoresistance in the superconducting state at the (111) LaAlO3/SrTiO3 interface

NASA Astrophysics Data System (ADS)

Davis, S.; Huang, Z.; Han, K.; Ariando, Venkatesan, T.; Chandrasekhar, V.

2017-10-01

Condensed-matter systems that simultaneously exhibit superconductivity and ferromagnetism are rare due the antagonistic relationship between conventional spin-singlet superconductivity and ferromagnetic order. In materials in which superconductivity and magnetic order are known to coexist (such as some heavy-fermion materials), the superconductivity is thought to be of an unconventional nature. Recently, the conducting gas that lives at the interface between the perovskite band insulators LaAlO3 (LAO) and SrTiO3 (STO) has also been shown to host both superconductivity and magnetism. Most previous research has focused on LAO/STO samples in which the interface is on the (001) crystal plane. Relatively little work has focused on the (111) crystal orientation, which has hexagonal symmetry at the interface, and has been predicted to have potentially interesting topological properties, including unconventional superconducting pairing states. Here we report measurements of the magnetoresistance of (111) LAO/STO heterostructures at temperatures at which they are also superconducting. As with the (001) structures, the magnetoresistance is hysteretic, indicating the coexistence of magnetism and superconductivity, but in addition, we find that this magnetoresistance is anisotropic. Such an anisotropic response is completely unexpected in the superconducting state and suggests that (111) LAO/STO heterostructures may support unconventional superconductivity.

Tilted Dirac Cone Effect on Interlayer Magnetoresistance in α-(BEDT-TTF)2I3

NASA Astrophysics Data System (ADS)

Tajima, Naoya; Morinari, Takao

2018-04-01

We report the effect of Dirac cone tilting on interlayer magnetoresistance in α-(BEDT-TTF)2I3, which is a Dirac semimetal under pressure. Fitting of the experimental data by the theoretical formula suggests that the system is close to a type-II Dirac semimetal.

Magnetoresistance and noise properties of chevron stretcher detectors for field access bubble domain devices

NASA Technical Reports Server (NTRS)

George, P. K.; Oeffinger, T. R.; Chen, T. T.

1976-01-01

Experiments were devised to study the angular variation of the resistance and noise properties of one- and two-level chevron stretcher magnetoresistive detectors for use in field access bubble memory devices. All measurements, made with an electronic system, were performed on glass or garnet samples upon which 1 micron of SiO2 was sputter-deposited, followed by 4000 A of Permalloy for the 28-micron-period devices and 0.8 microns of SiO2, followed by 3000 A of Permalloy for the 20-micron-period devices. The geometrical and drive-state dependence of the zero-state noise were studied, as was its frequency dependence. It is found that both types of detectors operate primarily in the amplitude-shift mode for drive fields of interest and that the presence of a bubble in a detector causes a magnetoresistance change equal to that produced by increasing the in-plane drive field about 8 Oe in the absence of a bubble.

Spin-orbit interaction and negative magnetoresistance for localized electrons in InSb quantum wells

NASA Astrophysics Data System (ADS)

Ishida, S.; Manago, T.; Nishizako, N.; Geka, H.; Shibasaki, I.

2010-02-01

Weak-field magnetoresistance (MR) in the variable-range hopping (VRH) in the presence of spin-orbit interaction (SOI) for 2DEGs at the hetero-interface of InSb quantum wells was examined in view of the quantum interference (QI) effect. Samples with the sheet resistance, ρ> ρc= h/ e2, exhibit VRH, while those with ρ< ρc exhibit weak localiz ation (WL) at low temperatures, where h/ e2 is the quantum resistance. In the WL regime, a positive magnetoresistance (MR) peak due to the weak anti-localization (WAL) with SOI is clearly observed in low magnetic field. In contrast, the low-field hopping MR remains entirely negative surviving the SOI, indicating that the hopping MR due to the QI is completely negative regardless of the SOI. This result supports the predictions based on the directed-path approach for forward-scattering paths ignoring the back-scattering return loops for the QI in the VRH.

Large linear magnetoresistance in heavily-doped Nb:SrTiO3 epitaxial thin films

PubMed Central

Jin, Hyunwoo; Lee, Keundong; Baek, Seung-Hyub; Kim, Jin-Sang; Cheong, Byung-ki; Park, Bae Ho; Yoon, Sungwon; Suh, B. J.; Kim, Changyoung; Seo, S. S. A.; Lee, Suyoun

2016-01-01

Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin films. These phenomena are associated with the interplay between the large classical MR due to high carrier mobility and the electronic localization effect due to strong spin-orbit coupling, implying that heavily Nb-doped Sr(Nb0.2Ti0.8)O3 is promising for the application in spintronic devices. PMID:27703222

Asymmetrical external effects on transmission, conductance and giant tunneling magnetoresistance in silicene

NASA Astrophysics Data System (ADS)

Oubram, O.; Navarro, O.; Guzmán, E. J.; Rodríguez-Vargas, I.

2018-01-01

Electron transport in a silicene structure, composed of a pair of magnetic gates, is studied in a ferromagnetic and antiferromagnetic configuration. The transport properties are investigated for asymmetrical external effects like an electrostatic potential, a magnetic field and for asymmetrical geometric structure. This theoretical study, has been done using the matrix transfer method to calculate the transmission, the conductance for parallel and antiparallel magnetic alignment and the tunneling magnetoresistance (TMR). In Particular, we have found that the transmission, conductance and magnetoresistance oscillate as a function of the width of barriers. It is also found that a best control and high values of TMR spectrum are achieved by an asymmetrical application of the contact voltage. Besides, we have shown that the TMR is enhanced several orders of magnitude by the combined asymmetrical magnetization effect with an adequate applied electrostatic potential. Whereby, the asymmetrical external effects play an important role to improve TMR than symmetrical ones. Finally, the giant TMR can be flexibly modulated by incident energy and a specific asymmetrical application of control voltage. These results could be useful to design filters and digital nanodevices.

Study of optoelectronic switch for satellite-switched time-division multiple access

NASA Technical Reports Server (NTRS)

Su, Shing-Fong; Jou, Liz; Lenart, Joe

1987-01-01

The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix.

Ultrafast Modulation and Switching of Quantum-Well Lasers using Terahertz Fields

NASA Technical Reports Server (NTRS)

Ning, Cun-Zheng; Hughes, S.; Citrin, D.; Saini, Subhash (Technical Monitor)

1998-01-01

Modulation and switching of semiconductor lasers are important for laser-based information technology. Typically the speed of modulation and switching is limited by interband processes such as stimulated and spontaneous recombinations which occur on a nanosecond time scale. This is why the diode laser modulation has been restricted to tens of GHz. Modulation at higher speed is highly desirable as the information technology enters into the so-called tera-era. In this paper, we study the possibility of utilizing THz-field-induced plasma heating to modulate quantum-well lasers. This is a timely study since, with the advancement of THz solid-state sources and free-electron lasers, THz physics and related technology is currently coming out of its infancy. The investigation of interplaying THz and optical fields is also of intruiging fundamental interest. First, we introduce theoretical plasma heating results for the quantum-well optical amplifier in the presense of an intense half-cycle THz pulse. The heated carrier distributions are then utilized to calculate the THz-pulse-induced change in refractive index and gain profile. Since the electron-hole-plasma is heated using intraband transitions, we circumvent the usual complications due to an overall change in density, and the nonlinear recovery is governed solely by the carrier-LO-phonon interactions, typically 5 ps for a complete recovery. This procedure implies THz and sub-THz switching and recovery rates, respectively; using either gain modulation or index modulation. Plasma heating via steady-state THz fields is also studied. Finally, numerical simulation of a coupled set of equations to investigate the THz modulation based on a simplified model for quantum-well lasers is presented. Our results show that a semiconductor laser can be modulated at up to 1 THz with little distortion with a THz field amplitude at the order of a few kV/cm. Laser responses to a change in THz frequency will be shown. Constraints

Realisation of all 16 Boolean logic functions in a single magnetoresistance memory cell.

PubMed

Gao, Shuang; Yang, Guang; Cui, Bin; Wang, Shouguo; Zeng, Fei; Song, Cheng; Pan, Feng

2016-07-07

Stateful logic circuits based on next-generation nonvolatile memories, such as magnetoresistance random access memory (MRAM), promise to break the long-standing von Neumann bottleneck in state-of-the-art data processing devices. For the successful commercialisation of stateful logic circuits, a critical step is realizing the best use of a single memory cell to perform logic functions. In this work, we propose a method for implementing all 16 Boolean logic functions in a single MRAM cell, namely a magnetoresistance (MR) unit. Based on our experimental results, we conclude that this method is applicable to any MR unit with a double-hump-like hysteresis loop, especially pseudo-spin-valve magnetic tunnel junctions with a high MR ratio. Moreover, after simply reversing the correspondence between voltage signals and output logic values, this method could also be applicable to any MR unit with a double-pit-like hysteresis loop. These results may provide a helpful solution for the final commercialisation of MRAM-based stateful logic circuits in the near future.

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads.

PubMed

Weymann, Ireneusz

2010-01-13

We analyze numerically the spin-dependent transport through coherent chains of three coupled quantum dots weakly connected to external magnetic leads. In particular, using the diagrammatic technique on the Keldysh contour, we calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the sequential and cotunneling regimes. We show that transport characteristics greatly depend on the strength of the interdot Coulomb correlations, which determines the spatial distribution of the electron wavefunction in the chain. When the correlations are relatively strong, depending on the transport regime, we find both negative TMR as well as TMR enhanced above the Julliere value, accompanied with negative differential conductance (NDC) and super-Poissonian shot noise. This nontrivial behavior of tunnel magnetoresistance is associated with selection rules that govern tunneling processes and various high-spin states of the chain that are relevant for transport. For weak interdot correlations, on the other hand, the TMR is always positive and not larger than the Julliere TMR, although super-Poissonian shot noise and NDC can still be observed.

Magnetostructural Properties of Colossal Magnetoresistance Manganites Under External Magnetic Fields and Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Kaplan, Michael; Zimmerman, George

2002-03-01

In the colossal magnetoresistance manganites the transport and magnetostructural properties are tightly connected [1,2]. Many magnetic field induced structural phase transitions and anomalous magnetoacoustical properties continue to be discovered in various manganite derivatives. Nevertheless the mechanism of structural transitions and microscopic theory of corresponding anomalous properties are still to be completely understood. Here we present a microscopic model of magnetic field and uniaxial pressure induced structural phase transitions in lightly doped manganites. The model is based on the cooperative Jahn-Teller effect which takes into account the Mn3+-ground doublet and excited triplet electronic states. Numerous calculations for different orientation magnetic field suggest the explanations of the origin of the structural transitions and of the measured magnetostriction data. The calculations for the two-sublattice antiferrodistortive crystals under uniaxial pressure support the idea of metaelasticity - a property typical for Jahn-Teller antiferroelastics. 1.Y. Tokura, ed. Colossal Magnetoresistance Oxides. Gordon & Breach, London, 2000. 2.M. Kaplan, G. Zimmerman, eds. Vibronic Interactions: Jahn-Teller Effect in Crystal and Molecules. NATO Science Series, Dordrecht/Boston/London, 2001

Evolution of the linear-polarization-angle-dependence of the radiation-induced magnetoresistance-oscillations with microwave power

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Tianyu; Mani, R. G.; Wegscheider, W.

2014-11-10

We examine the role of the microwave power in the linear polarization angle dependence of the microwave radiation induced magnetoresistance oscillations observed in the high mobility GaAs/AlGaAs two dimensional electron system. The diagonal resistance R{sub xx} was measured at the fixed magnetic fields of the photo-excited oscillatory extrema of R{sub xx} as a function of both the microwave power, P, and the linear polarization angle, θ. Color contour plots of such measurements demonstrate the evolution of the lineshape of R{sub xx} versus θ with increasing microwave power. We report that the non-linear power dependence of the amplitude of the radiation-inducedmore » magnetoresistance oscillations distorts the cosine-square relation between R{sub xx} and θ at high power.« less

49 CFR 218.103 - Hand-operated switches, including crossover switches.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 4 2013-10-01 2013-10-01 false Hand-operated switches, including crossover switches. 218.103 Section 218.103 Transportation Other Regulations Relating to Transportation (Continued... Equipment, Switches, and Fixed Derails § 218.103 Hand-operated switches, including crossover switches. (a)(1...

49 CFR 218.103 - Hand-operated switches, including crossover switches.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Hand-operated switches, including crossover switches. 218.103 Section 218.103 Transportation Other Regulations Relating to Transportation (Continued... Equipment, Switches, and Fixed Derails § 218.103 Hand-operated switches, including crossover switches. (a)(1...

49 CFR 218.103 - Hand-operated switches, including crossover switches.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Hand-operated switches, including crossover switches. 218.103 Section 218.103 Transportation Other Regulations Relating to Transportation (Continued... Equipment, Switches, and Fixed Derails § 218.103 Hand-operated switches, including crossover switches. (a)(1...

49 CFR 218.103 - Hand-operated switches, including crossover switches.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Hand-operated switches, including crossover switches. 218.103 Section 218.103 Transportation Other Regulations Relating to Transportation (Continued... Equipment, Switches, and Fixed Derails § 218.103 Hand-operated switches, including crossover switches. (a)(1...

49 CFR 218.103 - Hand-operated switches, including crossover switches.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 4 2010-10-01 2010-10-01 false Hand-operated switches, including crossover switches. 218.103 Section 218.103 Transportation Other Regulations Relating to Transportation (Continued... Equipment, Switches, and Fixed Derails § 218.103 Hand-operated switches, including crossover switches. (a)(1...

Simulation and analysis of main steam control system based on heat transfer calculation

NASA Astrophysics Data System (ADS)

Huang, Zhenqun; Li, Ruyan; Feng, Zhongbao; Wang, Songhan; Li, Wenbo; Cheng, Jiwei; Jin, Yingai

2018-05-01

In this paper, after thermal power plant 300MW boiler was studied, mat lab was used to write calculation program about heat transfer process between the main steam and boiler flue gas and amount of water was calculated to ensure the main steam temperature keeping in target temperature. Then heat transfer calculation program was introduced into Simulink simulation platform based on control system multiple models switching and heat transfer calculation. The results show that multiple models switching control system based on heat transfer calculation not only overcome the large inertia of main stream temperature, a large hysteresis characteristic of main stream temperature, but also adapted to the boiler load changing.

Optically-switched submillimeter-wave oscillator and radiator having a switch-to-switch propagation delay

NASA Technical Reports Server (NTRS)

Spencer, Michael G. (Inventor); Maserjian, Joseph (Inventor)

1995-01-01

A submillimeter wave-generating integrated circuit includes an array of N photoconductive switches biased across a common voltage source and an optical path difference from a common optical pulse of repetition rate f sub 0 providing a different optical delay to each of the switches. In one embodiment, each incoming pulse is applied to successive ones of the N switches with successive delays. The N switches are spaced apart with a suitable switch-to-switch spacing so as to generate at the output load or antenna radiation of a submillimeter wave frequency f on the order of N f sub 0. Preferably, the optical pulse has a repetition rate of at least 10 GHz and N is of the order of 100, so that the circuit generates radiation of frequency of the order of or greater than 1 Terahertz.

Effects of AEA Cell-Bypass-Switch Closure on Charged EOS-Aqua NiH2 Cell

NASA Technical Reports Server (NTRS)

Keys, Denney; Rao, Gopalakrishna M.; Sullivan, David; Wannemacher, Harry

2001-01-01

The nominal performance of AEA CBPD under simulated EOS-Aqua/Aura flight hardware configuration has been demonstrated. There is no evidence of cell rupture or excessive heat production during or after CBPD switch activation under simulated high cell impedance (open-circuit cell failure mode). Inadvertent CBPD switch activation with a charged cell (low impedance path) intermittently closes and opens up the switch, therefore the device may or may not provide protection against future open-circuit cell failure. Further testing with switches F01 and F02 may provide clarification. The formation of a continuous low impedance path (a homogeneous low melting point alloy), has been confirmed - which is the expected mode of operation.

Switching control of an R/C hovercraft: stabilization and smooth switching.

PubMed

Tanaka, K; Iwasaki, M; Wang, H O

2001-01-01

This paper presents stable switching control of an radio-controlled (R/C) hovercraft that is a nonholonomic (nonlinear) system. To exactly represent its nonlinear dynamics, more importantly, to maintain controllability of the system, we newly propose a switching fuzzy model that has locally Takagi-Sugeno (T-S) fuzzy models and switches them according to states, external variables, and/or time. A switching fuzzy controller is constructed by mirroring the rule structure of the switching fuzzy model of an R/C hovercraft. We derive linear matrix inequality (LMI) conditions for ensuring the stability of the closed-loop system consisting of a switching fuzzy model and controller. Furthermore, to guarantee smooth switching of control input at switching boundaries, we also derive a smooth switching condition represented in terms of LMIs. A stable switching fuzzy controller satisfying the smooth switching condition is designed by simultaneously solving both of the LMIs. The simulation and experimental results for the trajectory control of an R/C hovercraft show the validity of the switching fuzzy model and controller design, particularly, the smooth switching condition.

Magnetocardiography with sensors based on giant magnetoresistance

NASA Astrophysics Data System (ADS)

Pannetier-Lecoeur, M.; Parkkonen, L.; Sergeeva-Chollet, N.; Polovy, H.; Fermon, C.; Fowley, C.

2011-04-01

Biomagnetic signals, mostly due to the electrical activity in the body, are very weak and they can only be detected by the most sensitive magnetometers, such as Superconducting Quantum Interference Devices (SQUIDs). We report here biomagnetic recordings with hybrid sensors based on Giant MagnetoResistance (GMR). We recorded magnetic signatures of the electric activity of the human heart (magnetocardiography) in healthy volunteers. The P-wave and QRS complex, known from the corresponding electric recordings, are clearly visible in the recordings after an averaging time of about 1 min. Multiple recordings at different locations over the chest yielded a dipolar magnetic field map and allowed localizing the underlying current sources. The sensitivity of the GMR-based sensors is now approaching that of SQUIDs and paves way for spin electronics devices for functional imaging of the body.

Polymer thermal optical switch for a flexible photonic circuit.

PubMed

Sun, Yue; Cao, Yue; Wang, Qi; Yi, Yunji; Sun, Xiaoqiang; Wu, Yuanda; Wang, Fei; Zhang, Daming

2018-01-01

Flexible and wearable optoelectronic devices are the new trend for an active lifestyle. These devices are polymer-based for flexibility. We demonstrated flexible polymer waveguide optical switches for a flexible photonic integrated circuit. The optical switches are composed of a single-mode inverted waveguide with dimensions of 5 μm waveguide width, 3 μm ridge height, and 3 μm slab height. A Mach-Zehnder structure was used in the device, with the Y-branch horizontal length of 0.1 cm, the distance between two heating branches of 30 μm, and the heating branch length of 1 cm. The optical field of the device was simulated by beam propagation to optimize the electrode position. The switching properties of the flexible optical switch with different working conditions, such as contact to the polymer, silicon, and skin, were simulated. The device was prepared based on the photo curved polymer and lithography method. The end faces of the flexible film device were processed using an excimer laser with optimized parameters of 28  mJ/cm 2 and 15 Hz. The response rise time and fall time on the PMMA substrate were measured as 1.98 ms and 2.71 ms, respectively. The power consumption was 16 mW and the extinction ratio was 11 dB. The response rise and fall times on the Si substrate were measured as 1.08 ms and 1.62 ms, respectively. The power consumption was 17 mW and the extinction ratio was 11 dB. The demonstrated properties indicate that this flexible optical waveguide structure can be used in the light control area of a wearable device.

Extreme magnetoresistance and SdH oscillation in compensated semimetals of NbSb2 single crystals

NASA Astrophysics Data System (ADS)

Guo, Lei; Liu, Yu-Kuai; Gao, Guan-Yin; Huang, Ye-Yu; Gao, Heng; Chen, Lei; Zhao, Weiyao; Ren, Wei; Li, Shi-Yan; Li, Xiao-Guang; Dong, Shuai; Zheng, Ren-Kui

2018-04-01

Topological semimetals represent one of the most interesting classes of materials that continue to attract worldwide interest. Here, we report magnetotransport properties of MPn2-type (M = Nb, Ta; Pn = P, As, Sb) NbSb2 single-crystal semimetals with a centrosymmetric C12/m1 space group, paramagnetic ground state, and non-saturation parabolic-like magnetoresistance. The NbSb2 crystals show metallic conductivity down to 2 K and undergo a metal-to-insulator-like transition under a magnetic field B (B ≥ 4 T) and exhibit a resistivity plateau in the low-temperature region (T ≤ 10 K), where the value of resistivity strongly depends on the magnitude and direction of the magnetic field. Upon sweeping the magnetic field from 0 to 14.5 T in the transverse configuration at T = 1.5 K, the NbSb2 crystal shows a large positive magnetoresistance (4.2 × 103% at B = 14.5 T) with Shubnikov-de Haas (SdH) oscillation. Hall measurements reveal that both the carrier compensation between electrons and holes and the high mobility and large mean free path of carriers contribute to the large magnetoresistance. Fast Fourier transform analyses of angle-resolved SdH oscillation indicate that the Fermi surface of the NbSb2 crystal is quasi-two-dimensional with three-dimensional components. These findings, together with the theoretically calculated electronic band structure obtained within the framework of density functional theory, suggest that NbSb2 is a good candidate compensated semimetal for further theoretical and experimental investigation of this family of materials.

First principles investigation of the unipolar resistive switching mechanism in an interfacial phase change memory based on a GeTe/Sb2Te3 superlattice

NASA Astrophysics Data System (ADS)

Shirakawa, Hiroki; Araidai, Masaaki; Shiraishi, Kenji

2018-04-01

The interfacial phase change memory (iPCM) based on a GeTe/Sb2Te3 superlattice is one of the candidates for future storage class memories. However, the atomic structures of the high and low resistance states (HRS/LRS) remain unclear and the resistive switching mechanism is still under debate. Clarifying the switching mechanism is essential for developing further high-reliability and low-power-consumption iPCM. We propose, on the basis of the results of first-principles molecular dynamics simulations, a mechanism for resistive switching, and describe the atomic structures of the high and low resistance states of iPCM for unipolar switching. Our simulations indicated that switching from HRS to LRS occurs with Joule heating only, while that from LRS to HRS occurs with both hole injection and Joule heating.

Optimization of spin-torque switching using AC and DC pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunn, Tom; Kamenev, Alex; Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455

2014-06-21

We explore spin-torque induced magnetic reversal in magnetic tunnel junctions using combined AC and DC spin-current pulses. We calculate the optimal pulse times and current strengths for both AC and DC pulses as well as the optimal AC signal frequency, needed to minimize the Joule heat lost during the switching process. The results of this optimization are compared against numeric simulations. Finally, we show how this optimization leads to different dynamic regimes, where switching is optimized by either a purely AC or DC spin-current, or a combination AC/DC spin-current, depending on the anisotropy energies and the spin-current polarization.

Transport properties of high-performance all-Heusler Co2CrSi/Cu2CrAl/Co2CrSi giant magnetoresistance device

NASA Astrophysics Data System (ADS)

Bai, Z. Q.; Lu, Y. H.; Shen, L.; Ko, V.; Han, G. C.; Feng, Y. P.

2012-05-01

Transport properties of giant magnetoresistance (MR) junction consisting of trilayer Co2CrSi/Cu2CrAl/Co2CrSi Heusler alloys (L21) are studied using first-principles approach based on density functional theory and the non-equilibrium Green's function method. Highly conductive channels are found in almost the entire k-plane when the magnetizations of the electrodes are parallel, while they are completely blocked in the antiparallel configuration, which leads to a high magnetoresistance ratio (the pessimistic MR ratio is nearly 100%). Furthermore, the calculated I-V curve shows that the device behaves as a good spin valve with a considerable disparity in currents under the parallel and antiparallel magnetic configurations of the electrodes. The Co2CrSi/Cu2CrAl/Co2CrSi junction could be useful for high-performance all-metallic current-perpendicular-to-plane giant magnetoresistance reading head for the next generation high density magnetic storage.

Exciter switch

NASA Technical Reports Server (NTRS)

Mcpeak, W. L.

1975-01-01

A new exciter switch assembly has been installed at the three DSN 64-m deep space stations. This assembly provides for switching Block III and Block IV exciters to either the high-power or 20-kW transmitters in either dual-carrier or single-carrier mode. In the dual-carrier mode, it provides for balancing the two drive signals from a single control panel located in the transmitter local control and remote control consoles. In addition to the improved switching capabilities, extensive monitoring of both the exciter switch assembly and Transmitter Subsystem is provided by the exciter switch monitor and display assemblies.

Sub-100 fJ and sub-nanosecond thermally driven threshold switching in niobium oxide crosspoint nanodevices.

PubMed

Pickett, Matthew D; Williams, R Stanley

2012-06-01

We built and measured the dynamical current versus time behavior of nanoscale niobium oxide crosspoint devices which exhibited threshold switching (current-controlled negative differential resistance). The switching speeds of 110 × 110 nm(2) devices were found to be Δt(ON) = 700 ps and Δt(OFF) = 2:3 ns while the switching energies were of the order of 100 fJ. We derived a new dynamical model based on the Joule heating rate of a thermally driven insulator-to-metal phase transition that accurately reproduced the experimental results, and employed the model to estimate the switching time and energy scaling behavior of such devices down to the 10 nm scale. These results indicate that threshold switches could be of practical interest in hybrid CMOS nanoelectronic circuits.

A Switch Is Not a Switch: Syntactically-Driven Bilingual Language Control

ERIC Educational Resources Information Center

Gollan, Tamar H.; Goldrick, Matthew

2018-01-01

The current study investigated the possibility that language switches could be relatively automatically triggered by context. "Single-word switches," in which bilinguals switched languages on a single word in midsentence and then immediately switched back, were contrasted with more complete "whole-language switches," in which…

Switching Phenomena in a System with No Switches

NASA Astrophysics Data System (ADS)

Preis, Tobias; Stanley, H. Eugene

2010-02-01

It is widely believed that switching phenomena require switches, but this is actually not true. For an intriguing variety of switching phenomena in nature, the underlying complex system abruptly changes from one state to another in a highly discontinuous fashion. For example, financial market fluctuations are characterized by many abrupt switchings creating increasing trends ("bubble formation") and decreasing trends ("financial collapse"). Such switching occurs on time scales ranging from macroscopic bubbles persisting for hundreds of days to microscopic bubbles persisting only for a few seconds. We analyze a database containing 13,991,275 German DAX Future transactions recorded with a time resolution of 10 msec. For comparison, a database providing 2,592,531 of all S&P500 daily closing prices is used. We ask whether these ubiquitous switching phenomena have quantifiable features independent of the time horizon studied. We find striking scale-free behavior of the volatility after each switching occurs. We interpret our findings as being consistent with time-dependent collective behavior of financial market participants. We test the possible universality of our result by performing a parallel analysis of fluctuations in transaction volume and time intervals between trades. We show that these financial market switching processes have properties similar to those of phase transitions. We suggest that the well-known catastrophic bubbles that occur on large time scales—such as the most recent financial crisis—are no outliers but single dramatic representatives caused by the switching between upward and downward trends on time scales varying over nine orders of magnitude from very large (≈102 days) down to very small (≈10 ms).

Heat pump with freeze-up prevention

DOEpatents

Ecker, Amir L.

1981-01-01

What is disclosed is a heat pump apparatus for conditioning a fluid characterized by a fluid handler and path for circulating the fluid in heat exchange relationship with a refrigerant fluid; at least two refrigerant heat exchangers, one for effecting heat exchange with the fluid and a second for effecting heat exchange between refrigerant and a heat exchange fluid and the ambient air; a compressor for efficiently compressing the refrigerant; at least one throttling valve for throttling liquid refrigerant; a refrigerant circuit; refrigerant; a source of heat exchange fluid; heat exchange fluid circulating device and heat exchange fluid circuit for circulating the heat exchange fluid in heat exchange relationship with the refrigerant; and valves or switches for selecting the heat exchangers and direction of flow of the refrigerant therethrough for selecting a particular mode of operation. The heat exchange fluid prevents freeze up of the second heat exchanger by keeping the temperature above the dew point; and, optionally, provides heat for efficient operation.

The effect of band Jahn-Teller distortion on the magnetoresistivity of manganites: a model study.

PubMed

Rout, G C; Panda, Saswati; Behera, S N

2011-10-05

We present a model study of magnetoresistance through the interplay of magnetisation, structural distortion and external magnetic field for the manganite systems. The manganite system is described by the Hamiltonian which consists of the s-d type double exchange interaction, Heisenberg spin-spin interaction among the core electrons, and the static and dynamic band Jahn-Teller (JT) interaction in the e(g) band. The relaxation time of the e(g) electron is found from the imaginary part of the Green's function using the total Hamiltonian consisting of the interactions due to the electron and phonon. The calculated resistivity exhibits a peak in the pure JT distorted insulating phase separating the low temperature metallic ferromagnetic phase and the high temperature paramagnetic phase. The resistivity is suppressed with the increase of the external magnetic field. The e(g) electron band splitting and its effect on magnetoresistivity is reported here. © 2011 IOP Publishing Ltd

Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature

DOE PAGES

Dong, Bo -Wen; Cramer, Joel; Ganzhorn, Kathrin; ...

2017-12-14

We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usualmore » $${\\rm si}{{{\\rm n}}^{2}}\\theta $$ relation well established in the collinear magnet yttrium iron garnet, with $$\\theta $$ the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex angular dependence with four maxima are observed within one sweep cycle. The number of maxima as well as the relative strength of different maxima depend strongly on temperature and field strength. Lastly, our results evidence a complex SMR behavior in the non-collinear magnetic regime that goes beyond the conventional formalism developed for collinear magnetic structures.« less

Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Bo -Wen; Cramer, Joel; Ganzhorn, Kathrin

We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usualmore » $${\\rm si}{{{\\rm n}}^{2}}\\theta $$ relation well established in the collinear magnet yttrium iron garnet, with $$\\theta $$ the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex angular dependence with four maxima are observed within one sweep cycle. The number of maxima as well as the relative strength of different maxima depend strongly on temperature and field strength. Lastly, our results evidence a complex SMR behavior in the non-collinear magnetic regime that goes beyond the conventional formalism developed for collinear magnetic structures.« less

The temperature dependence of the pressure switching of Jahn Teller deformation in the deuterated ammonium copper Tutton salt

NASA Astrophysics Data System (ADS)

Augustyniak, Maria A.; Krupski, Marcin

1999-09-01

The pressure switch of the Jahn-Teller deformation direction in (ND 4) 2Cu(SO 4) 2·6D 2O was investigated in the temperature range 130-320 K. Below 295 K, the new, pressure-induced phase, is stable under ambient pressure. Switching back is observed on heating to above 297 K. In the range 150-295 K a strong temperature dependence of the switching pressure (from 24 to 450 MPa) is observed. Below 150 K, the switching process is slow and a coexistence of two phases is observed. We conclude that the switch of the Cu(D 2O) 6 complex deformation direction is the Jahn-Teller response to the changes in the hydrogen bond system.

Electrochemical heat engine

DOEpatents

Elliott, Guy R. B.; Holley, Charles E.; Houseman, Barton L.; Sibbitt, Jr., Wilmer L.

1978-01-01

Electrochemical heat engines produce electrochemical work, and mechanical motion is limited to valve and switching actions as the heat-to-work cycles are performed. The electrochemical cells of said heat engines use molten or solid electrolytes at high temperatures. One or more reactions in the cycle will generate a gas at high temperature which can be condensed at a lower temperature with later return of the condensate to electrochemical cells. Sodium, potassium, and cesium are used as the working gases for high temperature cells (above 600 K) with halogen gases or volatile halides being used at lower temperature. Carbonates and halides are used as molten electrolytes and the solid electrolyte in these melts can also be used as a cell separator.

Micro-Ball-Lens Optical Switch Driven by SMA Actuator

NASA Technical Reports Server (NTRS)

Yang, Eui-Hyeok

2003-01-01

The figure is a simplified cross section of a microscopic optical switch that was partially developed at the time of reporting the information for this article. In a fully developed version, light would be coupled from an input optical fiber to one of two side-by-side output optical fibers. The optical connection between the input and the selected output fiber would be made via a microscopic ball lens. Switching of the optical connection from one output fiber to another would be effected by using a pair of thin-film shape-memory-alloy (SMA) actuators to toggle the lens between two resting switch positions. There are many optical switches some made of macroscopic parts by conventional fabrication techniques and some that are microfabricated and, hence, belong to the class of microelectromechanical systems (MEMS). Conventionally fabricated optical switches tend to be expensive. MEMS switches can be mass-produced at relatively low cost, but their attractiveness has been diminished by the fact that, heretofore, MEMS switches have usually been found to exhibit high insertion losses. The present switch is intended to serve as a prototype of low-loss MEMS switches. In addition, this is the first reported SMA-based optical switch. The optical fibers would be held in V grooves in a silicon frame. The lens would have a diameter of 1 m; it would be held by, and positioned between, the SMA actuators, which would be made of thin films of TiNi alloy. Although the SMA actuators are depicted here as having simple shapes for the sake of clarity of illustration, the real actuators would have complex, partly net-like shapes. With the exception of the lens and the optical fibers, the SMA actuators and other components of the switch would be made by microfabrication techniques. The components would be assembled into a sandwich structure to complete the fabrication of the switch. To effect switching, an electric current would be passed through one of the SMA actuators to heat it above

Magnon Spin Hall Magnetoresistance of a Gapped Quantum Paramagnet.

PubMed

Ulloa, Camilo; Duine, R A

2018-04-27

Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.

Magnon Spin Hall Magnetoresistance of a Gapped Quantum Paramagnet

NASA Astrophysics Data System (ADS)

Ulloa, Camilo; Duine, R. A.

2018-04-01

Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.

Molecular hyperfine fields in organic magnetoresistance devices

NASA Astrophysics Data System (ADS)

Giro, Ronaldo; Rosselli, Flávia P.; dos Santos Carvalho, Rafael; Capaz, Rodrigo B.; Cremona, Marco; Achete, Carlos A.

2013-03-01

We calculate molecular hyperfine fields in organic magnetoresistance (OMAR) devices using ab initio calculations. To do so, we establish a protocol for the accurate determination of the average hyperfine field Bhf and apply it to selected molecular ions: NPB, TPD, and Alq3. Then, we make devices with precisely the same molecules and perform measurements of the OMAR effect, in order to address the role of hole-transport layer in the characteristic magnetic field B0 of OMAR. Contrary to common belief, we find that molecular hyperfine fields are not only caused by hydrogen nuclei. We also find that dipolar contributions to the hyperfine fields can be comparable to the Fermi contact contributions. However, such contributions are restricted to nuclei located in the same molecular ion as the charge carrier (intramolecular), as extramolecular contributions are negligible.

Influence of the Ar-ion irradiation on the giant magnetoresistance in Fe/Cr multilayers

NASA Astrophysics Data System (ADS)

Kopcewicz, M.; Stobiecki, F.; Jagielski, J.; Szymański, B.; Schmidt, M.; Dubowik, J.; Kalinowska, J.

2003-05-01

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in Fe/Cr multilayers exhibiting the giant magnetoresistance (GMR) effect is studied by the conversion electron Mössbauer spectroscopy (CEMS), vibrating sample magnetometer hysteresis loops, magnetoresistivity, and electric resistivity measurements and supplemented by the small-angle x-ray diffraction. The increase of Ar-ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step sites detected by CEMS. The modification of microstructure induces changes in magnetization reversal indicating a gradual loss of antiferromagnetic (AF) coupling correlated with the degradation of the GMR effect. Distinctly weaker degradation of AF coupling and the GMR effect observed for irradiated samples with a thicker Cr layer thickness suggest that observed effects are caused by pinholes creation. The measurements of temperature dependence of remanence magnetization confirm increase of pinhole density and sizes during implantation. Other effects which can influence spin dependent contribution to the resistance, such as interface roughness as well as shortening of mean-free path of conduction electrons, are also discussed.

Negative slope of resistivity-temperature curve and positive magnetoresistance in antiperovskite ZnCNi3- x Mn x (1.15≤ x≤1.5)

NASA Astrophysics Data System (ADS)

Shi, Lei; Chu, Songnan; Zhao, Jiyin; Wang, Yang; Guo, Yuqiao; Wang, Cailin

2014-03-01

In antiperovskite intermetallics ZnCNi3- x Mn x , the negative slope coefficient (NSC) d ρ/d T of resistivity-temperature curves is observed when x=1.15,1.25,1.4,1.5. The sample with x=1.25 shows a semiconductor-like behavior in the whole temperature range of 15-290 K. By study of the magnetization, magnetoresistance, and low-temperature X-ray diffraction, it is found that Mn dopant significantly affects the physical properties of ZnCNi3- x Mn x by changing both the carrier density and the magnetism. The origin of the NSC d ρ/d T can be ascribed to the change of hole-like carrier density, which is adjusted by Mn content. The existence of hole-like carriers can be understood rationally by the two-band model. The change of sign of magnetoresistance from positive to negative has been observed in ZnCNi3- x Mn x with the change of Mn content, which could be ascribed to the competition between the contribution from field-induced suppression of the thermally excited ferromagnetic spin fluctuations and the Lorentz contribution. When Mn content is low, the Lorentz contribution dominates the sign of magnetoresistance. On the other hand, when Mn content is high, the contribution from field-induced suppression of the thermally excited ferromagnetic spin fluctuations dominates the sign of magnetoresistance.

49 CFR 236.6 - Hand-operated switch equipped with switch circuit controller.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 4 2010-10-01 2010-10-01 false Hand-operated switch equipped with switch circuit..., AND APPLIANCES Rules and Instructions: All Systems General § 236.6 Hand-operated switch equipped with switch circuit controller. Hand-operated switch equipped with switch circuit controller connected to the...

49 CFR 236.6 - Hand-operated switch equipped with switch circuit controller.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 4 2013-10-01 2013-10-01 false Hand-operated switch equipped with switch circuit..., AND APPLIANCES Rules and Instructions: All Systems General § 236.6 Hand-operated switch equipped with switch circuit controller. Hand-operated switch equipped with switch circuit controller connected to the...

49 CFR 236.6 - Hand-operated switch equipped with switch circuit controller.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Hand-operated switch equipped with switch circuit..., AND APPLIANCES Rules and Instructions: All Systems General § 236.6 Hand-operated switch equipped with switch circuit controller. Hand-operated switch equipped with switch circuit controller connected to the...

49 CFR 236.6 - Hand-operated switch equipped with switch circuit controller.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Hand-operated switch equipped with switch circuit..., AND APPLIANCES Rules and Instructions: All Systems General § 236.6 Hand-operated switch equipped with switch circuit controller. Hand-operated switch equipped with switch circuit controller connected to the...

49 CFR 236.6 - Hand-operated switch equipped with switch circuit controller.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Hand-operated switch equipped with switch circuit..., AND APPLIANCES Rules and Instructions: All Systems General § 236.6 Hand-operated switch equipped with switch circuit controller. Hand-operated switch equipped with switch circuit controller connected to the...

Measurement of dielectric properties at low temperatures: application to the study of magnetoresistive manganite/ insulating oxide bulk composites

NASA Astrophysics Data System (ADS)

Vanderbemden, P.; Rivas-Murias, B.; Lovchinov, V.; Vertruyen, B.

2010-11-01

In this paper, we report low temperature dielectric measurements of bulk composite electroceramic samples containing a colossal magnetoresistive (CMR) manganite phase (La0.7Ca0.3MnO3 [abbreviated LCMO]) and an insulating phase (Mn3O4). Details of the experimental system are given and possible experimental artefacts due to moisture are outlined. For a LCMO volume fraction of ~ 16%, the permittivity of the LCMO/ Mn3O4 composite at T = 50 K is found to be much higher than that of pure Mn3O4 and magnetic field dependent. This effect is related to an extrinsic space charge polarization mechanism between the insulating phase (Mn3O4) and the conducting magnetoresistive phase (LCMO).

Preparation and thermo-optic switch properties based on chiral azobenzene-containing polyurethane

NASA Astrophysics Data System (ADS)

Ye, Feiyan; Qiu, Fengxian; Yang, Dongya; Cao, Guorong; Guan, Yijun; Zhuang, Lin

2013-07-01

A chiral azo chromophore compound 4-(4'-nitro-phenyl-diazenyl)-phenyl-1,2-propanediol ether (NPDPPE) was prepared with p-nitroaniline, phenol and R(-)-3-chloro-1,2-propanediol by the diazo-coupling reaction. Then, the chromophore molecule NPDPPE was polymerized with isophorone diisocyanate (IPDI) to obtain novel chiral azobenzene-containing polyurethane (CACPU). The chemical structures of chromophore molecule and CACPU were characterized by the FT-IR and UV-visible spectroscopy. The physical properties (thermal conductivity, thermal diffusion coefficient, and specific heat capacity) and mechanical properties (tensile strength, elongation at break and hardness) of CACPU thin films were measured. The refractive index and thermo-optic (TO) coefficient (dn/dT) of CACPU thin film was investigated for TE (transversal electric) polarizations by using an attenuated total reflection (ATR) configuration at the wavelengths of 532, 650 and 850 nm. The transmission loss of film was measured using the charge coupled device (CCD) digital imaging devices. A Y-branch switch and Mach-Zehnder interferometer (MZI) thermo-optic switches based on thermo-optic effect were proposed and the performances of switches were simulated. The results showed that the power consumption of the Y-branch thermo-optic switch was only 3.28 mW. The rising and falling times of Y-branch and MZI switches were 12.0 ms and 2.0 ms, respectively. The conclusion has potential significance to improve and develop new Y-branch digital optical switch (DOS), MZI thermo-optic switch, directional coupler (DC) switch and optical modulators.

Magnetoresistive biosensors for quantitative proteomics

NASA Astrophysics Data System (ADS)

Zhou, Xiahan; Huang, Chih-Cheng; Hall, Drew A.

2017-08-01

Quantitative proteomics, as a developing method for study of proteins and identification of diseases, reveals more comprehensive and accurate information of an organism than traditional genomics. A variety of platforms, such as mass spectrometry, optical sensors, electrochemical sensors, magnetic sensors, etc., have been developed for detecting proteins quantitatively. The sandwich immunoassay is widely used as a labeled detection method due to its high specificity and flexibility allowing multiple different types of labels. While optical sensors use enzyme and fluorophore labels to detect proteins with high sensitivity, they often suffer from high background signal and challenges in miniaturization. Magnetic biosensors, including nuclear magnetic resonance sensors, oscillator-based sensors, Hall-effect sensors, and magnetoresistive sensors, use the specific binding events between magnetic nanoparticles (MNPs) and target proteins to measure the analyte concentration. Compared with other biosensing techniques, magnetic sensors take advantage of the intrinsic lack of magnetic signatures in biological samples to achieve high sensitivity and high specificity, and are compatible with semiconductor-based fabrication process to have low-cost and small-size for point-of-care (POC) applications. Although still in the development stage, magnetic biosensing is a promising technique for in-home testing and portable disease monitoring.

Crystal growth of Dirac semimetal ZrSiS with high magnetoresistance and mobility.

PubMed

Sankar, Raman; Peramaiyan, G; Muthuselvam, I Panneer; Butler, Christopher J; Dimitri, Klauss; Neupane, Madhab; Rao, G Narsinga; Lin, M-T; Chou, F C

2017-01-18

High quality single crystal ZrSiS as a theoretically predicted Dirac semimetal has been grown successfully using a vapor phase transport method. The single crystals of tetragonal structure are easy to cleave into perfect square-shaped pieces due to the van der Waals bonding between the sulfur atoms of the quintuple layers. Physical property measurement results including resistivity, Hall coefficient (R H ), and specific heat are reported. The transport and thermodynamic properties suggest a Fermi liquid behavior with two Fermi pockets at low temperatures. At T = 3 K and magnetic field of Hǁc up to 9 Tesla, large magneto-resistance up to 8500% and 7200% for Iǁ (100) and Iǁ (110) were found. Shubnikov de Haas (SdH) oscillations were identified from the resistivity data, revealing the existence of two Fermi pockets at the Fermi level via the fast Fourier transform (FFT) analysis. The Hall coefficient (R H ) showed hole-dominated carriers with a high mobility of 3.05 × 10 4  cm 2 V -1 s -1 at 3 K. ZrSiS has been confirmed to be a Dirac semimetal by the Dirac cone mapping near the X-point via angle resolved photoemission spectroscopy (ARPES) with a Dirac nodal line near the Fermi level identified using scanning tunneling spectroscopy (STS).

Uniting Gradual and Abrupt set Processes in Resistive Switching Oxides

NASA Astrophysics Data System (ADS)

Fleck, Karsten; La Torre, Camilla; Aslam, Nabeel; Hoffmann-Eifert, Susanne; Böttger, Ulrich; Menzel, Stephan

2016-12-01

Identifying limiting factors is crucial for a better understanding of the dynamics of the resistive switching phenomenon in transition-metal oxides. This improved understanding is important for the design of fast-switching, energy-efficient, and long-term stable redox-based resistive random-access memory devices. Therefore, this work presents a detailed study of the set kinetics of valence change resistive switches on a time scale from 10 ns to 104 s , taking Pt /SrTiO3/TiN nanocrossbars as a model material. The analysis of the transient currents reveals that the switching process can be subdivided into a linear-degradation process that is followed by a thermal runaway. The comparison with a dynamical electrothermal model of the memory cell allows the deduction of the physical origin of the degradation. The origin is an electric-field-induced increase of the oxygen-vacancy concentration near the Schottky barrier of the Pt /SrTiO3 interface that is accompanied by a steadily rising local temperature due to Joule heating. The positive feedback of the temperature increase on the oxygen-vacancy mobility, and thereby on the conductivity of the filament, leads to a self-acceleration of the set process.

Unidirectional magnetoresistance in magnetic thin films with non-uniform thickness

NASA Astrophysics Data System (ADS)

Jia, M. W.; Zhou, C.; Zeng, F. L.; Wu, Y. Z.

2018-05-01

The magnetoresistance (MR) of Co film and Co/Pt bilayers was studied systematically as a function of Co and Pt thickness at room temperature. In the samples with the wedge shape, we found the unidirectional MR which has the characteristics of R (Mz )≠R (-Mz ) with the magnetization normal to the film. The measured unidirectional MR is attributed to the differential anomalous Hall resistance due to the thickness difference at the electrodes for the longitudinal resistance measurements. The unidirectional MR effect in the Co/Pt bilayers can be greatly suppressed by a non-magnetic Cu inserting layer.

Optimal control of switching time in switched stochastic systems with multi-switching times and different costs

NASA Astrophysics Data System (ADS)

Liu, Xiaomei; Li, Shengtao; Zhang, Kanjian

2017-08-01

In this paper, we solve an optimal control problem for a class of time-invariant switched stochastic systems with multi-switching times, where the objective is to minimise a cost functional with different costs defined on the states. In particular, we focus on problems in which a pre-specified sequence of active subsystems is given and the switching times are the only control variables. Based on the calculus of variation, we derive the gradient of the cost functional with respect to the switching times on an especially simple form, which can be directly used in gradient descent algorithms to locate the optimal switching instants. Finally, a numerical example is given, highlighting the validity of the proposed methodology.

Transient-Switch-Signal Suppressor

NASA Technical Reports Server (NTRS)

Bozeman, Richard J., Jr.

1995-01-01

Circuit delays transmission of switch-opening or switch-closing signal until after preset suppression time. Used to prevent transmission of undesired momentary switch signal. Basic mode of operation simple. Beginning of switch signal initiates timing sequence. If switch signal persists after preset suppression time, circuit transmits switch signal to external circuitry. If switch signal no longer present after suppression time, switch signal deemed transient, and circuit does not pass signal on to external circuitry, as though no transient switch signal. Suppression time preset at value large enough to allow for damping of underlying pressure wave or other mechanical transient.

Giant magnetoresistance (GMR) behavior of electrodeposited NiFe/Cu multilayers: Dependence of non-magnetic and magnetic layer thicknesses

NASA Astrophysics Data System (ADS)

Kuru, Hilal; Kockar, Hakan; Alper, Mursel

2017-12-01

Giant magnetoresistance (GMR) behavior in electrodeposited NiFe/Cu multilayers was investigated as a function of non-magnetic (Cu) and ferromagnetic (NiFe) layer thicknesses, respectively. Prior to the GMR analysis, structural and magnetic analyses of the multilayers were also studied. The elemental analysis of the multilayers indicated that the Cu and Ni content in the multilayers increase with increasing Cu and NiFe layer thickness, respectively. The structural studies by X-ray diffraction revealed that all multilayers have face centred cubic structure with preferred (1 1 0) crystal orientation as their substrates. The magnetic properties studied with the vibrating sample magnetometer showed that the magnetizations of the samples are significantly affected by the layer thicknesses. Saturation magnetisation, Ms increases from 45 to 225 emu/cm3 with increasing NiFe layer thickness. The increase in the Ni content of the multilayers with a small Fe content causes an increase in the Ms. And, the coercivities ranging from 2 to 24 Oe are between the soft and hard magnetic properties. Also, the magnetic easy axis of the multilayers was found to be in the film plane. Magnetoresistance measurements showed that all multilayers exhibited the GMR behavior. The GMR magnitude increases with increasing Cu layer thickness and reaches its maximum value of 10% at the Cu layer thickness of 1 nm, then it decreases. And similarly, the GMR magnitude increases and reaches highest value of pure GMR (10%) for the NiFe layer thickness of 3 nm, and beyond this point GMR decreases with increasing NiFe layer thickness. Some small component of the anisotropic magnetoresistance was also observed at thin Cu and thick NiFe layer thicknesses. It is seen that the highest GMR values up to 10% were obtained in electrodeposited NiFe/Cu multilayers up to now. The structural, magnetic and magnetoresistance properties of the NiFe/Cu were reported via the variations of the thicknesses of Cu and Ni

Thermal management and performance evaluation of a dual bi-directional, soft-switched IGBT-based inverter for the 1st autonomous microgrid power system in Taiwan under various operating conditions

NASA Astrophysics Data System (ADS)

Chang, Tien-Chan; Fuh, Yiin-Kuen; Lu, Hong-Yi; Tu, Sheng-Xun

2016-06-01

The thermal management of the inverter system is of great importance since very high voltage/current will be switched intermittently and/or continuously and high temperature is excruciably detrimental to the service life of electronics, especially for the switching devices such as insulated gate bipolar transistor (IGBT). In this study, a newly developed dual bi-directional IGBT-based inverter in conjunction with autonomous microgrid system is investigated with particular focus on the thermal management and performance evaluation under various operation conditions. Locally enhanced heat transfer approach such as oblique orientation and heat dissipating materials are experimentally investigated. The studied inverter system is initially packaged by a galvanized steel plate (size 62 × 48 × 18 cm) and the switching power is set in the range of 0.5-3 kW. The module is operated at the switching and pulse frequencies of 60 Hz and 20 kHz, respectively. The adoption of heat dissipating material in either paste or film form had experimentally shown to possess the flexibility tailoring heat transfer performance locally. Experimental studies of heat dissipating film with various hotspot scenarios showed that the temperature difference can be appreciably reduced as much as 13.1 and 15.4 °C, respectively with facilitation of one- and two-layers of heat dissipating film. From the measurement results, the measured peak temperature is highly dominated by the thickness of heat dissipating film, showing the dominance of thickness-dependent thermal resistance and resultant heat accumulation phenomena.

A Shape Memory Alloy Based Cryogenic Thermal Conduction Switch

NASA Technical Reports Server (NTRS)

Notardonato, W. U.; Krishnan, V. B.; Singh, J. D.; Woodruff, T. R.; Vaidyanathan, R.

2005-01-01

Shape memory alloys (SMAs) can produce large strains when deformed (e.g., up to 8%). Heating results in a phase transformation and associated recovery of all the accumulated strain. This strain recovery can occur against large forces, resulting in their use as actuators. Thus an SMA element can integrate both sensory and actuation functions, by inherently sensing a change in temperature and actuating by undergoing a shape change as a result of a temperature-induced phase transformation. Two aspects of our work on cryogenic SMAs are addressed here. First - a shape memory alloy based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulkhead arrangement is discussed. Such a switch integrates the sensor element and the actuator element and can be used to create a variable thermal sink to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. Second - fabrication via arc-melting and subsequent materials testing of SMAs with cryogenic transformation temperatures for use in the aforementioned switch is discussed.

Generator powered electrically heated diesel particulate filter

DOEpatents

Gonze, Eugene V; Paratore, Jr., Michael J

2014-03-18

A control circuit for a vehicle powertrain includes a switch that selectivity interrupts current flow between a first terminal and a second terminal. A first power source provides power to the first terminal and a second power source provides power to the second terminal and to a heater of a heated diesel particulate filter (DPF). The switch is opened during a DPF regeneration cycle to prevent the first power source from being loaded by the heater while the heater is energized.

Magnetic-proximity-induced magnetoresistance on topological insulators

NASA Astrophysics Data System (ADS)

Chiba, Takahiro; Takahashi, Saburo; Bauer, Gerrit E. W.

2017-03-01

We theoretically study the magnetoresistance (MR) of two-dimensional massless Dirac electrons as found on the surface of three-dimensional topological insulators (TIs) that are capped by a ferromagnetic insulator (FI). We calculate charge and spin transport by Kubo and Boltzmann theories, taking into account the ladder-vertex correction and the in-scattering due to normal and magnetic disorder. The induced exchange splitting is found to generate an electric conductivity that depends on the magnetization orientation, but its form is very different from both the anisotropic and the spin Hall MR. The in-plane MR vanishes identically for nonmagnetic disorder, while out-of-plane magnetizations cause a large MR ratio. On the other hand, we do find an in-plane MR and planar Hall effect in the presence of magnetic disorder aligned with the FI magnetization. Our results may help us understand recent transport measurements on TI |FI systems.

Magnetoresistance of an Anderson insulator of bosons.

PubMed

Gangopadhyay, Anirban; Galitski, Victor; Müller, Markus

2013-07-12

We study the magnetoresistance of two-dimensional bosonic Anderson insulators. We describe the change in spatial decay of localized excitations in response to a magnetic field, which is given by an interference sum over alternative tunneling trajectories. The excitations become more localized with increasing field (in sharp contrast to generic fermionic excitations which get weakly delocalized): the localization length ξ(B) is found to change as ξ(-1)(B)-ξ(-1)(0)~B(4/5). The quantum interference problem maps onto the classical statistical mechanics of directed polymers in random media (DPRM). We explain the observed scaling using a simplified droplet model which incorporates the nontrivial DPRM exponents. Our results have implications for a variety of experiments on magnetic-field-tuned superconductor-to-insulator transitions observed in disordered films, granular superconductors, and Josephson junction arrays, as well as for cold atoms in artificial gauge fields.

230% room-temperature magnetoresistance in CoFeB /MgO/CoFeB magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Djayaprawira, David D.; Tsunekawa, Koji; Nagai, Motonobu; Maehara, Hiroki; Yamagata, Shinji; Watanabe, Naoki; Yuasa, Shinji; Suzuki, Yoshishige; Ando, Koji

2005-02-01

Magnetoresistance (MR) ratio up to 230% at room temperature (294% at 20 K) has been observed in spin-valve-type magnetic tunnel junctions (MTJs) using MgO tunnel barrier layer fabricated on thermally oxidized Si substrates. We found that such a high MR ratio can be obtained when the MgO barrier layer was sandwiched with amorphous CoFeB ferromagnetic electrodes. Microstructure analysis revealed that the MgO layer with (001) fiber texture was realized when the MgO layer was grown on amorphous CoFeB rather than on polycrystalline CoFe. Since there have been no theoretical studies on the MTJs with a crystalline tunnel barrier and amorphous electrodes, the detailed mechanism of the huge tunneling MR effect observed in this study is not clear at the present stage. Nevertheless, the present work is of paramount importance in realizing high-density magnetoresistive random access memory and read head for ultra high-density hard-disk drives into practical use.

Large positive magnetoresistance in intermetallic compound NdCo2Si2

NASA Astrophysics Data System (ADS)

Roy Chowdhury, R.; Dhara, S.; Das, I.; Bandyopadhyay, B.; Rawat, R.

2018-04-01

The magnetic, magneto-transport and magnetocaloric properties of antiferromagnetic intermetallic compound NdCo2Si2 (TN = 32K) have been studied. The compound yields a positive magnetoresistance (MR) of about ∼ 123 % at ∼ 5K in 8 T magnetic field. The MR value is significantly large vis - a - vis earlier reports of large MR in intermetallic compounds, and possibly associated with the changes in magnetic structure of the compound. The large MR value can be explained in terms of field induced pseudo-gaps on Fermi surface.

Low electron mobility of field-effect transistor determined by modulated magnetoresistance

NASA Astrophysics Data System (ADS)

Tauk, R.; Łusakowski, J.; Knap, W.; Tiberj, A.; Bougrioua, Z.; Azize, M.; Lorenzini, P.; Sakowicz, M.; Karpierz, K.; Fenouillet-Beranger, C.; Cassé, M.; Gallon, C.; Boeuf, F.; Skotnicki, T.

2007-11-01

Room temperature magnetotransport experiments were carried out on field-effect transistors in magnetic fields up to 10 T. It is shown that measurements of the transistor magnetoresistance and its first derivative with respect to the gate voltage allow the derivation of the electron mobility in the gated part of the transistor channel, while the access/contact resistances and the transistor gate length need not be known. We demonstrate the potential of this method using GaN and Si field-effect transistors and discuss its importance for mobility measurements in transistors with nanometer gate length.

Linear unsaturating magnetoresistance in disordered systems

NASA Astrophysics Data System (ADS)

Lai, Ying Tong; Lara, Silvia; Love, Cameron; Ramakrishnan, Navneeth; Adam, Shaffique

Theoretical works have shown that disordered systems exhibit classical magnetoresistance (MR). In this talk, we examine a variety of experimental systems that observe linear MR at high magnetic fields, including silver chalcogenides, graphene, graphite and Weyl semimetals. We show that a careful analysis of the magnitude of the MR, as well as the field strength at which the MR changes from quadratic to linear, reveal important properties of the system, such as the ratio of the root-mean-square fluctuations in the carrier density and the average carrier density. By looking at other properties such as the zero-field mobility, we show that this carrier density inhomogeneity is consistent with what is known about the microscopic impurities in these experiments. The application of this disorder-induced MR to a variety of different experimental scenarios underline the universality of these theoretical models. This work is supported by the Singapore National Research Foundation (NRF-NRFF2012-01) and the Singapore Ministry of Education and Yale-NUS College through Grant Number R-607-265-01312.

Ultrafast Silicon-based Modulators using Optical Switching of Vanadium Dioxide

DTIC Science & Technology

2014-12-04

demonstrated by using photothermal heating to induce the VO2 semiconductor-to- metal phase transition and modulate the transmitted optical signal...speeds. By utilizing the sub-picosecond semiconductor-to- metal transition (SMT) in VO2 as the active switching mechanism that enables direct... metallic phases. The steep slope, high contrast, and relatively narrow hysteresis exhibited by these reflectivity measurements indicate the high quality

Magnetoresistance Study in a GaAs/InGaAs/GaAs Delta-Doped Quantum Well

NASA Astrophysics Data System (ADS)

Hasbun, J. E.

1997-03-01

The magnetoresistance of a GaAs/Ga_0.87In_0.13As/GaAs with an electron concentration of N_s=6.3x10^11cm-2 is calculated at low temperature for a magnetic field range of 2-30 tesla and low electric field. The results obtained for the magnetotransport are compared with the experimental work of Herfort et al.(J. Herfort, K.-J. Friedland, H. Kostial, and R. Hey, Appl. Phys. Lett. V66, 23 (1995)). While the logitudinal magnetoresistance agrees reasonably well with experiment, the Hall resistance slope reflects a classical shape; however, its second derivative seems to show oscillations that are consistent with the Hall effect plateaus seen experimentally. Albeit with a much higher electron concentration, earlier calculationsfootnote J. Hasbun, APS Bull. V41, 419 (1996) for an Al_0.27Ga_0.73/GaAs /Al_0.27Ga_0.73As quantum well shows similar behavior. This work has been carried out with the use of a quantum many body approach employed in earlier work(J. Hasbun, APS Bull. V41, 1659 (1996)).

Digital switched hydraulics

NASA Astrophysics Data System (ADS)

Pan, Min; Plummer, Andrew

2018-06-01

This paper reviews recent developments in digital switched hydraulics particularly the switched inertance hydraulic systems (SIHSs). The performance of SIHSs is presented in brief with a discussion of several possible configurations and control strategies. The soft switching technology and high-speed switching valve design techniques are discussed. Challenges and recommendations are given based on the current research achievements.

Enhancement of resistive switching properties in Al2O3 bilayer-based atomic switches: multilevel resistive switching.

PubMed

Vishwanath, Sujaya Kumar; Woo, Hyunsuk; Jeon, Sanghun

2018-06-08

Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (10 5 ) with better endurance (∼2000 cycles) and longer data retention (10 4 s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.

Enhancement of resistive switching properties in Al2O3 bilayer-based atomic switches: multilevel resistive switching

NASA Astrophysics Data System (ADS)

Vishwanath, Sujaya Kumar; Woo, Hyunsuk; Jeon, Sanghun

2018-06-01

Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (105) with better endurance (∼2000 cycles) and longer data retention (104 s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.

Significant enhancement of magnetoresistance with the reduction of particle size in nanometer scale

PubMed Central

Das, Kalipada; Dasgupta, P.; Poddar, A.; Das, I.

2016-01-01

The Physics of materials with large magnetoresistance (MR), defined as the percentage change of electrical resistance with the application of external magnetic field, has been an active field of research for quite some times. In addition to the fundamental interest, large MR has widespread application that includes the field of magnetic field sensor technology. New materials with large MR is interesting. However it is more appealing to vast scientific community if a method describe to achieve many fold enhancement of MR of already known materials. Our study on several manganite samples [La1−xCaxMnO3 (x = 0.52, 0.54, 0.55)] illustrates the method of significant enhancement of MR with the reduction of the particle size in nanometer scale. Our experimentally observed results are explained by considering model consisted of a charge ordered antiferromagnetic core and a shell having short range ferromagnetic correlation between the uncompensated surface spins in nanoscale regime. The ferromagnetic fractions obtained theoretically in the nanoparticles has been shown to be in the good agreement with the experimental results. The method of several orders of magnitude improvement of the magnetoresistive property will have enormous potential for magnetic field sensor technology. PMID:26837285

Finite Ground Coplanar Waveguide Shunt MEMS Switches for Switched Line Phase Shifters

NASA Technical Reports Server (NTRS)

Ponchak, George E.; Simons, Rainee N.; Scardelletti, Maximillian; Varaljay, Nicholas C.

2000-01-01

Switches with low insertion loss and high isolation are required for switched line phase shifters and the transmit/receive switch at the front end of communication systems. A Finite Ground Coplanar (FGC) waveguide capacitive, shunt MEMS switch has been implemented on high resistivity Si. The switch has demonstrated an insertion loss of less than 0.3 dB and a return loss greater than 15 dB from 10 to 20, GHz. The switch design, fabrication, and characteristics are presented.

Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe

NASA Astrophysics Data System (ADS)

Encina, S.; Pedrazzini, P.; Sereni, J. G.; Geibel, C.

2018-05-01

In CeSc1-xTixGe, Ti-alloying reduces the record-high antiferromagnetic (AFM) ordering temperature found in CeScGe at TN = 46 K and induces ferromagnetism for x ≥ 0.5 . In this work we focus on the AFM side, i.e. Sc-rich samples, and study their thermopower S (T) and magnetoresistance ρ (H , T) . The measured S (T) is small in comparison with the thermopower of other Ce-systems and shows some features that are compatible with a weak hybridization between the 4 f and band states. This is a further hint pointing to the local character of magnetism in this alloy. Magnetic fields up to 16 T have a minor effect on the electrical resistivity of stoichiometric CeScGe. On the other hand, for x = 0.65 , we find that fields above 4 T suppress the hump in ρ (T) . Furthermore, the 4.2 K magnetoresistance displays a strong decrease in the same field range, also in coincidence with magnetization results from the literature. Our results indicate that ρ (T , H) is a proper tool to assess the H - T phase diagram of this system.

Electrical Transport and Magnetoresistance Properties of Tensile-Strained CaMnO3 Thin Films

NASA Astrophysics Data System (ADS)

Ullery, Dustin; Lawson, Bridget; Zimmerman, William; Neubauer, Samuel; Chaudhry, Adeel; Hart, Cacie; Yong, Grace; Smolyaninova, Vera; Kolagani, Rajeswari

We will present our studies of the electrical transport and magnetoresistance properties of tensile strained CaMnO3 thin films. We observe that the resistivity decreases significantly as the film thickness decreases which is opposite to what is observed in thin films of hole doped manganites. The decrease in resistivity is more pronounced in the films on (100) SrTiO3, with resistivity of the thinnest films being about 3 orders of magnitude lower than that of bulk CaMnO3. Structural changes accompanying resistivity changes cannot be fully explained as due to tensile strain, and indicate the presence of oxygen vacancies. These results also suggest a coupling between tensile strain and oxygen deficiency, consistent with predictions from models based on density functional theory calculations. We observe a change in resistance under the application of moderate magnetic field. Experiments are underway to understand the origin of the magnetoresistance and its possible relation to the tensile strain effects. We acknowledge support from: Towson Office of University Undergraduate Research, Fisher Endowment Grant and Undergraduate Research Grants from the Fisher College of Science and Mathematics, and Seed Funding Grant from the School of Emerging technologies.

Tuning the electronic and the crystalline structure of LaBi by pressure: From extreme magnetoresistance to superconductivity

DOE PAGES

Tafti, F. F.; Torikachvili, M. S.; Stillwell, R. L.; ...

2017-01-10

Here, extreme magnetoresistance (XMR) in topological semimetals is a recent discovery which attracts attention due to its robust appearance in a growing number of materials. To search for a relation between XMR and superconductivity, we study the effect of pressure on LaBi. By increasing pressure, we observe the disappearance of XMR followed by the appearance of superconductivity at P ≈ 3.5 GPa. We find a region of coexistence between superconductivity and XMR in LaBi in contrast to other superconducting XMR materials. The suppression of XMR is correlated with increasing zero-field resistance instead of decreasing in-field resistance. At higher pressures, Pmore » ≈ 11 GPa, we find a structural transition from the face-centered cubic lattice to a primitive tetragonal lattice, in agreement with theoretical predictions. The relationship between extreme magnetoresistance, superconductivity, and structural transition in LaBi is discussed.« less

Frequency-dependent polarization-angle-phase-shift in the microwave-induced magnetoresistance oscillations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Han-Chun; Ye, Tianyu; Mani, R. G.

2015-02-14

Linear polarization angle, θ, dependent measurements of the microwave radiation-induced oscillatory magnetoresistance, R{sub xx}, in high mobility GaAs/AlGaAs 2D electron devices have shown a θ dependence in the oscillatory amplitude along with magnetic field, frequency, and extrema-dependent phase shifts, θ{sub 0}. Here, we suggest a microwave frequency dependence of θ{sub 0}(f) using an analysis that averages over other smaller contributions, when those contributions are smaller than estimates of the experimental uncertainty.

Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton.

PubMed

Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

2015-05-22

Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology.

Intentional preparation of auditory attention-switches: Explicit cueing and sequential switch-predictability.

PubMed

Seibold, Julia C; Nolden, Sophie; Oberem, Josefa; Fels, Janina; Koch, Iring

2018-06-01

In an auditory attention-switching paradigm, participants heard two simultaneously spoken number-words, each presented to one ear, and decided whether the target number was smaller or larger than 5 by pressing a left or right key. An instructional cue in each trial indicated which feature had to be used to identify the target number (e.g., female voice). Auditory attention-switch costs were found when this feature changed compared to when it repeated in two consecutive trials. Earlier studies employing this paradigm showed mixed results when they examined whether such cued auditory attention-switches can be prepared actively during the cue-stimulus interval. This study systematically assessed which preconditions are necessary for the advance preparation of auditory attention-switches. Three experiments were conducted that controlled for cue-repetition benefits, modality switches between cue and stimuli, as well as for predictability of the switch-sequence. Only in the third experiment, in which predictability for an attention-switch was maximal due to a pre-instructed switch-sequence and predictable stimulus onsets, active switch-specific preparation was found. These results suggest that the cognitive system can prepare auditory attention-switches, and this preparation seems to be triggered primarily by the memorised switching-sequence and valid expectations about the time of target onset.

Air-bridge and Vertical CNT Switches for High Performance Switching Applications

NASA Technical Reports Server (NTRS)

Kaul, Anupama B.; Wong, Eric W.; Epp, Larry; Bronikowski, Michael J.; Hunt, BBrian D.

2006-01-01

Carbon nanotubes are attractive for switching applications since electrostatically-actuated CNT switches have low actuation voltages and power requirements, while allowing GHz switching speeds that stem from the inherently high elastic modulus and low mass of the CNT.Our first NEM structure, the air-bridge switch, consists of suspended single-walled nanotubes (SWNTs) that lie above a sputtered Nb base electrode, where contact to the CNTs is made using evaporated Au/Ti. Electrical measurements of these air-bridge devices show well-defined ON and OFF states as a dc bias of a few volts is applied between the CNT and the Nb-base electrode. The CNT air-bridge switches were measured to have switching times down to a few nanoseconds. Our second NEM structure, the vertical CNT switch, consists of nanotubes grown perpendicular to the substrate. Vertical multi-walled nanotubes (MWNTs) are grown directly on a heavily doped Si substrate, from 200 - 300 nm wide, approximately 1 micrometer deep nano-pockets, with Nb metal electrodes to result in the formation of a vertical single-pole-double-throw switch architecture.

Extremely large magnetoresistance in a high-quality WTe2 grown by flux method

NASA Astrophysics Data System (ADS)

Tsumura, K.; Yano, R.; Kashiwaya, H.; Koyanagi, M.; Masubuchi, S.; Machida, T.; Namiki, H.; Sasagawa, T.; Kashiwaya, S.

2018-03-01

We have grown single crystals of WTe2 by a self-flux method and evaluated the quality of the crystals. A Hall bar-type device was fabricated from an as-exfoliated film on a Si substrate and longitudinal resistance Rxx was measured. Rxx increased with an applied perpendicular magnetic field without saturation and an extremely large magnetoresistance as high as 376,059 % was observed at 8.27 T and 1.7 K.

Formation and anisotropic magnetoresistance of Co/Pt nano-contacts through aluminum oxide barrier

NASA Astrophysics Data System (ADS)

Al-Mahdawi, Muftah; Sahashi, Masashi

2014-01-01

We report on the observation of anisotropic magnetoresistance (AMR) in vertical asymmetric nano-contacts (NCs) made through AlOx nano-oxide layer (NOL) formed by ion-assisted oxidation method in the film stack of Co/AlOx-NOL/Pt. Analysis of NC formation was based on in situ conductive atomic force microscopy and transmission electron microscopy. Depending on the purity of NCs from Al contamination, we observed up to 29% AMR ratio at room temperature.

Terahertz Photovoltaic Detection of Cyclotron Resonance in the Regime of Radiation-Induced Magnetoresistance Oscillations

DTIC Science & Technology

2013-06-17

should not contrued as an official Department of the Army position, policy or decision, unless so designated by other documentation. 9. SPONSORING...construed as an official Department of the Army position, policy or decision, unless so designated by other documentation. ... PHYSICAL REVIEW B 87, 245308...oscillations in the diagonal magnetoresistance, Rxx , of the 2DES at cryogenic temperatures, T , with oscillatory nodes near integral and half- integral

The magnetoresistance of sub-micron Fe wires

NASA Astrophysics Data System (ADS)

Blundell, S. J.; Shearwood, C.; Gester, M.; Baird, M. J.; Bland, J. A. C.; Ahmed, H.

1994-07-01

A novel combination of electron- and ion-beam lithography has been used to prepare Fe gratings with wire widths of 0.5 μm and wire separations in the range 0.5-4 μm from an Fe/GaAs (001) film of thickness 25 nm. With an in-plane magnetic field applied perpendicular to the length of the wires, a harder magnetisation loop is observed using the magneto-optic Kerr effect (MOKE), compared with that observed in the unprocessed film. We observe a strong effect in the magnetoresistance (MR) when the magnetic field is applied transverse to the wires. It is believed that this effect originates from the highly non-uniform demagnetising field in each wire of the grating. These results demonstrate that the combination of MOKE and MR measurements can provide important information about the magnetisation reversal processes in magnetic gratings and can be used to understand the effect of shape anisotropy on magnetic properties.

Alarm toe switch

DOEpatents

Ganyard, Floyd P.

1982-01-01

An alarm toe switch inserted within a shoe for energizing an alarm circuit n a covert manner includes an insole mounting pad into which a miniature reed switch is fixedly molded. An elongated slot perpendicular to the reed switch is formed in the bottom surface of the mounting pad. A permanent cylindrical magnet positioned in the forward portion of the slot with a diameter greater than the pad thickness causes a bump above the pad. A foam rubber block is also positioned in the slot rearwardly of the magnet and holds the magnet in normal inoperative relation. A non-magnetic support plate covers the slot and holds the magnet and foam rubber in the slot. The plate minimizes bending and frictional forces to improve movement of the magnet for reliable switch activation. The bump occupies the knuckle space beneath the big toe. When the big toe is scrunched rearwardly the magnet is moved within the slot relative to the reed switch, thus magnetically activating the switch. When toe pressure is released the foam rubber block forces the magnet back into normal inoperative position to deactivate the reed switch. The reed switch is hermetically sealed with the magnet acting through the wall so the switch assembly S is capable of reliable operation even in wet and corrosive environments.

Remote switch actuator

DOEpatents

Haas, Edwin Gerard; Beauman, Ronald; Palo, Jr., Stefan

2013-01-29

The invention provides a device and method for actuating electrical switches remotely. The device is removably attached to the switch and is actuated through the transfer of a user's force. The user is able to remain physically removed from the switch site obviating need for protective equipment. The device and method allow rapid, safe actuation of high-voltage or high-current carrying electrical switches or circuit breakers.

Direct-heating solar-collector dump valve

NASA Technical Reports Server (NTRS)

Howikman, T. C.

1977-01-01

Five-port ganged valve isolates collector from primary load system pressure and drains collectors, allowing use of direct heating with all its advantages. Valve is opened and closed by same switch that controls pump or by temperature sensor set at O C, while providing direct dump option.

Switching antipsychotic medications.

PubMed

Weiden, P J; Aquila, R; Dalheim, L; Standard, J M

1997-01-01

Compared with conventional antipsychotics, the so-called "atypical" antipsychotics promise improved side effect profiles and better control of the symptoms of schizophrenia. Therefore, most patients currently taking conventional antipsychotics could potentially benefit from a switch to an atypical antipsychotic. Often, the key issue in deciding whether to switch is the presence of countervailing factors that mitigate against the change. This paper discusses the indications and contraindications for switching antipsychotics, plus issues that require consideration before a switch is made. Also, the advantages and disadvantages of various switching techniques are discussed, with a particular focus on the newer antipsychotic olanzapine.

An acoustic switch.

PubMed

Vanhille, Christian; Campos-Pozuelo, Cleofé

2014-01-01

The benefits derived from the development of acoustic transistors which act as switches or amplifiers have been reported in the literature. Here we propose a model of acoustic switch. We theoretically demonstrate that the device works: the input signal is totally restored at the output when the switch is on whereas the output signal nulls when the switch is off. The switch, on or off, depends on a secondary acoustic field capable to manipulate the main acoustic field. The model relies on the attenuation effect of many oscillating bubbles on the main travelling wave in the liquid, as well as on the capacity of the secondary acoustic wave to move the bubbles. This model evidences the concept of acoustic switch (transistor) with 100% efficiency. Copyright © 2013 Elsevier B.V. All rights reserved.

Evaluation of the tobacco heating system 2.2. Part 9: Application of systems pharmacology to identify exposure response markers in peripheral blood of smokers switching to THS2.2.

PubMed

Martin, Florian; Talikka, Marja; Ivanov, Nikolai V; Haziza, Christelle; Hoeng, Julia; Peitsch, Manuel C

2016-11-30

As part of current harm reduction strategies, candidate modified risk tobacco products (MRTP) are developed to offer adult smokers who want to continue using tobacco product an alternative to cigarettes while potentially reducing individual risk and population harm compared to smoking cigarettes. One of these candidate MRTPs is the Tobacco Heating System (THS) 2.2 which does not burn tobacco, but instead heats it, thus producing significantly reduced levels of harmful and potentially harmful constituents (HPHC) compared with combustible cigarettes (CC). A controlled, parallel group, open-label clinical study was conducted with subjects randomized to three monitored groups: (1) switching from CCs to THS2.2; (2) continuous use of non-menthol CC brand (CC arm); or (3) smoking abstinence (SA arm) for five days. Exposure response was assessed by measuring biomarkers of exposure to selected HPHCs. To complement the classical exposure response measurements, we have used the previously reported whole blood derived gene signature that can distinguish current smokers from either non-smokers or former smokers with high specificity and sensitivity. We tested the small signature consisting of only 11 genes on the blood transcriptome of subjects enrolled in the clinical study and showed a reduced exposure response in subjects that either stopped smoking or switched to a candidate MRTP, the THS2.2, compared with subjects who continued smoking their regular tobacco product. Copyright © 2016. Published by Elsevier Inc.

Coaxial Switch

DTIC Science & Technology

2014-04-23

0005] RF coaxial switches are typically used in environments that are prone to mechanical shocks and vibrations . For example, in military...withstand mechanical shocks and vibrations and to maintain an RF connection throughout a shock or a vibration event. Attorney Docket No. 102139...3 of 16 [0006] It has been found that shocks and vibrations on prior art rotary-type coaxial switches may cause the shaft in the coaxial switch

Effect of sputtering condition and heat treatment in Co/Cu/Co/FeMn spin valve

NASA Astrophysics Data System (ADS)

Kim, Hong Jin; Bae, Jun Soo; Lee, Taek Dong; Lee, Hyuck Mo

2002-03-01

The exchange field of Cu(50 Å)/FeMn(50 Å)/Co(50 Å) sputtered on Si substrate was studied in terms of surface roughness and phase formation of γ-FeMn under a variety of Ar pressures and powers in sputtering. It was found that the exchange field is stronger when the surface is smoother and the FeMn layer forms better. The exchange bias field increased by more than three times after heat treatment. The effect of heat treament on magnetoresistance (MR) and resistance of the top spin valve, substrate/Co(30 Å)/Cu(30 Å)/Co(30 Å)/FeMn(150 Å), was studied. It was observed that the MR started to increase with annealing temperature and the effect was significant at 150°C. The heat treatment led to the disappearance of the intermixed layer between Co and Cu, and the concentration profile of Cu became flat and smooth at this temperature.

Antiferromagnetic coupling and magnetoresistance enhancement in Co-Re metallic superlattices (abstract)

NASA Astrophysics Data System (ADS)

Freitas, P. P.; From, M.; Melo, L. V.; Ferreira, J.; Trindade, I.; Monteiro, P.

1991-11-01

Co-Re metallic superlattices were prepared that show antiferromagnetic exchange coupling and enhanced saturation magnetoresistance for particular values of the Re spacer thickness. We report studies on films with the structure glass /150 Å Re/[13 ÅCo/tRe]16/50 Å Re, with tRe ranging from 3 to 40 Å. These structures were grown by magnetron sputtering in a system with a base pressure of 1×10-7 Torr with deposition rates of 0.3 and 0.4 Å/s for Co and Re, respectively. x-ray diffractograms indicate the structure to be highly textured with the c axis perpendicular to the sample plane. The superlattice structure was obtained from high-angle θ-2θ scans. First-, second-, and third-order satellites are observed on both sides of the central [002] peak. Periodicity and bilayer composition are obtained from comparison of the data with a theoretical calculation of the x-ray diffractogram. Thickness calibration was confirmed by Rutherford backscattering and profilometer data. In-plane magnetization and magnetoresistance data (Δρ/ρ) indicate that stronger antiferromagnetic coupling and highest Δρ/ρ occur for tRe≊6 Å. The saturation field (Hs) needed to align contiguous antiferromagnetically coupled Co layers is about 1 T. This corresponds to an exchange coupling between the Co layer J≊-1 erg/cm2. (Δρ/ρ) reaches 2% in samples deposited at 170 °C. This data confirms results obtained by Parkin et al.1 in Co-Ru and Co-Cr superlattices.

Development of a Magneto-Resistive Angular Position Sensor for Space Mechanisms

NASA Technical Reports Server (NTRS)

Hahn, Robert; Schmidt, Tilo; Seifart, Klaus; Olberts, Bastian; Romera, Fernando

2016-01-01

Magnetic microsystems in the form of magneto-resistive (MR) sensors are firmly established in automobiles and industrial applications. They are used to measure travel, angle, electrical current, or magnetic fields. MR technology opens up new sensor possibilities in space applications and can be an enabling technology for optimal performance, high robustness and long lifetime at reasonable costs. In some science missions, the technology is already applied, however, the designs are proprietary and case specific, for instance in case of the angular sensors used for JPL/NASA's Mars rover Curiosity [1]. Since 2013 HTS GmbH and Sensitec GmbH have teamed up to develop and qualify a standardized yet flexible to use MR angular sensor for space mechanisms. Starting with a first assessment study and market survey performed under ESA contract, a very strong industry interest in novel, contactless position measurement means was found. Currently a detailed and comprehensive development program is being performed by HTS and Sensitec. The objective of this program is to advance the sensor design up to Engineering Qualification Model level and to perform qualification testing for a representative space application. The paper briefly reviews the basics of magneto-resistive effects and possible sensor applications and describes the key benefits of MR angular sensors with reference to currently operational industrial and space applications. The key applications and specification are presented and the preliminary baseline mechanical and electrical design will be discussed. An outlook on the upcoming development and test stages as well as the qualification program will be provided.

Magnetocardiography and magnetoencephalography measurements at room temperature using tunnel magneto-resistance sensors

NASA Astrophysics Data System (ADS)

Fujiwara, Kosuke; Oogane, Mikihiko; Kanno, Akitake; Imada, Masahiro; Jono, Junichi; Terauchi, Takashi; Okuno, Tetsuo; Aritomi, Yuuji; Morikawa, Masahiro; Tsuchida, Masaaki; Nakasato, Nobukazu; Ando, Yasuo

2018-02-01

Magnetocardiography (MCG) and magnetoencephalography (MEG) signals were detected at room temperature using tunnel magneto-resistance (TMR) sensors. TMR sensors developed with low-noise amplifier circuits detected the MCG R wave without averaging, and the QRS complex was clearly observed with averaging at a high signal-to-noise ratio. Spatial mapping of the MCG was also achieved. Averaging of MEG signals triggered by electroencephalography (EEG) clearly observed the phase inversion of the alpha rhythm with a correlation coefficient as high as 0.7 between EEG and MEG.

Methods for batch fabrication of cold cathode vacuum switch tubes

DOEpatents

Walker, Charles A [Albuquerque, NM; Trowbridge, Frank R [Albuquerque, NM

2011-05-10

Methods are disclosed for batch fabrication of vacuum switch tubes that reduce manufacturing costs and improve tube to tube uniformity. The disclosed methods comprise creating a stacked assembly of layers containing a plurality of adjacently spaced switch tube sub-assemblies aligned and registered through common layers. The layers include trigger electrode layer, cathode layer including a metallic support/contact with graphite cathode inserts, trigger probe sub-assembly layer, ceramic (e.g. tube body) insulator layer, and metallic anode sub-assembly layer. Braze alloy layers are incorporated into the stacked assembly of layers, and can include active metal braze alloys or direct braze alloys, to eliminate costs associated with traditional metallization of the ceramic insulator layers. The entire stacked assembly is then heated to braze/join/bond the stack-up into a cohesive body, after which individual switch tubes are singulated by methods such as sawing. The inventive methods provide for simultaneously fabricating a plurality of devices as opposed to traditional methods that rely on skilled craftsman to essentially hand build individual devices.

Switching kinetics of SiC resistive memory for harsh environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, K. A., E-mail: kam2g11@soton.ac.uk; Huang, R.; Groot, C. H. de

2015-07-15

Cu/a-SiC/Au resistive memory cells are measured using voltage pulses and exhibit the highest R{sub OFF}/R{sub ON} ratio recorded for any resistive memory. The switching kinetics are investigated and fitted to a numerical model, using thermal conductivity and resistivity properties of the dielectric. The SET mechanism of the Cu/a-SiC/Au memory cells is found to be due to ionic motion without joule heating contributions, whereas the RESET mechanism is found to be due to thermally assisted ionic motion. The conductive filament diameter is extracted to be around 4nm. The high thermal conductivity and resistivity for the Cu/a-SiC/Au memory cells result in slowmore » switching but with high thermal reliability and stability, showing potential for use in harsh environments. Radiation properties of SiC memory cells are investigated. No change was seen in DC sweep or pulsed switching nor in conductive mechanisms, up to 2Mrad(Si) using {sup 60}Co gamma irradiation.« less

Angular studies of the magnetoresistance in the density wave state of the quasi-two-dimensional purple bronze KMo6O17

NASA Astrophysics Data System (ADS)

Guyot, H.; Dumas, J.; Kartsovnik, M. V.; Marcus, J.; Schlenker, C.; Sheikin, I.; Vignolles, D.

2007-07-01

The purple molybdenum bronze KMo6O17 is a quasi-two-dimensional compound which shows a Peierls transition towards a commensurate metallic charge density wave (CDW) state. High magnetic field measurements have revealed several transitions at low temperature and have provided an unusual phase diagram “temperature-magnetic field”. Angular studies of the interlayer magnetoresistance are now reported. The results suggest that the orbital coupling of the magnetic field to the CDW is the most likely mechanism for the field induced transitions. The angular dependence of the magnetoresistance is discussed on the basis of a warped quasi-cylindrical Fermi surface and provides information on the geometry of the Fermi surface in the low temperature density wave state.

Unidirectional spin-wave heat conveyer.

PubMed

An, T; Vasyuchka, V I; Uchida, K; Chumak, A V; Yamaguchi, K; Harii, K; Ohe, J; Jungfleisch, M B; Kajiwara, Y; Adachi, H; Hillebrands, B; Maekawa, S; Saitoh, E

2013-06-01

When energy is introduced into a region of matter, it heats up and the local temperature increases. This energy spontaneously diffuses away from the heated region. In general, heat should flow from warmer to cooler regions and it is not possible to externally change the direction of heat conduction. Here we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic Y3Fe5O12, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes without time-reversal symmetry and to the conversion of spin waves into heat. When a Y3Fe5O12 film with low damping coefficients is used, spin waves are observed to emit heat at the sample end up to 10 mm away from the excitation source. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller.

Ballistic anisotropic magnetoresistance in core-shell nanowires and rolled-up nanotubes

NASA Astrophysics Data System (ADS)

Chang, Ching-Hao; Ortix, Carmine

2017-01-01

In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance (BAMR) is a change in the ballistic conductance with the direction of magnetization due to spin-orbit interaction. Very recently, a directional dependent ballistic conductance has been predicted to occur in a number of newly synthesized nonmagnetic semiconducting nanostructures subject to externally applied magnetic fields, without necessitating spin-orbit coupling. In this paper, we review past works on the prediction of this BAMR effect in core-shell nanowires (CSN) and rolled-up nanotubes (RUNTs). This is complemented by new results, we establish for the transport properties of tubular nanosystems subject to external magnetic fields.

Switching Vertical to Horizontal Graphene Growth Using Faraday Cage-Assisted PECVD Approach for High-Performance Transparent Heating Device.

PubMed

Qi, Yue; Deng, Bing; Guo, Xiao; Chen, Shulin; Gao, Jing; Li, Tianran; Dou, Zhipeng; Ci, Haina; Sun, Jingyu; Chen, Zhaolong; Wang, Ruoyu; Cui, Lingzhi; Chen, Xudong; Chen, Ke; Wang, Huihui; Wang, Sheng; Gao, Peng; Rummeli, Mark H; Peng, Hailin; Zhang, Yanfeng; Liu, Zhongfan

2018-02-01

Plasma-enhanced chemical vapor deposition (PECVD) is an applicable route to achieve low-temperature growth of graphene, typically shaped like vertical nanowalls. However, for transparent electronic applications, the rich exposed edges and high specific surface area of vertical graphene (VG) nanowalls can enhance the carrier scattering and light absorption, resulting in high sheet resistance and low transmittance. Thus, the synthesis of laid-down graphene (LG) is imperative. Here, a Faraday cage is designed to switch graphene growth in PECVD from the vertical to the horizontal direction by weakening ion bombardment and shielding electric field. Consequently, laid-down graphene is synthesized on low-softening-point soda-lime glass (6 cm × 10 cm) at ≈580 °C. This is hardly realized through the conventional PECVD or the thermal chemical vapor deposition methods with the necessity of high growth temperature (1000 °C-1600 °C). Laid-down graphene glass has higher transparency, lower sheet resistance, and much improved macroscopic uniformity when compare to its vertical graphene counterpart and it performs better in transparent heating devices. This will inspire the next-generation applications in low-cost transparent electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning the Colors of the Dark Isomers of Photochromic Boron Compounds with Fluoride Ions: Four-State Color Switching.

PubMed

Mellerup, Soren K; Rao, Ying-Li; Amarne, Hazem; Wang, Suning

2016-09-02

Combining a three-coordinated boron (BMes2) moiety with a four-coordinated photochromic organoboron unit leads to a series of new diboron compounds that undergo four-state reversible color switching in response to stimuli of light, heat, and fluoride ions. Thus, these hybrid diboron systems allow both convenient color tuning/switching of such photochromic systems, as well as visual fluoride sensing by color or fluorescent emission color change.

Enhancement of the giant magnetoresistance in spin valves via oxides formed from magnetic layers

NASA Astrophysics Data System (ADS)

Gillies, M. F.; Kuiper, A. E. T.

2000-11-01

An enhancement of the giant magnetoresistance effect is investigated in spin valves where oxide layers, which are formed from magnetic layers, are incorporated in the structure. Information about Co-Fe based nanooxide layer (NOL) is obtained via x-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. Cross-section transmission electron microscopy is also used to explore the effect of an NOL on the polycrystalline structure of the spin valve.

Alterations in heat loss and heat production mechanisms in rat exposed to hypergravic fields

NASA Technical Reports Server (NTRS)

Horowitz, J. M.; Horwitz, B. A.; Oyama, J.

1982-01-01

A review of studies investigating the thermal response of rats exposed to hypergravic fields well below maximum tolerance levels is presented. It is concluded that several lines of evidence indicate that the neural switching network for temperature regulation and cardiovascular channeling of blood flow is transiently affected during the first hour a rat is exposed to hypergravity. Moreover, even after one hour of exposure, when the core temperature has fallen several degrees, shivering and nonshivering thermogenesis are not fully activated. Only after prolonged exposure to hypergravic fields do heat production mechanisms recover sufficiently to bring the core temperature back to a normal level. Thus, the data indicate a more rapid recovery of effector mechanisms for heat loss than for heat production.

A Compact, Continuous Adiabatic Demagnetization Refrigerator with High Heat Sink Temperature

NASA Technical Reports Server (NTRS)

Shirron, P. J.; Canavan, E. R.; DiPirro, M. J.; Jackson, M.; Tuttle, J. G.

2003-01-01

In the continuous adiabatic demagnetization refrigerator (ADR), the existence of a constant temperature stage attached to the load breaks the link between the requirements of the load (usually a detector array) and the operation of the ADR. This allows the ADR to be cycled much faster, which yields more than an order of magnitude improvement in cooling power density over single-shot ADRs. Recent effort has focused on developing compact, efficient higher temperature stages. An important part of this work has been the development of passive gas-gap heat switches that transition (from conductive to insulating) at temperatures around 1 K and 4 K without the use of an actively heated getter. We have found that by carefully adjusting available surface area and the number of He-3 monolayers, gas-gap switches can be made to operate passively. Passive operation greatly reduces switching time and eliminates an important parasitic heat load. The current four stage ADR provides 6 micro W of cooling at 50 mK (21 micro W at 100 mK) and weighs less than 8 kg. It operates from a 4.2 K heat sink, which can be provided by an unpumped He bath or many commercially available mechanical cryocoolers. Reduction in critical current with temperature in our fourth stage NbTi magnet presently limits the maximum temperature of our system to approx. 5 K. We are developing compact, low-current Nb3Sn magnets that will raise the maximum heat sink temperature to over 10 K.

Origin of the magnetoresistance in oxide tunnel junctions determined through electric polarization control of the interface

DOE PAGES

Inoue, Hisashi; Swartz, Adrian G.; Harmon, Nicholas J.; ...

2015-11-11

The observed magnetoresistance (MR) in three-terminal (3T) ferromagnet-nonmagnet (FM-NM) tunnel junctions has historically been assigned to ensemble dephasing (Hanle effect) of a spin accumulation, thus offering a powerful approach for characterizing the spin lifetime of candidate materials for spintronics applications. However, due to crucial discrepancies of the extracted spin parameters with known materials properties, this interpretation has come under intense scrutiny. By employing epitaxial artificial dipoles as the tunnel barrier in oxide heterostructures, the band alignments between the FM and NM channels can be controllably engineered, providing an experimental platform for testing the predictions of the various spin accumulation models.more » Using this approach, we have been able to definitively rule out spin accumulation as the origin of the 3T MR. Instead, we assign the origin of the magnetoresistance to spin-dependent hopping through defect states in the barrier, a fundamental phenomenon seen across diverse systems. In conclusion, a theoretical framework is developed that can account for the signal amplitude, linewidth, and anisotropy.« less

Miniature intermittent contact switch

NASA Technical Reports Server (NTRS)

Sword, A.

1972-01-01

Design of electric switch for providing intermittent contact is presented. Switch consists of flexible conductor surrounding, but separated from, fixed conductor. Flexing of outside conductor to contact fixed conductor completes circuit. Advantage is small size of switch compared to standard switches.

Thermal Control Using Liquid-Metal Bridge Switches

NASA Technical Reports Server (NTRS)

Hirsa, Amir H.; Olles, Joseph; Tilger, Christopher

2013-01-01

A short term effort (3-months) was undertaken to demonstrate the feasibility of a novel method to locally control the heat transfer rate and demonstrate the potential to achieve a turndown ratio of approximately 10:1. The technology had to be demonstrated to be at a TRL of 2-3, with a plan to advance it to a TRL 5-6. Here, we show that the concept recently developed in our laboratory, namely the pinned-contact, double droplet switch made by overfilling a hole drilled in a suitable substrate can be implemented with a low-melting temperature metal. When toggled near a second substrate, a liquid bridge can be reversibly connected or disconnected, on demand. We have shown experimentally that liquid-metal bridge switches can be made from gallium with a suitable choice of substrate materials, activation strategies, and control techniques. Individual as well as arrays of gallium bridge switches were shown to be feasible and can be robustly controlled. The very short response time of the bridge connection and disconnection (on the order of 1 millisecond) provides for utility in a wide range of applications. The liquid bridge switches may be controlled actively or passively. We have shown through computations and analysis that liquid bridge switches provide locally large turndown ratios (on the order of 103:1), so a relatively sparse packing of them would be needed to obtain the desired turndown ratio of 10:1. For the laboratory demonstrations, pressure activation was utilized. Simple designs for a passive control strategy are presented which are highly attractive for several reasons, including i) large turndown ratio, ii) no solid-moving parts, and iii) stable operation. Finally, we note that passive systems do not require any electronics for their control. This along with the relatively small molecular weight of candidate materials for the system, makes for a robust design outside of Earth?s magnetic field, where spacecraft are subject to significant radiation bombardment.

Radiation hard vacuum switch

DOEpatents

Boettcher, Gordon E.

1990-01-01

A vacuum switch with an isolated trigger probe which is not directly connected to the switching electrodes. The vacuum switch within the plasmatron is triggered by plasma expansion initiated by the trigger probe which travels through an opening to reach the vacuum switch elements. The plasma arc created is directed by the opening to the space between the anode and cathode of the vacuum switch to cause conduction.

Radiation hard vacuum switch

DOEpatents

Boettcher, Gordon E.

1990-03-06

A vacuum switch with an isolated trigger probe which is not directly connected to the switching electrodes. The vacuum switch within the plasmatron is triggered by plasma expansion initiated by the trigger probe which travels through an opening to reach the vacuum switch elements. The plasma arc created is directed by the opening to the space between the anode and cathode of the vacuum switch to cause conduction.

Electronic logic to enhance switch reliability in detecting openings and closures of redundant switches

DOEpatents

Cooper, James A.

1986-01-01

A logic circuit is used to enhance redundant switch reliability. Two or more switches are monitored for logical high or low output. The output for the logic circuit produces a redundant and failsafe representation of the switch outputs. When both switch outputs are high, the output is high. Similarly, when both switch outputs are low, the logic circuit's output is low. When the output states of the two switches do not agree, the circuit resolves the conflict by memorizing the last output state which both switches were simultaneously in and produces the logical complement of this output state. Thus, the logic circuit of the present invention allows the redundant switches to be treated as if they were in parallel when the switches are open and as if they were in series when the switches are closed. A failsafe system having maximum reliability is thereby produced.

Hot-carrier trap-limited transport in switching chalcogenides

NASA Astrophysics Data System (ADS)

Piccinini, Enrico; Cappelli, Andrea; Buscemi, Fabrizio; Brunetti, Rossella; Ielmini, Daniele; Rudan, Massimo; Jacoboni, Carlo

2012-10-01

Chalcogenide materials have received great attention in the last decade owing to their application in new memory systems. Recently, phase-change memories have, in fact, reached the early stages of production. In spite of the industrial exploitation of such materials, the physical processes governing the switching mechanism are still debated. In this paper, we work out a complete and consistent model for transport in amorphous chalcogenide materials based on trap-limited conduction accompanied by carrier heating. A previous model is here extended to include position-dependent carrier concentration and field, consistently linked by the Poisson equation. The results of the new model reproduce the experimental electrical characteristics and their dependences on the device length and temperature. Furthermore, the model provides a sound physical interpretation of the switching phenomenon and is able to give an estimate of the threshold condition in terms of the material parameters, a piece of information of great technological interest.

Magnetostrictive Micro Mirrors for an Optical Switch Matrix

PubMed Central

Lee, Heung-Shik; Cho, Chongdu; Cho, Myeong-Woo

2007-01-01

We have developed a wireless-controlled compact optical switch by silicon micromachining techniques with DC magnetron sputtering. For the optical switching operation, micro mirror is designed as cantilever shape size of 5mm×800μm×50μm. TbDyFe film is sputter-deposited on the upper side of the mirror with the condition as: Ar gas pressure below 1.2×10-9 torr, DC input power of 180W and heating temperature of up to 250°C for the wireless control of each component. Mirrors are actuated by externally applied magnetic fields for the micro application. Applied beam path can be changed according to the direction and the magnitude of applied magnetic field. Reflectivity changes, M-H curves and X-ray diffractions of sputtered mirrors are measured to determine magneto-optical, magneto-elastic properties with variation in sputtered film thickness. The deflected angle-magnetic field characteristics of the fabricated mirror are measured. PMID:28903221

Magnetoresistivity and microstructure of YBa2Cu3Oy prepared using planetary ball milling

NASA Astrophysics Data System (ADS)

Hamrita, A.; Ben Azzouz, F.; Madani, A.; Ben Salem, M.

2012-01-01

We have studied the microstructure and the magnetoresistivity of polycrystalline YBa2Cu3Oy (YBCO or Y-123 for brevity) embedded with nanoparticles of Y-deficient YBCO, generated by the planetary ball milling technique. Bulk samples were synthesized from a precursor YBCO powder, which was prepared from commercial high purity Y2O3, Ba2CO3 and CuO via a one-step annealing process in air at 950 °C. After planetary ball milling of the precursor, the powder was uniaxially pressed and subsequently annealed at 950 °C in air. Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDXS) were carried out. TEM analyses show that nanoparticles of Y-deficient YBCO, generated by ball milling, are embedded in the superconducting matrix. Electrical resistance as a function of temperature, ρ(T), revealed that the zero resistance temperature, Tco, is 84.5 and 90 K for the milled and unmilled samples respectively. The milled ceramics exhibit a large magnetoresistance in weak magnetic fields at liquid nitrogen temperature. This attractive effect is of high significance as it makes these materials promising candidates for practical application in magnetic field sensor devices.

Magnetoresistance measurement of permalloy thin film rings with triangular fins

NASA Astrophysics Data System (ADS)

Lai, Mei-Feng; Hsu, Chia-Jung; Liao, Chun-Neng; Chen, Ying-Jiun; Wei, Zung-Hang

2010-01-01

Magnetization reversals in permalloy rings controlled by nucleation sites using triangular fins at the same side and diagonal with respect to the field direction are demonstrated by magnetoresistance measurement and micromagnetic simulation. In the ring with triangular fins at the same side, there exists two-step reversal from onion to flux-closure state (or vortex state) and then from flux-closure (or vortex state) to reverse onion state; in the ring with diagonal triangular fins, one-step reversal occurs directly from onion to reverse onion state. The reversal processes are repeatable and controllable in contrast to an ideal ring without triangular fins where one-step and two-step reversals occur randomly in sweep-up and sweep-down processes.

Effective switching frequency multiplier inverter

DOEpatents

Su, Gui-Jia [Oak Ridge, TN; Peng, Fang Z [Okemos, MI

2007-08-07

A switching frequency multiplier inverter for low inductance machines that uses parallel connection of switches and each switch is independently controlled according to a pulse width modulation scheme. The effective switching frequency is multiplied by the number of switches connected in parallel while each individual switch operates within its limit of switching frequency. This technique can also be used for other power converters such as DC/DC, AC/DC converters.

Chiral magnetoresistance in the Weyl semimetal NbP

NASA Astrophysics Data System (ADS)

Niemann, Anna Corinna; Gooth, Johannes; Wu, Shu-Chun; Bäßler, Svenja; Sergelius, Philip; Hühne, Ruben; Rellinghaus, Bernd; Shekhar, Chandra; Süß, Vicky; Schmidt, Marcus; Felser, Claudia; Yan, Binghai; Nielsch, Kornelius

2017-03-01

NbP is a recently realized Weyl semimetal (WSM), hosting Weyl points through which conduction and valence bands cross linearly in the bulk and exotic Fermi arcs appear. The most intriguing transport phenomenon of a WSM is the chiral anomaly-induced negative magnetoresistance (NMR) in parallel electric and magnetic fields. In intrinsic NbP the Weyl points lie far from the Fermi energy, making chiral magneto-transport elusive. Here, we use Ga-doping to relocate the Fermi energy in NbP sufficiently close to the W2 Weyl points, for which the different Fermi surfaces are verified by resultant quantum oscillations. Consequently, we observe a NMR for parallel electric and magnetic fields, which is considered as a signature of the chiral anomaly in condensed-matter physics. The NMR survives up to room temperature, making NbP a versatile material platform for the development of Weyltronic applications.

Negative Magnetoresistance without Chiral Anomaly in Topological Insulators.

PubMed

Dai, Xin; Du, Z Z; Lu, Hai-Zhou

2017-10-20

An intriguing phenomenon in topological semimetals and topological insulators is the negative magnetoresistance (MR) observed when a magnetic field is applied along the current direction. A prevailing understanding to the negative MR in topological semimetals is the chiral anomaly, which, however, is not well defined in topological insulators. We calculate the MR of a three-dimensional topological insulator, by using the semiclassical equations of motion, in which the Berry curvature explicitly induces an anomalous velocity and orbital moment. Our theoretical results are in quantitative agreement with the experiments. The negative MR is not sensitive to temperature and increases as the Fermi energy approaches the band edge. The orbital moment and g factors also play important roles in the negative MR. Our results give a reasonable explanation to the negative MR in 3D topological insulators and will be helpful in understanding the anomalous quantum transport in topological states of matter.

Anomalously large anisotropic magnetoresistance in a perovskite manganite

PubMed Central

Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X. Z.; Matsui, Y.; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E. Ward; Zhang, Jiandi

2009-01-01

The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La0.69Ca0.31MnO3, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a “colossal” AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings. PMID:19706504

Optimal Transmission Line Switching under Geomagnetic Disturbances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Mowen; Nagarajan, Harsha; Yamangil, Emre

Recently, there have been increasing concerns about how geomagnetic disturbances (GMDs) impact electrical power systems. Geomagnetically-induced currents (GICs) can saturate transformers, induce hot spot heating and increase reactive power losses. These effects can potentially cause catastrophic damage to transformers and severely impact the ability of a power system to deliver power. To address this problem, we develop a model of GIC impacts to power systems that includes 1) GIC thermal capacity of transformers as a function of normal Alternating Current (AC) and 2) reactive power losses as a function of GIC. We also use this model to derive an optimizationmore » problem that protects power systems from GIC impacts through line switching, generator dispatch, and load shedding. We then employ state-of-the-art convex relaxations of AC power flow equations to lower bound the objective. We demonstrate the approach on a modified RTS96 system and UIUC 150-bus system and show that line switching is an effective means to mitigate GIC impacts. We also provide a sensitivity analysis of decisions with respect to GMD direction.« less

Optimal Transmission Line Switching under Geomagnetic Disturbances

DOE PAGES

Lu, Mowen; Nagarajan, Harsha; Yamangil, Emre; ...

2017-10-11

Recently, there have been increasing concerns about how geomagnetic disturbances (GMDs) impact electrical power systems. Geomagnetically-induced currents (GICs) can saturate transformers, induce hot spot heating and increase reactive power losses. These effects can potentially cause catastrophic damage to transformers and severely impact the ability of a power system to deliver power. To address this problem, we develop a model of GIC impacts to power systems that includes 1) GIC thermal capacity of transformers as a function of normal Alternating Current (AC) and 2) reactive power losses as a function of GIC. We also use this model to derive an optimizationmore » problem that protects power systems from GIC impacts through line switching, generator dispatch, and load shedding. We then employ state-of-the-art convex relaxations of AC power flow equations to lower bound the objective. We demonstrate the approach on a modified RTS96 system and UIUC 150-bus system and show that line switching is an effective means to mitigate GIC impacts. We also provide a sensitivity analysis of decisions with respect to GMD direction.« less

Efficient Q-switched operation in 1.64 μm Er:YAG tapered rod laser

NASA Astrophysics Data System (ADS)

Polyakov, Vadim M.; Vitkin, Vladimir V.; Krylov, Alexandr A.; Uskov, Alexander V.; Mak, Andrey A.

2017-02-01

We model output characteristics of the 1645 nm 8 mJ 10 ns 100 Hz Q-switched Er:YAG DPSSL. The laser is end pumped at a wavelength of 1532 nm. Fiber-coupled diode laser module was 10 nm FWHM, 12 W CW, 200 μm, NA 0.22. Various tapering of the active rod has been considered for 1 mm diameter, 20 mm long and 0.5% Er doping. We discuss the heat deposition process, the energy storage efficiency and the average power limitations for Q-switched regime of generation and amplification, and find the system scalable for the high power operation.

Total internal reflection optical switch using the reverse breakdown of a pn junction in silicon.

PubMed

Kim, Jong-Hun; Park, Hyo-Hoon

2015-11-01

We demonstrate a new type of silicon total-internal-reflection optical switch with a simple pn junction functioning both as a reflector and a heater. The reflector is placed between asymmetrically y-branched multimode waveguides with an inclination angle corresponding to half of the branch angle. When the reflector is at rest, incident light is reflected in accordance to the refractive index difference due to the plasma dispersion effect of the pre-doped carriers. Switching to the transmission state is attained under a reverse breakdown of the pn junction by the thermo-optic effect which smears the refractive index difference. From this switching scheme, we confirmed the switching operation with a shallow total-internal-reflection region of 1 μm width. At a 6° branch angle, an extinction ratio of 12 dB and an insertion loss of -4.2  dB are achieved along with a thermal heating power of 151.5 mW.

Carbon footprints of heating oil and LPG heating systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Eric P., E-mail: ejohnson@ecosite.co.uk

For European homes without access to the natural gas grid, the main fuels-of-choice for heating are heating oil and LPG. How do the carbon footprints of these compare? Existing literature does not clearly answer this, so the current study was undertaken to fill this gap. Footprints were estimated in seven countries that are representative of the EU and constitute two-thirds of the EU-27 population: Belgium, France, Germany, Ireland, Italy, Poland and the UK. Novelties of the assessment were: systems were defined using the EcoBoiler model; well-to-tank data were updated according to most-recent research; and combustion emission factors were used thatmore » were derived from a survey conducted for this study. The key finding is that new residential heating systems fuelled by LPG are 20% lower carbon and 15% lower overall-environmental-impact than those fuelled by heating oil. An unexpected finding was that an LPG system's environmental impact is about the same as that of a bio heating oil system fuelled by 100% rapeseed methyl ester, Europe's predominant biofuel. Moreover, a 20/80 blend (by energy content) with conventional heating oil, a bio-heating-oil system generates a footprint about 15% higher than an LPG system's. The final finding is that fuel switching can pay off in carbon terms. If a new LPG heating system replaces an ageing oil-fired one for the final five years of its service life, the carbon footprint of the system's final five years is reduced by more than 50%.« less

Latching micro optical switch

DOEpatents

Garcia, Ernest J; Polosky, Marc A

2013-05-21

An optical switch reliably maintains its on or off state even when subjected to environments where the switch is bumped or otherwise moved. In addition, the optical switch maintains its on or off state indefinitely without requiring external power. External power is used only to transition the switch from one state to the other. The optical switch is configured with a fixed optical fiber and a movable optical fiber. The movable optical fiber is guided by various actuators in conjunction with a latching mechanism that configure the switch in one position that corresponds to the on state and in another position that corresponds to the off state.

ION SWITCH

DOEpatents

Cook, B.

1959-02-10

An ion switch capable of transferring large magnitudes of power is described. An ion switch constructed in accordance with the invention includes a pair of spaced control electrodes disposed in a highly evacuated region for connection in a conventional circuit to control the passing of power therethrough. A controllable ionic conduction path is provided directiy between the control electrodes by a source unit to close the ion switch. Conventional power supply means are provided to trigger the source unit and control the magnitude, durations and pulse repetition rate of the aforementioned ionic conduction path.

Positive magnetoresistance of single-crystal bilayer manganites (La{sub 1−z}Nd{sub z}){sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} (z = 0, 0.1)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shaykhutdinov, K. A.; Petrov, M. I.; Terent'ev, K. I.

2015-04-28

We investigate magnetoresistance, ρ{sub c}, of single-crystal bilayer lanthanum manganites (La{sub 1−z}Nd{sub z}){sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} (z = 0 and 0.1) at a transport current flowing along the crystal c axis and in external magnetic fields applied parallel to the crystal c axis or ab plane. It is demonstrated that the La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} manganite exhibits the positive magnetoresistance effect in the magnetic field applied in the ab sample plane at the temperatures T < 60 K, along with the negative magnetoresistance typical of all the substituted lanthanum manganites. In the (La{sub 0.9}Nd{sub 0.1}){sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} sample, the positive magnetoresistancemore » effect is observed at temperatures of 60–80 K in an applied field parallel to the c axis. The mechanism of this effect is shown to be fundamentally different from the colossal magnetoresistance effect typical of lanthanum manganites. The positive magnetoresistance originates from spin-dependent tunneling of carriers between the manganese-oxygen bilayers and can be explained by features of the magnetic structure of the investigated compounds.« less

Thickness dependence and the role of spin transfer torque in nonlinear giant magnetoresistance of permalloy dual spin valves

NASA Astrophysics Data System (ADS)

Banerjee, N.; Aziz, A.; Ali, M.; Robinson, J. W. A.; Hickey, B. J.; Blamire, M. G.

2010-12-01

The recent discovery of nonlinear current-dependent magnetoresistance in dual spin valve devices [A. Aziz, O. P. Wessely, M. Ali, D. M. Edwards, C. H. Marrows, B. J. Hickey, and M. G. Blamire, Phys. Rev. Lett. 103, 237203 (2009)10.1103/PhysRevLett.103.237203] opens up the possibility for distinct physics which extends the standard model of giant magnetoresistance. When the outer ferromagnetic layers of a dual spin valve are antiparallel, the resulting accumulation of spin in the middle ferromagnetic layer strongly modifies its bulk and interfacial spin asymmetry and resistance. Here, we report experimental evidence of the role of bulk spin accumulation in this nonlinear effect and show that interfacial spin accumulation alone cannot account for the observed dependence of the effect on the thickness of the middle ferromagnetic layer. It is also shown that spin torque acting on the middle ferromagnetic layer combined with the nonlinear effect might be useful in understanding the dynamical features associated with the nonlinear behavior.

Metastable states and intermittent switching of small populations of confined point vortices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmieder, R.W.

1995-07-01

We have found that small populations of point vortices confined in a box exhibit a variety of new and interesting metastable collective motions, ranging from rigid body rotation to complete chaos. These motions are induced by simulated heating and cooling of the vortices; they do not appear in adiabatic systems. By judicious choice of vortex circulations, heating and cooling rates, and box size, we have produced systems that switch intermittently between several metastable states, that oscillate quasi-periodically, and that show a variety of interesting collective behaviors that in some cases are suggestive of biological organisms.

Diplexer switch

NASA Technical Reports Server (NTRS)

Grauling, C. H., Jr.; Parker, T. W.

1977-01-01

Switch achieves high isolation and continuous input/output matching by using resonant coupling structure of diplexer. Additionally, dc bias network used to control switch is decoupled from RF input and output lines. Voltage transients in external circuits are thus minimized.

Noncontact vibration measurements using magnetoresistive sensing elements

NASA Astrophysics Data System (ADS)

Tomassini, R.; Rossi, G.

2016-06-01

Contactless instrumentations is more and more used in turbomachinery testing thanks to the non-intrusive character and the possibility to monitor all the components of the machine at the same time. Performances of blade tip timing (BTT) measurement systems, used for noncontact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor characteristics and processing methods. The sensors used for BTT generate pulses, used for precise measurements of turbine blades time of arrival. Nowadays proximity sensors used in this application are based on optical, capacitive, eddy current and microwave measuring principle. Pressure sensors has been also tried. This paper summarizes the results achieved using a novel instrumentation based on the magnetoresistive sensing elements. The characterization of the novel probe has been already published. The measurement system was validated in test benches and in a real jet-engine comparing different sensor technologies. The whole instrumentation was improved. The work presented in this paper focuses on the current developments. In particular, attention is given to the data processing software and new sensor configurations.

Tunneling magnetoresistance from a symmetry filtering effect

PubMed Central

Butler, William H

2008-01-01

This paper provides a brief overview of the young, but rapidly growing field of spintronics. Its primary objective is to explain how as electrons tunnel through simple insulators such as MgO, wavefunctions of certain symmetries are preferentially transmitted. This symmetry filtering property can be converted into a spin-filtering property if the insulator is joined epitaxially to a ferromagnetic electrode with the same two-dimensional symmetry parallel to the interface. A second requirement of the ferromagnetic electrodes is that a wavefunction with the preferred symmetry exists in one of the two spin channels but not in the other. These requirements are satisfied for electrons traveling perpendicular to the interface for Fe–MgO–Fe tunnel barriers. This leads to a large change in the resistance when the magnetic moment of one of the electrodes is rotated relative to those of the other electrode. This large tunneling magnetoresistance effect is being used as the read sensor in hard drives and may form the basis for a new type of magnetic memory. PMID:27877932

All-optical switching of silicon disk resonator based on photothermal effect in metal-insulator-metal absorber.

PubMed

Shi, Yuechun; Chen, Xi; Lou, Fei; Chen, Yiting; Yan, Min; Wosinski, Lech; Qiu, Min

2014-08-01

Efficient narrowband light absorption by a metal-insulator-metal (MIM) structure can lead to high-speed light-to-heat conversion at a micro- or nanoscale. Such a MIM structure can serve as a heater for achieving all-optical light control based on the thermo-optical (TO) effect. Here we experimentally fabricated and characterized a novel all-optical switch based on a silicon microdisk integrated with a MIM light absorber. Direct integration of the absorber on top of the microdisk reduces the thermal capacity of the whole device, leading to high-speed TO switching of the microdisk resonance. The measurement result exhibits a rise time of 2.0 μs and a fall time of 2.6 μs with switching power as low as 0.5 mW; the product of switching power and response time is only about 1.3  mW·μs. Since no auxiliary elements are required for the heater, the switch is structurally compact, and its fabrication is rather easy. The device potentially can be deployed for new kinds of all-optical applications.

Out of plane magnetoresistance of organic superconductors; κ-(BEDT)2 salts

NASA Astrophysics Data System (ADS)

Maki, Kazumi; Won, Hye Kyung

1998-03-01

It is well documented that the out of plane manetoresistances of κ-(BEDT)_2X with X=Cu(NCS)2 and Cu[N(Cu)_2]Br exhibit a sharp peak before disappearance in the superconducting state (H. Ito et al. J. of Superconductivity 7), 667 (1994). ^, (M. V. Kartsovnik, (private communication).). We analyze this feature in terms of the superconducting fluctuation. Indeed, generalizing the formula for the clean limit (V. V. Dorin et al. Phys. Rev. B 48), 12951 (1993)., the superconducting fluctuation accounts for both the field and the temperature dependence of the magnetoresistance. In this description, d-wave nature of the superconducting order parameter in organic superconductors is crucial.

Magnetoresistance due to domain walls in an epitaxial microfabricated Fe wire

NASA Astrophysics Data System (ADS)

Rüdiger, U.; Yu, J.; Kent, A. D.; Parkin, S. S. P.

1998-08-01

The domain wall (DW) contribution to magnetoresistance has been investigated using an epitaxial microfabricated bcc (110) Fe wires of 2 μm linewidth. A strong in-plane uniaxial component to the magnetic anisotropy perpendicular to the wire axis causes a regular stripe domain pattern with closure domains. The stripe domain width in zero-applied magnetic field is strongly affected by the magnetic history and can be continuously varied from 0.45 to 1.8 μm. This enables a measurement of the resistivity as a function of DW density in a single wire. Clear evidence is presented that the resistivity is reduced in the presence of DWs at low temperatures.

Effects of interface electric field on the magnetoresistance in spin devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanamoto, T., E-mail: tetsufumi.tanamoto@toshiba.co.jp; Ishikawa, M.; Inokuchi, T.

2014-04-28

An extension of the standard spin diffusion theory is presented by using a quantum diffusion theory via a density-gradient (DG) term that is suitable for describing interface quantum tunneling phenomena. The magnetoresistance (MR) ratio is greatly modified by the DG term through an interface electric field. We have also carried out spin injection and detection measurements using four-terminal Si devices. The local measurement shows that the MR ratio changes depending on the current direction. We show that the change of the MR ratio depending on the current direction comes from the DG term regarding the asymmetry of the two interfacemore » electronic structures.« less

Hydrodynamic theory of thermoelectric transport and negative magnetoresistance in Weyl semimetals

PubMed Central

Lucas, Andrew; Davison, Richard A.

2016-01-01

We present a theory of thermoelectric transport in weakly disordered Weyl semimetals where the electron–electron scattering time is faster than the electron–impurity scattering time. Our hydrodynamic theory consists of relativistic fluids at each Weyl node, coupled together by perturbatively small intervalley scattering, and long-range Coulomb interactions. The conductivity matrix of our theory is Onsager reciprocal and positive semidefinite. In addition to the usual axial anomaly, we account for the effects of a distinct, axial–gravitational anomaly expected to be present in Weyl semimetals. Negative thermal magnetoresistance is a sharp, experimentally accessible signature of this axial–gravitational anomaly, even beyond the hydrodynamic limit. PMID:27512042

Control of Nanofilament Structure and Observations of Quantum Point Contact Behavior in Ni/NiO Nanowire Junctions

NASA Astrophysics Data System (ADS)

Oliver, Sean; Fairfield, Jessamyn; Lee, Sunghun; Bellew, Allen; Stone, Iris; Ruppalt, Laura; Boland, John; Vora, Patrick

Resistive switching is ideal for use in non-volatile memory where information is stored in a metallic or insulating state. Nanowire junctions formed at the intersection of two Ni/NiO core/shell nanowires have emerged as a leading candidate structure where resistive switching occurs due to the formation and destruction of conducting filaments. However, significant knowledge gaps remain regarding the conduction mechanisms as measurements are typically only performed at room temperature. Here, we combine temperature-dependent current-voltage (IV) measurements from 15 - 300 K with magnetoresistance studies and achieve new insight into the nature of the conducting filaments. We identify a novel semiconducting state that behaves as a quantum point contact and find evidence for a possible electric-field driven phase transition. The insulating state exhibits unexpectedly complex IV characteristics that highlight the disordered nature of the ruptured filament while we find clear signs of anisotropic magnetoresistance in the metallic state. Our results expose previously unobserved behaviors in nanowire resistive switching devices and pave the way for future applications where both electrical and magnetic switching can be achieved in a single device. This work was supported by ONR Grant N-00014-15-1-2357.

H∞ control for switched fuzzy systems via dynamic output feedback: Hybrid and switched approaches

NASA Astrophysics Data System (ADS)

Xiang, Weiming; Xiao, Jian; Iqbal, Muhammad Naveed

2013-06-01

Fuzzy T-S model has been proven to be a practical and effective way to deal with the analysis and synthesis problems for complex nonlinear systems. As for switched nonlinear system, describing its subsystems as fuzzy T-S models, namely switched fuzzy system, naturally is an alternative method to conventional control approaches. In this paper, the H∞ control problem for a class of switched fuzzy systems is addressed. Hybrid and switched design approaches are proposed with different availability of switching signal information at switching instant. The hybrid control strategy includes two parts: fuzzy controllers for subsystems and state updating controller at switching instant, and the switched control strategy contains the controllers for subsystems. It is demonstrated that the conservativeness is reduced by introducing the state updating behavior but its cost is an online prediction of switching signal. Numerical examples are given to illustrate the effectiveness of proposed approaches and compare the conservativeness of two approaches.

Low-temperature specific heat of the quasi-two-dimensional charge-density wave compound KMo6O17

NASA Astrophysics Data System (ADS)

Wang, Junfeng; Xiong, Rui; Yin, Di; Li, Changzhen; Tang, Zheng; Wang, Ququan; Shi, Jing; Wang, Yue; Wen, Haihu

2006-05-01

Low temperature specific heat (Cp) of quasi-two-dimensional charge-density wave (CDW) compound KMo6O17 has been studied by a relaxation method from 2to48K under zero and 12T magnetic fields. The results show that no specific heat anomaly is found at 16K under both zero and 12T magnetic fields, although an anomaly is clearly observed in the resistivity and magnetoresistance measurements. From the data between 2 and 4K , the density of states at Fermi level is estimated as 0.2eV-1permolecule and the Debye temperature is extracted to be 418K . A bump appearing in Cp/T3 is found between 4 and 48K centered around 12.5-15K , indicating that the phason excitations contribute to the total specific heat similarly as in quasi-one-dimensional CDW conductors. Using a modified Debye model, a pinning frequency of 0.73THz for KMo6O17 is estimated from the phason contribution.

Task Uncertainty Can Account for Mixing and Switch Costs in Task-Switching

PubMed Central

Rennie, Jaime L.

2015-01-01

Cognitive control is required in situations that involve uncertainty or change, such as when resolving conflict, selecting responses and switching tasks. Recently, it has been suggested that cognitive control can be conceptualised as a mechanism which prioritises goal-relevant information to deal with uncertainty. This hypothesis has been supported using a paradigm that requires conflict resolution. In this study, we examine whether cognitive control during task switching is also consistent with this notion. We used information theory to quantify the level of uncertainty in different trial types during a cued task-switching paradigm. We test the hypothesis that differences in uncertainty between task repeat and task switch trials can account for typical behavioural effects in task-switching. Increasing uncertainty was associated with less efficient performance (i.e., slower and less accurate), particularly on switch trials and trials that afford little opportunity for advance preparation. Interestingly, both mixing and switch costs were associated with a common episodic control process. These results support the notion that cognitive control may be conceptualised as an information processor that serves to resolve uncertainty in the environment. PMID:26107646

Investigating a method for reducing residual switch costs in cued task switching.

PubMed

Schneider, Darryl W

2016-07-01

Residual switch costs in cued task switching are performance decrements that occur despite a long cue-target interval (CTI) to prepare for a task switch. Verbruggen, Liefooghe, Vandierendonck, and Demanet (Journal of Experimental Psychology: Learning, Memory, and Cognition, 33; 342-356, 2007) showed that briefly presenting the cue during the CTI and leaving it absent after target onset yielded smaller residual switch costs than those obtained when the cue was available for the full CTI and remained present after target onset. The potential effects of cue availability during the CTI (full or partial) and cue status after target onset (present or absent) on residual switch costs were investigated in the present study. In Experiments 1 and 2, cue status was manipulated while holding cue availability constant. In Experiments 3 and 4, cue status and cue availability were manipulated factorially. Residual switch costs were obtained, but they were not modulated consistently by cue status or cue availability across experiments. In Experiment 5, a direct replication of one of Verbruggen and colleagues' experiments yielded divergent results. Implications for understanding task switching are discussed.

Adaptive synchronized switch damping on an inductor: a self-tuning switching law

NASA Astrophysics Data System (ADS)

Kelley, Christopher R.; Kauffman, Jeffrey L.

2017-03-01

Synchronized switch damping (SSD) techniques exploit low-power switching between passive circuits connected to piezoelectric material to reduce structural vibration. In the classical implementation of SSD, the piezoelectric material remains in an open circuit for the majority of the vibration cycle and switches briefly to a shunt circuit at every displacement extremum. Recent research indicates that this switch timing is only optimal for excitation exactly at resonance and points to more general optimal switch criteria based on the phase of the displacement and the system parameters. This work proposes a self-tuning approach that implements the more general optimal switch timing for synchronized switch damping on an inductor (SSDI) without needing any knowledge of the system parameters. The law involves a gradient-based search optimization that is robust to noise and uncertainties in the system. Testing of a physical implementation confirms this law successfully adapts to the frequency and parameters of the system. Overall, the adaptive SSDI controller provides better off-resonance steady-state vibration reduction than classical SSDI while matching performance at resonance.

Controllability of multi-agent systems with periodically switching topologies and switching leaders

NASA Astrophysics Data System (ADS)

Tian, Lingling; Zhao, Bin; Wang, Long

2018-05-01

This paper considers controllability of multi-agent systems with periodically switching topologies and switching leaders. The concept of m-periodic controllability is proposed, and a criterion for m-periodic controllability is established. The effect of the duration of subsystems on controllability is analysed by utilising a property of analytic functions. In addition, the influence of switching periods on controllability is investigated, and an algorithm is proposed to search for the fewest periods to ensure controllability. A necessary condition for m-periodic controllability is obtained from the perspective of eigenvectors of the subsystems' Laplacian matrices. For a system with switching leaders, it is proved that switching-leader controllability is equivalent to multiple-leader controllability. Furthermore, both the switching order and the tenure of agents being leaders have no effect on the controllability. Some examples are provided to illustrate the theoretical results.