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Sample records for room temperature magnetic

  1. Electric control of magnetism at room temperature.

    PubMed

    Wang, Liaoyu; Wang, Dunhui; Cao, Qingqi; Zheng, Yuanxia; Xuan, Haicheng; Gao, Jinlong; Du, Youwei

    2012-01-01

    In the single-phase multiferroics, the coupling between electric polarization (P) and magnetization (M) would enable the magnetoelectric (ME) effect, namely M induced and modulated by E, and conversely P by H. Especially, the manipulation of magnetization by an electric field at room-temperature is of great importance in technological applications, such as new information storage technology, four-state logic device, magnetoelectric sensors, low-power magnetoelectric device and so on. Furthermore, it can reduce power consumption and realize device miniaturization, which is very useful for the practical applications. In an M-type hexaferrite SrCo(2)Ti(2)Fe(8)O(19), large magnetization and electric polarization were observed simultaneously at room-temperature. Moreover, large effect of electric field-controlled magnetization was observed even without magnetic bias field. These results illuminate a promising potential to apply in magnetoelectric devices at room temperature and imply plentiful physics behind them.

  2. Electric control of magnetism at room temperature

    PubMed Central

    Wang, Liaoyu; Wang, Dunhui; Cao, Qingqi; Zheng, Yuanxia; Xuan, Haicheng; Gao, Jinlong; Du, Youwei

    2012-01-01

    In the single-phase multiferroics, the coupling between electric polarization (P) and magnetization (M) would enable the magnetoelectric (ME) effect, namely M induced and modulated by E, and conversely P by H. Especially, the manipulation of magnetization by an electric field at room-temperature is of great importance in technological applications, such as new information storage technology, four-state logic device, magnetoelectric sensors, low-power magnetoelectric device and so on. Furthermore, it can reduce power consumption and realize device miniaturization, which is very useful for the practical applications. In an M-type hexaferrite SrCo2Ti2Fe8O19, large magnetization and electric polarization were observed simultaneously at room-temperature. Moreover, large effect of electric field-controlled magnetization was observed even without magnetic bias field. These results illuminate a promising potential to apply in magnetoelectric devices at room temperature and imply plentiful physics behind them. PMID:22355737

  3. Magnetic heat pumping near room temperature

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1976-01-01

    It is shown that magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point at or near operating temperature and an appropriate regenerative thermodynamic cycle. Measurements are performed which show that gadolinium is a resonable working material and it is found that the application of a 7-T magnetic field to gadolinium at the Curie point (293 K) causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 K under adiabatic conditions. A regeneration technique can be used to lift the load of the lattice and electronic heat capacities off the magnetic system in order to span a reasonable temperature difference and to pump as much entropy per cycle as possible

  4. Magnetic heat pumping near room temperature

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1976-01-01

    It is shown that magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point at or near operating temperature and an appropriate regenerative thermodynamic cycle. Measurements are performed which show that gadolinium is a resonable working material and it is found that the application of a 7-T magnetic field to gadolinium at the Curie point (293 K) causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 K under adiabatic conditions. A regeneration technique can be used to lift the load of the lattice and electronic heat capacities off the magnetic system in order to span a reasonable temperature difference and to pump as much entropy per cycle as possible

  5. Sub-room Temperature Magnetic Refrigerator

    NASA Astrophysics Data System (ADS)

    Zimm, Carl

    1998-03-01

    Magnetic refrigeration has been predicted to be an efficient cooling technology because of the highly reversible nature of the magnetocaloric effect for some materials. However, cooling power and efficiency of past devices has been limited because of the difficulties in exchanging heat with the solid magnetic refrigerant. Astronautics in a joint project with Ames DOE Laboratory has constructed a regenerative magnetic refrigerator that provides cooling near room temperature using gadolinium as a refrigerant and water as a heat transfer fluid. Using a superconducting magnet at 5 T, cooling of 500 watts was obtained at coefficients of performance of 5 or more watts of cooling per watt of work input. Cooling of 150 watts was obtained using a 1.5 T field, which can be obtained from permanent magnet sources. The main losses in the present device are magnet AC losses and seal friction, although limits on temperature span may also be imposed by magnetic material properties. We have identified design, magnet, and magnetic material improvements that should reduce such losses, allowing the construction of devices whose efficiency well exceeds that obtainable from conventional technology. The fluid used in such magnetic refrigerators presents no toxicity, ozone depletion or global warming hazard. This talk will include test results and projections of the capabilities and limitations of the technology.

  6. Room temperature organic magnets derived from sp3 functionalized graphene

    NASA Astrophysics Data System (ADS)

    Tuček, Jiří; Holá, Kateřina; Bourlinos, Athanasios B.; Błoński, Piotr; Bakandritsos, Aristides; Ugolotti, Juri; Dubecký, Matúš; Karlický, František; Ranc, Václav; Čépe, Klára; Otyepka, Michal; Zbořil, Radek

    2017-02-01

    Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp2-conjugated diradical motifs embedded in an sp3 matrix and superexchange interactions via -OH functionalization.

  7. Room temperature organic magnets derived from sp(3) functionalized graphene.

    PubMed

    Tuček, Jiří; Holá, Kateřina; Bourlinos, Athanasios B; Błoński, Piotr; Bakandritsos, Aristides; Ugolotti, Juri; Dubecký, Matúš; Karlický, František; Ranc, Václav; Čépe, Klára; Otyepka, Michal; Zbořil, Radek

    2017-02-20

    Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp(3) coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp(2)-conjugated diradical motifs embedded in an sp(3) matrix and superexchange interactions via -OH functionalization.

  8. Room temperature organic magnets derived from sp3 functionalized graphene

    PubMed Central

    Tuček, Jiří; Holá, Kateřina; Bourlinos, Athanasios B.; Błoński, Piotr; Bakandritsos, Aristides; Ugolotti, Juri; Dubecký, Matúš; Karlický, František; Ranc, Václav; Čépe, Klára; Otyepka, Michal; Zbořil, Radek

    2017-01-01

    Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp2-conjugated diradical motifs embedded in an sp3 matrix and superexchange interactions via –OH functionalization. PMID:28216636

  9. Magnetic properties of stainless steels at room and cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Oxley, Paul; Goodell, Jennifer; Molt, Robert

    2009-07-01

    The magnetic properties of ten types of ferritic and martensitic stainless steels have been measured at room temperature and at 77 K. The steel samples studied were in the annealed state as received from the manufacturer. Our room temperature measurements indicate significantly harder magnetic properties than those quoted in the ASM International Handbook, which studied fully annealed stainless steel samples. Despite having harder magnetic properties than fully annealed steels some of the as-received steels still display soft magnetic properties adequate for magnetic applications. The carbon content of the steels was found to affect the permeability and coercive force, with lower-carbon steels displaying significantly higher permeability and lower coercive force. The decrease in coercive force with reduced carbon content is attributed to fewer carbide inclusions which inhibit domain wall motion. Cooling to 77 K resulted in harder magnetic properties. Averaged over the ten steels tested the maximum permeability decreased by 8%, the coercive force increased by 14%, and the residual and saturation flux densities increased by 4% and 3%, respectively. The change in coercive force when cooled is comparable to the theoretical prediction for iron, based on a model of domain wall motion inhibited by inclusions. The modest changes of the magnetic properties indicate that the stainless steels can still be used in magnetic applications at very low temperatures.

  10. Magnetic refrigeration-towards room-temperature applications

    NASA Astrophysics Data System (ADS)

    Brück, E.; Tegus, O.; Li, X. W.; de Boer, F. R.; Buschow, K. H. J.

    2003-04-01

    Modern society relies very much on readily available cooling. Magnetic refrigeration based on the magneto-caloric effect (MCE) has become a promising competitive technology for the conventional gas-compression/expansion technique in use today. Recently, there have been two breakthroughs in magnetic-refrigeration research: one is that American scientists demonstrated the world's first room-temperature, permanent-magnet, magnetic refrigerator; the other one is that we discovered a new class of magnetic refrigerant materials for room-temperature applications. The new materials are manganese-iron-phosphorus-arsenic (MnFe(P,As)) compounds. This new material has important advantages over existing magnetic coolants: it exhibits a huge MCE, which is larger than that of Gd metal; and its operating temperature can be tuned from about 150 to about 335 K by adjusting the P/As ratio. Here we report on further improvement of the materials by increasing the Mn content. The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field. Addition of Mn reduces the thermal hysteresis, which is intrinsic to the first-order transition. This implies that already moderate applied magnetic fields of below 2 T may suffice.

  11. Room Temperature Characterization of a Magnetic Bearing for Turbomachinery

    NASA Technical Reports Server (NTRS)

    Montague, Gerald; Jansen, Mark; Provenza, Andrew; Jansen, Ralph; Ebihara, Ben; Palazzolo, Alan

    2002-01-01

    Open loop, experimental force and power measurements of a three-axis, radial, heteropolar magnetic bearing at room temperature for rotor speeds up to 20,000 RPM are presented in this paper. The bearing, NASA Glenn Research Center's and Texas A&M's third generation high temperature magnetic bearing, was designed to operate in a 1000 F (540 C) environment and was primarily optimized for maximum load capacity. The experimentally measured force produced by one C-core of this bearing was 630 lb. (2.8 kN) at 16 A, while a load of 650 lbs (2.89 kN) was predicted at 16 A using 1D circuit analysis. The maximum predicted radial load for one of the three axes is 1,440 lbs (6.41 kN) at room temperature. The maximum measured load of an axis was 1050 lbs. (4.73 kN). Results of test under rotating conditions showed that rotor speed has a negligible effect on the bearing's load capacity. A single C-core required approximately 70 W of power to generate 300 lb (1.34 kN) of magnetic force. The room temperature data presented was measured after three thermal cycles up to 1000 F (540 C), totaling six hours at elevated temperatures.

  12. Tuning magnetic spirals beyond room temperature with chemical disorder

    NASA Astrophysics Data System (ADS)

    Morin, Mickaël; Canévet, Emmanuel; Raynaud, Adrien; Bartkowiak, Marek; Sheptyakov, Denis; Ban, Voraksmy; Kenzelmann, Michel; Pomjakushina, Ekaterina; Conder, Kazimierz; Medarde, Marisa

    2016-12-01

    In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature.

  13. Tuning magnetic spirals beyond room temperature with chemical disorder

    PubMed Central

    Morin, Mickaël; Canévet, Emmanuel; Raynaud, Adrien; Bartkowiak, Marek; Sheptyakov, Denis; Ban, Voraksmy; Kenzelmann, Michel; Pomjakushina, Ekaterina; Conder, Kazimierz; Medarde, Marisa

    2016-01-01

    In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature. PMID:27982127

  14. Tuning magnetic spirals beyond room temperature with chemical disorder.

    PubMed

    Morin, Mickaël; Canévet, Emmanuel; Raynaud, Adrien; Bartkowiak, Marek; Sheptyakov, Denis; Ban, Voraksmy; Kenzelmann, Michel; Pomjakushina, Ekaterina; Conder, Kazimierz; Medarde, Marisa

    2016-12-16

    In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature.

  15. Enhanced magnetic Purcell effect in room-temperature masers

    PubMed Central

    Breeze, Jonathan; Tan, Ke-Jie; Richards, Benjamin; Sathian, Juna; Oxborrow, Mark; Alford, Neil McN

    2015-01-01

    Recently, the world’s first room-temperature maser was demonstrated. The maser consisted of a sapphire ring housing a crystal of pentacene-doped p-terphenyl, pumped by a pulsed rhodamine-dye laser. Stimulated emission of microwaves was aided by the high quality factor and small magnetic mode volume of the maser cavity yet the peak optical pumping power was 1.4 kW. Here we report dramatic miniaturization and 2 orders of magnitude reduction in optical pumping power for a room-temperature maser by coupling a strontium titanate resonator with the spin-polarized population inversion provided by triplet states in an optically excited pentacene-doped p-terphenyl crystal. We observe maser emission in a thimble-sized resonator using a xenon flash lamp as an optical pump source with peak optical power of 70 W. This is a significant step towards the goal of continuous maser operation. PMID:25698634

  16. Magnetic Sensors with Picotesla Magnetic Field Sensitivity at Room Temperature

    DTIC Science & Technology

    2008-06-01

    concern MTJ - magnetic tunneling junction pT - the picotesla (10-12 tesla) SQUID - Superconducting quantum interference device MFC - magnetic flux...magnetic noise by annealing of MTJ in high magnetic field and a hydrogen environment, and (3) increasing signal by the use of external low-noise...indicate the reference layer pinning direction. Fig. 2 The structure of the magnetic tunnel junctions ( MTJs ) is 5 nm Ta / 5 nm

  17. Room-temperature Magnetic Ordering in Functionalized Graphene

    PubMed Central

    Hong, Jeongmin; Bekyarova, Elena; Liang, Ping; de Heer, Walt A.; Haddon, Robert C.; Khizroev, Sakhrat

    2012-01-01

    Despite theoretical predictions, the question of room-temperature magnetic order in graphene must be conclusively resolved before graphene can fully achieve its potential as a spintronic medium. Through scanning tunneling microscopy (STM) and point I-V measurements, the current study reveals that unlike pristine samples, graphene nanostructures, when functionalized with aryl radicals, can sustain magnetic order. STM images show 1-D and 2-D periodic super-lattices originating from the functionalization of a single sub-lattice of the bipartite graphene structure. Field-dependent super-lattices in 3-nm wide “zigzag” nanoribbons indicate local moments with parallel and anti-parallel ordering along and across the edges, respectively. Anti-parallel ordering is observed in 2-D segments with sizes of over 20 nm. The field dependence of STM images and point I-V curves indicates a spin polarized local density of states (LDOS), an out-of-plane anisotropy field of less than 10 Oe, and an exchange coupling field of 100 Oe at room temperature. PMID:22953045

  18. Magnetic antiskyrmions above room temperature in tetragonal Heusler materials

    NASA Astrophysics Data System (ADS)

    Nayak, Ajaya K.; Kumar, Vivek; Ma, Tianping; Werner, Peter; Pippel, Eckhard; Sahoo, Roshnee; Damay, Franoise; Rößler, Ulrich K.; Felser, Claudia; Parkin, Stuart S. P.

    2017-08-01

    . Direct imaging by Lorentz transmission electron microscopy shows field-stabilized antiskyrmion lattices and isolated antiskyrmions from 100 kelvin to well beyond room temperature, and zero-field metastable antiskyrmions at low temperatures. These results enlarge the family of magnetic skyrmions and pave the way to the engineering of complex bespoke designed skyrmionic structures.

  19. SQUID Microscopy: Magnetic Images of Room Temperature Samples

    NASA Astrophysics Data System (ADS)

    Grossman, Helene

    1998-10-01

    We use a microscope based on a high-Tc Superconducting Quantum Interference Device (SQUID) to study room temperature samples. The SQUID, which measures magnetic flux, is mounted on a sapphire rod and maintained at 77 K inside a vacuum chamber. A sample, separated from the vacuum chamber by a window, is placed above the SQUID, and the entire microscope is enclosed within a magnetic shield. The sample can be scanned over the SQUID to obtain a magnetic image. We have used the microscope to study magnetotactic bacteria, which have a permanent magnetic dipole moment of about 1.5 x 10-16 Am^2. The bacteria, suspended in an aqueous medium, are placed in a cell which is separated from the vacuum chamber by a 3 micron thick SiN membrane. The sample is brought as close as 15 micron to the SQUID, and the magnetic flux noise from the motion of the bacteria is measured. Data from non-motile cells, which undergo Brownian motion, give us information about the distribution of lengths of the bacteria. By applying a magnetic field, we can determine the average dipole moment. Noise measurements of the live bacteria give us the rates of flagellar rotation and body-roll, as well as the amplitudes of the vibrational and precessional motions. Another application of the microscope is non-destructive evaluation of steel. We have investigated the effects of both thermal and mechanical stresses on the remnant magnetization of steel. A third application of the microscope is in studying the properties of ferromagnetic nanocrystals of Co and Fe_3O_4.

  20. Room-temperature magnetic properties of oxy- and carbonmonoxyhemoglobin

    PubMed Central

    Cerdonio, M.; Congiu-Castellano, A.; Calabrese, L.; Morante, S.; Pispisa, B.; Vitale, S.

    1978-01-01

    The magnetic susceptibility and the density of human oxy-(HbO2) and carbonmonoxyhemoglobin (HbCO) solutions of various concentrations have been measured at room temperature, with pure water used as a calibrant. Solutions of unstripped and stripped HbO2 at pH 7.2 in unbuffered water solvent were always found to be less diamagnetic than pure water, whereas solutions of HbCO in identical conditions were always found to be more diamagnetic than pure water. After correcting for concentration-dependent density changes and assuming the HbCO samples to be fully diamagnetic, the paramagnetic reduction of the diamagnetic susceptibility of HbO2 corresponds to a molar susceptibility per heme (χMheme) of 2460 ± 600 × 10-6 cgs/mol. PMID:16592578

  1. Detection of printed magnetic inks using a room-temperature scanning magnetic microscope

    NASA Astrophysics Data System (ADS)

    Howells, G.; Prance, R. J.; Clark, T. D.; Prance, H.

    1997-07-01

    We describe a room-temperature scanning magnetic microscope of novel design which can be used at a spatial resolution of a few microns to image information stored on magnetic inks used in a variety of printing processes. We suggest that this imaging technique could find general application in the inspection of currency notes and credit cards.

  2. Room-Temperature Spin-Mediated Coupling in Hybrid Magnetic, Organic, and Oxide Structures and Devices

    DTIC Science & Technology

    2015-12-07

    SECURITY CLASSIFICATION OF: During the full period of this project we have (1) demonstrated room -temperature effects of the remanent magnetization...the effects of traps and unpaired spins on room -temperature magnetoresistance, (4) developed a theory for spin diffusion in hopping transport due to...Jun-2014 Approved for Public Release; Distribution Unlimited Final Report: Room -Temperature Spin-Mediated Coupling in Hybrid Magnetic, Organic, and

  3. Magnetic switching of ferroelectric domains at room temperature in multiferroic PZTFT

    PubMed Central

    Evans, D.M.; Schilling, A.; Kumar, Ashok; Sanchez, D.; Ortega, N.; Arredondo, M.; Katiyar, R.S.; Gregg, J.M.; Scott, J.F.

    2013-01-01

    Single-phase magnetoelectric multiferroics are ferroelectric materials that display some form of magnetism. In addition, magnetic and ferroelectric order parameters are not independent of one another. Thus, the application of either an electric or magnetic field simultaneously alters both the electrical dipole configuration and the magnetic state of the material. The technological possibilities that could arise from magnetoelectric multiferroics are considerable and a range of functional devices has already been envisioned. Realising these devices, however, requires coupling effects to be significant and to occur at room temperature. Although such characteristics can be created in piezoelectric-magnetostrictive composites, to date they have only been weakly evident in single-phase multiferroics. Here in a newly discovered room temperature multiferroic, we demonstrate significant room temperature coupling by monitoring changes in ferroelectric domain patterns induced by magnetic fields. An order of magnitude estimate of the effective coupling coefficient suggests a value of ~1 × 10−7 sm−1. PMID:23443562

  4. Current-Induced Nucleation and Annihilation of Magnetic Skyrmions at Room Temperature in a Chiral Magnet.

    PubMed

    Yu, Xiuzhen; Morikawa, Daisuke; Tokunaga, Yusuke; Kubota, Masashi; Kurumaji, Takashi; Oike, Hiroshi; Nakamura, Masao; Kagawa, Fumitaka; Taguchi, Yasujiro; Arima, Taka-Hisa; Kawasaki, Masashi; Tokura, Yoshinori

    2017-06-01

    A magnetic skyrmion is a nanometer-scale magnetic vortex carrying an integer topological charge. Skyrmions show a promise for potential application in low-power-consumption and high-density memory devices. To promote their use in applications, it is attempted to control the existence of skyrmions using low electric currents at room temperature (RT). This study presents real-space observations for the current-induced formation and annihilation of a skyrmion lattice (SkL) as well as isolated skyrmions in a microdevice composed of a thin chiral magnet Co8 Zn9 Mn3 with a Curie temperature, TC ≈ 325 K, above RT. It is found that the critical current for the manipulation of Bloch-type skyrmions is on the order of 10(8) A m(-2) , approximately three orders of magnitude lower than that needed for the creation and drive of ferromagnetic (FM) domain walls in thin FM films. The in situ real-space imaging also demonstrates the dynamical topological transition from a helical or conical structure to a SkL induced by the flow of DC current, thus paving the way for the electrical control of magnetic skyrmions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Low and room temperature magnetic features of the traffic related urban airborne PM

    NASA Astrophysics Data System (ADS)

    Winkler, A.; Sagnotti, L.

    2012-04-01

    We used magnetic measurements and analyses - such as hysteresis loops and FORCs both at room temperature and at 10K, isothermal remanent magnetization (IRM) vs temperature curves (from 10K to 293K) and IRM vs time decay curves - to characterize the magnetic properties of the traffic related airborne particulate matter (PM) in Rome. This study was specifically addressed to the identification of the ultrafine superparamagnetic (SP) particles, which are particularly sensitive to thermal relaxation effects, and on the eventual detection of low temperature phase transitions which may affect various magnetic minerals. We compared the magnetic properties at 10K and at room temperature of Quercus ilex leaves, disk brakes, diesel and gasoline exhaust pipes powders collected from vehicles circulating in Rome. The magnetic properties of the investigated powders significantly change upon cooling, and no clear phase transition occurs, suggesting that the thermal dependence is mainly triggered by the widespread presence of ultrafine SP particles. The contribution of the SP fraction to the total remanence of traffic related PM samples was quantified at room temperature measuring the decay of a IRM 100 s after the application of a saturation magnetic field. This same method has been also tested at 10K to investigate the temperature dependence of the observed time decay.

  6. Transition-metal-based magnetic refrigerants for room-temperature applications.

    PubMed

    Tegus, O; Brück, E; Buschow, K H J; de Boer, F R

    2002-01-10

    Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.

  7. Multiferroic Nanopatterned Hybrid Material with Room-Temperature Magnetic Switching of the Electric Polarization.

    PubMed

    Cai, Ronggang; Antohe, Vlad-Andrei; Hu, Zhijun; Nysten, Bernard; Piraux, Luc; Jonas, Alain M

    2017-02-01

    A nanopatterned hybrid layer is designed, wherein the electric polarization can be flipped at room temperature by a magnetic field aided by an electrical field. This is achieved by embedding ferromagnetic nanopillars in a continuous organic ferroelectric layer, and amplifying the magnetostriction-generated stress gradients by scaling down the supracrystalline cell of the material.

  8. A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

    PubMed Central

    Liu, Wenjian; Zhang, Hongxia; Shi, Jin-an; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

    2016-01-01

    Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III–V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p–n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V−1 s−1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities. PMID:27929059

  9. A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

    NASA Astrophysics Data System (ADS)

    Liu, Wenjian; Zhang, Hongxia; Shi, Jin-An; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

    2016-12-01

    Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V-1 s-1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

  10. Optical multichannel room temperature magnetic field imaging system for clinical application

    PubMed Central

    Lembke, G.; Erné, S. N.; Nowak, H.; Menhorn, B.; Pasquarelli, A.

    2014-01-01

    Optically pumped magnetometers (OPM) are a very promising alternative to the superconducting quantum interference devices (SQUIDs) used nowadays for Magnetic Field Imaging (MFI), a new method of diagnosis based on the measurement of the magnetic field of the human heart. We present a first measurement combining a multichannel OPM-sensor with an existing MFI-system resulting in a fully functional room temperature MFI-system. PMID:24688820

  11. Room-temperature magnetic gradiometry with fiber-coupled nitrogen-vacancy centers in diamond.

    PubMed

    Blakley, S M; Fedotov, I V; Kilin, S Ya; Zheltikov, A M

    2015-08-15

    Differential optical detection of a magnetic resonance induced in nitrogen-vacancy (NV) centers in diamond is shown to enable a high-spatial-resolution room-temperature magnetic-field gradiometry on a fiber platform. An ultracompact design of this fiber-based solid-state magnetic gradiometer is achieved by integrating an NV-diamond magnetic sensor with a two-fiber opto-microwave interface, which couples NV centers to microwave and optical fields, used to resonantly drive and interrogate the spin of NV centers.

  12. Thirty Years of Near Room Temperature Magnetic Cooling: Where we are Today and Future Prospects

    SciTech Connect

    K.A. Gschneidner, Jr; V.K. Pecharsky'

    2008-05-01

    The seminal study by Brown in 1976 showed that it was possible to use the magnetocaloric effect to produce a substantial cooling effect near room temperature. About 15 years later Green et al. built a device which actually cooled a load other than the magnetocaloric material itself and the heat exchange fluid. The major breakthrough, however, occurred in 1997 when the Ames Laboratory/Astronautics proof-of-principle refrigerator showed that magnetic refrigeration was competitive with conventional gas compression cooling. Since then, over 25 magnetic cooling units have been built and tested throughout the world. The current status of near room temperature magnetic cooling is reviewed, including a discussion of the major problems facing commercialization and potential solutions thereof. The future outlook for this revolutionary technology is discussed.

  13. Advances in methods to obtain and characterise room temperature magnetic ZnO

    SciTech Connect

    Lorite, I.; Kumar, P.; Esquinazi, P.; Straube, B.; Villafuerte, M.; Ohldag, H.; Rodríguez Torres, C. E.; Perez de Heluani, S.; Antonov, V. N.; Bekenov, L. V.; Ernst, A.; and others

    2015-02-23

    We report the existence of magnetic order at room temperature in Li-doped ZnO microwires after low energy H{sup +} implantation. The microwires with diameters between 0.3 and 10 μm were prepared by a carbothermal process. We combine spectroscopy techniques to elucidate the influence of the electronic structure and local environment of Zn, O, and Li and their vacancies on the magnetic response. Ferromagnetism at room temperature is obtained only after implanting H{sup +} in Li-doped ZnO. The overall results indicate that low-energy proton implantation is an effective method to produce the necessary amount of stable Zn vacancies near the Li ions to trigger the magnetic order.

  14. Magnetic microscopy based on high-Tc SQUIDs for room temperature samples

    NASA Astrophysics Data System (ADS)

    Wang, H. W.; Kong, X. Y.; Ren, Y. F.; Yu, H. W.; Ding, H. S.; Zhao, S. P.; Chen, G. H.; Zhang, L. H.; Zhou, Y. L.; Yang, Q. S.

    2003-11-01

    The SQUID microscope is the most suitable instrument for imaging magnetic fields above sample surfaces if one is mainly interested in field sensitivity. In this paper, both the magnetic moment sensitivity and spatial resolution of the SQUID microscope are analysed with a simple point moment model. The result shows that the ratio of SQUID sensor size to sensor-sample distance effectively influences the sensitivity and spatial resolution. In comparison with some experimental results of magnetic images for room temperature samples from our high-Tc SQUID microscope in an unshielded environment, a brief discussion for further improvement is presented.

  15. Detection of pico-Tesla magnetic fields using magneto-electric sensors at room temperature

    SciTech Connect

    Zhai Junyi; Xing Zengping; Dong Shuxiang; Li Jiefang; Viehland, D.

    2006-02-06

    The measurement of low-frequency (10{sup -2}-10{sup 3} Hz) minute magnetic field variations (10{sup -12} Tesla) at room temperature in a passive mode of operation would be critically enabling for deployable neurological signal interfacing and magnetic anomaly detection applications. However, there is presently no magnetic field sensor capable of meeting all of these requirements. Here, we present new bimorph and push-pull magneto-electric laminate composites, which incorporate a charge compensation mechanism (or bridge) that dramatically enhances noise rejection, enabling achievement of such requirements.

  16. Designing switchable polarization and magnetization at room temperature in an oxide

    NASA Astrophysics Data System (ADS)

    Mandal, P.; Pitcher, M. J.; Alaria, J.; Niu, H.; Borisov, P.; Stamenov, P.; Claridge, J. B.; Rosseinsky, M. J.

    2015-09-01

    Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d0 or s2 cations, whereas ferromagnetic order requires open-shell dn configurations with unpaired electrons. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure precludes bulk magnetization and linear magnetoelectric coupling. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization with glassy magnetization, although it lacks long-range magnetic order. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold

  17. Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films

    SciTech Connect

    Kozioł-Rachwał, A.; Ślęzak, T.; Przewoźnik, J.; Skowroński, W.; Stobiecki, T.; Wilgocka-Ślęzak, D.; Qin, Q. H.; Dijken, S. van; Korecki, J.

    2013-12-14

    We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4 Å to 14 Å. For the iron deposited at 140 K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c} = (9 ± 1) Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

  18. The Magnetocaloric Effect and Magnetic Refrigeration Near Room Temperature: Materials and Models

    NASA Astrophysics Data System (ADS)

    Franco, V.; Blázquez, J. S.; Ingale, B.; Conde, A.

    2012-08-01

    In the past 20 years, there has been a surge in research on the magnetocaloric response of materials, due mainly to the possibility of applying this effect for magnetic refrigeration close to room temperature. This review is devoted to the main families of materials suitable for this application and to the procedures proposed to predict their response. Apart from the possible technological applications, we also discuss the use of magnetocaloric characterization to gain fundamental insight into the nature of the underlying phase transition.

  19. A new class of chiral materials hosting magnetic skyrmions beyond room temperature

    PubMed Central

    Tokunaga, Y.; Yu, X. Z.; White, J. S.; Rønnow, H. M.; Morikawa, D.; Taguchi, Y.; Tokura, Y.

    2015-01-01

    Skyrmions, topologically protected vortex-like nanometric spin textures in magnets, have been attracting increasing attention for emergent electromagnetic responses and possible technological applications for spintronics. In particular, metallic magnets with chiral and cubic/tetragonal crystal structure may have high potential to host skyrmions that can be driven by low electrical current excitation. However, experimental observations of skyrmions have been limited to below room temperature for the metallic chiral magnets, specifically for the MnSi-type B20 compounds. Towards technological applications, transcending this limitation is crucial. Here we demonstrate the formation of skyrmions with unique spin helicity both at and above room temperature in a family of cubic chiral magnets: β-Mn-type Co-Zn-Mn alloys with a different chiral space group from that of B20 compounds. Lorentz transmission electron microscopy, magnetization and small-angle neutron scattering measurements unambiguously reveal formation of a skyrmion crystal under application of a magnetic field in both thin-plate and bulk forms. PMID:26134284

  20. A new class of chiral materials hosting magnetic skyrmions beyond room temperature.

    PubMed

    Tokunaga, Y; Yu, X Z; White, J S; Rønnow, H M; Morikawa, D; Taguchi, Y; Tokura, Y

    2015-07-02

    Skyrmions, topologically protected vortex-like nanometric spin textures in magnets, have been attracting increasing attention for emergent electromagnetic responses and possible technological applications for spintronics. In particular, metallic magnets with chiral and cubic/tetragonal crystal structure may have high potential to host skyrmions that can be driven by low electrical current excitation. However, experimental observations of skyrmions have been limited to below room temperature for the metallic chiral magnets, specifically for the MnSi-type B20 compounds. Towards technological applications, transcending this limitation is crucial. Here we demonstrate the formation of skyrmions with unique spin helicity both at and above room temperature in a family of cubic chiral magnets: β-Mn-type Co-Zn-Mn alloys with a different chiral space group from that of B20 compounds. Lorentz transmission electron microscopy, magnetization and small-angle neutron scattering measurements unambiguously reveal formation of a skyrmion crystal under application of a magnetic field in both thin-plate and bulk forms.

  1. Performance predictions for a room temperature, Ericsson cycle, magnetic heat pump

    NASA Astrophysics Data System (ADS)

    Purnell, J. G.

    1982-05-01

    The performance potential of a room temperature magnetic heat pump utilizing Gadolinium and operating on an Ericsson Cycle was investigated at magnetic flux densities of 2 and 7-Tesla which represent the upper limits of conventional and superconducting electromagnetics, respectively. At a coefficient of performance of 5, a 7-Tesla system would provide a cooling capacity of at best 1200 BTU per hour per pound of Gadolinium while a 2-Tesla system would operate at approximately 130 BTU per hour per pound of Gadolinium. Magnetic circuit efficiency was not determined but must be high (95-percent or better) in order for the magnetic heat pump performance to compete with conventional cooling systems. It is unlikely the magnetic heat pump investigated could approach the performance and compactness of the conventional cooling systems unless field strengths much greater than 7-Tesla are possible.

  2. Magnetism in transition metal-substituted germanane: A search for room temperature spintronic devices

    SciTech Connect

    Sun, Minglei; Tang, Wencheng; Ren, Qingqiang; Zhao, Yiming; Wang, Sake; Yu, Jin

    2016-04-14

    Using first-principles calculations, we investigated the geometric structure, binding energy, and magnetic behavior of monolayer germanane substitutional doped with transition metals. Our work demonstrates that germanane with single vacancy forms strong bonds with all studied impurity atoms. Magnetism is observed for Ti, V, Cr, Mn, Fe, and Ni doping. Doping of Ti and Mn atoms results in half-metallic properties, while doping of Cr results in dilute magnetic semiconducting state. We estimate a Curie temperature of about 735 K for Mn-substituted system in the mean-field approximation at impurity concentration 5.56%. Furthermore, when increasing the impurity concentration to 12.5%, Curie temperatures of Ti and Mn-substituted systems are 290 and 1120 K, respectively. Our studies demonstrate the potential of Ti and Mn-substituted germanane for room temperature spintronic devices.

  3. Metastable gamma-Iron Nickel Nanostructures for Magnetic Refrigeration Near Room Temperature

    NASA Astrophysics Data System (ADS)

    Ucar, Huseyin

    The observation of a giant magnetocaloric effect in Gd5Ge 1.9Si2Fe0.1 has stimulated the magnetocaloric research in the last two decades. However, the high price of Gd and its proclivity to corrosion of these compounds have prevented their commercial use. To reduce raw materials cost, transition metal-based alloys are investigated to replace rare earth-based materials. Environmental considerations, substitution for scarce and strategic elements, and cost considerations all speak to potential contributions of these new materials to sustainability. Efforts in improving the refrigeration capacity (RC) of refrigerants mainly rely on broadening the magnetic entropy change. One promising technique is to couple two phases of magnetic materials with desirable properties. Second is the investigation of nanoparticle synthesis routes, with ball milling being the most widely used one. The motivation for the nanoparticles synthesis is rooted in their inherent tendency to have distributed exchange coupling, which will broaden the magnetic entropy curve. As proven with the cost analysis, the focus is believed to shift from improving the RC of refrigerants toward finding the most economically advantageous magnetic refrigerant with the highest performance. Mechanically alloyed Fe70Ni30 and Fe72Ni 28 alloys were characterized in terms of their structural and magnetic properties. Previous studies showed that single phase FCC gamma-FeNi alloys with 26-30 at. % Ni have Curie temperatures, TC, near room temperature. Having TC near room temperatures along with large magnetization makes gamma-FeNi alloys attractive for room temperature magnetocaloric cooling technologies. To obtain a single gamma-phase, particles were solution annealed in the gamma-phase field and water quenched. The preferential oxidation of Fe during ball milling was used as a means to tune the TC of the alloy. Refrigeration capacities, RCFWHM, of the Fe70Ni30 and the Fe72Ni28 alloys were calculated to be 470 J/kg and

  4. Non-magnetic organic/inorganic spin injector at room temperature

    SciTech Connect

    Mathew, Shinto P.; Mondal, Prakash Chandra; Naaman, Ron; Moshe, Hagay; Mastai, Yitzhak

    2014-12-15

    Spin injection into solid-state devices is commonly performed by use of ferromagnetic metal electrodes. Here, we present a spin injector design without permanent magnet; rather, the spin selectivity is determined by a chiral tunneling barrier. The chiral tunneling barrier is composed of an ultrathin Al{sub 2}O{sub 3} layer that is deposited on top of a chiral self-assembled monolayer (SAM), which consists of cysteine or oligopeptide molecules. The experimentally observed magnetoresistance can be up to 20% at room temperature, and it displays an uncommon asymmetric curve as a function of the applied magnetic field. These findings show that the spin injector transmits only one spin orientation, independent of external magnetic field. The sign of the magnetoresistance depends on the handedness of the molecules in the SAM, which act as a spin filter, and the magnitude of the magnetoresistance depends only weakly on temperature.

  5. Room Temperature Magnetically Ordered Polar Corundum GaFeO3 Displaying Magnetoelectric Coupling.

    PubMed

    Niu, Hongjun; Pitcher, Michael J; Corkett, Alex J; Ling, Sanliang; Mandal, Pranab; Zanella, Marco; Dawson, Karl; Stamenov, Plamen; Batuk, Dmitry; Abakumov, Artem M; Bull, Craig L; Smith, Ronald I; Murray, Claire A; Day, Sarah J; Slater, Ben; Cora, Furio; Claridge, John B; Rosseinsky, Matthew J

    2017-02-01

    The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d(5) cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A(3+)/Fe(3+) cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.

  6. Hidden spin-order-induced room-temperature ferroelectricity in a peculiar conical magnetic structure

    NASA Astrophysics Data System (ADS)

    Shen, Shi-Peng; Liu, Xin-Zhi; Chai, Yi-Sheng; Studer, Andrew; Rule, Kirrily; Zhai, Kun; Yan, Li-Qin; Shang, Da-Shan; Klose, Frank; Liu, Yun-Tao; Chen, Dong-Feng; Sun, Young

    2017-03-01

    A novel mechanism of spin-induced ferroelectricity is unraveled in the alternating longitudinal conical (ALC) magnetic structure. Because the noncollinear ALC structure possesses a c -axis component with collinear ↑-↑-↓-↓ spin order, spin-driven ferroelectricity along the c axis due to the exchange striction mechanism is predicted. Our experiments verify this prediction in the Y-type hexaferrite B a0.3S r1.7C o2F e11Al O22 , where ferroelectricity along the c axis is observed up to room temperature. Neutron diffraction data clearly reveal the ALC phase and its evolution with magnetic fields. The c -axis electric polarization can be well modulated by applying either a b -plane or c -axis magnetic fields, even at 305 K. This kind of spin-induced ferroelectricity associated with the ALC magnetic structure provides a new resource of type II multiferroics.

  7. FAST TRACK COMMUNICATION: Magnetic control of large room-temperature polarization

    NASA Astrophysics Data System (ADS)

    Kumar, Ashok; Sharma, G. L.; Katiyar, R. S.; Pirc, R.; Blinc, R.; Scott, J. F.

    2009-09-01

    Numerous authors have referred to room-temperature magnetic switching of large electric polarizations as 'the Holy Grail' of magnetoelectricity. We report this long-sought effect, obtained using a new physical process of coupling between magnetic and ferroelectric nanoregions. Solid state solutions of PFW [Pb(Fe2/3W1/3)O3] and PZT [Pb(Zr0.53Ti0.47)O3] exhibit some bi-relaxor qualities, with both ferroelectric relaxor characteristics and magnetic relaxor phenomena. Near 20% PFW the ferroelectric relaxor state is nearly unstable at room temperature against long-range ferroelectricity. Here we report magnetic switching between the normal ferroelectric state and a magnetically quenched ferroelectric state that resembles relaxors. This gives both a new room-temperature, single-phase, multiferroic magnetoelectric, (PbFe0.67W0.33O3)0.2(PbZr0.53Ti0.47O3)0.8 ('0.2PFW/0.8PZT'), with polarization, loss (<1%), and resistivity (typically 108-109 Ω cm) equal to or superior to those of BiFeO3, and also a new and very large magnetoelectric effect: switching not from +Pr to -Pr with applied H, but from Pr to zero with applied H of less than a tesla. This switching of the polarization occurs not because of a conventional magnetically induced phase transition, but because of dynamic effects: increasing H lengthens the relaxation time by 500 × from<200 ns to>100 µs, and it strongly couples the polarization relaxation and spin relaxations. The diverging polarization relaxation time accurately fits a modified Vogel-Fulcher equation in which the freezing temperature Tf is replaced by a critical freezing field Hf that is 0.92 ± 0.07 T. This field dependence and the critical field Hc are derived analytically from the spherical random bond random field model with no adjustable parameters and an E2H2 coupling. This device permits three-state logic (+Pr,0,-Pr) and a condenser with >5000% magnetic field change in its capacitance; for H = 0 the coercive voltage is 1.4 V across 300 nm for

  8. Electric-field manipulation of magnetization rotation and tunneling magnetoresistance of magnetic tunnel junctions at room temperature

    NASA Astrophysics Data System (ADS)

    Chen, Aitian; Li, Peisen; Li, Dalai; Zhao, Yonggang; Zhang, Sen; Yang, Lifeng; Liu, Yan; Zhu, Meihong; Zhang, Huiyun; Han, Xiufeng

    2015-03-01

    Recent studies on the electric-field control of tunneling magnetoresistance (TMR) have attracted considerable attention for low power consumption. So far two methods have been demonstrated for electric-field control of TMR. One method uses ferroelectric or multiferroic barriers, which is limited by low temperature. The other is nanoscale thin film magnetic tunnel junction (MTJ), but the assistance of a magnetic field is required. Therefore, electric-field control of TMR at room temperature without a magnetic field is highly desired. One promising way is to employ strain-mediated coupling in ferromagnetic/piezoelectric structure. Though MTJs/piezoelectric has been predicted by theory, experiment work is still lacking. We deposited CoFeB/AlOx/CoFeB on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric single crystal. Under external electric fields, PMN-PT will produce a piezostrain due to piezoelectric effect, and the piezostrain transfers to ferromagnetic film to change the magnetic anisotropy. We demonstrate a reversible, continuous magnetization rotation and manipulation of TMR at room temperature by electric fields without the assistance of a magnetic field.

  9. Tunable room-temperature magnetic skyrmions in Ir/Fe/Co/Pt multilayers

    NASA Astrophysics Data System (ADS)

    Soumyanarayanan, Anjan; Raju, M.; Gonzalez Oyarce, A. L.; Tan, Anthony K. C.; Im, Mi-Young; Petrović, A. P.; Ho, Pin; Khoo, K. H.; Tran, M.; Gan, C. K.; Ernult, F.; Panagopoulos, C.

    2017-09-01

    Magnetic skyrmions are nanoscale topological spin structures offering great promise for next-generation information storage technologies. The recent discovery of sub-100-nm room-temperature (RT) skyrmions in several multilayer films has triggered vigorous efforts to modulate their physical properties for their use in devices. Here we present a tunable RT skyrmion platform based on multilayer stacks of Ir/Fe/Co/Pt, which we study using X-ray microscopy, magnetic force microscopy and Hall transport techniques. By varying the ferromagnetic layer composition, we can tailor the magnetic interactions governing skyrmion properties, thereby tuning their thermodynamic stability parameter by an order of magnitude. The skyrmions exhibit a smooth crossover between isolated (metastable) and disordered lattice configurations across samples, while their size and density can be tuned by factors of two and ten, respectively. We thus establish a platform for investigating functional sub-50-nm RT skyrmions, pointing towards the development of skyrmion-based memory devices.

  10. Electric field control of nonvolatile four-state magnetization at room temperature

    NASA Astrophysics Data System (ADS)

    Chun, Sae Hwan; Chai, Yi Sheng; Jeon, Byung-Gu; Kim, Hyung Joon; Oh, Yoon Seok; Kim, Ingyu; Kim, Hanbit; Jeon, Byeong Jo; Haam, So Young; Park, Ju-Young; Lee, Suk Ho; Kim, Kee Hoon; Chung, Jae-Ho; Park, Jae-Hoon

    2012-02-01

    We find the realization of large converse magnetoelectric (ME) effects at room temperature in a multiferroic hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62 μB/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be described by an effective free energy with a distinct set of ME coefficients. *These authors contributed equally to this work.

  11. Electric Field Control of Nonvolatile Four-State Magnetization at Room Temperature

    NASA Astrophysics Data System (ADS)

    Chun, Sae Hwan; Chai, Yi Sheng; Jeon, Byung-Gu; Kim, Hyung Joon; Oh, Yoon Seok; Kim, Ingyu; Kim, Hanbit; Jeon, Byeong Jo; Haam, So Young; Park, Ju-Young; Lee, Suk Ho; Chung, Jae-Ho; Park, Jae-Hoon; Kim, Kee Hoon

    2012-04-01

    We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200ps/m. The modulation of magnetization then reaches up to 0.62μB/f.u. in an electric field of 1.14MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.

  12. Magnetic refrigeration at room temperature - from magnetocaloric materials to a prototype

    NASA Astrophysics Data System (ADS)

    Theil Kuhn, L.; Pryds, N.; Bahl, C. R. H.; Smith, A.

    2011-07-01

    Based on the magnetocaloric effect, magnetic refrigeration at room temperature has for the past decade been a promising, environmentally friendly new energy technology predicted to have a significantly higher efficiency than the present conventional methods. However, so far only a few prototype refrigeration machines have been presented worldwide and there are still many scientific and technological challenges to be overcome. We report here on the MagCool project, which spans all the way from basic materials studies to the construction of a prototype. Emphasis has been on ceramic magnetocaloric materials, their shaping and graded composition for technological use. Modelling the performance of a permanent magnet with optimum use of the flux and relatively low weight, and designing and constructing a prototype continuous magnetic refrigeration device have also been major tasks in the project.

  13. Electric field control of nonvolatile four-state magnetization at room temperature.

    PubMed

    Chun, Sae Hwan; Chai, Yi Sheng; Jeon, Byung-Gu; Kim, Hyung Joon; Oh, Yoon Seok; Kim, Ingyu; Kim, Hanbit; Jeon, Byeong Jo; Haam, So Young; Park, Ju-Young; Lee, Suk Ho; Chung, Jae-Ho; Park, Jae-Hoon; Kim, Kee Hoon

    2012-04-27

    We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.

  14. Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

    NASA Astrophysics Data System (ADS)

    Lee, Juwon; Subramaniam, Nagarajan Ganapathi; Agnieszka Kowalik, Iwona; Nisar, Jawad; Lee, Jaechul; Kwon, Younghae; Lee, Jaechoon; Kang, Taewon; Peng, Xiangyang; Arvanitis, Dimitri; Ahuja, Rajeev

    2015-11-01

    The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1-x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1-x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1-x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states.

  15. Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

    PubMed Central

    Lee, Juwon; Subramaniam, Nagarajan Ganapathi; Agnieszka Kowalik, Iwona; Nisar, Jawad; Lee, Jaechul; Kwon, Younghae; Lee, Jaechoon; Kang, Taewon; Peng, Xiangyang; Arvanitis, Dimitri; Ahuja, Rajeev

    2015-01-01

    The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1−x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1−x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1−x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states. PMID:26592564

  16. Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature

    PubMed Central

    Phillips, L. C.; Cherifi, R. O.; Ivanovskaya, V.; Zobelli, A.; Infante, I. C.; Jacquet, E.; Guiblin, N.; Ünal, A. A.; Kronast, F.; Dkhil, B.; Barthélémy, A.; Bibes, M.; Valencia, S.

    2015-01-01

    Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide into domains with different orientations of their order parameter. Coupling between different ferroic systems creates new functionalities, for instance the electrical control of macroscopic magnetic properties including magnetization and coercive field. Here we show that ferroelastic domains can be used to control both magnetic order and magnetization direction at the nanoscale with a voltage. We use element-specific X-ray imaging to map the magnetic domains as a function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3. Exploiting the nanoscale phase-separation of FeRh, we locally interconvert between ferromagnetic and antiferromagnetic states with a small electric field just above room temperature. Imaging and ab initio calculations show the antiferromagnetic phase of FeRh is favoured by compressive strain on c-oriented BaTiO3 domains, and the resultant magnetoelectric coupling is larger and more reversible than previously reported from macroscopic measurements. Our results emphasize the importance of nanoscale ferroic domain structure and the promise of first-order transition materials to achieve enhanced coupling in artificial multiferroics. PMID:25969926

  17. Magnetic refrigeration: an eco-friendly technology for the refrigeration at room temperature

    NASA Astrophysics Data System (ADS)

    Aprea, C.; Greco, A.; Maiorino, A.; Masselli, C.

    2015-11-01

    Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). In the case of ferromagnetic materials MCE is a warming as the magnetic moments of the atom are aligned by the application of a magnetic field, and the corresponding cooling upon removal of the magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle) where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. In this paper, attention is directed towards the near room-temperature range. We compare the energetic performance of a commercial R134a refrigeration plant to that of a magnetic refrigerator working with an AMR cycle. Attention is devoted to the evaluation of the environmental impact in terms of a greenhouse effect. The comparison is performed in term of TEWI index (Total Equivalent Warming Impact) that takes into account both direct and indirect contributions to global warming. In this paper the AMR cycle works with different magnetic refrigerants: pure gadolinium, second order phase magnetic transition (Pr0.45Sr0.35MnO3) and first order phase magnetic transition alloys (Gd5Si2Ge2, LaFe11.384Mn0.356Si1.26H1.52, LaFe1105Co0.94Si110 and MnFeP0.45As0.55). The comparison, carried out by means of a mathematical model, clearly shows that GdSi2Ge2 and LaFe11.384Mn0.356Si1.26H1.52 has a TEWI index always lower than that of a vapor compression plant. Furthermore, the TEWI of the AMR

  18. Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons.

    PubMed

    Magda, Gábor Zsolt; Jin, Xiaozhan; Hagymási, Imre; Vancsó, Péter; Osváth, Zoltán; Nemes-Incze, Péter; Hwang, Chanyong; Biró, László P; Tapasztó, Levente

    2014-10-30

    The possibility that non-magnetic materials such as carbon could exhibit a novel type of s-p electron magnetism has attracted much attention over the years, not least because such magnetic order is predicted to be stable at high temperatures. It has been demonstrated that atomic-scale structural defects of graphene can host unpaired spins, but it remains unclear under what conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that, in contrast to random defect distributions, atomic-scale engineering of graphene edges with specific crystallographic orientation--comprising edge atoms from only one sub-lattice of the bipartite graphene lattice--can give rise to a robust magnetic order. We use a nanofabrication technique based on scanning tunnelling microscopy to define graphene nanoribbons with nanometre precision and well-defined crystallographic edge orientations. Although so-called 'armchair' ribbons display quantum confinement gaps, ribbons with the 'zigzag' edge structure that are narrower than 7 nanometres exhibit an electronic bandgap of about 0.2-0.3 electronvolts, which can be identified as a signature of interaction-induced spin ordering along their edges. Moreover, upon increasing the ribbon width, a semiconductor-to-metal transition is revealed, indicating the switching of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hopes of graphene-based spintronic devices operating under ambient conditions.

  19. Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Magda, Gábor Zsolt; Jin, Xiaozhan; Hagymási, Imre; Vancsó, Péter; Osváth, Zoltán; Nemes-Incze, Péter; Hwang, Chanyong; Biró, László P.; Tapasztó, Levente

    2014-10-01

    The possibility that non-magnetic materials such as carbon could exhibit a novel type of s-p electron magnetism has attracted much attention over the years, not least because such magnetic order is predicted to be stable at high temperatures. It has been demonstrated that atomic-scale structural defects of graphene can host unpaired spins, but it remains unclear under what conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that, in contrast to random defect distributions, atomic-scale engineering of graphene edges with specific crystallographic orientation--comprising edge atoms from only one sub-lattice of the bipartite graphene lattice--can give rise to a robust magnetic order. We use a nanofabrication technique based on scanning tunnelling microscopy to define graphene nanoribbons with nanometre precision and well-defined crystallographic edge orientations. Although so-called `armchair' ribbons display quantum confinement gaps, ribbons with the `zigzag' edge structure that are narrower than 7 nanometres exhibit an electronic bandgap of about 0.2-0.3 electronvolts, which can be identified as a signature of interaction-induced spin ordering along their edges. Moreover, upon increasing the ribbon width, a semiconductor-to-metal transition is revealed, indicating the switching of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hopes of graphene-based spintronic devices operating under ambient conditions.

  20. The Other Iron Minerals: Magnetic Properties at Room and Low Temperature

    NASA Astrophysics Data System (ADS)

    Hirt, A. M.

    2003-12-01

    The magnetic properties of iron oxides and iron sulfides that are carriers of paleomagnetic fields have been well studied. Less is known about the magnetic properties of iron phases that are not common carriers of remanent magnetization, or those that are paramagnetic at room temperature. They include iron (oxy-)hydroxides, iron carbonates, iron phosphates and iron sulfates. Many of these phases are not easily identifiable with traditional X ray diffraction or spectroscopic methods, due to their poor crystallinity or low concentration in soils and sediments. Since they are important indicators of the environmental conditions under which they form and are preserved, alternative methods for their identification are of interest. AC and DC magnetometry are very sensitive in detecting low concentrations of magnetic phases. A short overview will be given on the magnetic properties of less-considered iron phases, including the iron (oxy-)hydroxides goethite, lepidocrocite and ferrihydrite; siderite, an iron carbonate; the iron phosphate vivianite; and iron sulfate, schwertmannite. Factors that influence the magnetic properties, such as cation substitution, grain size and particle interaction will be discussed, as well as the environmental conditions under which they form and are preserved.

  1. Magnetic ordering in relation to the room-temperature magnetoelectric effect of Sr3Co2Fe24O41.

    PubMed

    Soda, Minoru; Ishikura, Taishi; Nakamura, Hiroyuki; Wakabayashi, Yusuke; Kimura, Tsuyoshi

    2011-02-25

    The origin of a room-temperature magnetoelectric (ME) effect has been examined by means of neutron powder diffraction measurements for a Z-type hexaferrite Sr(3)Co(2)Fe(24)O(41). The temperature and magnetic-field dependence of the electric polarization P and several magnetic Bragg reflections show that a commensurate magnetic order with a (0,0,1) propagation vector has an intimate connection with the ME effect. The room-temperature ME effect can be understood in terms of the appearance of P which is induced by a transverse conical spin structure through the inverse Dzyaloshinskii-Moriya mechanism in analogy with Y-type hexaferrites.

  2. Extremely strong room-temperature transient photocurrent-detected magnetic resonance in organic devices

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Liu, Rui; Cai, Min; Shinar, Ruth; Shinar, Joseph

    2012-12-01

    An extremely strong room-temperature photocurrent- (PC- or IPC-) detected magnetic resonance (PCDMR) that elucidates transport and trapping phenomena in organic devices, in particular solar cells, is described. When monitoring the transient PCDMR in indium tin oxide (ITO)/poly(2-methoxy-5-(2'-ethyl)-hexoxy-1,4-phenylenevinylene) (MEH-PPV)/Al devices, where the MEH-PPV film was baked overnight at 100 °C in O2, it is observed that |ΔIPC/IPC| peaks at values ≫1, where ΔIPC is the change in IPC induced by magnetic resonance conditions. Importantly, ΔIPC and IPC are of different origin. The mechanism most likely responsible for this effect is the spin-dependent formation of spinless bipolarons adjacent to negatively charged deep traps, apparently induced in particular by oxygen centers, to form trions.

  3. Characterization of ZnO:Co particles prepared by hydrothermal method for room temperature magnetism

    NASA Astrophysics Data System (ADS)

    Peng, Yingzi; Huo, Dexuan; He, Haiping; Li, Yuan; Li, Lingwei; Wang, Huawen; Qian, Zhenghong

    2012-03-01

    ZnO based diluted magnetic semiconductor particles (ZnO:Co) have been grown using a hydrothermal method with good crystallinity. The atomic percentage of Co presented in the specimen is about 0.01. Based on the x-ray diffraction and high-resolution transition electron, Co is found to be incorporated into ZnO lattice without evidence of obvious Co precipitates. However, from photoluminescence (PL) spectra in the range of 1.94 -3.45 eV, a strong broad emission centered around 600 nm (2.07 eV) in the visible range as well as a relatively weak peak at 2.81 eV are observed, indicating the presence of Co impurities. Moreover, intrinsic emissions such as DOX suggest that at least some Co have been doped into ZnO lattice, substituting for Zn2+ ions. The PL results further confirm the substitution of Zn2+ ions by Co, which leads to the changes of the electronic band structures. Magnetism could be realized at room temperature for the ZnO:Co nanoparticles under our experimental conditions although with low coercivity. The field-cooled and zero-field-cooled curves can be explained as a result of competition between the ferromagnetic and the antiferromagnetic ordering in the ZnO:Co nanoparticles. Combining the results from PL and magnetism characterization, it is reasonable to think that both doped Co in the ZnO lattice and Co impurities contribute to magnetism in ZnO:Co nanoparticles at room temperature.

  4. Spatial resolution of SQUID magnetometers and comparison with low noise room temperature magnetic sensors

    NASA Astrophysics Data System (ADS)

    Dolabdjian, C.; Qasimi, A.; Bloyet, D.; Mosser, V.

    2002-03-01

    Any magnetic sensor placed in a spatially inhomogeneous magnetic field delivers a signal proportional the mean field value taken over an effective area or volume which depends on the type of sensor considered. In the case of the field produced by a magnetic dipole and detected by a square or circular planar sensor, the overall measured spatial resolution ideally depends on the ratio of the mean dipole-sensor distance z0 to the square root of the effective sensor area AE. For Z 0/ A E≪1 , the spatial resolution is limited by the size of the sensor, whereas for z 0/ A E≫1 the dipole-sensor distance is the predominant factor. To compare various low noise magnetic sensors operating either at low temperature or at room temperature, we have measured their sensitivities and spatial responses to the field produced by a magnetic moment having the form of a tiny circular current loop. The sensors could be moved in all directions with respect to the current loop. The transfer of each sensor to the magnetic dipole field was compared to their response in a homogeneous field so as to deduce their effective area and compare this area to that deduced from independent spatial resolution measurements. We report the experimental results given by four types of sensors namely a dc-SQUID, a Hall effect sensor, a giant magneto-resistive sensor and a flux-gate sensor and discuss them by mean of a “figure of merit” criterion combining their spatial resolution and their sensitivity.

  5. Room-temperature magnetic microscopy using a high-T(c) SQUID

    NASA Astrophysics Data System (ADS)

    Chatraphorn, Sojiphong

    I fabricated high-Tc YBa2Cu3O7-X dc SQUIDs and incorporated them into a liquid-nitrogen cooled scanning SQUID microscope for imaging magnetic fields from objects at room-temperature. The SQUID is maintained at 78 K in vacuum, and separated from air by a 25 mum thick sapphire window. The SQUID is operated using a direct bias current and a 100 kHz flux-locked loop feedback electronics. The frequency response is flat below 10 kHz and the bandwidth is approximately 20 kHz. The maximum slew rate of my system is about 30 x 104 (phi0/S from about 100 Hz to 20 kHz. The system has 1/f flux noise at 10 Hz of about 200 muphi0/Hzl/2 (˜345 pT/Hz1/2) and the level of white noise is about 20 muphi0/Hzl/2 (˜34.5 pT/Hz1/2). I used the microscope in conjunction with a magnetic inverse technique to image currents flow in commercial integrated circuits and multi-chip modules for fault isolation of electrical short circuits. I also developed Fourier space filters for improved magnetic imaging of current paths in circuits. With this technique, I was able to obtain a highest spatial resolution s of about 32 mum, with the SQUID-sample separation z ≈ 150 mum, i.e. z/s ˜5, about 5 times better than the standard near-field limit. I also describe a mathematical model that relates the noise and spatial resolution found in current density images obtained from a magnetic inverse technique. I find that the spatial resolutions is related logarithmically to the signal-to-noise ratio, and the data sampling interval, but linearly to the SQUID-sample separation z. I also used the microscope to image static magnetic fields from ferromagnetic colossal magnetoresistive thin-films and developed an algorithm to convert magnetic field images to magnetic pole density images. This enhances the spatial resolution in the raw magnetic field images. I also show how to obtain magnetization of the CMR thin-film using a magnetic line charge model. I also developed an x-SQUID, which images magnetic fields

  6. Electric control of magnon frequencies and magnetic moment of bismuth ferrite thin films at room temperature

    PubMed Central

    Kumar, Ashok; Scott, J. F.; Katiyar, R. S.

    2011-01-01

    Here, we report the tuning of room-temperature magnon frequencies from 473 GHz to 402 GHz (14%) and magnetic moment from 4 to 18 emu∕cm3 at 100 Oe under the application of external electric fields (E) across interdigital electrodes in BiFeO3 (BFO) thin films. A decrease in magnon frequencies and increase in phonon frequencies were observed with Magnon and phonon Raman intensities are asymmetric with polarity, decreasing with positive E (+E) and increasing with negative E (−E) where polarity is with respect to in-plane polarization P. The magnetoelectric coupling (α) is proved to be linear and a rather isotropic α = 8.5 × 10−12 sm−1. PMID:21901050

  7. Electric control of magnon frequencies and magnetic moment of bismuth ferrite thin films at room temperature.

    PubMed

    Kumar, Ashok; Scott, J F; Katiyar, R S

    2011-08-08

    Here, we report the tuning of room-temperature magnon frequencies from 473 GHz to 402 GHz (14%) and magnetic moment from 4 to 18 emu∕cm(3) at 100 Oe under the application of external electric fields (E) across interdigital electrodes in BiFeO(3) (BFO) thin films. A decrease in magnon frequencies and increase in phonon frequencies were observed with Magnon and phonon Raman intensities are asymmetric with polarity, decreasing with positive E (+E) and increasing with negative E (-E) where polarity is with respect to in-plane polarization P. The magnetoelectric coupling (α) is proved to be linear and a rather isotropic α = 8.5 × 10(-12) sm(-1).

  8. Oxygen-vacancy-induced room-temperature magnetization in lamellar V2O5 thin films

    NASA Astrophysics Data System (ADS)

    Cezar, A. B.; Graff, I. L.; Varalda, J.; Schreiner, W. H.; Mosca, D. H.

    2014-10-01

    In this work, we study the local atomic and electronic structures as well as oxygen-vacancy-induced magnetic properties of electrodeposited V2O5 films. Unlike stoichiometric V2O5, which is a diamagnetic lamellar semiconductor, our oxygen-defective V2O5 films are ferromagnetic at room-temperature and their saturation magnetization decreases with air exposure time. X-ray absorption spectroscopy was used to monitor the aging effect on these films, revealing that freshly-made samples exhibit only local crystalline order, whereas the aged ones undoubtedly show an enhancement of crystallinity and coordination symmetry. The mean number of oxygen atoms around V tends to increase, indicating a decrease of oxygen vacancies with time. Concurrently with the decrease of oxygen vacancies, a loss of saturation magnetization is also observed. Hence, it can be concluded that the ferromagnetism of the V2O5 films originates from a vacancy-induced mechanism, confirming the universality of this class of ferromagnetism.

  9. One-thousand-fold enhancement of high field liquid nuclear magnetic resonance signals at room temperature.

    PubMed

    Liu, Guoquan; Levien, Marcel; Karschin, Niels; Parigi, Giacomo; Luchinat, Claudio; Bennati, Marina

    2017-07-01

    Nuclear magnetic resonance (NMR) is a fundamental spectroscopic technique for the study of biological systems and materials, molecular imaging and the analysis of small molecules. It detects interactions at very low energies and is thus non-invasive and applicable to a variety of targets, including animals and humans. However, one of its most severe limitations is its low sensitivity, which stems from the small interaction energies involved. Here, we report that dynamic nuclear polarization in liquid solution and at room temperature can enhance the NMR signal of (13)C nuclei by up to three orders of magnitude at magnetic fields of ∼3 T. The experiment can be repeated within seconds for signal averaging, without interfering with the sample magnetic homogeneity. The method is therefore compatible with the conditions required for high-resolution NMR. Enhancement of (13)C signals on various organic compounds opens up new perspectives for dynamic nuclear polarization as a general tool to increase the sensitivity of liquid NMR.

  10. One-thousand-fold enhancement of high field liquid nuclear magnetic resonance signals at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Guoquan; Levien, Marcel; Karschin, Niels; Parigi, Giacomo; Luchinat, Claudio; Bennati, Marina

    2017-07-01

    Nuclear magnetic resonance (NMR) is a fundamental spectroscopic technique for the study of biological systems and materials, molecular imaging and the analysis of small molecules. It detects interactions at very low energies and is thus non-invasive and applicable to a variety of targets, including animals and humans. However, one of its most severe limitations is its low sensitivity, which stems from the small interaction energies involved. Here, we report that dynamic nuclear polarization in liquid solution and at room temperature can enhance the NMR signal of 13C nuclei by up to three orders of magnitude at magnetic fields of ∼3 T. The experiment can be repeated within seconds for signal averaging, without interfering with the sample magnetic homogeneity. The method is therefore compatible with the conditions required for high-resolution NMR. Enhancement of 13C signals on various organic compounds opens up new perspectives for dynamic nuclear polarization as a general tool to increase the sensitivity of liquid NMR.

  11. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Woo, Seonghoon; Litzius, Kai; Krüger, Benjamin; Im, Mi-Young; Caretta, Lucas; Richter, Kornel; Mann, Maxwell; Krone, Andrea; Reeve, Robert M.; Weigand, Markus; Agrawal, Parnika; Lemesh, Ivan; Mawass, Mohamad-Assaad; Fischer, Peter; Kläui, Mathias; Beach, Geoffrey S. D.

    2016-05-01

    Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s-1 as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures.

  12. Extraordinary high dielectric constant, electrical and magnetic properties of ferrite nanoparticles at room temperature

    NASA Astrophysics Data System (ADS)

    Batoo, Khalid Mujasam; Mir, Feroz Ahmed; Abd El-sadek, M.-S.; Shahabuddin, Md.; Ahmed, Niyaz

    2013-11-01

    Nanoparticles of spinel ferrites of basic composition Ni1- x Co x Fe2O4 (0.0 ≤ x ≤ 0.05) were synthesized through modified co-precipitation method, and were characterized for structural, transport electrical and magnetic properties using XRD, HRTEM, FTIR, LCR meter and VSM techniques, respectively. XRD analysis showed that all the samples are single-phase cubic spinel in structure. The average crystallite sizes of the nanoparticles were found between 30 nm to 45 nm. Real and imaginary parts of the impedance ( Z' and Z″) suggested coexistence of two relaxation regimes: one was introduced by electrode polarization, while the other was attributed to the coeffect of grain and grain boundary effects. The dielectric constant of the samples was found very high, which showed non-Debye relaxation phenomena, while conductivity of the samples exhibited a two-segment behavior with frequency. The room temperature M-H curves suggested that the samples exhibit supermagnetism, and the saturation magnetization increases with increasing Co2+ ion substitution.

  13. Atomic magnetic gradiometer for room temperature high sensitivity magnetic field detection

    DOEpatents

    Xu,Shoujun; Lowery, Thomas L.; Budker, Dmitry; Yashchuk, Valeriy V.; Wemmer, David E.; Pines, Alexander

    2009-08-11

    A laser-based atomic magnetometer (LBAM) apparatus measures magnetic fields, comprising: a plurality of polarization detector cells to detect magnetic fields; a laser source optically coupled to the polarization detector cells; and a signal detector that measures the laser source after being coupled to the polarization detector cells, which may be alkali cells. A single polarization cell may be used for nuclear magnetic resonance (NMR) by prepolarizing the nuclear spins of an analyte, encoding spectroscopic and/or spatial information, and detecting NMR signals from the analyte with a laser-based atomic magnetometer to form NMR spectra and/or magnetic resonance images (MRI). There is no need of a magnetic field or cryogenics in the detection step, as it is detected through the LBAM.

  14. Evidence for a magnetic proximity effect up to room temperature at Fe/(Ga, Mn)As interfaces.

    PubMed

    Maccherozzi, F; Sperl, M; Panaccione, G; Minár, J; Polesya, S; Ebert, H; Wurstbauer, U; Hochstrasser, M; Rossi, G; Woltersdorf, G; Wegscheider, W; Back, C H

    2008-12-31

    We report x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry experiments to study magnetic order and coupling in thin Fe/(Ga, Mn)As(100) films. We observe induced magnetic order in the (Ga, Mn)As layer that extends over more than 2 nm, even at room temperature. We find spectroscopic evidences of a hybridized d configuration of Mn atoms in Fe/(Ga, Mn)As, with negligible Mn diffusion and/or MnFe intermixing. We show by experiment as well as by theory that the magnetic moment of the Mn ions couples antiparallel to the moment of the Fe overlayer.

  15. Understanding and optimizing microemulsions with magnetic room temperature ionic liquids (MRTILs).

    PubMed

    Klee, Andreas; Prevost, Sylvain; Gasser, Urs; Gradzielski, Michael

    2015-03-12

    Nonaqueous microemulsions containing the magnetic room temperature ionic liquid (MRTIL) bmimFeCl4 as polar phase were studied with respect to their macroscopic phase behavior and structure by means of small angle neutron scattering (SANS). The phase behavior was studied in detail for different alcohols as cosurfactant and different oils as nonpolar phase and mainly by varying the chain length of the used ionic surfactant (CnmimCl with n = 14, 16, 18). In general, phase behavior and structural ordering in the mesophases were found to be comparable to water systems where with increasing content of MRTIL the microemulsions seems to become less and less structured leading to a rough and softer interface with less long-range ordering. The extent of structuring increases with increasing chain length of the surfactant. However, the pure surfactant is not able to form microemulsions and a rather large amount of alcohol is required for stabilization, where the effectiveness of the alcohol increases with increasing chain length of the alcohol. From this comprehensive investigation systematic trends can be deduced in order to formulate correspondingly structured microemulsions with MRTIL as polar phase.

  16. High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature

    NASA Astrophysics Data System (ADS)

    Trifunovic, Luka; Pedrocchi, Fabio L.; Hoffman, Silas; Maletinsky, Patrick; Yacoby, Amir; Loss, Daniel

    2015-06-01

    Magnetic resonance techniques not only provide powerful imaging tools that have revolutionized medicine, but they have a wide spectrum of applications in other fields of science such as biology, chemistry, neuroscience and physics. However, current state-of-the-art magnetometers are unable to detect a single nuclear spin unless the tip-to-sample separation is made sufficiently small. Here, we demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy magnetometer and a target spin, the magnetometer sensitivity is improved dramatically. Using materials and techniques that are already experimentally available, our proposed set-up is sensitive enough to detect a single nuclear spin within ten milliseconds of data acquisition at room temperature. The sensitivity is practically unchanged when the ferromagnet surface to the target spin separation is smaller than the ferromagnet lateral dimensions; typically about a tenth of a micrometre. This scheme further benefits when used for nitrogen-vacancy ensemble measurements, enhancing sensitivity by an additional three orders of magnitude.

  17. Room-temperature Magnetism in Carbon Dots and Enhanced Ferromagnetism in Carbon Dots-Polyaniline Nanocomposite.

    PubMed

    Liu, Jian; Bi, Hong; Cesar Morais, Paulo; Zhang, Xiang; Zhang, Fapei; Hu, Lin

    2017-05-19

    Room temperature magnetic ordering is reported for very small carbon dots (CDs), mat-like polyaniline nanofibers (Mat-PANI) and a composite of CDs@Mat-PANI containing 0.315 wt% CDs. We have found saturation magnetization (M S ) of CDs, Mat-PANI and CDs@Mat-PANI at 5 (20/300) K equals to 0.0079 (0.0048/0.0019), 0.0116 (0.0065/0.0055) and 0.0349 (0.0085/0.0077) emu/g, respectively. The M S enhancement in CDs@Mat-PANI (200% and 40% at 5 K and 300 K, respectively) is attributed to electron transfer from Mat-PANI imine N-atoms to the encapsulated CDs. Changes in M S values reveal that 0.81 (0.08) electron/CD is transferred at 5 (300) K, which is supported by observation of CDs photoluminescence (PL) redshift while in CDs@Mat-PANI. Band-bending and bandgap-renormalization calculations are used to predict a redshift of 117 meV at 300 K as a result of the electron transfer, in excellent agreement with the PL data (110 meV). Raman, X-ray diffraction and X-ray photoelectron spectroscopy data are used to confirm the electron transfer process as well as the strong interaction of CDs with PANI within CDs@Mat-PANI, which increases the crystalline domain size of Mat-PANI from about 4.8 nm to 9.2 nm while reducing the tensile strain from about 6.2% to 1.8%.

  18. Near fifty percent sodium substituted lanthanum manganites—A potential magnetic refrigerant for room temperature applications

    SciTech Connect

    Sethulakshmi, N.; Anantharaman, M. R.; Al-Omari, I. A.; Suresh, K. G.

    2014-03-03

    Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300 K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J·kg{sup −1}·K{sup −1} was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300 K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300 K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62 K at 280 K.

  19. Room temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO{sub 3} ceramics

    SciTech Connect

    Basith, M. A. E-mail: arima@yz.yamagata-u.ac.jp; Kurni, O.; Alam, M. S.; Sinha, B. L.; Ahmmad, Bashir E-mail: arima@yz.yamagata-u.ac.jp

    2014-01-14

    Room temperature dielectric and magnetic properties of BiFeO{sub 3} samples, co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe, respectively, were reported. The nominal compositions of Bi{sub 0.9}Gd{sub 0.1}Fe{sub 1–x}Ti{sub x}O{sub 3} (x = 0.00-0.25) ceramics were synthesized by conventional solid state reaction technique. X-ray diffraction patterns revealed that the substitution of Fe by Ti induces a phase transition from rhombohedral to orthorhombic at x > 0.20. Morphological studies demonstrated that the average grain size was reduced from ∼1.5 μm to ∼200 nm with the increase in Ti content. Due to Ti substitution, the dielectric constant was stable over a wide range of high frequencies (30 kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric properties of the compounds are associated with their improved morphologies and reduced leakage current densities probably due to the lower concentration of oxygen vacancies in the compositions. Magnetic properties of Bi{sub 0.9}Gd{sub 0.1}Fe{sub 1–x}Ti{sub x}O{sub 3} (x = 0.00-0.25) ceramics measured at room temperature were enhanced with Ti substitution up to 20% compared to that of pure BiFeO{sub 3} and Ti undoped Bi{sub 0.9}Gd{sub 0.1}FeO{sub 3} samples. The enhanced magnetic properties might be attributed to the substitution induced suppression of spiral spin structure of BiFeO{sub 3}. An asymmetric shifts both in the field and magnetization axes of magnetization versus magnetic field curves was observed. This indicates the presence of exchange bias effect in these compounds notably at room temperature.

  20. Magneto-caloric effect of FexZryB100-x-y metallic ribbons for room temperature magnetic refrigeration

    NASA Astrophysics Data System (ADS)

    Guo, D. Q.; Chan, K. C.; Xia, L.; Yu, P.

    2017-02-01

    Among various amorphous magnetic materials, even though Fe-based materials do not have high magnetocaloric effect (MCE), their advantages of tunable Curie temperature (TC) and low cost have attracted considerable attention in regard to room temperature magnetic refrigeration applications. With the aim of enhancing the MCE, the influence of boron addition on Fe-based amorphous materials was investigated in this study. Fe94-xZr6Bx (x=5, 6, 8 and 10), Fe91-yZr9By (y=3, 4, 5, 6, 8 and 10) and Fe89-zZr11Bz (z=3, 4, 5, 6, 8 and 10) specimens were made in ribbon form and their magnetocaloric effect was investigated. The Curie temperature (TC) of all three series of ribbons underwent an almost linear increase, and the peak magnetic entropy change, | Δ SMpeak | (obtained in a magnetic field of 1.5 T), generally increases with increasing boron content. The results further show that the Fe86Zr9B5 ribbon exhibits a relatively large | Δ SMpeak | value of 1.13 J/kgK at 330 K and a large refrigerant capacity value of 135.6 J/kg under 1.5 T. On the basis of these results, although there is still much scope for improvement before totally replacing the conventional cooling method, the Fe-based amorphous ribbon can be seen as a promising magnetocaloric material for room temperature magnetic refrigeration applications.

  1. Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions.

    PubMed

    Yuasa, Shinji; Nagahama, Taro; Fukushima, Akio; Suzuki, Yoshishige; Ando, Koji

    2004-12-01

    The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs) is the key to developing magnetoresistive random-access-memory (MRAM), magnetic sensors and novel programmable logic devices. Conventional MTJs with an amorphous aluminium oxide tunnel barrier, which have been extensively studied for device applications, exhibit a magnetoresistance ratio up to 70% at room temperature. This low magnetoresistance seriously limits the feasibility of spintronics devices. Here, we report a giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs. The origin of this enormous TMR effect is coherent spin-polarized tunnelling, where the symmetry of electron wave functions plays an important role. Moreover, we observed that their tunnel magnetoresistance oscillates as a function of tunnel barrier thickness, indicating that coherency of wave functions is conserved across the tunnel barrier. The coherent TMR effect is a key to making spintronic devices with novel quantum-mechanical functions, and to developing gigabit-scale MRAM.

  2. Cobalt-doped anatase TiO2: A room temperature dilute magnetic dielectric material

    NASA Astrophysics Data System (ADS)

    Griffin, K. A.; Pakhomov, A. B.; Wang, C. M.; Heald, S. M.; Krishnan, Kannan M.

    2005-05-01

    We experimentally investigate the room temperature ferromagnetism observed in insulating Co doped anatase TiO2 thin films grown by sputter deposition. The Co was uniformly incorporated in the lattice as Co(II) with no evidence of Co metal. A series of annealing treatments were carried out to optimize the ferromagnetic ordering and a saturation moment of 1.1μB/Co atom at 300 K was obtained with UHV annealing at 450 °C. Both as-deposited and annealed films were highly insulating at room temperature. Results show that the ferromagnetism is strongly dependent on the number and distribution of oxygen vacancies in the Co:TiO2 lattice.

  3. Room Temperature Magnetic Behavior In Nanocrystalline Ni-Doped Zro2 By Microwave-Assisted Polyol Synthesis

    NASA Astrophysics Data System (ADS)

    Parimita Rath, Pragyan; Parhi, Pankaj Kumar; Ranjan Panda, Sirish; Priyadarshini, Barsharani; Ranjan Sahoo, Tapas

    2017-08-01

    This article, deals with a microwave-assisted polyol method to demonstrate a low temperature route < 250°C, to prepare a high temperature cubic zirconia phase. Powder XRD pattern shows broad diffraction peaks suggesting nanometric size of the particles. Magnetic behavior of 1-5 at% Ni doped samples show a threshold for substitutional induced room temperature ferromagnetism up to 3 at% of Ni. TGA data reveals that Ni-doped ZrO2 polyol precursors decompose exothermically below 300°C. IR data confirms the reduction of Zr(OH)4 precipitates to ZrO2, in agreement with the conclusions drawn from the TGA analysis.

  4. Sol-gel derived Zn1-xFexS diluted magnetic semiconductor thin films: Compositional dependent room or above room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Goktas, A.

    2015-06-01

    Zn1-xFexS (where x = 0.00, 0.01, 0.03, 0.05, 0.1 and 0.2) thin films were synthesized by sol-gel method. To investigate the origin of room or above room temperature ferromagnetism in these films several tools such as XRD, SEM, XPS, UV-Vis spectrophotometer and SQUİD magnetometer were used. The XRD studies showed that the phase singularity of ZnS zinc blende (hexagonal) structure. The SEM images indicated the homogeneous film surface with no cracking and increased particle size with increasing Fe-doping ratio except for 1 at.% Fe dopant. The presence of Zn, Fe, S, Si and O atoms in the films was observed in EDS spectrum. The XPS studies confirmed that the existence of Fe3+ ions in host ZnS thin films. In the UV-Vis measurements the band gap energy corresponding to the absorption edge was estimated to be approximately in the range of 3.59-2.08 eV, depending on the Fe doping level. The magnetization measurements revealed that the films had paramagnetic or ferromagnetic order depending on Fe doping ratio at 5, 100, 200, 300 and 350 K. The observed room or above room temperature ferromagnetism can be attributed to the strong p-d exchange interaction between Fe3+ d and anion (S2-) p orbitals as well as impurities.

  5. Magnetic properties and magnetocaloric effect at room temperature of Ni50- x Ag x Mn37Sn13 alloys

    NASA Astrophysics Data System (ADS)

    Thanh, Tran Dang; Mai, Nguyen Thi; Dan, Nguyen Huy; Phan, The-Long; Yu, Seong-Cho

    2014-11-01

    In this work, we present a detailed study of the magnetic properties and the magnetocaloric effect at room temperature of Ni50- x Ag x Mn37Sn13 alloys with x = 1, 2, and 4, which were prepared by using an arc-melting method. Experimental results reveal that a partial replacement of Ag for Ni leads to a decrease in the anti-FM phase in the alloys. In addition, the martensitic-austenitic phase transition shifts towards lower temperature and is broaded. The Curie temperature ( T C A ) for the austenitic phase also shifts toward to lower temperature, but not by much. The Curie temperature was found to be 308, 305, and 298 K for x = 1, 2, and 4, respectively. The magnetic entropy change (Δ S m ) of the samples was calculated by using isothermal magnetization data. Under an applied magnetic field change of 10 kOe, the maximum value of Δ S m (|Δ S max |) was achieved at around room temperature and did not change much (~0.8 J·kg-1·K-1) with increasing Ag-doping concentration. Particularly, the M 2 vs. H/ M curves prove that all the samples exhibited a second-order magnetic phase transition. Based on Landau's phase-transition theory and careful analyses of the magnetic data around the T C A , we have determined the critical parameters β, γ, δ, and T C . The results show that the β values are located between those expected for the 3D-Heisenberg model ( β = 0.365) and mean-field theory ( β = 0.5). Such a result proves the coexistence of short-range and long-range ferromagnetic interactions in Ni50- x Ag x Mn37Sn13 alloys. The nature of the changes in the critical parameters and the |Δ S max | is thoroughly discussed by means of structural analyses.

  6. Vacuum insulated room temperature bore horizontal cryostat for 4-Tesla superconducting magnet

    SciTech Connect

    Sundar Rajan, S.; Sinha, A.K.; Sachan, Udai G.P.; Malhotra, Sanjay; Taly, Y.K.; Krishnamurthy, N.

    2014-07-01

    4-Tesla warm bore superconducting magnet is being constructed at Bhabha Atomic Research Centre in India. The adiabatically cooled superconducting magnet will be used for corrosion and Magneto Hydro Dynamic (MHD) studies related to development of Lead Lithium Cooled Ceramic Breeder (LLCB) test blanket module (TBM). Magnet aperture is of 300 mm diameter and is accessible from both ends. Magnet is completely immersed in liquid helium bath at 4.2K. The stored magnetic energy during normal operation is 2.6 MJ. Huge amount of Lorentz forces acts on the magnet coils during operation. These forces try to axially compress the coils and cause outward radial movement of the conductor. Micro meter movement of the coils result in energy deposition due to large operating fields. This energy, albeit small, is still sufficient to cause quench in the magnet as the heat capacities at cryogenic temperatures are very low. Pre-stressing and banding of the superconducting strands help to overcome conductor movement by increasing structural rigidity. This paper describes the thermal, structural and magnetic design the superconducting solenoid magnet. (author)

  7. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature

    NASA Astrophysics Data System (ADS)

    Staruch, Margo; Gopman, Daniel B.; Iunin, Yury L.; Shull, Robert D.; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-11-01

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

  8. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature.

    PubMed

    Staruch, Margo; Gopman, Daniel B; Iunin, Yury L; Shull, Robert D; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-11-21

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

  9. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature

    PubMed Central

    Staruch, Margo; Gopman, Daniel B.; Iunin, Yury L.; Shull, Robert D.; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-01-01

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices. PMID:27869152

  10. Ferromagnetism at room temperature with a large magnetic moment in anatase V-doped TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Hong, Nguyen Hoa; Sakai, Joe; Hassini, Awatef

    2004-04-01

    V-doped TiO2 thin films were grown by laser ablation on LaAlO3 substrates. In the chosen range of the growth conditions, all V:TiO2 films have an anatase structure and exhibit semiconducting and ferromagnetic behaviors at room temperature. V:TiO2 films have a giant magnetic moment and they seem to be far better ferromagnetic than Co/Fe/Ni-doped TiO2 films. This study has proved that a few percent of V substituting for Ti in TiO2 can result in a potential diluted magnetic semiconductor.

  11. Room-temperature decay and light reactivation of high-Tc ferromagnetism in an oxide-diluted magnetic semiconductor.

    PubMed

    Pan, Dengyu; Wan, Jianguo; Xu, Guoliang; Lv, Liya; Wu, Yujie; Min, Han; Liu, Junming; Wang, Guanghou

    2006-10-04

    We present a novel route for manipulation of the ferromagnetic order in Co-doped TiO2 using UV laser irradiation. The ferromagnetic order of the nanocrystal films decays with aging in air at room temperature, which can be reactivated and enhanced by UV irradiation, whereas the coercive force reduces with irradiation time. Photoinduced trapped electrons were suggested to induce the ferromagnetic order. We believe that light manipulation is a general method for tuning the magnetic properties of oxide-based diluted magnetic semiconductors, which can find practical applications in future integrated magneto-optical nanoelectronics.

  12. Novel room temperature ferromagnetic semiconductors

    SciTech Connect

    Gupta, Amita

    2004-06-01

    Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous distribution of Mn substituting

  13. Room-temperature photomagnetism in the spinel ferrite (Mn,Zn,Fe)3O4 as seen via soft x-ray magnetic circular dichroism

    SciTech Connect

    Bettinger, J.S.; Piamonteze, C.; Chopdekar, R.V.; Liberati, M.; Arenholz, E.; Suzuki, Y.

    2009-08-01

    We have used X-ray magnetic circular dichroism (XMCD) in conjunction with multiplet simulations to directly probe the origin of photomagnetism in nanocrystalline (Mn,Zn,Fe){sub 3}O{sub 4}. A photomagnetic effect at room temperature has been observed in these films with HeNe illumination. We have verified an intervalence charge transfer among octahedral Fe cations to account for the increase in magnetization observed at and above room temperature in small magnetic fields. Using XMCD, we demonstrate that the dichroism of Fe in octahedral sites increases by 18% at room temperature while the dichroism of Fe in tetrahedral sites does not change.

  14. Imaging of room-temperature ferromagnetic nano-domains at the surface of a non-magnetic oxide

    NASA Astrophysics Data System (ADS)

    Taniuchi, T.; Motoyui, Y.; Morozumi, K.; Rödel, T. C.; Fortuna, F.; Santander-Syro, A. F.; Shin, S.

    2016-06-01

    Two-dimensional electron gases at oxide surfaces or interfaces show exotic ordered states of matter, like superconductivity, magnetism or spin-polarized states, and are a promising platform for alternative oxide-based electronics. Here we directly image a dense population of randomly distributed ferromagnetic domains of ~40 nm typical sizes at room temperature at the oxygen-deficient surface of SrTiO3, a non-magnetic transparent insulator in the bulk. We use laser-based photoemission electron microscopy, an experimental technique that gives selective spin detection of the surface carriers, even in bulk insulators, with a high spatial resolution of 2.6 nm. We furthermore find that the Curie temperature in this system is as high as 900 K. These findings open perspectives for applications in nano-domain magnetism and spintronics using oxide-based devices, for instance through the nano-engineering of oxygen vacancies at surfaces or interfaces of transition-metal oxides.

  15. Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet

    SciTech Connect

    Kataoka, Y.; Kitagawa, J.; Ono, T.; Tsubota, M.

    2015-11-15

    The sustainable society requires the recycling of rare metals. Rare earth Nd is one of rare metals, accompanying huge consumption especially in Nd-Fe-B magnets. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between Nd and Fe at room temperature is desired. We have proposed a pretreatment of corrosion before the dissolution into HCl and the oxalic acid precipitation. The corrosion produces γ-FeOOH and a Nd hydroxide, which have high selectivity for HCl solution at room temperature. Nd can be recovered as Mn{sub 2}O{sub 3}-type Nd{sub 2}O{sub 3}. The estimated recovery-ratio of Nd reaches to 97%.

  16. Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet

    NASA Astrophysics Data System (ADS)

    Kataoka, Y.; Ono, T.; Tsubota, M.; Kitagawa, J.

    2015-11-01

    The sustainable society requires the recycling of rare metals. Rare earth Nd is one of rare metals, accompanying huge consumption especially in Nd-Fe-B magnets. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between Nd and Fe at room temperature is desired. We have proposed a pretreatment of corrosion before the dissolution into HCl and the oxalic acid precipitation. The corrosion produces γ-FeOOH and a Nd hydroxide, which have high selectivity for HCl solution at room temperature. Nd can be recovered as Mn2O3-type Nd2O3. The estimated recovery-ratio of Nd reaches to 97%.

  17. Engineered spatial inversion symmetry breaking in an oxide hetero-structure built from isosymmetric room temperature magnetically ordered components

    NASA Astrophysics Data System (ADS)

    Claridge, John; Alaria, Jonathan; Dyer, Matthew; Rosseinsky, Matthew; Borisov, Pavel; Manning, Troy; Lepadatu, Serban; Cain, Markys; Mishina, Elena; Sherstyuck, Natalia; Ilyin, N. A.; Hadermann, Joke; Lederman, David

    2014-03-01

    The oxide heterostructure [(YFeO3)5(LaFeO3)5]40,which is magnetically ordered and piezoelectric at room temperature, has been constructed from two weak ferromagnetic AFeO3 perovskites with different A cations using RHEED-monitored pulsed laser deposition. The polarisation arises by combining ordering on the A site, imposed by the periodicity of the grown structure, with appropriate orientations of the octahedral tilting, according to simple symmetry-controlled rules. Magnetization and MOKE measurements show that the heterostructure's magnetic structure is similar to that of the individual components. Evidence of the polarity was obtained from second harmonic generation and piezoelectric force microscopy measurements. Modeling of the piezoresponse allows extraction of d33 (approximately 10 pC/N) of the heterostructure, which is in agreement with DFT calculations.

  18. Room-Temperature Magnetic and Magneto-Optical Properties of Sr2FeMoO6 Thin Films

    NASA Astrophysics Data System (ADS)

    Asano, Hidefumi; Osugi, Masahiro; Kohara, Yasuhiro; Higashida, Daisuke; Matsui, Masaaki

    2001-08-01

    Epitaxial thin films of a half-metallic ferromagnet Sr2FeMoO6 have been grown on (001) SrTiO3, and MgO substrates by magnetron sputtering in Ar+H2 mixture gas. Their structural, magnetic, magneto-optical and transport properties at room temperature were investigated and compared. Large difference has been observed especially in the magnetic and magneto-optical properties between thin films on SrTiO3 and MgO@. The films on SrTiO3 exhibited stronger out-of-plane magnetic anisotropy and larger complex polar Kerr effect with a rotation θk up to -0.32\\circ at 1.6 eV and RT@. The observed difference in the properties of the films on the two substrates can be interpreted in terms of the structural disorder.

  19. Highly Efficient Extraction of Phenolic Compounds by Use of Magnetic Room Temperature Ionic Liquids for Environmental Remediation

    PubMed Central

    Deng, Ning; Li, Min; Zhao, Lijie; Lu, Chengfei; de Rooy, Sergio L.; Warner, Isiah M.

    2011-01-01

    A hydrophobic magnetic room temperature ionic liquid (MRTIL), trihexyltetradecylphosphonium tetrachloroferrate(III) ([3C6PC14][FeCl4]), was synthesized from trihexyltetradecylphosphonium chloride and FeCl3·6H2O. This MRTIL was investigated as a possible separation agent for solvent extraction of phenolic compounds from aqueous solution. Due to its strong paramagnetism, [3C6PC14][FeCl4] responds to an external neodymium magnet, which was employed in the design of a novel magnetic extraction technique. The conditions for extraction, including extraction time, volume ratio between MRTIL and aqueous phase, pH of aqueous solution, and structures of phenolic compounds were investigated and optimized. The magnetic extraction of phenols achieved equilibrium in 20 min and the phenolic compounds were found to have higher distribution ratios under acidic conditions. In addition, it was observed that phenols containing a greater number of chlorine or nitro substitutents exhibited higher distribution ratios. For example, the distribution ratio of phenol (DPh) was 107. In contrast, 3,5-dichlorophenol distribution ratio (D3,5-DCP) had a much higher value of 6372 under identical extraction conditions. When compared with four selected traditional non-magnetic room temperature ionic liquids, our [3C6PC14][FeCl4] exhibited significantly higher extraction efficiency under the same experimental conditions used in this work. Pentachlorophenol, a major component in the contaminated soil sample obtained from a superfund site, was successfully extracted and removed by use of [3C6PC14][FeCl4] with high extraction efficiency. Pentachlorophenol concentration was dramatically reduced from 7.8 μg.mL−1 to 0.2 μg.mL−1 after the magnetic extraction by use of [3C6PC14][FeCl4]. PMID:21783320

  20. Thiol-capped ZnO nanowire/nanotube arrays with tunable magnetic properties at room temperature.

    PubMed

    Deng, Su-Zi; Fan, Hai-Ming; Wang, Miao; Zheng, Min-Rui; Yi, Jia-Bao; Wu, Rong-Qin; Tan, Hui-Ru; Sow, Chorng-Haur; Ding, Jun; Feng, Yuan-Ping; Loh, Kian-Ping

    2010-01-26

    The present study reports room-temperature ferromagnetic behaviors in three-dimensional (3D)-aligned thiol-capped single-crystalline ZnO nanowire (NW) and nanotube (NT) arrays as well as polycrystalline ZnO NT arrays. Besides the observation of height-dependent saturation magnetization, a much higher M(s) of 166 microemu cm(-2) has been found in NTs compared to NWs (36 microemu cm(-2)) due to larger surface area in ZnO NTs, indicating morphology-dependent magnetic properties in ZnO NW/NT systems. Density functional calculations have revealed that the origin of ferromagnetism is mainly attributed to spin-polarized 3p electrons in S sites and, therefore, has a strong correlation with Zn-S bond anisotropy. The preferential magnetization direction of both single-crystalline NTs and NWs lies perpendicular to the tube/wire axis due to the aligned high anisotropy orientation of the Zn-S bonds on the lateral (100) face of ZnO NWs and NTs. Polycrystalline ZnO NTs, however, exhibit a preferential magnetization direction parallel to the tube axis which is ascribed to shape anisotropy dominating the magnetic response. Our results demonstrate the interplay of morphology, dimensions, and crystallinity on spin alignment and magnetic anisotropy in a 3D semiconductor nanosystem with interfacial magnetism.

  1. Carboxylate-based molecular magnet: One path toward achieving stable quantum correlations at room temperature

    DOE PAGES

    Cruz, C.; Soares-Pinto, D. O.; Brandão, P.; ...

    2016-03-07

    The control of quantum correlations in solid-state systems by means of material engineering is a broad avenue to be explored, since it makes possible steps toward the limits of quantum mechanics and the design of novel materials with applications on emerging quantum technologies. This letter explores the potential of molecular magnets to be prototypes of materials for quantum information technology in this context. More precisely, we engineered a material and from its geometric quantum discord we found significant quantum correlations up to 9540 K (even without entanglement); and, a pure singlet state occupied up to around 80 K (above liquidmore » nitrogen temperature), additionally. Our results could only be achieved due to the carboxylate group promoting a metal-to-metal huge magnetic interaction.« less

  2. Carboxylate-based molecular magnet: One path toward achieving stable quantum correlations at room temperature

    SciTech Connect

    Cruz, C.; Soares-Pinto, D. O.; Brandão, P.; dos Santos, A. M.; Reis, M. S.

    2016-03-07

    The control of quantum correlations in solid-state systems by means of material engineering is a broad avenue to be explored, since it makes possible steps toward the limits of quantum mechanics and the design of novel materials with applications on emerging quantum technologies. This letter explores the potential of molecular magnets to be prototypes of materials for quantum information technology in this context. More precisely, we engineered a material and from its geometric quantum discord we found significant quantum correlations up to 9540 K (even without entanglement); and, a pure singlet state occupied up to around 80 K (above liquid nitrogen temperature), additionally. Our results could only be achieved due to the carboxylate group promoting a metal-to-metal huge magnetic interaction.

  3. Carboxylate-based molecular magnet: One path toward achieving stable quantum correlations at room temperature

    NASA Astrophysics Data System (ADS)

    Cruz, C.; Soares-Pinto, D. O.; Brandão, P.; dos Santos, A. M.; Reis, M. S.

    2016-02-01

    The control of quantum correlations in solid-state systems by means of material engineering is a broad avenue to be explored, since it makes possible steps toward the limits of quantum mechanics and the design of novel materials with applications on emerging quantum technologies. In this context, this letter explores the potential of molecular magnets to be prototypes of materials for quantum information technology. More precisely, we engineered a material and from its geometric quantum discord we found significant quantum correlations up to 9540 K (even without entanglement); and, in addition, a pure singlet state occupied up to around 80 K (above liquid nitrogen temperature). These results could only be achieved due to the carboxylate group promoting a metal-to-metal huge magnetic interaction.

  4. Tailoring of magnetic orderings in Fe substituted GdMnO3 bulk samples towards room temperature

    NASA Astrophysics Data System (ADS)

    Pal, A.; Dhana Sekhar, C.; Venimadhav, A.; Murugavel, P.

    2017-10-01

    The evolution of various magnetic ordering has been studied for the orthorhombic perovskite GdMn1‑x Fe x O3 (0  ⩽  x  ⩽  0.7) system to obtain its comprehensive magnetic phase diagram. We observed that the substitution of Fe in GdMnO3 increases the antiferromagnetic Neel temperature (T N) from 40 K to above 400 K and importantly induces a spin-reorientation transition (T SR) for x  ⩾  0.4. These transitions are close to room temperature at x  =  0.5 and then gradually separated at a higher x value. The static orbital ordering induced by the Jahn–Teller distortion seems to play an important role in changing the T N. The variations of spin-reorientation ordering along with the competition between the magnetic orderings as a function of the composition were discussed with respect to antisymmetric exchange interactions and Mn3+ single-ion anisotropy in detail. In addition, the correlation between structural and magnetic properties suggests that the subtle structural change at composition x  =  0.4 may affect the magnetic ordering. The observed tunable T SR and T N in GdMn1‑x Fe x O3 could add a practical value for these compositions in fields like spintronics and sensors.

  5. Electrical Switching of Magnetic Polarity in a Multiferroic BiFeO3 Device at Room Temperature

    NASA Astrophysics Data System (ADS)

    Waterfield Price, N.; Johnson, R. D.; Saenrang, W.; Bombardi, A.; Chmiel, F. P.; Eom, C. B.; Radaelli, P. G.

    2017-07-01

    We have directly imaged reversible electrical switching of the cycloidal rotation direction (magnetic polarity) in a (111 )pc-BiFeO3 epitaxial-film device at room temperature by nonresonant x-ray magnetic scattering. Consistent with previous reports, fully relaxed (111 )pc-BiFeO3 epitaxial films consisting of a single ferroelectric domain are found to comprise a submicron-scale mosaic of magnetoelastic domains, all sharing a common direction of the magnetic polarity, which is found to switch reversibly upon reversal of the ferroelectric polarization without any measurable change of the magnetoelastic domain population. A real-space polarimetry map of our device clearly distinguishes between regions of the sample electrically addressed into the two magnetic states with a resolution of a few tens of micron. Contrary to the general belief that the magneto-electric coupling in BiFeO3 is weak, we find that electrical switching has a dramatic effect on the magnetic structure, with the magnetic moments rotating on average by 90° at every cycle.

  6. Room-temperature ferromagnetism observed in Nd-doped In2O3 dilute magnetic semiconducting nanowires

    NASA Astrophysics Data System (ADS)

    Lv, Zhanpeng; Zhang, Junran; Niu, Wei; Zhang, Minhao; Song, Li; Zhu, Hairong; Wang, Xuefeng

    2016-09-01

    Nd-doped In2O3 nanowires were fabricated by an Au-catalyzed chemical vapor deposition method. Nd atoms were successfully doped into the In2O3 host lattice structure, as revealed by energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. Robust room temperature ferromagnetism was observed in Nd-doped In2O3 nanowires, which was attributed to the long-range-mediated magnetization among Nd3+-vacancy complexes through percolation-bound magnetic polarons. Project supported by the National Natural Science Foundation of China (Grant No. 11274003), the Priority Academic Program Development of Jiangsu Higher Education Institutions, China, and the Fundamental Research Funds for the Central Universities, China.

  7. Zero-field magnetic resonance of the photo-excited triplet state of pentacene at room temperature

    NASA Astrophysics Data System (ADS)

    Yang, Tran-Chin; Sloop, David J.; Weissman, S. I.; Lin, Tien-Sung

    2000-12-01

    The pulsed EPR free induction decay (FID) signals of the photo-excited pentacene triplet state are reported for three mixed crystals at room temperature: pentacene-h14 in p-terphenyl, pentacene-h14 in benzoic acid, and pentacene-d14 in p-terphenyl. The recorded FID signals have relatively long decay times of about four microseconds, presumably due to the reduced hyperfine interactions in the zero magnetic field. The time domain FID signals transform to spectral components typically narrower than 500 kHz, allowing us to determine the pentacene triplet zero field splitting parameters to better accuracy than previously reported. Further, a new experimental technique using the high speed magnetic field jumping capability enables us to examine the anisotropic hyperfine and quadrupole interactions.

  8. A dynamic sandwich assay on magnetic beads for selective detection of single-nucleotide mutations at room temperature.

    PubMed

    Wang, Junxiu; Xiong, Guoliang; Ma, Liang; Wang, Shihui; Zhou, Xu; Wang, Lei; Xiao, Lehui; Su, Xin; Yu, Changyuan

    2017-08-15

    Single-nucleotide mutation (SNM) has proven to be associated with a variety of human diseases. Development of reliable methods for the detection of SNM is crucial for molecular diagnosis and personalized medicine. The sandwich assays are widely used tools for detecting nucleic acid biomarkers due to their low cost and rapid signaling. However, the poor hybridization specificity of signal probe at room temperature hampers the discrimination of mutant and wild type. Here, we demonstrate a dynamic sandwich assay on magnetic beads for SNM detection based on the transient binding between signal probe and target. By taking the advantage of mismatch sensitive thermodynamics of transient DNA binding, the dynamic sandwich assay exhibits high discrimination factor for mutant with a broad range of salt concentration at room temperature. The beads used in this assay serve as a tool for separation, and might be helpful to enhance SNM selectivity. Flexible design of signal probe and facile magnetic separation allow multiple-mode downstream analysis including colorimetric detection and isothermal amplification. With this method, BRAF mutations in the genomic DNA extracted from cancer cell lines were tested, allowing sensitive detection of SNM at very low abundances (0.1-0.5% mutant/wild type). Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Electric field control of magnetization in Cu2O/porous anodic alumina hybrid structures at room temperature

    NASA Astrophysics Data System (ADS)

    Qi, L. Q.; Liu, H. Y.; Sun, H. Y.; Liu, L. H.; Han, R. S.

    2016-04-01

    Cu2O nanoporous films are deposited on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. This paper focuses on voltage driven magnetization switching in Cu2O/PAA (CP) composite films prepared by DC-reactive magnetron sputtering. By applying a dc electric field, the magnetization of the CP composite films can be controlled in a reversible and reproducible way and shows an analogous on-off behavior. The magnitude of the change in the magnetization was about 75 emu/cm3 as the electric field was switched on and off. Resistive switching behavior was also observed in as-prepared CP composite films. Further analysis indicated that the formation/rupture of conducting filaments composed of oxygen vacancies is likely responsible for the changes in the magnetization as well as in the resistivity. Such reversible change of magnetization controlled by an electric field at room temperature may have applications in spintronics and power efficient data storage technologies.

  10. Imaging of room-temperature ferromagnetic nano-domains at the surface of a non-magnetic oxide.

    PubMed

    Taniuchi, T; Motoyui, Y; Morozumi, K; Rödel, T C; Fortuna, F; Santander-Syro, A F; Shin, S

    2016-06-10

    Two-dimensional electron gases at oxide surfaces or interfaces show exotic ordered states of matter, like superconductivity, magnetism or spin-polarized states, and are a promising platform for alternative oxide-based electronics. Here we directly image a dense population of randomly distributed ferromagnetic domains of ∼40 nm typical sizes at room temperature at the oxygen-deficient surface of SrTiO3, a non-magnetic transparent insulator in the bulk. We use laser-based photoemission electron microscopy, an experimental technique that gives selective spin detection of the surface carriers, even in bulk insulators, with a high spatial resolution of 2.6 nm. We furthermore find that the Curie temperature in this system is as high as 900 K. These findings open perspectives for applications in nano-domain magnetism and spintronics using oxide-based devices, for instance through the nano-engineering of oxygen vacancies at surfaces or interfaces of transition-metal oxides.

  11. Imaging of room-temperature ferromagnetic nano-domains at the surface of a non-magnetic oxide

    PubMed Central

    Taniuchi, T.; Motoyui, Y.; Morozumi, K.; Rödel, T. C.; Fortuna, F.; Santander-Syro, A. F.; Shin, S.

    2016-01-01

    Two-dimensional electron gases at oxide surfaces or interfaces show exotic ordered states of matter, like superconductivity, magnetism or spin-polarized states, and are a promising platform for alternative oxide-based electronics. Here we directly image a dense population of randomly distributed ferromagnetic domains of ∼40 nm typical sizes at room temperature at the oxygen-deficient surface of SrTiO3, a non-magnetic transparent insulator in the bulk. We use laser-based photoemission electron microscopy, an experimental technique that gives selective spin detection of the surface carriers, even in bulk insulators, with a high spatial resolution of 2.6 nm. We furthermore find that the Curie temperature in this system is as high as 900 K. These findings open perspectives for applications in nano-domain magnetism and spintronics using oxide-based devices, for instance through the nano-engineering of oxygen vacancies at surfaces or interfaces of transition-metal oxides. PMID:27283225

  12. Impact of Fe on structural modification and room temperature magnetic ordering in BaTiO3

    NASA Astrophysics Data System (ADS)

    Rajan, Soumya; Gazzali, P. M. Mohammed; Chandrasekaran, G.

    2017-01-01

    Ba1 - xFexTiO3 (x = 0, 0.005, 0.01) polycrystalline ceramics are prepared using solid state reaction method. Structural studies through XRD, Raman and XPS confirm single tetragonal phase for BaTiO3 whereas a structural disorder tends to intervene with the introduction of smaller Fe ions which reduces the tolerance factor and tetragonality ratio. Grain size of the samples is estimated using SEM micrographs with ImageJ software and chemical composition is confirmed using EDX spectra. Raman spectra measured in the temperature range of 303 K to 573 K showers light on the structural phase transition exploiting a significant disappearance of the 306 cm- 1 mode. Further, structural analyses suggest the entry of Fe into the B-site upon increasing its concentration in BaTiO3. The dopant sensitive modes lying at around 640 cm- 1 and 650 cm- 1 are assigned to lattice strain. A reduction in ferroelectric to paraelectric transition temperature is observed with a transformation from diffused type to normal ferroelectric upon the increased Fe content. The oxidation state of Fe in the BaTiO3 lattice has been decided using EPR Spectra precisely. Room temperature magnetic ordering is observed in Fe substituted BaTiO3 using PPMS. The coexistence of ferroelectric and magnetic ordering is established in the present study for optimized Fe substituted BaTiO3.

  13. Recent advances in the microstructure design of materials for near room temperature magnetic cooling (invited)

    SciTech Connect

    Lyubina, Julia

    2011-04-01

    Successful operation of a magnetic cooling device depends crucially on the performance of active magnetic refrigerant material. Extensive research activity has been concentrated on optimizing the magnetic properties of these materials by chemical composition modification. Here, it is shown how the design of appropriate microstructure can be used to control the magnetic properties as well as mechanical stability of refrigerant materials experiencing a first-order magnetic phase transition. In particular, introducing porosity in LaFe{sub 13-x}Si{sub x} alloys provides long-term stability by sacrificing only a small fraction of the magnetocaloric effect and results in the desired reduction of the magnetic and thermal hysteresis by a factor of 5, as compared to bulk alloys. Reducing crystallite size down to the nanometer range is shown to substantially lower magnetic hysteresis. On the other hand, the magnetocaloric effect is weakened by about 40% and 60% in alloys with grain size of 70 and 44 nm, respectively.

  14. Room temperature polyesterification

    SciTech Connect

    Moore, J.S.; Stupp, S.I. . Dept. of Materials Science and Engineering)

    1990-01-01

    A new room temperature polymerization method has been developed for the synthesis of high molecular weight polyesters directly from carboxylic acids and phenols. The solution polymerization reaction proceeds under mild conditions, near neutral pH, and also avoids the use of preactivated acid derivatives for esterification. The reaction is useful in the preparation of isoregic ordered chains with translational polar symmetry and also in the polymerization of functionalized or chiral monomers. The conditions required for polymerization in the carbodiimide-based reaction included catalysis by the 1:1 molecular complex formed by 4-(dimethylamino)pyridine and p-toluenesulfonic acid. These conditions were established through studies on a model system involving esterification of p-toluic acid and p-cresol. Self-condensation of several hydroxy acid monomers by this reaction has produced routinely good yields of polyesters with molecular weights greater than 15,000. It is believed that the high extents of reaction required for significant degrees of polymerization result from suppression of the side reaction leading to N-acylurea. The utility of this reaction in the formation of polar chains from sensitive monomers is demonstrated hereby the polycondensation of a chiral hydroxy acid.

  15. system at room temperature

    NASA Astrophysics Data System (ADS)

    Li, Shaoyuan; Ma, Wenhui; Zhou, Yang; Chen, Xiuhua; Xiao, Yongyin; Ma, Mingyu; Zhu, Wenjie; Wei, Feng

    2014-04-01

    In this paper, the moderately and lightly doped porous silicon nanowires (PSiNWs) were fabricated by the `one-pot procedure' metal-assisted chemical etching (MACE) method in the HF/H2O2/AgNO3 system at room temperature. The effects of H2O2 concentration on the nanostructure of silicon nanowires (SiNWs) were investigated. The experimental results indicate that porous structure can be introduced by the addition of H2O2 and the pore structure could be controlled by adjusting the concentration of H2O2. The H2O2 species replaces Ag+ as the oxidant and the Ag nanoparticles work as catalyst during the etching. And the concentration of H2O2 influences the nucleation and motility of Ag particles, which leads to formation of different porous structure within the nanowires. A mechanism based on the lateral etching which is catalyzed by Ag particles under the motivation by H2O2 reduction is proposed to explain the PSiNWs formation.

  16. Magnetic circular dichroism studies of myoglobin, hemoglobin and peroxidase at room and low temperatures. Ferrous high spin derivatives.

    PubMed

    Sharonov, Y A; Mineyev, A P; Livshitz, M A; Sharonova, N A; Zhurkin, V B; Lysov, Y P

    1978-04-13

    The magnetic circular dichroism spectra (MCD) recorded for the visible and near-UV regions of high-spin ferrous derivatives of myoglobin, hemoglobin, hemoglobin dimers and isolated chains as well as of horseradish peroxidase at pH 6.8 and 11.4 have been compared at the room and liquid nitrogen temperatures. The MCD of the Q00- and QV-bands have been shown to be sensitive to structural differences in the heme environment of these hemoproteins. The room temperature visible MCD of native hemoglobin differs from that of myoglobin, hemoglobin dimers and isolated chains as well as from that of model pentacoordinated complex. The MCD of hemoglobin is characterized by the greater value of the MCD intensity ratio of derivative shape A-term in the Q00-band to the A-term in the QV-band. The evidneces are presented for the existence of two pH-dependent forms of ferroperoxidase, the neutral peroxidase shows the "hemoglobin-like" MCD, while the alkaline ferroperoxidase is characterized by the "myoglobin-like" MCD spectrum in the visible region. The differences in the MCD of deoxyhemoglobin and neutral ferroperoxidase as compared with other high-spin ferrous hemoproteins are considered to result from the constraints on heme group imposed by quaternary and/or tertiary protein structure. The differences between hemoporteins which are seen at the room temperature become more pronounced at liquid nitrogen temperature. Except the peak at approximately 580 nm in the MCD of deoxymyoglobin and reduced peroxidase at pH 11.4 the visible MCD does not show appreciable temperature dependent C-terms. The nature of the temperature dependent effect at approximately 580 nm is not clear. The Soret MCD of all hemoproteins studied are similar and are predominantly composed of the derivative-shaped C-terms as revealed by the increase of the MCD peaks approximately in accordance with Boltzmann distribution. The interpretation of temperature-dependent MCD observed for the Soret band has been made in

  17. Preparation of Soft Magnetic Fe-Ni-Pb-B Alloy Nanoparticles by Room Temperature Solid-Solid Reaction

    PubMed Central

    Zhong, Qin

    2013-01-01

    The Fe-Ni-Pb-B alloy nanoparticles was prepared by a solid-solid chemical reaction of ferric trichloride, nickel chloride, lead acetate, and potassium borohydride powders at room temperature. The research results of the ICP and thermal analysis indicate that the resultants are composed of iron, nickel, lead, boron, and PVP, and the component of the alloy is connected with the mole ratio of potassium borohydride and the metal salts. The TEM images show that the resultants are ultrafine and spherical particles, and the particle size is about a diameter of 25 nm. The largest saturation magnetization value of the 21.18 emu g−1 is obtained in the Fe-Ni-Pb-B alloy. The mechanism of the preparation reaction for the Fe-Ni-Pb-B multicomponent alloys is discussed. PMID:24348196

  18. Nanogranular metallic Fe oxygen deficient TiO2-δ composite films: a room temperature, highly carrier polarized magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Yoon, S. D.; Widom, A.; Miller, K. E.; McHenry, M. E.; Vittoria, C.; Harris, V. G.

    2008-05-01

    Nanogranular metallic iron (Fe) and titanium dioxide (TiO2-δ) were sequentially deposited on (100) lanthanum aluminate (LaAlO3) substrates in a low oxygen chamber pressure using a pulsed laser ablation deposition (PLD) technique. By sequential deposition, ≈10 nm diameter metallic Fe spherical grains were suspended within a TiO2-δ matrix. The films show ferromagnetic behavior with a saturation magnetization of 3100 G at room temperature. Our estimate of the saturation magnetization based on the size and distribution of the Fe spheres agreed with the measured value. The film composite structure was characterized as a p-type magnetic semiconductor at 300 K with a carrier density of the order of ≈1022 cm-3. The hole carriers were excited at the interface between the nanogranular Fe and TiO2-δ matrix, similar to holes excited in the metal/n-type semiconductor interface commonly observed in metal-oxide-semiconductor (MOS) devices. From the large anomalous Hall effect measured in these films, we observed that the holes at the interface were strongly spin polarized. Structure and magnetotransport properties suggested that these PLD films have potential spintronics applications.

  19. Oxygen-vacancy-induced room-temperature magnetization in lamellar V{sub 2}O{sub 5} thin films

    SciTech Connect

    Cezar, A. B.; Graff, I. L. Varalda, J.; Schreiner, W. H.; Mosca, D. H.

    2014-10-28

    In this work, we study the local atomic and electronic structures as well as oxygen-vacancy-induced magnetic properties of electrodeposited V{sub 2}O{sub 5} films. Unlike stoichiometric V{sub 2}O{sub 5}, which is a diamagnetic lamellar semiconductor, our oxygen-defective V{sub 2}O{sub 5} films are ferromagnetic at room-temperature and their saturation magnetization decreases with air exposure time. X-ray absorption spectroscopy was used to monitor the aging effect on these films, revealing that freshly-made samples exhibit only local crystalline order, whereas the aged ones undoubtedly show an enhancement of crystallinity and coordination symmetry. The mean number of oxygen atoms around V tends to increase, indicating a decrease of oxygen vacancies with time. Concurrently with the decrease of oxygen vacancies, a loss of saturation magnetization is also observed. Hence, it can be concluded that the ferromagnetism of the V{sub 2}O{sub 5} films originates from a vacancy-induced mechanism, confirming the universality of this class of ferromagnetism.

  20. Synthesis, sustained release properties of magnetically functionalized organic-inorganic materials: Amoxicillin anions intercalated magnetic layered double hydroxides via calcined precursors at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Liu, Qi; Zhang, Guangchun; Li, Zhanshuang; Yang, Piaoping; Jing, Xiaoyan; Zhang, Milin; Liu, Tianfu; Jiang, Zhaohua

    2009-09-01

    Zinc-aluminum-carbonate-layered double hydroxides (ZnAl-CO 3-LDHs), loaded with magnetic substrates (Fe 3O 4), were prepared for sustained drug-targeting delivery. From the X-ray diffraction results, it was found that the magnetic substrates were successfully incorporated with LDHs and highly dispersed in the hydrotalcite structure. After intercalation with an antibiotic drug (amoxicillin) by using a calcinations-reconstruction method, the basal spacing of layered double hydroxides increased from 7.51 Å to 12.35 Å, indicating that amoxicillin was successfully intercalated into the interlay space of LDHs as a monolayer. Furthermore, in vitro drug release experiments in pH 7.4 phosphate buffer solution (PBS) showed sustained release profiles with amoxicillin as a model drug. Magnetic measurements revealed that the composite possessed paramagnetic properties at room temperature.

  1. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature.

    PubMed

    Gao, Ya; Hu, Jia-Mian; Nelson, C T; Yang, T N; Shen, Y; Chen, L Q; Ramesh, R; Nan, C W

    2016-03-31

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface.

  2. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature

    NASA Astrophysics Data System (ADS)

    Gao, Ya; Hu, Jia-Mian; Nelson, C. T.; Yang, T. N.; Shen, Y.; Chen, L. Q.; Ramesh, R.; Nan, C. W.

    2016-03-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface.

  3. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature

    PubMed Central

    Gao, Ya; Hu, Jia-Mian; Nelson, C. T.; Yang, T. N.; Shen, Y.; Chen, L. Q.; Ramesh, R.; Nan, C. W.

    2016-01-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface. PMID:27029464

  4. Cobalt nanoparticles doped emaraldine salt of polyaniline: A promising room temperature magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Hatamie, Shadie; Kulkarni, M. V.; Kulkarni, S. D.; Ningthoujam, R. S.; Vatsa, R. K.; Kale, S. N.

    2010-12-01

    Incorporation of magnetic nanoparticles in polymers with organic functional groups working as semiconducting substrate is of immense interest in the field of dilute magnetic semiconductors (DMS) and spintronics. In this article we report on synthesis and evaluation of dilutely doped (0-10 wt%) cobalt nanoparticles in emaraldine salt (ES) of polyaniline in the presence of dodecyl benzene sulfonic acid (DBSA) and p-toluene sulfonic acid (p-TSA) using a sonochemical-assisted-reduction approach as a possible DMS candidate. The X-ray diffraction pattern and high resolution transmission electron microscopy (HRTEM) image show the ES to be polycrystalline, in which 10 nm sized Co nanoparticles get embedded in its FCC structural form. From Fourier transform infrared (FT-IR) and UV-visible (UV-vis) spectroscopy studies, it is predicted that cobalt particles get electrostatically bound to the specific SO3- ion sites of ES, thereby modifying torsional degrees of freedom of the system. The applied field dependent magnetization study shows that the sample exhibits hysteresis loop with a minimal doping of 3 wt% of Co nanoparticles and increases with the amount of Co nanoparticles in ES due to dipolar interaction. The electron transport data show that with increase in Co wt% there is a gradual shift from ohmic to non-ohmic response to the sample bias, accompanied by opening of electrical hysteresis and an increased resistance. The non-linear response of higher doped systems has been attributed to the combination of direct and Fowler-Nordheim tunneling phenomena in these systems. Persistence of optical and transport properties of the polymer, with an introduction of magnetic moment in the system, envisages the system to be a fine magnetic semiconductor.

  5. Room temperature ferroelectricity in one-dimensional single chain molecular magnets [{M(Δ)M(Λ)}(ox)2(phen)2]n (M = Fe and Mn)

    NASA Astrophysics Data System (ADS)

    Bhatt, Pramod; Mukadam, M. D.; Meena, S. S.; Mishra, S. K.; Mittal, R.; Sastry, P. U.; Mandal, B. P.; Yusuf, S. M.

    2017-03-01

    The ferroelectric materials are mainly focused on pure inorganic oxides; however, the organic molecule based materials have recently attracted great attention because of their multifunctional properties. The mixing of oxalate and phenanthroline ligands with metal ions (Fe or Mn) at room temperature followed by hydrothermal treatment results in the formation of one-dimensional single chain molecular magnets which exhibit room temperature dielectric and ferroelectric behavior. The compounds are chiral in nature, and exhibit a ferroelectric behavior, attributed to the polar point group C2, in which they crystallized. The compounds are also associated with a dielectric loss and thus a relaxation process. The observed electric dipole moment, essential for a ferroelectricity, has been understood quantitatively in terms of lattice distortions at two different lattice sites within the crystal structure. The studied single chain molecular magnetic materials with room temperature ferroelectric and dielectric properties could be of great technological importance in non-volatile memory elements, and high-performance insulators.

  6. Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature

    SciTech Connect

    Raut, Suyog A.; Kanhe, Nilesh S.; Bhoraskar, S. V.; Mathe, V. L.; Das, A. K.

    2014-10-28

    Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125–1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.

  7. Electric field-induced tuning of magnetism in PbFe{sub 0.5}Nb{sub 0.5}O{sub 3} at room temperature

    SciTech Connect

    Rayaprol, S. E-mail: brangadi@gmail.com; Mukherjee, S.; Kaushik, S. D.; Matteppanavar, S.; Angadi, B. E-mail: brangadi@gmail.com

    2015-08-07

    We study the influence of electrical poling, carried out at room temperature, on the structure and magnetism of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} by analyzing the differences observed in structural and magnetic properties before and after the electrical poling. The changes observed in magnetization of Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} before and after electrical poling exhibit considerably strong converse magnetoelectric effect at room temperature. In addition, the strengthening of Fe/Nb-O bond due to electrical poling is discussed on the basis of Raman spectral studies and analysis of neutron diffraction patterns. The potential tunability of magnetization with electrical poling can be an ideal tool for realization of application potential of this multiferroic material.

  8. Sub-nano tesla magnetic imaging based on room-temperature magnetic flux sensors with vibrating sample magnetometry

    NASA Astrophysics Data System (ADS)

    Adachi, Yoshiaki; Oyama, Daisuke

    2017-05-01

    We developed a two-dimensional imaging method for weak magnetic charge distribution using a commercially available magnetic impedance sensor whose magnetic field resolution is 10 pT/Hz1/2 at 10 Hz. When we applied the vibrating sample magnetometry, giving a minute mechanical vibration to the sample and detecting magnetic signals modulated by the vibration frequency, the effects of 1/f noise and the environmental low-frequency band noise were suppressed, and a weak magnetic charge distribution was obtained without magnetic shielding. Furthermore, improvement in the spatial resolution was also expected when the signals were demodulated at the second harmonic frequency of the vibration. In this paper, a preliminary magnetic charge imaging using the vibrating sample magnetometry and its results are demonstrated.

  9. Electrical bistability around room temperature in an unprecedented one-dimensional coordination magnetic polymer.

    PubMed

    Amo-Ochoa, Pilar; Delgado, Esther; Gómez-García, Carlos J; Hernández, Diego; Hernández, Elisa; Martin, Avelino; Zamora, Félix

    2013-05-20

    The synthesis, crystal structure, and physical properties of an unprecedented one-dimensional (1D) coordination polymer containing [Fe2(S2C6H2Cl2)4](2-) entities bridged by dicationic [K2(μ-H2O)2(THF)4](2+) units are described. The magnetic properties show that the title compound presents pairwise Fe-Fe antiferromagnetic interactions that can be well reproduced with a S = 1/2 dimer model with an exchange coupling, J = -23 cm(-1). The electrical conductivity measurements show that the title compound is a semiconductor with an activation energy of about 290 meV and two different transitions, both with large hysteresis of about 60 and 30 K at 260-320 K and 350-380 K, respectively. These two transitions are assumed to be due to slight structural changes in the cation-anion interactions. Differential Scanning Calorimetry confirms the presence of both transitions. This compound represents the first sample of a coordination polymer showing electrical bistability.

  10. Room temperature transparent conducting magnetic oxide (TCMO) properties in heavy ion doped oxide semiconductor

    NASA Astrophysics Data System (ADS)

    Lee, Juwon; Nagarajan, Ganapathi Subramaniam; Shon, Yoon; Kwon, Younghae; Kang, Tae Won; Kim, Deuk Yong; Kim, Hyungsang; Im, Hyunsik; Park, Chang-Soo; Kim, Eun Kyu

    2017-08-01

    Bismuth doped ZnO (ZnBi0.03O0.97) thin films are grown using pulsed laser deposition. The existence of positively charged Bi, absence of metallic zinc and the Zn-O bond formation in Bi doped ZnO are confirmed using X-ray Photoelectron Spectroscopy (XPS). Temperature dependent resistivity and UV-visible absorption spectra show lowest resistivity with 8.44 × 10-4 Ω cm at 300 K and average transmittance of 93 % in the visible region respectively. The robust ferromagnetic signature is observed at 350 K (7.156 × 10-4 emu/g). This study suggests that Bi doped ZnO films should be a potential candidate for spin based optoelectronic applications.

  11. Fast Room Temperature Very Low Field-Magnetic Resonance Imaging System Compatible with MagnetoEncephaloGraphy Environment

    PubMed Central

    Galante, Angelo; Sinibaldi, Raffaele; Conti, Allegra; De Luca, Cinzia; Catallo, Nadia; Sebastiani, Piero; Pizzella, Vittorio; Romani, Gian Luca; Sotgiu, Antonello; Della Penna, Stefania

    2015-01-01

    In recent years, ultra-low field (ULF)-MRI is being given more and more attention, due to the possibility of integrating ULF-MRI and Magnetoencephalography (MEG) in the same device. Despite the signal-to-noise ratio (SNR) reduction, there are several advantages to operating at ULF, including increased tissue contrast, reduced cost and weight of the scanners, the potential to image patients that are not compatible with clinical scanners, and the opportunity to integrate different imaging modalities. The majority of ULF-MRI systems are based, until now, on magnetic field pulsed techniques for increasing SNR, using SQUID based detectors with Larmor frequencies in the kHz range. Although promising results were recently obtained with such systems, it is an open question whether similar SNR and reduced acquisition time can be achieved with simpler devices. In this work a room-temperature, MEG-compatible very-low field (VLF)-MRI device working in the range of several hundred kHz without sample pre-polarization is presented. This preserves many advantages of ULF-MRI, but for equivalent imaging conditions and SNR we achieve reduced imaging time based on preliminary results using phantoms and ex-vivo rabbits heads. PMID:26630172

  12. Enhanced Room Temperature Ferromagnetism by Fe Doping in Zn0.96Cu0.04O Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Muthukumaran, S.; Ashokkumar, M.

    2016-02-01

    Zn0.96- x Cu0.04Fe x O (0 ≤ x ≤ 0.04) nanoparticles synthesized via the sol-gel technique had a hexagonal wurtzite ZnO structure without any Fe/Cu-related secondary phases. The crystallite size was reduced from Fe = 0% (23 nm) to Fe = 4% (16 nm) due to the suppression of grain surface growth by foreign impurities. Doping of higher Fe concentrations into Zn-Cu-O suppressed the ultra-violet (UV) emission band and balanced the defect-related visible emissions. The decrease of the UV and green emission intensity ratio ( I UV/ I green) and the UV and blue emission intensity ratio ( I UV/ I blue) in photoluminescence spectra implied an increase of defect states with the increase of Fe concentrations. All the samples showed clear room temperature ferromagnetism. The saturation magnetization was increased by Fe co-doping which was attributed to the interaction between Fe-Fe ions. X-ray photoelectron spectra confirmed the absence of secondary phases like Fe3O4.

  13. Magnetic-field-dependent spin decoherence and dephasing in room-temperature CdSe nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Fumani, A. Khastehdel; Berezovsky, J.

    2013-10-01

    We perform and analyze a series of time-resolved Faraday rotation measurements of coherent spin dynamics in a room-temperature ensemble of CdSe nanocrystal quantum dots (NCQDs) to study the decoherence and dephasing mechanisms that limit the transverse spin lifetime. Coherent spin lifetimes on the order of nanoseconds have been previously observed in CdSe NCQDs, but the presence of multiple components with distinct dynamics and strong inhomogeneous dephasing have made it difficult to study the relevant spin decay mechanisms quantitatively. Here, we obtain reliable fitting results by ensuring that cross-correlations between model parameters are minimized for the parameters of interest. Furthermore, we characterize the morphological inhomogeneity of the NCQD ensemble using transmission electron microscopy to constrain the model parameters that specify inhomogeneous dephasing. We find that g-factor inhomogeneity-induced dephasing (gID) is not sufficient to explain the magnetic-field-dependent decay of the spin signal. We propose an additional decoherence mechanism arising from rapid transitions between the fine structure states of the exciton referred to as fine-structure decoherence (FSD). By including both gID and FSD in the model, excellent fits are obtained to the data, including a prominent short-time-scale feature, which has typically been excluded from the fits in previous work.

  14. Optical detection of magnetic field with Mn4+:K2SiF6 phosphor from room to liquid helium temperatures

    NASA Astrophysics Data System (ADS)

    Zhong, Zhiqiang; Wang, Xia; Zhang, Junpei; Zhong, Haizheng; Han, Jun-Bo

    2017-05-01

    An optical method for detecting magnetic fields is developed based on the photoluminescence (PL) properties of a Mn4+:K2SiF6 phosphor. Under excitation by a 457-nm argon laser, strong red PL was observed in Mn4+:K2SiF6 microcrystals from room to liquid helium temperatures. The Lande factor (g) of the Zeeman splitting peaks remained close to 2 within the measured temperature range. These features make this Mn4+:K2SiF6 phosphor an idea optical material for remote sensing of high magnetic fields over a broad temperature range.

  15. Room-temperature switching of magnetic hysteresis by reversible single-crystal-to-single-crystal solvent exchange in imidazole-inspired Fe(ii) complexes.

    PubMed

    Huang, Wei; Shen, Fuxing; Zhang, Ming; Wu, Dayu; Pan, Feifei; Sato, Osamu

    2016-10-14

    The recent upsurge in molecular magnetism reflects its application in the areas of sensors and molecular switches. Thermal hysteresis is crucial to the molecular bistability and information storage, a wide hysteresis near room temperature is expected to be of practical sense for the molecular compound. In this work, spin crossover iron(ii) complexes [Fe(Liq)2](BF4)2·(CH3CH2)2O (1-Et2O) and [Fe(Liq)2](BF4)2·3H2O (1-3H2O) were prepared and structurally and magnetically analysed. The single-crystal-to-single-crystal (SCSC) solvation transformation and the influence on the crystal structures and magnetic hysteresis were investigated in an etherification-hydration cycle. At room temperature, X-ray diffraction experiments indicated a transformation from one crystal (1-Et2O, P21212) to another crystal (1-3H2O, P212121) upon humidity exposure and reversible recovery of its crystallinity upon exposure to ether vapor. The etherified phase 1-Et2O exhibits room temperature spin crossover (T1/2 = 305 K) but negligible thermal hysteresis, however the hydrated phase 1-3H2O exhibits the apparent hysteresis loop (T1/2↑ = 346 K, T1/2↓ = 326 K) which expands to room temperature. This effect is associated with the change of intermolecular cooperativity in the etherification-hydration recyclability.

  16. Toward room temperature superconductivity?

    PubMed Central

    Patel, C. K. N.; Dynes, R. C.

    1988-01-01

    The last 12 months have witnessed frenzied activity in condensed matter physics, unmatched by any other since the invention of the laser. In this article, we summarize the status, promise, and problems in the field of high-temperature superconductivity. We also comment on the mechanisms and policies needed for the United States to economically benefit from the recent discoveries in the face of what can be best described as an international race to win the battle. Images

  17. Giant magnetoresistance and superparamagnetism in Dy{sub x}Fe{sub 100-x} nanogranular magnetic thin films at room temperature

    SciTech Connect

    Mekala, Laxman Shameem, Muhammed P.V.; Singh, Dushyanth; Kumar, M. Senthil

    2016-05-06

    In this article, Dy{sub x}Fe{sub 100-x} nanogranular (15 ≤ x ≤ 25) thin films have been prepared at ambient temperature by dc magnetron sputtering. The correlation between the microstructure, magneto transport and magnetization properties is discussed. The grain size of Dy (Dysprosium) and Fe (Iron) was measured to be about 2 to 3 nm, respectively and the distribution of grains was homogenous throughout the sample. The magnetoresistance is sensitive to microstructural changes (particle size as well as Dy concentration). At the room temperature, the magnetoresistance [MR %] increased from 0.2 to 2.2 with increase in atomic concentration of Dy from x = 15 to 25 and we obtained maximum 2.2 MR [%] for x = 25 in this series of samples. The magnetization studies have revealed that all the samples are superparamagnetic (SPM) at room temperature.

  18. Free-standing and single-crystalline Fe(1-x)Mn(x)Si nanowires with room-temperature ferromagnetism and excellent magnetic response.

    PubMed

    Hung, Min-Hsiu; Wang, Chiu-Yen; Tang, Jianshi; Lin, Ching-Chun; Hou, Te-Chien; Jiang, Xiaowei; Wang, Kang L; Chen, Lih-Juann

    2012-06-26

    High-aspect-ratio Fe(1-x)Mn(x)Si nanowires with room-temperature ferromagnetism were synthesized by a chemical vapor deposition (CVD) method in one step. This is the first report of ternary silicide nanowires using magnetic Mn ions to partially replace metal sites in the host matrix. Here we report the excellent magnetic characteristics of Fe(1-x)Mn(x)Si nanowires, which exhibit strong ferromagnetism at room temperature and high magnetoresistance (MR) variation. As-synthesized Fe(1-x)Mn(x)Si nanowires show a hyperbranched morphology and a spin-disorder behavior. The strong spin interaction in Fe(1-x)Mn(x)Si nanowires, induced by the substitution of Fe sublattices for magnetic Mn ions, was revealed in the hysteresis loops. The magnetization versus magnetic field (M-H) curves of Fe(1-x)Mn(x)Si nanowires are much less sensitive to the temperature variation from 10 to 300 K than those of FeSi nanowires. Remarkably, the excellent MR performance, -41.6% at 25 K with a magnetic field of 9 T, was demonstrated in an individual Fe(0.88)Mn(0.12)Si nanowire.

  19. Room temperature terahertz polariton emitter

    SciTech Connect

    Geiser, Markus; Scalari, Giacomo; Castellano, Fabrizio; Beck, Mattias; Faist, Jerome

    2012-10-01

    Terahertz (THz) range electroluminescence from intersubband polariton states is observed in the ultra strong coupling regime, where the interaction energy between the collective excitation of a dense electron gas and a photonic mode is a significant portion of the uncoupled excitation energy. The polariton's increased emission efficiency along with a parabolic electron confinement potential allows operation up to room temperature in a nonresonant pumping scheme. This observation of room temperature electroluminescence of an intersubband device in the THz range is a promising proof of concept for more powerful THz sources.

  20. Room temperature ferromagnetism in single-phase Zn1- x Mn x S diluted magnetic semiconductors fabricated by co-precipitation technique

    NASA Astrophysics Data System (ADS)

    Hassan, M.; Younas, S.; Sher, F.; Husain, S. S.; Riaz, S.; Naseem, S.

    2017-05-01

    In this study, we have prepared Mn-doped zinc sulfide diluted magnetic semiconductors with varying manganese concentrations ( x Mn = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10 mol%) using co-precipitation method. The single-phase nano-crystalline Zn1 - x Mn x S powders have been confirmed with X-ray diffraction. The residual strains also have been calculated, and have been observed to affect the lattice constants. The surface morphology is investigated with scanning electron microscopy, which illustrates the presence of smaller grains, which coalescence to form larger grains. The presence of the ferromagnetism at room temperature has been observed; however, significant paramagnetic contribution is also present. The observed weak ferromagnetism might be due to the structural and surface imperfections. The single-phase Zn1 - x Mn x S exhibiting magnetism at room temperature evidences the potential spintronic applications.

  1. Investigation of multiferroicity, spin-phonon coupling, and unusual magnetic ordering close to room temperature in LuMn0.5Fe0.5O3

    NASA Astrophysics Data System (ADS)

    Sarkar, Tanushree; Manna, Kaustuv; Elizabeth, Suja; Anil Kumar, P. S.

    2017-02-01

    We report the detailed experimental characteristics of LuMn0.5Fe0.5O3 synthesized by the wet chemical method and proclaim it as a new member of the multiferroic family. The compound stabilizes in P63cm crystal symmetry. It exhibits a spin re-orientation transition at TSR and an antiferromagnetic transition at TN. In addition, our magnetization vs. temperature data reveals an extra broad maximum close to room temperature; unseen in earlier studies. By invoking the compatible nature of the magnetic exchange path in P63cm symmetry, we have argued that the origin lies in the intraplane short-range spin ordering. Heat capacity is measured and analysed to elucidate the magnetic entropy. Though long-range antiferromagnetic ordering vanishes at TN ˜ 103 K, we find the experimental magnetic entropy calculated till 200 K is less by a significant amount from the value of theoretical spin randomization magnetic entropy; further supporting the existence of spin ordering beyond TN and even above 200 K. While the specific heat data and phonon modes of Raman spectra show a signature of spin-phonon coupling at TSR and TN both, dielectric anomaly indicating a magnetoelectric effect is seen only at TN. Piezoresponse force microscopy and ferroelectric hysteresis loop measurement confirm the room-temperature weak ferroelectricity with a saturation polarization value 0.007 μC/cm2 and low coercive field. Furthermore high-temperature dielectric characteristics reveal the ferroelectric transition at around 900 K and exhibit Maxwell-Wagner type relaxation. The present work serves as a bridge between h-RMnO3 and rare earth ferrite RFeO3. It assumes significance in the light of recent research developments in hexagonal RFeO3 (mainly h-LuFeO3) in the context of room-temperature multiferroicity and magnetoelectricity.

  2. Magnetic properties of nitrogen-doped ZrO2: Theoretical evidence of absence of room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Albanese, Elisa; Leccese, Mirko; di Valentin, Cristiana; Pacchioni, Gianfranco

    2016-08-01

    N-dopants in bulk monoclinic ZrO2 and their magnetic interactions have been investigated by DFT calculations, using the B3LYP hybrid functional. The electronic and magnetic properties of the paramagnetic N species, substitutionals and interstitials, are discussed. Their thermodynamic stability has been estimated as a function of the oxygen partial pressure. At 300 K, N prefers interstitial sites at any range of oxygen pressure, while at higher temperatures (700–1000 K), oxygen poor-conditions facilitate substitutional dopants. We have considered the interaction of two N defects in various positions in order to investigate the possible occurrence of ferromagnetic ordering. A very small magnetic coupling constant has been calculated for several 2N-ZrO2 configurations, thus demonstrating that magnetic ordering can be achieved only at very low temperatures, well below liquid nitrogen. Furthermore, when N atoms replace O at different sites, resulting in slightly different positions of the corresponding N 2p levels, a direct charge transfer can occur between the two dopants with consequent quenching of the magnetic moment. Another mechanism that contributes to the quenching of the N magnetic moments is the interplay with oxygen vacancies. These effects contribute to reduce the concentration of magnetic impurities, thus limiting the possibility to establish magnetic ordering.

  3. Magnetic properties of nitrogen-doped ZrO2: Theoretical evidence of absence of room temperature ferromagnetism

    PubMed Central

    Albanese, Elisa; Leccese, Mirko; Di Valentin, Cristiana; Pacchioni, Gianfranco

    2016-01-01

    N-dopants in bulk monoclinic ZrO2 and their magnetic interactions have been investigated by DFT calculations, using the B3LYP hybrid functional. The electronic and magnetic properties of the paramagnetic N species, substitutionals and interstitials, are discussed. Their thermodynamic stability has been estimated as a function of the oxygen partial pressure. At 300 K, N prefers interstitial sites at any range of oxygen pressure, while at higher temperatures (700–1000 K), oxygen poor-conditions facilitate substitutional dopants. We have considered the interaction of two N defects in various positions in order to investigate the possible occurrence of ferromagnetic ordering. A very small magnetic coupling constant has been calculated for several 2N-ZrO2 configurations, thus demonstrating that magnetic ordering can be achieved only at very low temperatures, well below liquid nitrogen. Furthermore, when N atoms replace O at different sites, resulting in slightly different positions of the corresponding N 2p levels, a direct charge transfer can occur between the two dopants with consequent quenching of the magnetic moment. Another mechanism that contributes to the quenching of the N magnetic moments is the interplay with oxygen vacancies. These effects contribute to reduce the concentration of magnetic impurities, thus limiting the possibility to establish magnetic ordering. PMID:27527493

  4. Room-temperature ferromagnetism in Zn{sub 1-x}Co{sub x}O magnetic semiconductors prepared by sputtering

    SciTech Connect

    Dinia, A.; Schmerber, G.; Meny, C.; Pierron-Bohnes, V.; Beaurepaire, E.

    2005-06-15

    We have used magnetron cosputtering to grow Zn{sub 1-x}Co{sub x}O magnetic dilute semiconductors. The growth has been performed on SiO{sub 2}/Si and Al{sub 2}O{sub 3}(0001) substrates. The Co concentration has been varied between 0.1 and 0.25 and the substrate temperature between room temperature and 600 deg. C. X-ray diffraction analysis has shown that for the films grown on Si substrates the structural quality of the film is improved by increasing the growth temperature and/or postgrowth annealing. The films are textured with c axis of the wurtzite structure along the growth direction. However, for the films grown on Al{sub 2}O{sub 3} substrate quasi-epitaxial films have been obtained for 600 deg. C substrate temperature. Magnetization measurements have shown that the ferromagnetism is directly correlated to the structural quality and appears by increasing the growth temperature and/or postgrowth annealing. Moreover, for the highly textured film a clear magnetic perpendicular anisotropy has been evidenced with the easy magnetization axis along the growth direction. To evidence the intrinsic nature of the ferromagnetism in the films, transmission optical measurements have been used. They show three absorption bands that are characteristics of d-d transitions of tetrahedrally coordinated Co{sup 2+}. This has been supported by nuclear magnetic resonance and magnetic thermal variation.

  5. Bi and InSb Nano-Hall Probes for direct magnetic imaging with Room Temperature Scanning Hall Probe Microscopy(RT-SHPM)

    NASA Astrophysics Data System (ADS)

    Oral, Ahmet; Dede, Munir; Sandhu, Adarsh; Masuda, Hiroshi; Bending, Simon J.

    2002-03-01

    Scanning Hall Probe Microscopy (SHPM)[1] is a quantitative and non-invasive technique to image magnetic samples with high spatial and magnetic field resolution: ~ 120nm & 60mG/Hz^1/2 at room temperature. A nano-Hall probe is scanned over the sample surface to measure the surface magnetic fields using conventional scanning tunneling microscopy-positioning techniques. We have developed new down to ~120x120nm size Bi and InSb Hall probes machined FIB milling. 120nm Bi sensors[2] have a sensitivity of 3.3x10-4 Ω/G and a noise level of 7.2 G/Hz^1/2 . The new InSb sensors have a sensitivity of 0.03 Ω/G and a noise level of 8 mG/Hz^1/2 at room temperature. This corresponds to ×8 better noise performance compared to conventional GaAs, based sensors used in RT-SHPM. We used these new sensors to study magnetic domain structures of crystalline garnet films and Ni_80Fe_20 rectangular permalloy microstructures microfabricated by lift-off technique. Bi and InSb nano-Hall probes are shown to be high spatial resolution, high sensitivity and low noise alternatives to GaAs sensors for RT-SHPM. There seems to be more room for improving the spatial resolution down to <50nm and the noise of Hall probes to 1mG/Hz^1/2 at room temperature. [1] A. Oral et. al. Appl. Phys. Lett., 69, 1324 (1996), A. Sandhu et. al., Jpn. J. Appl. Phys. 40(5B), L524 (2001) [2] A. Sandhu, H. Masuda, K. Kurosawa K, A. Oral and S.J. Bending, Electronics Letters 37 (22), 1335-1336 (2001).

  6. Demagnetization of magnetically shielded rooms

    SciTech Connect

    Thiel, F.; Schnabel, A.; Knappe-Grueneberg, S.; Stollfuss, D.; Burghoff, M.

    2007-03-15

    Magnetically shielded rooms for specific high resolution physiological measurements exploiting the magnetic field, e.g., of the brain (dc-magnetoencephalograpy), low-field NMR, or magnetic marker monitoring, need to be reproducibly demagnetized to achieve reliable measurement conditions. We propose a theoretical, experimental, and instrumental base whereupon the parameters which affect the quality of the demagnetization process are described and how they have to be handled. It is demonstrated how conventional demagnetization equipment could be improved to achieve reproducible conditions. The interrelations between the residual field and the variability at the end of the demagnetization process are explained on the basis of the physics of ferromagnetism and our theoretical predictions are evaluated experimentally.

  7. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy

    SciTech Connect

    Goschew, A. Scott, M.; Fumagalli, P.

    2016-08-08

    We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.

  8. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Goschew, A.; Scott, M.; Fumagalli, P.

    2016-08-01

    We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.

  9. Large magnetic response in (Bi4Nd)Ti3(Fe0.5Co0.5)O15 ceramic at room-temperature

    NASA Astrophysics Data System (ADS)

    Yang, F. J.; Su, P.; Wei, C.; Chen, X. Q.; Yang, C. P.; Cao, W. Q.

    2011-12-01

    Ceramics of Nd/Co co-substituted Bi5Ti3FeO15, i.e., (Bi4Nd)Ti3(Fe0.5Co0.5)O15 were prepared by the conventional solid-state reaction method. The X-ray diffraction pattern demonstrates that the sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi2Ti2O7 also existed. The ferroelectric and magnetic Curie temperatures were determined to be 1077 K and 497 K, respectively. The multiferroic property of the sample at room temperature was demonstrated by ferroelectric and magnetic measurements. Remarkably, by Nd/Co co-substituting, the sample exhibited large magnetic response with 2Mr = 330 memu/g and 2Hc = 562 Oe at applied magnetic field of 8 kOe at room temperature. The present work suggests the possibility of doped Bi5Ti3FeO15 as a potential multiferroic.

  10. The magnetic phase diagram and large reversible room-temperature magnetocaloric effect in antiperovskite compounds Zn1-xSnxCFe3 (0 ≤ x ≤ 1)

    NASA Astrophysics Data System (ADS)

    Lin, S.; Wang, B. S.; Tong, P.; Huang, Y. N.; Huang, Z. H.; Liu, Y.; Tan, S. G.; Lu, W. J.; Zhao, B. C.; Song, W. H.; Sun, Y. P.

    2012-09-01

    We report the magnetic phase diagram of antiperovskite compounds Zn1-xSnxCFe3 (0 ≤ x ≤ 1). The effects of the ratio of Zn/Sn on the structure, magnetic and electrical transport properties have been investigated systematically. With increasing the Sn content x, the lattice constant increases while both the Curie temperature (TC) and the saturated magnetization decrease gradually. All the resistivity curves of Zn1-xSnxCFe3 show a metal-like behavior in measured temperature range (2-350 K). In particular, the T2-power-law dependence of the electrical resistivity is obtained at low temperatures for all samples with x ≤ 0.3. It is noteworthy that, for x = 0.1, the TC is tuned just at the room temperature (˜300 K). Around TC, the magnetocaloric effect is considerably large with a magnetic entropy change of 2.78 J/kg K (ΔH = 45 kOe) as well as a relative cooling power (RCP) of 320 J/kg (ΔH = 45 kOe). Considering the considerably large RCP, suitable working temperature, inexpensive and innoxious raw materials, Zn0.9Sn0.1CFe3 is suggested to be a promising candidate for practical application in magnetic refrigeration.

  11. Room-Temperature Ferromagnetism of Cu-Doped ZnO Films Probed by Soft X-Ray Magnetic Circular Dichroism

    SciTech Connect

    Herng, T.S.; Ku, W.; Qi, D.-C.; Berlijn, T.; Yi, J.B.; Yang, K.S.; Dai, Y.; Feng, Y.P.; Santoso, I.; Sanchez-Hanke, C.; Gao, X.Y.; Wee, A.T.S.; Ding, J.; Rusydi, A.

    2010-11-08

    We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu{sup 2+} ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V{sub O}) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic 'indirect double-exchange' model, in which alignments of localized large moments of Cu in the vicinity of the V{sub O} are mediated by the large-sized vacancy orbitals.

  12. Polariton condensates at room temperature

    NASA Astrophysics Data System (ADS)

    Guillet, Thierry; Brimont, Christelle

    2016-10-01

    We review the recent developments of the polariton physics in microcavities featuring the exciton-photon strong coupling at room temperature, and leading to the achievement of room-temperature polariton condensates. Such cavities embed active layers with robust excitons that present a large binding energy and a large oscillator strength, i.e. wide bandgap inorganic or organic semiconductors, or organic molecules. These various systems are compared, in terms of figures of merit and of common features related to their strong oscillator strength. The various demonstrations of polariton laser are compared, as well as their condensation phase diagrams. The room-temperature operation indeed allows a detailed investigation of the thermodynamic and out-of-equilibrium regimes of the condensation process. The crucial role of the spatial dynamics of the condensate formation is discussed, as well as the debated issue of the mechanism of stimulated relaxation from the reservoir to the condensate under non-resonant excitation. Finally the prospects of polariton devices are presented.

  13. Room temperature neutron diffraction, optical and magnetic properties of Co(Cr1-xMnx)2O4 (x =0.0 and 0.30)

    NASA Astrophysics Data System (ADS)

    Kumar, Ram; Padam, R.; Rayaprol, S.; Siruguri, V.; Pal, D.

    2017-05-01

    We report here the effect of 30% Mn substitution on structure and magnetic properties of multiferroic CoCr2O4. Room temperature neutron diffraction studies were carried out on polycrystalline Co(Cr1-xMnx)2O4 (x=0.00 and 0.30) samples to determine structural properties. It has been observed that 30% Mn substitution for Cr in CoCr2O4 leads to increase in the ferrimagnetic transition temperature, (Tc) from ˜96 K to ˜114 K along with the magneto-structural transition temperature, (Ts) from ˜26 K to ˜32 K. In addition, optical properties were studied by UV-visible technique in the range of 200-800 nm. The energy band gap is found to decrease in compare to parent compound. Both magnetization and band gap variation can be explained using the spin-exchange interactions present in these systems.

  14. Band-edge exciton transitions in (Ga 1- xMn x)N diluted magnetic semiconductor films with above room temperature ferromagnetic transition

    NASA Astrophysics Data System (ADS)

    Jeon, H. C.; Kang, T. W.; Kim, T. W.; Cho, Y. H.

    2006-06-01

    (Ga 1- xMn x)N thin films grown on GaN buffer layers by using molecular beam epitaxy were investigated with the goal of producing diluted magnetic semiconductors (DMSs) with band-edge exciton transitions for applications in optomagnetic devices. The magnetization curve as a function of the magnetic field at 5 K indicated that ferromagnetism existed in the (Ga 1- xMn x)N thin films, and the magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature of the (Ga 1- xMn x)N thin film was above room temperature. Photoluminescence and photoluminescence excitation spectra showed that band-edge exciton transitions in (Ga 1- xMn x)N thin films appeared. These results indicate that the (Ga 1- xMn x)N DMSs with a magnetic single phase hold promise for potential applications in spin optoelectronic devices in the blue region of the spectrum.

  15. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Room-Temperature Anisotropic Ferromagnetism in Fe-Doped In2O3 Heteroepitaxial Films

    NASA Astrophysics Data System (ADS)

    Xing, Peng-Fei; Chen, Yan-Xue; Tang, Min-Jian; Yan, Shi-Shen; Liu, Guo-Lei; Mei, Liang-Mo; Jiao, Jun

    2009-11-01

    Fe-doped In2O3 films are grown epitaxially on YSZ (100) substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the (100) direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2.5kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.

  16. Room Temperature Ferromagnetic Mn:Ge(001)

    PubMed Central

    Lungu, George Adrian; Stoflea, Laura Elena; Tanase, Liviu Cristian; Bucur, Ioana Cristina; Răduţoiu, Nicoleta; Vasiliu, Florin; Mercioniu, Ionel; Kuncser, Victor; Teodorescu, Cristian-Mihail

    2014-01-01

    We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed. PMID:28788444

  17. Room temperature optically detected magnetic resonance (photoluminescence detected magnetic resonance) of radical ion pairs induced by vacuum ultraviolet in thin polymeric films

    SciTech Connect

    Verkhovlyuk, V. N. Anisimov, O. A.; Fedotov, K. Yu.

    2016-05-15

    A setup for recording optically detected electron paramagnetic resonance spectra of radical ions involved in geminate recombination and generated by vacuum ultraviolet is described. The setup allows registration of EPR spectra from short-lived radical ions in polymeric films at room temperature by recombination fluorescence modulated by a resonance microwave field.

  18. Room-temperature magnetic topological Weyl fermion and nodal line semimetal states in half-metallic Heusler Co2TiX (X=Si, Ge, or Sn)

    NASA Astrophysics Data System (ADS)

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Singh, Bahadur; Hsu, Chuang-Han; Bian, Guang; Alidoust, Nasser; Belopolski, Ilya; Sanchez, Daniel S.; Zhang, Songtian; Lin, Hsin; Hasan, M. Zahid

    2016-12-01

    Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal states in the ferromagnetic half-metal compounds Co2TiX (X = Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, in the absence of spin-orbit coupling, Co2TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperature, but also suggest potential applications such as unusual anomalous Hall effect in engineered monolayers of the Co2TiX compounds at high temperature.

  19. Room-temperature magnetic topological Weyl fermion and nodal line semimetal states in half-metallic Heusler Co2TiX (X=Si, Ge, or Sn)

    DOE PAGES

    Chang, Guoqing; Xu, Su -Yang; Zheng, Hao; ...

    2016-12-15

    Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal states in the ferromagnetic half-metal compounds Co2TiX (X = Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, inmore » the absence of spin-orbit coupling, Co2TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Lastly, our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperature, but also suggest potential applications such as unusual anomalous Hall effect in engineered monolayers of the Co2TiX compounds at high temperature.« less

  20. Room-temperature magnetic topological Weyl fermion and nodal line semimetal states in half-metallic Heusler Co2TiX (X=Si, Ge, or Sn)

    PubMed Central

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Singh, Bahadur; Hsu, Chuang-Han; Bian, Guang; Alidoust, Nasser; Belopolski, Ilya; Sanchez, Daniel S.; Zhang, Songtian; Lin, Hsin; Hasan, M. Zahid

    2016-01-01

    Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal states in the ferromagnetic half-metal compounds Co2TiX (X = Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, in the absence of spin-orbit coupling, Co2TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperature, but also suggest potential applications such as unusual anomalous Hall effect in engineered monolayers of the Co2TiX compounds at high temperature. PMID:27974837

  1. Room-temperature magnetic topological Weyl fermion and nodal line semimetal states in half-metallic Heusler Co2TiX (X=Si, Ge, or Sn).

    PubMed

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Singh, Bahadur; Hsu, Chuang-Han; Bian, Guang; Alidoust, Nasser; Belopolski, Ilya; Sanchez, Daniel S; Zhang, Songtian; Lin, Hsin; Hasan, M Zahid

    2016-12-15

    Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal states in the ferromagnetic half-metal compounds Co2TiX (X = Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, in the absence of spin-orbit coupling, Co2TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperature, but also suggest potential applications such as unusual anomalous Hall effect in engineered monolayers of the Co2TiX compounds at high temperature.

  2. Room-temperature solid-state maser.

    PubMed

    Oxborrow, Mark; Breeze, Jonathan D; Alford, Neil M

    2012-08-16

    The invention of the laser has resulted in many innovations, and the device has become ubiquitous. However, the maser, which amplifies microwave radiation rather than visible light, has not had as large an impact, despite being instrumental in the laser's birth. The maser's relative obscurity has mainly been due to the inconvenience of the operating conditions needed for its various realizations: atomic and free-electron masers require vacuum chambers and pumping; and solid-state masers, although they excel as low-noise amplifiers and are occasionally incorporated in ultrastable oscillators, typically require cryogenic refrigeration. Most realizations of masers also require strong magnets, magnetic shielding or both. Overcoming these various obstacles would pave the way for improvements such as more-sensitive chemical assays, more-precise determinations of biomolecular structure and function, and more-accurate medical diagnostics (including tomography) based on enhanced magnetic resonance spectrometers incorporating maser amplifiers and oscillators. Here we report the experimental demonstration of a solid-state maser operating at room temperature in pulsed mode. It works on a laboratory bench, in air, in the terrestrial magnetic field and amplifies at around 1.45 gigahertz. In contrast to the cryogenic ruby maser, in our maser the gain medium is an organic mixed molecular crystal, p-terphenyl doped with pentacene, the latter being photo-excited by yellow light. The maser's pumping mechanism exploits spin-selective molecular intersystem crossing into pentacene's triplet ground state. When configured as an oscillator, the solid-state maser's measured output power of around -10 decibel milliwatts is approximately 100 million times greater than that of an atomic hydrogen maser, which oscillates at a similar frequency (about 1.42 gigahertz). By exploiting the high levels of spin polarization readily generated by intersystem crossing in photo-excited pentacene and other

  3. Manipulation of magnetism in perpendicularly magnetized Heusler alloy Co2FeAl0.5Si0.5 by electric-field at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, H. L.; Wu, Y.; Yu, H. J.; Jiang, Y.; Zhao, J. H.

    2016-09-01

    The electrical manipulation of magnetic properties in perpendicularly magnetized Co2FeAl0.5Si0.5 ultra-thin films has been investigated. An electric-field is applied by utilizing either a solid-state dielectric HfO2 film or an ionic gel film as the gate insulator in the form of a field effect parallel capacitor. Obvious changes of the coercive field and Curie temperature (˜24 K) by gating voltage are observed for a 0.8 nm thick film, while a clear change of the magnetic anisotropy is obtained for the 1.1 nm thick one. The experimental results have been attributed to both the electric-field-induced modulation of carrier density near the interface and the oxidation-reduction effect inside the magnetic films.

  4. 80% tunneling magnetoresistance at room temperature for thin Al-O barrier magnetic tunnel junction with CoFeB as free and reference layers

    NASA Astrophysics Data System (ADS)

    Wei, H. X.; Qin, Q. H.; Ma, M.; Sharif, R.; Han, X. F.

    2007-05-01

    Magnetic tunnel junctions (MTJs) with structures of Ta(5)/Cu(10)/Ta(5)/Ir21Mn79(10)/Co75Fe25(2)/Ru(0.75)/Co40Fe40B20(3)/Al(0.6)-O /Co40Fe40B20(2.5)/Ta(3)/Ru(7) (units in nanometers) were deposited via ultrahigh vacuum magnetron sputtering (ULVAC). Microscale ring-type magnetic tunnel junctions (RMTJs) with an outer radius of 2μm and an inner radius of 1μm were patterned using standard UV lithography combined with ion milling. Both reference and free layers were Co40Fe40B20 and a very thin Al-O (0.6nm) barrier layer was used. Tunneling magnetoresistances (TMRs) of up to 81% at room temperature and 107% at 4.2K were observed. These RMTJs with high TMR and low coercivity, of about 26Oe, combined with the ring-type geometry, which greatly reduces stray magnetic field, are ideal for certain magnetic field sensor applications.

  5. Topological Insulators at Room Temperature

    SciTech Connect

    Zhang, Haijun; Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-25

    Topological insulators are new states of quantum matter with surface states protected by the time-reversal symmetry. In this work, we perform first-principle electronic structure calculations for Sb{sub 2}Te{sub 3}, Sb{sub 2}Se{sub 3}, Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} crystals. Our calculations predict that Sb{sub 2}Te{sub 3}, Bi{sub 2}T e{sub 3} and Bi{sub 2}Se{sub 3} are topological insulators, while Sb{sub 2}Se{sub 3} is not. In particular, Bi{sub 2}Se{sub 3} has a topologically non-trivial energy gap of 0.3eV , suitable for room temperature applications. We present a simple and unified continuum model which captures the salient topological features of this class of materials. These topological insulators have robust surface states consisting of a single Dirac cone at the {Lambda} point.

  6. Ultrahigh magnetoresistance at room temperature in molecular wires.

    PubMed

    Mahato, R N; Lülf, H; Siekman, M H; Kersten, S P; Bobbert, P A; de Jong, M P; De Cola, L; van der Wiel, W G

    2013-07-19

    Systems featuring large magnetoresistance (MR) at room temperature and in small magnetic fields are attractive owing to their potential for applications in magnetic field sensing and data storage. Usually, the magnetic properties of materials are exploited to achieve large MR effects. Here, we report on an exceptionally large (>2000%), room-temperature, small-field (a few millitesla) MR effect in one-dimensional, nonmagnetic systems formed by molecular wires embedded in a zeolite host crystal. This ultrahigh MR effect is ascribed to spin blockade in one-dimensional electron transport. Its generic nature offers very good perspectives to exploit the effect in a wide range of low-dimensional systems.

  7. Influence of pulsating magnetic field on softening behavior of cold rolled AISI 4340 steel at room temperature

    SciTech Connect

    Prasad, S.N.; Singh, P.N.; Singh, V.

    1996-06-15

    The mechanical behavior of a ferromagnetic material is influenced by presence of magnetic field. The rate of stress relaxation in nickel increases by a.c. magnetic field of 11 Oersted (Oe) and 60 Hz. The application of 800 Oe steady magnetic field accelerates the process of creeping in high purity iron. The purpose of the present investigation was to examine the influence of pulsating magnetic field of 942 Oe, produced by a.c. current (50Hz), on the softening behavior of AISI 4340 steel, cold rolled to 20, 60, and 80%.

  8. Room temperature magnetic ordering, enhanced magnetization and exchange bias of GdMnO3 nanoparticles in (GdMnO3)0.70(CoFe2O4)0.30

    NASA Astrophysics Data System (ADS)

    Mitra, A.; Mahapatra, A. S.; Mallick, A.; Chakrabarti, P. K.

    2017-02-01

    Nanoparticles of GdMnO3 (GMO) are prepared by sol-gel method. To enhance the magnetic property and also to obtain the magnetic ordering at room temperature (RT), nanoparticles of GMO are incorporated in the matrix of CoFe2O4 (CFO). Desired crystallographic phases of CFO, GMO and GMO-CFO are confirmed by analyzing X-ray diffractrograms (XRD) using Rietveld method. The average size of nanoparticles and their distribution, crystallographic phase, nanocrystallinity etc. are studied by high-resolution transmission electron microscope (HRTEM). Magnetic hysteresis loops (M-H) of GMO-CFO under zero field cooled (ZFC) and field cooled (FC) conditions are observed at different temperatures down to 5 K. Magnetization vs. temperature (M-T) under ZFC and FC conditions are also recorded. Interestingly, exchange bias (EB) is found at low temperature which suggests the encapsulation of the ferromagnetic (FM) nanoparticles of GMO by the ferrimagnetic nanoparticles of CFO below 100 K. Enhanced magnetization, EB effect and RT magnetic ordering of GMO-CFO would be interesting for both theoretical and experimental investigations.

  9. Magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations and tunnel magnetoresistance effect at room temperature

    SciTech Connect

    Nagahama, Taro Matsuda, Yuya; Tate, Kazuya; Kawai, Tomohiro; Takahashi, Nozomi; Hiratani, Shungo; Watanabe, Yusuke; Yanase, Takashi; Shimada, Toshihiro

    2014-09-08

    Fe{sub 3}O{sub 4} is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe{sub 3}O{sub 4} electrodes have demonstrated a small tunnel magnetoresistance (TMR) effect. Not even the sign of the tunnel magnetoresistance ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe{sub 3}O{sub 4}(110) films exhibited in-plane uniaxial magnetic anisotropy. With respect to the squareness of hysteresis, Fe{sub 3}O{sub 4} (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe{sub 3}O{sub 4}(110) electrodes and obtained a TMR effect of −12% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe{sub 3}O{sub 4} predicted from band calculations.

  10. Toward room temperature ferromagnetism of Ge:Mn systems

    NASA Astrophysics Data System (ADS)

    D'Orazio, F.; Lucari, F.; Pinto, N.; Morresi, L.; Murri, R.

    2004-05-01

    We investigate the magnetic properties of Mn xGe 1- x/Ge(1 0 0) films. We show that the choice of growth temperature and Mn content is crucial for achieving optimal magnetic performance. With a substrate temperature of 160°C during film deposition, and Mn concentration between 2.7% and 4.4%, hysteresis is observed up to about 250 K. However, the magnetic loop maintains a saturating behaviour at high fields up to room temperature. For larger Mn concentrations the magnetic response is strongly suppressed, suggesting a possible segregation of manganese.

  11. Magneto-optical controlled transmittance alteration of PbS quantum dots by moderately applied magnetic fields at room temperature

    NASA Astrophysics Data System (ADS)

    Singh, Akhilesh K.; Barik, Puspendu; Ullrich, Bruno

    2014-12-01

    We observed changes of the transmitted monochromatic light passing through a colloidal PbS quantum dot film on glass owing to an applied moderate (smaller than 1 T) magnetic field under ambient conditions. The observed alterations show a square dependence on the magnetic field increase that cannot be achieved with bulk semiconductors. The findings point to so far not recognized application potentials of quantum dots.

  12. Magneto-optical controlled transmittance alteration of PbS quantum dots by moderately applied magnetic fields at room temperature

    SciTech Connect

    Singh, Akhilesh K.; Barik, Puspendu; Ullrich, Bruno E-mail: bruno.ullrich@yahoo.com

    2014-12-15

    We observed changes of the transmitted monochromatic light passing through a colloidal PbS quantum dot film on glass owing to an applied moderate (smaller than 1 T) magnetic field under ambient conditions. The observed alterations show a square dependence on the magnetic field increase that cannot be achieved with bulk semiconductors. The findings point to so far not recognized application potentials of quantum dots.

  13. Electronic structure, optical and magnetic studies of PLD-grown (Mn, P)-doped ZnO nanocolumns at room temperature

    NASA Astrophysics Data System (ADS)

    Phan, The-Long; Ho, T. A.; Dang, N. T.; Nguyen, Manh Cuong; Dao, Van-Duong

    2017-07-01

    We prepared well-aligned Zn1-x Mn x O:yP nanocolumns (x  =  0-0.02, and y  =  0 and 1 mol%) on SiO2/Si(0 0 1) substrates by using pulsed laser deposition (PLD) and then investigated their electronic structure and optical and magnetic properties at room temperature. The analyses of x-ray photoelectron and x-ray absorption fine structure spectra revealed Mn2+ and/or P ions existing in nanocolumns, where Mn2+ ions are situated in the Zn2+ site of the ZnO-wurtzite structure. Although the incorporation of Mn2+ and/or P ions did not form secondary phases, as confirmed by x-ray and electron diffraction patterns, more lattice defects were created, and consequently changed the band-gap energy as well as the electron-phonon interactions in the nanocolumns. Magnetization versus magnetic-field measurements revealed that all the samples exhibited FM order. In particular, the (Mn, P) co-doping with x  =  0.02 and y  =  1 remarkably enhanced the magnetic moment up to 2.92 µ B/Mn. Based on the results obtained from analyzing the electronic structures, UV-Vis absorption and resonant Raman scattering spectra, and theoretical calculations, we believe that the enhancement of the FM order in (Mn, P)-doped ZnO nanocolumns is due to exchange interactions taking place between vacancy-mediated Mn2+ ions.

  14. Influence of interstitial Mn on magnetism in the room-temperature ferromagnet Mn1+δSb

    DOE PAGES

    Taylor, Alice E.; Berlijn, Tom; Hahn, Steven E.; ...

    2015-06-15

    We repormore » t elastic and inelastic neutron scattering measurements of the high-TC ferromagnet Mn1+δSb. Measurements were performed on a large, TC = 434 K, single crystal with interstitial Mn content of δ ≈ 0.13. The neutron diffraction results reveal that the interstitial Mn has a magnetic moment, and that it is aligned antiparallel to the main Mn moment. We perform density functional theory calculations including the interstitial Mn, and find the interstitial to be magnetic in agreement with the diffraction data. The inelastic neutron scattering measurements reveal two features in the magnetic dynamics: i) a spin-wave-like dispersion emanating from ferromagnetic Bragg positions (H K 2n), and ii) a broad, non-dispersive signal centered at forbidden Bragg positions (H K 2n+1). The inelastic spectrum cannot be modeled by simple linear spin-wave theory calculations, and appears to be significantly altered by the presence of the interstitial Mn ions. Finally, the results show that the influence of the interstitial Mn on the magnetic state in this system is more important than previously understood.« less

  15. Room temperature creep in metals and alloys

    SciTech Connect

    Deibler, Lisa Anne

    2014-09-01

    Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 Tm for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.

  16. IMPROVED SYNTHESIS OF ROOM TEMPERATURE IONIC LIQUIDS

    EPA Science Inventory

    Room temperature ionic liquids (RTILs), molten salts comprised of N-alkylimidazolium cations and various anions, have received significant attention due to their commercial potential in a variety of chemical applications especially as substitutes for conventional volatile organic...

  17. IMPROVED SYNTHESIS OF ROOM TEMPERATURE IONIC LIQUIDS

    EPA Science Inventory

    Room temperature ionic liquids (RTILs), molten salts comprised of N-alkylimidazolium cations and various anions, have received significant attention due to their commercial potential in a variety of chemical applications especially as substitutes for conventional volatile organic...

  18. Determining Camera Gain in Room Temperature Cameras

    SciTech Connect

    Joshua Cogliati

    2010-12-01

    James R. Janesick provides a method for determining the amplification of a CCD or CMOS camera when only access to the raw images is provided. However, the equation that is provided ignores the contribution of dark current. For CCD or CMOS cameras that are cooled well below room temperature, this is not a problem, however, the technique needs adjustment for use with room temperature cameras. This article describes the adjustment made to the equation, and a test of this method.

  19. Room temperature water Leidenfrost droplets.

    PubMed

    Celestini, Franck; Frisch, Thomas; Pomeau, Yves

    2013-10-28

    We experimentally investigate the Leidenfrost effect at pressures ranging from 1 to 0.05 atmospheric pressure. As a direct consequence of the Clausius–Clapeyron phase diagram of water, the droplet temperature can be at ambient temperature in a non-sophisticated lab environment. Furthermore, the lifetime of the Leidenfrost droplet is significantly increased in this low pressure environment. The temperature and pressure dependence of the evaporation rate is successfully tested against a recently proposed model. These results may pave the way for reaching efficient Leidenfrost micro-fluidic and milli-fluidic applications.

  20. Self-assembly of imidazolium-based surfactants in magnetic room-temperature ionic liquids: binary mixtures.

    PubMed

    Klee, Andreas; Prevost, Sylvain; Gradzielski, Michael

    2014-12-15

    The phase behaviour of binary mixtures of ionic surfactants (1-alkyl-3-imidazolium chloride, C(n)mimCl with n=14, 16 and 18) and imidazolium-based ionic liquids (1-alkyl-3-methylimidazolium tetrachloroferrate, C(n)mimFeCl4, with n=2 and 4) over a broad temperature range and the complete range of compositions is described. By using many complementary methods including differential scanning calorimetry (DSC), polarised microscopy, small-angle neutron and X-ray scattering (SANS/SAXS), and surface tension, the ability of this model system to support self-assembly is described quantitatively and this behaviour is compared with common water systems. The existence of micelles swollen by the solvent can be deduced from SANS experiments and represent a possible model for aggregates, which has barely been considered for ionic-liquid systems until now, and can be ascribed to the rather low solvophobicity of the surfactants. Our investigation shows that, in general, C(n)mimCl is a rather weak amphiphile in these ionic liquids. The amphiphilic strength increases systematically with the length of the alkyl chain, as seen from the phase behaviour, the critical micelle concentration, and also the level of definition of the aggregates formed.

  1. One-step, room-temperature synthesis of glutathione-capped iron-oxide nanoparticles and their application in in vivo T1-weighted magnetic resonance imaging.

    PubMed

    Liu, Chien-Liang; Peng, Yung-Kang; Chou, Shang-Wei; Tseng, Wei-Hsuan; Tseng, Yu-Jui; Chen, Hsieh-Chih; Hsiao, Jong-Kai; Chou, Pi-Tai

    2014-10-15

    The room-temperature, aqueous-phase synthesis of iron-oxide nanoparticles (IO NPs) with glutathione (GSH) is reported. The simple, one-step reduction involves GSH as a capping agent and tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the reducing agent; GSH is an anti-oxidant that is abundant in the human body while THPC is commonly used in the synthesis of noble-metal clusters. Due to their low magnetization and good water-dispersibility, the resulting GSH-IO NPs, which are 3.72 ± 0.12 nm in diameter, exhibit a low r2 relaxivity (8.28 mm(-1) s(-1)) and r2/r1 ratio (2.28)--both of which are critical for T1 contrast agents. This, together with the excellent biocompatibility, makes these NPs an ideal candidate to be a T1 contrast agent. Its capability in cellular imaging is illustrated by the high signal intensity in the T1-weighted magnetic resonance imaging (MRI) of treated HeLa cells. Surprisingly, the GSH-IO NPs escape ingestion by the hepatic reticuloendothelial system, enabling strong vascular enhancement at the internal carotid artery and superior sagittal sinus, where detection of the thrombus is critical for diagnosing a stroke. Moreover, serial T1- and T2-weighted time-dependent MR images are resolved for a rat's kidneys, unveiling detailed cortical-medullary anatomy and renal physiological functions. The newly developed GSH-IO NPs thus open a new dimension in efforts towards high-performance, long-circulating MRI contrast agents that have biotargeting potential. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Towards Room Temperature Spin Filtering in Oxide Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Iwata-Harms, Jodi; Wong, Franklin; Arenholz, Elke; Suzuki, Yuri

    2012-02-01

    Spin filtering, in which the magnetic tunnel barrier preferentially filters spin-up and spin-down electrons from a nonmagnetic electrode, has been demonstrated in junction heterostructures. By incorporating two spin filtering barriers, double spin filter magnetic tunnel junctions (DSF-MTJs) were predicted to yield magnetoresistance (MR) values orders of magnitude larger than that of conventional magnetic tunnel junctions. Recently, DSF-MTJs have exhibited spin filtering with magnetic electrodes at room temperature and at low temperature with nonmagnetic electrodes in EuS-based devices [1,2]. We have fabricated DSF-MTJs with nonmagnetic SrRuO3 electrodes and room temperature ferrimagnets, NiFe2O4 and CoFe2O4, for spin filters in pursuit of room temperature functionality. Atomic force microscopy shows smooth films quantified by roughness values between 0.1--0.5nm. X-ray magnetic circular dichroism reveals ferromagnetic Ni^2+ and Co^2+, and element-specific hysteresis loops indicate the independent switching of the two spin filters. Transport data reveals junction MR and non-linear I-V characteristics consistent with tunneling. [4pt] [1] M.G. Chapline et al., PRB, 74, 014418 (2006).[0pt] [2] G.- X. Miao et al., PRL, 102, 076601 (2009).

  3. Room temperature skyrmion ground state stabilized through interlayer exchange coupling

    SciTech Connect

    Chen, Gong Schmid, Andreas K.; Mascaraque, Arantzazu; N'Diaye, Alpha T.

    2015-06-15

    Possible magnetic skyrmion device applications motivate the search for structures that extend the stability of skyrmion spin textures to ambient temperature. Here, we demonstrate an experimental approach to stabilize a room temperature skyrmion ground state in chiral magnetic films via exchange coupling across non-magnetic spacer layers. Using spin polarized low-energy electron microscopy to measure all three Cartesian components of the magnetization vector, we image the spin textures in Fe/Ni films. We show how tuning the thickness of a copper spacer layer between chiral Fe/Ni films and perpendicularly magnetized Ni layers permits stabilization of a chiral stripe phase, a skyrmion phase, and a single domain phase. This strategy to stabilize skyrmion ground states can be extended to other magnetic thin film systems and may be useful for designing skyrmion based spintronics devices.

  4. Room-Temperature Spin Polariton Diode Laser

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Aniruddha; Baten, Md Zunaid; Iorsh, Ivan; Frost, Thomas; Kavokin, Alexey; Bhattacharya, Pallab

    2017-08-01

    A spin-polarized laser offers inherent control of the output circular polarization. We have investigated the output polarization characteristics of a bulk GaN-based microcavity polariton diode laser at room temperature with electrical injection of spin-polarized electrons via a FeCo /MgO spin injector. Polariton laser operation with a spin-polarized current is characterized by a threshold of ˜69 A / cm2 in the light-current characteristics, a significant reduction of the electroluminescence linewidth and blueshift of the emission peak. A degree of output circular polarization of ˜25 % is recorded under remanent magnetization. A second threshold, due to conventional photon lasing, is observed at an injection of ˜7.2 kA /cm2 . The variation of output circular and linear polarization with spin-polarized injection current has been analyzed with the carrier and exciton rate equations and the Gross-Pitaevskii equations for the condensate and there is good agreement between measured and calculated data.

  5. Preparation of Pd/Fe3O4 nanoparticles by use of Euphorbia stracheyi Boiss root extract: A magnetically recoverable catalyst for one-pot reductive amination of aldehydes at room temperature.

    PubMed

    Nasrollahzadeh, Mahmoud; Sajadi, S Mohammad

    2016-02-15

    We describe a method for supporting palladium nanoparticles on magnetic nanoparticles using Euphorbia stracheyi Boiss root extract as the natural source of reducing and stabilizing agent. The progress of the reaction was monitored using UV-visible spectroscopy. The nanocatalyst was characterized by FE-SEM, TEM, XRD, EDS, FT-IR spectroscopy and ICP. The nanocatalyst was applied as an efficient, magnetically recoverable, highly reusable and heterogeneous catalyst for one-pot reductive amination of aldehydes at room temperature. The nanocatalyst was easily recovered by applying an external magnet and reused several times without considerable loss of activity. Copyright © 2015 Elsevier Inc. All rights reserved.

  6. Room Temperature Ferromagnetic Polymer and the Correlated Anomalous Magnetoresistance Phenomenon

    NASA Astrophysics Data System (ADS)

    Huang, Jinsong; Yang, Bin; Shield, Jeffrey

    2011-03-01

    Organic magnetoresistance (OMAR) has been observed in organic semiconductor devices where resistance can change in a relatively small external magnetic field at room temperature. Since a weak magnetic field is involved, the hyperfine interaction (HFI) is employed to explain OMAR in the reported literatures. None of these issues consider the magnetic properties of the organic semiconductors themselves. However, the we recently discovered that polymer semiconductors, such as poly(3-hexylthiophene) P3HT, can have room temperature (RT) ferromagnetic properties in their crystalline phase and when mixed with phenyl-C61-butyric acid methyl ester (PCBM). Here, we will report the possible correlation between the ferromagnetic property of the P3HT:PCBM and anomalous OMAR phenomenon including the anisotropic and hysteretic OMAR behavior. The magnetic property of the polymer including the anisotropic and photo induced change of magnetism will be also discussed to explore the possible mechanism of the room temperature ferromagnetism.~ This work is partially supported by the NSF MRSEC program at University.

  7. Dynamics of Glass Relaxation at Room Temperature

    NASA Astrophysics Data System (ADS)

    Welch, Roger C.; Smith, John R.; Potuzak, Marcel; Guo, Xiaoju; Bowden, Bradley F.; Kiczenski, T. J.; Allan, Douglas C.; King, Ellyn A.; Ellison, Adam J.; Mauro, John C.

    2013-06-01

    The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature. Remarkably, this relaxation follows a stretched exponential decay rather than simple exponential relaxation, and the value of the stretching exponent (β=3/7) follows a theoretical prediction made by Phillips for homogeneous glasses.

  8. Widely tunable room temperature semiconductor terahertz source

    SciTech Connect

    Lu, Q. Y.; Slivken, S.; Bandyopadhyay, N.; Bai, Y.; Razeghi, M.

    2014-11-17

    We present a widely tunable, monolithic terahertz source based on intracavity difference frequency generation within a mid-infrared quantum cascade laser at room temperature. A three-section ridge waveguide laser design with two sampled grating sections and a distributed-Bragg section is used to achieve the terahertz (THz) frequency tuning. Room temperature single mode THz emission with a wide tunable frequency range of 2.6–4.2 THz (∼47% of the central frequency) and THz power up to 0.1 mW is demonstrated, making such device an ideal candidate for THz spectroscopy and sensing.

  9. Room temperature ferromagnetism in Teflon due to carbon dangling bonds.

    PubMed

    Ma, Y W; Lu, Y H; Yi, J B; Feng, Y P; Herng, T S; Liu, X; Gao, D Q; Xue, D S; Xue, J M; Ouyang, J Y; Ding, J

    2012-03-06

    The ferromagnetism in many carbon nanostructures is attributed to carbon dangling bonds or vacancies. This provides opportunities to develop new functional materials, such as molecular and polymeric ferromagnets and organic spintronic materials, without magnetic elements (for example, 3d and 4f metals). Here we report the observation of room temperature ferromagnetism in Teflon tape (polytetrafluoroethylene) subjected to simple mechanical stretching, cutting or heating. First-principles calculations indicate that the room temperature ferromagnetism originates from carbon dangling bonds and strong ferromagnetic coupling between them. Room temperature ferromagnetism has also been successfully realized in another polymer, polyethylene, through cutting and stretching. Our findings suggest that ferromagnetism due to networks of carbon dangling bonds can arise in polymers and carbon-based molecular materials.

  10. Above room temperature ferromagnetism in Mn-ion implanted Si

    NASA Astrophysics Data System (ADS)

    Bolduc, M.; Awo-Affouda, C.; Stollenwerk, A.; Huang, M. B.; Ramos, F. G.; Agnello, G.; Labella, V. P.

    2005-01-01

    Above room temperature ferromagnetic behavior is achieved in Si through Mn ion implantation. Three-hundred-keV Mn+ ions were implanted to 0.1% and 0.8% peak atomic concentrations, yielding a saturation magnetization of 0.3emu/g at 300K for the highest concentration as measured using a SQUID magnetometer. The saturation magnetization increased by ˜2× after annealing at 800°C for 5min . The Curie temperature for all samples was found to be greater than 400K . A significant difference in the temperature-dependent remnant magnetization between the implanted p-type and n-type Si is observed, giving strong evidence that a Si-based diluted magnetic semiconductor can be achieved.

  11. Room-temperature helimagnetism in FeGe thin films.

    PubMed

    Zhang, S L; Stasinopoulos, I; Lancaster, T; Xiao, F; Bauer, A; Rucker, F; Baker, A A; Figueroa, A I; Salman, Z; Pratt, F L; Blundell, S J; Prokscha, T; Suter, A; Waizner, J; Garst, M; Grundler, D; van der Laan, G; Pfleiderer, C; Hesjedal, T

    2017-03-09

    Chiral magnets are promising materials for the realisation of high-density and low-power spintronic memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii-Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain α intr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.

  12. Room temperature synthesis of biodiesel using sulfonated ...

    EPA Pesticide Factsheets

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature. Prepared for submission to Royal Society of Chemistry (RSC) journal, Green Chemistry as a communication.

  13. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Columnar growth of crystalline silicon films on aluminium-coated glass by inductively coupled plasma CVD at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, Jin-Xiao; Qin, Yan-Li; Yan, Heng-Qing; Gao, Ping-Qi; Li, Jun-Shuai; Yin, Min; He, De-Yan

    2009-02-01

    Silicon films were grown on aluminium-coated glass by inductively coupled plasma CVD at room temperature using a mixture of SiH4 and H2 as the source gas. The microstructure of the films was evaluated using Raman spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the films are composed of columnar grains and their surfaces show a random and uniform distribution of silicon nanocones. Such a microstructure is highly advantageous to the application of the films in solar cells and electron emission devices. Field electron emission measurement of the films demonstrated that the threshold field strength is as low as ~9.8 V/μm and the electron emission characteristic is reproducible. In addition, a mechanism is suggested for the columnar growth of crystalline silicon films on aluminium-coated glass at room temperature.

  14. Imprinting bulk amorphous alloy at room temperature

    SciTech Connect

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.

  15. Imprinting bulk amorphous alloy at room temperature

    PubMed Central

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  16. Irreconcilable room temperature magnetotransport properties of polypyrrole nanoparticles and nanorods

    NASA Astrophysics Data System (ADS)

    Rehman Sagar, Rizwan Ur; Stadler, Florian J.; Navale, Sachin T.; Mane, Rajaram S.; Nazir, Adnan; Nabi, Ghulam

    2017-09-01

    The morphology of nanostructures plays a vital role in determining the conductivity of specimens and, consequently, affects the efficiency of magnetoelectronic devices such as magnetic field sensors. Herein, nanoparticles (NPs) and nanorods (NRs) of conducting polymer polypyrrole have been synthesized at room temperature via the chemical oxidative polymerization method. The positive and negative magnetoresistance signatures are respectively obtained in NPs and NRs morphology, respectively. Both morphologies have conduction in the variable range-hopping regime with the average charge carrier hopping length being highly influenced by the sign of magnetoresistance. This morphology dependence is not only interesting for fundamental research but it also allows for tuning magnetic field sensor materials to be usable at room temperature for the desired characteristics.

  17. Room-temperature semiconductor heterostructure refrigeration

    NASA Astrophysics Data System (ADS)

    Chao, K. A.; Larsson, Magnus; Mal'shukov, A. G.

    2005-07-01

    With the proper design of semiconductor tunneling barrier structures, we can inject low-energy electrons via resonant tunneling, and take out high-energy electrons via a thermionic process. This is the operation principle of our semiconductor heterostructure refrigerator (SHR) without the need of applying a temperature gradient across the device. Even for the bad thermoelectric material AlGaAs, our calculation shows that at room temperature, the SHR can easily lower the temperature by 5-7K. Such devices can be fabricated with the present semiconductor technology. Besides its use as a kitchen refrigerator, the SHR can efficiently cool microelectronic devices.

  18. Giant room temperature magnetoelectric response in strain controlled nanocomposites

    NASA Astrophysics Data System (ADS)

    Rafique, Mohsin; Herklotz, Andreas; Dörr, Kathrin; Manzoor, Sadia

    2017-05-01

    We report giant magnetoelectric coupling at room temperature in a self-assembled nanocomposite of BiFeO3-CoFe2O4 (BFO-CFO) grown on a BaTiO3 (BTO) crystal. The nanocomposite consisting of CFO nanopillars embedded in a BFO matrix exhibits weak perpendicular magnetic anisotropy due to a small out-of-plane compression (˜0.3%) of the magnetostrictive (CFO) phase, enabling magnetization rotation under moderate in-plane compression. Temperature dependent magnetization measurements demonstrate strong magnetoelastic coupling between the BaTiO3 substrate and the nanocomposite film, which has been exploited to produce a large magnetoelectric response in the sample. The reorientation of ferroelectric domains in the BTO crystal upon the application of an electric field (E) alters the strain state of the nanocomposite film, thus enabling control of its magnetic anisotropy. The strain mediated magnetoelectric coupling coefficient α = μ o d M / d E calculated from remnant magnetization at room temperature is 2.6 × 10-7 s m-1 and 1.5 × 10-7 s m-1 for the out-of-plane and in-plane orientations, respectively.

  19. Large magnetic response in (Bi{sub 4}Nd)Ti{sub 3}(Fe{sub 0.5}Co{sub 0.5})O{sub 15} ceramic at room-temperature

    SciTech Connect

    Yang, F. J.; Su, P.; Wei, C.; Chen, X. Q.; Yang, C. P.; Cao, W. Q.

    2011-12-15

    Ceramics of Nd/Co co-substituted Bi{sub 5}Ti{sub 3}FeO{sub 15}, i.e., (Bi{sub 4}Nd)Ti{sub 3}(Fe{sub 0.5}Co{sub 0.5})O{sub 15} were prepared by the conventional solid-state reaction method. The X-ray diffraction pattern demonstrates that the sample of the layered perovskite phase was successfully obtained, even if little Bi-deficient pyrochlore Bi{sub 2}Ti{sub 2}O{sub 7} also existed. The ferroelectric and magnetic Curie temperatures were determined to be 1077 K and 497 K, respectively. The multiferroic property of the sample at room temperature was demonstrated by ferroelectric and magnetic measurements. Remarkably, by Nd/Co co-substituting, the sample exhibited large magnetic response with 2M{sub r} = 330 memu/g and 2H{sub c} = 562 Oe at applied magnetic field of 8 kOe at room temperature. The present work suggests the possibility of doped Bi{sub 5}Ti{sub 3}FeO{sub 15} as a potential multiferroic.

  20. Remote control of magnetostriction-based nanocontacts at room temperature.

    PubMed

    Jammalamadaka, S Narayana; Kuntz, Sebastian; Berg, Oliver; Kittler, Wolfram; Kannan, U Mohanan; Chelvane, J Arout; Sürgers, Christoph

    2015-09-01

    The remote control of the electrical conductance through nanosized junctions at room temperature will play an important role in future nano-electromechanical systems and electronic devices. This can be achieved by exploiting the magnetostriction effects of ferromagnetic materials. Here we report on the electrical conductance of magnetic nanocontacts obtained from wires of the giant magnetostrictive compound Tb0.3Dy0.7Fe1.95 as an active element in a mechanically controlled break-junction device. The nanocontacts are reproducibly switched at room temperature between "open" (zero conductance) and "closed" (nonzero conductance) states by variation of a magnetic field applied perpendicularly to the long wire axis. Conductance measurements in a magnetic field oriented parallel to the long wire axis exhibit a different behaviour where the conductance switches between both states only in a limited field range close to the coercive field. Investigating the conductance in the regime of electron tunneling by mechanical or magnetostrictive control of the electrode separation enables an estimation of the magnetostriction. The present results pave the way to utilize the material in devices based on nano-electromechanical systems operating at room temperature.

  1. Remote control of magnetostriction-based nanocontacts at room temperature

    PubMed Central

    Jammalamadaka, S. Narayana; Kuntz, Sebastian; Berg, Oliver; Kittler, Wolfram; Kannan, U. Mohanan; Chelvane, J. Arout; Sürgers, Christoph

    2015-01-01

    The remote control of the electrical conductance through nanosized junctions at room temperature will play an important role in future nano-electromechanical systems and electronic devices. This can be achieved by exploiting the magnetostriction effects of ferromagnetic materials. Here we report on the electrical conductance of magnetic nanocontacts obtained from wires of the giant magnetostrictive compound Tb0.3Dy0.7Fe1.95 as an active element in a mechanically controlled break-junction device. The nanocontacts are reproducibly switched at room temperature between “open” (zero conductance) and “closed” (nonzero conductance) states by variation of a magnetic field applied perpendicularly to the long wire axis. Conductance measurements in a magnetic field oriented parallel to the long wire axis exhibit a different behaviour where the conductance switches between both states only in a limited field range close to the coercive field. Investigating the conductance in the regime of electron tunneling by mechanical or magnetostrictive control of the electrode separation enables an estimation of the magnetostriction. The present results pave the way to utilize the material in devices based on nano-electromechanical systems operating at room temperature. PMID:26323326

  2. Room-temperature magnetoelectric multiferroic thin films and applications thereof

    SciTech Connect

    Katiyar, Ram S; Kuman, Ashok; Scott, James F.

    2014-08-12

    The invention provides a novel class of room-temperature, single-phase, magnetoelectric multiferroic (PbFe.sub.0.67W.sub.0.33O.sub.3).sub.x (PbZr.sub.0.53Ti.sub.0.47O.sub.3).sub.1-x (0.2.ltoreq.x.ltoreq.0.8) (PFW.sub.x-PZT.sub.1-x) thin films that exhibit high dielectric constants, high polarization, weak saturation magnetization, broad dielectric temperature peak, high-frequency dispersion, low dielectric loss and low leakage current. These properties render them to be suitable candidates for room-temperature multiferroic devices. Methods of preparation are also provided.

  3. Room-temperature chiral charge pumping in Dirac semimetals

    PubMed Central

    Zhang, Cheng; Zhang, Enze; Wang, Weiyi; Liu, Yanwen; Chen, Zhi-Gang; Lu, Shiheng; Liang, Sihang; Cao, Junzhi; Yuan, Xiang; Tang, Lei; Li, Qian; Zhou, Chao; Gu, Teng; Wu, Yizheng; Zou, Jin; Xiu, Faxian

    2017-01-01

    Chiral anomaly, a non-conservation of chiral charge pumped by the topological nontrivial gauge fields, has been predicted to exist in Weyl semimetals. However, until now, the experimental signature of this effect exclusively relies on the observation of negative longitudinal magnetoresistance at low temperatures. Here, we report the field-modulated chiral charge pumping process and valley diffusion in Cd3As2. Apart from the conventional negative magnetoresistance, we observe an unusual nonlocal response with negative field dependence up to room temperature, originating from the diffusion of valley polarization. Furthermore, a large magneto-optic Kerr effect generated by parallel electric and magnetic fields is detected. These new experimental approaches provide a quantitative analysis of the chiral anomaly phenomenon which was inaccessible previously. The ability to manipulate the valley polarization in topological semimetal at room temperature opens up a route towards understanding its fundamental properties and utilizing the chiral fermions. PMID:28067234

  4. Room-temperature chiral charge pumping in Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Zhang, Enze; Wang, Weiyi; Liu, Yanwen; Chen, Zhi-Gang; Lu, Shiheng; Liang, Sihang; Cao, Junzhi; Yuan, Xiang; Tang, Lei; Li, Qian; Zhou, Chao; Gu, Teng; Wu, Yizheng; Zou, Jin; Xiu, Faxian

    2017-01-01

    Chiral anomaly, a non-conservation of chiral charge pumped by the topological nontrivial gauge fields, has been predicted to exist in Weyl semimetals. However, until now, the experimental signature of this effect exclusively relies on the observation of negative longitudinal magnetoresistance at low temperatures. Here, we report the field-modulated chiral charge pumping process and valley diffusion in Cd3As2. Apart from the conventional negative magnetoresistance, we observe an unusual nonlocal response with negative field dependence up to room temperature, originating from the diffusion of valley polarization. Furthermore, a large magneto-optic Kerr effect generated by parallel electric and magnetic fields is detected. These new experimental approaches provide a quantitative analysis of the chiral anomaly phenomenon which was inaccessible previously. The ability to manipulate the valley polarization in topological semimetal at room temperature opens up a route towards understanding its fundamental properties and utilizing the chiral fermions.

  5. Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite

    NASA Astrophysics Data System (ADS)

    Lin, Aigu L.; Rodrigues, J. N. B.; Su, Chenliang; Milletari, M.; Loh, Kian Ping; Wu, Tom; Chen, Wei; Neto, A. H. Castro; Adam, Shaffique; Wee, Andrew T. S.

    2015-06-01

    Magnetic materials have found wide application ranging from electronics and memories to medicine. Essential to these advances is the control of the magnetic order. To date, most room-temperature applications have a fixed magnetic moment whose orientation is manipulated for functionality. Here we demonstrate an iron-oxide and graphene oxide nanocomposite based device that acts as a tunable ferromagnet at room temperature. Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m2/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process. We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.

  6. Room temperature ferromagnetism in a phthalocyanine based carbon material

    SciTech Connect

    Honda, Z. Sato, K.; Sakai, M.; Fukuda, T.; Kamata, N.; Hagiwara, M.; Kida, T.

    2014-02-07

    We report on a simple method to fabricate a magnetic carbon material that contains nitrogen-coordinated transition metals and has a large magnetic moment. Highly chlorinated iron phthalocyanine was used as building blocks and potassium as a coupling reagent to uniformly disperse nitrogen-coordinated iron atoms on the phthalocyanine based carbon material. The iron phthalocyanine based carbon material exhibits ferromagnetic properties at room temperature and the ferromagnetic phase transition occurs at T{sub c} = 490 ± 10 K. Transmission electron microscopy observation, X-ray diffraction analysis, and the temperature dependence of magnetization suggest that the phthalocyanine molecules form three-dimensional random networks in the iron phthalocyanine based carbon material.

  7. Theory of room temperature ferromagnetism in Cr modified DNA nanowire

    NASA Astrophysics Data System (ADS)

    Paruğ Duru, Izzet; Değer, Caner; Eldem, Vahap; Kalayci, Taner; Aktaş, Şahin

    2016-04-01

    We investigated the magnetic properties of Cr3+ (J  <  0) ion-modified DNA (M-DNA) nanowire (1000 base) at room temperature under a uniform magnetic field (˜100 Oe) for different doping concentrations. A Monte Carlo simulation method-based Metropolis algorithm is used to figure out the thermodynamic quantities of nanowire formed by Cr M-DNA followed by analysing the dependency of the ferromagnetic behaviour of the M-DNA to dopant concentration. It is understood that ion density/base and ion density/helical of Cr3+ ions can be a tuning parameter, herewith the dopant ratio has an actual importance on the magnetic characterization of M-DNA nanowire (3%-20%). We propose the source of magnetism as an exchange interaction between Cr and DNA helical atoms indicated in the Heisenberg Hamiltonian.

  8. Physical understanding of negative bias temperature instability below room temperature

    NASA Astrophysics Data System (ADS)

    Ji, Xiaoli; Liao, Yiming; Yan, Feng; Zhu, Chenxin; Shi, Yi; Guo, Qiang

    2012-11-01

    The physical mechanism of VT degradations under negative bias temperature stress below room temperature has been studied for SiO2 and plasma nitrided oxide (PNO-based) pMOSFETs. It is found that VT degradations in both devices exhibit strong dependence on the electric field and temperature. The analysis shows that this strong dependence follows multi-phonon field-assisted tunneling theory, which indicates the inelastic hole trapping mechanism in the low temperature negative bias temperature instability (NBTI). On the other hand, by applying a low temperature sweeping technique, the energy distribution of these NBTI-induced hole traps below room temperature is indentified. The energy distribution of hole traps has two obvious peaks, one in the lower and one in the upper half of the silicon band gap. Both peaks gradually develop with increasing the stress time and temperature. We attempt to compare the energy profile for SiO2 and PNO devices to identify the trap precursors in NBTI below room temperature.

  9. Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

    SciTech Connect

    Ravikumar, Patta; Kisan, Bhagaban; Perumal, A.

    2015-08-15

    We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μ{sub B}/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (T{sub C}) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high T{sub C} and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

  10. Noninvasive liver iron measurements with a room-temperature susceptometer

    PubMed Central

    Avrin, W F; Kumar, S

    2011-01-01

    Magnetic susceptibility measurements on the liver can quantify iron overload accurately and noninvasively. However, established susceptometer designs, using Superconducting QUantum Interference Devices (SQUIDs) that work in liquid helium, have been too expensive for widespread use. This paper presents a less expensive liver susceptometer that works at room temperature. This system uses oscillating magnetic fields, which are produced and detected by copper coils. The coil design cancels the signal from the applied field, eliminating noise from fluctuations of the source-coil current and sensor gain. The coil unit moves toward and away from the patient at 1 Hz, cancelling drifts due to thermal expansion of the coils. Measurements on a water phantom indicated instrumental errors less than 30 μg of iron per gram of wet liver tissue, which is small compared with other errors due to the response of the patient’s body. Liver iron measurements on eight thalassemia patients yielded a correlation coefficient r=0.98 between the room-temperature susceptometer and an existing SQUID. These results indicate that the fundamental accuracy limits of the room-temperature susceptometer are similar to those of the SQUID. PMID:17395991

  11. High temperature superconducting magnetic refrigeration

    NASA Astrophysics Data System (ADS)

    Blumenfeld, P. E.; Prenger, F. C.; Sternberg, A.; Zimm, C.

    2002-05-01

    A near-room temperature active magnetic regenerative refrigerator (AMRR) was designed and built using a high-temperature superconducting (HTS) magnet in a charge-discharge cycle and a gadolinium-packed regenerative bed as the magnetocaloric component. Current to the HTS magnet was ramped periodically from zero to 100 amperes, which generated a ramp in field strength from zero to 1.7 tesla. Water was moved periodically through the bed and through hot and cold heat exchangers to accomplish a continuous refrigeration cycle. Cycle periods as short as 30 seconds were realized. Refrigerator performance was measured in terms of cooling capacity as a function of temperature span and in terms of efficiency expressed as a percentage of maximum obtainable (Carnot) efficiency. A three-watt cooling capacity was measured over a temperature span of 15 degrees C between hot and cold end temperatures of 25 degrees C and 10 degrees C. This experiment is directed to two possible applications for magnetic refrigeration: a no-moving part cryogenic refrigerator for space applications, and a compact permanent magnet refrigerator for commercial and consumer applications.

  12. Imprinting bulk amorphous alloy at room temperature

    DOE PAGES

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; ...

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the abilitymore » of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.« less

  13. Disorder-induced room temperature ferromagnetism in glassy chromites.

    PubMed

    Araujo, C Moyses; Nagar, Sandeep; Ramzan, Muhammad; Shukla, R; Jayakumar, O D; Tyagi, A K; Liu, Yi-Sheng; Chen, Jeng-Lung; Glans, Per-Anders; Chang, Chinglin; Blomqvist, Andreas; Lizárraga, Raquel; Holmström, Erik; Belova, Lyubov; Guo, Jinghua; Ahuja, Rajeev; Rao, K V

    2014-04-15

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  14. Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites

    NASA Astrophysics Data System (ADS)

    Araujo, C. Moyses; Nagar, Sandeep; Ramzan, Muhammad; Shukla, R.; Jayakumar, O. D.; Tyagi, A. K.; Liu, Yi-Sheng; Chen, Jeng-Lung; Glans, Per-Anders; Chang, Chinglin; Blomqvist, Andreas; Lizárraga, Raquel; Holmström, Erik; Belova, Lyubov; Guo, Jinghua; Ahuja, Rajeev; Rao, K. V.

    2014-04-01

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  15. Signature of room temperature ferromagnetism in Mn doped CeO{sub 2} nanoparticles

    SciTech Connect

    Kumar, Shalendra; Ahmed, Faheem; Anwar, M.S.; Choi, H.K.; Chung, Hanshik; Koo, B.H.

    2012-10-15

    We report structural and magnetic properties of Mn doped CeO{sub 2} nanoparticles using X-ray diffraction (XRD), field emission transmission electron microscopy (FE-TEM) and dc magnetization measurements. XRD results infer that all the samples have single phase nature and lattice parameters decrease with Mn doping. The particle size calculated using XRD and TEM analysis was found to decrease with Mn doping. Field cooled magnetization measurement shows that the transition temperature is above room temperature. Magnetic hysteresis loop studies indicate that undoped and Mn doped CeO{sub 2} nanoparticles show weak ferromagnetic behavior at room temperature.

  16. Absorber Materials at Room and Cryogenic Temperatures

    SciTech Connect

    F. Marhauser, T.S. Elliott, A.T. Wu, E.P. Chojnacki, E. Savrun

    2011-09-01

    We recently reported on investigations of RF absorber materials at cryogenic temperatures conducted at Jefferson Laboratory (JLab). The work was initiated to find a replacement material for the 2 Kelvin low power waveguide Higher Order Mode (HOM) absorbers employed within the original cavity cryomodules of the Continuous Electron Beam Accelerator Facility (CEBAF). This effort eventually led to suitable candidates as reported in this paper. Furthermore, though constrained by small funds for labor and resources, we have analyzed a variety of lossy ceramic materials, several of which could be usable as HOM absorbers for both normal conducting and superconducting RF structures, e.g. as loads in cavity waveguides and beam tubes either at room or cryogenic temperatures and, depending on cooling measures, low to high operational power levels.

  17. Room-temperature magnetic topological Weyl fermion and nodal line semimetal states in half-metallic Heusler Co2TiX (X=Si, Ge, or Sn)

    SciTech Connect

    Chang, Guoqing; Xu, Su -Yang; Zheng, Hao; Singh, Bahadur; Hsu, Chuang -Han; Bian, Guang; Alidoust, Nasser; Belopolski, Ilya; Sanchez, Daniel S.; Zhang, Songtian; Lin, Hsin; Hasan, M. Zahid

    2016-12-15

    Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal states in the ferromagnetic half-metal compounds Co2TiX (X = Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, in the absence of spin-orbit coupling, Co2TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Lastly, our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperature, but also suggest potential applications such as unusual anomalous Hall effect in engineered monolayers of the Co2TiX compounds at high temperature.

  18. Room-temperature ferromagnetism in pure ZnO nanoflowers

    NASA Astrophysics Data System (ADS)

    Bie, Xiaofei; Wang, Chunzhong; Ehrenberg, H.; Wei, Yingjin; Chen, Gang; Meng, Xing; Zou, Guangtian; Du, Fei

    2010-08-01

    ZnO nanoflowers are synthesized by hydrothermal method. The morphology of ZnO is captured by SEM, TEM and HRTEM, which is composed of closely packed nanorods of about 100 nm in diameter and 1 μm in length. The ZFC/FC curves show superparamagnetic features. The abnormal increase in magnetization curves below 14 K comes from the isolated vacancy clusters with no interaction. The magnetic hysteresis at 300 K displays saturation state and confirms room-temperature ferromagnetism. While the magnetic hysteresis at 5 K shows nonsaturation state due to the enhanced effects of vacancy clusters. The O 1s XPS results can be fitted to three Gaussian peaks. The existence of medium-binding energy located at 531.16 eV confirms the deficiency of O ions at the surface of ZnO nanoflowers.

  19. Electric-field control of magnetization in Co40Fe40B20 / Pb(Mg1/3Nb2/3)0.7Ti0.3O3 structure at room temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Sen; Zhao, Y. G.; Rizwan, S.; Han, X. F.; Zhang, J. X.; Ramesh, R.

    2012-02-01

    Electric-field control of magnetization is important for new generation information storage technology with high integration density and low power consumption. A lot of work has been carried out on electric-field control of magnetization in artificial ferromagnetic-ferroelectric (FM-FE) two-phase systems via the piezo-strain effect. Beside strain, electric/elastic domains and phase structure also play important roles in the electric-field control of magnetization, especially in the case of amorphous FM film without magnetocrystalline anisotropy. We report a large magnetoelectric effect in a Co40Fe40B20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 structure at room temperature. Investigations on the ferroelectric domains, phase structures, magnetic domains and strain with in situ electric fields reveal a new mechanism for electric-field control of magnetization. This work provides a new way to realize large magnetoelectric coupling and is significant for applications, especially in the field of CoFeB-based spin valves to achieve electric-controlled magnetic random access memories.

  20. Existence of the multiferroic property at room temperature in Ti doped CoFeO

    NASA Astrophysics Data System (ADS)

    Dwivedi, G. D.; Joshi, Amish G.; Kevin, H.; Shahi, P.; Kumar, A.; Ghosh, A. K.; Yang, H. D.; Chatterjee, Sandip

    2012-03-01

    The appearance of ferroelectricity has been observed in magnetically ordered Co(Fe1-xTix)2O4 at room temperature. Magnetization and dielectric constant is found to increase with Ti doping. It is observed from an X-ray Photoemission Spectroscopy study that Ti goes to the octahedral site with (+4) ionic state. An M-H hysteresis curve at room temperature shows the ferrimagnetic ordering and a P-E loop at room temperature clearly indicates the existence of ferroelectricity.

  1. Electrical creation of spin polarization in silicon at room temperature

    NASA Astrophysics Data System (ADS)

    Jansen, Ron

    2010-03-01

    The integration of magnetism and mainstream semiconductor electronics could impact information technology in ways beyond imagination. A pivotal step is the implementation of spin-based electronic functionality in silicon devices. Much of the interest in silicon derives from its prevalence in semiconductor technology and from the robustness and longevity of spin as it is only weakly coupled to other degrees of freedom in the material. Recently it has become possible to induce and detect spin polarization in otherwise non-magnetic semiconductors (GaAs and Si) using all-electrical structures, but so far at temperatures below 150 K and only in n-type material. The main challenges are: (i) to design fully electrical silicon-based spintronic devices with large spin signals, (ii) to demonstrate device operation at room temperature, (iii) to do so for n-type and p-type material, and (iv) to find ways to manipulate spins and spin flow with a gate electric field. After a brief overview of the state of affairs, our recent advances in these areas are described. In particular, we demonstrate room-temperature electrical injection of spin polarization into n-type and p-type silicon from a ferromagnetic tunnel contact, spin manipulation using the Hanle effect, and the electrical detection of the induced spin accumulation. It is shown that a spin splitting as large as 2.9 meV can be created in Si at room temperature, corresponding to an electron spin polarization of 4.6%. The results open the way to the implementation of spin functionality in complementary silicon devices and electronic circuits operating at ambient temperature, and to the exploration of their prospects as well as the fundamental rules that govern their behavior. [4pt] [1] S.P. Dash, S. Sharma, R.S. Patel, M.P. de Jong and R. Jansen, Nature 462, 491 (2009).

  2. Magnetic and electrical properties on possible room temperature hybrid multiferroic BaTiO3/La2/3Sr1/3MnO3

    NASA Astrophysics Data System (ADS)

    Ordoñez, John Edward; Gómez, María Elena; Lopera Muñoz, Wilson; Prieto, Pedro Antonio; Thin Film Group Team; Center of Excellence on Novel Materials-CENM, Cali, Colombia Team

    2015-03-01

    We addressed to deposit the ferromagnetic phase of the La1-xSrxMnO3 and the ferroelectric BaTiO3 for possible hybrid multiferroic heterostructure. We have optimized the growth parameters for depositing BaTiO3(BTO) / La2/3Ca1/3MnO3(LCMO) / (001) SrTiO3 by sputtering RF and DC, respectively, in pure oxygen atmosphere and a substrate temperature of 830°C. Keeping fixed the magnetic layer thickness (tLSMO = 40 nm) and varying the thickness of the ferroelectric layer (tBTO = 20, 40, 80, 100 nm). We want to point out the influence of the thicknesses ratio (tBTO/tLSMO) on electrical and magnetic properties. From x-ray diffraction (XRD) analysis, we found the bragg peaks for LSMO maintain its position but BTO peak shift to lower Bragg angle indicating a strained BTO film. Magnetization and polarization measurements indicate a possible multiferroic behavior in the bilayers. Hysteresis loop measurements of bilayers show ferromagnetic behavior. Authors thank Instituto de Nanociencia de Aragón, Zaragoza, Spain. Work partially supported by COLCIENCIAS-UNIVALLE Project 110656933104 Contract No. 2013-0002, CI 7917 and CI 7978.

  3. Magnetic nanoparticle temperature estimation.

    PubMed

    Weaver, John B; Rauwerdink, Adam M; Hansen, Eric W

    2009-05-01

    The authors present a method of measuring the temperature of magnetic nanoparticles that can be adapted to provide in vivo temperature maps. Many of the minimally invasive therapies that promise to reduce health care costs and improve patient outcomes heat tissue to very specific temperatures to be effective. Measurements are required because physiological cooling, primarily blood flow, makes the temperature difficult to predict a priori. The ratio of the fifth and third harmonics of the magnetization generated by magnetic nanoparticles in a sinusoidal field is used to generate a calibration curve and to subsequently estimate the temperature. The calibration curve is obtained by varying the amplitude of the sinusoidal field. The temperature can then be estimated from any subsequent measurement of the ratio. The accuracy was 0.3 degree K between 20 and 50 degrees C using the current apparatus and half-second measurements. The method is independent of nanoparticle concentration and nanoparticle size distribution.

  4. Magnetic nanoparticle temperature estimation

    PubMed Central

    Weaver, John B.; Rauwerdink, Adam M.; Hansen, Eric W.

    2009-01-01

    The authors present a method of measuring the temperature of magnetic nanoparticles that can be adapted to provide in vivo temperature maps. Many of the minimally invasive therapies that promise to reduce health care costs and improve patient outcomes heat tissue to very specific temperatures to be effective. Measurements are required because physiological cooling, primarily blood flow, makes the temperature difficult to predict a priori. The ratio of the fifth and third harmonics of the magnetization generated by magnetic nanoparticles in a sinusoidal field is used to generate a calibration curve and to subsequently estimate the temperature. The calibration curve is obtained by varying the amplitude of the sinusoidal field. The temperature can then be estimated from any subsequent measurement of the ratio. The accuracy was 0.3 °K between 20 and 50 °C using the current apparatus and half-second measurements. The method is independent of nanoparticle concentration and nanoparticle size distribution. PMID:19544801

  5. Room-temperature ferromagnetism observed in alumina films

    NASA Astrophysics Data System (ADS)

    Zheng, Y. L.; Zhen, C. M.; Wang, X. Q.; Ma, L.; Li, X. L.; Hou, D. L.

    2011-08-01

    We have prepared alumina thin films on Si substrates using a radio frequency (RF) sputtering method, and have observed room-temperature ferromagnetism (RTFM) in the thin films. When the thin films were annealed in vacuum, the saturation magnetization (Ms) increased, while annealing the sample in the air contributed to a decrease in the value of Ms. The Ms of the thin film also decreased as the thickness increased. We confirm that the unpaired electron spins responsible for ferromagnetism (FM) in Al 2O 3-δ thin films have their origin in the oxygen vacancies, especially at the interface of the Al 2O 3-δ thin film and the Si substrate.

  6. Mobile Neel skyrmions at room temperature: Status and future

    DOE PAGES

    Jiang, Wanjun; Zhang, Wei; Yu, Guoqiang; ...

    2016-03-07

    Magnetic skyrmions are topologically protected spin textures that exhibit many fascinating features. As compared to the well-studied cryogenic Bloch skyrmions in bulk materials, we focus on the room- temperature Néel skyrmions in thin-film systems with an interfacial broken inversion symmetry in this article. Specifically, we show the stabilization, the creation, and the implementation of Néel skyrmions that are enabled by the electrical current-induced spin-orbit torques. As a result, towards the nanoscale Néel skyrmions, we further discuss the challenges from both material optimization and imaging characterization perspectives.

  7. Atomically resolved force microscopy at room temperature

    SciTech Connect

    Morita, Seizo

    2014-04-24

    Atomic force microscopy (AFM) can now not only image individual atoms but also construct atom letters using atom manipulation method even at room temperature (RT). Therefore, the AFM is the second generation atomic tool following the scanning tunneling microscopy (STM). However the AFM can image even insulating atoms, and also directly measure/map the atomic force and potential at the atomic scale. Noting these advantages, we have been developing a bottom-up nanostructuring system at RT based on the AFM. It can identify chemical species of individual atoms and then manipulate selected atom species to the predesigned site one-by-one to assemble complex nanostructures consisted of multi atom species at RT. Here we introduce our results toward atom-by-atom assembly of composite nanostructures based on the AFM at RT including the latest result on atom gating of nano-space for atom-by-atom creation of atom clusters at RT for semiconductor surfaces.

  8. Room-temperature ionic liquid battery electrolytes

    SciTech Connect

    Carlin, R.T.; Fuller, J.

    1997-12-01

    The room-temperature molten salts possess a number of unique properties that make them ideal battery electrolytes. In particular, they are nonflammable, nonvolatile, and chemically inert, and they display wide electrochemical windows, high inherent conductivities, and wide thermal operating ranges. Although the ionic liquids have excellent characteristics, the chemical and electrochemical properties of desirable battery electrode materials are not well understood in these electrolytes. The research has focused on rechargeable electrodes and has included work on metallic lithium and sodium anodes in buffered neutral chloroaluminate melts, graphite-intercalation electrodes in neutral chloroaluminate and non-chloroaluminate melts, and silane-imidazole polymeric cathodes in acidic chloroaluminate melts. This paper will provide an overview of the research in these areas.

  9. Structure of room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Yethiraj, Arun

    2016-10-01

    The structure of room temperature ionic liquids is studied using molecular dynamics simulations and integral equation theory. Three ionic liquids 1-alkyl-3-methylimidazolium hexfluorophosphate, [C n MIM] [PF6], for n  =  1, 4, and 8, are studied using a united atom model of the ions. The primary interest is a study of the pair correlation functions and a test of the reference interaction site model theory. There is liquid-like ordering in the liquid that arises from electrostatic attractions and steric packing considerations. The theory is not in quantitative agreement with the simulation results and underestimates the degree of liquid-like order. A pre-peak in the static structure factor is seen in both simulations and theory, suggesting that this is a geometric effect arising from a packing of the alkyl chains.

  10. Room Temperature Chemical Oxidation of Delafossite-Type Oxides

    NASA Astrophysics Data System (ADS)

    Trari, M.; Töpfer, J.; Doumerc, J. P.; Pouchard, M.; Ammar, A.; Hagenmuller, P.

    1994-07-01

    Examination of the delafossite-type structure of CuLaO 2 and CuYO 2 suggests that there is room enough to accomodate intercalated oxide ions and the charge compensation resulting simply from the oxidation of an equivalent amount of Cu + into Cu 2+. Reaction with hypohalites in an aqueous solution leads to color change. Evidence of the formation of Cu 2+ is given by TGA, iodometric titration, and magnetic (static and EPR) measurements. The obtained La and Y compounds seem to behave in a different way: whereas CuLaO 2+ x appears as a single phase, CuYO 2+ x corresponds to a two-phase mixture, with respectively low and high x values, the latter being isostructural with the thermally oxidized compound recently reported by Cava et al. Comparison is stressed between the oxides obtained by oxidation at room and those obtained at higher temperatures.

  11. Green synthesis of the Cu/Fe3O4 nanoparticles using Morinda morindoides leaf aqueous extract: A highly efficient magnetically separable catalyst for the reduction of organic dyes in aqueous medium at room temperature

    NASA Astrophysics Data System (ADS)

    Nasrollahzadeh, Mahmoud; Atarod, Monireh; Sajadi, S. Mohammad

    2016-02-01

    This paper reports the green and in-situ preparation of the Cu/Fe3O4 magnetic nanocatalyst synthesized using Morinda morindoides leaf extract without stabilizers or surfactants. The catalyst was characterized by XRD, SEM, EDS, UV-visible, TEM, VSM and TGA-DTA. The catalytic performance of the resulting nanocatalyst was examined for the reduction of 4-nitrophenol (4-NP), Congo red (CR) and Rhodamine B (RhB) in an environmental friendly medium at room temperature. The catalyst was recovered using an external magnet and reused several times without appreciable loss of its catalytic activity. In addition, the stability of the recycled catalyst has been proved by SEM and EDS techniques.

  12. Investigation of Room temperature Ferromagnetism in Mn doped Ge

    NASA Astrophysics Data System (ADS)

    Colakerol Arslan, Leyla; Toydemir, Burcu; Onel, Aykut Can; Ertas, Merve; Doganay, Hatice; Gebze Inst of Tech Collaboration; Research Center Julich Collaboration

    2014-03-01

    We present a systematic investigation of structural, magnetic and electronic properties of MnxGe1 -x single crystals. MnxGe1-x films were grown by sequential deposition of Ge and Mn by molecular-beam epitaxy at low substrate temperatures in order to avoid precipitation of ferromagnetic Ge-Mn intermetallic compounds. Reflected high energy electron diffraction and x-ray diffraction observations revealed that films are epitaxially grown on Si (001) substrates from the initial stage without any other phase formation. Magnetic measurements carried out using a physical property measurement system showed that all samples exhibited ferromagnetism at room temperature. Electron spin resonance indicates the presence of magnetically ordered localized spins of divalent Mn ions. X-ray absorption measurements at the Mn L-edge confirm significant substitutional doping of Mn into Ge-sites. The ferromagnetism was mainly induced by Mn substitution for Ge site, and indirect exchange interaction of these magnetic ions with the intrinsic charge carriers is the origin of ferromagnetism. The magnetic interactions were better understood by codoping with nonmagnetic impurities. This work was supported by Marie-Curie Reintegration Grant (PIRG08-GA-2010-276973).

  13. Digital magnetic temperature transducer.

    NASA Technical Reports Server (NTRS)

    Tchernev, D. I.; Collier, T. E.

    1971-01-01

    A new digital magnetic temperature transducer is reported. The device utilizes the discontinuous behavior of the initial permeability with temperature at the Curie temperature of some magnetic materials. Since the Curie temperature is determined by the chemical and crystallographic composition of the particular material only, the transducer requires no calibration and has extremely high stability and reproducibility with time. The output of the transducer is inherently digital and, therefore, is directly compatible with the digital information processing and control without A/D conversion. The temperature-sensing portion of the transducer consists only of magnetic cores and wire and, therefore, has extremely high reliability, is shock and radiation insensitive, small, and virtually indestructible.

  14. Digital magnetic temperature transducer.

    NASA Technical Reports Server (NTRS)

    Tchernev, D. I.; Collier, T. E.

    1971-01-01

    A new digital magnetic temperature transducer is reported. The device utilizes the discontinuous behavior of the initial permeability with temperature at the Curie temperature of some magnetic materials. Since the Curie temperature is determined by the chemical and crystallographic composition of the particular material only, the transducer requires no calibration and has extremely high stability and reproducibility with time. The output of the transducer is inherently digital and, therefore, is directly compatible with the digital information processing and control without A/D conversion. The temperature-sensing portion of the transducer consists only of magnetic cores and wire and, therefore, has extremely high reliability, is shock and radiation insensitive, small, and virtually indestructible.

  15. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    PubMed Central

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-01-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques. PMID:27138030

  16. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy.

    PubMed

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-03

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  17. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  18. Electrorecovery of actinides at room temperature

    SciTech Connect

    Stoll, Michael E; Oldham, Warren J; Costa, David A

    2008-01-01

    There are a large number of purification and processing operations involving actinide species that rely on high-temperature molten salts as the solvent medium. One such application is the electrorefining of impure actinide metals to provide high purity material for subsequent applications. There are some drawbacks to the electrodeposition of actinides in molten salts including relatively low yields, lack of accurate potential control, maintaining efficiency in a highly corrosive environment, and failed runs. With these issues in mind we have been investigating the electrodeposition of actinide metals, mainly uranium, from room temperature ionic liquids (RTILs) and relatively high-boiling organic solvents. The RTILs we have focused on are comprised of 1,3-dialkylimidazolium or quaternary ammonium cations and mainly the {sup -}N(SO{sub 2}CF{sub 3}){sub 2} anion [bis(trif1uoromethylsulfonyl)imide {equivalent_to} {sup -}NTf{sub 2}]. These materials represent a class of solvents that possess great potential for use in applications employing electrochemical procedures. In order to ascertain the feasibility of using RTILs for bulk electrodeposition of actinide metals our research team has been exploring the electron transfer behavior of simple coordination complexes of uranium dissolved in the RTIL solutions. More recently we have begun some fundamental electrochemical studies on the behavior of uranium and plutonium complexes in the organic solvents N-methylpyrrolidone (NMP) and dimethylsulfoxide (DMSO). Our most recent results concerning electrodeposition will be presented in this account. The electrochemical behavior of U(IV) and U(III) species in RTILs and the relatively low vapor pressure solvents NMP and DMSO is described. These studies have been ongoing in our laboratory to uncover conditions that will lead to the successful bulk electrodeposition of actinide metals at a working electrode surface at room temperature or slightly elevated temperatures. The RTILs we

  19. Can doping graphite trigger room temperature superconductivity? Evidence for granular high-temperature superconductivity in water-treated graphite powder.

    PubMed

    Scheike, T; Böhlmann, W; Esquinazi, P; Barzola-Quiquia, J; Ballestar, A; Setzer, A

    2012-11-14

    Granular superconductivity in powders of small graphite grains (several tens of micrometers) is demonstrated after treatment with pure water. The temperature, magnetic field and time dependence of the magnetic moment of the treated graphite powder provides evidence for the existence of superconducting vortices with some similarities to high-temperature granular superconducting oxides but even at temperatures above 300 K. Room temperature superconductivity in doped graphite or at its interfaces appears to be possible.

  20. Permeameter for high-temperature magnetic measurements

    NASA Technical Reports Server (NTRS)

    Barranger, J. P.

    1972-01-01

    A permeameter is described that measures the magnetizing force and the corresponding magnetic induction up to 1000 C. The two symmetrical yokes are made of an alloy of 9 percent iron, 91 percent cobalt. A coil surrounding the specimen supplies a magnetizing force of up to 100 oersteds. The instrument uses the magnetic potentiometer principle to cancel the effects of the reluctance of the yoke and the joint gaps. Very close agreement was obtained at room temperature when compared to an MH type permeameter. The effect of temperature on the normal induction curves for the yoke material is also presented.

  1. Robust isothermal electric control of exchange bias at room temperature.

    PubMed

    He, Xi; Wang, Yi; Wu, Ning; Caruso, Anthony N; Vescovo, Elio; Belashchenko, Kirill D; Dowben, Peter A; Binek, Christian

    2010-07-01

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr(2)O(3) has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr(2)O(3) single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

  2. Robust isothermal electric control of exchange bias at room temperature

    NASA Astrophysics Data System (ADS)

    He, Xi; Wang, Yi; Wu, Ning; Caruso, Anthony N.; Vescovo, Elio; Belashchenko, Kirill D.; Dowben, Peter A.; Binek, Christian

    2010-07-01

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

  3. Robust isothermal electric control of exchange bias at room temperature

    SciTech Connect

    He, X.; Vescovo, E.; Wang, Y.; Caruso, A.N.; Belashchenko, K.D.; Dowben, P.A.; Binek, C.

    2010-06-20

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr{sub 2}O{sub 3} has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr{sub 2}O{sub 3} single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Neel temperature.

  4. Room-temperature nanowire terahertz photodetectors

    NASA Astrophysics Data System (ADS)

    Romeo, Lorenzo; Coquillant, Dominique; Viti, Leonardo; Ercolani, Daniele; Sorba, Lucia; Knap, Wojciech; Tredicucci, Alessandro; Vitiello, Miriam S.

    2013-01-01

    Semiconductor nanowires (NWs) represent an ideal building block for implementing rectifying diodes or plasma­ wave detectors that could operate well into the THz, thanks to the typical attofarad-order capacitance. Despite the strong effort in developing these nanostructures for a new generation of complementary metal-oxide semi­ conductors (CMOS), memory and photonic devices, their potential as radiation sensors into the Terahertz is just starting to be explored. We report on the development of NW-based field effect transistors operating as high sensitivity THz detectors in the 0.3 - 2.8 THz range. By feeding the radiation field of either an electronic THz source or a quantum cascade laser (QCL) at the gate-source electrodes by means of a wide band dipole antenna, we measured a photovoltage signal corresponding to responsivity values up to 100 V IW, with impressive noise equivalent power levels < 6 x 10-11W/Hz at room temperature and a > 300kHz modulation bandwidth. The potential scalability to even higher frequencies and the technological feasibility of realizing multi-pixel arrays coupled with QCL sources make the proposed technology highly competitive for a future generation of THz detection systems.

  5. Room temperature molecular up conversion in solution

    PubMed Central

    Nonat, Aline; Chan, Chi Fai; Liu, Tao; Platas-Iglesias, Carlos; Liu, Zhenyu; Wong, Wing-Tak; Wong, Wai-Kwok; Wong, Ka-Leung; Charbonnière, Loïc J.

    2016-01-01

    Up conversion is an Anti-Stokes luminescent process by which photons of low energy are piled up to generate light at a higher energy. Here we show that the addition of fluoride anions to a D2O solution of a macrocyclic erbium complex leads to the formation of a supramolecular [(ErL)2F]+ assembly in which fluoride is sandwiched between two complexes, held together by the synergistic interactions of the Er-F-Er bridging bond, four intercomplex hydrogen bonds and two aromatic stacking interactions. Room temperature excitation into the Er absorption bands at 980 nm of a solution of the complex in D2O results in the observation of up converted emission at 525, 550 and 650 nm attributed to Er centred transitions via a two-step excitation. The up conversion signal is dramatically increased upon formation of the [(ErL)2F]+ dimer in the presence of 0.5 equivalents of fluoride anions. PMID:27302144

  6. Room temperature ferroelectric and magnetic investigations and detailed phase analysis of Aurivillius phase Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Co{sub 0.3}O{sub 15} thin films

    SciTech Connect

    Keeney, Lynette; Kulkarni, Santosh; Deepak, Nitin; Schmidt, Michael; Petkov, Nikolay; Zhang, Panfeng F.; Roy, Saibal; Pemble, Martyn E.; Whatmore, Roger W.; Cavill, Stuart

    2012-09-01

    Aurivillius phase Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Co{sub 0.3}O{sub 15} (BTF7C3O) thin films on {alpha}-quartz substrates were fabricated by a chemical solution deposition method and the room temperature ferroelectric and magnetic properties of this candidate multiferroic were compared with those of thin films of Mn{sup 3+} substituted, Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Mn{sub 0.3}O{sub 15} (BTF7M3O). Vertical and lateral piezoresponse force microscopy (PFM) measurements of the films conclusively demonstrate that BTF7C3O and BTF7M3O thin films are piezoelectric and ferroelectric at room temperature, with the major polarization vector in the lateral plane of the films. No net magnetization was observed for the in-plane superconducting quantum interference device (SQUID) magnetometry measurements of BTF7M3O thin films. In contrast, SQUID measurements of the BTF7C3O films clearly demonstrated ferromagnetic behavior, with a remanent magnetization, B{sub r}, of 6.37 emu/cm{sup 3} (or 804 memu/g), remanent moment = 4.99 Multiplication-Sign 10{sup -5} emu. The BTF7C3O films were scrutinized by x-ray diffraction, high resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis mapping to assess the prospect of the observed multiferroic properties being intrinsic to the main phase. The results of extensive micro-structural phase analysis demonstrated that the BTF7C3O films comprised of a 3.95% Fe/Co-rich spinel phase, likely CoFe{sub 2-x}Ti{sub x}O{sub 4}, which would account for the observed magnetic moment in the films. Additionally, x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) imaging confirmed that the majority of magnetic response arises from the Fe sites of Fe/Co-rich spinel phase inclusions. While the magnetic contribution from the main phase could not be determined by the XMCD-PEEM images, these data however imply that the Bi{sub 5}Ti{sub 3}Fe{sub 0.7}Co{sub 0.3}O{sub 15} thin

  7. Room temperature quantum coherence in a potential molecular qubit

    NASA Astrophysics Data System (ADS)

    Bader, Katharina; Dengler, Dominik; Lenz, Samuel; Endeward, Burkhard; Jiang, Shang-Da; Neugebauer, Petr; van Slageren, Joris

    2014-10-01

    The successful development of a quantum computer would change the world, and current internet encryption methods would cease to function. However, no working quantum computer that even begins to rival conventional computers has been developed yet, which is due to the lack of suitable quantum bits. A key characteristic of a quantum bit is the coherence time. Transition metal complexes are very promising quantum bits, owing to their facile surface deposition and their chemical tunability. However, reported quantum coherence times have been unimpressive. Here we report very long quantum coherence times for a transition metal complex of 68 μs at low temperature (qubit figure of merit QM=3,400) and 1 μs at room temperature, much higher than previously reported values for such systems. We show that this achievement is because of the rigidity of the lattice as well as removal of nuclear spins from the vicinity of the magnetic ion.

  8. Room temperature quantum coherence in a potential molecular qubit.

    PubMed

    Bader, Katharina; Dengler, Dominik; Lenz, Samuel; Endeward, Burkhard; Jiang, Shang-Da; Neugebauer, Petr; van Slageren, Joris

    2014-10-20

    The successful development of a quantum computer would change the world, and current internet encryption methods would cease to function. However, no working quantum computer that even begins to rival conventional computers has been developed yet, which is due to the lack of suitable quantum bits. A key characteristic of a quantum bit is the coherence time. Transition metal complexes are very promising quantum bits, owing to their facile surface deposition and their chemical tunability. However, reported quantum coherence times have been unimpressive. Here we report very long quantum coherence times for a transition metal complex of 68 μs at low temperature (qubit figure of merit QM=3,400) and 1 μs at room temperature, much higher than previously reported values for such systems. We show that this achievement is because of the rigidity of the lattice as well as removal of nuclear spins from the vicinity of the magnetic ion.

  9. Multi-functional single electron device at room temperature

    NASA Astrophysics Data System (ADS)

    Nguyen, Chieu; Ong, Jason Kee Yang; Saraf, Ravi F.

    2014-03-01

    Smart designs of sub-wavelength structures enable observation of unusual properties of materials as in metamaterials. Typically, Coulomb blockade is observed in array of conducting particles at cryogenic temperature due to local charging of few particles by a single electron in the percolation path. We will report 1-D network of cemented Au nanoparticles in a multi-functional single electron device exhibiting Coulomb blockade at room temperature. The 1-D array is a self-assembled monolayer network spanning between electrodes 10-100 μm apart. It is formed by first bridging the negatively charged 10nm Au NPs with positive ions (Cd2+or Fe3+) followed by cementing with reactive gas to form a robust 2-D network. The network array cemented with CdS and Iron oxide exhibits robust single electron effect at room temperature with electroluminescence (EL) or ferromagnetism, respectively. The nature of EL in this symmetric structure is explained in term of field induced ionization. The EL is specular where the spots are independent of bias magnitude. The magnetic array exhibits ``spin-valve'' behavior with Barkhausen effect. These unique nano materials, fully self-assembled where, properties can be tailored by varying the cement chemistry, have potential applications in solid state lighting.

  10. The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    SciTech Connect

    Ohldag, Hendrik

    2011-08-12

    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon {pi} states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top {approx}10 nm of the irradiated sample where the actual magnetization reaches {approx_equal} 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite.

  11. Compton imager using room temperature silicon detectors

    NASA Astrophysics Data System (ADS)

    Kurfess, James D.; Novikova, Elena I.; Phlips, Bernard F.; Wulf, Eric A.

    2007-08-01

    We have been developing a multi-layer Compton Gamma Ray Imager using position-sensitive, intrinsic silicon detectors. Advantages of this approach include room temperature operation, reduced Doppler broadening, and use of conventional silicon fabrication technologies. We have obtained results on the imaging performance of a multi-layer instrument where each layer consists of a 2×2 array of double-sided strip detectors. Each detector is 63 mm×63 mm×2 mm thick and has 64 strips providing a strip pitch of approximately 0.9 mm. The detectors were fabricated by SINTEF ICT (Oslo Norway) from 100 mm diameter wafers. The use of large arrays of silicon detectors appears especially advantageous for applications that require excellent sensitivity, spectral resolution and imaging such as gamma ray astrophysics, detection of special nuclear materials, and medical imaging. The multiple Compton interactions (three or more) in the low-Z silicon enable the energy and direction of the incident gamma ray to be determined without full deposition of the incident gamma-ray energy in the detector. The performance of large volume instruments for various applications are presented, including an instrument under consideration for NASA's Advanced Compton Telescope (ACT) mission and applications to Homeland Security. Technology developments that could further extend the sensitivity and performance of silicon Compton Imagers are presented, including the use of low-energy (few hundred keV) electron tracking within novel silicon detectors and the potential for a wafer-bonding approach to produce thicker, position-sensitive silicon detectors with an associated reduction of required electronics and instrument cost.

  12. Room temperature micro-hydrogen-generator

    NASA Astrophysics Data System (ADS)

    Gervasio, Don; Tasic, Sonja; Zenhausern, Frederic

    A new compact and cost-effective hydrogen-gas generator has been made that is well suited for supplying hydrogen to a fuel-cell for providing base electrical power to hand-carried appliances. This hydrogen-generator operates at room temperature, ambient pressure and is orientation-independent. The hydrogen-gas is generated by the heterogeneous catalytic hydrolysis of aqueous alkaline borohydride solution as it flows into a micro-reactor. This reactor has a membrane as one wall. Using the membrane keeps the liquid in the reactor, but allows the hydrogen-gas to pass out of the reactor to a fuel-cell anode. Aqueous alkaline 30 wt% borohydride solution is safe and promotes long application life, because this solution is non-toxic, non-flammable, and is a high energy-density (≥2200 W-h per liter or per kilogram) hydrogen-storage solution. The hydrogen is released from this storage-solution only when it passes over the solid catalyst surface in the reactor, so controlling the flow of the solution over the catalyst controls the rate of hydrogen-gas generation. This allows hydrogen generation to be matched to hydrogen consumption in the fuel-cell, so there is virtually no free hydrogen-gas during power generation. A hydrogen-generator scaled for a system to provide about 10 W electrical power is described here. However, the technology is expected to be scalable for systems providing power spanning from 1 W to kW levels.

  13. Towards force detected single electron spin resonance at room temperature

    NASA Astrophysics Data System (ADS)

    Williams, C. C.; Payne, A.; Ambal, K.; Boehme, C.

    2013-03-01

    Electrically detected magnetic resonance (EDMR) spectroscopy has shown that electron tunneling at or within silicon dioxide layers is strongly dependent on spin-selection rules. Also demonstrated is the detection of single electron tunneling events by electrostatic force with sub-nanometer spatial resolution. Here we propose to combine force detected single electron tunneling microscopy with EDMR to demonstrate a new kind of single spin force microscope. This approach has much better sensitivity than magnetic force based single spin microscopes, since electrostatic forces are much larger than corresponding magnetic forces. In this method, a paramagnetic state in an oxidized AFM probe tip is brought within tunneling range of a paramagnetic state in an oxide surface. Under appropriate energy conditions, one of the unpaired electrons can randomly tunnel between the two states causing a random telegraph signal (RTS) to appear on the AFM cantilever frequency. Simulations predict that if magnetic resonance conditions are achieved, a measurable change in the RTS signal is detectable at room temperature. The theory and a quantitative simulation of this atomic scale spin resonance measurement will be presented, along with experimentally observed random telegraph signals.

  14. Optically Pumped Subwavelength Lasers Operated at Room Temperature

    DTIC Science & Technology

    2012-05-06

    REPORT NACHOS Project Final Report_University of Michigan Optically pumped subwavelength lasers operated at room temperature 14. ABSTRACT 16. SECURITY...28-Feb-2011 NACHOS Project Final Report_University of Michigan Optically pumped subwavelength lasers operated at room temperature Report Title

  15. Room temperature ferromagnetism with large magnetic moment at low field in rare-earth-doped BiFeO₃ thin films.

    PubMed

    Kim, Tae-Young; Hong, Nguyen Hoa; Sugawara, T; Raghavender, A T; Kurisu, M

    2013-05-22

    Thin films of rare earth (RE)-doped BiFeO3 (where RE=Sm, Ho, Pr and Nd) were grown on LaAlO3 substrates by using the pulsed laser deposition technique. All the films show a single phase of rhombohedral structure with space group R3c. The saturated magnetization in the Ho- and Sm-doped films is much larger than the values reported in the literature, and is observed at quite a low field of 0.2 T. For Ho and Sm doping, the magnetization increases as the film becomes thinner, suggesting that the observed magnetism is mostly due to a surface effect. In the case of Nd doping, even though the thin film has a large magnetic moment, the mechanism seems to be different.

  16. Understanding the magnetic interaction between intrinsic defects and impurity ions in room-temperature ferromagnetic Mg1-x Fe x O thin films

    NASA Astrophysics Data System (ADS)

    Kapilashrami, Mukes; Wang, Yung Jui; Li, Xin; Glans, Per-Anders; Fang, Mei; Riazanova, Anastasia V.; Belova, Lyubov M.; Rao, K. V.; Luo, Yi; Barbiellini, Bernardo; Lin, Hsin; Markiewicz, Robert; Bansil, Arun; Hussain, Zahid; Guo, Jinghua

    2016-04-01

    Understanding the nature and characteristics of the intrinsic defects and impurities in the dielectric barrier separating the ferromagnetic electrodes in a magnetic tunneling junction is of great importance for understanding the often observed ‘barrier-breakdown’ therein. In this connection, we present herein systematic experimental (SQUID and synchrotron-radiation-based x-ray absorption spectroscopy) and computational studies on the electronic and magnetic properties of Mg1-x Fe x O thin films. Our studies reveal: (i) defect aggregates comprised of basic and trimer units (Fe impurity coupled to 1 or 2 Mg vacancies) and (ii) existence of two competing magnetic orders, defect- and dopant-induced, with spin densities aligning anti-parallel if the trimer is present in the oxide matrix. These findings open up new avenues for designing tunneling barriers with high endurance and tunneling effect upon tuning the concentration/distribution of the two magnetic orders.

  17. Realization of ground-state artificial skyrmion lattices at room temperature

    PubMed Central

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai

    2015-01-01

    The topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. Here, we demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. The imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices. PMID:26446515

  18. Realization of ground-state artificial skyrmion lattices at room temperature

    SciTech Connect

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai

    2015-10-08

    We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.

  19. Realization of ground-state artificial skyrmion lattices at room temperature.

    PubMed

    Gilbert, Dustin A; Maranville, Brian B; Balk, Andrew L; Kirby, Brian J; Fischer, Peter; Pierce, Daniel T; Unguris, John; Borchers, Julie A; Liu, Kai

    2015-10-08

    The topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. Here, we demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. The imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.

  20. Realization of ground-state artificial skyrmion lattices at room temperature

    DOE PAGES

    Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; ...

    2015-10-08

    We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from themore » dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.« less

  1. Robust isothermal electric control of exchange bias at room temperature

    NASA Astrophysics Data System (ADS)

    Binek, Christian

    2011-03-01

    Voltage-controlled spintronics is of particular importance to continue progress in information technology through reduced power consumption, enhanced processing speed, integration density, and functionality in comparison with present day CMOS electronics. Almost all existing and prototypical solid-state spintronic devices rely on tailored interface magnetism, enabling spin-selective transmission or scattering of electrons. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is a key challenge to better spintronics. Currently, most attempts to electrically control magnetism focus on potentially large magnetoelectric effects of multiferroics. We report on our interest in magnetoelectric Cr 2 O3 (chromia). Robust isothermal electric control of exchange bias is achieved at room temperature in perpendicular anisotropic Cr 2 O3 (0001)/CoPd exchange bias heterostructures. This discovery promises significant implications for potential spintronics. From the perspective of basic science, our finding serves as macroscopic evidence for roughness-insensitive and electrically controllable equilibrium boundary magnetization in magnetoelectric antiferromagnets. The latter evolves at chromia (0001) surfaces and interfaces when chromia is in one of its two degenerate antiferromagnetic single domain states selected via magnetoelectric annealing. Theoretical insight into the boundary magnetization and its role in electrically controlled exchange bias is gained from first-principles calculations and general symmetry arguments. Measurements of spin-resolved ultraviolet photoemission, magnetometry at Cr 2 O3 (0001) surfaces, and detailed investigations of the unique exchange bias properties of Cr 2 O3 (0001)/CoPd including its electric controllability provide macroscopically averaged information about the boundary magnetization of chromia. Laterally resolved X-ray PEEM and temperature dependent MFM reveal detailed microscopic information of the chromia

  2. Realization of a flux-driven memtranstor at room temperature

    NASA Astrophysics Data System (ADS)

    Shi-Peng, Shen; Da-Shan, Shang; Yi-Sheng, Chai; Young, Sun

    2016-02-01

    The memtranstor has been proposed to be the fourth fundamental circuit memelement in addition to the memristor, memcapacitor, and meminductor. Here, we demonstrate the memtranstor behavior at room temperature in a device made of the magnetoelectric hexaferrite (Ba0.5Sr1.5Co2Fe11AlO22) where the electric polarization is tunable by external magnetic field. This device shows a nonlinear q-φ relationship with a butterfly-shaped hysteresis loop, in agreement with the anticipated memtranstor behavior. The memtranstor, like other memelements, has a great potential in developing more advanced circuit functionalities. Project supported by the National Natural Science Foundation of China (Grants Nos. 11227405, 11534015, 11274363, and 11374347) and the Natural Science Foundation from the Chinese Academy of Sciences (Grant No. XDB07030200).

  3. Imaging spin diffusion in germanium at room temperature

    NASA Astrophysics Data System (ADS)

    Zucchetti, C.; Bottegoni, F.; Vergnaud, C.; Ciccacci, F.; Isella, G.; Ghirardini, L.; Celebrano, M.; Rortais, F.; Ferrari, A.; Marty, A.; Finazzi, M.; Jamet, M.

    2017-07-01

    We report on the nonlocal detection of optically oriented spins in lightly n -doped germanium at room temperature. Localized spin generation is achieved by scanning a circularly polarized laser beam (λ =1550 nm) on an array of lithographically defined Pt microstructures. The in-plane oriented spin generated at the edges of such microstructures, placed at different distances from a spin-detection element, allows for a direct imaging of spin diffusion in the semiconductor, leading to a measured spin diffusion length of about 10 μ m . Two different spin-detection blocks are employed, consisting of either a magnetic tunnel junction or a platinum stripe where the spin current is converted in an electrical signal by the inverse spin-Hall effect. The second solution represents the realization of a nonlocal spin-injection/detection scheme that is completely free from ferromagnetic functional blocks.

  4. Efficient room-temperature nuclear spin hyperpolarization of a defect atom in a semiconductor.

    PubMed

    Puttisong, Y; Wang, X J; Buyanova, I A; Geelhaar, L; Riechert, H; Ptak, A J; Tu, C W; Chen, W M

    2013-01-01

    Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (~150 Gauss) and nuclear spin polarization (~15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in <5 μs at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications.

  5. Lead palladium titanate: A room-temperature multiferroic

    NASA Astrophysics Data System (ADS)

    Gradauskaite, Elzbieta; Gardner, Jonathan; Smith, Rebecca M.; Morrison, Finlay D.; Lee, Stephen L.; Katiyar, Ram S.; Scott, James F.

    2017-09-01

    There have been a large number of papers on bismuth ferrite (BiFe O3 ) over the past few years, trying to exploit its room-temperature magnetoelectric multiferroic properties. Although these are attractive, BiFe O3 is not the ideal multiferroic due to weak magnetization and the difficulty in limiting leakage currents. Thus there is an ongoing search for alternatives, including such materials as gallium ferrite (GaFe O3 ). In the present work we report a comprehensive study of the perovskite PbT i1 -xP dxO3 with 0 magnetization measurements, conductivity analysis, and study of crystallographic phases present in the samples, with special attention paid to minor phases identified as PdO, PbPd O2 , and P d3Pb . The work is remarkable in two ways: Pd is difficult to substitute into A B O3 perovskite oxides (where it might be useful for catalysis), and Pd is magnetic under only unusual conditions (under strain or internal electric fields).

  6. Room temperature electromechanical and magnetic investigations of ferroelectric Aurivillius phase Bi5Ti3(FexMn1-x)O15 (x = 1 and 0.7) chemical solution deposited thin films

    NASA Astrophysics Data System (ADS)

    Keeney, Lynette; Groh, Claudia; Kulkarni, Santosh; Roy, Saibal; Pemble, Martyn E.; Whatmore, Roger W.

    2012-07-01

    Aurivillius phase thin films of Bi5Ti3(FexMn1-x)O15 with x = 1 (Bi5Ti3FeO15) and 0.7 (Bi5Ti3Fe0.7Mn0.3O15) on SiO2-Si(100) and Pt/Ti/SiO2-Si substrates were fabricated by chemical solution deposition. The method was optimized in order to suppress formation of pyrochlore phase Bi2Ti2O7 and improve crystallinity. The structural properties of the films were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Optimum crystallinity and pyrochlore phase suppression was achieved by the addition of 15 to 25 mol. % excess bismuth to the sols. Based on this study, 17.5 mol. % excess bismuth was used in the preparation of Bi2Ti2O7-free films of Bi5Ti3FeO15 on SrTiO3(100) and NdGaO3(001) substrates, confirming the suppression of pyrochlore phase using this excess of bismuth. Thirty percent of the Fe3+ ions in Bi5Ti3FeO15 was substituted with Mn3+ ions to form Bi2Ti2O7-free thin films of Bi5Ti3Fe0.7Mn0.3O15 on Pt/Ti/SiO2-Si, SiO2-Si(100), SrTiO3(100), and NdGaO3(001) substrates. Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15 thin films on Pt/Ti/SiO2-Si and SiO2-Si(100) substrates were achieved with a higher degree of a-axis orientation compared with the films on SrTiO3(100) and NdGaO3(001) substrates. Room temperature electromechanical and magnetic properties of the thin films were investigated in order to assess the potential of these materials for piezoelectric, ferroelectric, and multiferroic applications. Vertical piezoresponse force microscopy measurements of the films demonstrate that Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15 thin films are piezoelectric at room temperature. Room temperature switching spectroscopy-piezoresponse force microscopy measurements in the presence and absence of an applied bias demonstrate local ferroelectric switching behaviour (180°) in the films. Superconducting quantum interference device magnetometry measurements do not show any room temperature ferromagnetic hysteresis down to an upper detection limit of 2.53 × 10

  7. Magnetic hysterysis evolution of Ni-Al alloy with Fe and Mn substitution by vacuum arc melting to produce the room temperature magnetocaloric effect material

    SciTech Connect

    Notonegoro, Hamdan Akbar; Kurniawan, Budhy; Manaf, Azwar; Setiawan, Jan

    2016-06-17

    The development of magnetocaloric effect (MCE) material is done in order to reduce the damage of the ozone layer caused by the chlorofluorocarbons (CFCs) emitted into the air. The research dealing with synthesis of magnetocaloric materials based of Ni-Al Heusler Alloy structure and by varying substitution some atoms of Ni with Fe and Al with Mn on Ni-Al Heusler Alloy structure to become Ni{sub 44}Fe{sub 6}Mn{sub 32}Al{sub 18}. Vacuum Arc Melting (VAM) equipment is used to form the alloys on vacuum condition and by flowing argon gas atmosphere and then followed by annealing process for 72 hours. X-Ray Diffraction (XRD) reveals that crystallite structure of material is observed. We define that Ni{sub 44}Fe{sub 6} as X{sub 2}, Mn{sub 25} as Y, and Al{sub 18}Mn{sub 7} as Z. Based on the XRD result, we observed that the general formula X{sub 2}YZ is not changed. The PERMAGRAF measurement revealed that there exists of magnetic hysterysis. The hysterysis show that the magnetic structures of the system undego evolution from diamagnetic to soft ferromagnetic material which all of the compound have the same crystallite structure. This evolution indicated that the change in the composition has led to changes the magnetic composition. Mn is the major element that gives strong magnetic properties to the sample. When Mn partially replaced position of Al, the sample became dominant to be influenced to improve their magnetic properties. In addition, substitution a part of Ni by Fe in the composition reveals a pinning of the domain walls in the sample.

  8. Preparation and characterization of (001)- and (110)-oriented 0.6FeTiO{sub 3}{center_dot}0.4Fe{sub 2}O{sub 3} films for room temperature magnetic semiconductors

    SciTech Connect

    Takada, Yusuke; Nakanishi, Makoto; Fujii, Tatsuo; Takada, Jun

    2008-06-23

    Thin films of ilmenite-hematite solid solution 0.6FeTiO{sub 3}{center_dot}0.4Fe{sub 2}O{sub 3} were prepared on {alpha}-Al{sub 2}O{sub 3} (001) and (110) single-crystalline substrates. The oxide phases formed in the thin films strongly depended on the oxygen partial pressure (P{sub O{sub 2}}) during deposition. At P{sub O{sub 2}}=1.3x10{sup -3} Pa, regardless of thesubstrate orientation, well-ordered 0.6FeTiO{sub 3}{center_dot}0.4Fe{sub 2}O{sub 3} films with R3 symmetry were epitaxially formed. Large saturation magnetization at room temperature was observed in both (001)- and (110)-oriented films. The differences in the magnetization and electrical resistivity curves between the (001)- and (110)-oriented films indicated the anisotropic nature of 0.6FeTiO{sub 3}{center_dot}0.4Fe{sub 2}O{sub 3}.

  9. Room temperature neutron diffraction and magnetic studies of multiferroic Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} solid solution

    SciTech Connect

    Dadami, S. T.; Matteppanavar, S.; Shivaraja, I.; Angadi, B.; Rayaprol, S.; Deshpande, S. K.

    2016-05-23

    The Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} (PBFNO) solid solution was synthesized by single step solid state reaction method and the optimized parameters are 700°C for 2hr (calcination) and 800°C for 3hr (sintering). The formation of desired material was confirmed using X-Ray Diffraction (XRD) and Neutron Diffraction (ND) studies. The structural and magnetic properties of the sintered pellets were investigated at room temperature (RT) through XRD, ND and Magnetic (M-H) studies. The structural analysis was carried out by Rietveld refinement through the Full Prof program. Rietveld refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.651(2) Å, b = 5.658(2) Å, c = 4.005(1) Å and α = 90°, β = 89.98(1)°, γ = 90°. RT M-H curve studies have been carried out. It shows the clear opening of hysteresis (M–H) loop, is evidenced as the existence of weak ferromagnetism at RT. The M-H data shows existence weak ferromagnetism embedded in an antiferromagnetic matrix structure. The dielectric constant with frequency shows the formation of barrier layers at the grain and grain boundary interfaces gives rise to interfacial space charge polarization.

  10. Entanglement and Bell's inequality violation above room temperature in metal carboxylates.

    SciTech Connect

    Souza, A M; Soares-Pinto, D O; Sarthour, R S; Oliveira, I S; Reis, Mario S; Brandao, Paula; Moreira Dos Santos, Antonio F

    2009-01-01

    In the present work we show that a particular family of materials, the metal carboxylates, may have entangled states up to very high temperatures. From magnetic-susceptibility measurements, we have estimated the critical temperature below which entanglement exists in the copper carboxylate {Cu-2(O2CH)(4)}{Cu(O2CH)(2)(2-methylpyridine)(2)}, and we have found this to be above room temperature (T-e similar to 630 K). Furthermore, the results show that the system remains maximally entangled until close to similar to 100 K and the Bell's inequality is violated up to nearly room temperature (similar to 290 K).

  11. The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    SciTech Connect

    Ohldag, H.; Esquinazi, P.; Arenholz, E.; Spemann, D.; Rothermel, M.; Setzer, A.; Butz, T.

    2010-05-01

    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon {pi} states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top {approx}10 nm of the irradiated sample where the average magnetization reaches {approx_equal} 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite. Also, our findings show that the magnetic properties of graphite surfaces, thin films or two dimensional graphene samples can be reliably studied using soft x-ray dichroism. Fundamental new insight into the magnetic properties of carbon based systems can thus be obtained.

  12. Room-temperature ferromagnetism in (Zn,Cr)Te

    NASA Astrophysics Data System (ADS)

    Saito, Hidekazu

    2006-03-01

    Ferromagnetic diluted magnetic semiconductors (DMSs) are the key material to developing semiconductor spintronic devices. One of the most characteristics physical phenomena in DMS is a strong interaction between sp-carriers and localized d-spins (sp-d exchange interaction) [1]. Confirmation of this interaction is essential to prove a synthesis of real DMS, and can be done directly by the magneto-optical studies such as a magnetic circular dichroism (MCD) measurement [2]. Here, we report room-temperature (RT) ferromagnetism with the sp-d exchange interaction in Zn1-xCrxTe (x=0.20) [3]. Zn1-xCrxTe films with x.3ex<=x 0.20 were grown on GaAs (001) substrates by a molecular beam epitaxy method. No sign of a secondary phase was detected in any films by the reflection high-energy electron and X-ray diffractions. MCD spectra were measured in a transmission mode. Magnetization (M) measurements were carried out using a SQUID. The M-H curves of Zn1-xCrxTe (x=0.20) showed a ferromagnetic behavior up to about RT. Curie temperature TC was estimated to be 300±10 K by the Arrott plot analysis. A strong enhancement of the MCD signal at the optical transition energies of critical points of host ZnTe was observed in Zn1-xCrxTe, indicating a strong sp-d exchange interaction. The MCD spectra of Zn1-xCrxTe at any magnetic field could be superposed upon a single spectrum, indicating that the observed MCD signals come from a single material, that is, Zn1-xCrxTe. The magnetic field dependence of MCD intensity showed the ferromagnetic feature, which coincides with the M-H curves measured using a SQUID. Furthermore, the MCD data showed the same TC as that obtained from magnetization data. These results indicate that Zn1-xCrxTe (x=0.20) is an intrinsic DMS with RT ferromagnetism. References [1] J. K. Furdyna, J. Appl. Phys. 64, R29 (1988). [2] K. Ando, in Magneto-Optics, Springer Series in Solid-State Science, edited by S. Sugano and N. Kojima (Springer, Berlin, 2000), Vol.128, p. 211. [3

  13. Room temperature and productivity in office work

    SciTech Connect

    Seppanen, O.; Fisk, W.J.; Lei, Q.H.

    2006-07-01

    Indoor temperature is one of the fundamental characteristics of the indoor environment. It can be controlled with a degree of accuracy dependent on the building and its HVAC system. The indoor temperature affects several human responses, including thermal comfort, perceived air quality, sick building syndrome symptoms and performance at work. In this study, we focused on the effects of temperature on performance at office work. We included those studies that had used objective indicators of performance that are likely to be relevant in office type work, such as text processing, simple calculations (addition, multiplication), length of telephone customer service time, and total handling time per customer for call-center workers. We excluded data from studies of industrial work performance. We calculated from all studies the percentage of performance change per degree increase in temperature, and statistically analyzed measured work performance with temperature. The results show that performance increases with temperature up to 21-22 C, and decreases with temperature above 23-24 C. The highest productivity is at temperature of around 22 C. For example, at the temperature of 30 C, the performance is only 91.1% of the maximum i.e. the reduction in performance is 8.9%.

  14. Fabrication method for a room temperature hydrogen sensor

    NASA Technical Reports Server (NTRS)

    Seal, Sudipta (Inventor); Shukla, Satyajit V. (Inventor); Ludwig, Lawrence (Inventor); Cho, Hyoung (Inventor)

    2011-01-01

    A sensor for selectively determining the presence and measuring the amount of hydrogen in the vicinity of the sensor. The sensor comprises a MEMS device coated with a nanostructured thin film of indium oxide doped tin oxide with an over layer of nanostructured barium cerate with platinum catalyst nanoparticles. Initial exposure to a UV light source, at room temperature, causes burning of organic residues present on the sensor surface and provides a clean surface for sensing hydrogen at room temperature. A giant room temperature hydrogen sensitivity is observed after making the UV source off. The hydrogen sensor of the invention can be usefully employed for the detection of hydrogen in an environment susceptible to the incursion or generation of hydrogen and may be conveniently used at room temperature.

  15. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    SciTech Connect

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2016-12-19

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  16. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    NASA Astrophysics Data System (ADS)

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2016-12-01

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  17. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    EPA Science Inventory

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  18. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    EPA Science Inventory

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  19. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride.

    PubMed

    Baig, R B Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N; Varma, Rajender S

    2016-12-19

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  20. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    DOE PAGES

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; ...

    2016-12-01

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.

  1. Room temperature synthesis of biodiesel using sulfonated graphitic carbon nitride

    PubMed Central

    Baig, R. B. Nasir; Verma, Sanny; Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2016-01-01

    Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature. PMID:27991593

  2. Tunable Curie temperature around room temperature and magnetocaloric effect in ternary Ce-Fe-B amorphous ribbons

    NASA Astrophysics Data System (ADS)

    Li, Zhu-bai; Zhang, Le-le; Zhang, Xue-feng; Li, Yong-feng; Zhao, Qian; Zhao, Tong-yun; Shen, Bao-gen

    2017-01-01

    Ce13-x Fe81+x B6 (x  =  0, 0.5, 1, 1.5, and 2) amorphous magnets were prepared by melt-spinning method. These magnets are magnetically soft at low temperature, and undergo a second-order phase transition from ferromagnetic to paramagnetic state near room temperature with a broad temperature span. The phase-transition temperature is tunable by the variation of the Ce/Fe atomic ratio, which is mainly due to the change of the coordination number of Fe atoms in these ternary Ce-Fe-B amorphous magnets. Though the entropy change is low, the refrigeration capacities are in the ranges of 116-150 J kg-1 and 319-420 J kg-1, respectively, for the magnetic field changes of 0-2 T and 0-5 T, which is comparable with those of conventional magnetic materials for room-temperature refrigeration. Given the low cost of Fe and Ce, Ce-Fe-B amorphous magnets are attractive magnetic refrigerant candidates.

  3. Neutron absorbing room temperature vulcanizable silicone rubber compositions

    DOEpatents

    Zoch, Harold L.

    1979-11-27

    A neutron absorbing composition comprising a one-component room temperature vulcanizable silicone rubber composition or a two-component room temperature vulcanizable silicone rubber composition in which the composition contains from 25 to 300 parts by weight based on the base silanol or vinyl containing diorganopolysiloxane polymer of a boron compound or boron powder as the neutron absorbing ingredient. An especially useful boron compound in this application is boron carbide.

  4. Temperature compensation for miniaturized magnetic sector

    NASA Technical Reports Server (NTRS)

    Sinha, Mahadeva P. (Inventor)

    2002-01-01

    Temperature compensation for a magnetic sector used in mass spectrometry. A high temperature dependant magnetic sector is used. This magnetic sector is compensated by a magnetic shunt that has opposite temperature characteristics to those of the magnet.

  5. Ferromagnetism at room temperature in Cr-doped anodic titanium dioxide nanotubes

    SciTech Connect

    Liao, Yulong E-mail: hwzhang@uestc.edu.cn; Zhang, Huaiwu E-mail: hwzhang@uestc.edu.cn; Li, Jie; Yu, Guoliang; Zhong, Zhiyong; Bai, Feiming; Jia, Lijun; Zhang, Shihong; Zhong, Peng

    2014-05-07

    This study reports the room-temperature ferromagnetism in Cr-doped TiO{sub 2} nanotubes (NTs) synthesized via the electrochemical method followed by a novel Cr-doping process. Scanning electron microscopy and transmission electron microscopy showed that the TiO{sub 2} NTs were highly ordered with length up to 26 μm, outer diameter about 110 nm, and inner diameter about 100 nm. X-ray diffraction results indicated there were no magnetic contaminations of metallic Cr clusters or any other phases except anatase TiO{sub 2}. The Cr-doped TiO{sub 2} NTs were further annealed in oxygen, air and argon, and room-temperature ferromagnetism was observed in all Cr-doped samples. Moreover, saturation magnetizations and coercivities of the Cr-doped under various annealing atmosphere were further analyzed, and results indicate that oxygen content played a critical role in the room-temperature ferromagnetism.

  6. Room-temperature synthesis of three-dimensional porous ZnO@CuNi hybrid magnetic layers with photoluminescent and photocatalytic properties

    PubMed Central

    Guerrero, Miguel; Zhang, Jin; Altube, Ainhoa; García-Lecina, Eva; Roldan, Mònica; Baró, Maria Dolors; Pellicer, Eva; Sort, Jordi

    2016-01-01

    Abstract A facile synthetic approach to prepare porous ZnO@CuNi hybrid films is presented. Initially, magnetic CuNi porous layers (consisting of phase separated CuNi alloys) are successfully grown by electrodeposition at different current densities using H2 bubbles as a dynamic template to generate the porosity. The porous CuNi alloys serve as parent scaffolds to be subsequently filled with a solution containing ZnO nanoparticles previously synthesized by sol-gel. The dispersed nanoparticles are deposited dropwise onto the CuNi frameworks and the solvent is left to evaporate while the nanoparticles impregnate the interior of the pores, rendering ZnO-coated CuNi 3D porous structures. No thermal annealing is required to obtain the porous films. The synthesized hybrid porous layers exhibit an interesting combination of tunable ferromagnetic and photoluminescent properties. In addition, the aqueous photocatalytic activity of the composite is studied under UV−visible light irradiation for the degradation of Rhodamine B. The proposed method represents a fast and inexpensive approach towards the implementation of devices based on metal-semiconductor porous systems, avoiding the use of post-synthesis heat treatment steps which could cause deleterious oxidation of the metallic counterpart, as well as collapse of the porous structure and loss of the ferromagnetic properties. PMID:27877868

  7. Room-temperature synthesis of three-dimensional porous ZnO@CuNi hybrid magnetic layers with photoluminescent and photocatalytic properties.

    PubMed

    Guerrero, Miguel; Zhang, Jin; Altube, Ainhoa; García-Lecina, Eva; Roldan, Mònica; Baró, Maria Dolors; Pellicer, Eva; Sort, Jordi

    2016-01-01

    A facile synthetic approach to prepare porous ZnO@CuNi hybrid films is presented. Initially, magnetic CuNi porous layers (consisting of phase separated CuNi alloys) are successfully grown by electrodeposition at different current densities using H2 bubbles as a dynamic template to generate the porosity. The porous CuNi alloys serve as parent scaffolds to be subsequently filled with a solution containing ZnO nanoparticles previously synthesized by sol-gel. The dispersed nanoparticles are deposited dropwise onto the CuNi frameworks and the solvent is left to evaporate while the nanoparticles impregnate the interior of the pores, rendering ZnO-coated CuNi 3D porous structures. No thermal annealing is required to obtain the porous films. The synthesized hybrid porous layers exhibit an interesting combination of tunable ferromagnetic and photoluminescent properties. In addition, the aqueous photocatalytic activity of the composite is studied under UV-visible light irradiation for the degradation of Rhodamine B. The proposed method represents a fast and inexpensive approach towards the implementation of devices based on metal-semiconductor porous systems, avoiding the use of post-synthesis heat treatment steps which could cause deleterious oxidation of the metallic counterpart, as well as collapse of the porous structure and loss of the ferromagnetic properties.

  8. Large room-temperature rotating magnetocaloric effect in NdCo4Al polycrystalline alloy

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Hu, Q. B.; Wang, C. C.; Cao, Q. Q.; Gao, W. L.; Wang, D. H.; Du, Y. W.

    2017-01-01

    The magnetic refrigeration based on rotating magnetocaloric effect (MCE) is promising to build a simplified magnetic cooling system. Until now, most magnetic refrigerants for rotating MCE are single crystal and work at low temperature, which hinder the development of this refrigeration technology. In present paper, we report a large room-temperature rotating MCE in a magnetic-field-aligned NdCo4Al polycrystalline alloy. A large rotating magnetic entropy change of 1.3 J kg-1 K-1 under 10 kOe and a broad operating temperature window of 52 K are achieved. The origin of large rotating MCE in NdCo4Al polycrystalline alloy and its advantages for rotating magnetic refrigeration are discussed.

  9. Direct electrochemistry and electrocatalysis of heme proteins immobilised in carbon-coated nickel magnetic nanoparticle-chitosan-dimethylformamide composite films in room-temperature ionic liquids.

    PubMed

    Wang, Ting; Wang, Lu; Tu, Jiaojiao; Xiong, Huayu; Wang, Shengfu

    2013-12-01

    The direct electrochemistry and electrocatalysis of heme proteins entrapped in carbon-coated nickel magnetic nanoparticle-chitosan-dimethylformamide (CNN-CS-DMF) composite films were investigated in the hydrophilic ionic liquid [bmim][BF4]. The surface morphologies of a representative set of films were characterised via scanning electron microscopy. The proteins immobilised in the composite films were shown to retain their native secondary structure using UV-vis spectroscopy. The electrochemical performance of the heme proteins-CNN-CS-DMF films was evaluated via cyclic voltammetry and chronoamperometry. A pair of stable and well-defined redox peaks was observed for the heme protein films at formal potentials of -0.151 V (HRP), -0.167 V (Hb), -0.155 V (Mb) and -0.193 V (Cyt c) in [bmim][BF4]. Moreover, several electrochemical parameters of the heme proteins were calculated by nonlinear regression analysis of the square-wave voltammetry. The addition of CNN significantly enhanced not only the electron transfer of the heme proteins but also their electrocatalytic activity toward the reduction of H2O2. Low apparent Michaelis-Menten constants were obtained for the heme protein-CNN-CS-DMF films, demonstrating that the biosensors have a high affinity for H2O2. In addition, the resulting electrodes displayed a low detection limit and improved sensitivity for detecting H2O2, which indicates that the biocomposite film can serve as a platform for constructing new non-aqueous biosensors for real detection. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. Room temperature d{sup 0} ferromagnetism in ZnS nanocrystals

    SciTech Connect

    Proshchenko, Vitaly; Horoz, Sabit; Tang, Jinke; Dahnovsky, Yuri

    2016-06-14

    Room temperature ferromagnetic semiconductors have a great deal of advantage because of their easy integration into semiconductor devices. ZnS nanocrystals (NCs), bulk, and surfaces exhibit d{sup 0} ferromagnetism at room temperature. The experiments reveal that NC ferromagnetism takes place at low and room temperatures only due to Zn vacancies (S vacancies do not contribute). To understand the mechanism of d{sup 0} ferromagnetism, we introduce the surface-bulk model of a nanocrystal, which includes both surface and bulk magnetizations. The calculations demonstrate that the surface has the higher than bulk magnetization. We find the mechanism of the ferromagnetism is due to sulfur s- and p-electrons in a tetrahedral crystal field. The bulk magnetic moment increases with Zn vacancy concentration at small concentrations and then goes down at larger concentrations. A surface magnetic moment behaves differently with the concentration. It is always a monotonically rising function. We find that the total NC magnetic moment increases with the size and concentration of Zn vacancies (only low concentrations). We also study the magnetization per unit cell where we find that it decreases for the surface and increases for bulk magnetism with the NC size.

  11. Nature of room-temperature photoluminescence in ZnO

    SciTech Connect

    Shan, W.; Walukiewicz, W.; Ager III, J.W.; Yu, K.M.; Yuan, H.B.; Xin, H.P.; Cantwell, G.; Song, J.J.

    2004-11-11

    The temperature dependence of the photoluminescence (PL) transitions associated with various excitons and their phonon replicas in high-purity bulk ZnO has been studied at temperatures from 12 K to above room temperature (320 K). Several strong PL emission lines associated with LO phonon replicas of free and bound excitons are clearly observed. The room temperature PL spectrum is dominated by the phonon replicas of the free exciton transition with the maximum at the first LO phonon replica. The results explain the discrepancy between the transition energy of free exciton determined by reflection measurement and the peak position obtained by the PL measurement.

  12. Control and Room Temperature Optimization of Energy Efficient Buildings

    SciTech Connect

    Djouadi, Seddik M; Kuruganti, Phani Teja

    2012-01-01

    The building sector consumes a large part of the energy used in the United States and is responsible for nearly 40% of greenhouse gas emissions. It is therefore economically and environmentally important to reduce the building energy consumption to realize massive energy savings. In this paper, a method to control room temperature in buildings is proposed. The approach is based on a distributed parameter model represented by a three dimensional (3D) heat equation in a room with heater/cooler located at ceiling. The latter is resolved using finite element methods, and results in a model for room temperature with thousands of states. The latter is not amenable to control design. A reduced order model of only few states is then derived using Proper Orthogonal Decomposition (POD). A Linear Quadratic Regulator (LQR) is computed based on the reduced model, and applied to the full order model to control room temperature.

  13. Observation of sub-100 nm Néel skyrmions at room temperature

    NASA Astrophysics Data System (ADS)

    Te Velthuis, S. G. E.; Jiang, W.; Zhang, S.; Phatak, C.; Zhang, W.; Jungfleisch, M. B.; Pearson, J. E.; Petford-Long, A.; Hoffmann, A.

    Magnetic skyrmions are topologically stable spin textures that have attracted tremendous attention in the field of spintronics. As compared to Bloch skyrmions, which are typical for only few bulk chiral magnets, Néel skyrmions in magnetic multilayers [1, 2, 3] may be more ubiquitous and have the advantage that included layers of heavy metals provide efficient current induced spin-orbit torques. By optimizing the stacking structure, we present an experimental strategy towards nanometer-scale skyrmions at room temperature in the absence of a magnetic field. Furthermore, we discuss the experimental challenge of identifying the chiral nature of Néel skyrmions by using Lorentz transmission electron microscopy. Our results constitute an important step for enabling skyrmion based ultra-high density data storage, and for probing topological physics at room temperature Work supported by the Department of Energy, Office of Science, Basic Energy Science, Materials Sciences and Engineering Division.

  14. Room-temperature electron spin amplifier based on Ga(In)NAs alloys.

    PubMed

    Puttisong, Yuttapoom; Buyanova, Irina A; Ptak, Aaron J; Tu, Charles W; Geelhaar, Lutz; Riechert, Henning; Chen, Weimin M

    2013-02-06

    The first experimental demonstration of a spin amplifier at room temperature is presented. An efficient, defect-enabled spin amplifier based on a non-magnetic semiconductor, Ga(In)NAs, is proposed and demonstrated, with a large spin gain (up to 2700% at zero field) for conduction electrons and a high cut-off frequency of up to 1 GHz.

  15. Room-Temperature Spin-Orbit Torque Switching Induced by a Topological Insulator

    NASA Astrophysics Data System (ADS)

    Han, Jiahao; Richardella, A.; Siddiqui, Saima A.; Finley, Joseph; Samarth, N.; Liu, Luqiao

    2017-08-01

    The strongly spin-momentum coupled electronic states in topological insulators (TI) have been extensively pursued to realize efficient magnetic switching. However, previous studies show a large discrepancy of the charge-spin conversion efficiency. Moreover, current-induced magnetic switching with TI can only be observed at cryogenic temperatures. We report spin-orbit torque switching in a TI-ferrimagnet heterostructure with perpendicular magnetic anisotropy at room temperature. The obtained effective spin Hall angle of TI is substantially larger than the previously studied heavy metals. Our results demonstrate robust charge-spin conversion in TI and provide a direct avenue towards applicable TI-based spintronic devices.

  16. Stable room-temperature ferromagnetic phase at the FeRh(100) surface

    SciTech Connect

    Pressacco, Federico; Uhlir, Vojtech; Gatti, Matteo; Bendounan, Azzedine; Fullerton, Eric E.; Sirotti, Fausto

    2016-03-03

    Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. Furthermore, we find that the symmetry breaking induced at the Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings.

  17. Stable room-temperature ferromagnetic phase at the FeRh(100) surface

    PubMed Central

    Pressacco, Federico; Uhlίř, Vojtěch; Gatti, Matteo; Bendounan, Azzedine; Fullerton, Eric E.; Sirotti, Fausto

    2016-01-01

    Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. We find that the symmetry breaking induced at the Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings. PMID:26935274

  18. Enabling room temperature sodium metal batteries

    SciTech Connect

    Cao, Ruiguo; Mishra, Kuber; Li, Xiaolin; Qian, Jiangfeng; Engelhard, Mark H.; Bowden, Mark E.; Han, Kee Sung; Mueller, Karl T.; Henderson, Wesley A.; Zhang, Ji-Guang

    2016-12-01

    Rechargeable batteries based upon sodium (Na+) cations are at the core of many new battery chemistries beyond Li-ion batteries. Rather than using carbon or alloy-based anodes, the direct utilization of solid sodium metal as an anode would be highly advantageous, but its use has been highly problematic due to its high reactivity. In this work, however, it is demonstrated that, by tailoring the electrolyte formulation, solid Na metal can be electrochemically plated/stripped at ambient temperature with high efficiency (> 99%) on both copper and inexpensive aluminum current collectors thereby enabling a shift in focus to new battery chemical couples based upon Na metal operating at ambient temperature. These highly concentrated electrolytes has enabled stable cycling of Na metal batteries based on a Na metal anode and Na3V2(PO4)3 cathode at high rates with very high efficiency.

  19. Proposal for a room-temperature diamond maser

    PubMed Central

    Jin, Liang; Pfender, Matthias; Aslam, Nabeel; Neumann, Philipp; Yang, Sen; Wrachtrup, Jörg; Liu, Ren-Bao

    2015-01-01

    The application of masers is limited by its demanding working conditions (high vacuum or low temperature). A room-temperature solid-state maser is highly desirable, but the lifetimes of emitters (electron spins) in solids at room temperature are usually too short (∼ns) for population inversion. Masing from pentacene spins in p-terphenyl crystals, which have a long spin lifetime (∼0.1 ms), has been demonstrated. This maser, however, operates only in the pulsed mode. Here we propose a room-temperature maser based on nitrogen-vacancy centres in diamond, which features the longest known solid-state spin lifetime (∼5 ms) at room temperature, high optical pumping efficiency (∼106 s−1) and material stability. Our numerical simulation demonstrates that a maser with a coherence time of approximately minutes is feasible under readily accessible conditions (cavity Q-factor ∼5 × 104, diamond size ∼3 × 3 × 0.5 mm3 and pump power <10 W). A room-temperature diamond maser may facilitate a broad range of microwave technologies. PMID:26394758

  20. Proposal for a room-temperature diamond maser.

    PubMed

    Jin, Liang; Pfender, Matthias; Aslam, Nabeel; Neumann, Philipp; Yang, Sen; Wrachtrup, Jörg; Liu, Ren-Bao

    2015-09-23

    The application of masers is limited by its demanding working conditions (high vacuum or low temperature). A room-temperature solid-state maser is highly desirable, but the lifetimes of emitters (electron spins) in solids at room temperature are usually too short (∼ns) for population inversion. Masing from pentacene spins in p-terphenyl crystals, which have a long spin lifetime (∼0.1 ms), has been demonstrated. This maser, however, operates only in the pulsed mode. Here we propose a room-temperature maser based on nitrogen-vacancy centres in diamond, which features the longest known solid-state spin lifetime (∼5 ms) at room temperature, high optical pumping efficiency (∼10(6) s(-1)) and material stability. Our numerical simulation demonstrates that a maser with a coherence time of approximately minutes is feasible under readily accessible conditions (cavity Q-factor ∼5 × 10(4), diamond size ∼3 × 3 × 0.5 mm(3) and pump power <10 W). A room-temperature diamond maser may facilitate a broad range of microwave technologies.

  1. Room-temperature bonding of thin plastic sheets

    NASA Technical Reports Server (NTRS)

    Frazer, R. E.

    1979-01-01

    Thin sheets of plastic are bonded together, without heat, by depositing metal films on plastic and applying light pressure. Films are pressed together at room temperature, technique which makes it possible to join organic material without high temperatures necessary for conventional adhesive bonding.

  2. Giant electrocaloric effect in ferroelectric nanotubes near room temperature.

    PubMed

    Liu, Man; Wang, Jie

    2015-01-12

    Ferroelectric perovskite oxides possess large electrocaloric effect, but only at high temperature, which limits their potential as next generation solid state cooling devices. Here, we demonstrate from phase field simulations that a giant adiabatic temperature change exhibits near room temperature in the strained ferroelectric PbTiO₃ nanotubes, which is several times in magnitude larger than that of PbTiO₃ thin films. Such giant adiabatic temperature change is attributed to the extrinsic contribution of unusual domain transition, which involves a dedicated interplay among the electric field, strain, temperature and polarization. Careful selection of external strain allows one to harness the extrinsic contribution to obtain large adiabatic temperature change in ferroelectric nanotubes near room temperature. Our finding provides a novel insight into the electrocaloric response of ferroelectric nanostructures and leads to a new strategy to tailor and improve the electrocaloric properties of ferroelectric materials through domain engineering.

  3. Giant electrocaloric effect in ferroelectric nanotubes near room temperature

    PubMed Central

    Liu, Man; Wang, Jie

    2015-01-01

    Ferroelectric perovskite oxides possess large electrocaloric effect, but only at high temperature, which limits their potential as next generation solid state cooling devices. Here, we demonstrate from phase field simulations that a giant adiabatic temperature change exhibits near room temperature in the strained ferroelectric PbTiO3 nanotubes, which is several times in magnitude larger than that of PbTiO3 thin films. Such giant adiabatic temperature change is attributed to the extrinsic contribution of unusual domain transition, which involves a dedicated interplay among the electric field, strain, temperature and polarization. Careful selection of external strain allows one to harness the extrinsic contribution to obtain large adiabatic temperature change in ferroelectric nanotubes near room temperature. Our finding provides a novel insight into the electrocaloric response of ferroelectric nanostructures and leads to a new strategy to tailor and improve the electrocaloric properties of ferroelectric materials through domain engineering. PMID:25578434

  4. Room Temperature Silicene Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Akinwande, Deji

    Silicene, a buckled Si analogue of graphene, holds significant promise for future electronics beyond traditional CMOS. In our predefined experiments via encapsulated delamination with native electrodes approach, silicene devices exhibit an ambipolar charge transport behavior, corroborating theories on Dirac band in Ag-free silicene. Monolayer silicene device has extracted field-effect mobility within the theoretical expectation and ON/OFF ratio greater than monolayer graphene, while multilayer silicene devices show decreased mobility and gate modulation. Air-stability of silicene devices depends on the number of layers of silicene and intrinsic material structure determined by growth temperature. Few or multi-layer silicene devices maintain their ambipolar behavior for days in contrast to minutes time scale for monolayer counterparts under similar conditions. Multilayer silicene grown at different temperatures below 300oC possess different intrinsic structures and yield different electrical property and air-stability. This work suggests a practical prospect to enable more air-stable silicene devices with layer and growth condition control, which can be leveraged for other air-sensitive 2D materials. In addition, we describe quantum and classical transistor device concepts based on silicene and related buckled materials that exploit the 2D topological insulating phenomenon. The transistor device physics offer the potential for ballistic transport that is robust against scattering and can be employed for both charge and spin transport. This work was supported by the ARO.

  5. Room-Temperature Determination of Two-Dimensional Electron Gas Concentration and Mobility in Heterostructures

    NASA Technical Reports Server (NTRS)

    Schacham, S. E.; Mena, R. A.; Haugland, E. J.; Alterovitz, S. A.

    1993-01-01

    A technique for determination of room-temperature two-dimensional electron gas (2DEG) concentration and mobility in heterostructures is presented. Using simultaneous fits of the longitudinal and transverse voltages as a function of applied magnetic field, we were able to separate the parameters associated with the 2DEG from those of the parallel layer. Comparison with the Shubnikov-de Haas data derived from measurements at liquid helium temperatures proves that the analysis of the room-temperature data provides an excellent estimate of the 2DEG concentration. In addition we were able to obtain for the first time the room-temperature mobility of the 2DEG, an important parameter to device application. Both results are significantly different from those derived from conventional Hall analysis.

  6. Direct observation of a highly spin-polarized organic spinterface at room temperature

    PubMed Central

    Djeghloul, F.; Ibrahim, F.; Cantoni, M.; Bowen, M.; Joly, L.; Boukari, S.; Ohresser, P.; Bertran, F.; Le Fèvre, P.; Thakur, P.; Scheurer, F.; Miyamachi, T.; Mattana, R.; Seneor, P.; Jaafar, A.; Rinaldi, C.; Javaid, S.; Arabski, J.; Kappler, J. -P; Wulfhekel, W.; Brookes, N. B.; Bertacco, R.; Taleb-Ibrahimi, A.; Alouani, M.; Beaurepaire, E.; Weber, W.

    2013-01-01

    Organic semiconductors constitute promising candidates toward large-scale electronic circuits that are entirely spintronics-driven. Toward this goal, tunneling magnetoresistance values above 300% at low temperature suggested the presence of highly spin-polarized device interfaces. However, such spinterfaces have not been observed directly, let alone at room temperature. Thanks to experiments and theory on the model spinterface between phthalocyanine molecules and a Co single crystal surface, we clearly evidence a highly efficient spinterface. Spin-polarised direct and inverse photoemission experiments reveal a high degree of spin polarisation at room temperature at this interface. We measured a magnetic moment on the molecule's nitrogen π orbitals, which substantiates an ab-initio theoretical description of highly spin-polarised charge conduction across the interface due to differing spinterface formation mechanisms in each spin channel. We propose, through this example, a recipe to engineer simple organic-inorganic interfaces with remarkable spintronic properties that can endure well above room temperature. PMID:23412079

  7. Development of a compact magnetic resonance imaging system for a cold room

    NASA Astrophysics Data System (ADS)

    Adachi, Satoru; Ozeki, Toshihiro; Shigeki, Ryosuke; Handa, Shinya; Kose, Katsumi; Haishi, Tomoyuki; Aoki, Masaaki

    2009-05-01

    A compact magnetic resonance imaging (MRI) system for a cold (-5 °C) room has been developed to acquire MR images below the freezing point of water. The MRI system consists of a 1.0 T permanent magnet, a higher-order shim coil set, and a gradient coil probe, installed in the cold room, and a compact MRI console installed in a room at normal temperature (20-25 °C). The most difficult problem for the installation of the MRI system in the cold room was the degradation of the field homogeneity of the permanent magnet shimmed at 25 °C. To overcome this problem, higher-order shim coils were developed and the temperature variation of the magnetic field distribution was measured using a standard phantom with and without shim coil currents. As a result, it was confirmed that the homogeneity (the difference between the minimum and maximum values) of the magnetic field in the 17×17×19 mm3 rectangular parallelepiped region was improved from 117 to 59 ppm using an appropriate combination of shim coil currents. A snowpack immersed in dodecane (C12H26) was imaged using a driven-equilibrium three-dimensional (3D) spin-echo sequence at -5 °C. The visualized 3D structure of the snowpack demonstrated the effectiveness of our approach.

  8. Room temperature nanoscale ferroelectricity in magnetoelectric GaFeO3 epitaxial thin films.

    PubMed

    Mukherjee, Somdutta; Roy, Amritendu; Auluck, Sushil; Prasad, Rajendra; Gupta, Rajeev; Garg, Ashish

    2013-08-23

    We demonstrate room temperature ferroelectricity in the epitaxial thin films of magnetoelectric gallium ferrite. Piezoforce measurements show a 180° phase shift of piezoresponse upon switching the electric field indicating nanoscale ferroelectricity in the thin films. Further, temperature-dependent impedance analysis with and without the presence of an external magnetic field clearly reveals a pronounced magnetodielectric effect across the magnetic transition temperature. In addition, our first principles calculations show that Fe ions are not only responsible for ferrimagnetism as observed earlier but also give rise to the observed ferroelectricity, making gallium ferrite a unique single phase multiferroic.

  9. Low-temperature magnetic refrigerator

    DOEpatents

    Barclay, J.A.

    1983-05-26

    The invention relates to magnetic refrigeration and more particularly to low temperature refrigeration between about 4 and about 20 K, with an apparatus and method utilizing a belt of magnetic material passed in and out of a magnetic field with heat exchangers within and outside the field operably disposed to accomplish refrigeration.

  10. Low-temperature magnetic refrigerator

    DOEpatents

    Barclay, John A.

    1985-01-01

    The disclosure is directed to a low temperature 4 to 20 K. refrigeration apparatus and method utilizing a ring of magnetic material moving through a magnetic field. Heat exchange is accomplished in and out of the magnetic field to appropriately utilize the device to execute Carnot and Stirling cycles.

  11. Room Temperature Crystallization of Hydroxyapatite in Porous Silicon Structures.

    PubMed

    Santana, M; Estevez, J O; Agarwal, V; Herrera-Becerra, R

    2016-12-01

    Porous silicon (PS) substrates, with different pore sizes and morphology, have been used to crystallize hydroxyapatite (HA) nano-fibers by an easy and economical procedure using a co-precipitation method at room temperature. In situ formation of HA nanoparticles, within the meso- and macroporous silicon structure, resulted in the formation of nanometer-sized hydroxyapatite crystals on/within the porous structure. The X-ray diffraction technique was used to determine the tetragonal structure of the crystals. Analysis/characterization demonstrates that under certain synthesis conditions, growth and crystallization of hydroxyapatite layer on/inside PS can be achieved at room temperature. Such composite structures expand the possibility of designing a new bio-composite material based on the hydroxyapatite and silicon synthesized at room temperature.

  12. Giant room-temperature elastocaloric effect in ferroelectric ultrathin films.

    PubMed

    Liu, Yang; Infante, Ingrid C; Lou, Xiaojie; Bellaiche, Laurent; Scott, James F; Dkhil, Brahim

    2014-09-17

    Environmentally friendly ultrathin BaTiO3 capacitors can exhibit a giant stress-induced elastocaloric effect without hysteresis loss or Joule heating. By combining this novel elastocaloric effect with the intrinsic electrocaloric effect, an ideal refrigeration cycle with high performance (temperature change over 10 K with a wide working-temperature window of 60 K) at room temperature is proposed for future cooling applications.

  13. Nanostructured Materials for Room-Temperature Gas Sensors.

    PubMed

    Zhang, Jun; Liu, Xianghong; Neri, Giovanni; Pinna, Nicola

    2016-02-03

    Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

  14. Crystallization of bacteriorhodopsin from bicelle formulations at room temperature.

    PubMed

    Faham, Salem; Boulting, Gabriella L; Massey, Elizabeth A; Yohannan, Sarah; Yang, Dawn; Bowie, James U

    2005-03-01

    We showed previously that high-quality crystals of bacteriorhodopsin (bR) from Halobacterium salinarum can be obtained from bicelle-forming DMPC/CHAPSO mixtures at 37 degrees C. As many membrane proteins are not sufficiently stable for crystallization at this high temperature, we tested whether the bicelle method could be applied at a lower temperature. Here we show that bR can be crystallized at room temperature using two different bicelle-forming compositions: DMPC/CHAPSO and DTPC/CHAPSO. The DTPC/CHAPSO crystals grown at room temperature are essentially identical to the previous, twinned crystals: space group P21 with unit cell dimensions of a = 44.7 A, b = 108.7 A, c = 55.8 A, beta = 113.6 degrees . The room-temperature DMPC/CHAPSO crystals are untwinned, however, and belong to space group C222(1) with the following unit cell dimensions: a = 44.7 A, b = 102.5 A, c = 128.2 A. The bR protein packs into almost identical layers in the two crystal forms, but the layers stack differently. The new untwinned crystal form yielded clear density for a previously unresolved CHAPSO molecule inserted between protein subunits within the layers. The ability to grow crystals at room temperature significantly expands the applicability of bicelle crystallization.

  15. Robust room temperature ferromagnetism and band gap tuning in nonmagnetic Mg doped ZnO films

    NASA Astrophysics Data System (ADS)

    Quan, Zhiyong; Liu, Xia; Qi, Yan; Song, Zhilin; Qi, Shifei; Zhou, Guowei; Xu, Xiaohong

    2017-03-01

    Mg doped ZnO films with hexagonal wurtzite structure were deposited on c-cut sapphire Al2O3 substrates by pulsed laser deposition. Both room temperature ferromagnetism and band gap of the films simultaneously tuned by the concentration of oxygen vacancies were performed. Our results further reveal that the singly occupied oxygen vacancies should be responsible for the room temperature ferromagnetism and band gap narrowing. Singly occupied oxygen vacancies having the localized magnetic moments form bound magnetic polarons, which results in a long-range ferromagnetic ordering due to Mg doping. Moreover, band gap narrowing of the films is probably due to the formation of impurity band in the vicinity of valence band, originating from singly occupied oxygen vacancies. These results may build a bridge to understand the relationship between the magnetic and optical properties in oxide semiconductor, and are promising to integrate multiple functions in one system.

  16. Cavity-enhanced room-temperature high sensitivity optical Faraday magnetometry

    NASA Astrophysics Data System (ADS)

    Sun, Hui; Lei, Yaohua; Fan, Shuangli; Zhang, Qiaolin; Guo, Hong

    2017-01-01

    We propose a cavity QED system with two-photon Doppler-free configuration for weak magnetic field detection with high sensitivity at room temperature based on cavity electromagnetically induced transparency. Owing to the destructive interference induced by the control and driving fields, two transparency channels are opened. The Faraday rotation within two transparency channels can be used to detect weak magnetic field with high sensitivity at room temperature. The sensitivity with single photon and multiphoton probe inputs is analyzed. With single photon measurement, our numerical calculations demonstrate that the sensitivity with 3.8nT/√{Hz} and 6.4nT/√{Hz} could be achieved. When we measure the magnetic field with multiphoton input, the sensitivity can be improved to 7.7fT/√{Hz} and 25.6fT/√{Hz} under the realistic experimental conditions.

  17. Variable Temperature Equipment for a Commercial Magnetic Susceptibility Balance

    ERIC Educational Resources Information Center

    Lotz, Albert

    2008-01-01

    Variable temperature equipment for the magnetic susceptibility balance MSB-MK1 of Sherwood Scientific, Ltd., is described. The sample temperature is controlled with streaming air heated by water in a heat exchanger. Whereas the balance as sold commercially can be used only for room temperature measurements, the setup we designed extends the…

  18. Variable Temperature Equipment for a Commercial Magnetic Susceptibility Balance

    ERIC Educational Resources Information Center

    Lotz, Albert

    2008-01-01

    Variable temperature equipment for the magnetic susceptibility balance MSB-MK1 of Sherwood Scientific, Ltd., is described. The sample temperature is controlled with streaming air heated by water in a heat exchanger. Whereas the balance as sold commercially can be used only for room temperature measurements, the setup we designed extends the…

  19. Room Temperature Nanoimprint Technology Using Hydrogen Silsequioxane (HSQ)

    NASA Astrophysics Data System (ADS)

    Igaku, Yutaka; Matsui, Shinji; Ishigaki, Hiroyuki; Fujita, Jun-ichi; Ishida, Masahiko; Ochiai, Yukinori; Namatsu, Hideo; Komuro, Masanori; Hiroshima, Hiroshi

    2002-06-01

    Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement error due to thermal expansion in the conventional nanoimprint lithography (NIL) process. We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of PMMA used in conventional NIL, and demonstrate HSQ replicated patterns with 90 nm hole diameter and 50 nm linewidth realized by room-temperature replications. We performed step-and-repeat replications using HSQ on a 1.5 in. wafer and evaluated the uniformity of the imprinted HSQ patterns.

  20. Room-temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centres in diamond

    SciTech Connect

    King, Jonathan P.; Jeong, Keunhong; Vassiliou, Christophoros C.; Shin, Chang S.; Page, Ralph H.; Avalos, Claudia E.; Wang, Hai-Jing; Pines, Alexander

    2015-12-07

    Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ~170,000 over thermal equilibrium. The signal of the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. In conclusion, hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.

  1. Room-temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centres in diamond

    DOE PAGES

    King, Jonathan P.; Jeong, Keunhong; Vassiliou, Christophoros C.; ...

    2015-12-07

    Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ~170,000 over thermal equilibrium. The signal ofmore » the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. In conclusion, hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.« less

  2. Room-Temperature-Cured Copolymers for Lithium Battery Gel Electrolytes

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Tigelaar, Dean M.

    2009-01-01

    Polyimide-PEO copolymers (PEO signifies polyethylene oxide) that have branched rod-coil molecular structures and that can be cured into film form at room temperature have been invented for use as gel electrolytes for lithium-ion electric-power cells. These copolymers offer an alternative to previously patented branched rod-coil polyimides that have been considered for use as polymer electrolytes and that must be cured at a temperature of 200 C. In order to obtain sufficient conductivity for lithium ions in practical applications at and below room temperature, it is necessary to imbibe such a polymer with a suitable carbonate solvent or ionic liquid, but the high-temperature cure makes it impossible to incorporate and retain such a liquid within the polymer molecular framework. By eliminating the high-temperature cure, the present invention makes it possible to incorporate the required liquid.

  3. A novel NO2 gas sensor based on Hall effect operating at room temperature

    NASA Astrophysics Data System (ADS)

    Lin, J. Y.; Xie, W. M.; He, X. L.; Wang, H. C.

    2016-09-01

    Tungsten trioxide nanoparticles were obtained by a simple thermal oxidation approach. The structural and morphological properties of these nanoparticles are investigated using XRD, SEM and TEM. A WO3 thick film was deposited on the four Au electrodes to be a WO3 Hall effect sensor. The sensor was tested between magnetic field in a plastic test chamber. Room-temperature nitrogen dioxide sensing characteristics of Hall effect sensor were studied for various concentration levels of nitrogen dioxide at dry air and humidity conditions. A typical room-temperature response of 3.27 was achieved at 40 ppm of NO2 with a response and recovery times of 36 and 45 s, respectively. NO2 gas sensing mechanism of Hall effect sensor was also studied. The room-temperature operation, with the low deposition cost of the sensor, suggests suitability for developing a low-power cost-effective nitrogen dioxide sensor.

  4. Room-temperature spin-polarized organic light-emitting diodes with a single ferromagnetic electrode

    SciTech Connect

    Ding, Baofu Alameh, Kamal; Song, Qunliang

    2014-05-19

    In this paper, we demonstrate the concept of a room-temperature spin-polarized organic light-emitting diode (Spin-OLED) structure based on (i) the deposition of an ultra-thin p-type organic buffer layer on the surface of the ferromagnetic electrode of the Spin-OLED and (ii) the use of oxygen plasma treatment to modify the surface of that electrode. Experimental results demonstrate that the brightness of the developed Spin-OLED can be increased by 110% and that a magneto-electroluminescence of 12% can be attained for a 150 mT in-plane magnetic field, at room temperature. This is attributed to enhanced hole and room-temperature spin-polarized injection from the ferromagnetic electrode, respectively.

  5. Near room temperature magnetodielectric consequence in (Li, Ti) doped NiO ceramic

    SciTech Connect

    Mukherjee, S. E-mail: sudipm@barc.gov.in; Rayaprol, S.; Kaushik, S. D.; Chatterjee, S.; Bhattacharya, S.; Jana, P. K.

    2016-04-07

    In the quest for high-k dielectrics with decent magnetodielectric (MD) response, ball-milled processed (Li, Ti) doped NiO ceramics have been evaluated by various experimental techniques. Magnetic properties in these ceramics manifest with a pronounced anomaly appearing at ∼260 K, suggesting ferrimagnetic phase (related to cluster magnetism) and co-existence with a glassy-like antiferromagnetic phase at ∼7 K. Room temperature neutron diffraction pattern shows the existence of short-range magnetic correlations. In the magnetically ordered state below 250 K, the magnetic structure is found to be phase coexistence of G-type antiferromagnet and ferrimagnet. Impedance spectroscopy measurements over a wide temperature range can be perfectly described with appropriate microstructural model (internal barrier layer capacitor), based on domain and domain boundary relaxations, justifying the enhancement of the dielectric response. The low-temperature (T < 100 K) dielectric relaxation is polaronic in nature, associated with the charge ordering of a mixed valence states of Ti ions (co-existence of Ti{sup 3+} and Ti{sup 4+}). Finally, our investigations in external magnetic fields up to 15 T reveal the occurrence of negative MD effect near room temperature. This intriguing intrinsic feature has been understood by the mechanism of charge-hopping-mediated MD effects.

  6. Room temperature ferromagnetism in Mn-doped NiO nanoparticles

    NASA Astrophysics Data System (ADS)

    Layek, Samar; Verma, H. C.

    2016-01-01

    Mn-doped NiO nanoparticles of the series Ni1-xMnxO (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum.

  7. Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys.

    PubMed

    Lungu, George A; Apostol, Nicoleta G; Stoflea, Laura E; Costescu, Ruxandra M; Popescu, Dana G; Teodorescu, Cristian M

    2013-02-21

    Ferromagnetic FexGe1-x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe₃ to approximately FeGe₂, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

  8. Room temperature table-like magnetocaloric effect in amorphous Gd50Co45Fe5 ribbon

    NASA Astrophysics Data System (ADS)

    Liu, G. L.; Zhao, D. Q.; Bai, H. Y.; Wang, W. H.; Pan, M. X.

    2016-02-01

    Gd50Co45Fe5 amorphous alloy ribbon with a table-like magnetocaloric effect (MCE) suitable for the ideal Ericsson cycle at room temperature has been developed. In addition to a high magnetic transition temperature of 289 K very close to that of Gd (294 K), a relatively large value of refrigerant capacity (~521 J kg-1) has been achieved under a field change of 5 T. This value of refrigerant capacity (RC) is about 27% and 70% larger than those of Gd (~410 J kg-1) and Gd5Si2Ge2 (~306 J kg-1). More importantly, the peak value of magnetic entropy change (-Δ S\\text{M}\\max ) approaches a nearly constant value of ~3.8 J  ṡ  kg-1  ṡ  K-1 under an applied field change of 0~5 T in a wide temperature span over 40 K around room temperature, which could be used as the candidate working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature.

  9. Magnetically suspended stepping motors for clean room and vacuum environments

    NASA Technical Reports Server (NTRS)

    Higuchi, Toshiro

    1994-01-01

    To answer the growing needs for super-clean or contact free actuators for uses in clean rooms, vacuum chambers, and space, innovative actuators which combine the functions of stepping motors and magnetic bearings in one body were developed. The rotor of the magnetically suspended stepping motor is suspended like a magnetic bearing and rotated and positioned like a stepping motor. The important trait of the motor is that it is not a simple mixture or combination of a stepping motor and conventional magnetic bearing, but an amalgam of a stepping motor and a magnetic bearing. Owing to optimal design and feed-back control, a toothed stator and rotor are all that are needed structurewise for stable suspension. More than ten types of motors such as linear type, high accuracy rotary type, two-dimensional type, and high vacuum type were built and tested. This paper describes the structure and design of these motors and their performance for such applications as precise positioning rotary table, linear conveyor system, and theta-zeta positioner for clean room and high vacuum use.

  10. A device to investigate the delamination strength in laminates at room and cryogenic temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Xingyi; Liu, Wei; Zhou, Jun; Zhou, You-He

    2014-12-01

    We construct an instrument to study the behavior of delamination strength in laminates which can be defined as the critical transverse stress at which an actual delamination occurs. The device allows the anvil measurements at room temperature or the liquid nitrogen temperature. For the electro-magnetic laminated materials (e.g., a superconducting YaBa2Cu3O7-x coated conductor which has a typical laminated structure), the delamination strength was measured while the properties of transport current were also recorded. Moreover, the influences of external magnetic field on the delamination strength were presented.

  11. Coulomb blockade and Coulomb staircase behavior observed at room temperature

    NASA Astrophysics Data System (ADS)

    Uky Vivitasari, Pipit; Azuma, Yasuo; Sakamoto, Masanori; Teranishi, Toshiharu; Majima, Yutaka

    2017-02-01

    A single-electron transistor (SET) consists of source, drain, Coulomb island, and gate to modulate the number of electrons and control the current. For practical applications, it is important to operate a SET at room temperature. One proposal towards the ability to operate at room temperature is to decrease Coulomb island size down to a few nanometres. We investigate a SET using Sn-porphyrin (Sn-por) protected gold nanoparticles (AuNPs) with 1.4 nm in core diameter as a Coulomb island. The fabrication method of nanogap electrodes uses the combination of a top-down technique by electron beam lithography (EBL) and a bottom-up process through electroless gold plating (ELGP) as our group have described before. The electrical measurement was conducted at room temperature (300 K). From current-voltage (I d-V d) characteristics, we obtained clear Coulomb blockade phenomena together with a Coulomb staircase due to a Sn-por protected gold NP as a Coulomb island. Experimental results of I d-V d characteristics agree with a theoretical curve based on using the orthodox model. Clear dI d/dV d peaks are observed in the Coulomb staircase at 9 K which suggest the electron transports through excited energy levels of Au NPs. These results are a big step for obtaining SETs that can operate at room temperature.

  12. Required Be Capsule Strength For Room Temperature Transport

    SciTech Connect

    Cook, B

    2005-03-21

    The purpose of this memo is to lay out the criteria for the Be capsule strength necessary for room temperature transport. Ultimately we will test full thickness capsules by sealing high pressures inside, but currently we are limited to both thinner capsules and alternative measures of capsule material strength.

  13. Coherent population trapping in a crystalline solid at room temperature

    SciTech Connect

    Kolesov, Roman

    2005-11-15

    Observation of coherent population trapping (CPT) at ground-state Zeeman sublevels of Cr{sup 3+} ion in ruby at room temperature is reported. A mechanism of CPT, not owing to optical pumping, is revealed in a situation when the optical pulse duration is shorter than the population decay time from the excited optical state.

  14. Experimental epikeratophakia using tissue lathed at room temperature.

    PubMed Central

    Rostron, C. K.; Sandford-Smith, J. H.; Morton, D. B.

    1988-01-01

    This report presents for the first time the results of carrying out epikeratophakia with tissue lathed at room temperature. Using an experimental model of epikeratophakia in the rabbit, we evaluated tissue handling techniques for the preparation of donor lenticules. Details of the technique are described and the in-vivo and histopathological findings reported. Images PMID:3293653

  15. Room-Temperature Ionic Liquids for Electrochemical Capacitors

    NASA Technical Reports Server (NTRS)

    Fireman, Heather; Yowell, Leonard; Moloney, Padraig G.; Arepalli, Sivaram; Nikolaev, P.; Huffman, C.; Ready, Jud; Higgins, C.D.; Turano, S. P.; Kohl, P.A.; Kim, K.

    2009-01-01

    A document discusses room-temperature ionic liquids (RTILs) used as electrolytes in carbon-nanotube-based, electrochemical, double-layer capacitors. Unlike the previous electrolyte (EtNB4 in acetonitrile), the RTIL used here does not produce cyanide upon thermal decomposition and does not have a moisture sensitivity.

  16. Amination of allylic alcohols in water at room temperature.

    PubMed

    Nishikata, Takashi; Lipshutz, Bruce H

    2009-06-04

    The "trick" to carrying out regiocontrolled aminations of allylic alcohols in water as the only medium is use of a nanomicelle's interior as the organic reaction solvent. When HCO(2)Me is present, along with the proper base and source of catalytic Pd, allylic amines are cleanly formed at room temperature.

  17. Observation of anharmonicity for copper thin film near room temperatures.

    PubMed

    Yang, D S

    2001-03-01

    The fluorescence EXAFS spectra for a copper thin film with a thickness of 3000A measured at 300K, 350K and 400K were analyzed by the regularization method to directly obtain the radial distribution. The pair distribution was almost symmetric for 300K but asymmetric for 350K and 400K. This indicates that the atoms in copper vibrate anharmonically near room temperatures. The anharmonicity and the skewness of the asymmetric distribu-tion increases as temperature increases.

  18. Evaluation of Ceramic Honeycomb Core Compression Behavior at Room Temperature

    NASA Technical Reports Server (NTRS)

    Bird, Richard K.; Lapointe, Thomas S.

    2013-01-01

    Room temperature flatwise compression tests were conducted on two varieties of ceramic honeycomb core specimens that have potential for high-temperature structural applications. One set of specimens was fabricated using strips of a commercially-available thin-gage "ceramic paper" sheet molded into a hexagonal core configuration. The other set was fabricated by machining honeycomb core directly from a commercially available rigid insulation tile material. This paper summarizes the results from these tests.

  19. Room temperature dual ferroic behaviour of ball mill synthesized NdFeO{sub 3} orthoferrite

    SciTech Connect

    Aparnadevi, N.; Saravana Kumar, K.; Manikandan, M.; Venkateswaran, C.; Paul Joseph, D.

    2016-07-21

    Phase pure NdFeO{sub 3} has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO{sub 3} regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe{sup 3+} spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found due to the crystal ligand field of octahedral oxygen environment of Fe{sup 3+} ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm{sup 2} at room temperature is found to be driven by the non-collinear magnetic structure with reverse Dzyaloshinskii–Moriya effect. Magnetic field has influence on the dielectric constant as evident from the impedance spectroscopy, indicating the strong coupling between ferroelectric and the magnetic structure of NdFeO{sub 3}.

  20. FAST TRACK COMMUNICATION: Reproducible room temperature giant magnetocaloric effect in Fe-Rh

    NASA Astrophysics Data System (ADS)

    Manekar, Meghmalhar; Roy, S. B.

    2008-10-01

    We present the results of magnetocaloric effect (MCE) studies in polycrystalline Fe-Rh alloy over a temperature range of 250-345 K across the first order antiferromagnetic to ferromagnetic transition. By measuring the MCE under various thermomagnetic histories, contrary to the long held belief, we show here explicitly that the giant MCE in Fe-Rh near room temperature does not vanish after the first field cycle. In spite of the fact that the virgin magnetization curve is lost after the first field cycle near room temperature, reproducibility in the MCE under multiple field cycles can be achieved by properly choosing a combination of isothermal and adiabatic field variation cycles in the field-temperature phase space. This reproducible MCE leads to a large effective refrigerant capacity of 324.42 J kg-1, which is larger than that of the well-known magnetocaloric material Gd5Si2Ge2. This information could be important as Fe-Rh has the advantage of having a working temperature of around 300 K, which can be used for room temperature magnetic refrigeration.

  1. Micromachined room-temperature microbolometers for millimeter-wave detection

    NASA Astrophysics Data System (ADS)

    Rahman, Arifur; de Lange, Gert; Hu, Qing

    1996-04-01

    We have combined silicon micromachining technology with planar circuits to fabricate room-temperature niobium microbolometers for millimeter-wave detection. In this type of detector, a thin niobium film, with a dimension much smaller than the wavelength and fabricated on a 1 μm thick Si3N4 membrane, acts both as a radiation absorber and temperature sensor. Incident radiation is coupled into the microbolometer by a 0.37λ dipole antenna of center frequency 95 GHz with a 3 dB bandwidth of 15%, which is impedance matched with the Nb film. An electrical noise equivalent power (NEP) of 4.5×10-10 W/√Hz has been achieved. This is comparable to the best commercial room-temperature millimeter-wave detectors.

  2. Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

    NASA Astrophysics Data System (ADS)

    Náfrádi, Bálint; Choucair, Mohammad; Dinse, Klaus-Peter; Forró, László

    2016-07-01

    The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice and spin-spin relaxation times of electrons. Minimizing the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on spin-lattice and spin-spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin-lattice and spin-spin relaxation times of 175 ns at 300 K in 37+/-7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature.

  3. A simple method to obtain Fe-doped CeO2 nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Almeida, J. M. A.; Santos, P. E. C.; Cardoso, L. P.; Meneses, C. T.

    2013-02-01

    Ce1-xFexO2 nanocrystals (0room temperature using the coprecipitation method. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and magnetization measurements as a function of field. The XRD results and Rietveld refinement analysis show that all particles have a crystalline structure isomorphous to the host structure (CeO2), with average size of 9 nm. This information was also confirmed by TEM images in which it is shown that the particles present spherical-like shape. The magnetic measurements indicated that the Fe-doped samples exhibit a weak ferromagnetism at room temperature, which increases with the increasing of the Fe content.

  4. Room temperature ferrimagnetism and low temperature disorder effects in zinc ferrite thin films

    NASA Astrophysics Data System (ADS)

    Raghavan, Lisha; Pookat, Geetha; Thomas, Hysen; Ojha, Sunil; Avasthi, D. K.; Anantharaman, M. R.

    2015-07-01

    Zinc ferrite is a normal spinel and antiferromagnetic in nature with a Neel temperature of 10 K in the micron regime. It exhibits interesting features like superparamagnetism, spin glass and ferrimagnetism in the nano-regime. These anomalies make zinc ferrite striking among various other spinels. Further, in the thin film form, the magnetic properties are dependent on preparative techniques, annealing and deposition parameters. In the present work, zinc ferrite thin films were prepared by RF sputtering. The films were annealed at 400° C and 600° C. The thickness and composition of films were estimated by employing Rutherford Backscattering Spectrometry (RBS). The structural and microstructural studies conducted using Glancing X Ray Diffractometer (GXRD) and Transmission Electron Microscope (TEM) indicates the formation of a spinel phase and grain growth was observed with annealing. Magnetic measurements were carried out using a Superconducting Quantum Interferometer Device-Vibrating Sample Magnetometry (SQUID VSM). The films were found to be ferrimagnetic at room temperature and Field Cooling-Zero Field Cooling (FC-ZFC) studies indicate the presence of disorders.

  5. Nanoscale structural modulation and enhanced room-temperature multiferroic properties

    NASA Astrophysics Data System (ADS)

    Sun, Shujie; Huang, Yan; Wang, Guopeng; Wang, Jianlin; Fu, Zhengping; Peng, Ranran; Knize, Randy J.; Lu, Yalin

    2014-10-01

    Availability of a single-phase multiferroic material functional at room temperature poses a big challenge, although it is very important to both fundamental physics and application development. Recently, layered Aurivillius oxide materials, one of the most promising candidates, have attracted considerable interest. In this work, we investigated the nanoscale structural evolution of the six-layer Bi7Fe3-xCoxTi3O21 when substituting excessive Co. Nanoscale structural modulation (NSM) occurred at the boundaries when changing the material gradually from the originally designed six-layer nanoscale architecture down to five and then four, when increasing the Co content, inducing a previously unidentified analogous morphotropic transformation (AMT) effect. The AMT's net contribution to the enhanced intrinsic multiferroic properties at room temperature was confirmed by quantifying and deducting the contribution from the existing impurity phase using derivative thermo-magneto-gravimetry measurements (DTMG). Significantly, this new AMT effect may be caused by a possible coupling contribution from co-existing NSM phases, indicating a potential method for realizing multiferroic materials that function at room temperature.Availability of a single-phase multiferroic material functional at room temperature poses a big challenge, although it is very important to both fundamental physics and application development. Recently, layered Aurivillius oxide materials, one of the most promising candidates, have attracted considerable interest. In this work, we investigated the nanoscale structural evolution of the six-layer Bi7Fe3-xCoxTi3O21 when substituting excessive Co. Nanoscale structural modulation (NSM) occurred at the boundaries when changing the material gradually from the originally designed six-layer nanoscale architecture down to five and then four, when increasing the Co content, inducing a previously unidentified analogous morphotropic transformation (AMT) effect. The AMT

  6. Anion pairs in room temperature ionic liquids predicted by molecular dynamics simulation, verified by spectroscopic characterization

    SciTech Connect

    Schwenzer, Birgit; Kerisit, Sebastien N.; Vijayakumar, M.

    2014-01-01

    Molecular-level spectroscopic analyses of an aprotic and a protic room-temperature ionic liquid, BMIM OTf and BMIM HSO4, respectively, have been carried out with the aim of verifying molecular dynamics simulations that predict anion pair formation in these fluid structures. Fourier-transform infrared spectroscopy, Raman spectroscopy and nuclear magnetic resonance spectroscopy of various nuclei support the theoretically-determined average molecular arrangements.

  7. Room temperature recrystallization of 99. 999 PCT aluminum

    SciTech Connect

    Changhee Choi; Changseok, Oh; Dong Nyung Lee . Dept. of Metallurgical Engineering); Jaehan Jeong )

    1994-02-01

    It has been known that recrystallization of metals can be accelerated by a combined effect of high purity and a heavy deformation. There is an increasing interest in deformation and recrystallization behaviors of high purity aluminum, because of the sensitivity of its recrystallization temperature to impurities. Room temperature recrystallization of high purity aluminum is a typical example of this sensitivity and has been found and displayed in an earlier work. This result has been thought to occur statically, because aluminum was only known to undergo dynamic recovery (DRV) as a restoration mechanism due to a high stacking fault energy. However, some recent studies suggested the occurrence of dynamic recrystallization (DRX) in room temperature compression tests of 99.999 pct aluminum. Thus, the restoration mechanism of 99.999 pct aluminum during deformation is in dispute. The purpose of this study is to clarify whether or not DRX can occur in 99.999 pct aluminum that is subjected to plastic deformation at room temperature.

  8. Above room-temperature ferromagnetism of Mn delta-doped GaN nanorods

    SciTech Connect

    Lin, Y. T.; Wadekar, P. V.; Kao, H. S.; Chen, T. H.; Chen, Q. Y.; Tu, L. W.; Huang, H. C.; Ho, N. J.

    2014-02-10

    One-dimensional nitride based diluted magnetic semiconductors were grown by plasma-assisted molecular beam epitaxy. Delta-doping technique was adopted to dope GaN nanorods with Mn. The structural and magnetic properties were investigated. The GaMnN nanorods with a single crystalline structure and with Ga sites substituted by Mn atoms were verified by high-resolution x-ray diffraction and Raman scattering, respectively. Secondary phases were not observed by high-resolution x-ray diffraction and high-resolution transmission electron microscopy. In addition, the magnetic hysteresis curves show that the Mn delta-doped GaN nanorods are ferromagnetic above room temperature. The magnetization with magnetic field perpendicular to GaN c-axis saturates easier than the one with field parallel to GaN c-axis.

  9. Studies on magnetoelectric coupling in PFN-NZFO composite at room temperature

    NASA Astrophysics Data System (ADS)

    Pradhan, Dhiren K.; Sahoo, Satyaprakash; Barik, Sujit K.; Puli, Venkata S.; Misra, Pankaj; Katiyar, Ram S.

    2014-05-01

    We report magnetoelectric coupling and Raman spectroscopic studies on [(1 - x)Pb(Fe0.5Nb0.5)O3-xNi0.65Zn0.35Fe2O4] (x = 0.20) PFN-NZFO composite. Apart from the presence of zone centre Raman active modes of the parent compound, some new peaks are observed in the low frequency region. The electric field controlled peak position (˜48 cm-1) suggests that this mode is of magnetic origin. From temperature dependent Raman scattering studies, temperature coefficients for phonons of different symmetries were estimated. Our measurements on electrical control of magnetic order and magnetic control of electrical order confirmed the existence of converse and direct magnetoelectric coupling in this composite at room temperature.

  10. Room Temperature Antiferromagnetic Ordering of Nanocrystalline Tb1.90Ni0.10O3

    NASA Astrophysics Data System (ADS)

    Mandal, J.; Dalal, M.; Sarkar, B. J.; Chakrabarti, P. K.

    2017-02-01

    Nanocrystalline Ni-doped terbium oxide (Tb1.90Ni0.10O3) has been synthesized by the co-precipitation method followed by annealing at 700°C for 6 h in vacuum. The crystallographic phase and the substitution of Ni2+ ions in the lattice of Tb2O3 are confirmed by Rietveld analysis of the x-ray diffraction pattern using the software MAUD. High-resolution transmission electron microscopy is also carried out to study the morphology of the sample. Magnetic measurements are carried out at different temperatures from 5 K to 300 K using a superconducting quantum interference device (SQUID) magnetometer. The dependence of the magnetization of Tb1.90Ni0.10O3 as a function of temperature ( M- T) and magnetic field ( M- H) suggests the presence of both paramagnetic and antiferromagnetic phase at room temperature, but antiferromagnetic phase dominates below ˜120 K. The lack of saturation in the M- H curve and good fitting of the M- T curve by the Johnston formula also indicate the presence of both paramagnetic and antiferromagnetic phase at room temperature. Interestingly, an antiferromagnetic to ferromagnetic phase transition is observed below ˜40 K. The result also shows a high value of magnetization at 5 K.

  11. Outrunning free radicals in room-temperature macromolecular crystallography

    PubMed Central

    Owen, Robin L.; Axford, Danny; Nettleship, Joanne E.; Owens, Raymond J.; Robinson, James I.; Morgan, Ann W.; Doré, Andrew S.; Lebon, Guillaume; Tate, Christopher G.; Fry, Elizabeth E.; Ren, Jingshan; Stuart, David I.; Evans, Gwyndaf

    2012-01-01

    A significant increase in the lifetime of room-temperature macromolecular crystals is reported through the use of a high-brilliance X-ray beam, reduced exposure times and a fast-readout detector. This is attributed to the ability to collect diffraction data before hydroxyl radicals can propagate through the crystal, fatally disrupting the lattice. Hydroxyl radicals are shown to be trapped in amorphous solutions at 100 K. The trend in crystal lifetime was observed in crystals of a soluble protein (immunoglobulin γ Fc receptor IIIa), a virus (bovine enterovirus serotype 2) and a membrane protein (human A2A adenosine G-protein coupled receptor). The observation of a similar effect in all three systems provides clear evidence for a common optimal strategy for room-temperature data collection and will inform the design of future synchrotron beamlines and detectors for macro­molecular crystallography. PMID:22751666

  12. Nanostructured ZnO Films for Room Temperature Ammonia Sensing

    NASA Astrophysics Data System (ADS)

    Dhivya Ponnusamy; Sridharan Madanagurusamy

    2014-09-01

    Zinc oxide (ZnO) thin films have been deposited by a reactive dc magnetron sputtering technique onto a thoroughly cleaned glass substrate at room temperature. X-ray diffraction revealed that the deposited film was polycrystalline in nature. The field emission scanning electron micrograph (FE-SEM) showed the uniform formation of a rugby ball-shaped ZnO nanostructure. Energy dispersive x-ray analysis (EDX) confirmed that the film was stoichiometric and the direct band gap of the film, determined using UV-Vis spectroscopy, was 3.29 eV. The ZnO nanostructured film exhibited better sensing towards ammonia (NH3) at room temperature (˜30°C). The fabricated ZnO film based sensor was capable of detecting NH3 at as low as 5 ppm, and its parameters, such as response, selectivity, stability, and response/recovery time, were also investigated.

  13. Room Temperature Creep Of SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Gyekenyesi, Andrew; Levine, Stanley (Technical Monitor)

    2001-01-01

    During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar composites with carbon interphases, little or no time dependent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the interfacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interfacial shear stress with time at room temperature as measured by fiber push-in experiments.

  14. Broadband room temperature strong coupling between quantum dots and metamaterials.

    PubMed

    Indukuri, Chaitanya; Yadav, Ravindra Kumar; Basu, J K

    2017-08-17

    Herein, we report the first demonstration of room temperature enhanced light-matter coupling in the visible regime for metamaterials using cooperative coupled quasi two dimensional quantum dot assemblies located at precise distances from the hyperbolic metamaterial (HMM) templates. The non-monotonic variation of the magnitude of strong coupling, manifested in terms of strong splitting of the photoluminescence of quantum dots, can be explained in terms of enhanced LDOS near the surface of such metamaterials as well as the plasmon mediated super-radiance of closely spaced quantum dots (QDs). Our methodology of enhancing broadband, room temperature, light-matter coupling in the visible regime for metamaterials opens up new possibilities of utilising these materials for a wide range of applications including QD based thresholdless nanolasers and novel metamaterial based integrated photonic devices.

  15. Primary and secondary room temperature molten salt electrochemical cells

    NASA Astrophysics Data System (ADS)

    Reynolds, G. F.; Dymek, C. J., Jr.

    1985-07-01

    Three novel primary cells which use room temperature molten salt electrolytes are examined and found to have high open circuit potentials in the 1.75-2.19 V range, by comparison with the Al/AlCl3-MEICl concentration cell; their cathodes were of FeCl3-MEICl, WCl6-MEICl, and Br2/reticulated vitreous carbon together with Pt. Also, secondary electrochemical cell candidates were examined which combined the reversible Al/AlCl3-MEICl electrode with reversible zinc and cadmium molten salt electrodes to yield open circuit potentials of about 0.7 and 1.0 V, respectively. Room temperature molten salts' half-cell reduction potentials are given.

  16. Tribochemical Decomposition of Light Ionic Hydrides at Room Temperature.

    PubMed

    Nevshupa, Roman; Ares, Jose Ramón; Fernández, Jose Francisco; Del Campo, Adolfo; Roman, Elisa

    2015-07-16

    Tribochemical decomposition of magnesium hydride (MgH2) induced by deformation at room temperature was studied on a micrometric scale, in situ and in real time. During deformation, a near-full depletion of hydrogen in the micrometric affected zone is observed through an instantaneous (t < 1 s) and huge release of hydrogen (3-50 nmol/s). H release is related to a nonthermal decomposition process. After deformation, the remaining hydride is thermally decomposed at room temperature, exhibiting a much slower rate than during deformation. Confocal-microRaman spectroscopy of the mechanically affected zone was used to characterize the decomposition products. Decomposition was enhanced through the formation of the distorted structure of MgH2 with reduced crystal size by mechanical deformation.

  17. Room temperature electrodeposition of actinides from ionic solutions

    DOEpatents

    Hatchett, David W.; Czerwinski, Kenneth R.; Droessler, Janelle; Kinyanjui, John

    2017-04-25

    Uranic and transuranic metals and metal oxides are first dissolved in ozone compositions. The resulting solution in ozone can be further dissolved in ionic liquids to form a second solution. The metals in the second solution are then electrochemically deposited from the second solutions as room temperature ionic liquid (RTIL), tri-methyl-n-butyl ammonium n-bis(trifluoromethansulfonylimide) [Me.sub.3N.sup.nBu][TFSI] providing an alternative non-aqueous system for the extraction and reclamation of actinides from reprocessed fuel materials. Deposition of U metal is achieved using TFSI complexes of U(III) and U(IV) containing the anion common to the RTIL. TFSI complexes of uranium were produced to ensure solubility of the species in the ionic liquid. The methods provide a first measure of the thermodynamic properties of U metal deposition using Uranium complexes with different oxidation states from RTIL solution at room temperature.

  18. Quantum correlations from a room-temperature optomechanical cavity

    NASA Astrophysics Data System (ADS)

    Purdy, T. P.; Grutter, K. E.; Srinivasan, K.; Taylor, J. M.

    2017-06-01

    The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam’s thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks.

  19. Room temperature long range ferromagnetic ordering in Ni{sub 0.58}Zn{sub 0.42}Co{sub 0.10}Cu{sub 0.10}Fe{sub 1.8}O{sub 4} nano magnetic system

    SciTech Connect

    Sarveena, Chand, Jagdish; Verma, S.; Singh, M.; Kotnala, R. K.; Batoo, K. M.

    2015-06-24

    The structural and magnetic behavior of sol-gel autocombustion synthesized nanocrystalline Ni{sub 0.58}Zn{sub 0.42}Co{sub 0.10}Cu{sub 0.10}Fe{sub 1.8}O{sub 4} have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometer(VSM). Sample of high purity and high homogeneity was obtained by calcination at low temperature (500°C) resulting in nanoparticles of average diameter ∼15nm as determined by XRD and further confirmed by TEM. X-ray diffraction (XRD) and selective area diffraction (SAED) confirmed the single phase of the sample. Mössbauer results are supported by magnetization data. Well defined sextets and appearance of hysteresis at room temperature indicate the existence of ferromagnetic coupling at room temperature finding material utility in magnetic storage data. The existence of iron in ferric state confirmed by isomer shift is a clear evidence of improved magnetic properties of the present system.

  20. Room Temperature Source of Single Photons of Definite Polarization

    SciTech Connect

    Lukishova, S.G.; Schmid, A.W.; Knox, R.; Freivald, P.; Bissel, L.J.; Boyd, R.W.; Stroud, Jr., C.R.; Marshall, K.L.

    2007-02-12

    A definite polarization in fluorescence from single emitters (dye molecules) at room temperature is demonstrated. A planar-aligned, nematic liquid-crystal host provides definite alignment of single dye molecules in a preferred direction. Well-defined polarized fluorescence from single-emitters (single photon source) is important for applications in photonic quantum information. Polarized single-photon sources based on single-emitters, for example, are key hardware elements both for absolutely secure quantum communication and quantum computation systems.

  1. A Room Temperature Low-Threshold Ultraviolet Plasmonic Nanolaser

    DTIC Science & Technology

    2014-09-23

    Here we demonstrate the first strong room temperature ultraviolet (B370 nm) SP polariton laser with an extremely low threshold (B3.5MWcm 2). We find...localized surface plasmon and propagating surface plasmon polariton (SPP), has been demonstrated in metal nanosphere cavities6, metal-cladding...Quantum plasmonics. Nat. Phys. 9, 329–340 (2013). 4. Berini, P. & De Leon, I. Surface plasmon- polariton amplifiers and lasers. Nat. Photon. 6, 16–24 (2012

  2. Rapid Methods of Staining Bacterial Spores at Room Temperature

    PubMed Central

    Lechtman, M. D.; Bartholomew, J. W.; Phillips, A.; Russo, M.

    1965-01-01

    Lechtman, M. D. (University of Southern California, Los Angeles), J. W. Bartholomew, A. Phillips, and M. Russo. Rapid methods of staining bacterial spores at room temperature. J. Bacteriol. 89:848–854. 1965.—Spores of Bacillus subtilis var. niger were stained in 2 min at room temperature, after suitable pretreatment, with a dye reagent composed of 2% crystal violet in 1% phenol and 26% ethanol. Pretreatments included heat fixation to 260 C, mechanical rupture, and hydrolysis at room temperature in 44 n H3PO4 for 5 min, 33.4 n H3PO4 for 10 min, 12 n HCl for 5 sec, 6 n HCl for 2 min, 12 n HNO3 for 5 sec, and 6 n HNO3 for 60 sec. Acid hydrolysis at 60 C enabled the lowering of both acid concentration and time: 33.4 n H3PO4 for 15 sec, 25.9 n H3PO4 for 60 sec, 2 n HCl for 30 sec, 1 n HCl for 30 sec, 2 n HNO3 for 15 sec, and 1 n HNO3 for 30 sec. After acid treatment, 1 n NaOH was used as a neutralization agent. The cytological manifestations of these pretreatments, examined in an electron microscope after replication, showed definite degradation of spore coats, which probably explains the increase in dye permeability. The pretreatments were evaluated for use in a differential staining procedure for spores and vegetative cells. They were found to be too drastic in that they resulted in replacement of the primary dye by the 0.25% safranine counter stain in both vegetative cells and endospores. Less drastic pretreatments, such as 6 n HNO3 for 10 sec at room temperature, gave good differential stains, but failed to stain some free spores. The staining techniques above were evaluated with six species of Bacillus and were found to apply to all. Images PMID:14273671

  3. Experimental observation of negative capacitance in ferroelectrics at room temperature.

    PubMed

    Appleby, Daniel J R; Ponon, Nikhil K; Kwa, Kelvin S K; Zou, Bin; Petrov, Peter K; Wang, Tianle; Alford, Neil M; O'Neill, Anthony

    2014-07-09

    Effective negative capacitance has been postulated in ferroelectrics because there is a hysteresis in plots of polarization-electric field. Compelling experimental evidence of effective negative capacitance is presented here at room temperature in engineered devices, where it is stabilized by the presence of a paraelectric material. In future integrated circuits, the incorporation of such negative capacitance into MOSFET gate stacks would reduce the subthreshold slope, enabling low power operation and reduced self-heating.

  4. Mercuric iodine room temperature gamma-ray detectors

    NASA Technical Reports Server (NTRS)

    Patt, Bradley E.; Markakis, Jeffrey M.; Gerrish, Vernon M.; Haymes, Robert C.; Trombka, Jacob I.

    1990-01-01

    high resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis.

  5. Silicon photodiodes with high photoconductive gain at room temperature.

    PubMed

    Li, X; Carey, J E; Sickler, J W; Pralle, M U; Palsule, C; Vineis, C J

    2012-02-27

    Silicon photodiodes with high photoconductive gain are demonstrated. The photodiodes are fabricated in a complementary metal-oxide-semiconductor (CMOS)-compatible process. The typical room temperature responsivity at 940 nm is >20 A/W and the dark current density is ≈ 100 nA/cm2 at 5 V reverse bias, yielding a detectivity of ≈ 10(14) Jones. These photodiodes are good candidates for applications that require high detection sensitivity and low bias operation.

  6. Room Temperature Hydrosilylation of Silicon Nanocrystals with Bifunctional Terminal Alkenes

    PubMed Central

    Yu, Yixuan; Hessel, Colin M.; Bogart, Timothy; Panthani, Matthew G.; Rasch, Michael R.; Korgel, Brian A.

    2013-01-01

    H-terminated Si nanocrystals undergo room temperature hydrosilylation with bifunctional alkenes with distal polar moieties—ethyl-, methyl-ester or carboxylic acids—without the aid of light or added catalyst. The passivated Si nanocrystals exhibit bright photoluminescence (PL) and disperse in polar solvents, including water. We propose a reaction mechanism in which ester or carboxylic acid groups facilitate direct nucleophilic attack of the highly curved Si surface of the nanocrystals by the alkene. PMID:23312033

  7. Mercuric iodine room temperature gamma-ray detectors

    NASA Technical Reports Server (NTRS)

    Patt, Bradley E.; Markakis, Jeffrey M.; Gerrish, Vernon M.; Haymes, Robert C.; Trombka, Jacob I.

    1990-01-01

    high resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis.

  8. Chemoselective reductions of nitroaromatics in water at room temperature.

    PubMed

    Kelly, Sean M; Lipshutz, Bruce H

    2014-01-03

    A robust and green protocol for the reduction of functionalized nitroarenes to the corresponding primary amines has been developed. It relies on inexpensive zinc dust in water containing nanomicelles derived from the commercially available designer surfactant TPGS-750-M. This mild process takes place at room temperature and tolerates a wide range of functionalities. Highly selective reductions can also be achieved in the presence of common protecting groups.

  9. Room-temperature direct alkynylation of arenes with copper acetylides.

    PubMed

    Theunissen, Cédric; Evano, Gwilherm

    2014-09-05

    C-H bond in azoles and polyhalogenated arenes can be smoothly activated by copper acetylides to give the corresponding alkynylated (hetero)arenes by simple reaction at room temperature in the presence of phenanthroline and lithium tert-butoxide under an oxygen atmosphere. These stable, unreactive, and readily available polymers act as especially efficient and practical reagents for the introduction of an alkyne group to a wide number of arenes under remarkably mild conditions.

  10. Spontaneous Polarization Buildup in a Room-Temperature Polariton Laser

    SciTech Connect

    Baumberg, J. J.; Christopoulos, S.; Kavokin, A. V.; Grundy, A. J. D.; Baldassarri Hoeger von Hoegersthal, G.; Butte, R.; Christmann, G.; Feltin, E.; Carlin, J.-F.; Grandjean, N.; Solnyshkov, D. D.; Malpuech, G.

    2008-09-26

    We observe the buildup of strong ({approx}50%) spontaneous vector polarization in emission from a GaN-based polariton laser excited by short optical pulses at room temperature. The Stokes vector of emitted light changes its orientation randomly from one excitation pulse to another, so that the time-integrated polarization remains zero. This behavior is completely different from any previous laser. We interpret this observation in terms of the spontaneous symmetry breaking in a Bose-Einstein condensate of exciton polaritons.

  11. Room-temperature Formation of Hollow Cu2O Nanoparticles

    SciTech Connect

    Hung, Ling-I; Tsung, Chia-Kuang; Huang, Wenyu; Yang, Peidong

    2010-01-18

    Monodisperse Cu and Cu2O nanoparticles (NPs) are synthesized using tetradecylphosphonic acid as a capping agent. Dispersing the NPs in chloroform and hexane at room temperature results in the formation of hollow Cu2O NPs and Cu@Cu2O core/shell NPs, respectively. The monodisperse Cu2O NPs are used to fabricate hybrid solar cells with efficiency of 0.14percent under AM 1.5 and 1 Sun illumination.

  12. A highly reversible room-temperature sodium metal anode

    DOE PAGES

    Seh, Zhi Wei; Sun, Jie; Sun, Yongming; ...

    2015-11-02

    Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved overmore » 300 plating–stripping cycles at 0.5 mA cm–2. In this study, the long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies.« less

  13. A Highly Reversible Room-Temperature Sodium Metal Anode

    PubMed Central

    2015-01-01

    Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved over 300 plating–stripping cycles at 0.5 mA cm–2. The long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies. PMID:27163006

  14. Highly Directional Room-Temperature Single Photon Device.

    PubMed

    Livneh, Nitzan; Harats, Moshe G; Istrati, Daniel; Eisenberg, Hagai S; Rapaport, Ronen

    2016-04-13

    One of the most important challenges in modern quantum optical applications is the demonstration of efficient, scalable, on-chip single photon sources, which can operate at room temperature. In this paper we demonstrate a room-temperature single photon source based on a single colloidal nanocrystal quantum dot positioned inside a circular bulls-eye shaped hybrid metal-dielectric nanoantenna. Experimental results show that 20% of the photons are emitted into a very low numerical aperture (NA < 0.25), a 20-fold improvement over a free-standing quantum dot, and with a probability of more than 70% for a single photon emission. With an NA = 0.65 more than 35% of the single photon emission is collected. The single photon purity is limited only by emission from the metal, an obstacle that can be bypassed with careful design and fabrication. The concept presented here can be extended to many other types of quantum emitters. Such a device paves a promising route for a high purity, high efficiency, on-chip single photon source operating at room temperature.

  15. A Na+ Superionic Conductor for Room-Temperature Sodium Batteries

    NASA Astrophysics Data System (ADS)

    Song, Shufeng; Duong, Hai M.; Korsunsky, Alexander M.; Hu, Ning; Lu, Li

    2016-08-01

    Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10-3 S cm-1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor.

  16. A Na+ Superionic Conductor for Room-Temperature Sodium Batteries

    PubMed Central

    Song, Shufeng; Duong, Hai M.; Korsunsky, Alexander M.; Hu, Ning; Lu, Li

    2016-01-01

    Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10−3 S cm−1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor. PMID:27572915

  17. Outrunning free radicals in room-temperature macromolecular crystallography

    SciTech Connect

    Owen, Robin L. Axford, Danny; Nettleship, Joanne E.; Owens, Raymond J.; Robinson, James I.; Morgan, Ann W.; Doré, Andrew S.; Lebon, Guillaume; Tate, Christopher G.; Fry, Elizabeth E.; Ren, Jingshan; Stuart, David I.; Evans, Gwyndaf

    2012-06-15

    A systematic increase in lifetime is observed in room-temperature protein and virus crystals through the use of reduced exposure times and a fast detector. A significant increase in the lifetime of room-temperature macromolecular crystals is reported through the use of a high-brilliance X-ray beam, reduced exposure times and a fast-readout detector. This is attributed to the ability to collect diffraction data before hydroxyl radicals can propagate through the crystal, fatally disrupting the lattice. Hydroxyl radicals are shown to be trapped in amorphous solutions at 100 K. The trend in crystal lifetime was observed in crystals of a soluble protein (immunoglobulin γ Fc receptor IIIa), a virus (bovine enterovirus serotype 2) and a membrane protein (human A{sub 2A} adenosine G-protein coupled receptor). The observation of a similar effect in all three systems provides clear evidence for a common optimal strategy for room-temperature data collection and will inform the design of future synchrotron beamlines and detectors for macromolecular crystallography.

  18. Room temperature synthesis and high temperature frictional study of silver vanadate nanorods.

    PubMed

    Singh, D P; Polychronopoulou, K; Rebholz, C; Aouadi, S M

    2010-08-13

    We report the room temperature (RT) synthesis of silver vanadate nanorods (consisting of mainly beta-AgV O(3)) by a simple wet chemical route and their frictional study at high temperatures (HT). The sudden mixing of ammonium vanadate with silver nitrate solution under constant magnetic stirring resulted in a pale yellow coloured precipitate. Structural/microstructural characterization of the precipitate through x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the high yield and homogeneous formation of silver vanadate nanorods. The length of the nanorods was 20-40 microm and the thickness 100-600 nm. The pH variation with respect to time was thoroughly studied to understand the formation mechanism of the silver vanadate nanorods. This synthesis process neither demands HT, surfactants nor long reaction time. The silver vanadate nanomaterial showed good lubrication behaviour at HT (700 degrees C) and the friction coefficient was between 0.2 and 0.3. HT-XRD revealed that AgV O(3) completely transformed into silver vanadium oxide (Ag(2)V(4)O(11)) and silver with an increase in temperature from RT to 700 degrees C.

  19. Room temperature magnetocaloric effect of La-deficient bulk perovskite manganite La 0.7MnO 3- δ

    NASA Astrophysics Data System (ADS)

    Wang, Zhiming; Xu, Qingyu; Sun, Jingzhi; Pan, Jian; Zhang, He

    2011-04-01

    Room temperature magnetocaloric effect in La-deficient bulk perovskite manganite La 0.7MnO 3- δ prepared by conventional solid-state reaction has been reported. The maximum value of the magnetic entropy change (about-1.32 J/kg K) and the refrigerant capacity (approximately close to 37 J/kg) had been obtained at 290 K corresponding to a magnetic field variation of 1 T for La 0.7MnO 3- δ. It is the strong Jahn-Teller coupling that changes Mn-O bond length and Mn-O-Mn bond angles and then the canted spin arrangement and induces the strong double-exchange coupling to a comparatively high magnetic transition temperature. This Curie temperature near room temperature with easy fabrication and higher chemical stability makes La 0.7MnO 3- δ a potential candidate as a working substance in magnetic refrigeration technology.

  20. Enhancement of room temperature ferromagnetism in Mn-implanted Si by He implantation

    NASA Astrophysics Data System (ADS)

    Chen, Jihong; Guo, Liping; Liu, Congxiao; Luo, Fengfeng; Li, Tiecheng; Zheng, Zhongcheng; Jin, Shuoxue; Yang, Zheng

    2012-09-01

    Room temperature ferromagnetism in Mn-implanted p-Si was enhanced dramatically by implantation of He. A 75 nm end-of-range region was found in the sample, with large scale and inhomogeneous damaging but preserved Si lattice periodicity. The end-of-range region shows an intrinsic magnetization of ˜100 emu/cm3. High resolution transmission electron microscopy and x-ray photoelectron spectroscopy measurements indicate that the spin polarization of Si dangling bonds rather than Mn impurity was the major source for the enhanced magnetism.

  1. Demonstration of charge breeding in a compact room temperature electron beam ion trap

    NASA Astrophysics Data System (ADS)

    Vorobjev, G.; Sokolov, A.; Thorn, A.; Herfurth, F.; Kester, O.; Quint, W.; Stöhlker, Th.; Zschornack, G.

    2012-05-01

    For the first time, a small room-temperature electron beam ion trap (EBIT), operated with permanent magnets, was successfully used for charge breeding experiments. The relatively low magnetic field of this EBIT does not contribute to the capture of the ions; single-charged ions are only caught by the space charge potential of the electron beam. An over-barrier injection method was used to fill the EBIT's electrostatic trap with externally produced, single-charged potassium ions. Charge states as high as K19+ were reached after about a 3 s breeding time. The capture and breeding efficiencies up to 0.016(4)% for K17+ have been measured.

  2. Synthesis and properties of Ag-doped ZnO films with room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Xu, Qin; Wang, Zhi-Jun; Chang, Ze-Jiang; Liu, Jing-Jin; Ren, Ya-Xuan; Sun, Hui-Yuan

    2016-12-01

    A series of Ag-doped ZnO films were prepared by DC magnetron sputtering. XRD and SEM results showed that the doping amount of Ag had a great influence on the films' morphology and ferromagnetism, and their magnetism can be improved by doping an appropriate amount of Ag. The theoretical analysis suggested that the magnetism resulted mainly from the film grain boundary surfaces. Further research revealed that these films had strong timeliness. Such a result indicated that the room temperature ferromagnetism of Ag-doped ZnO films did not stem from the cation vacancies but from the oxygen vacancies on the boundary surfaces.

  3. Room temperature large magneto-absorption effect in Co-coated ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Hsu, Hua-Shu; Yeih, Syun-Long; Liu, Keng-Wen

    2017-06-01

    We report a room temperature sizable magneto-absorption (MA) effect in Co-coated ZnO nanowires. The MA effect is energy dependent, and its value reaches a maximum in the ultraviolet region. The appearance of the MA effect strongly depends on the spin-polarized semiconductor band in ZnO, which is supposedly induced by the interfacial hybridization between the Co d-orbitals and the defect-related band near the ZnO surfaces. A two-peaked density of states related to magnetic field-dependent spin splitting has been proposed to describe the MA, which is controlled by the energy and the magnetic field.

  4. Aging of ceramic carbonized hydroxyapatite at room temperature

    NASA Astrophysics Data System (ADS)

    Tkachenko, M. V.; Kamzin, A. S.

    2016-08-01

    The process of aging of ceramic carbonized hydroxyapatite (CHA) produced in a dry carbon dioxide atmosphere at temperatures of 800-1200°C has been studied by chemical and X-ray structural analysis, infrared spectroscopy, and scanning electron microscopy methods. The phase composition and structure of initial prepared ceramics samples and those aged for a year have been compared. It has been shown that relaxation of internal stresses occurring during pressed sample sintering causes plastic deformation of crystallites at room temperature, accompanied by redistribution of carbonate ions between A1, A2, B1, and B2 sites and CHA decomposition with the formation of CaO separations.

  5. Room temperature ferromagnetism in low dose ion implanted counter-doped Ge:Mn, As

    NASA Astrophysics Data System (ADS)

    Donarelli, M.; Kazakova, O.; Ortolani, L.; Morandi, V.; Impellizzeri, G.; Priolo, F.; Passacantando, M.; Ottaviano, L.

    2017-10-01

    We demonstrate room-temperature ferromagnetism in germanium counter-doped with manganese and arsenic at concentrations up to approximately 2.1 × 1020 at/cm3: these values are one order of magnitude lower than those at which ferromagnetic behavior has previously been observed. Synthesis proceeded by ion implantation at 513 K followed by annealing in argon at 673 K. High resolution TEM, STEM, and EDX show single-phase diamond cubic material lacking Mn or As precipitates. These findings are consistent with the prediction of Chen et al. that counter-doping with approximately equal concentrations of a single-electron donor permits Mn, a two-electron acceptor, to be incorporated at high enough concentrations to yield a diluted magnetic semiconductor with a Curie temperature above room temperature.

  6. Room-temperature superfluidity in a polariton condensate

    NASA Astrophysics Data System (ADS)

    Lerario, Giovanni; Fieramosca, Antonio; Barachati, Fábio; Ballarini, Dario; Daskalakis, Konstantinos S.; Dominici, Lorenzo; de Giorgi, Milena; Maier, Stefan A.; Gigli, Giuseppe; Kéna-Cohen, Stéphane; Sanvitto, Daniele

    2017-09-01

    Superfluidity--the suppression of scattering in a quantum fluid at velocities below a critical value--is one of the most striking manifestations of the collective behaviour typical of Bose-Einstein condensates. This phenomenon, akin to superconductivity in metals, has until now been observed only at prohibitively low cryogenic temperatures. For atoms, this limit is imposed by the small thermal de Broglie wavelength, which is inversely related to the particle mass. Even in the case of ultralight quasiparticles such as exciton-polaritons, superfluidity has been demonstrated only at liquid helium temperatures. In this case, the limit is not imposed by the mass, but instead by the small binding energy of Wannier-Mott excitons, which sets the upper temperature limit. Here we demonstrate a transition from supersonic to superfluid flow in a polariton condensate under ambient conditions. This is achieved by using an organic microcavity supporting stable Frenkel exciton-polaritons at room temperature. This result paves the way not only for tabletop studies of quantum hydrodynamics, but also for room-temperature polariton devices that can be robustly protected from scattering.

  7. Room temperature ferromagnetic ordering in indium substituted nano-nickel-zinc ferrite

    NASA Astrophysics Data System (ADS)

    Thakur, Sangeeta; Katyal, S. C.; Gupta, A.; Reddy, V. R.; Singh, M.

    2009-04-01

    Nano-nickel-zinc-indium ferrite (NZIFO)(Ni0.58Zn0.42InxFe2-xO4) with varied quantities of indium (x =0,0.1,0.2) have been synthesized via reverse micelle technique. X-ray diffraction and transmission electron microscopy confirmed the size, structure, and morphology of the nanoferrites. The addition of indium in nickel-zinc ferrite (NZFO) has been shown to play a crucial role in enhancing the magnetic properties. Room temperature Mössbauer spectra revealed that the nano-NZFO ferrite exhibit collective magnetic excitations, while indium doped NZFO samples have the ferromagnetic phase. The dependence of Mössbauer parameters, viz. isomer shift, quadrupole splitting, linewidth, and hyperfine magnetic field, on In3+ concentration has been studied. Mössbauer study on these nanosystems shows that the cation distribution not only depends on the particle size but also on the preparation route. Mössbauer results are also supported by magnetization data. Well defined sextets and appearance of hysteresis at room temperature indicate the existence of ferromagnetic couplings which makes nano-NZIFO ferrite suitable for magnetic storage data.

  8. Room-temperature spin-orbit torque in NiMnSb

    NASA Astrophysics Data System (ADS)

    Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

    2016-09-01

    Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

  9. Room temperature electrical spin injection into GaAs by an oxide spin injector

    PubMed Central

    Bhat, Shwetha G.; Kumar, P. S. Anil

    2014-01-01

    Spin injection, manipulation and detection are the integral parts of spintronics devices and have attracted tremendous attention in the last decade. It is necessary to judiciously choose the right combination of materials to have compatibility with the existing semiconductor technology. Conventional metallic magnets were the first choice for injecting spins into semiconductors in the past. So far there is no success in using a magnetic oxide material for spin injection, which is very important for the development of oxide based spintronics devices. Here we demonstrate the electrical spin injection from an oxide magnetic material Fe3O4, into GaAs with the help of tunnel barrier MgO at room temperature using 3-terminal Hanle measurement technique. A spin relaxation time τ ~ 0.9 ns for n-GaAs at 300 K is observed along with expected temperature dependence of τ. Spin injection using Fe3O4/MgO system is further established by injecting spins into p-GaAs and a τ of ~0.32 ns is obtained at 300 K. Enhancement of spin injection efficiency is seen with barrier thickness. In the field of spin injection and detection, our work using an oxide magnetic material establishes a good platform for the development of room temperature oxide based spintronics devices. PMID:24998440

  10. Ultralow field NMR spectrometer with an atomic magnetometer near room temperature.

    PubMed

    Liu, Guobin; Li, Xiaofeng; Sun, Xianping; Feng, Jiwen; Ye, Chaohui; Zhou, Xin

    2013-12-01

    We present a Cs atomic magnetometer with a sensitivity of 150fT/Hz(1/2) operating near room temperature. The nuclear magnetic resonance (NMR) signal of 125μL tap water was detected at an ultralow magnetic field down to 47nT, with the signal-to-noise ratio (SNR) of the NMR signal approaching 50 after eight averages. Relaxivity experiments with a Gd(DTPA) contrast agent in zero field were performed, in order to show the magnetometer's ability to measure spin-lattice relaxation time with high accuracy. This demonstrates the feasibility of an ultralow field NMR spectrometer based on a Cs atomic magnetometer, which has a low working temperature, short data acquisition time and high sensitivity. This kind of NMR spectrometer has great potential in applications such as chemical analysis and magnetic relaxometry detection in ultralow or zero fields. Copyright © 2013 Elsevier Inc. All rights reserved.

  11. Ultralow field NMR spectrometer with an atomic magnetometer near room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Guobin; Li, Xiaofeng; Sun, Xianping; Feng, Jiwen; Ye, Chaohui; Zhou, Xin

    2013-12-01

    We present a Cs atomic magnetometer with a sensitivity of 150 fT/Hz1/2 operating near room temperature. The nuclear magnetic resonance (NMR) signal of 125 μL tap water was detected at an ultralow magnetic field down to 47 nT, with the signal-to-noise ratio (SNR) of the NMR signal approaching 50 after eight averages. Relaxivity experiments with a Gd(DTPA) contrast agent in zero field were performed, in order to show the magnetometer's ability to measure spin-lattice relaxation time with high accuracy. This demonstrates the feasibility of an ultralow field NMR spectrometer based on a Cs atomic magnetometer, which has a low working temperature, short data acquisition time and high sensitivity. This kind of NMR spectrometer has great potential in applications such as chemical analysis and magnetic relaxometry detection in ultralow or zero fields.

  12. Investigation of room temperature ferromagnetic nanoparticles of Gd5Si4

    DOE PAGES

    Hadimani, R. L.; Gupta, S.; Harstad, S. M.; ...

    2015-07-06

    Gd5(SixGe1-x)4 compounds undergo first-order phase transitions close to room temperature when x ~ = 0.5, which are accompanied by extreme changes of properties. We report the fabrication of the nanoparticles of one of the parent compounds-Gd5Si4-using high-energy ball milling. Crystal structure, microstructure, and magnetic properties have been investigated. Particles agglomerate at long milling times, and the particles that are milled >20 min lose crystallinity and no longer undergo magnetic phase transition close to 340 K, which is present in a bulk material. The samples milled for >20 min exhibit a slightly increased coercivity. As a result, magnetization at a highmore » temperature of 275K decreases with the increase in the milling time.« less

  13. Room-temperature resonant quantum tunneling transport of macroscopic systems.

    PubMed

    Xiong, Zhengwei; Wang, Xuemin; Yan, Dawei; Wu, Weidong; Peng, Liping; Li, Weihua; Zhao, Yan; Wang, Xinmin; An, Xinyou; Xiao, Tingting; Zhan, Zhiqiang; Wang, Zhuo; Chen, Xiangrong

    2014-11-21

    A self-assembled quantum dots array (QDA) is a low dimensional electron system applied to various quantum devices. This QDA, if embedded in a single crystal matrix, could be advantageous for quantum information science and technology. However, the quantum tunneling effect has been difficult to observe around room temperature thus far, because it occurs in a microcosmic and low temperature condition. Herein, we show a designed a quasi-periodic Ni QDA embedded in a single crystal BaTiO3 matrix and demonstrate novel quantum resonant tunneling transport properties around room-temperature according to theoretical calculation and experiments. The quantum tunneling process could be effectively modulated by changing the Ni QDA concentration. The major reason was that an applied weak electric field (∼10(2) V cm(-1)) could be enhanced by three orders of magnitude (∼10(5) V cm(-1)) between the Ni QDA because of the higher permittivity of BaTiO3 and the 'hot spots' of the Ni QDA. Compared with the pure BaTiO3 films, the samples with embedded Ni QDA displayed a stepped conductivity and temperature (σ-T curves) construction.

  14. Energy-filtered cold electron transport at room temperature

    PubMed Central

    Bhadrachalam, Pradeep; Subramanian, Ramkumar; Ray, Vishva; Ma, Liang-Chieh; Wang, Weichao; Kim, Jiyoung; Cho, Kyeongjae; Koh, Seong Jin

    2014-01-01

    Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically <1 K. Here we show that electron thermal excitation can be effectively suppressed at room temperature, and energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45 K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport. The quantum well (~2 nm of Cr2O3) is formed between source (Cr) and tunnelling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunnelling through CdSe quantum dots, with full widths at half maximum of only ~15 mV at room temperature. PMID:25204839

  15. Single-molecule spectroscopy and dynamics at room temperature

    SciTech Connect

    Xie, X.S.

    1996-12-01

    The spirit of studying single-molecule behaviors dates back to the turn of the century. In addition to Einstein`s well-known work on Brownian motion, there has been a tradition for studying single {open_quotes}macromolecules{close_quotes} or a small number of molecules either by light scattering or by fluorescence using an optical microscope. Modern computers have allowed detailed studies of single-molecule behaviors in condensed media through molecular dynamics simulations. Optical spectroscopy offers a wealth of information on the structure, interaction, and dynamics of molecular species. With the motivation of removing {open_quotes}inhomogeneous broadening{close_quotes}, spectroscopic techniques have evolved from spectral hole burning, fluorescence line narrowing, and photo-echo to the recent pioneering work on single-molecule spectroscopy in solids at cryogenic temperatures. High-resolution spectroscopic work on single molecules relies on zero phonon lines which appear at cryogenic temperatures, and have narrow line widths and large absorption cross sections. Recent advances in near-field and confocal fluorescence have allowed not only fluorescence imaging of single molecules with high spatial resolutions but also single-molecule spectroscopy at room temperature. In this Account, the author provides a physical chemist`s perspective on experimental and theoretical developments on room-temperature single-molecule spectroscopy and dynamics, with the emphasis on the information obtainable from single-molecule experiments. 61 refs., 9 figs.

  16. Room-temperature creation and spin-orbit torque-induced manipulation of skyrmions in thin film

    NASA Astrophysics Data System (ADS)

    Yu, Guoqiang; Upadhyaya, Pramey; Li, Xiang; Li, Wenyuan; Im, Se Kwon K.; Fan, Yabin; Wong, Kin L.; Tserkovnyak, Yaroslav; Amiri, Pedram Khalili; Wang, Kang L.

    Magnetic skyrmions, which are topologically protected spin texture, are promising candidates for ultra-low energy and ultra-high density magnetic data storage and computing applications1, 2. To date, most experiments on skyrmions have been carried out at low temperatures. The choice of materials available is limited and there is a lack of electrical means to control of skyrmions. Here, we experimentally demonstrate a method for creating skyrmion bubbles phase in the ferromagnetic thin film at room temperature. We further demonstrate that the created skyrmion bubbles can be manipulated by electric current. This room-temperature creation and manipulation of skyrmion in thin film is of particular interest for applications, being suitable for room-temperature operation and compatible with existing semiconductor manufacturing tools. 1. Nagaosa, N., Tokura, Y. Nature Nanotechnology 8, 899-911 (2013). 2. Fert, A., et al., Nature Nanotechnology 8, 152-156 (2013).

  17. Rare-Earth Ions in Niobium-Based Devices as a Quantum Memory: Magneto-Optical Effects on Room Temperature Electrical Transport

    DTIC Science & Technology

    2016-09-01

    TECHNICAL REPORT 3050 September 2016 Rare-Earth Ions in Niobium-based Devices as a Quantum Memory Magneto-Optical Effects on Room Temperature...study the effect of optical illumination and magnetic stimulus on the transport of the devices at room temperature, as it is important to understand...5 5. Two-dimensional EDX images of detection of niobium (left) and red

  18. Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic

    NASA Astrophysics Data System (ADS)

    Mundy, Julia A.; Brooks, Charles M.; Holtz, Megan E.; Moyer, Jarrett A.; Das, Hena; Rébola, Alejandro F.; Heron, John T.; Clarkson, James D.; Disseler, Steven M.; Liu, Zhiqi; Farhan, Alan; Held, Rainer; Hovden, Robert; Padgett, Elliot; Mao, Qingyun; Paik, Hanjong; Misra, Rajiv; Kourkoutis, Lena F.; Arenholz, Elke; Scholl, Andreas; Borchers, Julie A.; Ratcliff, William D.; Ramesh, Ramamoorthy; Fennie, Craig J.; Schiffer, Peter; Muller, David A.; Schlom, Darrell G.

    2016-09-01

    Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications. Here we present a methodology for constructing single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO3—the geometric ferroelectric with the greatest known planar rumpling—we introduce individual monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 (refs 17, 18) within the LuFeO3 matrix, that is, (LuFeO3)m/(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighbouring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state, while also reducing the LuFe2O4 spin frustration. This increases the magnetic transition temperature substantially—from 240 kelvin for LuFe2O4 (ref. 18) to 281 kelvin for (LuFeO3)9/(LuFe2O4)1. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics by exploiting a combination of geometric frustration, lattice distortions and epitaxial engineering.

  19. Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic.

    PubMed

    Mundy, Julia A; Brooks, Charles M; Holtz, Megan E; Moyer, Jarrett A; Das, Hena; Rébola, Alejandro F; Heron, John T; Clarkson, James D; Disseler, Steven M; Liu, Zhiqi; Farhan, Alan; Held, Rainer; Hovden, Robert; Padgett, Elliot; Mao, Qingyun; Paik, Hanjong; Misra, Rajiv; Kourkoutis, Lena F; Arenholz, Elke; Scholl, Andreas; Borchers, Julie A; Ratcliff, William D; Ramesh, Ramamoorthy; Fennie, Craig J; Schiffer, Peter; Muller, David A; Schlom, Darrell G

    2016-09-22

    Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications. Here we present a methodology for constructing single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO3-the geometric ferroelectric with the greatest known planar rumpling-we introduce individual monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 (refs 17, 18) within the LuFeO3 matrix, that is, (LuFeO3)m/(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighbouring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state, while also reducing the LuFe2O4 spin frustration. This increases the magnetic transition temperature substantially-from 240 kelvin for LuFe2O4 (ref. 18) to 281 kelvin for (LuFeO3)9/(LuFe2O4)1. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics by exploiting a combination of geometric frustration, lattice distortions and epitaxial engineering.

  20. Controllable effects of quantum fluctuations on spin free-induction decay at room temperature.

    PubMed

    Liu, Gang-Qin; Pan, Xin-Yu; Jiang, Zhan-Feng; Zhao, Nan; Liu, Ren-Bao

    2012-01-01

    Fluctuations of local fields cause decoherence of quantum objects. Usually at high temperatures, thermal noises are much stronger than quantum fluctuations unless the thermal effects are suppressed by certain techniques such as spin echo. Here we report the discovery of strong quantum-fluctuation effects of nuclear spin baths on free-induction decay of single electron spins in solids at room temperature. We find that the competition between the quantum and thermal fluctuations is controllable by an external magnetic field. These findings are based on Ramsey interference measurement of single nitrogen-vacancy center spins in diamond and numerical simulation of the decoherence, which are in excellent agreement.

  1. Giant magnetocaloric effect near room temperature in the off-stoichiometric Mn-Co-Ge alloy

    NASA Astrophysics Data System (ADS)

    Sharma, V. K.; Manekar, M. A.; Srivastava, Himanshu; Roy, S. B.

    2016-12-01

    We report a giant magnetocaloric effect near room temperature in an off-stoichiometric Mn-Co-Ge alloy, across the magnetostructural transition. The isothermal entropy change accompanying this transition has a peak value of nearly 40 J kg-1 K-1 near 297 K for a field excursion of 70 kOe, and a refrigerant capacity of 270 J kg-1 with the hot end at 302.5 K and cold end at 293.5 K. We also present an experimental protocol to avoid spurious peaks in the magnetocaloric effect across a sharp first order magnetostructural transition, not confined to Mn-Co-Ge alone, where metastability during the transition could influence the measured magnetization and thus the estimated entropy change. The estimated entropy change in the present off-stoichiometric Mn-Co-Ge alloy is possibly the highest reported value near room temperature in undoped Mn-Co-Ge alloys and underlines the potential of the alloy for technological applications in room temperature magnetic refrigeration.

  2. Does the electric power grid need a room temperature superconductor?

    NASA Astrophysics Data System (ADS)

    Malozemoff, A. P.

    2013-11-01

    Superconductivity can revolutionize electric power grids, for example with high power underground cables to open urban power bottlenecks and fault current limiters to solve growing fault currents problems. Technology based on high temperature superconductor (HTS) wire is beginning to meet these critical needs. Wire performance is continually improving. For example, American Superconductor has recently demonstrated long wires with up to 500 A/cm-width at 77 K, almost doubling its previous production performance. But refrigeration, even at 77 K, is a complication, driving interest in discovering room temperature superconductors (RTS). Unfortunately, short coherence lengths and accelerated flux creep will make RTS applications unlikely. Existing HTS technology, in fact, offers a good compromise of relatively high operating temperature but not so high as to incur coherence-length and flux-creep limitations. So - no, power grids do not need RTS; existing HTS wire is proving to be what grids really need.

  3. Terahertz pulsed photogenerated current in microdiodes at room temperature

    SciTech Connect

    Ilkov, Marjan; Torfason, Kristinn; Manolescu, Andrei Valfells, Ágúst

    2015-11-16

    Space-charge modulation of the current in a vacuum diode under photoemission leads to the formation of beamlets with time periodicity corresponding to THz frequencies. We investigate the effect of the emitter temperature and internal space-charge forces on the formation and persistence of the beamlets. We find that temperature effects are most important for beam degradation at low values of the applied electric field, whereas at higher fields, intra-beamlet space-charge forces are dominant. The current modulation is most robust when there is only one beamlet present in the diode gap at a time, corresponding to a macroscopic version of the Coulomb blockade. It is shown that a vacuum microdiode can operate quite well as a tunable THz oscillator at room temperature with an applied electric field above 10 MV/m and a diode gap of the order of 100 nm.

  4. Large electrocaloric effect in ferroelectric polymers near room temperature.

    PubMed

    Neese, Bret; Chu, Baojin; Lu, Sheng-Guo; Wang, Yong; Furman, E; Zhang, Q M

    2008-08-08

    Applying an electrical field to a polar polymer may induce a large change in the dipolar ordering, and if the associated entropy changes are large, they can be explored in cooling applications. With the use of the Maxwell relation between the pyroelectric coefficient and the electrocaloric effect (ECE), it was determined that a large ECE can be realized in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer at temperatures above the ferroelectric-paraelectric transition (above 70 degrees C), where an isothermal entropy change of more than 55 joules per kilogram per kelvin degree and adiabatic temperature change of more than 12 degrees C were observed. We further showed that a similar level of ECE near room temperature can be achieved by working with the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene).

  5. Large Electrocaloric Effect in Ferroelectric Polymers Near Room Temperature

    NASA Astrophysics Data System (ADS)

    Neese, Bret; Chu, Baojin; Lu, Sheng-Guo; Wang, Yong; Furman, E.; Zhang, Q. M.

    2008-08-01

    Applying an electrical field to a polar polymer may induce a large change in the dipolar ordering, and if the associated entropy changes are large, they can be explored in cooling applications. With the use of the Maxwell relation between the pyroelectric coefficient and the electrocaloric effect (ECE), it was determined that a large ECE can be realized in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer at temperatures above the ferroelectric-paraelectric transition (above 70°C), where an isothermal entropy change of more than 55 joules per kilogram per kelvin degree and adiabatic temperature change of more than 12°C were observed. We further showed that a similar level of ECE near room temperature can be achieved by working with the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene).

  6. Exhaled breath temperature in healthy children is influenced by room temperature and lung volume.

    PubMed

    Logie, Karla M; Kusel, Merci M H; Sly, Peter D; Hall, Graham L

    2011-11-01

    Exhaled breath temperature (EBT) has been proposed for the non-invasive assessment of airway inflammation. Previous studies have not examined the influence of room temperature or lung size on the EBT. This study aimed to address these issues in healthy children. We assessed the effects of room temperature and lung volume in 60 healthy children aged 9-11 years (mean age 10.3 years, 33 male). Static lung volumes were assessed using multiple breath nitrogen washout. Questionnaire and skin prick tests were also used to establish respiratory health in the children. We obtained the EBT parameters of slope, end plateau temperature (PLET) and normalized plateau temperature (nPLET; plateau temperature minus inspired air temperature), and ascertained physiological factors influencing EBT. End plateau temperature was shown to be proportionally affected by room temperature (r = 0.532, P < 0.001) whereas slope and nPLET decreased with increasing room temperature (r = -0.392 P < 0.02 and r = -0.507 P = 0.002). After adjusting for room temperature, height and age, the total lung capacity (r(2)  = 0.435, P = 0.006) and slow vital capacity (SVC; r(2)  = 0.44, P = 0.005) were found to be the strongest predictors of end PLET in healthy children. When all factors were included in a multiple regression model, SVC and room temperature were the only predictors of plateau and nPLET. Slope was only influenced by room temperature. Exhaled breath temperature measurements are highly feasible in children with a 95% success rate in this healthy population. Room temperature and SVC significantly influence EBT variables in healthy children. Further studies are required to investigate the ability of EBT to assess airway inflammation in children with respiratory disease. Pediatr. Pulmonol. 2011; 46:1062-1068. © 2011 Wiley Periodicals, Inc. Copyright © 2011 Wiley Periodicals, Inc.

  7. In vitro comparison of output fluid temperatures for room temperature and prewarmed fluids.

    PubMed

    Soto, N; Towle Millard, H A; Lee, R A; Weng, H Y

    2014-08-01

    To determine if prewarmed intravenous fluids produce superior fluid output temperatures compared with room temperature fluids at common anaesthetic fluid rates for small animal patients. A prospective, randomised, in vitro fluid line test-vein study was performed. Nine flow rates were analysed (10, 20, 60, 100, 140, 180, 220, 260 and 300 mL/hour) for room temperature fluids (21°C) and for five prewarmed fluids (40, 45, 50, 55 and 60°C). For each flow rate tested, room temperature fluids never exceeded 25°C at any time point for each trial (range 18 to 25°C). For each flow rate tested, prewarmed fluids never exceeded 25 · 5°C at any time point for each trial (range 18 to 25 · 5°C). The mean output fluid temperature of prewarmed fluids was significantly warmer than room temperature fluids only at 300 mL/hour for 40°C (P = 0 · 0012), 45°C (P = 0 · 004), 50°C (P = 0 · 0002), 55°C (P = 0 · 0001) and 60°C (P < 0 · 0001). There was no thermodynamic benefit to utilising prewarmed intravenous fluids (up to 60°C) compared with room temperature intravenous fluids at common anaesthetic fluid rates for small animals. © 2014 British Small Animal Veterinary Association.

  8. Xenon Recovery at Room Temperature using Metal-Organic Frameworks.

    PubMed

    Elsaidi, Sameh K; Ongari, Daniele; Xu, Wenqian; Mohamed, Mona H; Haranczyk, Maciej; Thallapally, Praveen K

    2017-08-10

    Xenon is known to be a very efficient anesthetic gas, but its cost prohibits the wider use in medical industry and other potential applications. It has been shown that Xe recovery and recycling from anesthetic gas mixtures can significantly reduce its cost as anesthetic. The current technology uses series of adsorbent columns followed by low-temperature distillation to recover Xe; this method is expensive to use in medical facilities. Herein, we propose a much simpler and more efficient system to recover and recycle Xe from exhaled anesthetic gas mixtures at room temperature using metal-organic frameworks (MOFs). Among the MOFs tested, PCN-12 exhibits unprecedented performance with high Xe capacity and Xe/O2 , Xe/N2 and Xe/CO2 selectivity at room temperature. The in situ synchrotron measurements suggest that Xe is occupies the small pockets of PCN-12 compared to unsaturated metal centers (UMCs). Computational modeling of adsorption further supports our experimental observation of Xe binding sites in PCN-12. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Xenon Recovery at Room Temperature using Metal Organic Frameworks

    SciTech Connect

    Elsaidi, Sameh K.; Ongari, Daniele; Xu, Wenqian; Mohamed, Mona H.; Haranczyk, Maciej; Thallapally, Praveen K.

    2017-01-01

    Xenon is known to be a very efficient anesthetic gas but its cost prohibits the wider use in medical industry and other potential applications. It has been shown that Xe recovery and recycle from anesthetic gas mixture can significantly reduce its cost as anesthetic. The current technology uses series of adsorbent columns followed by low temperature distillation to recover Xe, which is expensive to use in medical facilities. Herein, we propose much efficient and simpler system to recover and recycle Xe from simulant exhale anesthetic gas mixture at room temperature using metal organic frameworks. Among the MOFs tested, PCN-12 exhibits unprecedented performance with high Xe capacity, Xe/O2, Xe/N2 and Xe/CO2 selectivity at room temperature. The in-situ synchrotron measurements suggest the Xe is occupied in the small pockets of PCN-12 compared to unsaturated metal centers (UMCs). Computational modeling of adsorption further supports our experimental observation of Xe binding sites in PCN-12.

  10. Conformation of protonated glutamic acid at room and cryogenic temperatures.

    PubMed

    Bouchet, Aude; Klyne, Johanna; Ishiuchi, Shun-Ichi; Fujii, Masaaki; Dopfer, Otto

    2017-05-03

    Recognition properties of biologically relevant molecules depend on their conformation. Herein, the conformation of protonated glutamic acid (H(+)Glu) isolated in quadruple ion traps is characterized by vibrational spectroscopy at room and cryogenic temperatures and dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level. The infrared multiple photon dissociation (IRMPD) spectrum recorded in the fingerprint range at room temperature using an IR free electron laser is attributed to the two most stable and nearly isoenergetic conformations (1-cc and 2-cc) with roughly equal population (ΔG298 = 0.0 kJ mol(-1)). Both have bridging C[double bond, length as m-dash]O(HNH)(+)O[double bond, length as m-dash]C ionic H-bonds of rather different strengths but cannot be distinguished by their similar IRMPD spectra. In contrast, the higher-resolution single-photon IRPD spectrum of H2-tagged H(+)Glu recorded in the conformation-sensitive X-H stretch range in a trap held at 10 K distinguishes both conformers. At low temperature, 1-cc is roughly twice more abundant than 2-cc, in line with its slightly lower calculated energy (ΔE0 = 0.5 kJ mol(-1)). This example illustrates the importance of cryogenic cooling, single-photon absorption conditions, and the consideration of the X-H stretch range for the identification of biomolecular conformations involving hydrogen bonds.

  11. A room temperature low-threshold ultraviolet plasmonic nanolaser.

    PubMed

    Zhang, Qing; Li, Guangyuan; Liu, Xinfeng; Qian, Fang; Li, Yat; Sum, Tze Chien; Lieber, Charles M; Xiong, Qihua

    2014-09-23

    Constrained by large ohmic and radiation losses, plasmonic nanolasers operated at visible regime are usually achieved either with a high threshold (10(2)-10(4) MW cm(-2)) or at cryogenic temperatures (4-120 K). Particularly, the bending-back effect of surface plasmon (SP) dispersion at high energy makes the SP lasing below 450 nm more challenging. Here we demonstrate the first strong room temperature ultraviolet (~370 nm) SP polariton laser with an extremely low threshold (~3.5 MW cm(-2)). We find that a closed-contact planar semiconductor-insulator-metal interface greatly lessens the scattering loss, and more importantly, efficiently promotes the exciton-SP energy transfer thus furnishes adequate optical gain to compensate the loss. An excitation polarization-dependent lasing action is observed and interpreted with a microscopic energy-transfer process from excitons to SPs. Our work advances the fundamental understanding of hybrid plasmonic waveguide laser and provides a solution of realizing room temperature UV nanolasers for biological applications and information technologies.

  12. A room temperature low-threshold ultraviolet plasmonic nanolaser

    NASA Astrophysics Data System (ADS)

    Zhang, Qing; Li, Guangyuan; Liu, Xinfeng; Qian, Fang; Li, Yat; Sum, Tze Chien; Lieber, Charles M.; Xiong, Qihua

    2014-09-01

    Constrained by large ohmic and radiation losses, plasmonic nanolasers operated at visible regime are usually achieved either with a high threshold (102-104 MW cm-2) or at cryogenic temperatures (4-120 K). Particularly, the bending-back effect of surface plasmon (SP) dispersion at high energy makes the SP lasing below 450 nm more challenging. Here we demonstrate the first strong room temperature ultraviolet (~370 nm) SP polariton laser with an extremely low threshold (~3.5 MW cm-2). We find that a closed-contact planar semiconductor-insulator-metal interface greatly lessens the scattering loss, and more importantly, efficiently promotes the exciton-SP energy transfer thus furnishes adequate optical gain to compensate the loss. An excitation polarization-dependent lasing action is observed and interpreted with a microscopic energy-transfer process from excitons to SPs. Our work advances the fundamental understanding of hybrid plasmonic waveguide laser and provides a solution of realizing room temperature UV nanolasers for biological applications and information technologies.

  13. Spin-valley caloritronics in silicene near room temperature

    NASA Astrophysics Data System (ADS)

    Zhai, Xuechao; Gao, Wenwen; Cai, Xinlong; Fan, Ding; Yang, Zhihong; Meng, Lan

    2016-12-01

    Two-dimensional silicene, with an observable intrinsic spin-orbit coupling, has a great potential to perform fascinating physics and new types of applications in spintronics and valleytronics. By introducing an electromotive force from a temperature difference in ferromagnetic silicene, we discover that a longitudinal spin Seebeck effect can be driven even near room temperature, with spin-up and spin-down currents flowing in opposite directions, originating from the asymmetric electron-hole spin band structures. We further propose a silicene field-effect transistor constructed of two ferromagnetic electrodes and a central dual-gated region, and find that a valley Seebeck effect appears, with currents from two different valleys flowing in opposite directions. The forbidden transport channels are determined by either spin-valley dependent band gaps or spin mismatch. By tuning the electric field in the central region, the transport gaps depending on spin and valley vary correspondingly, and a transition from valley Seebeck effect to spin Seebeck effect is observed. These spin-valley caloritronic results near room temperature are robust against many real perturbations, and thus suggest silicene to be an excellent candidate for future energy-saving technologies and bidirectional information processing in solid-state circuits.

  14. Toward realizing high power semiconductor terahertz laser sources at room temperature

    NASA Astrophysics Data System (ADS)

    Razeghi, Manijeh

    2011-05-01

    The terahertz (THz) spectral range offers promising applications in science, industry, and military. THz penetration through nonconductors (fabrics, wood, plastic) enables a more efficient way of performing security checks (for example at airports), as illegal drugs and explosives could be detected. Being a non-ionizing radiation, THz radiation is environment-friendly enabling a safer analysis environment than conventional X-ray based techniques. However, the lack of a compact room temperature THz laser source greatly hinders mass deployment of THz systems in security check points and medical centers. In the past decade, tremendous development has been made in GaAs/AlGaAs based THz Quantum Cascade Laser (QCLs), with maximum operating temperatures close to 200 K (without magnetic field). However, higher temperature operation is severely limited by a small LO-phonon energy (~ 36 meV) in this material system. With a much larger LO-phonon energy of ~ 90 meV, III-Nitrides are promising candidates for room temperature THz lasers. However, realizing high quality material for GaN-based intersubband devices presents a significant challenge. Advances with this approach will be presented. Alternatively, recent demonstration of InP based mid-infrared QCLs with extremely high peak power of 120 W at room temperature opens up the possibility of producing high power THz emission with difference frequency generation through two mid-infrared wavelengths.

  15. Room Temperature Electrical Detection of Spin Polarized Currents in Topological Insulators.

    PubMed

    Dankert, André; Geurs, Johannes; Kamalakar, M Venkata; Charpentier, Sophie; Dash, Saroj P

    2015-12-09

    Topological insulators (TIs) are a new class of quantum materials that exhibit a current-induced spin polarization due to spin-momentum locking of massless Dirac Fermions in their surface states. This helical spin polarization in three-dimensional (3D) TIs has been observed using photoemission spectroscopy up to room temperatures. Recently, spin polarized surface currents in 3D TIs were detected electrically by potentiometric measurements using ferromagnetic detector contacts. However, these electric measurements are so far limited to cryogenic temperatures. Here we report the room temperature electrical detection of the spin polarization on the surface of Bi2Se3 by employing spin sensitive ferromagnetic tunnel contacts. The current-induced spin polarization on the Bi2Se3 surface is probed by measuring the magnetoresistance while switching the magnetization direction of the ferromagnetic detector. A spin resistance of up to 70 mΩ is measured at room temperature, which increases linearly with current bias, reverses sign with current direction, and decreases with higher TI thickness. The magnitude of the spin signal, its sign, and control experiments, using different measurement geometries and interface conditions, rule out other known physical effects. These findings provide further information about the electrical detection of current-induced spin polarizations in 3D TIs at ambient temperatures and could lead to innovative spin-based technologies.

  16. Directional molecular sliding at room temperature on a silicon runway.

    PubMed

    Bouju, Xavier; Chérioux, Frédéric; Coget, Sébastien; Rapenne, Gwénaël; Palmino, Frank

    2013-08-07

    The design of working nanovehicles is a key challenge for the development of new devices. In this context, 1D controlled sliding of molecules on a silicon-based surface is successfully achieved by using an optimized molecule-substrate pair. Even though the molecule and surface are compatible, the molecule-substrate interaction provides a 1D template effect to guide molecular sliding along a preferential surface orientation. Molecular motion is monitored by STM experiments under ultra-high vacuum at room temperature. Molecule-surface interactions are elucidated by semi-empirical calculations.

  17. Laser phosphoroscope and applications to room-temperature phosphorescence.

    PubMed

    Payne, Sarah J; Zhang, Guoqing; Demas, James N; Fraser, Cassandra L; Degraff, Ben A

    2011-11-01

    A simple phosphoroscope with no moving parts is described. In one scan the total luminescence, the long-lived phosphorescence, and the short-lived fluorescence can be determined. A 50% duty cycle excitation from a diode laser is used to excite the sample, and from the digitized waveform the phosphorescence is extracted from the off period, the total emission from the full cycle, and the fluorescence from the on period corrected for the phosphorescence contribution. The performance of the system is demonstrated using room-temperature phosphorescence of organic dyes in boric acid glasses, a multi-emissive boron-polymer dye, and a europium chelate.

  18. Room-temperature phonon boundary scattering below the Casimir limit

    SciTech Connect

    Sadhu, J; Sinha, S

    2011-09-26

    Thermal conductivity data for rough surface silicon nanowires suggest the breakdown of the Casimir limit which assumes completely diffuse phonon boundary scattering. We show that coherent effects in phonon transport at room temperature indeed lead to such breakdown. Correlated multiple scattering of phonons off the rough surface lead to a reduced thermal conductivity that is dependent not only on the roughness amplitude but more importantly on the roughness correlation length. A correlation length less than the diameter of the wire is typically necessary for lowering the thermal conductivity below the Casimir limit. Our model explains seeming anomalies in data reported for electrolessly etched and electron beam lithography defined nanowires.

  19. Development of bulk GaAs room temperature radiation detectors

    SciTech Connect

    McGregor, D.S.; Knoll, G.F. . Dept. of Nuclear Engineering); Eisen, Y. . Soreq Nuclear Research Center); Brake, R. )

    1992-10-01

    This paper reports on GaAs, a wide band gap semiconductor with potential use as a room temperature radiation detector. Various configurations of Schottky diode detectors were fabricated with bulk crystals of liquid encapsulated Czochralski (LEC) semi-insulating undoped GaAs material. Basic detector construction utilized one Ti/Au Schottky contact and one Au/Ge/Ni alloyed ohmic contact. Pulsed X-ray analysis indicated pulse decay times dependent on bias voltage. Pulse height analysis disclosed non-uniform electric field distributions across the detectors tentatively explained as a consequence of native deep level donors (EL2) in the crystal.

  20. Ultrafast excitonic room temperature nonlinearity in neutron irradiated quantum wells

    SciTech Connect

    Ten, S.; Williams, J.G.; Guerreiro, P.T.; Khitrova, G.; Peyghambarian, N.

    1997-01-01

    Sharp room temperature exciton features and complete recovery of the excitonic absorption with 21 ps time constant are demonstrated in neutron irradiated (Ga,Al)As/GaAs multiple quantum wells. Carrier lifetime reduction is consistent with the EL2 midgap defect which is efficiently generated by fast neutrons. Influence of gamma rays accompanying neutron irradiation is discussed. Neutron irradiation provides a straightforward way to control carrier lifetime in semiconductor heterostructures with minor deterioration of their excitonic properties. {copyright} {ital 1997 American Institute of Physics.}

  1. Room temperature peierls distortion in small diameter nanotubes.

    PubMed

    Connétable, D; Rignanese, G-M; Charlier, J-C; Blase, X

    2005-01-14

    By means of ab initio simulations, we investigate the phonon band structure and electron-phonon coupling in small 4-A diameter nanotubes. We show that both the C(5,0) and C(3,3) tubes undergo above room temperature a Peierls transition mediated by an acoustical long wavelength and an optical q=2k(F) phonon, respectively. In the armchair geometry, we verify that the electron-phonon coupling parameter lambda originates mainly from phonons at q=2k(F) and is strongly enhanced when the diameter decreases. These results question the origin of superconductivity in small diameter nanotubes.

  2. A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection

    PubMed Central

    Xi, Hao; Qian, Xiaoshi; Lu, Meng-Chien; Mei, Lei; Rupprecht, Sebastian; Yang, Qing X.; Zhang, Q. M.

    2016-01-01

    Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron. PMID:27465206

  3. A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection.

    PubMed

    Xi, Hao; Qian, Xiaoshi; Lu, Meng-Chien; Mei, Lei; Rupprecht, Sebastian; Yang, Qing X; Zhang, Q M

    2016-07-28

    Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron.

  4. Giant room-temperature magnetodielectric coupling in spark plasma sintered brownmillerite ceramics

    SciTech Connect

    Wu, J. W.; Wang, J.; Liu, G.; Wu, Y. J.; Liu, X. Q. Chen, X. M.

    2014-12-01

    The dielectric, magnetic, and magnetodielectric properties of Ca{sub 2}FeAO{sub 5+δ} (A = Al, Ga) ceramics were investigated together with their crystal structures. Rietveld refinement of the X-ray diffraction data indicated that the space group of the Ca{sub 2}FeAlO{sub 5+δ} ceramic was Ibm2, whereas that of the Ca{sub 2}FeGaO{sub 5+δ} ceramic was Pcmn. Dielectric relaxation above room temperature, originating from the Maxwell–Wagner effect and polaronic hole hopping between Fe{sup 3+} and Fe{sup 4+} ions, was observed in both ceramics. Weak ferrimagnetic behavior was identified from the magnetic-field-dependent magnetization in these ceramics, which was attributed to the non-cancelled spins of the antiferromagnetic-ordered Fe{sup 3+} and Fe{sup 4+} ions. An intrinsic, giant, room-temperature magnetodielectric coefficient of up to −23.3% was achieved in the Ca{sub 2}FeAlO{sub 5+δ} ceramic at 50 MHz, which was attributed to the suppression of charge fluctuations of Fe{sup 3+} and Fe{sup 4+} ions in the magnetic field.

  5. A Room Temperature Ultrasensitive Magnetoelectric Susceptometer for Quantitative Tissue Iron Detection

    NASA Astrophysics Data System (ADS)

    Xi, Hao; Qian, Xiaoshi; Lu, Meng-Chien; Mei, Lei; Rupprecht, Sebastian; Yang, Qing X.; Zhang, Q. M.

    2016-07-01

    Iron is a trace mineral that plays a vital role in the human body. However, absorbing and accumulating excessive iron in body organs (iron overload) can damage or even destroy an organ. Even after many decades of research, progress on the development of noninvasive and low-cost tissue iron detection methods is very limited. Here we report a recent advance in a room-temperature ultrasensitive biomagnetic susceptometer for quantitative tissue iron detection. The biomagnetic susceptometer exploits recent advances in the magnetoelectric (ME) composite sensors that exhibit an ultrahigh AC magnetic sensitivity under the presence of a strong DC magnetic field. The first order gradiometer based on piezoelectric and magnetostrictive laminate (ME composite) structure shows an equivalent magnetic noise of 0.99 nT/rt Hz at 1 Hz in the presence of a DC magnetic field of 0.1 Tesla and a great common mode noise rejection ability. A prototype magnetoelectric liver susceptometry has been demonstrated with liver phantoms. The results indicate its output signals to be linearly responsive to iron concentrations from normal iron dose (0.05 mg Fe/g liver phantom) to 5 mg Fe/g liver phantom iron overload (100X overdose). The results here open up many innovative possibilities for compact-size, portable, cost-affordable, and room-temperature operated medical systems for quantitative determinations of tissue iron.

  6. Prediction of near-room-temperature quantum anomalous Hall effect on honeycomb materials.

    PubMed

    Wu, Shu-Chun; Shan, Guangcun; Yan, Binghai

    2014-12-19

    Recently, the long-sough quantum anomalous Hall effect was realized in a magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic (FM) order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and, consequently, an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.

  7. Direct evidence for significant spin-polarization of EuS in Co/EuS multilayers at room temperature

    PubMed Central

    Pappas, S. D.; Poulopoulos, P.; Lewitz, B.; Straub, A.; Goschew, A.; Kapaklis, V.; Wilhelm, F.; Rogalev, A.; Fumagalli, P.

    2013-01-01

    The new era of spintronics promises the development of nanodevices, where the electron spin will be used to store information and charge currents will be replaced by spin currents. For this, ferromagnetic semiconductors at room temperature are needed. We report on significant room-temperature spin polarization of EuS in Co/EuS multilayers recorded by x-ray magnetic circular dichroism (XMCD). The films were found to contain a mixture of divalent and trivalent europium, but only Eu++ is responsible for the ferromagnetic behavior of EuS. The magnetic XMCD signal of Eu at room temperature could unambiguously be assigned to magnetic ordering of EuS and was found to be only one order of magnitude smaller than that at 2.5 K. The room temperature magnetic moment of EuS is as large as the one of bulk ferromagnetic Ni. Our findings pave the path for fabrication of room–temperature spintronic devices using spin polarized EuS layers. PMID:23434820

  8. Room-Temperature Electron Spin Relaxation of Triarylmethyl Radicals at X- and Q-bands

    PubMed Central

    Krumkacheva, Olesya A.; Strizhakov, Rodion K.; Rogozhnikova, Olga Yu.; Troitskaya, Tatiana I.

    2016-01-01

    Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form) , mono-, di-, and tri-ester derivatives of Finland-D36 trityl, deuterated form of OX63, dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed Electron Paramagnetic Resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm~T2) on magnetic field: room-temperature Tm values are ~1.5-2.5 times smaller at Q-band (34 GHz, 1.2 T) compared to X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligible at lower magnetic fields but comes into play at Q-band. In agreement with this, while T1~Tm at X-band, we observe T1>Tm at Q-band due to increased contributions from incomplete motional averaging of g-anisotropy. In addition, the viscosity dependence shows that (1/Tm-1/T1) is proportional to the tumbling correlation time of trityls. Based on the analysis of previous data and results of the present work, we conclude that in general situation where spin label is at least partly mobile, X-band is most suitable for application of trityls for room-temperature pulsed EPR distance measurements. PMID:26001103

  9. Origin of room temperature ferromagnetism in SnO2 films

    NASA Astrophysics Data System (ADS)

    Li, Jing; Bai, Guohua; Jiang, Yinzhu; Du, Youwei; Wu, Chen; Yan, Mi

    2017-03-01

    SnO2 films exhibiting room temperature ferromagnetism (RTFM) have been prepared on Si (001) by pulsed laser deposition. The saturation magnetization (Ms) of the films experiences a decreasing trend followed by increasing with the growth temperature increased from RT to 400 ℃. The growth temperature affects both the concentration and the location of the oxygen vacancies as the origin of the RTFM. With lower growth temperatures (<300 ℃), more oxygen vacancies exist in the inner film for the samples with less crystallinity, resulting in enhanced magnetism. Higher deposition temperature leads to less oxygen vacancies in the inner film but more oxygen defects at the film surface, which is also beneficial to achieve greater magnetism. Various oxygen pressures during growth and post-annealing have also been used to confirm the role of oxygen vacancies. The study demonstrates that the surface oxygen defects and the positively charged monovalent O vacancies (VO+) in the inner film are the origin of the magnetism in SnO2 films.

  10. Temperature-Dependent Giant Magnetoimpedance Effect in Amorphous Soft Magnets

    NASA Astrophysics Data System (ADS)

    Kurniawan, M.; Roy, R. K.; Panda, A. K.; Greve, D. W.; Ohodnicki, P.; McHenry, M. E.

    2014-12-01

    Giant magnetoimpedance (GMI)-based devices offer potential as next-generation low-cost, flexible, ultrasensitive sensors. They can be used in applications that include current sensors, field sensors, stress sensors, and others. Challenging applications involve operation at high temperatures, and therefore studies of GMI temperature dependence and performance of soft magnetic materials are needed. We present a high-temperature GMI study on an amorphous soft magnetic microwire from room temperature to 560°C. The GMI ratio was observed to be nearly constant at ˜86% at low temperatures and to decrease rapidly at ˜290°C, finally reaching a near-zero value at 500°C. The rapid drop in GMI ratio at 290°C is associated with a reduction in the long-range ferromagnetic order as measured by the spontaneous magnetization ( M) at the Curie temperature ( T c). We also correlated the impedance with the magnetic properties of the material. From room temperature to 290°C, the impedance was found to be proportional to the square root of the magnetization to magnetic anisotropy ratio. Lastly, M( T) has been fit using a Handrich-Kobe model, which describes the system with a modified Brillouin function and an asymmetrical distribution of exchange interactions. We infer that the structural fluctuations of the amorphous phase result in a relatively small asymmetry in the fluctuation parameters.

  11. Stable room-temperature ferromagnetic phase at the FeRh(100) surface

    DOE PAGES

    Pressacco, Federico; Uhlir, Vojtech; Gatti, Matteo; ...

    2016-03-03

    Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. Furthermore, we find that the symmetry breaking induced at themore » Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings.« less

  12. Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers.

    PubMed

    Parkin, Stuart S P; Kaiser, Christian; Panchula, Alex; Rice, Philip M; Hughes, Brian; Samant, Mahesh; Yang, See-Hun

    2004-12-01

    Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

  13. Room temperature magnetoelectric coupling in Zn1-xCoxO/BaTiO3 bilayer system

    NASA Astrophysics Data System (ADS)

    Sundararaj, Anuraj; Annal Therese, Helen; Ramaswamy, Shivaraman; Chandrasekaran, Gopalakrishnan; Annamalai, Karthigeyan

    2014-09-01

    We report on room temperature magnetoelectric coupling in Zn1-xCoxO/BaTiO3 (x = 0.02, 0.05, and 0.10) bilayer thinfilm multiferroic system (BLS) grown on SrTiO3 (100) substrate. All the BLSs exhibit room temperature ferroelectric response. The BLS with x = 0.02 is paramagnetic, while the BLS with x = 0.05 and 0.10 is weakly ferromagnetic. Increase in Co concentration of the BLS results in reduction of permittivity and electric polarization along with increase of coercive voltage, coercive field, and magnetic moment. The d33 value change from 23 pm/V to 30 pm/V with increase in external magnetic field from 1500 G to 2500 G for BLS with x = 0.05. This shows that Zn1-xCoxO/BaTiO3 is magnetoelectrically coupled at room temperature.

  14. Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

    SciTech Connect

    Zhao, K.; Xia, X. X.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

    2011-04-04

    We report a high entropy metallic glass of Zn{sub 20}Ca{sub 20}Sr{sub 20}Yb{sub 20}(Li{sub 0.55}Mg{sub 0.45}){sub 20} via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

  15. Room-Temperature Equation of State for CO2-I

    NASA Astrophysics Data System (ADS)

    Scott, H. P.; Kinney, T. W.; Frank, M. R.; Lin, J.

    2010-12-01

    We have measured the room-temperature bulk modulus (K0T) and its pressure derivative (K') for solid carbon dioxide in its relatively low-pressure phase I (space group: Pa3; CO2-I) between 0.9 and 9 GPa. This pressure range closely matches the actual room-temperature stability field for this phase. The motivation for our investigation is to address an apparent discrepancy in two earlier publications and provide a complete and internally consistent set of equation of state (EoS) parameters for future investigators to conveniently predict the diffraction peak positions for CO2-I at elevated pressures. We note that there is much interest in the chemical reactivity of CO2 at elevated pressures and temperatures and anticipate that this will be a useful addition to the literature. Because the solid phase is unquenchable at room temperature, we used the estimated zero-pressure volume extrapolated to 300 K from lower temperatures by Olinger (1982) and held this value fixed: V0 = 197.9 Å3/unit cell. We performed fits with both the Vinet (K0T = 3.1 ± 0.1 GPa, K' = 9.1 ± 0.2) and Birch-Murnaghan (K0T = 2.5 ± 0.2 GPa, K' = 13.0 ± 0.9) EoS models. The observed difference is not surprising given the very high compressibility of this phase and the inherent covariance between K0T and K'. Although we note that both sets of EoS parameters produce acceptable fits to our data, we favor the Vinet values, especially in terms of determining a realistic value for K', because the phase is so compressible. However, many workers utilize software with built-in routines for calculating peak positions at high pressures, and these often assume a Birch Murnaghan EoS. To facilitate the usage of our results with such programs, we have also performed a Birch-Murnaghan fit for which the K' value from the Vinet fit was held fixed and K0T was the only fit parameter. Accordingly, we present the following EoS parameters for the convenient calculation of expected peak positions for CO2-I at high

  16. Dynamics and structure of room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Fayer, Michael D.

    2014-11-01

    Room temperature ionic liquids (RTIL) are intrinsically interesting because they simultaneously have properties that are similar to organic liquids and liquid salts. In addition, RTILs are increasingly being considered for and used in technological applications. RTILs are usually composed of an organic cation and an inorganic anion. The organic cation, such as imidazolium, has alkyl chains of various lengths. The disorder in the liquid produced by the presence of the alkyl groups lowers the temperature for crystallization below room temperature and can also result in supercooling and glass formation rather than crystallization. The presence of the alkyl moieties also results in a segregation of the liquid into ionic and organic regions. In this article, experiments are presented that address the relationship between RTIL dynamics and structure. Time resolved fluorescence anisotropy measurements were employed to study the local environments in the organic and ionic regions of RTILs using a nonpolar chromophore that locates in the organic regions and an ionic chromophore that locates in the ionic regions. In the alkyl regions, the in plane and out of plane orientational friction coefficients change in different manners as the alkyl chains get longer. Both friction coefficients converge toward those of a long chain length hydrocarbon as the RTIL chains increase in length, which demonstrates that for sufficiently long alkyl chains the RTIL organic regions have properties similar to a hydrocarbon. However, putting Li+ in the ionic regions changes the friction coefficients in the alkyl regions, which demonstrates that changes of the ion structural organization influences the organization of the alkyl chains. Optical heterodyne detected optical Kerr effect (OHD-OKE) experiments were used to examine the orientational relaxation dynamics of RTILs over times scales of a hundred femtoseconds to a hundred nanoseconds. Detailed temperature dependent studies in the liquid and

  17. Airway narrowing measured by spirometry and impulse oscillometry following room temperature and cold temperature exercise.

    PubMed

    Evans, Tina M; Rundell, Kenneth W; Beck, Kenneth C; Levine, Alan M; Baumann, Jennifer M

    2005-10-01

    The efficacy of using impulse oscillometry (IOS) as an indirect measure of airflow obstruction compared to spirometry after exercise challenges in the evaluation of exercise-induced bronchoconstriction (EIB) has not been fully appreciated. The objective was to compare airway responses following room temperature and cold temperature exercise challenges, and to compare whether IOS variables relate to spirometry variables. Spirometry and IOS were performed at baseline and for 20 min after challenge at 5-min intervals. Two 6-min exercise challenges, inhaling either room temperature (22.0 degrees C) or cold temperature (- 1 degrees C) dry medical-grade bottled air. At least 48 h was observed between these randomly assigned challenges. Twenty-two physically active individuals (12 women and 10 men) with probable EIB. Subjects performed 6 min of stationary cycle ergometry while breathing either cold or room temperature medical-grade dry bottled air. Subjects were instructed to exercise at the highest intensity sustainable for the duration of the challenge. Heart rate and kilojoules of work performed were documented to verify exercise intensity. Strong correlations were observed within testing modalities for post-room temperature and post-cold temperature exercise spirometry and IOS values. Spirometry revealed no differences in postexercise peak falls in lung function between conditions; however, IOS identified significant differences in respiratory resistance (p < 0.05), with room temperature-inspired air being more potent than cold temperature-inspired air. Correlations were found between spirometric and IOS measures of change in airway function for both exercise challenges, indicating close equivalency of the methods. The challenges appeared to elicit the EIB response by a similar mechanism of water loss, and cold temperature did not have an additive effect. IOS detected a difference in degree of response between the temperatures, whereas spirometry indicated no

  18. Investigation of the room temperature annealing peak in ionomers

    SciTech Connect

    Goddard, R.J.; Grady, B.P.; Cooper, S.L.

    1993-12-31

    A number of studies appearing in the literature have documented an endothermic peak in differential scanning calorimetry (DSC) scans for ethylene-methacrylic acid copolymer ionomers which appears only upon annealing at room temperature. This peak has been attributed to either polyethylene crystallites, ionic crystallite, or water absorption. In a novel polyurethane cationomer with a quarternized amine contained in hard segment, the same phenomena has been found in DSC scans when the neutralizing anion is bromine or iodine. Since this material does not crystallize, the authors were able to conclusively eliminate crystallization as the cause of the endotherm. The extended x-ray absorption fine structure (EXAFS) of bromine has been measured to differentiate between water absorption and ionic crystallites. Spectra were collected above and below the temperature corresponding to the endothermic peak. The results of the EXAFS analysis will be presented.

  19. New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

    SciTech Connect

    Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L.; Banyai, Douglas; Savaikar, Madhusudan A.; Jaszczak, John A.; Yap, Yoke Khin

    2016-02-05

    Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). Ultimately, as suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

  20. Airtight metallic sealing at room temperature under small mechanical pressure

    NASA Astrophysics Data System (ADS)

    Stagon, Stephen P.; Huang, Hanchen

    2013-10-01

    Metallic seals can be resistant to air leakage, resistant to degradation under heat, and capable of carrying mechanical loads. Various technologies - such as organic solar cells and organic light emitting diodes - need, at least benefit from, such metallic seals. However, these technologies involve polymeric materials and can tolerate neither the high-temperature nor the high-pressure processes of conventional metallic sealing. Recent progress in nanorod growth opens the door to metallic sealing for these technologies. Here, we report a process of metallic sealing using small well-separated Ag nanorods; the process is at room temperature, under a small mechanical pressure of 9.0 MPa, and also in ambient. The metallic seals have an air leak rate of 1.1 × 10-3 cm3atm/m2/day, and a mechanical shear strength higher than 8.9 MPa. This leak rate meets the requirements of organic solar cells and organic light emitting diodes.

  1. Room-temperature metastability of multilayer graphene oxide films.

    PubMed

    Kim, Suenne; Zhou, Si; Hu, Yike; Acik, Muge; Chabal, Yves J; Berger, Claire; de Heer, Walt; Bongiorno, Angelo; Riedo, Elisa

    2012-05-06

    Graphene oxide potentially has multiple applications. The chemistry of graphene oxide and its response to external stimuli such as temperature and light are not well understood and only approximately controlled. This understanding is crucial to enable future applications of this material. Here, a combined experimental and density functional theory study shows that multilayer graphene oxide produced by oxidizing epitaxial graphene through the Hummers method is a metastable material whose structure and chemistry evolve at room temperature with a characteristic relaxation time of about one month. At the quasi-equilibrium, graphene oxide reaches a nearly stable reduced O/C ratio, and exhibits a structure deprived of epoxide groups and enriched in hydroxyl groups. Our calculations show that the structural and chemical changes are driven by the availability of hydrogen in the oxidized graphitic sheets, which favours the reduction of epoxide groups and the formation of water molecules.

  2. Generation of coherent terahertz pulses in ruby at room temperature

    SciTech Connect

    Kuznetsova, Elena; Rostovtsev, Yuri; Kalugin, Nikolai G.; Kolesov, Roman; Kocharovskaya, Olga; Scully, Marlan O.

    2006-08-15

    We have shown that a coherently driven solid state medium can potentially produce strong controllable short pulses of THz radiation. The high efficiency of the technique is based on excitation of maximal THz coherence by applying resonant optical pulses to the medium. The excited coherence in the medium is connected to macroscopic polarization coupled to THz radiation. We have performed detailed simulations by solving the coupled density matrix and Maxwell equations. By using a simple V-type energy scheme for ruby, we have demonstrated that the energy of generated THz pulses ranges from hundreds of pico-Joules to nano-Joules at room temperature and micro-Joules at liquid helium temperature, with pulse durations from picoseconds to tens of nanoseconds. We have also suggested a coherent ruby source that lases on two optical wavelengths and simultaneously generates THz radiation. We discussed also possibilities of extension of the technique to different solid-state materials.

  3. Cadmium selenide: a promising novel room temperature radiation detector

    SciTech Connect

    Burger, A.; Schieber, M.; Shilo, I.

    1983-02-01

    Large single crystals of CdSe weighing about 30g were grown by the vertical unseeded vapor growth technique at a linear growth rate of 5mm/day and a temperature gradient of 10/sup 0/C/cm. Crystal perfection and homogeneity were evaluated by Laue X-ray diffraction, etch pit density, SEM and microprobe analysis methods. The dark resistivity of the as-grown and the heat treated crystal was about 1..cap omega..cm and 10/sup 12/..cap omega..cm respectively. Slices were used to fabricate room temperature detectors for nuclear radiation energy. The detectors showed high efficiency and stability as a function of time for radiation sources from 10KeV to 660KeV.

  4. Magnesium Electrorefining in Non-Aqueous Electrolyte at Room Temperature

    NASA Astrophysics Data System (ADS)

    Kwon, Kyungjung; Park, Jesik; Kusumah, Priyandi; Dilasari, Bonita; Kim, Hansu; Lee, Churl Kyoung

    Magnesium, of which application is often limited by its poor corrosion resistance, is more vulnerable to corrosion with existence of metal impurities such as Fe. Therefore, for the refining and recycling of magnesium, high temperature electrolysis using molten salts has been frequently adopted. In this report, the purification of magnesium scrap by electrolysis at room temperature is investigated with non-aqueous electrolytes. An aprotic solvent of tetrahydrofuran (THF) was used as a solvent of the electrolyte. Magnesium scrap was used as anode materials and ethyl magnesium bromide (EtMgBr) was dissolved in THF for magnesium source. The purified magnesium can be uniformly electrodeposited on copper electrode under potentiostatic conditions. The deposits were confirmed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis.

  5. New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

    PubMed

    Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L; Banyai, Douglas; Savaikar, Madhusudan A; Jaszczak, John A; Yap, Yoke Khin

    2016-02-05

    Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

  6. Silicon Nanowires Light Emitting Devices at Room Temperature

    NASA Astrophysics Data System (ADS)

    Artoni, Pietro; Irrera, A.; Franzò', G.; Fazio, B.; Galli, M.; Pecora, E.; Iacona, F.; Priolo, F.

    Group-IV semiconductor nanowires (NWs) are attracting interest among the scientific community as building blocks for a wide range of future nanoscaled devices. Vapor-liquid-Solid (VLS) is the most used technique for semiconductor NWs growth. Si NWs are promising as building blocks for photovoltaic elements, sensors and high-performance batteries; however, Si NWs are less explored for photonic applications, probably since there are many drawbacks due to the NW structure obtained by VLS. In fact, there is a minimum obtainable size which reduces the possibility to have quantum confinement effects without high temperature oxidation processes; metal used as a catalyst may be incorporated inside the NW thus affecting its electrical and optical properties. Moreover, by VLS method the doping is no easily controllable because of the segregation of the dopants at the NWs interface. Indeed, the possibility of obtaining light from silicon at room temperature under optical and electrical pumping is strategic for the communication technology.

  7. Room temperature ferroelectricity in continuous croconic acid thin films

    SciTech Connect

    Jiang, Xuanyuan; Lu, Haidong; Yin, Yuewei; Ahmadi, Zahra; Costa, Paulo S.; Zhang, Xiaozhe; Wang, Xiao; Yu, Le; Cheng, Xuemei; DiChiara, Anthony D.; Gruverman, Alexei E-mail: a.enders@me.com Enders, Axel E-mail: a.enders@me.com Xu, Xiaoshan E-mail: a.enders@me.com

    2016-09-05

    Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50–100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.

  8. Room temperature ferroelectricity in continuous croconic acid thin films

    NASA Astrophysics Data System (ADS)

    Jiang, Xuanyuan; Lu, Haidong; Yin, Yuewei; Zhang, Xiaozhe; Wang, Xiao; Yu, Le; Ahmadi, Zahra; Costa, Paulo S.; DiChiara, Anthony D.; Cheng, Xuemei; Gruverman, Alexei; Enders, Axel; Xu, Xiaoshan

    2016-09-01

    Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50-100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.

  9. A stable room-temperature sodium–sulfur battery

    PubMed Central

    Wei, Shuya; Xu, Shaomao; Agrawral, Akanksha; Choudhury, Snehashis; Lu, Yingying; Tu, Zhengyuan; Ma, Lin; Archer, Lynden A.

    2016-01-01

    High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium–sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. Here we report a room-temperature sodium–sulfur battery that uses a microporous carbon–sulfur composite cathode, and a liquid carbonate electrolyte containing the ionic liquid 1-methyl-3-propylimidazolium-chlorate tethered to SiO2 nanoparticles. We show that these cells can cycle stably at a rate of 0.5 C (1 C=1675, mAh g−1) with 600 mAh g−1 reversible capacity and nearly 100% Coulombic efficiency. By means of spectroscopic and electrochemical analysis, we find that the particles form a sodium-ion conductive film on the anode, which stabilizes deposition of sodium. We also find that sulfur remains interred in the carbon pores and undergo solid-state electrochemical reactions with sodium ions. PMID:27277345

  10. Unconditional polarization qubit quantum memory at room temperature

    NASA Astrophysics Data System (ADS)

    Namazi, Mehdi; Kupchak, Connor; Jordaan, Bertus; Shahrokhshahi, Reihaneh; Figueroa, Eden

    2016-05-01

    The creation of global quantum key distribution and quantum communication networks requires multiple operational quantum memories. Achieving a considerable reduction in experimental and cost overhead in these implementations is thus a major challenge. Here we present a polarization qubit quantum memory fully-operational at 330K, an unheard frontier in the development of useful qubit quantum technology. This result is achieved through extensive study of how optical response of cold atomic medium is transformed by the motion of atoms at room temperature leading to an optimal characterization of room temperature quantum light-matter interfaces. Our quantum memory shows an average fidelity of 86.6 +/- 0.6% for optical pulses containing on average 1 photon per pulse, thereby defeating any classical strategy exploiting the non-unitary character of the memory efficiency. Our system significantly decreases the technological overhead required to achieve quantum memory operation and will serve as a building block for scalable and technologically simpler many-memory quantum machines. The work was supported by the US-Navy Office of Naval Research, Grant Number N00141410801 and the Simons Foundation, Grant Number SBF241180. B. J. acknowledges financial assistance of the National Research Foundation (NRF) of South Africa.

  11. A stable room-temperature sodium-sulfur battery

    NASA Astrophysics Data System (ADS)

    Wei, Shuya; Xu, Shaomao; Agrawral, Akanksha; Choudhury, Snehashis; Lu, Yingying; Tu, Zhengyuan; Ma, Lin; Archer, Lynden A.

    2016-06-01

    High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium-sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. Here we report a room-temperature sodium-sulfur battery that uses a microporous carbon-sulfur composite cathode, and a liquid carbonate electrolyte containing the ionic liquid 1-methyl-3-propylimidazolium-chlorate tethered to SiO2 nanoparticles. We show that these cells can cycle stably at a rate of 0.5 C (1 C=1675, mAh g-1) with 600 mAh g-1 reversible capacity and nearly 100% Coulombic efficiency. By means of spectroscopic and electrochemical analysis, we find that the particles form a sodium-ion conductive film on the anode, which stabilizes deposition of sodium. We also find that sulfur remains interred in the carbon pores and undergo solid-state electrochemical reactions with sodium ions.

  12. [Preservation and stability of corn tortillas at room temperature].

    PubMed

    Higuera-Ciapara, I; Nieblas, J M

    1995-06-01

    Three treatments with chemical preservative (sodium propionate, potassium sorbate-methylparaben and hydrogen peroxidemethyl paraben) were tested to delay microbial spoilage and extend shelf-life of corn tortillas at room temperature (25 degrees C). The treatment with the best results was selected for further studies using two types of packaging: Paper and high density polyethylene. Quality of corn tortillas during storage was assessed by measuring water content, microbial analysis (Total Plate Count, molds and yeast) and throguh sensory evaluation. Results were analyzed by covariance analysis and slope contrast between packaging materials at p<0.05. Spoilage of tortilla without preservative occurred within 24 hours due to a large number of gram negative bacteria, molds and yeasts, which were responsible for offensive odors. Only the combination of hydrogen peroxide-methyl paraben had a significant effect on retarding bacterial yeast spoilage. In addition, hydrogen peroxide residues could not [correction of no] be chemically detected after 2 days of storage. Results from this study show that tortilla can be kept for up to six days at room temperature with acceptable sensory properties with proper preservative treatment and packaging.

  13. Experiments on room temperature optical fiber-fiber direct bonding

    NASA Astrophysics Data System (ADS)

    Hao, Jinping; Yan, Ping; Xiao, Qirong; Wang, Yaping; Gong, Mali

    2012-08-01

    High quality permanent connection between optical fibers is a significant issue in optics and communication. Studies on room temperature optical large diameter fiber-fiber direct bonding, which is essentially surface interactions of glass material, are presented here. Bonded fiber pairs are obtained for the first time through the bonding technics illustrated here. Two different kinds of bonding technics are provided-fresh surface (freshly grinded and polished) bonding and hydrophobic surface (activated by H2SO4 and HF) bonding. By means of fresh surface bonding, a bonded fiber pair with light transmitting efficiency of 98.1% and bond strength of 21.2 N is obtained. Besides, in the bonding process, chemical surface treatment of fibers' end surfaces is an important step. Therefore, various ways of surface treatment are analyzed and compared, based on atomic force microscopy force curves of differently disposed surfaces. According to the comparison, fresh surfaces are suggested as the prior choice in room temperature optical fiber-fiber bonding, owing to their larger adhesive force, attractive force, attractive distance, and adhesive range.

  14. Optically pumped room-temperature GaAs nanowire lasers

    NASA Astrophysics Data System (ADS)

    Saxena, Dhruv; Mokkapati, Sudha; Parkinson, Patrick; Jiang, Nian; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

    2013-12-01

    Near-infrared lasers are important for optical data communication, spectroscopy and medical diagnosis. Semiconductor nanowires offer the possibility of reducing the footprint of devices for three-dimensional device integration and hence are being extensively studied in the context of optoelectronic devices. Although visible and ultraviolet nanowire lasers have been demonstrated widely, progress towards room-temperature infrared nanowire lasers has been limited because of material quality issues and Auger recombination. (Al)GaAs is an important material system for infrared lasers that is extensively used for conventional lasers. GaAs has a very large surface recombination velocity, which is a serious issue for nanowire devices because of their large surface-to-volume ratio. Here, we demonstrate room-temperature lasing in core-shell-cap GaAs/AlGaAs/GaAs nanowires by properly designing the Fabry-Pérot cavity, optimizing the material quality and minimizing surface recombination. Our demonstration is a major step towards incorporating (Al)GaAs nanowire lasers into the design of nanoscale optoelectronic devices operating at near-infrared wavelengths.

  15. Exfoliated black phosphorus gas sensing properties at room temperature

    NASA Astrophysics Data System (ADS)

    Donarelli, M.; Ottaviano, L.; Giancaterini, L.; Fioravanti, G.; Perrozzi, F.; Cantalini, C.

    2016-06-01

    Room temperature gas sensing properties of chemically exfoliated black phosphorus (BP) to oxidizing (NO2, CO2) and reducing (NH3, H2, CO) gases in a dry air carrier have been reported. To study the gas sensing properties of BP, chemically exfoliated BP flakes have been drop casted on Si3N4 substrates provided with Pt comb-type interdigitated electrodes in N2 atmosphere. Scanning electron microscopy and x-ray photoelectron spectroscopy characterizations show respectively the occurrence of a mixed structure, composed of BP coarse aggregates dispersed on BP exfoliated few layer flakes bridging the electrodes, and a clear 2p doublet belonging to BP, which excludes the occurrence of surface oxidation. Room temperature electrical tests in dry air show a p-type response of multilayer BP with measured detection limits of 20 ppb and 10 ppm to NO2 and NH3 respectively. No response to CO and CO2 has been detected, while a slight but steady sensitivity to H2 has been recorded. The reported results confirm, on an experimental basis, what was previously theoretically predicted, demonstrating the promising sensing properties of exfoliated BP.

  16. Identifying multiexcitons in Mo S2 monolayers at room temperature

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Seok; Kim, Min Su; Kim, Hyun; Lee, Young Hee

    2016-04-01

    One of the unique features of atomically thin two-dimensional materials is strong Coulomb interactions due to the reduced dielectric screening effect; this feature enables the study of many-body phenomena such as excitons, trions, and biexcitons. However, identification of biexcitons remains unresolved owing to their broad peak feature at room temperature. Here, we investigate multiexcitons in monolayer Mo S2 using both electrical and optical doping and identify the transition energies for each exciton. The binding energy of the assigned biexciton is twice that of the trion, in quantitative agreement with theoretical predictions. The biexciton population is predominant under optical doping but negligible under electrical doping. The biexciton population is quadratically proportional to the exciton population, obeying the mass-action theory. Our results illustrate the stable formation of not only trions but also biexcitons due to strong Coulomb interaction even at room temperature; therefore, these results provide a deeper understanding of the complex excitonic behaviors in two-dimensional semiconductors.

  17. Self-transducing silicon nanowire electromechanical systems at room temperature.

    PubMed

    He, Rongrui; Feng, X L; Roukes, M L; Yang, Peidong

    2008-06-01

    Electronic readout of the motions of genuinely nanoscale mechanical devices at room temperature imposes an important challenge for the integration and application of nanoelectromechanical systems (NEMS). Here, we report the first experiments on piezoresistively transduced very high frequency Si nanowire (SiNW) resonators with on-chip electronic actuation at room temperature. We have demonstrated that, for very thin (~90 nm down to ~30 nm) SiNWs, their time-varying strain can be exploited for self-transducing the devices' resonant motions at frequencies as high as approximately 100 MHz. The strain of wire elongation, which is only second-order in doubly clamped structures, enables efficient displacement transducer because of the enhanced piezoresistance effect in these SiNWs. This intrinsically integrated transducer is uniquely suited for a class of very thin wires and beams where metallization and multilayer complex patterning on devices become impractical. The 30 nm thin SiNW NEMS offer exceptional mass sensitivities in the subzeptogram range. This demonstration makes it promising to advance toward NEMS sensors based on ultrathin and even molecular-scale SiNWs, and their monolithic integration with microelectronics on the same chip.

  18. A stable room-temperature sodium-sulfur battery.

    PubMed

    Wei, Shuya; Xu, Shaomao; Agrawral, Akanksha; Choudhury, Snehashis; Lu, Yingying; Tu, Zhengyuan; Ma, Lin; Archer, Lynden A

    2016-06-09

    High-energy rechargeable batteries based on earth-abundant materials are important for mobile and stationary storage technologies. Rechargeable sodium-sulfur batteries able to operate stably at room temperature are among the most sought-after platforms because such cells take advantage of a two-electron-redox process to achieve high storage capacity from inexpensive electrode materials. Here we report a room-temperature sodium-sulfur battery that uses a microporous carbon-sulfur composite cathode, and a liquid carbonate electrolyte containing the ionic liquid 1-methyl-3-propylimidazolium-chlorate tethered to SiO2 nanoparticles. We show that these cells can cycle stably at a rate of 0.5 C (1 C=1675, mAh g(-1)) with 600 mAh g(-1) reversible capacity and nearly 100% Coulombic efficiency. By means of spectroscopic and electrochemical analysis, we find that the particles form a sodium-ion conductive film on the anode, which stabilizes deposition of sodium. We also find that sulfur remains interred in the carbon pores and undergo solid-state electrochemical reactions with sodium ions.

  19. The heat is on: room temperature affects laboratory equipment--an observational study.

    PubMed

    Butler, Julia M; Johnson, Jane E; Boone, William R

    2013-10-01

    To evaluate the effect of ambient room temperature on equipment typically used in in vitro fertilization (IVF). We set the control temperature of the room to 20 °C (+/-0.3) and used CIMScan probes to record temperatures of the following equipment: six microscope heating stages, four incubators, five slide warmers and three heating blocks. We then increased the room temperature to 26 °C (+/-0.3) or decreased it to 17 °C (+/-0.3) and monitored the same equipment again. We wanted to determine what role, if any, changing room temperature has on equipment temperature fluctuation. There was a direct relationship between room temperature and equipment temperature stability. When room temperature increased or decreased, equipment temperature reacted in a corresponding manner. Statistical differences between equipment were found when the room temperature changed. What is also noteworthy is that temperature of equipment responded within 5 min to a change in room temperature. Clearly, it is necessary to be aware of the affect of room temperature on equipment when performing assisted reproductive procedures. Room and equipment temperatures should be monitored faithfully and adjusted as frequently as needed, so that consistent culture conditions can be maintained. If more stringent temperature control can be achieved, human assisted reproduction success rates may improve.

  20. Synthesis and characterization of nano crystalline nickel zinc ferrite for chlorine gas sensor at room temperature

    SciTech Connect

    Pawar, C. S.; Gujar, M. P.; Mathe, V. L.

    2015-06-24

    Nano crystalline Nickel Zinc ferrite (Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4}) thin films were synthesized by Sol Gel method for gas response. The phase and microstructure of the obtained Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanostructured Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} thin film shows single spinel phase. Magnetic study was obtained with the help of VSM. The effects of working temperature on the gas response were studied. The results reveal that the Ni{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} thin film gas sensor shows good selectivity to chlorine gas at room temperature. The sensor shows highest sensitivity (∼50%) at room temperature, indicating its application in detecting chlorine gas at room temperature in the future.

  1. Dense nanocrystalline yttrium iron garnet films formed at room temperature by aerosol deposition

    SciTech Connect

    Johnson, Scooter D. Glaser, Evan R.; Cheng, Shu-Fan; Hite, Jennifer

    2016-04-15

    Highlights: • We deposit yttrium iron garnet films at room temperature using aerosol deposition. • Films are 96% of theoretical density for yttrium iron garnet. • We report magnetic and structural properties post-deposition and post-annealing. • Low-temperature annealing decreases the FMR linewidth. • We discuss features of the FMR spectra at each anneal temperature. - Abstract: We have employed aerosol deposition to form polycrystalline yttrium iron garnet (YIG) films on sapphire at room temperature that are 90–96% dense. We characterize the structural and dynamic magnetic properties of the dense films using scanning electron microscopy, X-ray diffraction, and ferromagnetic resonance techniques. We find that the as-deposited films are pure single-phase YIG formed of compact polycrystallites ∼20 nm in size. The ferromagnetic resonance mode occurs at 2829 G with a linewidth of 308 G. We perform a series of successive anneals up to 1000 °C on a film to explore heat treatment on the ferromagnetic resonance linewidth. We find the narrowest linewidth of 98 G occurs after a 750 °C anneal.

  2. Mechanical and Thermal Characteristics of Insulation Materials for the KSTAR Magnet System at Cryogenic Temperature

    NASA Astrophysics Data System (ADS)

    Chung, Wooho; Lim, Bungsu; Kim, Myungkyu; Park, Hyunki; Kim, Keeman; Chu, Yong; Lee, Sangil

    2004-06-01

    The KSTAR(Korea Superconducting Tokamak Advanced Research) superconducting magnet is electrically insulated by the composite material of epoxy resin and glass fiber (2.5 kV/mm) and Kapton (8 kV/mm). The insulation composite material of epoxy resin and glass fiber is prepared using a VPI (Vacuum Pressure Impregnation) process. The superconducting magnet is under mechanical stress caused by the large temperature difference between the operation temperature of the magnet and room temperature. The large electro-magnetic force during the operation of the magnet is also exerted on the magnet. Therefore, the characteristics of the insulation material at cryogenic temperatures are very important and the tensile stress and thermal expansion coefficient for the insulation materials of the KSTAR superconducting magnet are measured. This paper presents results on mechanical properties of the insulation material for KSTAR magnets, such as density, ultimate tensile stress and thermal contraction between room temperature and cryogenic temperatures.

  3. Finding new superconductors: the spin-fluctuation gateway to high Tc and possible room temperature superconductivity.

    PubMed

    Pines, David

    2013-10-24

    We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that, since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

  4. Near-room-temperature refrigeration through voltage-controlled entropy change in multiferroics

    NASA Astrophysics Data System (ADS)

    Binek, Ch.; Burobina, V.

    2013-01-01

    Composite materials with large magnetoelectric effect are proposed for application in advanced near-room-temperature refrigeration. The key innovation rests on utilizing the magnetocaloric effect in zero applied magnetic fields. This approach promises sizable isothermal entropy change and virtually temperature-independent refrigerant capacity through pure voltage-control. It is in sharp contrast with the conventional method of exploiting the magnetocaloric effect through applied magnetic fields. We outline the thermodynamics and estimate an isothermal entropy change specifically for the La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)O3-PbTiO3(001) two-phase composite material. Finally, we propose structural variations of two-phase composites, which help in overcoming the challenging task of producing nanostructured material in macroscopic quantities.

  5. Advances in materials for room temperature hydrogen sensors.

    PubMed

    Arya, Sunil K; Krishnan, Subramanian; Silva, Hayde; Jean, Sheila; Bhansali, Shekhar

    2012-06-21

    Hydrogen (H(2)), as a source of energy, continues to be a compelling choice in applications ranging from fuel cells and propulsion systems to feedstock for chemical, metallurgical and other industrial processes. H(2), being a clean, reliable, and affordable source, is finding ever increasing use in distributed electric power generation and H(2) fuelled cars. Although still under 0.1%, the distributed use of H(2) is the fastest growing area. In distributed H(2) storage, distribution, and consumption, safety continues to be a critical aspect. Affordable safety systems for distributed H(2) applications are critical for the H(2) economy to take hold. Advances in H(2) sensors are driven by specificity, reliability, repeatability, stability, cost, size, response time, recovery time, operating temperature, humidity range, and power consumption. Ambient temperature sensors for H(2) detection are increasingly being explored as they offer specificity, stability and robustness of high temperature sensors with lower operational costs and significantly longer operational lifetimes. This review summarizes and highlights recent developments in room temperature H(2) sensors.

  6. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

    NASA Astrophysics Data System (ADS)

    Fernández-Posada, Carmen M.; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-09-01

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3-BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3-BiMnO3-PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

  7. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity.

    PubMed

    Fernández-Posada, Carmen M; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-09-28

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3-BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3-BiMnO3-PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

  8. A novel perovskite oxide chemically designed to show multiferroic phase boundary with room-temperature magnetoelectricity

    PubMed Central

    Fernández-Posada, Carmen M.; Castro, Alicia; Kiat, Jean-Michel; Porcher, Florence; Peña, Octavio; Algueró, Miguel; Amorín, Harvey

    2016-01-01

    There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3–BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3–BiMnO3–PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses. PMID:27677353

  9. Room temperature ferromagnetism in Co-incorporated TiO2 thin films.

    PubMed

    Sharma, Sudesh; Chaudhary, Sujeet; Panwar, N; Kashyap, Subhash C; Pandya, D K

    2011-03-01

    Observation of room temperature ferromagnetism (RTFM) in nano-crystalline Co-incorporated titanium dioxide [Ti(1-x)Co(x)O2(x = 0.05)] thin films prepared by spray pyrolysis technique is reported. While only the anatase phase was detected in as-deposited 5 at.% Co-incorporated TiO2 film, a small amount of rutile phase developed following its vacuum annealing. Besides, no X-ray diffraction peak corresponding to cobalt metal could be detected in any of the two films. SQUID magnetometry of both pristine and Co-doped thin films at room temperature elucidated distinct ferromagnetic behavior in 5 at.% Co-incorporated as-deposited film with saturation moment M(s) approximately 5.6 emu/cm3 which got enhanced up to 11.8 emu/cm3 on subsequent vacuum annealing. From the zero field cooled magnetization measurement we confirmed the absence of Co-metal clusters. The electrical resistivity was found to be greater than 108 omega-cm for the films. Based on the magnetic and electrical measurements the origin of RTFM has been attributed to the bound magnetic polaron (BMP) model.

  10. [Magnetic shielded room to measure very low magnetic and electric fields].

    PubMed

    Mager, A

    1982-08-01

    An extraordinary magnetically shielded room was designed and constructed for the Physikalisch-Technische Bundesanstalt Institut Berlin to measure extremely weak magnetic fields of the human body with SQUID-magnetometers. The inner and the outer dimensions of the cube-shaped room are 2.25 m and about 5 m. The shield has 6 magnetic shells of a high-permeability alloy and an inner shell welded of massive copper plates. The total weight of the magnetic alloy is about 10 t and about 5 t for the inner copper shell. The required shielding factor of 1000 for the very low frequencies was greatly surpassed by the real measured value of 10000 (measured without any compensating or idealizing method). With rising frequencies the shielding factor reaches higher values, at 50 Hz more than 100000 and a million for 1000 Hz. First measurements in the shielded room with high-resolution magnetocardiograms (HR MCG) and high-resolution electrocardiograms (HR ECG) showed new methods for non-invasive electrophysiological investigations in man.

  11. Enhanced Room-Temperature Geometric Magnetoresistance in Inhomogeneous Narrow-Gap Semiconductors.

    PubMed

    Solin; Thio; Hines; Heremans

    2000-09-01

    A symmetric van der Pauw disk of homogeneous nonmagnetic indium antimonide with an embedded concentric gold inhomogeneity is found to exhibit room-temperature geometric magnetoresistance as high as 100, 9100, and 750,000 percent at magnetic fields of 0.05, 0.25, and 4.0 teslas, respectively. For inhomogeneities of sufficiently large diameter relative to that of the surrounding disk, the resistance is field-independent up to an onset field above which it increases rapidly. These results can be understood in terms of the field-dependent deflection of current around the inhomogeneity.

  12. Room temperature spin relaxation length in spin light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Soldat, Henning; Li, Mingyuan; Gerhardt, Nils C.; Hofmann, Martin R.; Ludwig, Arne; Ebbing, Astrid; Reuter, Dirk; Wieck, Andreas D.; Stromberg, Frank; Keune, Werner; Wende, Heiko

    2011-08-01

    We investigate the spin relaxation length in GaAs spin light-emitting diode devices under drift transport at room temperature. The spin-polarised electrons are injected through a MgO tunnel barrier from a Fe/Tb multilayer in magnetic remanence. The decrease in circular polarization with increasing injection path length is investigated and found to be exponential, supporting drift-based transport. The spin relaxation length in our samples is 26 nm, and a lower bound for the spin injection efficiency at the spin injector/GaAs interface is estimated to be 25 ± 2%.

  13. A room-temperature semiconductor spaser operating near 1.5 μm.

    PubMed

    Flynn, R A; Kim, C S; Vurgaftman, I; Kim, M; Meyer, J R; Mäkinen, A J; Bussmann, K; Cheng, L; Choa, F-S; Long, J P

    2011-04-25

    Room temperature spasing of surface plasmon polaritons at 1.46 μm wavelength has been demonstrated by sandwiching a gold-film plasmonic waveguide between optically pumped InGaAs quantum-well gain media. The spaser exhibits gain narrowing, the expected transverse-magnetic polarization, and mirror feedback provided by cleaved facets in a 1-mm long cavity fabricated with a flip-chip approach. The 1.06-μm pump-threshold of ~60 kW/cm2 is in good agreement with calculations. The architecture is readily adaptable to all-electrical operation on an integrated microchip.

  14. Room temperature ferromagnetism of tin oxide nanocrystal based on synthesis methods

    NASA Astrophysics Data System (ADS)

    Sakthiraj, K.; Hema, M.; Balachandrakumar, K.

    2016-04-01

    The experimental conditions used in the preparation of nanocrystalline oxide materials play an important role in the room temperature ferromagnetism of the product. In the present work, a comparison was made between sol-gel, microwave assisted sol-gel and hydrothermal methods for preparing tin oxide nanocrystal. X-ray diffraction analysis indicates the formation of tetragonal rutile phase structure for all the samples. The crystallite size was estimated from the HRTEM images and it is around 6-12 nm. Using optical absorbance measurement, the band gap energy value of the samples has been calculated. It reveals the existence of quantum confinement effect in all the prepared samples. Photoluminescence (PL) spectra confirms that the luminescence process originates from the structural defects such as oxygen vacancies present in the samples. Room temperature hysteresis loop was clearly observed in M-H curve of all the samples. But the sol-gel derived sample shows the higher values of saturation magnetization (Ms) and remanence (Mr) than other two samples. This study reveals that the sol-gel method is superior to the other two methods for producing room temperature ferromagnetism in tin oxide nanocrystal.

  15. Influence of non-resonant effects on the dynamics of quantum logic gates at room temperature

    NASA Astrophysics Data System (ADS)

    Berman, G. P.; Bishop, A. R.; Doolen, G. D.; López, G. V.; Tsifrinovich, V. I.

    2001-01-01

    We study numerically the influence of non-resonant effects on the dynamics of a single- π-pulse quantum CONTROL-NOT (CN) gate in a macroscopic ensemble of four-spin molecules at room temperature. The four nuclear spins in each molecule represent a four-qubit register. The qubits are “labeled” by the characteristic frequencies, ωk, ( k=0-3) due to the Zeeman interaction of the nuclear spins with the magnetic field. The qubits interact with each other through an Ising interaction of strength J. The paper examines the feasibility of implementing a single-pulse quantum CN gate in an ensemble of quantum molecules at room temperature. We determine a parameter region, ωk and J, in which a single-pulse quantum CN gate can be implemented at room temperature. We also show that there exist characteristic critical values of parameters, Δ ωcr≡| ωk‧ - ωk| cr and Jcr, such that for J< Jcr and Δ ωk≡| ωk‧ - ωk|<Δ ωcr, non-resonant effects are sufficient to destroy the dynamics required for quantum logic operations.

  16. Room-temperature effects of UV radiation in KBr:? crystals

    NASA Astrophysics Data System (ADS)

    Pérez-Salas, R.; Meléndrez, R.; Aceves, R.; Rodriguez, R.; Barboza-Flores, M.

    1996-07-01

    Thermoluminescence and optical absorption measurements have been carried out in KBr:0953-8984/8/27/009/img9 crystals irradiated with monochromatic UV light (200 - 300 nm) and x-rays at room temperature. For UV- and x-irradiated crystals strong similarities between the thermoluminescence glow curves have been found, suggesting that the low-energy UV radiation produces the same defects as produced by x-irradiation in this material. The thermoluminescence glow curves are composed of six glow peaks located at 337, 383, 403, 435, 475 and 509 K. Thermal annealing experiments in previously irradiated crystals show clearly a correlation between the glow peak located at 383 K and the F-centre thermal bleaching process. Also, the excitation spectrum for each thermoluminescence glow peak has been investigated, showing that the low-energy radiation induces the formation of F centres.

  17. Quantum memory, entanglement and sensing with room temperature atoms

    NASA Astrophysics Data System (ADS)

    Jensen, K.; Wasilewski, W.; Krauter, H.; Fernholz, T.; Nielsen, B. M.; Petersen, J. M.; Renema, J. J.; Balabas, M. V.; Owari, M.; Plenio, M. B.; Serafini, A.; Wolf, M. M.; Muschik, C. A.; Cirac, J. I.; Müller, J. H.; Polzik, E. S.

    2011-01-01

    Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.

  18. Room-temperature ferromagnetism in cerium dioxide powders

    SciTech Connect

    Rakhmatullin, R. M. Pavlov, V. V.; Semashko, V. V.; Korableva, S. L.

    2015-08-15

    Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

  19. Pressure-responsive mesoscopic structures in room temperature ionic liquids.

    PubMed

    Russina, Olga; Lo Celso, Fabrizio; Triolo, Alessandro

    2015-11-28

    Among the most spectacular peculiarities of room temperature ionic liquids, their mesoscopically segregated structural organization keeps on attracting attention, due to its major consequences for the bulk macroscopic properties. Herein we use molecular dynamics simulations to explore the nm-scale architecture in 1-octyl-3-methylimidazolium tetrafluoroborate, as a function of pressure. This study reveals an intriguing new feature: the mesoscopic segregation in ionic liquids is characterized by a high level of pressure-responsiveness, which progressively vanishes upon application of high enough pressure. These results are in agreement with recent X-ray scattering data and are interpreted in terms of the microscopic organization. This new feature might lead to new methods of developing designer solvents for enhanced solvation capabilities and selectivity.

  20. Mesoscopic structural organization in triphilic room temperature ionic liquids.

    PubMed

    Russina, Olga; Lo Celso, Fabrizio; Di Michiel, Marco; Passerini, Stefano; Appetecchi, Giovanni Battista; Castiglione, Franca; Mele, Andrea; Caminiti, Ruggero; Triolo, Alessandro

    2013-01-01

    Room temperature ionic liquids are one of the most exciting classes of materials in the last decade. The interest for these low melting, ionic compounds stems from both their technological impact and the stimulating plethora of structural and dynamic peculiarities in the mesoscopic space-time scales. It is nowadays well-established that they are characterised by an enhanced degree of mesoscopic order originating from their inherent amphiphilicity. In this contribution we highlight the existence of a further degree of mesoscopic complexity when dealing with RTILs bearing a medium length fluorous tail: such triphilic materials (they simultaneously contain polar, hydrophobic and fluorophilic moieties that mutually segregate from each other) turn out to be highly structurally compartmentalised at the mesoscopic level, thus paving the way to new smart applications for this new class of RTILs.

  1. Cavity-Enhanced Room-Temperature Broadband Raman Memory

    NASA Astrophysics Data System (ADS)

    Saunders, D. J.; Munns, J. H. D.; Champion, T. F. M.; Qiu, C.; Kaczmarek, K. T.; Poem, E.; Ledingham, P. M.; Walmsley, I. A.; Nunn, J.

    2016-03-01

    Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali-vapor Raman memories combine high-bandwidth storage, on-demand readout, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and have suffered from four-wave-mixing noise. Here, we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering antiresonance for the anti-Stokes field, we also suppress the four-wave-mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapor memory, (15 ±2 )×10-3 photons per pulse, with a total efficiency of (9.5 ±0.5 )%.

  2. Using room temperature current noise to characterize single molecular spectra.

    PubMed

    Vasudevan, Smitha; Ghosh, Avik W

    2014-03-25

    We propose a way to use room temperature random telegraph noise to characterize single molecules adsorbed on a backgated silicon field-effect transistor. The overlap of molecule and silicon electronic wave functions generates a set of trap levels that impose their unique scattering signatures on the voltage-dependent current noise spectrum. Our results are based on numerical modeling of the current noise, obtained by coupling a density functional treatment of the trap placement within the silicon band gap, a quantum kinetic treatment of the output current, and a Monte Carlo evaluation of the trap occupancy under resonance. As an illustrative example, we show how we can extract molecule-specific "fingerprints" of four benzene-based molecules directly from a frequency-voltage colormap of the noise statistics. We argue that such a colormap carries detailed information about the trap dynamics at the Fermi energy, including the presence of correlated interactions, observed experimentally in backgated carbon nanotubes.

  3. Thermoelectricity in atom-sized junctions at room temperatures

    PubMed Central

    Tsutsui, Makusu; Morikawa, Takanori; Arima, Akihide; Taniguchi, Masateru

    2013-01-01

    Atomic and molecular junctions are an emerging class of thermoelectric materials that exploit quantum confinement effects to obtain an enhanced figure of merit. An important feature in such nanoscale systems is that the electron and heat transport become highly sensitive to the atomic configurations. Here we report the characterization of geometry-sensitive thermoelectricity in atom-sized junctions at room temperatures. We measured the electrical conductance and thermoelectric power of gold nanocontacts simultaneously down to the single atom size. We found junction conductance dependent thermoelectric voltage oscillations with period 2e2/h. We also observed quantum suppression of thermovoltage fluctuations in fully-transparent contacts. These quantum confinement effects appeared only statistically due to the geometry-sensitive nature of thermoelectricity in the atom-sized junctions. The present method can be applied to various nanomaterials including single-molecules or nanoparticles and thus may be used as a useful platform for developing low-dimensional thermoelectric building blocks. PMID:24270238

  4. Ratcheting fatigue behavior of Zircaloy-2 at room temperature

    NASA Astrophysics Data System (ADS)

    Rajpurohit, R. S.; Sudhakar Rao, G.; Chattopadhyay, K.; Santhi Srinivas, N. C.; Singh, Vakil

    2016-08-01

    Nuclear core components of zirconium alloys experience asymmetric stress or strain cycling during service which leads to plastic strain accumulation and drastic reduction in fatigue life as well as dimensional instability of the component. Variables like loading rate, mean stress, and stress amplitude affect the influence of asymmetric loading. In the present investigation asymmetric stress controlled fatigue tests were conducted with mean stress from 80 to 150 MPa, stress amplitude from 270 to 340 MPa and stress rate from 30 to 750 MPa/s to study the process of plastic strain accumulation and its effect on fatigue life of Zircaloy-2 at room temperature. It was observed that with increase in mean stress and stress amplitude accumulation of ratcheting strain was increased and fatigue life was reduced. However, increase in stress rate led to improvement in fatigue life due to less accumulation of ratcheting strain.

  5. Microstructure of room temperature ionic liquids at stepped graphite electrodes

    SciTech Connect

    Feng, Guang; Li, Song; Zhao, Wei; Cummings, Peter T.

    2015-07-14

    Molecular dynamics simulations of room temperature ionic liquid (RTIL) [emim][TFSI] at stepped graphite electrodes were performed to investigate the influence of the thickness of the electrode surface step on the microstructure of interfacial RTILs. A strong correlation was observed between the interfacial RTIL structure and the step thickness in electrode surface as well as the ion size. Specifically, when the step thickness is commensurate with ion size, the interfacial layering of cation/anion is more evident; whereas, the layering tends to be less defined when the step thickness is close to the half of ion size. Furthermore, two-dimensional microstructure of ion layers exhibits different patterns and alignments of counter-ion/co-ion lattice at neutral and charged electrodes. As the cation/anion layering could impose considerable effects on ion diffusion, the detailed information of interfacial RTILs at stepped graphite presented here would help to understand the molecular mechanism of RTIL-electrode interfaces in supercapacitors.

  6. Room-temperature spin-photon interface for quantum networks

    NASA Astrophysics Data System (ADS)

    Hong, Fang-Yu; Fu, Jing-Li; Wu, Yan; Zhu, Zhi-Yan

    2017-02-01

    Although remarkable progress has been achieved recently, to construct an optical cavity where a nitrogen-vacancy (NV) colour centre in diamond is coupled to an optical field in the strong coupling regime is rather difficult. We propose an architecture for a scalable quantum interface capable of interconverting photonic and NV spin qubits, which can work well without the strong coupling requirement. The dynamics of the interface applies an adiabatic passage to sufficiently reduce the decoherence from an excited state of a NV colour centre in diamond. This quantum interface can accomplish many quantum network operations like state transfer and entanglement distribution between qubits at distant nodes. Exact numerical simulations show that high-fidelity quantum interface operations can be achieved under room-temperature and realistic experimental conditions.

  7. Dissolution of cellulose in room temperature ionic liquids: anion dependence.

    PubMed

    Payal, Rajdeep Singh; Bejagam, Karteek K; Mondal, Anirban; Balasubramanian, Sundaram

    2015-01-29

    The dissolution of cellulosic biomass in room temperature ionic liquids (RTILs) is studied through free energy calculations of its monomer, viz., cellobiose, within a molecular dynamics simulation approach. The solvation free energy (SFE) of cellobiose in ionic liquids containing any of seven different anions has been calculated. The ranking of these liquids based on SFE compares well with experimental data on the solubility of cellulose. The dissolution is shown to be enthalpically dominated, which is correlated with the strength of intermolecular hydrogen bonding between cellobiose and the anions of the IL. Large entropic changes upon solvation in [CF3SO3](-) and [OAc](-) based ionic liquids have been explained in terms of the solvent-aided conformational flexibility of cellobiose.

  8. A room-temperature refuelable lithium, iodine and air battery.

    PubMed

    Tan, Kim Seng; Grimsdale, Andrew C; Yazami, Rachid

    2017-07-26

    We demonstrate a new refuelable lithium cell using lithium solvated electron solution (Li-SES) as anolyte and iodine solutions as catholyte. This cell shows a high OCV (~3 V). Unlike conventional rechargeable Li batteries, this kind of cell can be re-fueled in several minutes by replacing the spent liquids. We also show for the first time, that Li-SES/I2 cells which operate at room temperature, can be prepared in a fully discharged state (~0 V OCV) for safe handling, transportation and storage. Li-SES and iodine are then electrochemically generated during charge as is confirmed by UV-VIS and a qualitative test. We have also conducted proof-of-concept tests for an "indirect lithium-air" cell in which iodine is reduced at the cathode and subsequently is catalytically re-oxidized by oxygen dissolved in the catholyte.

  9. Oxidative decomposition of formaldehyde by metal oxides at room temperature

    NASA Astrophysics Data System (ADS)

    Sekine, Yoshika

    Formaldehyde (HCHO) is still a major indoor air pollutant in Japanese air-tight houses and is the subject of numerous complaints regarding health disorders. Authors have developed a passive-type air-cleaning material and an air cleaner using manganese oxide (77% MnO 2) as an active component and successfully reduced indoor HCHO concentrations in newly built multi-family houses. In this study, the reactivity between manganese oxide and HCHO was discussed. We tested the removal efficiencies of several metal oxides for HCHO in a static reaction vessel and found manganese oxide could react with HCHO and release carbon dioxide even at room temperature. The reactivity and mechanisms were discussed for the proposed chemical reactions. A mass balance study proved that a major product through the heterogeneous reaction between manganese oxide and HCHO was carbon dioxide. Harmful by-products (HCOOH and CO) were not found.

  10. Thermoelectricity in atom-sized junctions at room temperatures.

    PubMed

    Tsutsui, Makusu; Morikawa, Takanori; Arima, Akihide; Taniguchi, Masateru

    2013-11-25

    Atomic and molecular junctions are an emerging class of thermoelectric materials that exploit quantum confinement effects to obtain an enhanced figure of merit. An important feature in such nanoscale systems is that the electron and heat transport become highly sensitive to the atomic configurations. Here we report the characterization of geometry-sensitive thermoelectricity in atom-sized junctions at room temperatures. We measured the electrical conductance and thermoelectric power of gold nanocontacts simultaneously down to the single atom size. We found junction conductance dependent thermoelectric voltage oscillations with period 2e(2)/h. We also observed quantum suppression of thermovoltage fluctuations in fully-transparent contacts. These quantum confinement effects appeared only statistically due to the geometry-sensitive nature of thermoelectricity in the atom-sized junctions. The present method can be applied to various nanomaterials including single-molecules or nanoparticles and thus may be used as a useful platform for developing low-dimensional thermoelectric building blocks.

  11. Experimental evidence for ice formation at room temperature.

    PubMed

    Jinesh, K B; Frenken, J W M

    2008-07-18

    The behavior of water under extreme confinement and, in particular, the lubrication properties under such conditions are subjects of long-standing controversy. Using a dedicated, high-resolution friction force microscope, scanning a sharp tungsten tip over a graphite surface, we demonstrate that water nucleating between the tip and the surface due to capillary condensation rapidly transforms into crystalline ice at room temperature. At ultralow scan speeds and modest relative humidities, we observe that the tip exhibits stick-slip motion with a period of 0.38+/-0.03 nm, very different from the graphite lattice. We interpret this as the consequence of the repeated sequence of shear-induced fracture and healing of the crystalline condensate. This phenomenon causes a significant increase of the friction force and introduces relaxation time scales of seconds for the rearrangements after shearing.

  12. Tailoring room temperature photoluminescence of antireflective silicon nanofacets

    SciTech Connect

    Basu, Tanmoy; Kumar, M.; Ghatak, J.; Som, T.; Kanjilal, A.; Sahoo, P. K.

    2014-09-21

    In this paper, a fluence-dependent antireflection performance is presented from ion-beam fabricated nanofaceted-Si surfaces. It is also demonstrated that these nanofacets are capable of producing room temperature ultra-violet and blue photoluminescence which can be attributed to inter-band transitions of the localized excitonic states of different Si-O bonds at the Si/SiO{sub x} interface. Time-resolved photoluminescence measurements further confirm defect-induced radiative emission from the surface of silicon nanofacets. It is observed that the spectral characteristics remain unchanged, except an enhancement in the photoluminescence intensity with increasing ion-fluence. The increase in photoluminescence intensity by orders of magnitude stronger than that of a planar Si substrate is due to higher absorption of incident photons by nanofaceted structures.

  13. Photo-activated oxygen sensitivity of graphene at room temperature

    NASA Astrophysics Data System (ADS)

    Berholts, Artjom; Kahro, Tauno; Floren, Aare; Alles, Harry; Jaaniso, Raivo

    2014-10-01

    Photo-induced changes in the electrical conductivity and the sensitivity to oxygen gas of graphene sheets grown by chemical vapor deposition and transferred onto Al2O3 and SiO2 thin film substrates were studied at ambient conditions. The pristine graphene sensors were initially completely insensitive to oxygen gas at room temperature but showed significant (up to 100%) response when illuminated with weak ultraviolet (300 nm or 365 nm) light. Oxygen response was governed by Langmuir law and its activation was insensitive to humidity. The mechanism of sensitization is analyzed together with other photo-induced effects—negative persistent photo-conduction and photo-induced hysteresis of field effect transistor characteristics. While the reduction of conductivity in air is persistent effect, the oxygen sensitization and enlargement of hysteresis take place only under the direct influence of light. It is concluded that the charge traps with differently adsorbed oxygen and water are involved in these phenomena.

  14. Room temperature photon number resolving detector for infared wavelengths.

    PubMed

    Pomarico, Enrico; Sanguinetti, Bruno; Thew, Rob; Zbinden, Hugo

    2010-05-10

    In this paper we present a photon number resolving detector at infrared wavelengths, operating at room temperature and with a large dynamic range. It is based on the up-conversion of a signal at 1559 nm into visible wavelength and on its detection by a thermoelectrically cooled multi-pixel silicon avalanche photodiodode, also known as a Silicon Photon Multiplier. With the appropriate up-conversion this scheme can be implemented for arbitrary wavelengths above the visible spectral window. The preservation of the poissonian statistics when detecting coherent states is studied and the cross-talk effects on the detected signal can be easily estimated in order to calibrate the detector. This system is well suited for measuring very low intensities at infrared wavelengths and for analyzing multiphoton quantum states. (c) 2010 Optical Society of America.

  15. Gas sensing properties of nanocrystalline diamond at room temperature

    PubMed Central

    Kulha, Pavel; Laposa, Alexandr; Hruska, Karel; Demo, Pavel; Kromka, Alexander

    2014-01-01

    Summary This study describes an integrated NH3 sensor based on a hydrogenated nanocrystalline diamond (NCD)-sensitive layer coated on an interdigitated electrode structure. The gas sensing properties of the sensor structure were examined using a reducing gas (NH3) at room temperature and were found to be dependent on the electrode arrangement. A pronounced response of the sensor, which was comprised of dense electrode arrays (of 50 µm separation distance), was observed. The sensor functionality was explained by the surface transfer doping effect. Moreover, the three-dimensional model of the current density distribution of the hydrogenated NCD describes the transient flow of electrons between interdigitated electrodes and the hydrogenated NCD surface, that is, the formation of a closed current loop. PMID:25551062

  16. Gas sensing properties of nanocrystalline diamond at room temperature.

    PubMed

    Davydova, Marina; Kulha, Pavel; Laposa, Alexandr; Hruska, Karel; Demo, Pavel; Kromka, Alexander

    2014-01-01

    This study describes an integrated NH3 sensor based on a hydrogenated nanocrystalline diamond (NCD)-sensitive layer coated on an interdigitated electrode structure. The gas sensing properties of the sensor structure were examined using a reducing gas (NH3) at room temperature and were found to be dependent on the electrode arrangement. A pronounced response of the sensor, which was comprised of dense electrode arrays (of 50 µm separation distance), was observed. The sensor functionality was explained by the surface transfer doping effect. Moreover, the three-dimensional model of the current density distribution of the hydrogenated NCD describes the transient flow of electrons between interdigitated electrodes and the hydrogenated NCD surface, that is, the formation of a closed current loop.

  17. Room temperature quantum emission from cubic silicon carbide nanoparticles.

    PubMed

    Castelletto, Stefania; Johnson, Brett C; Zachreson, Cameron; Beke, David; Balogh, István; Ohshima, Takeshi; Aharonovich, Igor; Gali, Adam

    2014-08-26

    The photoluminescence (PL) arising from silicon carbide nanoparticles has so far been associated with the quantum confinement effect or to radiative transitions between electronically active surface states. In this work we show that cubic phase silicon carbide nanoparticles with diameters in the range 45-500 nm can host other point defects responsible for photoinduced intrabandgap PL. We demonstrate that these nanoparticles exhibit single photon emission at room temperature with record saturation count rates of 7 × 10(6) counts/s. The realization of nonclassical emission from SiC nanoparticles extends their potential use from fluorescence biomarker beads to optically active quantum elements for next generation quantum sensing and nanophotonics. The single photon emission is related to single isolated SiC defects that give rise to states within the bandgap.

  18. Radiation stability of some room temperature ionic liquids

    NASA Astrophysics Data System (ADS)

    Jagadeeswara Rao, Ch.; Venkatesan, K. A.; Tata, B. V. R.; Nagarajan, K.; Srinivasan, T. G.; Vasudeva Rao, P. R.

    2011-05-01

    Radiation stability of some room temperature ionic liquids (RTILs) that find useful electrochemical applications in nuclear fuel cycle has been evaluated. The ionic liquids such as protonated betaine bis(trifluoromethylsulfonyl)imide (HbetNTf 2), aliquat 336 (tri-n-octlymethylammonium chloride), 1-butyl-3-methylimidazolium chloride (bmimCl), 1-hexyl-3-methylimidazolium chloride (hmimCl), N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyNTf 2) and N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPiNTf 2) have been irradiated to various absorbed dose levels, up to 700 kGy. The effect of gamma radiation on these ionic liquids has been evaluated by determining the variations in the physical properties such as color, density, viscosity, refractive index and electrochemical window. The changes in density, viscosity and refractive index of these ionic liquids upon irradiation were insignificant; however, the color and electrochemical window varied significantly with increase of absorbed dose.

  19. Room temperature magnesium electrorefining by using non-aqueous electrolyte

    NASA Astrophysics Data System (ADS)

    Park, Jesik; Jung, Yeojin; Kusumah, Priyandi; Dilasari, Bonita; Ku, Heesuk; Kim, Hansu; Kwon, Kyungjung; Lee, Churl Kyoung

    2016-09-01

    The increasing usage of magnesium inevitably leads to a fast increase in magnesium scrap, and magnesium recycling appears extremely beneficial for cost reduction, preservation of natural resources and protection of the environment. Magnesium refining for the recovery of high purity magnesium from metal scrap alloy (AZ31B composed of magnesium, aluminum, zinc, manganese and copper) at room temperature is investigated with a non-aqueous electrolyte (tetrahydrofuran with ethyl magnesium bromide). A high purity (99.999%) of electrorefined magneisum with a smooth and dense surface is obtained after potentiostatic electrolysis with an applied voltage of 2 V. The selective dissolution of magnesium from magnesium alloy is possible by applying an adequate potential considering the tolerable impurity level in electrorefined magnesium and processing time. The purity estimation method suggested in this study can be useful in evaluating the maximum content of impurity elements.

  20. Calculation of the room-temperature shapes of unsymmetric laminates

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.

    1981-01-01

    A theory explaining the characteristics of the cured shapes of unsymmetric laminates is presented. The theory is based on an extension of classical lamination theory which accounts for geometric nonlinearities. A Rayleigh-Ritz approach to minimizing the total potential energy is used to obtain quantitative information regarding the room temperature shapes of square T300/5208 (0(2)/90(2))T and (0(4)/90(4))T graphite-epoxy laminates. It is shown that, depending on the thickness of the laminate and the length of the side the square, the saddle shape configuration is actually unstable. For values of length and thickness that render the saddle shape unstable, it is shown that two stable cylindrical shapes exist. The predictions of the theory are compared with existing experimental data.