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Sample records for anisotropic magnetoresistive sensor

  1. Highly Sensitive Flexible Magnetic Sensor Based on Anisotropic Magnetoresistance Effect.

    PubMed

    Wang, Zhiguang; Wang, Xinjun; Li, Menghui; Gao, Yuan; Hu, Zhongqiang; Nan, Tianxiang; Liang, Xianfeng; Chen, Huaihao; Yang, Jia; Cash, Syd; Sun, Nian-Xiang

    2016-11-01

    A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated. A limit of detection of 150 nT is observed and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm. The flexible AMR sensor is used to read a magnetic pattern with a thickness of 10 μm that is formed by ferrite magnetic inks.

  2. Space magnetometer based on an anisotropic magnetoresistive hybrid sensor.

    PubMed

    Brown, P; Whiteside, B J; Beek, T J; Fox, P; Horbury, T S; Oddy, T M; Archer, M O; Eastwood, J P; Sanz-Hernández, D; Sample, J G; Cupido, E; O'Brien, H; Carr, C M

    2014-12-01

    We report on the design and development of a low resource, dual sensor vector magnetometer for space science applications on very small spacecraft. It is based on a hybrid device combining an orthogonal triad of commercial anisotropic magnetoresistive (AMR) sensors with a totem pole H-Bridge drive on a ceramic substrate. The drive enables AMR operation in the more sensitive flipped mode and this is achieved without the need for current spike transmission down a sensor harness. The magnetometer has sensitivity of better than 3 nT in a 0-10 Hz band and a total mass of 104 g. Three instruments have been launched as part of the TRIO-CINEMA space weather mission, inter-calibration against the International Geomagnetic Reference Field model makes it possible to extract physical signals such as field-aligned current deflections of 20-60 nT within an approximately 45,000 nT ambient field.

  3. Space magnetometer based on an anisotropic magnetoresistive hybrid sensor

    NASA Astrophysics Data System (ADS)

    Brown, P.; Whiteside, B. J.; Beek, T. J.; Fox, P.; Horbury, T. S.; Oddy, T. M.; Archer, M. O.; Eastwood, J. P.; Sanz-Hernández, D.; Sample, J. G.; Cupido, E.; O'Brien, H.; Carr, C. M.

    2014-12-01

    We report on the design and development of a low resource, dual sensor vector magnetometer for space science applications on very small spacecraft. It is based on a hybrid device combining an orthogonal triad of commercial anisotropic magnetoresistive (AMR) sensors with a totem pole H-Bridge drive on a ceramic substrate. The drive enables AMR operation in the more sensitive flipped mode and this is achieved without the need for current spike transmission down a sensor harness. The magnetometer has sensitivity of better than 3 nT in a 0-10 Hz band and a total mass of 104 g. Three instruments have been launched as part of the TRIO-CINEMA space weather mission, inter-calibration against the International Geomagnetic Reference Field model makes it possible to extract physical signals such as field-aligned current deflections of 20-60 nT within an approximately 45 000 nT ambient field.

  4. Molecular anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy

    2015-12-01

    Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

  5. Remote detection of nuclear magnetic resonance with an anisotropic magnetoresistive sensor.

    PubMed

    Verpillat, F; Ledbetter, M P; Xu, S; Michalak, D J; Hilty, C; Bouchard, L-S; Antonijevic, S; Budker, D; Pines, A

    2008-02-19

    We report the detection of nuclear magnetic resonance (NMR) using an anisotropic magnetoresistive (AMR) sensor. A "remote-detection" arrangement was used in which protons in flowing water were prepolarized in the field of a superconducting NMR magnet, adiabatically inverted, and subsequently detected with an AMR sensor situated downstream from the magnet and the adiabatic inverter. AMR sensing is well suited for NMR detection in microfluidic "lab-on-a-chip" applications because the sensors are small, typically on the order of 10 mum. An estimate of the sensitivity for an optimized system indicates that approximately 6 x 10(13) protons in a volume of 1,000 mum(3), prepolarized in a 10-kG magnetic field, can be detected with a signal-to-noise ratio of 3 in a 1-Hz bandwidth. This level of sensitivity is competitive with that demonstrated by microcoils in superconducting magnets and with the projected sensitivity of microfabricated atomic magnetometers.

  6. Remote detection of nuclear magnetic resonance with an anisotropic magnetoresistive sensor

    PubMed Central

    Verpillat, F.; Ledbetter, M. P.; Xu, S.; Michalak, D. J.; Hilty, C.; Bouchard, L.-S.; Antonijevic, S.; Budker, D.; Pines, A.

    2008-01-01

    We report the detection of nuclear magnetic resonance (NMR) using an anisotropic magnetoresistive (AMR) sensor. A “remote-detection” arrangement was used in which protons in flowing water were prepolarized in the field of a superconducting NMR magnet, adiabatically inverted, and subsequently detected with an AMR sensor situated downstream from the magnet and the adiabatic inverter. AMR sensing is well suited for NMR detection in microfluidic “lab-on-a-chip” applications because the sensors are small, typically on the order of 10 μm. An estimate of the sensitivity for an optimized system indicates that ≈6 × 1013 protons in a volume of 1,000 μm3, prepolarized in a 10-kG magnetic field, can be detected with a signal-to-noise ratio of 3 in a 1-Hz bandwidth. This level of sensitivity is competitive with that demonstrated by microcoils in superconducting magnets and with the projected sensitivity of microfabricated atomic magnetometers. PMID:18268323

  7. DNA-magnetic bead detection using disposable cards and the anisotropic magnetoresistive sensor

    NASA Astrophysics Data System (ADS)

    Hien, L. T.; Quynh, L. K.; Huyen, V. T.; Tu, B. D.; Hien, N. T.; Phuong, D. M.; Nhung, P. H.; Giang, D. T. H.; Duc, N. H.

    2016-12-01

    A disposable card incorporating specific DNA probes targeting the 16 S rRNA gene of Streptococcus suis was developed for magnetically labeled target DNA detection. A single-stranded target DNA was hybridized with the DNA probe on the SPA/APTES/PDMS/Si as-prepared card, which was subsequently magnetically labeled with superparamagnetic beads for detection using an anisotropic magnetoresistive (AMR) sensor. An almost linear response between the output signal of the AMR sensor and amount of single-stranded target DNA varied from 4.5 to 18 pmol was identified. From the sensor output signal response towards the mass of magnetic beads which were directly immobilized on the disposable card surface, the limit of detection was estimated about 312 ng ferrites, which corresponds to 3.8 μemu. In comparison with DNA detection by conventional biosensor based on magnetic bead labeling, disposable cards are featured with higher efficiency and performances, ease of use and less running cost with respects to consumables for biosensor in biomedical analysis systems operating with immobilized bioreceptor.

  8. Giant magnetoresistive sensor

    DOEpatents

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

    1999-01-01

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

  9. Magnetoresistive sensors for string instruments

    NASA Astrophysics Data System (ADS)

    Lenssen, K.-M. H.; Somers, G. H. J.; van Zon, J. B. A. D.

    2002-05-01

    Pickup elements for string instruments, in particular for electric guitars, represent a new application area for magnetoresistive sensors. Recently we developed a sensor configuration with permanent magnets for this purpose. For the first experiments we used commercial anisotropic magnetoresistance sensors (Philips KMZ10) mounted on small ferrite bias magnets. Recently we equipped an electric guitar with prototypes comprising giant magnetoresistance (GMR) sensors. These prototype MR pickup elements showed several clear advantages compared to the presently commonly used inductive pickup units. They are much less sensitive to disturbing electromagnetic fields (>1000×at 5 kHz), mainly because their active sensor area is several orders of magnitude smaller (a few mm2 instead of cm2). Also the larger freedom in the choice of the permanent magnets (due to the larger sensitivity of the GMR elements) is advantageous: employing smaller magnets reduces the damping and thus significantly improves the sustain, the magnets can be less expensive and more stable magnet materials can be chosen so that aging effects are eliminated.

  10. Modeling anisotropic magnetoresistance in layered antiferromagnets

    NASA Astrophysics Data System (ADS)

    Santos, D. L. R.; Pinheiro, F. A.; Velev, J.; Chshiev, M.; Castro, J. d.'Albuquerque e.; Lacroix, C.

    2017-06-01

    We have investigated the electronic transport and the anisotropic magnetoresistance in systems consisting of pairs of antiferromagnetically aligned layers separated by a non-magnetic layer, across which an antiferromagnetic coupling between the double layers is established. Calculations have been performed within the framework of the tight-binding model, taking into account the exchange coupling within the ferromagnetic layers and the Rashba spin-orbit interaction. Conductivities have been evaluated in the ballistic regime, based on Kubo formula. We have systematically studied the dependence of the conductivity and of the anisotropic magnetoresistance on several material and structural parameters, such as the orientation of the magnetic moments relative to the crystalline axis, band filling, out-of-plane hopping and spin-orbit parameter.

  11. Measurement system for temperature dependent noise characterization of magnetoresistive sensors.

    PubMed

    Nording, F; Weber, S; Ludwig, F; Schilling, M

    2017-03-01

    Magnetoresistive (MR) sensors and sensor systems are used in a large variety of applications in the field of industrial automation, automotive business, aeronautic industries, and instrumentation. Different MR sensor technologies like anisotropic magnetoresistive, giant magnetoresistive, and tunnel magnetoresistive sensors show strongly varying properties in terms of magnetoresistive effect, response to magnetic fields, achievable element miniaturization, manufacturing effort, and signal-to-noise ratio. Very few data have been reported so far on the comparison of noise performance for different sensor models and technologies, especially including the temperature dependence of their characteristics. In this paper, a stand-alone measurement setup is presented that allows a comprehensive characterization of MR sensors including sensitivity and noise over a wide range of temperatures.

  12. Measurement system for temperature dependent noise characterization of magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Nording, F.; Weber, S.; Ludwig, F.; Schilling, M.

    2017-03-01

    Magnetoresistive (MR) sensors and sensor systems are used in a large variety of applications in the field of industrial automation, automotive business, aeronautic industries, and instrumentation. Different MR sensor technologies like anisotropic magnetoresistive, giant magnetoresistive, and tunnel magnetoresistive sensors show strongly varying properties in terms of magnetoresistive effect, response to magnetic fields, achievable element miniaturization, manufacturing effort, and signal-to-noise ratio. Very few data have been reported so far on the comparison of noise performance for different sensor models and technologies, especially including the temperature dependence of their characteristics. In this paper, a stand-alone measurement setup is presented that allows a comprehensive characterization of MR sensors including sensitivity and noise over a wide range of temperatures.

  13. Tunneling anisotropic magnetoresistance driven by magnetic phase transition.

    PubMed

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

    2017-09-06

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

  14. Recent Developments of Magnetoresistive Sensors for Industrial Applications

    PubMed Central

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

    2015-01-01

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

  15. Recent Developments of Magnetoresistive Sensors for Industrial Applications.

    PubMed

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

    2015-11-12

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

  16. New method for detecting traffic information based on anisotropic magnetoresistive technology

    NASA Astrophysics Data System (ADS)

    Liu, Kun; Xiong, Hui; He, Hui

    2013-03-01

    Three-axis magnetoresistive sensor based on Anisotropic Magnetoresistive Technology(AMR) has excellent performance on detecting traffic Information. Data results for some features of microscopic magnetic field changes were obtained for road traffic after designing the test equipment of three-axis magnetic sensor and some experiments on road vehicles. The rules between the feature of microscopic magnetic field changes on road traffic and the impact by vehicles are found to realize the traffic Information detector for providing accurate data for intelligent transportation systems(ITS).

  17. Magnetoresistive sensor for weak magnetic fields

    NASA Astrophysics Data System (ADS)

    Moran, Timothy J.; Dahlberg, E. Dan

    1997-04-01

    A new excitation technique is described for the measurement of weak magnetic fields (<0.01 Oe). The resistance variation of a magnetoresistive element due to an oscillating excitation field is converted into a voltage proportional to the environmental field. The excitation field amplitude is set large enough to saturate the magnetization during each half-cycle, greatly reducing hysteresis effects in the output signal. Both anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) structures have been used to measure fields with sufficient accuracy for compass applications. Such devices could be made with extremely small dimensions and power requirements.

  18. Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts.

    PubMed

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

    2016-02-10

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

  19. Magnetoresistive Sensors in Biological Assays

    NASA Astrophysics Data System (ADS)

    Tondra, Mark

    2010-03-01

    Magnetic beads or nanoparticles can be used as ``labels'' in biochemical assays by attaching the beads to the biospecies of interest using a bio-specific attachment. Once the labels are attached, they can be used to manipulate, capture, and detect the species to be analyzed. Magnetoresistive (MR) sensors may be used to detect and count these labels, and thus make an inference about the concentration of the species of interest. MR technology is especially promising for biosensor applications where making the detector small and integrated with related sample handling tools to form a ``lab-on-a-chip'' miniaturized system. The function of the MR sensors is to detect stray magnetic fields from the beads while they are exposed to a magnetic excitation field. Generally, the stray fields from beads and clusters of beads are complicated functions of geometry, so some care is required to relate the detected magnetic signal to the number and location of the bead labels. This presentation will begin with a broad overview of results from many groups working in this area. For convenience, the applications are divided into three categories, detection of: flowing magnetic beads, immobilized beads, and scanned samples. Next will be some discussion of how the choice of spintronic sensor technology might affect detection capabilities (AMR, GMR, TMR, Hall effect, etc). Then, challenges relating to integration of MR sensors into microfluidic products will be discussed. This is the focus of the presenter's current day-to-day work on developing and producing MR-based biosensors. And finally, a description of possible future avenues of study and development will be presented.

  20. Anisotropic giant magnetoresistance in NbSb₂

    DOE PAGES

    Wang, Kefeng; Graf, D.; Li, Lijun; ...

    2014-12-05

    We report large transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 10⁵% in 2 K and 9 T field, and 4.3 × 10⁶% in 0.4 K and 32 T field, without saturation) and field-induced metal semiconductor-like transition in NbSb₂. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed tomore » the change of the Fermi surface induced by the magnetic field in addition to the high mobility metal.« less

  1. Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

    NASA Astrophysics Data System (ADS)

    Galceran, R.; Fina, I.; Cisneros-Fernández, J.; Bozzo, B.; Frontera, C.; López-Mir, L.; Deniz, H.; Park, K.-W.; Park, B.-G.; Balcells, Ll.; Martí, X.; Jungwirth, T.; Martínez, B.

    2016-10-01

    Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature.

  2. Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn.

    PubMed

    Galceran, R; Fina, I; Cisneros-Fernández, J; Bozzo, B; Frontera, C; López-Mir, L; Deniz, H; Park, K-W; Park, B-G; Balcells, Ll; Martí, X; Jungwirth, T; Martínez, B

    2016-10-20

    Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature.

  3. Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

    PubMed Central

    Galceran, R.; Fina, I.; Cisneros-Fernández, J.; Bozzo, B.; Frontera, C.; López-Mir, L.; Deniz, H.; Park, K.-W.; Park, B.-G.; Balcells, Ll.; Martí, X.; Jungwirth, T.; Martínez, B.

    2016-01-01

    Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature. PMID:27762278

  4. Anomalously large anisotropic magnetoresistance in a perovskite manganite.

    PubMed

    Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X Z; Matsui, Y; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E Ward; Zhang, Jiandi

    2009-08-25

    The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La(0.69)Ca(0.31)MnO(3), leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a "colossal" AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings.

  5. Anomalously large anisotropic magnetoresistance in a perovskite manganite

    PubMed Central

    Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X. Z.; Matsui, Y.; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E. Ward; Zhang, Jiandi

    2009-01-01

    The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La0.69Ca0.31MnO3, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a “colossal” AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings. PMID:19706504

  6. Insensitivity of tunneling anisotropic magnetoresistance to non-magnetic electrodes

    SciTech Connect

    Wang, Y. Y.; Song, C. Wang, G. Y.; Zeng, F.; Pan, F.

    2013-11-11

    Ferromagnetic electrodes play a crucial role in magnetoresistance effect and spin injection, whereas the essential features of non-magnetic metal electrodes in spintronics are commonly ignored except for their electrical conductivity. Here, we verify that the room-temperature tunneling anisotropic magnetoresistance (TAMR) behavior in antiferromagnet-based [Pt/Co]/IrMn/AlO{sub x}/metal (metal = Pt, Au, Cu, Al) junctions is insensitive to the top metal electrodes. Similar out-of-plane signals are detected for different electrodes, in contrast to the varied shapes of in-plane TAMR curves which are most likely attributed to the differences in the multidomain structure of the magnetic electrode. This would add a different dimension to spintronics.

  7. Gamma irradiation of magnetoresistive sensors for planetary exploration.

    PubMed

    Sanz, Ruy; Fernández, Ana B; Dominguez, Jose A; Martín, Boris; Michelena, Marina D

    2012-01-01

    A limited number of Anisotropic Magnetoresistive (AMR) commercial-off-the-shelf (COTS) magnetic sensors of the HMC series by Honeywell, with and without integrated front-end electronics, were irradiated with gamma rays up to a total irradiation dose of 200 krad (Si), following the ESCC Basic Specification No. 22900. Due to the magnetic cleanliness required for these tests a special set-up was designed and successfully employed. Several parameters of the sensors were monitored during testing and the results are reported in this paper. The authors conclude that AMR sensors without front-end electronics seem to be robust against radiation doses of up to 200 krad (Si) with a dose rate of 5 krad (Si)/hour and up to a resolution of tens of nT, but sensors with an integrated front-end seem to be more vulnerable to radiation.

  8. Angular dependence of anisotropic magnetoresistance in magnetic systems

    NASA Astrophysics Data System (ADS)

    Zhang, Steven S.-L.; Zhang, Shufeng

    2014-05-01

    Anisotropic magnetoresistance (AMR), whose physical origin is attributed to the combination of spin dependent scattering and spin orbital coupling (SOC), usually displays simple angular dependence for polycrystalline ferromagnetic metals. By including generic spin dependent scattering and spin Hall (SH) terms in the Ohm's law, we explicitly show that various magneto-transport phenomena such as anomalous Hall (AH), SH, planar Hall (PH) and AMR could be quantitatively related for bulk polycrystalline ferromagnetic metals. We also discuss how AMR angular dependence is affected by the presence of interfacial SOC in magnetic layered structure.

  9. Angular dependence of anisotropic magnetoresistance in magnetic systems

    SciTech Connect

    Zhang, Steven S.-L. Zhang, Shufeng

    2014-05-07

    Anisotropic magnetoresistance (AMR), whose physical origin is attributed to the combination of spin dependent scattering and spin orbital coupling (SOC), usually displays simple angular dependence for polycrystalline ferromagnetic metals. By including generic spin dependent scattering and spin Hall (SH) terms in the Ohm's law, we explicitly show that various magneto-transport phenomena such as anomalous Hall (AH), SH, planar Hall (PH) and AMR could be quantitatively related for bulk polycrystalline ferromagnetic metals. We also discuss how AMR angular dependence is affected by the presence of interfacial SOC in magnetic layered structure.

  10. Giant Magnetoresistive Sensors for DNA Microarray

    PubMed Central

    Xu, Liang; Yu, Heng; Han, Shu-Jen; Osterfeld, Sebastian; White, Robert L.; Pourmand, Nader; Wang, Shan X.

    2009-01-01

    Giant magnetoresistive (GMR) sensors are developed for a DNA microarray. Compared with the conventional fluorescent sensors, GMR sensors are cheaper, more sensitive, can generate fully electronic signals, and can be easily integrated with electronics and microfluidics. The GMR sensor used in this work has a bottom spin valve structure with an MR ratio of 12%. The single-strand target DNA detected has a length of 20 bases. Assays with DNA concentrations down to 10 pM were performed, with a dynamic range of 3 logs. A double modulation technique was used in signal detection to reduce the 1/f noise in the sensor while circumventing electromagnetic interference. The logarithmic relationship between the magnetic signal and the target DNA concentration can be described by the Temkin isotherm. Furthermore, GMR sensors integrated with microfluidics has great potential of improving the sensitivity to 1 pM or below, and the total assay time can be reduced to less than 1 hour. PMID:20824116

  11. Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    It has been predicted that the anisotropic magnetoresistance (AMR) is greatly enhanced in the ballistic transport regime. Results from break junctions in a magnetic field can be explained in terms of this ballistic AMR (BAMR), although the interpretation is controversal due to the unknown atomic geometry of the junction. Here, we demonstrate the emergence of BAMR in single-atom contacts. Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110), which is used to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. AMR is observed and changes drastically between tunneling and the ballistic regime. First-principles calculations and tight-binding modeling demonstrate that this change is due to a competition of delocalized and localized d states of different orbital symmetry.

  12. Exchange biased anisotropic magnetoresistance in Co/CoO bilayer

    NASA Astrophysics Data System (ADS)

    Sahoo, S.; Polisetty, S.; Wang, Yi; Mukherjee, T.; He, Xi; Binek, Ch.

    2008-03-01

    We measured the anisotropic magnetoresistance of a Co(11nm)/CoO bilayer in exchange biased and unbiased states. The bilayer was fabricated on a-Al2O3 substrate maintained at 300^oC by molecular beam epitaxy at a base pressure of 10-11mbar. θ-2θ X-ray diffraction scans reveal hcp (001) texture of the Co film. No peak associated with the naturally formed CoO top layer was identified. Small angle X-ray reflectivity scans yield the Co and CoO thicknesses as 11 and 2.4nm, respectively. Exchange bias was obtained from field cooled magnetoresistance measurements at various temperatures carried out in a closed cycle cryostat. Exchange bias varies quasi linearly with temperature and vanishes at the blocking temperature, TB=97K. The latter is less than 2/3 of the bulk N'eel temperature allowing to estimate the T=0 antiferromagnetic correlation length of CoO to be 1.84 nm in accordance with the geometrical confinement.

  13. Linearization strategies for high sensitivity magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Silva, Ana V.; Leitao, Diana C.; Valadeiro, João; Amaral, José; Freitas, Paulo P.; Cardoso, Susana

    2015-10-01

    Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of ˜40 pT/√Hz at 30 Hz, representing a step forward the low field detection at room temperature.

  14. Magnetocardiography with sensors based on giant magnetoresistance

    NASA Astrophysics Data System (ADS)

    Pannetier-Lecoeur, M.; Parkkonen, L.; Sergeeva-Chollet, N.; Polovy, H.; Fermon, C.; Fowley, C.

    2011-04-01

    Biomagnetic signals, mostly due to the electrical activity in the body, are very weak and they can only be detected by the most sensitive magnetometers, such as Superconducting Quantum Interference Devices (SQUIDs). We report here biomagnetic recordings with hybrid sensors based on Giant MagnetoResistance (GMR). We recorded magnetic signatures of the electric activity of the human heart (magnetocardiography) in healthy volunteers. The P-wave and QRS complex, known from the corresponding electric recordings, are clearly visible in the recordings after an averaging time of about 1 min. Multiple recordings at different locations over the chest yielded a dipolar magnetic field map and allowed localizing the underlying current sources. The sensitivity of the GMR-based sensors is now approaching that of SQUIDs and paves way for spin electronics devices for functional imaging of the body.

  15. Gilbert damping and anisotropic magnetoresistance in iron-based alloys

    NASA Astrophysics Data System (ADS)

    Berger, L.

    2016-07-01

    We use the two-current model of Campbell and Fert to understand the compositional dependence of the Gilbert damping parameter in certain iron alloys. In that model, spin-up and spin-down carriers have different resistivities ρ↑ and ρ↓. We emphasize the part of the Gilbert parameter, called Gsf, generated by spin-flip interband processes. Both Gsf and the anisotropic magnetoresistance Δρ are proportional to the square of the spin-orbit parameter, and also proportional to ρ↑. In bcc alloys of iron with V, Cr, Mo, etc. solutes on the left of iron in the periodic table, ρ↑ is increased by a scattering resonance (Gomes and Campbell, 1966, 1968). Then ρ↑, Δρ, and Gsf all exhibit a peak at the same moderate concentration of the solute. We find the best fit between this theory and existing experimental data of Gilbert damping for Fe-V epitaxial films at room temperature (Cheng, 2006; Scheck et al., 2007). At room temperature, the predicted Gsf peak is masked by a background arising from non-flip intraband processes. At elevated temperatures, the peak is expected to become more prominent, and less hidden in the background.

  16. Giant anisotropic magnetoresistance in a quantum anomalous Hall insulator

    NASA Astrophysics Data System (ADS)

    Kandala, Abhinav; Richardella, Anthony; Kempinger, Susan; Liu, Chao-Xing; Samarth, Nitin

    2015-07-01

    When a three-dimensional ferromagnetic topological insulator thin film is magnetized out-of-plane, conduction ideally occurs through dissipationless, one-dimensional (1D) chiral states that are characterized by a quantized, zero-field Hall conductance. The recent realization of this phenomenon, the quantum anomalous Hall effect, provides a conceptually new platform for studies of 1D transport, distinct from the traditionally studied quantum Hall effects that arise from Landau level formation. An important question arises in this context: how do these 1D edge states evolve as the magnetization is changed from out-of-plane to in-plane? We examine this question by studying the field-tilt-driven crossover from predominantly edge-state transport to diffusive transport in Crx(Bi,Sb)2-xTe3 thin films. This crossover manifests itself in a giant, electrically tunable anisotropic magnetoresistance that we explain by employing a Landauer-Büttiker formalism. Our methodology provides a powerful means of quantifying dissipative effects in temperature and chemical potential regimes far from perfect quantization.

  17. Giant anisotropic magnetoresistance in a quantum anomalous Hall insulator.

    PubMed

    Kandala, Abhinav; Richardella, Anthony; Kempinger, Susan; Liu, Chao-Xing; Samarth, Nitin

    2015-07-07

    When a three-dimensional ferromagnetic topological insulator thin film is magnetized out-of-plane, conduction ideally occurs through dissipationless, one-dimensional (1D) chiral states that are characterized by a quantized, zero-field Hall conductance. The recent realization of this phenomenon, the quantum anomalous Hall effect, provides a conceptually new platform for studies of 1D transport, distinct from the traditionally studied quantum Hall effects that arise from Landau level formation. An important question arises in this context: how do these 1D edge states evolve as the magnetization is changed from out-of-plane to in-plane? We examine this question by studying the field-tilt-driven crossover from predominantly edge-state transport to diffusive transport in Crx(Bi,Sb)(2-x)Te3 thin films. This crossover manifests itself in a giant, electrically tunable anisotropic magnetoresistance that we explain by employing a Landauer-Büttiker formalism. Our methodology provides a powerful means of quantifying dissipative effects in temperature and chemical potential regimes far from perfect quantization.

  18. Temperature-Dependent Asymmetry of Anisotropic Magnetoresistance in Silicon p-n Junctions

    PubMed Central

    Yang, D. Z.; Wang, T.; Sui, W. B.; Si, M. S.; Guo, D. W.; Shi, Z.; Wang, F. C.; Xue, D. S.

    2015-01-01

    We report a large but asymmetric magnetoresistance in silicon p-n junctions, which contrasts with the fact of magnetoresistance being symmetric in magnetic metals and semiconductors. With temperature decreasing from 293 K to 100 K, the magnetoresistance sharply increases from 50% to 150% under a magnetic field of 2 T. At the same time, an asymmetric magnetoresistance, which manifests itself as a magnetoresistance voltage offset with respect to the sign of magnetic field, occurs and linearly increases with magnetoresistance. More interestingly, in contrast with other materials, the lineshape of anisotropic magnetoresistance in silicon p-n junctions significantly depends on temperature. As temperature decreases from 293 K to 100 K, the width of peak shrinks from 90° to 70°. We ascribe these novel magnetoresistance to the asymmetric geometry of the space charge region in p-n junction induced by the magnetic field. In the vicinity of the space charge region the current paths are deflected, contributing the Hall field to the asymmetric magnetoresistance. Therefore, the observed temperature-dependent asymmetry of magnetoresistance is proved to be a direct consequence of the spatial configuration evolution of space charge region with temperature. PMID:26323495

  19. Tunneling anisotropic magnetoresistance in C60-based organic spintronic systems

    NASA Astrophysics Data System (ADS)

    Wang, K.; Sanderink, J. G. M.; Bolhuis, T.; van der Wiel, W. G.; de Jong, M. P.

    2014-05-01

    C60 fullerenes are interesting molecular semiconductors for spintronics since they exhibit weak spin-orbit and hyperfine interactions, which is a prerequisite for long spin lifetimes. We report spin-polarized transport in spin-valve-like structures containing ultrathin (<10 nm) C60 layers, ferromagnetic (FM) epitaxial face-centered-cubic (fcc) Co (111) contacts, AlOx tunnel barriers, and nonmagnetic Al counter electrodes. Even though genuine spin-valve behavior cannot occur for only one FM contact, we find significant tunneling anisotropic magnetoresistance (TAMR) upon rotating the in-plane magnetization, originating from spin-orbit interaction (SOI) induced anisotropy of the fcc (111) Co bands. The uniaxial magnetocrystalline anisotropy of the Co electrodes results in a predominantly twofold symmetric in-plane TAMR effect. We investigated the TAMR effect in the direct tunneling regime (2 nm C60), at the transition point to two-step tunneling (4 nm C60), and in the multistep regime (8 nm C60). A sizable TAMR of 4.5% is found at 5 K under application of a 500-mT in-plane magnetic field for C60 layers of 2 nm, which is strongly suppressed at 8 nm thickness, indicating that TAMR may strongly contribute to the "spin-valve" signal for direct tunneling, but not for multistep tunneling. The TAMR effect is proposed to be due to a combination of SOI induced modulation of the tunneling DOS upon rotating the in-plane magnetization of the fcc epitaxial Co thin film, resonant tunneling processes involving interfacial states, and different Bychkov-Rashba SOI at the different interfaces.

  20. Tunneling magnetoresistance sensor with pT level 1/f magnetic noise

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  1. Lateral flow immunoassay using magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Taton, Kristin; Johnson, Diane; Guire, Patrick; Lange, Erik; Tondra, Mark

    2009-05-01

    Magnetic particles have been adapted for use as labels in biochemical lateral flow strip tests. Standard gold particle lateral flow assays are generally qualitative; however, with magnetic particles, quantitative results can be obtained by using electronic detection systems with giant magnetoresistive (GMR) sensors. As described here, these small integrated sensor chips can detect the presence of magnetic labels in capture spots whose volume is approximately 150 μm×150 μm×150 μm. The range of linear detection is better than two orders of magnitude; the total range is up to four orders of magnitude. The system was demonstrated with both indirect and sandwich enzyme-linked immunosorbent assays (ELISAs) for protein detection of rabbit IgG and interferon-γ, respectively, achieving detection of 12 pg/ml protein. Ultimately, the goal is for the detector to be fully integrated into the lateral flow strip backing to form a single consumable item that is interrogated by a handheld electronic reader.

  2. The MAGIC of CINEMA: first in-flight science results from a miniaturised anisotropic magnetoresistive magnetometer

    NASA Astrophysics Data System (ADS)

    Archer, M. O.; Horbury, T. S.; Brown, P.; Eastwood, J. P.; Oddy, T. M.; Whiteside, B. J.; Sample, J. G.

    2015-06-01

    We present the first in-flight results from a novel miniaturised anisotropic magnetoresistive space magnetometer, MAGIC (MAGnetometer from Imperial College), aboard the first CINEMA (CubeSat for Ions, Neutrals, Electrons and MAgnetic fields) spacecraft in low Earth orbit. An attitude-independent calibration technique is detailed using the International Geomagnetic Reference Field (IGRF), which is temperature dependent in the case of the outboard sensor. We show that the sensors accurately measure the expected absolute field to within 2% in attitude mode and 1% in science mode. Using a simple method we are able to estimate the spacecraft's attitude using the magnetometer only, thus characterising CINEMA's spin, precession and nutation. Finally, we show that the outboard sensor is capable of detecting transient physical signals with amplitudes of ~ 20-60 nT. These include field-aligned currents at the auroral oval, qualitatively similar to previous observations, which agree in location with measurements from the DMSP (Defense Meteorological Satellite Program) and POES (Polar-orbiting Operational Environmental Satellites) spacecraft. Thus, we demonstrate and discuss the potential science capabilities of the MAGIC instrument onboard a CubeSat platform.

  3. Analog isolated electronic dynamometer based on a magnetoresistive current sensor

    NASA Astrophysics Data System (ADS)

    Arcos Carrasco, C.; Ramírez Muñoz, D.; Ravelo Arias, S. I.; Sánchez Moreno, J.; Maset Sancho, E.; Garrigós Sirvent, A.

    2017-03-01

    In this work, an electronic system is presented to measure the force applied by a solenoid. The originality of the work is focused on the use of a magnetoresistive current sensor to provide the isolation barrier needed in the actual industrial plant where the solenoids are working. The design of the electronic system is presented as well as experimental measurements as a result of a calibration process showing a negligible hysteresis with that specific sensor. The magnetoresistive current sensor is used to develop transmission functions rather than playing its usual sensing roles.

  4. Giant Magnetoresistive (GMR) Sensor Microelectromechanical System (MEMS) Device

    NASA Technical Reports Server (NTRS)

    Ramesham, R.

    1999-01-01

    The measurement of acceleration has been accomplished using several technologies in high-reliability applications such as guidance control, detonation, and shock/vibration measurement. Electromechanical, piezoelectric, piezoresistive, and capacitive acceleration sensors are available and the literature pertinent to giant magnetoresistive sensors (GMR) for the above applications are scanty.

  5. Magnon planar Hall effect and anisotropic magnetoresistance in a magnetic insulator

    NASA Astrophysics Data System (ADS)

    Liu, J.; Cornelissen, L. J.; Shan, J.; Kuschel, T.; van Wees, B. J.

    2017-04-01

    Electrical resistivities can be different for charge currents traveling parallel or perpendicular to the magnetization in magnetically ordered conductors or semiconductors, resulting in the well-known planar Hall effect and anisotropic magnetoresistance. Here we study the analogous anisotropic magnetotransport behavior for magnons in a magnetic insulator Y3Fe5O12 . Electrical and thermal magnon injection, and electrical detection methods, are used at room temperature with transverse and longitudinal geometries to measure the magnon planar Hall effect and anisotropic magnetoresistance, respectively. We observe that the relative difference between magnon current conductivities parallel and perpendicular to the magnetization, with respect to the average magnon conductivity, i.e., | (σ∥m-σ⊥m) /σ0m| , is approximately 5% with the majority of the measured devices showing σ⊥m>σ∥m .

  6. Detection of magnetic resonance signals using a magnetoresistive sensor

    DOEpatents

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

    2013-10-01

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

  7. Anisotropic giant magnetoresistance in NbSb2

    PubMed Central

    Wang, Kefeng; Graf, D.; Li, Lijun; Wang, Limin; Petrovic, C.

    2014-01-01

    The magnetic field response of the transport properties of novel materials and then the large magnetoresistance effects are of broad importance in both science and application. We report large transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 105% in 2 K and 9 T field, and 4.3 × 106% in 0.4 K and 32 T field, without saturation) and field-induced metal-semiconductor-like transition, in NbSb2 single crystal. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed to the change of the Fermi surface induced by the magnetic field which is related to the Dirac-like point, in addition to orbital MR expected for high mobility metals. PMID:25476239

  8. Tunnel Magnetoresistance Sensors with Magnetostrictive Electrodes: Strain Sensors.

    PubMed

    Tavassolizadeh, Ali; Rott, Karsten; Meier, Tobias; Quandt, Eckhard; Hölscher, Hendrik; Reiss, Günter; Meyners, Dirk

    2016-11-11

    Magnetostrictive tunnel magnetoresistance (TMR) sensors pose a bright perspective in micro- and nano-scale strain sensing technology. The behavior of TMR sensors under mechanical stress as well as their sensitivity to the applied stress depends on the magnetization configuration of magnetic tunnel junctions (MTJ)s with respect to the stress axis. Here, we propose a configuration resulting in an inverse effect on the tunnel resistance by tensile and compressive stresses. Numerical simulations, based on a modified Stoner-Wohlfarth (SW) model, are performed in order to understand the magnetization reversal of the sense layer and to find out the optimum bias magnetic field required for high strain sensitivity. At a bias field of -3.2 kA/m under a 0.2 × 10 - 3 strain, gauge factors of 2294 and -311 are calculated under tensile and compressive stresses, respectively. Modeling results are investigated experimentally on a round junction with a diameter of 30 ± 0.2 μ m using a four-point bending apparatus. The measured field and strain loops exhibit nearly the same trends as the calculated ones. Also, the gauge factors are in the same range. The junction exhibits gauge factors of 2150 ± 30 and -260 for tensile and compressive stresses, respectively, under a -3.2 kA/m bias magnetic field. The agreement of the experimental and modeling results approves the proposed configuration for high sensitivity and ability to detect both tensile and compressive stresses by a single TMR sensor.

  9. Tunnel anisotropic magnetoresistance in CoFeB|MgO|Ta junctions

    SciTech Connect

    Hatanaka, S.; Miwa, S. Matsuda, K.; Nawaoka, K.; Tanaka, K.; Morishita, H.; Goto, M.; Mizuochi, N.; Shinjo, T.; Suzuki, Y.

    2015-08-24

    We found that CoFeB|MgO|Ta tunnel junctions exhibit tunnel anisotropic magnetoresistance (TAMR) at room temperature. The tunnel junctions exhibit positive magnetoresistance with the application of a magnetic field normal to the film plane. The dependencies on the applied magnetic field angle and MgO thickness reveal that the magnetoresistance originates from the TAMR, caused by the spin polarization and the spin-orbit interaction at the CoFeB|MgO interface. We also found that the TAMR can be used to detect ferromagnetic resonance in the CoFeB. This detection method could be useful for the characterization of nanomagnets that are free from the spin-transfer effect and the stray field of a reference layer, unlike conventional magnetic tunnel junctions.

  10. Measurement and simulation of anisotropic magnetoresistance in single GaAs/MnAs core/shell nanowires

    NASA Astrophysics Data System (ADS)

    Liang, J.; Wang, J.; Paul, A.; Cooley, B. J.; Rench, D. W.; Dellas, N. S.; Mohney, S. E.; Engel-Herbert, R.; Samarth, N.

    2012-04-01

    We report four probe measurements of the low field magnetoresistance (MR) in single core/shell GaAs/MnAs nanowires (NWs) synthesized by molecular beam epitaxy, demonstrating clear signatures of anisotropic magnetoresistance that track the field-dependent magnetization. A comparison with micromagnetic simulations reveals that the principal characteristics of the magnetoresistance data can be unambiguously attributed to the nanowire segments with a zinc blende GaAs core. The direct correlation between magnetoresistance, magnetization, and crystal structure provides a powerful means of characterizing individual hybrid ferromagnet/semiconductor nanostructures.

  11. Tunnel Magnetoresistance Sensors with Magnetostrictive Electrodes: Strain Sensors

    PubMed Central

    Tavassolizadeh, Ali; Rott, Karsten; Meier, Tobias; Quandt, Eckhard; Hölscher, Hendrik; Reiss, Günter; Meyners, Dirk

    2016-01-01

    Magnetostrictive tunnel magnetoresistance (TMR) sensors pose a bright perspective in micro- and nano-scale strain sensing technology. The behavior of TMR sensors under mechanical stress as well as their sensitivity to the applied stress depends on the magnetization configuration of magnetic tunnel junctions (MTJ)s with respect to the stress axis. Here, we propose a configuration resulting in an inverse effect on the tunnel resistance by tensile and compressive stresses. Numerical simulations, based on a modified Stoner–Wohlfarth (SW) model, are performed in order to understand the magnetization reversal of the sense layer and to find out the optimum bias magnetic field required for high strain sensitivity. At a bias field of −3.2 kA/m under a 0.2×10-3 strain, gauge factors of 2294 and −311 are calculated under tensile and compressive stresses, respectively. Modeling results are investigated experimentally on a round junction with a diameter of 30±0.2μm using a four-point bending apparatus. The measured field and strain loops exhibit nearly the same trends as the calculated ones. Also, the gauge factors are in the same range. The junction exhibits gauge factors of 2150±30 and −260 for tensile and compressive stresses, respectively, under a −3.2 kA/m bias magnetic field. The agreement of the experimental and modeling results approves the proposed configuration for high sensitivity and ability to detect both tensile and compressive stresses by a single TMR sensor. PMID:27845708

  12. Development of eddy current probes based on magnetoresistive sensors arrays

    NASA Astrophysics Data System (ADS)

    Sergeeva-Chollet, N.; Decitre, J.-M.; Fermon, C.; Pelkner, M.; Reimund, V.; Kreutzbruck, M.

    2014-02-01

    Eddy Current Technique is a powerful method for detection of surface notches and of buried flaws during inspection of metallic parts. Recent EC array probes have demonstrated a fast and efficient control of large surfaces. Nevertheless, when the size of flaws decreases or the defect is rather deep, traditional winding coil probes turn out to be useless. Magnetoresistive sensors present the advantages of flat frequency response and micron size. These sensors are hence very attractive for the detection of buried defects that require low frequencies because of skin depth effect. An optimization of the probe with magnetoresistive sensors as receivers has been made by simulations using CIVA software and finite elements methods with OPERA. EC probes for buried flaw detection have been designed. Experimental results have been compared with simulations.

  13. A Magnetoresistive Tactile Sensor for Harsh Environment Applications

    PubMed Central

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

    2016-01-01

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

  14. Anisotropic magnetotransport and exotic longitudinal linear magnetoresistance in WTe2 crystals

    DOE PAGES

    Zhao, Yanfei; Liu, Haiwen; Yan, Jiaqiang; ...

    2015-07-06

    Recently, the WTe2 semimetal, as a typical layered transition-metal dichalcogenide, attracted much attention due to an extremely large, non-saturating parabolic magnetoresistance in the perpendicular field. Here, we report a systematic study of the angular dependence of the magnetoresistance in a WTe2 single crystal. The significant anisotropic magnetotransport behavior in different magnetic field directions and violation of the Kohler's rule are observed. Unexpectedly, when the applied field and excitation current are both parallel to the tungsten chains of WTe2, an exotic large longitudinal linear magnetoresistance as high as 1200% at 15T and 2K is identified. These results imply that the WTe2more » semimetal, due to its balanced hole and electron populations, seems to be the first material for which a large longitudinal linear magnetoresistance appears when the external magnetic field is parallel to the applied current. Finally, our work may stimulate studies of double-carrier correlated materials and the corresponding quantum physics.« less

  15. Anisotropic magnetotransport and exotic longitudinal linear magnetoresistance in WTe2 crystals

    SciTech Connect

    Zhao, Yanfei; Liu, Haiwen; Yan, Jiaqiang; An, Wei; Liu, Jun; Zhang, Xi; Wang, Huichao; Liu, Yi; Jiang, Hua; Li, Qing; Wang, Yong; Li, Xin-Zheng; Mandrus, David; Xie, X. C.; Pan, Minghu; Wang, Jian

    2015-07-06

    Recently, the WTe2 semimetal, as a typical layered transition-metal dichalcogenide, attracted much attention due to an extremely large, non-saturating parabolic magnetoresistance in the perpendicular field. Here, we report a systematic study of the angular dependence of the magnetoresistance in a WTe2 single crystal. The significant anisotropic magnetotransport behavior in different magnetic field directions and violation of the Kohler's rule are observed. Unexpectedly, when the applied field and excitation current are both parallel to the tungsten chains of WTe2, an exotic large longitudinal linear magnetoresistance as high as 1200% at 15T and 2K is identified. These results imply that the WTe2 semimetal, due to its balanced hole and electron populations, seems to be the first material for which a large longitudinal linear magnetoresistance appears when the external magnetic field is parallel to the applied current. Finally, our work may stimulate studies of double-carrier correlated materials and the corresponding quantum physics.

  16. Anisotropic magnetoresistance and current-perpendicular-to-plane giant magnetoresistance in epitaxial NiMnSb-based multilayers

    NASA Astrophysics Data System (ADS)

    Kwon, B.; Sakuraba, Y.; Sukegawa, H.; Li, S.; Qu, G.; Furubayashi, T.; Hono, K.

    2016-01-01

    We fabricated (001)-oriented C1b-NiMnSb epitaxial films on MgO substrate by a magnetron sputtering system and systematically investigated the structure, magnetic property, and anisotropic magnetoresistance (AMR) effect. NiMnSb film was deposited using a stoichiometric NiMnSb target which has Mn-deficient (Mn ˜ 28.7 at. %) off-stoichiometric composition ratio. We have investigated bulk spin-polarization in NiMnSb films by measuring AMR on the basis of recent study for half-metallic L21-Heusler compounds. Although the negative sign of AMR ratio, which is indicative of half-metallic nature, was observed in the single layer NiMnSb films, the magnitude of AMR ratio (-0.10% at RT) was about half of the largest value reported for half-metallic L21-Heusler compounds. The current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) devices of NiMnSb/Ag/NiMnSb show MR ratio of 13.2% at 10 K and 4.2% at 300 K, which is higher than the previous result for NiMnSb/Cu/NiMnSb CPP-GMR devices [Caballero et al., J. Magn. Magn. Mater. 198-199, 55 (1999)], but much less than the CPP-GMR using L21-Heusler electrodes. The reduction of intrinsic bulk spin-polarization originating from the Mn-deficiency in NiMnSb layer is expected to be the main reason for small MR values.

  17. Anisotropic magnetoresistance and current-perpendicular-to-plane giant magnetoresistance in epitaxial NiMnSb-based multilayers

    SciTech Connect

    Kwon, B.; Sakuraba, Y. Sukegawa, H.; Li, S.; Furubayashi, T.; Qu, G.; Hono, K.

    2016-01-14

    We fabricated (001)-oriented C1{sub b}-NiMnSb epitaxial films on MgO substrate by a magnetron sputtering system and systematically investigated the structure, magnetic property, and anisotropic magnetoresistance (AMR) effect. NiMnSb film was deposited using a stoichiometric NiMnSb target which has Mn-deficient (Mn ∼ 28.7 at. %) off-stoichiometric composition ratio. We have investigated bulk spin-polarization in NiMnSb films by measuring AMR on the basis of recent study for half-metallic L2{sub 1}-Heusler compounds. Although the negative sign of AMR ratio, which is indicative of half-metallic nature, was observed in the single layer NiMnSb films, the magnitude of AMR ratio (−0.10% at RT) was about half of the largest value reported for half-metallic L2{sub 1}-Heusler compounds. The current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) devices of NiMnSb/Ag/NiMnSb show MR ratio of 13.2% at 10 K and 4.2% at 300 K, which is higher than the previous result for NiMnSb/Cu/NiMnSb CPP-GMR devices [Caballero et al., J. Magn. Magn. Mater. 198–199, 55 (1999)], but much less than the CPP-GMR using L2{sub 1}-Heusler electrodes. The reduction of intrinsic bulk spin-polarization originating from the Mn-deficiency in NiMnSb layer is expected to be the main reason for small MR values.

  18. Anisotropic magnetoresistance and piezoelectric effect in GaAs Hall samples

    NASA Astrophysics Data System (ADS)

    Ciftja, Orion

    2017-02-01

    Application of a strong magnetic field perpendicular to a two-dimensional electron system leads to a variety of quantum phases ranging from incompressible quantum Hall liquid to Wigner solid, charge density wave, and exotic non-Abelian states. A few quantum phases seen in past experiments on GaAs Hall samples of electrons show pronounced anisotropic magnetoresistance values at certain weak magnetic fields. We argue that this might be due to the piezoelectric effect that is inherent in a semiconductor host such as GaAs. Such an effect has the potential to create a sufficient in-plane internal strain that will be felt by electrons and will determine the direction of high and low resistance. When Wigner solid, charge density wave, and isotropic liquid phases are very close in energy, the overall stability of the system is very sensitive to local order and, thus, can be strongly influenced even by a weak perturbation such as the piezoelectric-induced effective electron-electron interaction, which is anisotropic. In this work, we argue that an anisotropic interaction potential may stabilize anisotropic liquid phases of electrons even in a strong magnetic field regime where normally one expects to see only isotropic quantum Hall or isotropic Fermi liquid states. We use this approach to support a theoretical framework that envisions the possibility of an anisotropic liquid crystalline state of electrons in the lowest Landau level. In particular, we argue that an anisotropic liquid state of electrons may stabilize in the lowest Landau level close to the liquid-solid transition region at filling factor ν =1 /6 for a given anisotropic Coulomb interaction potential. Quantum Monte Carlo simulations for a liquid crystalline state with broken rotational symmetry indicate stability of liquid crystalline order consistent with the existence of an anisotropic liquid state of electrons stabilized by anisotropy at filling factor ν =1 /6 of the lowest Landau level.

  19. Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers.

    PubMed

    Wang, K; Sanderink, J G M; Bolhuis, T; van der Wiel, W G; de Jong, M P

    2015-10-21

    A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the rotation of antiferromagnetic moments of an insulating CoO layer, incorporated into a tunnel junction consisting of sapphire(substrate)/fcc-Co/CoO/AlOx/Al. The ferromagnetic Co layer is exchange coupled to the AFM CoO layer and drives rotation of the AFM moments in an external magnetic field. The results may help pave the way towards the development of spintronic devices based on AFM insulators.

  20. Ballistic anisotropic magnetoresistance in core-shell nanowires and rolled-up nanotubes

    NASA Astrophysics Data System (ADS)

    Chang, Ching-Hao; Ortix, Carmine

    2017-01-01

    In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance (BAMR) is a change in the ballistic conductance with the direction of magnetization due to spin-orbit interaction. Very recently, a directional dependent ballistic conductance has been predicted to occur in a number of newly synthesized nonmagnetic semiconducting nanostructures subject to externally applied magnetic fields, without necessitating spin-orbit coupling. In this paper, we review past works on the prediction of this BAMR effect in core-shell nanowires (CSN) and rolled-up nanotubes (RUNTs). This is complemented by new results, we establish for the transport properties of tubular nanosystems subject to external magnetic fields.

  1. Disentangling interface and bulk contributions to the anisotropic magnetoresistance in Pt/Co/Pt sandwiches

    NASA Astrophysics Data System (ADS)

    Kobs, André; Oepen, Hans Peter

    2016-01-01

    We report on interfacial contributions to the anisotropic magnetoresistance (AMR) in Co layers sandwiched between Pt. Utilizing the Fuchs-Sondheimer formalism interface contributions can be separated from bulklike AMR. We demonstrate that for all-metal systems interfacial AMR is also present when varying the magnetization within the film plane. This interfacial in-plane AMR is two times smaller than the contribution that arises when the magnetization is varied within the plane perpendicular to the current direction. This finding is in contrast to the spin Hall MR found for ferromagnetic insulator/Pt bilayers revealing the existence of different MR effects at the interfaces of Pt with conducting and insulating ferromagnets.

  2. Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers

    NASA Astrophysics Data System (ADS)

    Wang, K.; Sanderink, J. G. M.; Bolhuis, T.; van der Wiel, W. G.; de Jong, M. P.

    2015-10-01

    A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the rotation of antiferromagnetic moments of an insulating CoO layer, incorporated into a tunnel junction consisting of sapphire(substrate)/fcc-Co/CoO/AlOx/Al. The ferromagnetic Co layer is exchange coupled to the AFM CoO layer and drives rotation of the AFM moments in an external magnetic field. The results may help pave the way towards the development of spintronic devices based on AFM insulators.

  3. Asymmetric anisotropic magnetoresistance in epitaxial Fe3O4 thin films

    NASA Astrophysics Data System (ADS)

    Chen, B. L.; Ding, Z.; Ma, D. H.; Li, J. X.; Xiao, X.; Wu, Y. Z.

    2015-09-01

    We aimed to study the effect of current orientation on the anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in a single-crystalline Fe3O4 (001) thin film at room temperature. AMR exhibits an unusual asymmetric behavior with respect to the current direction when the current does not flow along the high symmetry crystal axes, such as the <100> or <110> directions. AMR and PHE strongly depend upon the current direction angle, θJ, with an in-plane fourfold symmetry. The amplitude and phase shift of AMR and PHE can be understood quantitatively by a phenomenological description of the anisotropic resistivity tensor in a single-crystalline system. These results prove that the current direction can be used to modify the AMR effect.

  4. Magnetoresistive performance and comparison of supermagnetic nanoparticles on giant magnetoresistive sensor-based detection system

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Wang, Yi; Tu, Liang; Feng, Yinglong; Klein, Todd; Wang, Jian-Ping

    2014-07-01

    Giant magnetoresistive (GMR) biosensors have emerged as powerful tools for ultrasensitive, multiplexed, real-time electrical readout, and rapid biological/chemical detection while combining with magnetic particles. Finding appropriate magnetic nanoparticles (MNPs) and its influences on the detection signal is a vital aspect to the GMR bio-sensing technology. Here, we report a GMR sensor based detection system capable of stable and convenient connection, and real-time measurement. Five different types of MNPs with sizes ranging from 10 to 100 nm were investigated for GMR biosensing. The experiments were accomplished with the aid of DNA hybridization and detection architecture on GMR sensor surface. We found that different MNPs markedly affected the final detection signal, depending on their characteristics of magnetic moment, size, and surface-based binding ability, etc. This work may provide a useful guidance in selecting or preparing MNPs to enhance the sensitivity of GMR biosensors, and eventually lead to a versatile and portable device for molecular diagnostics.

  5. Magnetoresistive performance and comparison of supermagnetic nanoparticles on giant magnetoresistive sensor-based detection system.

    PubMed

    Wang, Wei; Wang, Yi; Tu, Liang; Feng, Yinglong; Klein, Todd; Wang, Jian-Ping

    2014-07-21

    Giant magnetoresistive (GMR) biosensors have emerged as powerful tools for ultrasensitive, multiplexed, real-time electrical readout, and rapid biological/chemical detection while combining with magnetic particles. Finding appropriate magnetic nanoparticles (MNPs) and its influences on the detection signal is a vital aspect to the GMR bio-sensing technology. Here, we report a GMR sensor based detection system capable of stable and convenient connection, and real-time measurement. Five different types of MNPs with sizes ranging from 10 to 100 nm were investigated for GMR biosensing. The experiments were accomplished with the aid of DNA hybridization and detection architecture on GMR sensor surface. We found that different MNPs markedly affected the final detection signal, depending on their characteristics of magnetic moment, size, and surface-based binding ability, etc. This work may provide a useful guidance in selecting or preparing MNPs to enhance the sensitivity of GMR biosensors, and eventually lead to a versatile and portable device for molecular diagnostics.

  6. Temperature dependence of anisotropic magnetoresistance in antiferromagnetic Sr{sub 2}IrO{sub 4}

    SciTech Connect

    Wang, C.; Seinige, H.; Tsoi, M.; Cao, G.; Zhou, J.-S.; Goodenough, J. B.

    2015-05-07

    Temperature-dependent magnetotransport properties of the antiferromagnetic semiconductor Sr{sub 2}IrO{sub 4} are investigated with point-contact devices. The point-contact technique allows to probe very small volumes and, therefore, to look for electronic transport on a microscopic scale. Point-contact measurements with single crystals of Sr{sub 2}IrO{sub 4} were intended to see whether the additional local resistance associated with a small contact area between a sharpened Cu tip and the antiferromagnet shows magnetoresistance (MR) such as that seen in bulk crystals. Point-contact measurements at liquid nitrogen temperature revealed large MRs (up to 28%) for modest magnetic fields (250 mT) applied within an IrO{sub 2} (ab) plane with angular dependence showing a crossover from four-fold to two-fold symmetry with an increasing magnetic field. Point contact measurement exhibits distinctive anisotropic magnetoresistance (AMR) in comparison to a bulk experiment, imposing intriguing questions about the mechanism of AMR in this material. Temperature-dependent MR measurements show that the MR falls to zero at the Neel temperature, but the temperature dependence of the MR ratio differs qualitatively from that of the resistivity. This AMR study helps to unveil the entanglement between electronic transport and magnetism in Sr{sub 2}IrO{sub 4} while the observed magnetoresistive phenomena can be potentially used to sense the antiferromagnetic order parameter in spintronic applications.

  7. Tunneling anisotropic magnetoresistance effect of single adatoms on a noncollinear magnetic surface.

    PubMed

    Caffrey, Nuala M; Schröder, Silke; Ferriani, Paolo; Heinze, Stefan

    2014-10-01

    The tunneling anisotropic magnetoresistance (TAMR) effect demonstrates the sensitivity of spin-polarized electron transport to the orientation of the magnetization with respect to the crystallographic axes. As the TAMR effect requires only a single magnetic electrode, in contrast to the tunneling magnetoresistance effect, it offers an attractive route to alternative spintronic applications. In this work we consider the TAMR effect at the single-atom limit by investigating the anisotropy of the local density of states (LDOS) in the vacuum above transition-metal adatoms adsorbed on a noncollinear magnetic surface, the monolayer of Mn on W(1 1 0). This surface presents a cycloidal spin spiral ground state with an angle of 173° between neighboring spins and thus allows a quasi-continuous exploration of the angular dependence of the TAMR of adsorbed adatoms using scanning tunneling microscopy. Using first-principle calculations, we investigate the TAMR of Co, Rh and Ir adatoms on Mn/W(1 1 0) and relate our results to the magnetization-direction-dependent changes in the LDOS. The anisotropic effect is found to be enhanced dramatically on the adsorption of heavy transition-metal atoms, with values of up to 50% predicted from our calculations. This effect will be measurable even with a non-magnetic STM tip.

  8. Anisotropic magnetoresistance and piezoresistivity in structured Fe3O4-silver particles in PDMS elastomers at room temperature.

    PubMed

    Mietta, José L; Ruiz, Mariano M; Antonel, P Soledad; Perez, Oscar E; Butera, Alejandro; Jorge, Guillermo; Negri, R Martín

    2012-05-01

    ) increases exponentially when a pressure, P, is applied, and the magnitude of the change strongly depends on what direction P is exerted (anisotropic piezoresistivity). In addition, at a fixed pressure, σ increases exponentially in the presence of an external magnetic field (H) only when the field H is applied in the collinear direction with respect to the electrical flux, J. Excellent fits of the experimental data σ versus H and P were achieved using a model that considers the intergrain electron transport where an H-dependent barrier was considered in addition to the intrinsic intergrain resistance in a percolation process. The H-dependent barrier decreases with the applied field, which is attributed to the increasing match of spin-polarization in the silver covers between grains. The effect is anisotropic (i.e., the sensitivity of the magnetoresistive effect is dependent on the relative orientation between H and the current flow J). In the case of Fe(3)O(4)@ Ag, when H and J are parallel to the needles in the PDMS matrix, we obtain changes in σ up to 50% for fields of 400 mT and with resistances on the order of 1-10 Ω. Magnetoresistive and magnetoelastic properties make these materials very interesting for applications in flexible electronics, electronic skins, anisotropic pressure, and magnetic field sensors.

  9. Temperature dependence of in-plane magnetic anisotropy and anisotropic magnetoresistance in (Ga,Mn)As codoped with Li

    NASA Astrophysics Data System (ADS)

    Miyakozawa, Shohei; Chen, Lin; Matsukura, Fumihiro; Ohno, Hideo

    2016-03-01

    We evaluate the temperature dependence of in-plane magnetic anisotropy and anisotropic magnetoresistance (AMR) in (Ga,Mn)As codoped with Li by magnetotransport measurements. We find that the signs of in-plane uniaxial anisotropy and AMR change at the same temperature of ˜75 K, and that the sign of planar Hall effect does not depend on temperature.

  10. Extrinsic anisotropic magnetoresistance contribution to measured domain wall resistances of in-plane magnetized (Ga,Mn)As

    NASA Astrophysics Data System (ADS)

    Roberts, H. G.; Crampin, S.; Bending, S. J.

    2007-07-01

    We demonstrate the presence of an important extrinsic anisotropic magnetoresistance contribution to the domain wall resistance recently measured in thin-film (Ga,Mn)As with in-plane magnetic anisotropy. Analytic results for simple domain wall orientations supplemented by numerical results for more general cases show that this previously omitted contribution can largely explain the observed negative resistance.

  11. Tunnelling anisotropic magnetoresistance due to antiferromagnetic CoO tunnel barriers

    PubMed Central

    Wang, K.; Sanderink, J. G. M.; Bolhuis, T.; van der Wiel, W. G.; de Jong, M. P.

    2015-01-01

    A new approach in spintronics is based on spin-polarized charge transport phenomena governed by antiferromagnetic (AFM) materials. Recent studies have demonstrated the feasibility of this approach for AFM metals and semiconductors. We report tunneling anisotropic magnetoresistance (TAMR) due to the rotation of antiferromagnetic moments of an insulating CoO layer, incorporated into a tunnel junction consisting of sapphire(substrate)/fcc-Co/CoO/AlOx/Al. The ferromagnetic Co layer is exchange coupled to the AFM CoO layer and drives rotation of the AFM moments in an external magnetic field. The results may help pave the way towards the development of spintronic devices based on AFM insulators. PMID:26486931

  12. Pressure-induced topological phase transitions and strongly anisotropic magnetoresistance in bulk black phosphorus

    NASA Astrophysics Data System (ADS)

    Li, Chun-Hong; Long, Yu-Jia; Zhao, Ling-Xiao; Shan, Lei; Ren, Zhi-An; Zhao, Jian-Zhou; Weng, Hong-Ming; Dai, Xi; Fang, Zhong; Ren, Cong; Chen, Gen-Fu

    2017-03-01

    We report the anisotropic magnetotransport measurement on a noncompound band semiconductor black phosphorus (BP) with magnetic field B up to 16 Tesla applied in both perpendicular and parallel to electric current I under hydrostatic pressures. The BP undergoes a topological Lifshitz transition from band semiconductor to a zero-gap Dirac semimetal state at a critical pressure Pc, characterized by a weak localization-weak antilocalization transition at low magnetic fields and the emergence of a nontrivial Berry phase of π detected by SdH magneto-oscillations in magnetoresistance curves. In the transition region, we observe a pressure-dependent negative MR only in the B ∥I configuration. This negative longitudinal MR is attributed to the Adler-Bell-Jackiw anomaly (topological E .B term) in the presence of weak antilocalization corrections.

  13. Temperature-dependent anisotropic magnetoresistance inversion behaviors in Fe3O4 films

    NASA Astrophysics Data System (ADS)

    Yoon, Kap Soo; Hong, Jin Pyo

    2017-02-01

    We address the abnormal anisotropic magnetoresistance (AMR) reversal feature of half-metallic polycrystalline Fe3O4 films occurring at a specific temperature. Experimental results revealed a positive to negative MR transition in the Fe3O4 films at 264 K, which reflect the influence of additional domain wall scattering. These features was described by a correlation between domain wall resistance and inversion behavior of AMR with additional domain wall scattering factors. We further describe a possible model based on systematic structural and electrical measurements that employs a temperature-dependent domain wall width and spin diffusion length of the conducting electrons. This model allows for spin-flipping scattering of spin polarized electrons inside a proper domain width.

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

    SciTech Connect

    Yamanoi, K.; Yokotani, Y.; Cui, X.; Yakata, S.; Kimura, T.

    2015-12-21

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

  15. Determination of magnetic anisotropy constants in Fe ultrathin film on vicinal Si(111) by anisotropic magnetoresistance

    PubMed Central

    Ye, Jun; He, Wei; Wu, Qiong; Liu, Hao-Liang; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

    2013-01-01

    The epitaxial growth of ultrathin Fe film on Si(111) surface provides an excellent opportunity to investigate the contribution of magnetic anisotropy to magnetic behavior. Here, we present the anisotropic magnetoresistance (AMR) effect of Fe single crystal film on vicinal Si(111) substrate with atomically flat ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the tiny misorientation from Fe(111) plane, the symmetry of magnetocrystalline anisotropy energy changes from the six-fold to a superposition of six-fold, four-fold and a weakly uniaxial contribution. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from torque curves on the basis of AMR results. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of various magnetic anisotropy constants. PMID:23828508

  16. Four-fold symmetric anisotropic magnetoresistance of single-crystalline Ni(001) film

    SciTech Connect

    Xiao, X.; Li, J. X.; Ding, Z.; Wu, Y. Z.

    2015-11-28

    Temperature, current-direction, and film-thickness dependent anisotropic magnetoresistance measurements were performed on single-crystalline face-centered-cubic nickel films. An additional four-fold symmetry was confirmed besides the typical two-fold term even at room temperature. The angular-dependent longitudinal resistivity resolves into a two-fold term, which varies as a function of current direction, and a four-fold term, which is isotropically independent of current direction. The experimental results are interpreted well using an expression based on the phenomenological model. Both the two- and four-fold terms vary inversely proportional to film thickness, indicating that interfacial scattering can significantly influence the spin-dependent transport properties.

  17. Tunneling Anisotropic Magnetoresistance in Fe Nanoparticles Embedded in MgO Matrix

    NASA Astrophysics Data System (ADS)

    Pham, T. V.; Miwa, S.; Suzuki, Y.

    2016-05-01

    The tunnel magnetoresistance (TMR) effect is related to the relative orientation of the magnetizations of the two ferromagnetic electrodes in magnetic tunnel junctions (MTJs). The tunnel anisotropic magnetoresistance (TAMR) effect is related to the orientation of the magnetization with respect to the current direction or the crystallographic axes. Beyond the TMR, the TAMR is not only present in MTJs in which both electrodes are ferromagnetic but may also appear in tunnel structures with a single magnetic electrode. We investigated the magnetotransport properties in an Au/MgO/Fe nanoparticles/MgO/Cu tunnel junction. We found that both the TMR and TAMR can appear in tunnel junctions with Fe nanoparticles embedded in an MgO matrix. The TMR is attributed to spin-dependent tunneling between Fe nanoparticles, so the device resistance depends on the magnetization directions of adjacent Fe nanoparticles. The TAMR is attributed to the interfacial spin-orbit interaction, so the device resistance depends on each magnetization direction of an Fe nanoparticle. This is the first observation of the TAMR in Fe nanoparticles embedded in an MgO matrix.

  18. Anisotropic magnetoresistance in thin films of the Mott metal CaVO3

    NASA Astrophysics Data System (ADS)

    Lu, Jiwei; Gu, Man

    2012-02-01

    Bulk CaVO3 (CVO) is a Pauli paramagnetic metal with a singe 3d electron. Some unusual drastic changes in the magneto-resistance, magnetic susceptibility and the Hall effect have been reported in single crystal CVO. We have simultaneously synthesized epitaxial CVO films grown on three differently oriented SrTiO3 substrates. Colossal magneto-resistance (MR) as well as large crystalline anisotropic was observed at low temperatures. The maximum MR, defined as (R(7 T)-R(0 T))/R(0 T)*100 %, was over 1,0000 % at 2 K and 35 Tesla (parallel magnetic field) on the CVO films deposited on a (110) SrTiO3 single crystal substrate, and didn't show any sign of saturation. When the magnetic field was perpendicular, MR was dropped to 6,000%. The MR ratio was much larger than that of single crystal CVO. We have also investigated the magneto-transport behaviors of CVO films deposited on (111) and (100) STO and will discussed the dependence of MR in CVO on the crystal orientation as well as the orientation of external magnetic field.

  19. Long phase coherence length and anisotropic magnetoresistance in MgZnO thin film

    SciTech Connect

    Lv, Meng; Xu, Yonggang; Yu, Guolin Lin, Tie; Hu, Gujin; Chu, Junhao; Wang, Hao; Zhang, Huahan; Dai, Ning

    2015-04-21

    We comprehensively investigate magnetotransport properties of MgZnO thin film grown on ZnO substrate by molecular-beam epitaxy. We measure the weak localization effect and extract the electron phase coherence length by fitting to a three-dimensional weak localization theory and by analyzing the different changing rate of the magnetoresistance, results of which are in good agreement with each other. The phase coherence length ranges from 38.4±1    nm at 50 K to 99.8±3.6 nm at 1.4  K, almost the same as that of ZnO nanoplates and In-doped ZnO nanowires, and its temperature dependence is found to scale as T{sup −3/4}. Meanwhile, we study the anisotropic magnetoresistance resulting from the geometric effect as well as the Lorentz force induced path-length effect, which will be enhanced in higher magnetic fields.

  20. Large and Anisotropic Linear Magnetoresistance in Single Crystals of Black Phosphorus Arising From Mobility Fluctuations

    PubMed Central

    Hou, Zhipeng; Yang, Bingchao; Wang, Yue; Ding, Bei; Zhang, Xiaoming; Yao, Yuan; Liu, Enke; Xi, Xuekui; Wu, Guangheng; Zeng, Zhongming; Liu, Zhongyuan; Wang, Wenhong

    2016-01-01

    Black Phosphorus (BP) is presently attracting immense research interest on the global level due to its high mobility and suitable band gap for potential application in optoelectronics and flexible devices. It was theoretically predicted that BP has a large direction-dependent electrical and magnetotransport anisotropy. Investigations on magnetotransport of BP may therefore provide a new platform for studying the nature of electron transport in layered materials. However, to the best of our knowledge, magnetotransport studies, especially the anisotropic magnetoresistance (MR) effect in layered BP, are rarely reported. Here, we report a large linear MR up to 510% at a magnetic field of 7 Tesla in single crystals of BP. Analysis of the temperature and angle dependence of MR revealed that the large linear MR in our sample originates from mobility fluctuations. Furthermore, we reveal that the large linear MR of layered BP in fact follows a three-dimensional behavior rather than a two-dimensional one. Our results have implications to both the fundamental understanding and magnetoresistive device applications of BP. PMID:27030141

  1. Magnetoresistive-superconducting mixed sensors for biomagnetic applications

    NASA Astrophysics Data System (ADS)

    Pannetier-Lecoeur, M.; Fermon, C.; Dyvorne, H.; Jacquinot, J. F.; Polovy, H.; Walliang, A. L.

    2010-05-01

    When coupled to a giant magnetoresistive (GMR) sensor, a superconducting loop containing a constriction can be a very sensitive magnetometer. It has thermal noise levels of few fT/sqrt(Hz), comparable to low- Tc SQUID noise, with a flat frequency response. These mixed sensors are good candidates for detection of weak biomagnetic signals, like a cardiac or neuronal signature. Furthermore, being sensitive to the flux, mixed sensors can be used for nuclear magnetic resonance (NMR) detection and Magnetic Resonance Imaging (MRI) especially at low fields. They are very robust and accept strong RF pulses with a very short recovery time compared to tuned RF coils, which allow measurements of broad signals (short relaxation time or multiple resonances). We will first present the last generation sensors having a noise level of 3 fT/sqrt(Hz) and we will show signals measured at low frequency (magnetocardiography-magnetoencephalography range) and at higher frequency (NMR signals). The use of additional flux transformers for improving the signal-to-noise will be discussed. Finally, we will present perspectives for low-field MRI, which can be combined with neural signal detection (MEG), especially for brain anatomy and temporal response on the same experimental setup.

  2. A Magnetoresistance Measuring Probe.

    DTIC Science & Technology

    The in line four point probe, commonly used for measuring the sheet resistance in a conductor, cannot measure the anisotropic ferromagnetic magnetoresistance. However, the addition of two contact points that are not collinear with the current contacts give the probe the ability to non-destructively measure the anistropic magnetoresistance. Keywords: Magnetoresistance; Anisotropic; Thin-Film; Permalloy; Four Point Probe; Anisotropic Resistance.

  3. Unexploded ordnance detection using imaging giant magnetoresistive (GMR) sensor arrays

    SciTech Connect

    Chaiken, A., LLNL

    1997-05-06

    False positive detections account for a great part of the expense associated with unexploded ordnance (UXO) remediation. Presently fielded systems like pulsed electromagnetic induction systems and cesium-vapor magnetometers are able to distinguish between UXO and other metallic ground clutter only with difficulty. The discovery of giant magnetoresistance (GMR) has led to the development of a new generation of integrated-circuit magnetic sensors that are far more sensitive than previously available room-temperature-operation electronic devices. The small size of GMR sensors makes possible the construction of array detectors that can be used to image the flux emanating from a ferrous object or from a non-ferrous object with eddy currents imposed by an external coil. The purpose of a GMR-based imaging detector would be to allow the operator to easily distinguish between UXO and benign objects (like shrapnel or spent bullets) that litter formerly used defense sites (FUDS). In order to demonstrate the potential of a GMR-based imaging technology, a crude magnetic imaging system has been constructed using commercially available sensors. The ability to roughly determine the outline and disposition of magnetic objects has been demonstrated. Improvements to the system which are necessary to make it into a high-performance UXO detector are outlined.

  4. A novel CMOS transducer for giant magnetoresistance sensors.

    PubMed

    Luong, Van Su; Lu, Chih-Cheng; Yang, Jing-Wen; Jeng, Jen-Tzong

    2017-02-01

    In this work, an ASIC (application specific integrated circuits) transducer circuit for field modulated giant magnetoresistance (GMR) sensors was designed and fabricated using a 0.18-μm CMOS process. The transducer circuits consist of a frequency divider, a digital phase shifter, an instrument amplifier, and an analog mixer. These comprise a mix of analog and digital circuit techniques. The compact chip size of 1.5 mm × 1.5 mm for both analog and digital parts was achieved using the TSMC18 1P6M (1-polysilicon 6-metal) process design kit, and the characteristics of the system were simulated using an HSpice simulator. The output of the transducer circuit is the result of the first harmonic detection, which resolves the modulated field using a phase sensitive detection (PSD) technique and is proportional to the measured magnetic field. When the dual-bridge GMR sensor is driven by the transducer circuit with a current of 10 mA at 10 kHz, the observed sensitivity of the field sensor is 10.2 mV/V/Oe and the nonlinearity error was 3% in the linear range of ±1 Oe. The performance of the system was also verified by rotating the sensor system horizontally in earth's magnetic field and recording the sinusoidal output with respect to the azimuth angle, which exhibits an error of less than ±0.04 Oe. These results prove that the ASIC transducer is suitable for driving the AC field modulated GMR sensors applied to geomagnetic measurement.

  5. A novel CMOS transducer for giant magnetoresistance sensors

    NASA Astrophysics Data System (ADS)

    Luong, Van Su; Lu, Chih-Cheng; Yang, Jing-Wen; Jeng, Jen-Tzong

    2017-02-01

    In this work, an ASIC (application specific integrated circuits) transducer circuit for field modulated giant magnetoresistance (GMR) sensors was designed and fabricated using a 0.18-μ m CMOS process. The transducer circuits consist of a frequency divider, a digital phase shifter, an instrument amplifier, and an analog mixer. These comprise a mix of analog and digital circuit techniques. The compact chip size of 1.5 mm × 1.5 mm for both analog and digital parts was achieved using the TSMC18 1P6M (1-polysilicon 6-metal) process design kit, and the characteristics of the system were simulated using an HSpice simulator. The output of the transducer circuit is the result of the first harmonic detection, which resolves the modulated field using a phase sensitive detection (PSD) technique and is proportional to the measured magnetic field. When the dual-bridge GMR sensor is driven by the transducer circuit with a current of 10 mA at 10 kHz, the observed sensitivity of the field sensor is 10.2 mV/V/Oe and the nonlinearity error was 3% in the linear range of ±1 Oe. The performance of the system was also verified by rotating the sensor system horizontally in earth's magnetic field and recording the sinusoidal output with respect to the azimuth angle, which exhibits an error of less than ±0.04 Oe. These results prove that the ASIC transducer is suitable for driving the AC field modulated GMR sensors applied to geomagnetic measurement.

  6. Twofold and Fourfold Symmetric Anisotropic Magnetoresistance Effect in a Model with Crystal Field

    NASA Astrophysics Data System (ADS)

    Kokado, Satoshi; Tsunoda, Masakiyo

    2015-09-01

    We theoretically study the twofold and fourfold symmetric anisotropic magnetoresistance (AMR) effects of ferromagnets. We here use the two-current model for a system consisting of a conduction state and localized d states. The localized d states are obtained from a Hamiltonian with a spin-orbit interaction, an exchange field, and a crystal field. From the model, we first derive general expressions for the coefficient of the twofold symmetric term (C2) and that of the fourfold symmetric term (C4) in the AMR ratio. In the case of a strong ferromagnet, the dominant term in C2 is proportional to the difference in the partial densities of states (PDOSs) at the Fermi energy (EF) between the dɛ and dγ states, and that in C4 is proportional to the difference in the PDOSs at EF among the dɛ states. Using the dominant terms, we next analyze the experimental results for Fe4N, in which |C2| and |C4| increase with decreasing temperature. The experimental results can be reproduced by assuming that the tetragonal distortion increases with decreasing temperature.

  7. Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe

    PubMed Central

    Kriegner, D.; Výborný, K.; Olejník, K.; Reichlová, H.; Novák, V.; Marti, X.; Gazquez, J.; Saidl, V.; Němec, P.; Volobuev, V. V.; Springholz, G.; Holý, V.; Jungwirth, T.

    2016-01-01

    Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Néel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets. PMID:27279433

  8. Electrical detection of magnetic domain wall in Fe4N nanostrip by negative anisotropic magnetoresistance effect

    NASA Astrophysics Data System (ADS)

    Gushi, Toshiki; Ito, Keita; Higashikozono, Soma; Takata, Fumiya; Oosato, Hirotaka; Sugimoto, Yoshimasa; Toko, Kaoru; Honda, Syuta; Suemasu, Takashi

    2016-09-01

    The magnetic structure of the domain wall (DW) of a 30-nm-thick Fe4N epitaxial film with a negative spin polarization of the electrical conductivity is observed by magnetic force microscopy and is well explained by micromagnetic simulation. The Fe4N film is grown by molecular beam epitaxy on a SrTiO3(001) substrate and processed into arc-shaped ferromagnetic nanostrips 0.3 μm wide by electron beam lithography and reactive ion etching with Cl2 and BCl3 plasma. Two electrodes mounted approximately 12 μm apart on the nanostrip register an electrical resistance at 8 K. By changing the direction of an external magnetic field (0.2 T), the presence or absence of a DW positioned in the nanostrip between the two electrodes can be controlled. The resistance is increased by approximately 0.5 Ω when the DW is located between the electrodes, which signifies the negative anisotropic magnetoresistance effect of Fe4N. The electrical detection of the resistance change is an important step toward the electrical detection of current-induced DW motion in Fe4N.

  9. Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe.

    PubMed

    Kriegner, D; Výborný, K; Olejník, K; Reichlová, H; Novák, V; Marti, X; Gazquez, J; Saidl, V; Němec, P; Volobuev, V V; Springholz, G; Holý, V; Jungwirth, T

    2016-06-09

    Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II-VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Néel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets.

  10. Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ'-Fe4N thin films

    NASA Astrophysics Data System (ADS)

    Kabara, Kazuki; Tsunoda, Masakiyo; Kokado, Satoshi

    2016-05-01

    Transverse anisotropic magnetoresistance (AMR) effects, for which magnetization is rotated in an orthogonal plane to the current direction, were investigated at various temperatures, in order to clarify the structural transformation from a cubic to a tetragonal symmetry in a pseudo-single-crystal Fe4N film, which is predicted from the usual in-plane AMR measurements by the theory taking into account the spin-orbit interaction and crystal field splitting of 3d bands. According to a phenomenological theory of AMR, which derives only from the crystal symmetry, a cos 2θ component ( C2 tr ) exists in transverse AMR curves for a tetragonal system but does not for a cubic system. In the Fe4N film, the C2 tr shows a positive small value (0.12%) from 300 K to 50 K. However, the C2 t r increases to negative value below 50 K and reaches to -2% at 5 K. The drastic increasing of the C2 tr demonstrates the structural transformation from a cubic to a tetragonal symmetry below 50 K in the Fe4N film. In addition, the out-of-plane and in-plane lattice constants (c and a) were precisely determined with X-ray diffraction at room temperature using the Nelson-Riely function. As a result, the positive small C2 t r above 50 K is attributed to a slightly distorted Fe4N lattice (c/a = 1.002).

  11. Electrical detection of ferromagnetic resonance in ferromagnet/n-GaAs heterostructures by tunneling anisotropic magnetoresistance

    SciTech Connect

    Liu, C.; Boyko, Y.; Geppert, C. C.; Christie, K. D.; Stecklein, G.; Crowell, P. A.; Patel, S. J.; Palmstrøm, C. J.

    2014-11-24

    We observe a dc voltage peak at ferromagnetic resonance (FMR) in samples consisting of a single ferromagnetic (FM) layer grown epitaxially on the n-GaAs (001) surface. The FMR peak is detected as an interfacial voltage with a symmetric line shape and is present in samples based on various FM/n-GaAs heterostructures, including Co{sub 2}MnSi/n-GaAs, Co{sub 2}FeSi/n-GaAs, and Fe/n-GaAs. We show that the interface bias voltage dependence of the FMR signal is identical to that of the tunneling anisotropic magnetoresistance (TAMR) over most of the bias range. Furthermore, we show how the precessing magnetization yields a dc FMR signal through the TAMR effect and how the TAMR phenomenon can be used to predict the angular dependence of the FMR signal. This TAMR-induced FMR peak can be observed under conditions where no spin accumulation is present and no spin-polarized current flows in the semiconductor.

  12. Effects of Magnetic Domain Walls on the Anisotropic Magnetoresistance in NiFe Nanowires.

    PubMed

    Nam, Chunghee

    2015-10-01

    We show that a type of magnetic domain walls (DWs) can be monitored by anisotropic magnetoresistance (AMR) measurements due to a specific DW volume depending on the DW type in NiFe magnetic wires. A circular DW injection pad is used to generate DWs at a low magnetic field, resulting in reliable DW introduction into magnetic wires. DW pinning is induced by a change of DW energy at an asymmetric single notch. The injection of DW from the circular pad and its pinning at the notch is observed by using AMR and magnetic force microscope (MFM) measurements. A four-point probe AMR measurement allows us to distinguish the DW type in the switching process because DWs are pinned at the single notch, where voltage probes are closely placed around the notch. Two types of AMR behavior are observed in the AMR measurements, which is owing to a change of DW structures. MFM images and micromagnetic simulations are consistent with the AMR results.

  13. Tunneling anisotropic magnetoresistance in Co/AlOx/Al tunnel junctions with fcc Co (111) electrodes

    NASA Astrophysics Data System (ADS)

    Wang, K.; Tran, T. L. A.; Brinks, P.; Sanderink, J. G. M.; Bolhuis, T.; van der Wiel, W. G.; de Jong, M. P.

    2013-08-01

    Tunneling anisotropic magnetoresistance (TAMR) has been characterized in junctions comprised of face-centered cubic (fcc) Co (111) ferromagnetic electrodes grown epitaxially on sapphire substrates, amorphous AlOx tunnel barriers, and nonmagnetic Al counterelectrodes. Large TAMR ratios have been found, up to ˜7.5% and ˜11% (at 5 K), for the in-plane and out-of-plane magnetization geometry, respectively. Such large TAMR values were not expected a priori, given the weak anisotropy of the (bulk) Co bands due to spin-orbit interaction, and the absence of Co (111) surface states that cross the Fermi energy. Both the in-plane and out-of-plane TAMR effects exhibit a predominantly twofold symmetry, and a strong bias dependence. The in-plane TAMR shows a maximum along the (twofold) magnetic hard axis, suggesting a relation between magnetic anisotropy and TAMR. We propose that uniaxial strain in combination with Bychkov-Rashba spin-orbit interaction, producing an interfacial tunneling DOS that depends on the magnetization direction, is responsible for the TAMR effect. The importance of the interfacial Co/AlOx (electronic) structure for the TAMR effect is underlined by measurements on junctions with overoxidized AlOx barriers, which show markedly different bias and angle dependence.

  14. On the importance of sensor height variation for detection of magnetic labels by magnetoresistive sensors.

    PubMed

    Henriksen, Anders Dahl; Wang, Shan Xiang; Hansen, Mikkel Fougt

    2015-07-21

    Magnetoresistive sensors are widely used for biosensing by detecting the signal from magnetic labels bound to a functionalized area that usually covers the entire sensor structure. Magnetic labels magnetized by a homogeneous applied magnetic field weaken and strengthen the applied field when they are over and outside the sensor area, respectively, and the detailed origin of the sensor signal in experimental studies has not been clarified. We systematically analyze the signal from both a single sensor stripe and an array of sensor stripes as function of the geometrical parameters of the sensor stripes as well as the distribution of magnetic labels over the stripes. We show that the signal from sensor stripes with a uniform protective coating, contrary to conventional wisdom in the field, is usually dominated by the contribution from magnetic labels between the sensor stripes rather than by the labels on top of the sensor stripes because these are at a lower height. We therefore propose a shift of paradigm to maximize the signal due to magnetic labels between sensor stripes. Guidelines for this optimization are provided and illustrated for an experimental case from the literature.

  15. On the importance of sensor height variation for detection of magnetic labels by magnetoresistive sensors

    PubMed Central

    Henriksen, Anders Dahl; Wang, Shan Xiang; Hansen, Mikkel Fougt

    2015-01-01

    Magnetoresistive sensors are widely used for biosensing by detecting the signal from magnetic labels bound to a functionalized area that usually covers the entire sensor structure. Magnetic labels magnetized by a homogeneous applied magnetic field weaken and strengthen the applied field when they are over and outside the sensor area, respectively, and the detailed origin of the sensor signal in experimental studies has not been clarified. We systematically analyze the signal from both a single sensor stripe and an array of sensor stripes as function of the geometrical parameters of the sensor stripes as well as the distribution of magnetic labels over the stripes. We show that the signal from sensor stripes with a uniform protective coating, contrary to conventional wisdom in the field, is usually dominated by the contribution from magnetic labels between the sensor stripes rather than by the labels on top of the sensor stripes because these are at a lower height. We therefore propose a shift of paradigm to maximize the signal due to magnetic labels between sensor stripes. Guidelines for this optimization are provided and illustrated for an experimental case from the literature. PMID:26195089

  16. Spin polarization ratios of resistivity and density of states estimated from anisotropic magnetoresistance ratio for nearly half-metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Kokado, Satoshi; Sakuraba, Yuya; Tsunoda, Masakiyo

    2016-10-01

    We derive a simple relational expression between the spin polarization ratio of resistivity, Pρ, and the anisotropic magnetoresistance ratio Δρ/ρ, and that between the spin polarization ratio of the density of states at the Fermi energy, PDOS, and Δρ/ρ for nearly half-metallic ferromagnets. We find that Pρ and PDOS increase with increasing |Δρ/ρ| from 0 to a maximum value. In addition, we roughly estimate Pρ and PDOS for a Co2FeGa0.5Ge0.5 Heusler alloy by substituting its experimentally observed Δρ/ρ into the respective expressions.

  17. Signature of surface state coupling in thin films of the topological Kondo insulator SmB6 from anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Shaviv Petrushevsky, M.; Rout, P. K.; Levi, G.; Kohn, A.; Dagan, Y.

    2017-02-01

    The temperature and thickness dependencies of the in-plane anisotropic magnetoresistance (AMR) of SmB6 thin films are reported. We find that the AMR changes sign from negative (ρ||<ρ⊥ ) at high temperatures to positive (ρ||>ρ⊥ ) at low temperatures. The temperature, Ts, at which this sign change occurs, decreases with increasing film thickness t and Ts vanishes for t > 30 nm. We interpret our results in the framework of a competition between two components: a negative bulk contribution and a positive surface AMR.

  18. GMR sensors: magnetoresistive behaviour optimization for biological detection by means of superparamagnetic nanoparticles.

    PubMed

    Manteca, A; Mujika, M; Arana, S

    2011-04-15

    An immunomagnetic method for the selective and quantitative detection of biological species by means of a magnetoresistive biosensor and superparamagnetic particles has been optimized. In order to achieve this, a giant magnetoresistive [Co (5.10nm)/Cu (2.47 nm)](20) multilayer structure has been chosen as the sensitive material, showing a magnetoresistance of 3.60% at 215 Oe and a sensitivity up to 0.19 Ω/Oe between 145 Oe and 350 Oe. The outward gold surface of the sensor is biofunctionalized with a Self-Assembled Monolayer (SAM). In addition, three different types of magnetic labels have been tested. 2 μm diameter magnetic carriers (7.68 pg ferrite/particle) have shown the best response and they have induced a shift in the magnetoresistive hysteresis loops up to 9% at 175 Oe.

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

    NASA Astrophysics Data System (ADS)

    Slatter, Rolf; Goffin, Benoit

    2014-08-01

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

  20. Magnetic anisotropy and anisotropic magnetoresistance in strongly phase separated manganite thin films

    NASA Astrophysics Data System (ADS)

    Kandpal, Lalit M.; Singh, Sandeep; Kumar, Pawan; Siwach, P. K.; Gupta, Anurag; Awana, V. P. S.; Singh, H. K.

    2016-06-01

    The present study reports the impact of magnetic anisotropy (MA) on magnetotransport properties such as the magnetic transitions, magnetic liquid behavior, glass transition and anisotropic magnetoresistance (AMR) in epitaxial film (thickness 42 nm) of strongly phase separated manganite La5/8-yPryCa3/8MnO3 (y≈0.4). Angle dependent magnetization measurement confirms the out-of-plane magnetic anisotropy with the magnetic easy axes aligned in the plane of the film and the magnetic hard axis along the normal to the film plane. The more prominent divergence between the zero filed cooled (ZFC) and field cooled warming (FCW) and the stronger hysteresis between the field cooled cooling (FCC) and FCW magnetization for H ∥ shows the weakening of the magnetic liquid along the magnetic hard axis. The peak at Tp≈42 K in FCW magnetization, which characterizes the onset of spin freezing shifts down to Tp≈18 K as the field direction is switched from the easy axes (H ∥) to the hard axis (H ⊥). The glass transition, which appears at Tg≈28 K for H ∥ disappears for H ⊥. The easy axis magnetization (M∣∣) appears to saturate around H~20 kOe, but the hard axis counterpart (M⊥) does not show such tendency even up to H=50 kOe. MA appears well above the ferromagnetic (FM) transition at T≈170 K, which is nearly the same as the Neel temperature (TN) of M⊥ - T . The temperature dependent resistivity measured at H=10 kOe applied along the easy axis (ρ|| - T) and the hard axis (ρ⊥ - T) shows insulator metal transition (IMT) at ≈106 K and ≈99 K in the cooling cycle, respectively. The large difference between ρ⊥ - T and ρ|| - T during the cooling cycle and in the vicinity of IMT results in huge AMR of ≈-142% and -115%. The observed properties have been explained in terms of the MA induced variation in the relative fraction of the coexisting magnetic phases.

  1. Detection of current-driven magnetic domains in [Co/Pd] nanowire by tunneling magnetoresistive sensor

    NASA Astrophysics Data System (ADS)

    Okuda, Mitsunobu; Miyamoto, Yasuyoshi; Miyashita, Eiichi; Saito, Nobuo; Hayashi, Naoto; Nakagawa, Shigeki

    2015-05-01

    Current-driven magnetic domain walls in magnetic nanowires have attracted a great deal of interest in terms of both physical studies and engineering applications. The anomalous Hall effect measurement is widely used for detecting the magnetization direction of current-driven magnetic domains in a magnetic nanowire. However, the problem with this measurement is that the detection point for current-driven domain wall motion is fixed at only the installed sensing wire across the specimen nanowire. A potential solution is the magnetic domain scope method, whereby the distribution of the magnetic flux leaking from the specimen can be analyzed directly by contact-scanning a tunneling magnetoresistive field sensor on a sample. In this study, we fabricated specimen nanowires consisting of [Co (0.3)/Pd (1.2)]21/Ta(3) films (units in nm) with perpendicular magnetic anisotropy on Si substrates. A tunneling magnetoresistive sensor was placed on the nanowire surface and a predetermined current pulse was applied. Real-time detection of the current-driven magnetic domain motion was successful in that the resistance of the tunneling magnetoresistive sensor was changed with the magnetization direction beneath the sensor. This demonstrates that magnetic domain detection using a tunneling magnetoresistive sensor is effective for the direct analysis of micro magnetic domain motion.

  2. The relationship between anisotropic magnetoresistance and topology of Fermi surface in Td-MoTe2 crystal

    NASA Astrophysics Data System (ADS)

    Lv, Yang-Yang; Li, Xiao; Pang, Bin; Cao, Lin; Lin, Dajun; Zhang, Bin-Bin; Yao, Shu-Hua; Chen, Y. B.; Zhou, Jian; Dong, Song-Tao; Zhang, Shan-Tao; Lu, Ming-Hui; Chen, Yan-Feng

    2017-07-01

    Layered transition-metal dichalcogenides have been recently attracted a lot of attention because of their unique physical properties, such as extremely large and anisotropic magnetoresistance (MR) in WTe2. In this work, we observed the abnormally anisotropic MR on Td-MoTe2 crystal that is strongly dependent on the temperature, as well as the orientations of both magnetic field B and electric field E with respect to crystallographic axes of Td-MoTe2. When E//a-axis and B//c-axis, MR is parabolically dependent on B and is as high as 520% under 9 T and 2 K conditions; the MR is quasi-linearly dependent on B when E//a-axis and B//b-axis (E//b-axis and B//c-axis), and the corresponding MR is only 130% (220%); MR is initially parabolically dependent on B, then linearly on B, and finally shows a saturate trend under E//B//a-axis (or E//B//b-axis) conditions, and the MR is about 16% (30%). These anisotropic MR behaviors can be qualitatively explained by the features of the Fermi surface of Td-MoTe2. This work may demonstrate the rich anisotropic physical behavior in layered transition-metal dichalcognides.

  3. Optimization of magnetoresistive sensor current for on-chip magnetic bead detection using the sensor self-field

    NASA Astrophysics Data System (ADS)

    Henriksen, Anders Dahl; Rizzi, Giovanni; Østerberg, Frederik Westergaard; Hansen, Mikkel Fougt

    2015-04-01

    We investigate the self-heating of magnetoresistive sensors used for measurements on magnetic beads in magnetic biosensors. The signal from magnetic beads magnetized by the field due to the sensor bias current is proportional to the bias current squared. Therefore, we aim to maximize the bias current while limiting the sensor self-heating. We systematically characterize and model the Joule heating of magnetoresistive sensors with different sensor geometries and stack compositions. The sensor heating is determined using the increase of the sensor resistance as function of the bias current. The measured temperature increase is in good agreement with a finite element model and a simple analytical thermal model. The heat conductance of our system is limited by the 1 μm thick electrically insulating silicon dioxide layer between the sensor stack and the underlying silicon wafer, thus the heat conductance is proportional to the sensor area and inversely proportional to the oxide thickness. This simple heat conductance determines the relationship between bias current and sensor temperature, and we show that 25 μm wide sensor on a 1 μm oxide can sustain a bias current of 30 mA for an allowed temperature increase of 5 °C. The method and models used are generally applicable for thin film sensor systems. Further, the consequences for biosensor applications of the present sensor designs and the impact on future sensor designs are discussed.

  4. Measuring Dynamic Signals with Direct Sensor-to-Microcontroller Interfaces Applied to a Magnetoresistive Sensor

    PubMed Central

    Sifuentes, Ernesto; Gonzalez-Landaeta, Rafael; Cota-Ruiz, Juan; Reverter, Ferran

    2017-01-01

    This paper evaluates the performance of direct interface circuits (DIC), where the sensor is directly connected to a microcontroller, when a resistive sensor subjected to dynamic changes is measured. The theoretical analysis provides guidelines for the selection of the components taking into account both the desired resolution and the bandwidth of the input signal. Such an analysis reveals that there is a trade-off between the sampling frequency and the resolution of the measurement, and this depends on the selected value of the capacitor that forms the RC circuit together with the sensor resistance. This performance is then experimentally proved with a DIC measuring a magnetoresistive sensor exposed to a magnetic field of different frequencies, amplitudes, and waveforms. A sinusoidal magnetic field up to 1 kHz can be monitored with a resolution of eight bits and a sampling frequency of around 10 kSa/s. If a higher resolution is desired, the sampling frequency has to be lower, thus limiting the bandwidth of the dynamic signal under measurement. The DIC is also applied to measure an electrocardiogram-type signal and its QRS complex is well identified, which enables the estimation, for instance, of the heart rate. PMID:28524078

  5. Measuring Dynamic Signals with Direct Sensor-to-Microcontroller Interfaces Applied to a Magnetoresistive Sensor.

    PubMed

    Sifuentes, Ernesto; Gonzalez-Landaeta, Rafael; Cota-Ruiz, Juan; Reverter, Ferran

    2017-05-18

    This paper evaluates the performance of direct interface circuits (DIC), where the sensor is directly connected to a microcontroller, when a resistive sensor subjected to dynamic changes is measured. The theoretical analysis provides guidelines for the selection of the components taking into account both the desired resolution and the bandwidth of the input signal. Such an analysis reveals that there is a trade-off between the sampling frequency and the resolution of the measurement, and this depends on the selected value of the capacitor that forms the RC circuit together with the sensor resistance. This performance is then experimentally proved with a DIC measuring a magnetoresistive sensor exposed to a magnetic field of different frequencies, amplitudes, and waveforms. A sinusoidal magnetic field up to 1 kHz can be monitored with a resolution of eight bits and a sampling frequency of around 10 kSa/s. If a higher resolution is desired, the sampling frequency has to be lower, thus limiting the bandwidth of the dynamic signal under measurement. The DIC is also applied to measure an electrocardiogram-type signal and its QRS complex is well identified, which enables the estimation, for instance, of the heart rate.

  6. Anisotropic Magnetoresistance of Nano-conductive Filament in Co/HfO2/Pt Resistive Switching Memory

    NASA Astrophysics Data System (ADS)

    Li, Leilei; Liu, Yang; Teng, Jiao; Long, Shibing; Guo, Qixun; Zhang, Meiyun; Wu, Yu; Yu, Guanghua; Liu, Qi; Lv, Hangbing; Liu, Ming

    2017-03-01

    Conductive bridge random access memory (CBRAM) has been extensively studied as a next-generation non-volatile memory. The conductive filament (CF) shows rich physical effects such as conductance quantization and magnetic effect. But so far, the study of filaments is not very sufficient. In this work, Co/HfO2/Pt CBRAM device with magnetic CF was designed and fabricated. By electrical manipulation with a partial-RESET method, we controlled the size of ferromagnetic metal filament. The resistance-temperature characteristics of the ON-state after various partial-RESET behaviors have been studied. Using two kinds of magnetic measurement methods, we measured the anisotropic magnetoresistance (AMR) of the CF at different temperatures to reflect the magnetic structure characteristics. By rotating the direction of the magnetic field and by sweeping the magnitude, we obtained the spatial direction as well as the easy-axis of the CF. The results indicate that the easy-axis of the CF is along the direction perpendicular to the top electrode plane. The maximum magnetoresistance was found to appear when the angle between the direction of magnetic field and that of the electric current in the CF is about 30°, and this angle varies slightly with temperature, indicating that the current is tilted.

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

    PubMed

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

    2017-10-01

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

  8. On-chip magnetic bead-based DNA melting curve analysis using a magnetoresistive sensor

    NASA Astrophysics Data System (ADS)

    Rizzi, Giovanni; Østerberg, Frederik W.; Henriksen, Anders D.; Dufva, Martin; Hansen, Mikkel F.

    2015-04-01

    We present real-time measurements of DNA melting curves in a chip-based system that detects the amount of surface-bound magnetic beads using magnetoresistive magnetic field sensors. The sensors detect the difference between the amount of beads bound to the top and bottom sensor branches of the differential sensor geometry. The sensor surfaces are functionalized with wild type (WT) and mutant type (MT) capture probes, differing by a single base insertion (a single nucleotide polymorphism, SNP). Complementary biotinylated targets in suspension couple streptavidin magnetic beads to the sensor surface. The beads are magnetized by the field arising from the bias current passed through the sensors. We demonstrate the first on-chip measurements of the melting of DNA hybrids upon a ramping of the temperature. This overcomes the limitation of using a single washing condition at constant temperature. Moreover, we demonstrate that a single sensor bridge can be used to genotype a SNP.

  9. Weak magnetic field superconductor resistive sensors in comparison with semiconductor and magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Ichkitidze, L. P.

    2007-09-01

    Weak magnetic field superconductor resistive sensors are fabricated and compared with various known types of the magnetoresistive and semiconductor sensors. The magnetically sensitive characteristics of the sensors are analyzed at room temperature and liquid-nitrogen temperature. Their resolution by the magnetic field δ B and by the magnetic flux δ ϕ are unsatisfactory, namely, δ B ⩾ 3 nT and δ ϕ ⩾ 10 ϕ0. Thick films of the ceramic HTS material of the composition Bi-2223 were fabricated, for which the magnetic sensitivity S ∼ 44 V/T, δ B ∼ 2 nT, and δ ϕ ∼ 3 ϕ0 are realized. It is shown that the value of S of the film increases significantly due to the size effect. This effect is taken into account, and the expected characteristics are presented, namely, S ⩾ 1000 V/T, δ B ⩽ 0.01 nT, δ ϕ ⩽ 0.002 ϕ0, and the dynamic measurement range ⩾150 dB.

  10. Giant Magnetoresistive Sensors and Magnetic Labels for Chip-Scale Detection of Immunosorbent Assays

    SciTech Connect

    Millen, Rachel Lora

    2005-01-01

    The combination of giant magnetoresistive sensors, magnetic labeling strategies, and biomolecule detection is just beginning to be explored. New readout methods and assay formats are necessary for biomolecules detection to flourish. The work presented in this dissertation describes steps toward the creation of a novel detection method for bioassays utilizing giant magnetoresistive sensors as the readout method. The introduction section contains a brief review of some of the current methods of bioassay readout. The theoretical underpinnings of the giant magnetoresistive effect are also discussed. Finally, the more prominent types of giant magnetoresistive sensors are described, as well as their complicated fabrication. Four data chapters follow the introduction; each chapter is presented as a separate manuscript, either already published or soon to be submitted. Chapter 1 presents research efforts toward the production of a bioassay on the surface of a gold-modified GMR sensor. The testing of this methodology involved the capture of goat a-mouse-coated magnetic nanoparticles on the mouse IgG-modified gold surface. The second, third and fourth chapters describe the utilization of a self-referenced sample stick for scanning across the GMR sensor. The sample stick consisted of alternating magnetic reference and bioactive gold addresses. Chapter 2 is concerned with the characterization of both the scanning readout method and the binding and detection of streptavidin-coated magnetic particles to a biotinylated surface. Chapter 3 advances the sample stick readout with the use of the system for detection of a sandwich immunoassay with rabbit IgG proteins. Finally, simultaneous detection of three IgG proteins is demonstrated in Chapter 4. The dissertation is concluded with a brief summary of the research presented and a discussion of the possible future applications and direction of this work.

  11. Two-dimensional salt and temperature DNA denaturation analysis using a magnetoresistive sensor.

    PubMed

    Rizzi, Giovanni; Dufva, Martin; Hansen, Mikkel Fougt

    2017-06-27

    We present a microfluidic system and its use to measure DNA denaturation curves by varying the temperature or salt (Na(+)) concentration. The readout is based on real-time measurements of DNA hybridization using magnetoresistive sensors and magnetic nanoparticles (MNPs) as labels. We report the first melting curves of DNA hybrids measured as a function of continuously decreasing salt concentration at fixed temperature and compare them to the corresponding curves obtained vs. temperature at fixed salt concentration. The magnetoresistive sensor platform provided reliable results under varying temperature as well as salt concentration. The salt concentration melting curves were found to be more reliable than temperature melting curves. We performed a two-dimensional mapping of the melting profiles of a target to probes targeting its wild type (WT) and mutant type (MT) variants in the temperature-salt concentration plane. This map clearly showed a region of optimum ability to differentiate between the two variants. We finally demonstrated single nucleotide polymorphysm (SNP) genotyping using both denaturation methods on both separate sensors but also using a differential measurement on a single sensor. The results demonstrate that concentration melting provides an attractive alternative to temperature melting in on-chip DNA denaturation experiments and further show that the magnetoresistive platform is attractive due to its low cross-sensitivity to temperature and liquid composition.

  12. Measuring brain activity with magnetoresistive sensors integrated in micromachined probe needles

    NASA Astrophysics Data System (ADS)

    Amaral, José; Gaspar, João; Pinto, Vitor; Costa, Tiago; Sousa, Nuno; Cardoso, Susana; Freitas, Paulo

    2013-05-01

    An alternative neuroscience tool for magnetic field detection is described in this work, providing both micrometer-scale spatial resolution and high sensitivity to detect the extremely small magnetic fields (nT range) induced by the ionic currents flowing within electrically active neurons. The system combines an array of magnetoresistive sensors incorporated on micro-machined Si probes capable of being inserted within the brain current sources. The Si-etch based micromachining process for neural probes is demonstrated in the manufacture of a probe with 15 magnetoresistive sensors in the tip of each shaft. The probe shafts are formed by double-sided deep reactive ion etching on a double-side polished silicon wafer. The shafts typically have the dimensions 1.2 mm × 40 μm × 300 μm and end in chisel-shaped tips with an incorporated magnetoresistive sensor with dimensions of 30 μm × 2 μm. An accompanying interconnect flexible cable is glued and wirebonded enabling precise and flexible positioning of the probes in the neural tissue. Our analyses showed sharply defined probes and probe tips. The electrical and magnetic behavior of the sensors was verified, and a preliminary test with brain slices were performed.

  13. Giant anisotropic magneto-resistance in the magnetic topological insulator Cry(Bi1-xSbx)2-yTe3

    NASA Astrophysics Data System (ADS)

    Kandala, Abhinav; Richardella, Anthony; Liu, Chaoxing; Samarth, Nitin

    2015-03-01

    We demonstrate magnetization control of edge state transport and report the observation of a gate-tunable giant anisotropic magneto-resistance (GAMR) effect in the magnetic topological insulator Cry(Bi1-xSbx)2-yTe3 as an external field (and the magnetization M) is rotated from out-of-plane (polar angle θ =0°) to in-plane (θ =90°). The angular dependence of the GAMR deviates from the standard cos2 ϕ form (where ϕ is the angle between M and the current density J), and is instead explained by a Landauer-Buttiker formalism that accounts for bulk-edge mixing. However, the rotation of the magnetization in-plane produces a weak, conventional AMR. These results serve as evidence for a field tilt-tuned crossover between an ``imperfect'' quantum anomalous Hall insulator (QAH) and a gapless, ferromagnetic topological insulator. We expect the GAMR to become stronger in the ideal QAH regime where edge state conduction dominates over bulk conduction, thus providing a route toward proof-of-concept ferromagnetic topological insulator transistors and magnetic field sensors. Funded by DARPA.

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

    SciTech Connect

    Phillips, L. C. Yan, W.; Kar-Narayan, S.; Mathur, N. D.; Lombardo, A.; Barbone, M.; Milana, S.; Ferrari, A. C.; Ghidini, M.

    2016-03-14

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

  15. Configurational Statistics of Magnetic Bead Detection with Magnetoresistive Sensors.

    PubMed

    Henriksen, Anders Dahl; Ley, Mikkel Wennemoes Hvitfeld; Flyvbjerg, Henrik; Hansen, Mikkel Fougt

    2015-01-01

    Magnetic biosensors detect magnetic beads that, mediated by a target, have bound to a functionalized area. This area is often larger than the area of the sensor. Both the sign and magnitude of the average magnetic field experienced by the sensor from a magnetic bead depends on the location of the bead relative to the sensor. Consequently, the signal from multiple beads also depends on their locations. Thus, a given coverage of the functionalized area with magnetic beads does not result in a given detector response, except on the average, over many realizations of the same coverage. We present a systematic theoretical analysis of how this location-dependence affects the sensor response. The analysis is done for beads magnetized by a homogeneous in-plane magnetic field. We determine the expected value and standard deviation of the sensor response for a given coverage, as well as the accuracy and precision with which the coverage can be determined from a single sensor measurement. We show that statistical fluctuations between samples may reduce the sensitivity and dynamic range of a sensor significantly when the functionalized area is larger than the sensor area. Hence, the statistics of sampling is essential to sensor design. For illustration, we analyze three important published cases for which statistical fluctuations are dominant, significant, and insignificant, respectively.

  16. Configurational Statistics of Magnetic Bead Detection with Magnetoresistive Sensors

    PubMed Central

    Henriksen, Anders Dahl; Ley, Mikkel Wennemoes Hvitfeld; Flyvbjerg, Henrik; Hansen, Mikkel Fougt

    2015-01-01

    Magnetic biosensors detect magnetic beads that, mediated by a target, have bound to a functionalized area. This area is often larger than the area of the sensor. Both the sign and magnitude of the average magnetic field experienced by the sensor from a magnetic bead depends on the location of the bead relative to the sensor. Consequently, the signal from multiple beads also depends on their locations. Thus, a given coverage of the functionalized area with magnetic beads does not result in a given detector response, except on the average, over many realizations of the same coverage. We present a systematic theoretical analysis of how this location-dependence affects the sensor response. The analysis is done for beads magnetized by a homogeneous in-plane magnetic field. We determine the expected value and standard deviation of the sensor response for a given coverage, as well as the accuracy and precision with which the coverage can be determined from a single sensor measurement. We show that statistical fluctuations between samples may reduce the sensitivity and dynamic range of a sensor significantly when the functionalized area is larger than the sensor area. Hence, the statistics of sampling is essential to sensor design. For illustration, we analyze three important published cases for which statistical fluctuations are dominant, significant, and insignificant, respectively. PMID:26496495

  17. Bead magnetorelaxometry with an on-chip magnetoresistive sensor.

    PubMed

    Dalslet, Bjarke Thomas; Damsgaard, Christian Danvad; Donolato, Marco; Strømme, Maria; Strömberg, Mattias; Svedlindh, Peter; Hansen, Mikkel Fougt

    2011-01-21

    Magnetorelaxometry measurements on suspensions of magnetic beads are demonstrated using a planar Hall effect sensor chip embedded in a microfluidic system. The alternating magnetic field used for magnetizing the beads is provided by the sensor bias current and the complex magnetic susceptibility spectra are recorded as the 2nd harmonic of the sensor response. The complex magnetic susceptibility signal appears when a magnetic bead suspension is injected, it scales with the bead concentration, and it follows the Cole-Cole expression for Brownian relaxation. The complex magnetic susceptibility signal resembles that from conventional magnetorelaxometry done on the same samples apart from an offset in Brownian relaxation frequency. The time dependence of the signal can be rationalized as originating from sedimented beads.

  18. Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing

    PubMed Central

    Reig, Candid; Cubells-Beltran, María-Dolores; Muñoz, Diego Ramírez

    2009-01-01

    The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications. PMID:22408486

  19. Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing.

    PubMed

    Reig, Candid; Cubells-Beltran, María-Dolores; Muñoz, Diego Ramírez

    2009-01-01

    The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

  20. Sign of the spin-polarization in cobalt-iron nitride films determined by the anisotropic magnetoresistance effect

    SciTech Connect

    Ito, Keita; Kabara, Kazuki; Tsunoda, Masakiyo; Sanai, Tatsunori; Toko, Kaoru; Suemasu, Takashi; Imai, Yoji

    2014-08-07

    We present the anisotropic magnetoresistance (AMR) properties in Fe{sub 4}N, Co{sub 3}FeN and Co{sub 4}N epitaxial thin films grown on SrTiO{sub 3}(001) substrates using molecular beam epitaxy. A negative AMR effect was observed in the Fe{sub 4}N and Co{sub 3}FeN films below 300 K. This behavior was attributed to the negative spin-polarizations of both the electrical conductivity and density of states at the Fermi level. The sign of the AMR ratio changed at ∼140 K in the Co{sub 4}N film and was negative below 140 K. Diffraction lines corresponding to the (100) plane were clearly observed in the ϕ-2θ{sub χ} (in-plane) x-ray diffraction patterns for the Fe{sub 4}N and Co{sub 3}FeN films but not for the Co{sub 4}N film. This indicated that nitrogen atoms were present at the body center of each unit cell in the Fe{sub 4}N and Co{sub 3}FeN films, whereas they were lacking in the Co{sub 4}N film. This assumption is discussed with energetic calculations using a spin density-functional theory.

  1. Development of a Magneto-Resistive Angular Position Sensor for Space Mechanisms

    NASA Technical Reports Server (NTRS)

    Hahn, Robert; Schmidt, Tilo; Seifart, Klaus; Olberts, Bastian; Romera, Fernando

    2016-01-01

    Magnetic microsystems in the form of magneto-resistive (MR) sensors are firmly established in automobiles and industrial applications. They are used to measure travel, angle, electrical current, or magnetic fields. MR technology opens up new sensor possibilities in space applications and can be an enabling technology for optimal performance, high robustness and long lifetime at reasonable costs. In some science missions, the technology is already applied, however, the designs are proprietary and case specific, for instance in case of the angular sensors used for JPL/NASA's Mars rover Curiosity [1]. Since 2013 HTS GmbH and Sensitec GmbH have teamed up to develop and qualify a standardized yet flexible to use MR angular sensor for space mechanisms. Starting with a first assessment study and market survey performed under ESA contract, a very strong industry interest in novel, contactless position measurement means was found. Currently a detailed and comprehensive development program is being performed by HTS and Sensitec. The objective of this program is to advance the sensor design up to Engineering Qualification Model level and to perform qualification testing for a representative space application. The paper briefly reviews the basics of magneto-resistive effects and possible sensor applications and describes the key benefits of MR angular sensors with reference to currently operational industrial and space applications. The key applications and specification are presented and the preliminary baseline mechanical and electrical design will be discussed. An outlook on the upcoming development and test stages as well as the qualification program will be provided.

  2. Exchange Bias Tuning for Magnetoresistive Sensors by Inclusion of Non-Magnetic Impurities.

    PubMed

    Sharma, Parikshit Pratim; Albisetti, Edoardo; Monticelli, Marco; Bertacco, Riccardo; Petti, Daniela

    2016-07-04

    The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top- and bottom-pinned systems, comprising 5 nm thick Co40Fe40B20 and 6.5 nm thick Ir22Mn78 films. By inserting Ru impurities at different concentrations in the Ir22Mn78 layer, blocking temperatures ranging from 220 °C to 100 °C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies.

  3. Report on demonstration project: imaging detection of unexploded ordinance using giant magnetoresistive sensor arrays

    SciTech Connect

    Chaiken, A., LLNL

    1996-09-01

    The goal of the project was to demonstrate the feasibility of the detection of buried unexploded ordnance (UXO) using giant magnetoresistive (GMR) sensor arrays. 3x3 and 5x5 arrays of off-the-shelf GMR sensors were purchased from Nonvolatile Electronics (NVE) and were interfaced with a data acquisition card and a personal computer. Magnetic images were obtained from a number of ferrous objects, such as threadstock, bolts, and rebar. These images can be interpreted in terms of the remanent magnetic state of the objects. The ability of the GMR sensor approach to discriminate among magnetic objects is assessed and the design of a more realistic UXO detection system is discussed.

  4. Exchange Bias Tuning for Magnetoresistive Sensors by Inclusion of Non-Magnetic Impurities

    PubMed Central

    Sharma, Parikshit Pratim; Albisetti, Edoardo; Monticelli, Marco; Bertacco, Riccardo; Petti, Daniela

    2016-01-01

    The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top- and bottom-pinned systems, comprising 5 nm thick Co40Fe40B20 and 6.5 nm thick Ir22Mn78 films. By inserting Ru impurities at different concentrations in the Ir22Mn78 layer, blocking temperatures ranging from 220 °C to 100 °C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies. PMID:27384565

  5. Nanoparticle-Structured Highly Sensitive and Anisotropic Gauge Sensors.

    PubMed

    Zhao, Wei; Luo, Jin; Shan, Shiyao; Lombardi, Jack P; Xu, Yvonne; Cartwright, Kelly; Lu, Susan; Poliks, Mark; Zhong, Chuan-Jian

    2015-09-16

    The ability to tune gauge factors in terms of magnitude and orientation is important for wearable and conformal electronics. Herein, a sensor device is described which is fabricated by assembling and printing molecularly linked thin films of gold nanoparticles on flexible microelectrodes with unusually high and anisotropic gauge factors. A sharp difference in gauge factors up to two to three orders of magnitude between bending perpendicular (B(⊥)) and parallel (B(||)) to the current flow directions is observed. The origin of the unusual high and anisotropic gauge factors is analyzed in terms of nanoparticle size, interparticle spacing, interparticle structure, and other parameters, and by considering the theoretical aspects of electron conduction mechanism and percolation pathway. A critical range of resistivity where a very small change in strain and the strain orientation is identified to impact the percolation pathway in a significant way, leading to the high and anisotropic gauge factors. The gauge anisotropy stems from molecular and nanoscale fine tuning of interparticle properties of molecularly linked nanoparticle assembly on flexible microelectrodes, which has important implication for the design of gauge sensors for highly sensitive detection of deformation in complex sensing environment or on complex curved surfaces such as wearable electronics and skin sensors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Development of Magneto-Resistive Angular Position Sensors for Space Applications

    NASA Astrophysics Data System (ADS)

    Hahn, Robert; Langendorf, Sven; Seifart, Klaus; Slatter, Rolf; Olberts, Bastian; Romera, Fernando

    2015-09-01

    Magnetic microsystems in the form of magneto- resistive (MR) sensors are firmly established in automobiles and industrial applications. They measure path, angle, electrical current, or magnetic fields. MR technology opens up new sensor possibilities in space applications and can be an enabling technology for optimal performance, high robustness and long lifetime at reasonable costs. In a recent assessment study performed by HTS GmbH and Sensitec GmbH under ESA Contract a market survey has confirmed that space industry has a very high interest in novel, contactless position sensors based on MR technology. Now, a detailed development stage is pursued, to advance the sensor design up to Engineering Qualification Model (EQM) level and to perform qualification testing for a representative pilot space application.The paper briefly reviews the basics of magneto- resistive effects and possible sensor applications and describes the key benefits of MR angular sensors with reference to currently operational industrial and space applications. The results of the assessment study are presented and potential applications and uses of contactless magneto-resistive angular sensors for spacecraft are identified. The baseline mechanical and electrical sensor design will be discussed. An outlook on the EQM development and qualification tests is provided.

  7. Anisotropic magnetoresistance of epitaxial Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} film

    SciTech Connect

    Chen, X. G.; Yang, Y. B.; Wang, C. S.; Liu, S. Q.; Zhang, Y.; Han, J. Z.; Yang, Y. C.; Yang, J. B.

    2014-01-28

    The magnetic field and temperature dependent anisotropic magnetoresistance (AMR) of the epitaxial grown Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} thin films was investigated. It was found that the magnetoresistance exhibited the characteristics of magnetic polaron hopping. A two-fold symmetric AMR occurred in the ferromagnetic region (∼220 K < T < ∼150 K), while a four-fold symmetric AMR appeared under a high magnetic field in the antiferromagnetic orbital ordered region (T < ∼150 K). The angular dependence of the resistance showed a hysteresis effect under magnetic field at low temperature. It is believed that these phenomena are attributed to the spin canting effect, which originates from the melting of orbital ordering under the external magnetic field in the antiferromagnetic region.

  8. Fabrication of micro accelerometer and magnetoresistive sensor directly on a ceramic substrate

    NASA Astrophysics Data System (ADS)

    Aoyagi, Seiji

    2012-06-01

    Micro-electro-mechanical systems (MEMS) sensors have movable parts: thus, it is difficult to handle them at fabrication because of the possibility of fracture. If a MEMS sensor could be fabricated not only on a silicon substrate but also on a ceramic substrate, which can be used for a package of the end product, the above-mentioned problem about handling would be solved, and its fabrication cost would be reduced. In this presentation, as demonstrations of the sensors directly fabricated on a ceramic package, an accelerometer and a magnetoresistive (MR) sensor are focused on. A micro accelerometer is proposed, which consists of a proof mass and ferroelectric substrate under it. A screen-printed barium titanate (BTO) film on an alumina substrate was employed as ferroelectrics. The sensitivity of the fabricated accelerometer was 0.1 pF g-1. A triaxis MR sensor is proposed, which detects not only x- and y-axes' magnetic field intensities but also that of the z-axis. Namely, not only azimuth but also angle of elevation of the sensor can be detected from triaxis components of the geomagnetic field. A permalloy (FeNi) plate is stood aside from the MR element. The plate distorts magnetic field and generates the x- (or y-) component from the originally z-directional field. A triaxis geomagnetic field was successfully detected by the fabricated sensor.

  9. Apparatus and method for imaging metallic objects using an array of giant magnetoresistive sensors

    DOEpatents

    Chaiken, Alison

    2000-01-01

    A portable, low-power, metallic object detector and method for providing an image of a detected metallic object. In one embodiment, the present portable low-power metallic object detector an array of giant magnetoresistive (GMR) sensors. The array of GMR sensors is adapted for detecting the presence of and compiling image data of a metallic object. In the embodiment, the array of GMR sensors is arranged in a checkerboard configuration such that axes of sensitivity of alternate GMR sensors are orthogonally oriented. An electronics portion is coupled to the array of GMR sensors. The electronics portion is adapted to receive and process the image data of the metallic object compiled by the array of GMR sensors. The embodiment also includes a display unit which is coupled to the electronics portion. The display unit is adapted to display a graphical representation of the metallic object detected by the array of GMR sensors. In so doing, a graphical representation of the detected metallic object is provided.

  10. Giant Magnetoresistance Sensors: A Review on Structures and Non-Destructive Eddy Current Testing Applications

    PubMed Central

    Rifai, Damhuji; Abdalla, Ahmed N.; Ali, Kharudin; Razali, Ramdan

    2016-01-01

    Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper. PMID:26927123

  11. Sensitivity and 3 dB Bandwidth in Single and Series-Connected Tunneling Magnetoresistive Sensors

    PubMed Central

    Dąbek, Michał; Wiśniowski, Piotr; Stobiecki, Tomasz; Wrona, Jerzy; Cardoso, Susana; Freitas, Paulo P.

    2016-01-01

    As single tunneling magnetoresistive (TMR) sensor performance in modern high-speed applications is limited by breakdown voltage and saturation of the sensitivity, for higher voltage applications (i.e., compatible to 1.8 V, 3.3 V or 5 V standards) practically only a series connection can be applied. Thus, in this study we focused on sensitivity, 3 dB bandwidth and sensitivity-bandwidth product (SBP) dependence on the DC bias voltage in single and series-connected TMR sensors. We show that, below breakdown voltage, the strong bias influence on sensitivity and the 3 dB frequency of a single sensor results in higher SBP than in a series connection. However, the sensitivity saturation limits the single sensor SBP which, under 1 V, reaches the same level of 2000 MHz∙V/T as in a series connection. Above the single sensor breakdown voltage, linear sensitivity dependence on the bias and the constant 3 dB bandwidth of the series connection enable increasing its SBP up to nearly 10,000 MHz∙V/T under 5 V. Thus, although by tuning bias voltage it is possible to control the sensitivity-bandwidth product, the choice between the single TMR sensor and the series connection is crucial for the optimal performance in the high frequency range. PMID:27809223

  12. Sensitivity and 3 dB Bandwidth in Single and Series-Connected Tunneling Magnetoresistive Sensors.

    PubMed

    Dąbek, Michał; Wiśniowski, Piotr; Stobiecki, Tomasz; Wrona, Jerzy; Cardoso, Susana; Freitas, Paulo P

    2016-10-31

    As single tunneling magnetoresistive (TMR) sensor performance in modern high-speed applications is limited by breakdown voltage and saturation of the sensitivity, for higher voltage applications (i.e., compatible to 1.8 V, 3.3 V or 5 V standards) practically only a series connection can be applied. Thus, in this study we focused on sensitivity, 3 dB bandwidth and sensitivity-bandwidth product (SBP) dependence on the DC bias voltage in single and series-connected TMR sensors. We show that, below breakdown voltage, the strong bias influence on sensitivity and the 3 dB frequency of a single sensor results in higher SBP than in a series connection. However, the sensitivity saturation limits the single sensor SBP which, under 1 V, reaches the same level of 2000 MHz∙V/T as in a series connection. Above the single sensor breakdown voltage, linear sensitivity dependence on the bias and the constant 3 dB bandwidth of the series connection enable increasing its SBP up to nearly 10,000 MHz∙V/T under 5 V. Thus, although by tuning bias voltage it is possible to control the sensitivity-bandwidth product, the choice between the single TMR sensor and the series connection is crucial for the optimal performance in the high frequency range.

  13. Conditions for efficient on-chip magnetic bead detection via magnetoresistive sensors.

    PubMed

    Albisetti, E; Petti, D; Cantoni, M; Damin, F; Torti, A; Chiari, M; Bertacco, R

    2013-09-15

    A commonly used figure of merit of magnetoresistive sensors employed to detect magnetic beads labeling biomolecules in lab-on-chip applications is the sensor sensitivity (S0) to external magnetic fields in the linear region of the sensor. In this paper we show that, in case of lock-in detection and bead excitation by a small AC magnetic field, S0 is not the good figure of merit to optimize. Indeed, the highest sensitivity to the magnetic beads is achieved biasing the sensor in the region of its characteristics where the product between the DC bias field and the second derivative of the resistance with respect to the magnetic field is maximum. The validity of this criterion, derived from a phenomenological model of bead detection, is proved in case of magnetic tunneling junction sensors detecting magnetic beads with 250nm diameter. This work paves the way to the development of a new generation of sensors properly designed to maximize the bead sensitivity.

  14. Giant Magnetoresistance Sensors: A Review on Structures and Non-Destructive Eddy Current Testing Applications.

    PubMed

    Rifai, Damhuji; Abdalla, Ahmed N; Ali, Kharudin; Razali, Ramdan

    2016-02-26

    Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper.

  15. An efficient biosensor made of an electromagnetic trap and a magneto-resistive sensor.

    PubMed

    Li, Fuquan; Kosel, Jürgen

    2014-09-15

    Magneto-resistive biosensors have been found to be useful because of their high sensitivity, low cost, small size, and direct electrical output. They use super-paramagnetic beads to label a biological target and detect it via sensing the stray field. In this paper, we report a new setup for magnetic biosensors, replacing the conventional "sandwich" concept with an electromagnetic trap. We demonstrate the capability of the biosensor in the detection of E. coli. The trap is formed by a current-carrying microwire that attracts the magnetic beads into a sensing space on top of a tunnel magneto-resistive sensor. The sensor signal depends on the number of beads in the sensing space, which depends on the size of the beads. This enables the detection of biological targets, because such targets increase the volume of the beads. Experiments were carried out with a 6 µm wide microwire, which attracted the magnetic beads from a distance of 60 μm, when a current of 30 mA was applied. A sensing space of 30 µm in length and 6 µm in width was defined by the magnetic sensor. The results showed that individual E. coli bacterium inside the sensing space could be detected using super-paramagnetic beads that are 2.8 µm in diameter. The electromagnetic trap setup greatly simplifies the device and reduces the detection process to two steps: (i) mixing the bacteria with magnetic beads and (ii) applying the sample solution to the sensor for measurement, which can be accomplished within about 30 min with a sample volume in the µl range. This setup also ensures that the biosensor can be cleaned easily and re-used immediately. The presented setup is readily integrated on chips via standard microfabrication techniques. Copyright © 2014 Elsevier B.V. All rights reserved.

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

    SciTech Connect

    Brandl, F.; Grundler, D.

    2014-04-28

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

  17. In-plane tunneling anisotropic magnetoresistance in (Ga,Mn)As/GaAs Esaki diodes in the regime of the excess current

    SciTech Connect

    Shiogai, J.; Ciorga, M. Utz, M.; Schuh, D.; Bougeard, D.; Weiss, D.; Kohda, M.; Nitta, J.; Nojima, T.

    2015-06-29

    We investigate the angular dependence of the tunneling anisotropic magnetoresistance in (Ga,Mn)As/n-GaAs spin Esaki diodes in the regime where the tunneling process is dominated by the excess current through midgap states in (Ga,Mn)As. We compare it to similar measurements performed in the regime of band-to-band tunneling. Whereas the latter show biaxial symmetry typical for magnetic anisotropy observed in (Ga,Mn)As samples, the former is dominated by uniaxial anisotropy along the 〈110〉 axes.

  18. A Current Sensor Based on the Giant Magnetoresistance Effect: Design and Potential Smart Grid Applications

    PubMed Central

    Ouyang, Yong; He, Jinliang; Hu, Jun; Wang, Shan X.

    2012-01-01

    Advanced sensing and measurement techniques are key technologies to realize a smart grid. The giant magnetoresistance (GMR) effect has revolutionized the fields of data storage and magnetic measurement. In this work, a design of a GMR current sensor based on a commercial analog GMR chip for applications in a smart grid is presented and discussed. Static, dynamic and thermal properties of the sensor were characterized. The characterizations showed that in the operation range from 0 to ±5 A, the sensor had a sensitivity of 28 mV·A−1, linearity of 99.97%, maximum deviation of 2.717%, frequency response of −1.5 dB at 10 kHz current measurement, and maximum change of the amplitude response of 0.0335%·°C−1 with thermal compensation. In the distributed real-time measurement and monitoring of a smart grid system, the GMR current sensor shows excellent performance and is cost effective, making it suitable for applications such as steady-state and transient-state monitoring. With the advantages of having a high sensitivity, high linearity, small volume, low cost, and simple structure, the GMR current sensor is promising for the measurement and monitoring of smart grids. PMID:23202221

  19. A current sensor based on the giant magnetoresistance effect: design and potential smart grid applications.

    PubMed

    Ouyang, Yong; He, Jinliang; Hu, Jun; Wang, Shan X

    2012-11-09

    Advanced sensing and measurement techniques are key technologies to realize a smart grid. The giant magnetoresistance (GMR) effect has revolutionized the fields of data storage and magnetic measurement. In this work, a design of a GMR current sensor based on a commercial analog GMR chip for applications in a smart grid is presented and discussed. Static, dynamic and thermal properties of the sensor were characterized. The characterizations showed that in the operation range from 0 to ±5 A, the sensor had a sensitivity of 28 mV·A(-1), linearity of 99.97%, maximum deviation of 2.717%, frequency response of −1.5 dB at 10 kHz current measurement, and maximum change of the amplitude response of 0.0335%·°C(-1) with thermal compensation. In the distributed real-time measurement and monitoring of a smart grid system, the GMR current sensor shows excellent performance and is cost effective, making it suitable for applications such as steady-state and transient-state monitoring. With the advantages of having a high sensitivity, high linearity, small volume, low cost, and simple structure, the GMR current sensor is promising for the measurement and monitoring of smart grids.

  20. Current dependence of colossal anisotropic magnetoresistance in La 0.3 Pr 0.4 Ca 0.3 MnO 3 microbridges

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    The effect of the bias current on the in-plane colossal anisotropic magnetoresistance (C-AMR) is investigated in spatially confined La 0.3 Pr 0.4 Ca 0.3 MnO 3 microbridges. Dramatic increases of the C-AMR are found when the bias current is reduced. For example, in one of the samples, the C-AMR changed from ˜900% to over ˜24 000% as the current is decreased from 1 μA to 10 nA. The results indicate that the bias current can be used to manipulate the C-AMR in spatially confined manganite thin films via changes to the nature of the anisotropic percolation within the samples.

  1. Thermal magnetoresistance of potassium

    NASA Astrophysics Data System (ADS)

    Huberman, M. L.

    1988-11-01

    It has recently been shown that an inhomogeneous, anisotropic Hall coefficient, arising from a charge-density-wave domain structure, explains the nonsaturating electrical magnetoresistance of potassium. It is shown here that the same mechanism also explains the observed behavior of the thermal magnetoresistance. The transverse thermal magnetoresistance of a domain structure increases with increasing field, having both a linear and quadratic component. The longitudinal thermal magnetoresistance of a domain structure initially increases linearly with increasing field. Its behavior in higher fields, however, depends on whether or not the domain distribution is symmetric about the field direction. If the distribution is symmetric, saturation occurs; otherwise, a residual increase is possible.

  2. Magnetoresistance sensitivity mapping of the localized response of contiguous and lead-overlaid sensors

    NASA Astrophysics Data System (ADS)

    Sankar, Sandra

    2003-06-01

    Magnetoresistance sensitivity mapping (MSM) was used to investigate the local response of magnetic recording sensors without convolution of the writer, magnetic media and data channel. From a 2D map of the local sensor response, the intrinsic pulse shape and magnetic track profile are readily obtained. Pulse-width is a concern for high data rate since if pulse-width is too broad, individual transitions become difficult to distinguish. Track profiles are important because due to the small difference between magnetic write-width and magnetic read-width, side reading will lead to an increase in noise. Three experiments are discussed: the dependence of the pulse-width (PW50) of the standard contiguous junction (CJ) design on shield-to-shield spacing; a comparison of the pulse shape of lead-overlaid (LOL) and CJ designs; and a comparison of the magnetic track profile (including track-width and skirt ratio) of LOL and CJ designs. The LOL design offers an increased sensitivity; however, as seen from MSM, the penalties are broadening of the track and pulse profiles. These are a direct result of the finite current in the lead overlay region and an increased shield-to-shield spacing in that region. The MSM image shows a curvature, which is associated with the topography of the top shield due to the lead overlay.

  3. Magnetoresistive sensors for measurements of DNA hybridization kinetics – effect of TINA modifications

    PubMed Central

    Rizzi, G.; Dufva, M.; Hansen, M. F.

    2017-01-01

    We present the use of magnetoresistive sensors integrated in a microfluidic system for real-time studies of the hybridization kinetics of DNA labeled with magnetic nanoparticles to an array of surface-tethered probes. The nanoparticles were magnetized by the magnetic field from the sensor current. A local negative reference ensured that only the specific binding signal was measured. Analysis of the real-time hybridization using a two-compartment model yielded both the association and dissociation constants kon, and koff. The effect of probe modifications with ortho-Twisted Intercalating Nucleic Acid (TINA) was studied. Such modifications have been demonstrated to increase the melting temperature of DNA hybrids in solution and are also relevant for surface-based DNA sensing. Kinetic data for DNA probes with no TINA modification or with TINA modifications at the 5′ end (1 × TINA) or at both the 5′ and 3′ ends (2 × TINA) were compared. TINA modifications were found to provide a relative decrease of koff by a factor of 6-20 at temperatures from 57.5 °C to 60 °C. The values of kon were generally in the range between 0.5-2 × 105 M−1s−1 and showed lower values for the unmodified probe than for the TINA modified probes. The observations correlated well with measured melting temperatures of the DNA hybrids. PMID:28167835

  4. A high-resolution tunneling magneto-resistance sensor interface circuit

    NASA Astrophysics Data System (ADS)

    Li, Xiangyu; Yin, Liang; Chen, Weiping; Gao, Zhiqiang; Liu, Xiaowei

    2017-02-01

    In this paper, a chopper instrumentation amplifier and a high-precision and low-noise CMOS band gap reference in a standard 0.5 μm CMOS technology for a tunneling magneto-resistance (TMR) sensor is presented. The noise characteristic of TMR sensor is an important factor in determining the performance of the sensor. In order to obtain a larger signal to noise ratio (SNR), the analog front-end chip ASIC weak signal readout circuit of the sensor includes the chopper instrumentation amplifier; the high-precision and low-noise CMOS band gap reference. In order to achieve the low noise, the chopping technique is applied in the first stage amplifier. The low-frequency flicker noise is modulated to high-frequency by chopping switch, so that the modulator has a better noise suppression performance at the low frequency. The test results of interface circuit are shown as below: At a single 5 V supply, the power dissipation is 40 mW; the equivalent offset voltage is less than 10 uV; the equivalent input noise spectral density 30 nV/Hz1/2(@10 Hz), the equivalent input noise density of magnetic is 0.03 nTHz1/2(@10 Hz); the scale factor temperature coefficient is less than 10 ppm/∘C, the equivalent input offset temperature coefficient is less than 70 nV/∘C; the gain error is less than 0.05%, the common mode rejection ratio is greater than 120 dB, the power supply rejection ratio is greater than 115 dB; the nonlinear is 0.1% FS.

  5. A non-invasive thermal drift compensation technique applied to a spin-valve magnetoresistive current sensor.

    PubMed

    Sánchez Moreno, Jaime; Ramírez Muñoz, Diego; Cardoso, Susana; Casans Berga, Silvia; Navarro Antón, Asunción Edith; Peixeiro de Freitas, Paulo Jorge

    2011-01-01

    A compensation method for the sensitivity drift of a magnetoresistive (MR) Wheatstone bridge current sensor is proposed. The technique was carried out by placing a ruthenium temperature sensor and the MR sensor to be compensated inside a generalized impedance converter circuit (GIC). No internal modification of the sensor bridge arms is required so that the circuit is capable of compensating practical industrial sensors. The method is based on the temperature modulation of the current supplied to the bridge, which improves previous solutions based on constant current compensation. Experimental results are shown using a microfabricated spin-valve MR current sensor. The temperature compensation has been solved in the interval from 0 °C to 70 °C measuring currents from -10 A to +10 A.

  6. Magnetic properties and anisotropic magnetoresistance of antiperovskite nitride Mn{sub 3}GaN/Co{sub 3}FeN exchange-coupled bilayers

    SciTech Connect

    Sakakibara, H. Ando, H.; Kuroki, Y.; Kawai, S.; Ueda, K.; Asano, H.

    2015-05-07

    Epitaxial bilayers of antiferromagnetic Mn{sub 3}GaN/ferromagnetic Co{sub 3}FeN with an antiperovskite structure were grown by reactive magnetron sputtering, and their structural, magnetic, and electrical properties were investigated. Exchange coupling with an exchange field H{sub ex} of 0.4 kOe at 4 K was observed for Mn{sub 3}GaN (20 nm)/Co{sub 3}FeN (5 nm) bilayers. Negative anisotropic magnetoresistance (AMR) effect in Co{sub 3}FeN was observed and utilized to detect magnetization reversal in exchange-coupled Mn{sub 3}GaN/Co{sub 3}FeN bilayers. The AMR results showed evidence for current-induced spin transfer torque in antiferromagnetic Mn{sub 3}GaN.

  7. The Front-End Readout as an Encoder IC for Magneto-Resistive Linear Scale Sensors

    PubMed Central

    Tran, Trong-Hieu; Chao, Paul Chang-Po; Chien, Ping-Chieh

    2016-01-01

    This study proposes a front-end readout circuit as an encoder chip for magneto-resistance (MR) linear scales. A typical MR sensor consists of two major parts: one is its base structure, also called the magnetic scale, which is embedded with multiple grid MR electrodes, while another is an “MR reader” stage with magnets inside and moving on the rails of the base. As the stage is in motion, the magnetic interaction between the moving stage and the base causes the variation of the magneto-resistances of the grid electrodes. In this study, a front-end readout IC chip is successfully designed and realized to acquire temporally-varying resistances in electrical signals as the stage is in motions. The acquired signals are in fact sinusoids and co-sinusoids, which are further deciphered by the front-end readout circuit via newly-designed programmable gain amplifiers (PGAs) and analog-to-digital converters (ADCs). The PGA is particularly designed to amplify the signals up to full dynamic ranges and up to 1 MHz. A 12-bit successive approximation register (SAR) ADC for analog-to-digital conversion is designed with linearity performance of ±1 in the least significant bit (LSB) over the input range of 0.5–2.5 V from peak to peak. The chip was fabricated by the Taiwan Semiconductor Manufacturing Company (TSMC) 0.35-micron complementary metal oxide semiconductor (CMOS) technology for verification with a chip size of 6.61 mm2, while the power consumption is 56 mW from a 5-V power supply. The measured integral non-linearity (INL) is −0.79–0.95 LSB while the differential non-linearity (DNL) is −0.68–0.72 LSB. The effective number of bits (ENOB) of the designed ADC is validated as 10.86 for converting the input analog signal to digital counterparts. Experimental validation was conducted. A digital decoder is orchestrated to decipher the harmonic outputs from the ADC via interpolation to the position of the moving stage. It was found that the displacement measurement

  8. The Front-End Readout as an Encoder IC for Magneto-Resistive Linear Scale Sensors.

    PubMed

    Tran, Trong-Hieu; Chao, Paul Chang-Po; Chien, Ping-Chieh

    2016-09-02

    This study proposes a front-end readout circuit as an encoder chip for magneto-resistance (MR) linear scales. A typical MR sensor consists of two major parts: one is its base structure, also called the magnetic scale, which is embedded with multiple grid MR electrodes, while another is an "MR reader" stage with magnets inside and moving on the rails of the base. As the stage is in motion, the magnetic interaction between the moving stage and the base causes the variation of the magneto-resistances of the grid electrodes. In this study, a front-end readout IC chip is successfully designed and realized to acquire temporally-varying resistances in electrical signals as the stage is in motions. The acquired signals are in fact sinusoids and co-sinusoids, which are further deciphered by the front-end readout circuit via newly-designed programmable gain amplifiers (PGAs) and analog-to-digital converters (ADCs). The PGA is particularly designed to amplify the signals up to full dynamic ranges and up to 1 MHz. A 12-bit successive approximation register (SAR) ADC for analog-to-digital conversion is designed with linearity performance of ±1 in the least significant bit (LSB) over the input range of 0.5-2.5 V from peak to peak. The chip was fabricated by the Taiwan Semiconductor Manufacturing Company (TSMC) 0.35-micron complementary metal oxide semiconductor (CMOS) technology for verification with a chip size of 6.61 mm², while the power consumption is 56 mW from a 5-V power supply. The measured integral non-linearity (INL) is -0.79-0.95 LSB while the differential non-linearity (DNL) is -0.68-0.72 LSB. The effective number of bits (ENOB) of the designed ADC is validated as 10.86 for converting the input analog signal to digital counterparts. Experimental validation was conducted. A digital decoder is orchestrated to decipher the harmonic outputs from the ADC via interpolation to the position of the moving stage. It was found that the displacement measurement error is within

  9. Anisotropic magnetoresistance and planar Hall effect in La2/3Ca1/3MnO3 thin films with misfit strain

    NASA Astrophysics Data System (ADS)

    Li, J.; Wang, S. G.; Zhang, Y.; Cui, L. M.; Jin, Y. R.; Deng, H.; Zheng, D. N.; Zimmers, A.; Aubin, H.; Lang, P. L.

    2013-02-01

    In our previous study anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) of epitaxial La2/3Ca1/3MnO3 (LCMO) thin films grown on SrTiO3(001) (STO) substrates were studied, and a phenomenological model in the high field limit was developed based on the 4/mmm point group. The derived longitudinal resistivity includes a four-fold as well as a two-fold symmetry term of the in-plane field angle, which can fit the experimental results well. In this study, to highlight the effects of misfit strain, AMR and PHE of LCMO thin films epitaxially grown on LaAlO3(001) substrates were studied, along either the [110] or the [100] direction. Both values are around a few percent, comparable to those measured in films on STO. Nevertheless, only tiny four-fold oscillations appear below the metal-insulator transition temperature Tp along the [110] direction, in contrast to the case of STO, where the four-fold term is prominent. The relationship between this four-fold symmetry and the misfit strain is then discussed in terms of the partial recovery of orbital magnetic moment. The mechanism for AMR and PHE in manganites then can be understood as an anisotropic percolation at metal-insulator transition resulting in the peak, and the spin-orbital coupling effect that accounts for the remnant far below Tp.

  10. Slow Oscillations of In-plane Magnetoresistance in Strongly Anisotropic Quasi-Two-Dimensional Rare-Earth Tritellurides

    NASA Astrophysics Data System (ADS)

    Sinchenko, A. A.; Grigoriev, P. D.; Monceau, P.; Lejay, P.; Zverev, V. N.

    2016-12-01

    The slow oscillations of intralayer magnetoresistance in the quasi-2D metallic compounds TbTe_3 and GdTe_3 have been observed for the first time. These oscillations do not originate from small Fermi-surface pockets, as revealed usually by Shubnikov-de Haas oscillations, but from the entanglement of close frequencies due to a finite interlayer transfer integral t_z, either between the two Te planes forming a bilayer or between two adjacent bilayers, which allows to estimate its values. For TbTe_3 and GdTe_3, we obtain the estimate t_ z≈ 1 meV.

  11. Giant magnetoresistive sensor array for sensitive and specific multiplexed food allergen detection.

    PubMed

    Ng, Elaine; Nadeau, Kari C; Wang, Shan X

    2016-06-15

    Current common allergen detection methods, including enzyme-linked immunosorbent assays (ELISAs) and dip-stick methods, do not provide adequate levels of sensitivity and specificity for at-risk allergic patients. A method for performing highly sensitive and specific detection of multiple food allergens is thus imperative as food allergies are becoming increasingly recognized as a major healthcare concern, affecting an estimated 4% of the total population. We demonstrate first instance of sensitive and specific multiplexed detection of major peanut allergens Ara h 1 and Ara h 2, and wheat allergen Gliadin using giant magnetoresistive (GMR) sensor arrays. Commercialized ELISA kits for Ara h 1 and Ara h 2 report limits of detection (LODs) at 31.5 ng/mL and 0.2 ng/mL, respectively. In addition, the 96-well-based ELISA developed in-house for Gliadin was found to have a LOD of 40 ng/mL. Our multiplexed GMR-based assay demonstrates the ability to perform all three assays on the same chip specifically and with sensitivities at LODs about an order of magnitude lower than those of 96-well-based ELISAs. LODs of GMR-based assays developed for Ara h 1, Ara h 2, and Gliadin were 7.0 ng/mL, 0.2 ng/mL, and 1.5 ng/mL, respectively, with little to no cross-reactivity. These LODs are clinically important as some patients could react strongly against such low allergen levels. Given the limitations of current industrial detection technology, multiplexed GMR-based assays provide a method for highly sensitive and specific simultaneous detection of any combination of food-product allergens, thus protecting allergic patients from life-threatening events, including anaphylaxis, by unintentional consumption.

  12. On the development of a magnetoresistive sensor for blade tip timing and blade tip clearance measurement systems

    NASA Astrophysics Data System (ADS)

    Tomassini, R.; Rossi, G.; Brouckaert, J.-F.

    2016-10-01

    A simultaneous blade tip timing (BTT) and blade tip clearance (BTC) measurement system enables the determination of turbomachinery blade vibrations and ensures the monitoring of the existing running gaps between the blade tip and the casing. This contactless instrumentation presents several advantages compared to the well-known telemetry system with strain gauges, at the cost of a more complex data processing procedure. The probes used can be optical, capacitive, eddy current as well as microwaves, everyone with its dedicated electronics and many existing different signal processing algorithms. Every company working in this field has developed its own processing method and sensor technology. Hence, repeating the same test with different instrumentations, the answer is often different. Moreover, rarely it is possible to achieve reliability for in-service measurements. Developments are focused on innovative instrumentations and a common standard. This paper focuses on the results achieved using a novel magnetoresistive sensor for simultaneous tip timing and tip clearance measurements. The sensor measurement principle is described. The sensitivity to gap variation is investigated. In terms of measurement of vibrations, experimental investigations were performed at the Air Force Institute of Technology (ITWL, Warsaw, Poland) in a real aeroengine and in the von Karman Institute (VKI) R2 compressor rig. The advantages and limitations of the magnetoresistive probe for turbomachinery testing are highlighted.

  13. On the development of a magnetoresistive sensor for blade tip timing and blade tip clearance measurement systems.

    PubMed

    Tomassini, R; Rossi, G; Brouckaert, J-F

    2016-10-01

    A simultaneous blade tip timing (BTT) and blade tip clearance (BTC) measurement system enables the determination of turbomachinery blade vibrations and ensures the monitoring of the existing running gaps between the blade tip and the casing. This contactless instrumentation presents several advantages compared to the well-known telemetry system with strain gauges, at the cost of a more complex data processing procedure. The probes used can be optical, capacitive, eddy current as well as microwaves, everyone with its dedicated electronics and many existing different signal processing algorithms. Every company working in this field has developed its own processing method and sensor technology. Hence, repeating the same test with different instrumentations, the answer is often different. Moreover, rarely it is possible to achieve reliability for in-service measurements. Developments are focused on innovative instrumentations and a common standard. This paper focuses on the results achieved using a novel magnetoresistive sensor for simultaneous tip timing and tip clearance measurements. The sensor measurement principle is described. The sensitivity to gap variation is investigated. In terms of measurement of vibrations, experimental investigations were performed at the Air Force Institute of Technology (ITWL, Warsaw, Poland) in a real aeroengine and in the von Karman Institute (VKI) R2 compressor rig. The advantages and limitations of the magnetoresistive probe for turbomachinery testing are highlighted.

  14. On the development of a magnetoresistive sensor for blade tip timing and blade tip clearance measurement systems

    NASA Astrophysics Data System (ADS)

    Tomassini, R.; Rossi, G.; Brouckaert, J.-F.

    2014-05-01

    The accurate control of the gap between static and rotating components is vital to preserve the mechanical integrity and ensure a correct functioning of any rotating machinery. Moreover, tip leakage above the airfoil tip results in relevant aerodynamic losses. One way to measure and to monitor blade tip gaps is by the so-called Blade Tip Clearance (BTC) technique. Another fundamental phenomenon to control in the turbomachines is the vibration of the blades. For more than half a century, this has been performed by installing strain gauges on the blades and using telemetry to transmit the signals. The Blade Tip Timing (BTT) technique, (i.e. measuring the blade time of arrival from the casing at different angular locations with proximity sensors) is currently being adopted by all manufacturers as a replacement for the classical strain gauge technique because of its non-intrusive character. This paper presents a novel magnetoresistive sensor for blade tip timing and blade tip clearance systems, which offers high temporal and high spatial resolution simultaneously. The sensing element adopted is a Wheatstone bridge of Permalloy elements. The principle of the sensor is based on the variation of magnetic field at the passage of ferromagnetic objects. Two different configurations have been realized, a digital and an analogue sensor. Measurements of tip clearance have been performed in an high speed compressor and the calibration curve is reported. Measurements of blade vibration have been carried out in a dedicated calibration bench; results are presented and discussed. The magnetoresistive sensor is characterized by high repeatability, low manufacturing costs and measurement accuracy in line with the main probes used in turbomachinery testing. The novel sensor has great potential and is capable of fulfilling the requirements for a simultaneous BTC and BTT measurement system.

  15. Ultra-Sensitive Magnetoresistive Displacement Sensing Device

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  16. Angle dependence on the anisotropic magnetoresistance amplitude of a single-contacted Ni nanowire subjected to a thermo-mechanical strain

    NASA Astrophysics Data System (ADS)

    Melilli, G.; Madon, B.; Wegrowe, J.-E.; Clochard, M.-C.

    2015-12-01

    The effects of thermoelastic and piezoelectric strain of an active track-etched β-PVDF polymer matrix on an electrodeposited single-contacted Ni nanowire (NW) are investigated at the nanoscale by measuring the change of magnetization (i.e. using the inverse magnetostriction effect). The magnetization state is measured locally by anisotropic magnetoresistance (AMR). The ferromagnetic NW plays thus the role of a mechanical probe that allows the effects of mechanical strain to be characterized and described qualitatively and quantitatively. The inverse magnetostriction was found to be responsible for a quasi-disappearance of the AMR signal for a variation of the order of ΔT ≈ 10 K. In other terms, the variation of the magnetization due to the stress compensates the effect of external magnetic field applied on the NW resistance. The induced stress field in a single Ni NW was found 1000 time higher than the bulk stress field (due to thermal expansion measured on the PVDF). This amplification could be attributed to three nanoscopic effects: (1) a stress mismatch between the Ni NW and the membrane, (2) a non-negligible role of the surface tension on Ni NW Young modulus, and (3) the possibility of non-linear stress-strain law. We investigate here the role of these different contributions using track-etched polymer membranes irradiated at various angles (αirrad) leading to, after electrodeposition, embedded Ni NWs of different orientations.

  17. Determination of magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film by anisotropic magnetoresistance.

    PubMed

    Hu, Bo; He, Wei; Ye, Jun; Tang, Jin; Zhang, Yong-Sheng; Ahmad, Syed Sheraz; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2015-09-15

    It is challenging to determine domain wall pinning energy and magnetic anisotropy since both coherent rotation and domain wall displacement coexist during magnetization switching process. Here, angular dependence anisotropic magnetoresistance (AMR) measurements at different magnetic fields were employed to determine magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film. The AMR curves at magnetic fields which are high enough to ensure the coherent rotation of magnetization indicate a smooth behavior without hysteresis between clockwise (CW) and counter-clockwise (CCW) rotations. By analyzing magnetic torque, the magnetic anisotropy constants can be obtained. On the other hand, the AMR curves at low fields show abrupt transitions with hysteresis between CW and CCW rotations, suggesting the presence of multi-domain structures. The domain wall pinning energy can be obtained by analyzing different behaviors of AMR. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of magnetic anisotropy and domain wall pinning energy, which is still a critical issue for spintronics.

  18. Anisotropic magneto-resistance of 2D holes in GaAs/Al_xGa_1-xAs heterostructure under in-plane magnetic field

    NASA Astrophysics Data System (ADS)

    Noh, H.; Tsui, D. C.; Shayegan, M.; Yoon, Jongsoo

    2000-03-01

    We report on measurements of anisotropic in-plane magneto-resistance of the 2D hole system (2DHS) in a GaAs/AlGaAs (311)A heterostructure, which exhibits both zero-field and in-plane field induced metal-insulator transitions. For high hole densities, when the direction of B field is changed relative to the current(I), which is always kept in the high mobility direction, the resistivity with B allel I is larger at low field, while the resistivity with B ⊥ I becomes larger at high field. This behavior is consistent with recent measurements(S. J. Papadakis et al.), cond-mat/9911239. on a quantum well system. That the resistivity at high field is larger for B ⊥ I than for B allel I is also consistent with a recent theoretical argument(S. Das Sarma and E. H. Hwang, cond-mat/9909452.), though the difference is smaller than that from the theory. As the density is lowered, the resistivity with B allel I gets larger at high field, and it eventually becomes greater than that with B ⊥ I at all field ranges measured. This change in anisotropy has not been seen in previous measurements. The critical field B_c, beyond which the metallic phase becomes insulating, is also different for two different directions of B, while the change in I-V characteristics across Bc remains the same.

  19. Longitudinal magnetoresistance of potassium

    NASA Astrophysics Data System (ADS)

    Huberman, M. L.

    1987-06-01

    Recently, Zhu and Overhauser showed that the Hall coefficient of potassium is anisotropic, depending on the angle between the applied magnetic field and the charge-density wave. It follows that the Hall coefficient of a polydomain sample is inhomogeneous. By means of effective-medium theory, the magnetoresistance of a domain structure has been evaluated. It is shown that both the longitudinal and transverse magnetoresistance increase with increasing field. The Kohler slope depends on the domain distribution. For a random distribution, the longitudinal and transverse Kohler slopes are about (1/2)% and 1(1/2)%, respectively.

  20. Negative anisotropic magnetoresistance resulting from minority spin transport in NixFe4-xN (x = 1 and 3) epitaxial films

    NASA Astrophysics Data System (ADS)

    Takata, Fumiya; Kabara, Kazuki; Ito, Keita; Tsunoda, Masakiyo; Suemasu, Takashi

    2017-01-01

    We grew 50 nm-thick NixFe4-xN (x = 1 and 3) epitaxial films on a SrTiO3(001) single-crystal substrate by molecular beam epitaxy and measured their anisotropic magnetoresistance (AMR) ratios rAMR in the temperature range of 5-300 K with current directions set along either NixFe4-xN [100] or [110]. A negative rAMR was obtained up to 200 K or higher. Their magnitude | rAMR | increased with decreasing temperature. From the negative AMR effect and the negative spin-polarization of density of states for NixFe4-xN at the Fermi level, it can be stated that the minority spin transport is dominant in NixFe4-xN, similar to Fe4N and Co3FeN. The rAMR depends on the current direction that arises from the current direction dependence of s-d scattering. In the case of Ni3FeN, the rAMR decreased to nearly zero at 260 K. This temperature agreed well with the Curie temperature determined from the temperature dependence of magnetization. The AMR curves were reproduced well by using both cos2ϕ and cos4ϕ components below 100 K, whereas a cos2ϕ component was enough to fit those obtained above 100 K. It is assumed that the tetragonal crystal field was enhanced at low temperatures (<100 K) similar to Fe4N (<50 K).

  1. A phenomenological approach to the anisotropic magnetoresistance and planar Hall effect in tetragonal La(2/3)Ca(1/3)MnO3 thin films.

    PubMed

    Li, J; Li, S L; Wu, Z W; Li, S; Chu, H F; Wang, J; Zhang, Y; Tian, H Y; Zheng, D N

    2010-04-14

    A La(2/3)Ca(1/3)MnO(3) Hall bar with its long dimension roughly along the hard axis [110] was fabricated on a single-crystal-like tensilely strained film on SrTiO(3)(001). The anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) have been studied at various external magnetic fields and temperatures. A phenomenological model in the high field limit is developed, and the galvanomagnetic tensor based on a tetragonal symmetry 4/mmm (D(4h)), applicable to epitaxial films on a substrate, has been obtained by expanding the tensor to the sixth order. The derived in-plane transverse resistance R(xy) shows a sin2φ(M) angular dependence, while the longitudinal R(xx) is constituted by not only a two-fold cos2φ(M) term, but also a four-fold cos4φ(M) term due to the square symmetry of the lattice. The model is in good agreement with the experimental results in high fields, while deviations are observed near the {100} easy axis with the decreasing field. Close inspection of the fitting parameters reveals the evolution of these term weights with temperature and magnetic field, which is distinct from conventional ferromagnetic metals and cannot be explained by the phenomenological model. An alternative mechanism for AMR, stemming from the magnetization-induced local orbit deformation through spin-orbit interaction, as previously proposed by O'Donnell et al, may be prevalent in manganites and other systems of complicated crystal structure.

  2. A High-Spin Rate Measurement Method for Projectiles Using a Magnetoresistive Sensor Based on Time-Frequency Domain Analysis

    PubMed Central

    Shang, Jianyu; Deng, Zhihong; Fu, Mengyin; Wang, Shunting

    2016-01-01

    Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment. PMID:27322266

  3. A High-Spin Rate Measurement Method for Projectiles Using a Magnetoresistive Sensor Based on Time-Frequency Domain Analysis.

    PubMed

    Shang, Jianyu; Deng, Zhihong; Fu, Mengyin; Wang, Shunting

    2016-06-16

    Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment.

  4. Significant manipulation of output performance of a bridge-structured spin valve magnetoresistance sensor via an electric field

    NASA Astrophysics Data System (ADS)

    Zhang, Yue; Yan, Baiqian; Ou-Yang, Jun; Wang, Xianghao; Zhu, Benpeng; Chen, Shi; Yang, Xiaofei

    2016-01-01

    Through principles of spin-valve giant magnetoresistance (SV-GMR) effect and its application in magnetic sensors, we have investigated electric-field control of the output performance of a bridge-structured Co/Cu/NiFe/IrMn SV-GMR sensor on a PZN-PT piezoelectric substrate using the micro-magnetic simulation. We centered on the influence of the variation of uniaxial magnetic anisotropy constant (K) of Co on the output of the bridge, and K was manipulated via the stress of Co, which is generated from the strain of a piezoelectric substrate under an electric field. The results indicate that when K varies between 2 × 104 J/m3 and 10 × 104 J/m3, the output performance can be significantly manipulated: The linear range alters from between -330 Oe and 330 Oe to between -650 Oe and 650 Oe, and the sensitivity is tuned by almost 7 times, making it possible to measure magnetic fields with very different ranges. According to the converse piezoelectric effect, we have found that this variation of K can be realized by applying an electric field with the magnitude of about 2-20 kV/cm on a PZN-PT piezoelectric substrate, which is realistic in application. This result means that electric-control of SV-GMR effect has potential application in developing SV-GMR sensors with improved performance.

  5. Quantitative analysis of anisotropic magnetoresistance in Co{sub 2}MnZ and Co{sub 2}FeZ epitaxial thin films: A facile way to investigate spin-polarization in half-metallic Heusler compounds

    SciTech Connect

    Sakuraba, Y. Hirayama, Y.; Furubayashi, T.; Sukegawa, H.; Li, S.; Takahashi, Y. K.; Hono, K.; Kokado, S.

    2014-04-28

    Anisotropic magnetoresistance (AMR) effect has been systematically investigated in various Heusler compounds Co{sub 2}MnZ and Co{sub 2}FeZ (Z = Al, Si, Ge, and Ga) epitaxial films and quantitatively summarized against the total valence electron number N{sub V}. It was found that the sign of AMR ratio is negative when N{sub V} is between 28.2 and 30.3, and turns positive when N{sub V} becomes below 28.2 and above 30.3, indicating that the Fermi level (E{sub F}) overlaps with the valence or conduction band edges of half-metallic gap at N{sub V} ∼ 28.2 or 30.3, respectively. We also find out that the magnitude of negative AMR ratio gradually increases with shifting of E{sub F} away from the gap edges, and there is a clear positive correlation between the magnitude of negative AMR ratio and magnetoresistive output of the giant magnetoresistive devices using the Heusler compounds. This indicates that AMR can be used as a facile way to optimize a composition of half-metallic Heusler compounds having a high spin-polarization at room temperature.

  6. Contactless Measurement of Magnetic Nanoparticles on Lateral Flow Strips Using Tunneling Magnetoresistance (TMR) Sensors in Differential Configuration.

    PubMed

    Lei, Huaming; Wang, Kan; Ji, Xiaojun; Cui, Daxiang

    2016-12-14

    Magnetic nanoparticles (MNPs) are commonly used in biomedical detection due to their capability to bind with some specific antibodies. Quantification of biological entities could be realized by measuring the magnetic response of MNPs after the binding process. This paper presents a contactless scanning prototype based on tunneling magnetoresistance (TMR) sensors for quantification of MNPs present in lateral flow strips (LFSs). The sensing unit of the prototype composes of two active TMR elements, which are parallel and closely arranged to form a differential sensing configuration in a perpendicular magnetic field. Geometrical parameters of the configuration are optimized according to theoretical analysis of the stray magnetic field produced by the test line (T-line) while strips being scanned. A brief description of our prototype and the sample preparation is presented. Experimental results show that the prototype exhibits the performance of high sensitivity and strong anti-interference ability. Meanwhile, the detection speed has been improved compared with existing similar techniques. The proposed prototype demonstrates a good sensitivity for detecting samples containing human chorionic gonadotropin (hCG) at a concentration of 25 mIU/mL. The T-line produced by the sample with low concentration is almost beyond the visual limit and produces a maximum stray magnetic field some 0.247 mOe at the sensor in the x direction.

  7. Contactless Measurement of Magnetic Nanoparticles on Lateral Flow Strips Using Tunneling Magnetoresistance (TMR) Sensors in Differential Configuration

    PubMed Central

    Lei, Huaming; Wang, Kan; Ji, Xiaojun; Cui, Daxiang

    2016-01-01

    Magnetic nanoparticles (MNPs) are commonly used in biomedical detection due to their capability to bind with some specific antibodies. Quantification of biological entities could be realized by measuring the magnetic response of MNPs after the binding process. This paper presents a contactless scanning prototype based on tunneling magnetoresistance (TMR) sensors for quantification of MNPs present in lateral flow strips (LFSs). The sensing unit of the prototype composes of two active TMR elements, which are parallel and closely arranged to form a differential sensing configuration in a perpendicular magnetic field. Geometrical parameters of the configuration are optimized according to theoretical analysis of the stray magnetic field produced by the test line (T-line) while strips being scanned. A brief description of our prototype and the sample preparation is presented. Experimental results show that the prototype exhibits the performance of high sensitivity and strong anti-interference ability. Meanwhile, the detection speed has been improved compared with existing similar techniques. The proposed prototype demonstrates a good sensitivity for detecting samples containing human chorionic gonadotropin (hCG) at a concentration of 25 mIU/mL. The T-line produced by the sample with low concentration is almost beyond the visual limit and produces a maximum stray magnetic field some 0.247 mOe at the sensor in the x direction. PMID:27983659

  8. Significant manipulation of output performance of a bridge-structured spin valve magnetoresistance sensor via an electric field

    SciTech Connect

    Zhang, Yue; Yan, Baiqian; Ou-Yang, Jun; Zhu, Benpeng; Chen, Shi; Yang, Xiaofei; Wang, Xianghao

    2016-01-28

    Through principles of spin-valve giant magnetoresistance (SV-GMR) effect and its application in magnetic sensors, we have investigated electric-field control of the output performance of a bridge-structured Co/Cu/NiFe/IrMn SV-GMR sensor on a PZN-PT piezoelectric substrate using the micro-magnetic simulation. We centered on the influence of the variation of uniaxial magnetic anisotropy constant (K) of Co on the output of the bridge, and K was manipulated via the stress of Co, which is generated from the strain of a piezoelectric substrate under an electric field. The results indicate that when K varies between 2 × 10{sup 4 }J/m{sup 3} and 10 × 10{sup 4 }J/m{sup 3}, the output performance can be significantly manipulated: The linear range alters from between −330 Oe and 330 Oe to between −650 Oe and 650 Oe, and the sensitivity is tuned by almost 7 times, making it possible to measure magnetic fields with very different ranges. According to the converse piezoelectric effect, we have found that this variation of K can be realized by applying an electric field with the magnitude of about 2–20 kV/cm on a PZN-PT piezoelectric substrate, which is realistic in application. This result means that electric-control of SV-GMR effect has potential application in developing SV-GMR sensors with improved performance.

  9. Noise in small magnetic systems—applications to very sensitive magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Pannetier, M.; Fermon, C.; Le Goff, G.; Simola, J.; Kerr, E.; Coey, J. M. D.

    2005-04-01

    Reduction for 1/ f noise (or random telegraph noise) is a crucial issue for small magnetic sensors which is strongly related to structural properties and magnetic configuration. We show how it is possible to eliminate magnetic noise at low frequency in GMR/TMR sensors by a combination of cross anisotropies, window frame shapes and suitably designed magnetoresisitive stack. These sensors are superior to almost all existing field and flux sensors. Results are presented on a mixed sensor, where a superconducting loop acts as a flux-to-field transformer to the GMR sensor. This device is suitable for detection of biomagnetic signals, such as in magnetocardiography or in magnetoencephalography. Measurements on niobium-based and YBCO-based sensors are presented, leading to sensitivity of 30 fT/√Hz at 77 K for small samples. Sensitivity lower than 1 fT/√(Hz) is expected with appropriate design and use of TMR or CMR layers, which makes these a powerful alternative to SQUIDs.

  10. Solution Concentration and Flow Rate of Fe3+-modified Porphyrin (Red Blood Model) on Giant Magnetoresistance (GMR) Sensor Efficiency

    NASA Astrophysics Data System (ADS)

    Aminudin, A.; Tjahyono, D. H.; Suprijadi; Djamal, M.; Zaen, R.; Nandiyanto, A. B. D.

    2017-03-01

    Red blood has been of great interest for scientists since it relates to human’ and living creature’s life sustainability. One of the important compounds in red blood is porphyrin. Here, the purpose of this study was to develop a method for detecting porphyrin concentration using the assistance of giant magnetoresistance. In short of the method, we added Fe3+ solution to the porphyrin, and the mixed solution was introduced to the magnetic field. Next, the magnetized solution was introduced to the magnetic sensor to indicate the existence of porphyrin in the solution. To confirm the effectiveness of our method in detecting porphyrin, we varied the flow rate and concentration of Fe3+-modified porphyrin solution. The result showed that the more concentration and the slower flow rate affected the higher sensitivity gained. Since this developed method is simple but effective for detecting porphyrin concentration, we believe that further development of this method will be benefit for many applications, specifically relating to the medical uses.

  11. The Detection and Discrimination of Small Munitions using Giant Magnetoresistive (OMR) Sensors

    DTIC Science & Technology

    2010-09-01

    sensors along the three principal axes. GMR gradiometer sensors are also available. The cost of a single GMR chip is less than $10, and the cost per...150 2K SIOC8 AAH004-00 1.5 7.5 3.2 4.8 4 15 150 2K MSOP8 AAL002-02 1.5 10.5 3.0 4.2 2 2 150 5.5K SIOC8 Gradiometers Linear Range

  12. Soft Nanocomposite Based Multi-point, Multi-directional Strain Mapping Sensor Using Anisotropic Electrical Impedance Tomography.

    PubMed

    Lee, Hyosang; Kwon, Donguk; Cho, Haedo; Park, Inkyu; Kim, Jung

    2017-01-25

    The practical utilization of soft nanocomposites as a strain mapping sensor in tactile sensors and artificial skins requires robustness for various contact conditions as well as low-cost fabrication process for large three dimensional surfaces. In this work, we propose a multi-point and multi-directional strain mapping sensor based on multiwall carbon nanotube (MWCNT)-silicone elastomer nanocomposites and anisotropic electrical impedance tomography (aEIT). Based on the anisotropic resistivity of the sensor, aEIT technique can reconstruct anisotropic resistivity distributions using electrodes around the sensor boundary. This strain mapping sensor successfully estimated stretch displacements (error of 0.54 ± 0.53 mm), surface normal forces (error of 0.61 ± 0.62 N), and multi-point contact locations (error of 1.88 ± 0.95 mm in 30 mm × 30 mm area for a planar shaped sensor and error of 4.80 ± 3.05 mm in 40 mm × 110 mm area for a three dimensional contoured sensor). In addition, the direction of lateral stretch was also identified by reconstructing anisotropic distributions of electrical resistivity. Finally, a soft human-machine interface device was demonstrated as a practical application of the developed sensor.

  13. Soft Nanocomposite Based Multi-point, Multi-directional Strain Mapping Sensor Using Anisotropic Electrical Impedance Tomography

    NASA Astrophysics Data System (ADS)

    Lee, Hyosang; Kwon, Donguk; Cho, Haedo; Park, Inkyu; Kim, Jung

    2017-01-01

    The practical utilization of soft nanocomposites as a strain mapping sensor in tactile sensors and artificial skins requires robustness for various contact conditions as well as low-cost fabrication process for large three dimensional surfaces. In this work, we propose a multi-point and multi-directional strain mapping sensor based on multiwall carbon nanotube (MWCNT)-silicone elastomer nanocomposites and anisotropic electrical impedance tomography (aEIT). Based on the anisotropic resistivity of the sensor, aEIT technique can reconstruct anisotropic resistivity distributions using electrodes around the sensor boundary. This strain mapping sensor successfully estimated stretch displacements (error of 0.54 ± 0.53 mm), surface normal forces (error of 0.61 ± 0.62 N), and multi-point contact locations (error of 1.88 ± 0.95 mm in 30 mm × 30 mm area for a planar shaped sensor and error of 4.80 ± 3.05 mm in 40 mm × 110 mm area for a three dimensional contoured sensor). In addition, the direction of lateral stretch was also identified by reconstructing anisotropic distributions of electrical resistivity. Finally, a soft human-machine interface device was demonstrated as a practical application of the developed sensor.

  14. Soft Nanocomposite Based Multi-point, Multi-directional Strain Mapping Sensor Using Anisotropic Electrical Impedance Tomography

    PubMed Central

    Lee, Hyosang; Kwon, Donguk; Cho, Haedo; Park, Inkyu; Kim, Jung

    2017-01-01

    The practical utilization of soft nanocomposites as a strain mapping sensor in tactile sensors and artificial skins requires robustness for various contact conditions as well as low-cost fabrication process for large three dimensional surfaces. In this work, we propose a multi-point and multi-directional strain mapping sensor based on multiwall carbon nanotube (MWCNT)-silicone elastomer nanocomposites and anisotropic electrical impedance tomography (aEIT). Based on the anisotropic resistivity of the sensor, aEIT technique can reconstruct anisotropic resistivity distributions using electrodes around the sensor boundary. This strain mapping sensor successfully estimated stretch displacements (error of 0.54 ± 0.53 mm), surface normal forces (error of 0.61 ± 0.62 N), and multi-point contact locations (error of 1.88 ± 0.95 mm in 30 mm × 30 mm area for a planar shaped sensor and error of 4.80 ± 3.05 mm in 40 mm × 110 mm area for a three dimensional contoured sensor). In addition, the direction of lateral stretch was also identified by reconstructing anisotropic distributions of electrical resistivity. Finally, a soft human-machine interface device was demonstrated as a practical application of the developed sensor. PMID:28120886

  15. Eddy Current Testing with Giant Magnetoresistance (GMR) Sensors and a Pipe-Encircling Excitation for Evaluation of Corrosion under Insulation.

    PubMed

    Bailey, Joseph; Long, Nicholas; Hunze, Arvid

    2017-09-28

    This work investigates an eddy current-based non-destructive testing (NDT) method to characterize corrosion of pipes under thermal insulation, one of the leading failure mechanisms for insulated pipe infrastructure. Artificial defects were machined into the pipe surface to simulate the effect of corrosion wall loss. We show that by using a giant magnetoresistance (GMR) sensor array and a high current (300 A), single sinusoidal low frequency (5-200 Hz) pipe-encircling excitation scheme it is possible to quantify wall loss defects without removing the insulation or weather shield. An analysis of the magnetic field distribution and induced currents was undertaken using the finite element method (FEM) and analytical calculations. Simple algorithms to remove spurious measured field variations not associated with defects were developed and applied. The influence of an aluminium weather shield with discontinuities and dents was ascertained and found to be small for excitation frequency values below 40 Hz. The signal dependence on the defect dimensions was analysed in detail. The excitation frequency at which the maximum field amplitude change occurred increased linearly with the depth of the defect by about 3 Hz/mm defect depth. The change in magnetic field amplitude due to defects for sensors aligned in the azimuthal and radial directions were measured and found to be linearly dependent on the defect volume between 4400-30,800 mm³ with 1.2 × 10(-3)-1.6 × 10(-3) µT/mm³. The results show that our approach is well suited for measuring wall loss defects similar to the defects from corrosion under insulation.

  16. A nanoliter volume nuclear magnetic resonance (NMR) system using tunneling magneto-resistive (TMR) sensors to recognize biomolecules

    NASA Astrophysics Data System (ADS)

    Gomez, Pablo

    The need to incorporate advanced engineering tools in biology, biochemistry and medicine is in great demand. Many of the existing instruments and tools are usually expensive and require special facilities. With the advent of nanotechnology in the past decade, new approaches to develop devices and tools have been generated by academia and industry. One such technology, NMR spectroscopy, has been used by biochemists for more than 2 decades to study the molecular structure of chemical compounds. However, NMR spectrometers are very expensive and require special laboratory rooms for their proper operation. High magnetic fields with strengths in the order of several Tesla make these instruments unaffordable to most research groups. This doctoral research proposes a new technology to develop NMR spectrometers that can operate at field strengths of less than 0.5 Tesla using an inexpensive permanent magnet and spin dependent nanoscale magnetic devices. This portable NMR system is intended to analyze samples as small as a few nanoliters. The main problem to resolve when downscaling the variables is to obtain an NMR signal with high Signal-To-Noise-Ratio (SNR). A special Tunneling Magneto-Resistive (TMR) sensor design was developed to achieve this goal. The minimum specifications for each component of the proposed NMR system were established. A complete NMR system was designed based on these minimum requirements. The goat was always to find cost effective realistic components. The novel design of the NMR system uses technologies such as Direct Digital Synthesis (DDS), Digital Signal Processing (DSP) and a special Backpropagation Neural Network that finds the best match of the NMR spectrum. The system was designed, calculated and simulated with excellent results. In addition, a general method to design TMR Sensors was developed. The technique was automated and a computer program was written to help the designer perform this task interactively.

  17. Enhanced response and sensitivity of self-corrugated graphene sensors with anisotropic charge distribution

    NASA Astrophysics Data System (ADS)

    Yol Jeong, Seung; Jeong, Sooyeon; Won Lee, Sang; Tae Kim, Sung; Kim, Daeho; Jin Jeong, Hee; Tark Han, Joong; Baeg, Kang-Jun; Yang, Sunhye; Seok Jeong, Mun; Lee, Geon-Woong

    2015-06-01

    We introduce a high-performance molecular sensor using self-corrugated chemically modified graphene as a three dimensional (3D) structure that indicates anisotropic charge distribution. This is capable of room-temperature operation, and, in particular, exhibiting high sensitivity and reversible fast response with equilibrium region. The morphology consists of periodic, “cratered” arrays that can be formed by condensation and evaporation of graphene oxide (GO) solution on interdigitated electrodes. Subsequent hydrazine reduction, the corrugated edge area of the graphene layers have a high electric potential compared with flat graphene films. This local accumulation of electrons interacts with a large number of gas molecules. The sensitivity of 3D-graphene sensors significantly increases in the atmosphere of NO2 gas. The intriguing structures have several advantages for straightforward fabrication on patterned substrates, high-performance graphene sensors without post-annealing process.

  18. Enhanced response and sensitivity of self-corrugated graphene sensors with anisotropic charge distribution

    PubMed Central

    Yol Jeong, Seung; Jeong, Sooyeon; Won Lee, Sang; Tae Kim, Sung; Kim, Daeho; Jin Jeong, Hee; Tark Han, Joong; Baeg, Kang-Jun; Yang, Sunhye; Seok Jeong, Mun; Lee, Geon-Woong

    2015-01-01

    We introduce a high-performance molecular sensor using self-corrugated chemically modified graphene as a three dimensional (3D) structure that indicates anisotropic charge distribution. This is capable of room-temperature operation, and, in particular, exhibiting high sensitivity and reversible fast response with equilibrium region. The morphology consists of periodic, “cratered” arrays that can be formed by condensation and evaporation of graphene oxide (GO) solution on interdigitated electrodes. Subsequent hydrazine reduction, the corrugated edge area of the graphene layers have a high electric potential compared with flat graphene films. This local accumulation of electrons interacts with a large number of gas molecules. The sensitivity of 3D-graphene sensors significantly increases in the atmosphere of NO2 gas. The intriguing structures have several advantages for straightforward fabrication on patterned substrates, high-performance graphene sensors without post-annealing process. PMID:26053892

  19. The Preliminary Study Of Giant Magnetoresistance Sensor For Detection Of Oxygen In Human Blood

    NASA Astrophysics Data System (ADS)

    Ramli, Ramli; Muhtadi, Almas Hilman; Sahdan, Muhammad Fauzi; Haryanto, Freddy; Khairurrijal; Djamal, Mitra

    2010-12-01

    In recent years, there has been great progress for applications of nanomaterials in medicine field. Human body consists of many atoms and they can be treated like as nanomaterials. One of them is oxygen. Oxygen is always found in the human blood. Its concentration in human blood gives information about the metabolism in the body. The purpose of this study was to look for a possibility for developing tool to detect the concentration of oxygen in blood. In this study, the giant-magneto-resistance (GMR) sensor is implemented. The GMR sensor has many attractive features, for example: reduced size, low-power consumption, low price, as compared to other magnetic sensors and its electric and magnetic properties can be varied in very wide range. In this experiment, we developed the structure of GMR materials NiCoFe/Cu/NiCoFe sandwich as a GMR sensor. The NiCoFe/Cu/NiCoFe sandwiches were grown onto Si (111) substrates by the dc-opposed target magnetron sputtering (dc-OTMS) technique. The sputtering targets were NiCoFe and Cu. To achieve the aims of this study, the blood transports in human will be simulated using a simple experimental model. This model has some parameters representing those in blood transport. Furthermore, the nanomagnetic material will be made as a contaminant particle in blood. Using this material some properties of the transport will be investigated.

  20. Effect of a CoFeB layer on the anisotropic magnetoresistance of Ta/CoFeB/MgO/NiFe/MgO/CoFeB/Ta films

    NASA Astrophysics Data System (ADS)

    Li, Minghua; Shi, Hui; Dong, Yuegang; Ding, Lei; Han, Gang; Zhang, Yao; Liu, Ye; Yu, Guanghua

    2017-10-01

    The anisotropic magnetoresistance (AMR) and magnetic properties of NiFe films can be remarkably enhanced via CoFeB layer. In the case of an ultrathin NiFe film having a Ta/CoFeB/MgO/NiFe/MgO/CoFeB/Ta structure, the CoFeB/MgO layers suppressed the formation of magnetic dead layers and the interdiffusions and interface reactions between the NiFe and Ta layers. The AMR reached a maximum value of 3.56% at 450 °C. More importantly, a single NiFe (1 1 1) peak can be formed resulting in higher AMR values for films having CoFeB layer. This enhanced AMR also originated from the significant specular reflection of electrons owing to the crystalline MgO layer, together with the sharp interfaces with the NiFe layer. These factors together resulted in higher AMR and improved magnetic properties.

  1. Large tunneling anisotropic magnetoresistance in La0.7Sr0.3MnO3/pentacene/Cu structures prepared on SrTiO3 (110) substrates

    NASA Astrophysics Data System (ADS)

    Kamiya, Takeshi; Miyahara, Chihiro; Tada, Hirokazu

    2017-01-01

    We investigated tunneling anisotropic magnetoresistance (TAMR) at the interface between pentacene and La0.7Sr0.3MnO3 (LSMO) thin films prepared on SrTiO3 (STO) (110) substrates. The dependence of the TAMR ratio on the magnetic field strength was approximately ten times larger than that of the magnetic field angle at a high magnetic field. This large difference in the TAMR ratio is explained by the interface magnetic anisotropy of strain-induced LSMO thin films on a STO (110) substrate, which has an easy axis with an out-of-plane component. We also note that the TAMR owing to out-of-plane magnetization was positive at each angle of the in-plane magnetic field. This result implies that active control of the interface magnetic anisotropy between organic materials and ferromagnetic metals should realize nonvolatile and high-efficiency TAMR devices.

  2. Pulsed magnetic field measurement system based on colossal magnetoresistance-B-scalar sensors for railgun investigation.

    PubMed

    Stankevič, T; Medišauskas, L; Stankevič, V; Balevičius, S; Żurauskienė, N; Liebfried, O; Schneider, M

    2014-04-01

    A high pulsed magnetic field measurement system based on the use of CMR-B-scalar sensors was developed for the investigations of the electrodynamic processes in electromagnetic launchers. The system consists of four independent modules (channels) which are controlled by a personal computer. Each channel is equipped with a CMR-B-scalar sensor connected to the measurement device-B-scalar meter. The system is able to measure the magnitude of pulsed magnetic fields from 0.3 T to 20 T in the range from DC up to 20 kHz independently of the magnetic field direction. The measurement equipment circuit is electrically separated from the ground and shielded against low and high frequency electromagnetic noise. The B-scalar meters can be operated in the presence of ambient pulsed magnetic fields with amplitudes up to 0.2 T and frequencies higher than 1 kHz. The recorded signals can be transmitted to a personal computer in a distance of 25 m by means of a fiber optic link. The system was tested using the electromagnetic railgun RAFIRA installed at the French-German Research Institute of Saint-Louis, France.

  3. Magnetoresistive phenomena in nanoscale magnetic systems

    NASA Astrophysics Data System (ADS)

    Burton, John D.

    Nanomagnetic materials are playing an increasingly important role in modern technologies. A particular area of interest involves the interplay between magnetism and electric transport, i.e. magnetoresistive properties. Future generations of field sensors and memory elements will have to be on a length scale of a few nanometers or smaller. Magnetoresistive properties of such nanoscale objects exhibit novel features due to reduced dimensionality, complex surfaces and interfaces, and quantum effects. In this dissertation theoretical aspects of three such nanoscale magnetoresistive phenomena are discussed. Very narrow magnetic domain walls can strongly scatter electrons leading to an increased resistance. Specifically, this dissertation will cover the newly predicted effect of magnetic moment softening in magnetic nanocontacts or nanowires. Atomically thin domain walls in Ni exhibit a reduction, or softening, of the local magnetic moments due to the noncollinearity of the magnetization. This effect leads to a strong enhancement of the resistance of a domain wall. Magnetic tunnel junctions (MTJs) consist of two ferromagnetic electrodes separated by a thin layer of insulating material through which current can be carried by electron tunneling. The resistance of an MTJ depends on the relative orientation of the magnetization of the two ferromagnetic layers, an effect known as tunneling magnetoresistance (TMR). A first-principles analysis of CoFeB|MgO|CoFeB MTJs will be presented. Calculations reveal that it is energetically favorable for interstitial boron atoms to reside at the interface between the electrode and MgO tunneling barrier, which can be detrimental to the TMR effect. Anisotropic magnetoresistance (AMR) is the change in resistance of a ferromagnetic system as the orientation of the magnetization is altered. In this dissertation, the focus will be on AMR in the tunneling regime. Specifically we will present new theoretical results on tunneling AMR (TAMR) in two

  4. Evaluation of magnetic flux distribution from magnetic domains in [Co/Pd] nanowires by magnetic domain scope method using contact-scanning of tunneling magnetoresistive sensor

    SciTech Connect

    Okuda, Mitsunobu Miyamoto, Yasuyoshi; Miyashita, Eiichi; Hayashi, Naoto

    2014-05-07

    Current-driven magnetic domain wall motions in magnetic nanowires have attracted great interests for physical studies and engineering applications. The magnetic force microscope (MFM) is widely used for indirect verification of domain locations in nanowires, where relative magnetic force between the local domains and the MFM probe is used for detection. However, there is an occasional problem that the magnetic moments of MFM probe influenced and/or rotated the magnetic states in the low-moment nanowires. To solve this issue, the “magnetic domain scope for wide area with nano-order resolution (nano-MDS)” method has been proposed recently that could detect the magnetic flux distribution from the specimen directly by scanning of tunneling magnetoresistive field sensor. In this study, magnetic domain structure in nanowires was investigated by both MFM and nano-MDS, and the leakage magnetic flux density from the nanowires was measured quantitatively by nano-MDS. Specimen nanowires consisted from [Co (0.3)/Pd (1.2)]{sub 21}/Ru(3) films (units in nm) with perpendicular magnetic anisotropy were fabricated onto Si substrates by dual ion beam sputtering and e-beam lithography. The length and the width of the fabricated nanowires are 20 μm and 150 nm. We have succeeded to obtain not only the remanent domain images with the detection of up and down magnetizations as similar as those by MFM but also magnetic flux density distribution from nanowires directly by nano-MDS. The obtained value of maximum leakage magnetic flux by nano-MDS is in good agreement with that of coercivity by magneto-optical Kerr effect microscopy. By changing the protective diamond-like-carbon film thickness on tunneling magnetoresistive sensor, the three-dimensional spatial distribution of leakage magnetic flux could be evaluated.

  5. Magnetic and Magnetoresistive Properties of 3D Interconnected NiCo Nanowire Networks

    NASA Astrophysics Data System (ADS)

    da Câmara Santa Clara Gomes, Tristan; De La Torre Medina, Joaquín; Lemaitre, Matthieu; Piraux, Luc

    2016-10-01

    Track-etched polymer membranes with crossed nanochannels have been revealed to be most suitable as templates to produce large surface area and mechanically stable 3D interconnected nanowire (NW) networks by electrodeposition. Geometrically controlled NW superstructures made of NiCo ferromagnetic alloys exhibit appealing magnetoresistive properties. The combination of exact alloy compositions with the spatial arrangement of NWs in the 3D network is decisive to obtain specific magnetic and magneto-transport behavior. A proposed simple model based on topological aspects of the 3D NW networks is used to accurately determine the anisotropic magnetoresistance ratios. Despite of their complex topology, the microstructure of Co-rich NiCo NW networks display mixed fcc-hcp phases with the c-axis of the hcp phase oriented perpendicular to their axis. These interconnected NW networks have high potential as reliable and stable magnetic field sensors.

  6. Organic Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Epstein, Arthur

    2009-03-01

    In recent years a broad range of magnetoresistance phenomena have been reported for organic-based semiconductors, conductors and magnets. Organic systems illustrating magnetoresistance, include molecular- and polymer-based nonmagnetic semiconductors[1], organic-based spin polarized magnetic semiconductors,[2] nonmagnetic conducting polymers, and ferromagnet/organic semiconductor/ferromagnet heterojunctions. Examples of each of these organic-based systems will be presented together with a discussion of the roles of magnetotransport mechanisms including interconversion of singlets and triplets, compression of the electronic wavefunction in presence of a magnetic field, quantum interference phenomena, effects of a ``Coulomb gap'' in π* subbands of organic magnetic semiconductors with resulting near complete spin polarization in conduction and valence bands of magnetic organic semiconductors.[2,3] Opportunities for magnetotransport in Ferromagnet/Organic Semiconductor/Ferromagnet heterojunctions will be discussed.[4] [4pt] [1] V.N. Prigodin et al., Synth. Met. 156, 757 (2006); J.D. Bergeson et al., Phys. Rev. Lett. 100, 067201 (2008) [0pt] [2] V.N. Prigodin et al., Adv. Mater. 14, 1230 (2002. [0pt] [3] J.B. Kortright et al., Phys. Rev. Lett., 100, 257204 (2008). [0pt] [4] J.D. Bergeson, et al., Appl. Phys. Lett. 93, 172505 (2008).

  7. Evolution and sign control of square-wave-like anisotropic magneto-resistance in spatially confined La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3}/LaAlO{sub 3}(001) manganite thin films

    SciTech Connect

    Alagoz, H. S. Jeon, J.; Keating, S.; Chow, K. H. Jung, J.

    2016-04-14

    We investigated magneto-transport properties of a compressively strained spatially confined La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} (LPCMO) thin film micro-bridge deposited on LaAlO{sub 3}. Angular dependence of the magneto-resistance R(θ) of this bridge, where θ is the angle between the magnetic field and the current directions in the film plane, exhibits sharp positive and negative percolation jumps near T{sub MIT}. The sign and the magnitude of these jumps can be tuned using the magnetic field. Such behavior has not been observed in LPCMO micro-bridges subjected to tensile strain, indicating a correlation between the type of the lattice strain, the distribution of electronic domains, and the anisotropic magneto-resistance in spatially confined manganite systems.

  8. Monte Carlo calculations of the magnetoresistance in magnetic multilayer structures with giant magnetoresistance effects

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskiy, D. E.

    2016-06-01

    A Monte Carlo study of trilayer and spin-valve magnetic structures with giant magnetoresistance effects is carried out. The anisotropic Heisenberg model is used for description of magnetic properties of ultrathin ferromagnetic films forming these structures. The temperature and magnetic field dependences of magnetic characteristics are considered for ferromagnetic and antiferromagnetic configurations of these multilayer structures. The methodology for determination of the magnetoresistance by the Monte Carlo method is introduced; this permits us to calculate the magnetoresistance of multilayer structures for different thicknesses of the ferromagnetic films. The calculated temperature dependence of the magnetoresistance agrees very well with the experimental results measured for the Fe(0 0 1)-Cr(0 0 1) multilayer structure and CFAS-Ag-CFAS-IrMn spin-valve structure based on the half-metallic Heusler alloy Co2FeAl0.5Si0.5.

  9. Extraordinary magnetoresistance: sensing the future

    NASA Astrophysics Data System (ADS)

    Hewett, Thomas; Kusmartsev, Feodor

    2012-06-01

    Simulations utilising the finite element method (FEM) have been produced in order to investigate aspects of circular extraordinary magnetoresistance (EMR) devices. The effect of three specific features on the resultant magnetoresistance were investigated: the ratio of the metallic to semiconducting conductivities (σ M/σ S); the semiconductor mobility; and the introduction of an intermediate region at the semiconductormetal interface in order to simulate a contact resistance. In order to obtain a large EMR effect the conductivity ratio (σ M/σ S) is required to be larger than two orders of magnitude; below this critical value the resultant magnetoresistance effect is dramatically reduced. Large mobility semiconductors exhibit larger EMR values for a given field (below saturation) and reduce the magnetic field required to produce saturation of the magnetoresistance. This is due to a larger Hall angle produced at a given magnetic field and is consistent with the mechanism of the EMR effect. Since practical magnetic field sensors are required to operate at low magnetic fields, high mobility semiconductors are required in the production of more sensitive EMR sensors. The formation of a Schottky barrier at the semiconductor-metal interface has been modelled with the introduction of a contact resistance at the semiconductor-metal interface. Increasing values of contact resistance are found to reduce the EMR effect with it disappearing altogether for large values. This has been shown explicitly by looking at the current flow in the system and is consistent with the mechanism of the EMR effect. The interface resistance was used to fit the simulated model to existing experimental data. The best fit occurred with an interface with resistivity of 1.55×10-4 m (overestimate). The EMR effect holds great potential with regard to its future application to magnetic field sensors. The design of any such devices should incorporate high mobility materials (such as graphene) along

  10. Extraordinary magnetoresistance: sensing the future

    NASA Astrophysics Data System (ADS)

    Hewett, Thomas H.; Kusmartsev, Feodor V.

    2012-06-01

    Simulations utilising the finite element method (FEM) have been produced in order to investigate aspects of circular extraordinary magnetoresistance (EMR) devices. The effect of three specific features on the resultant magnetoresistance were investigated: the ratio of the metallic to semiconducting conductivities ( σ M / σ S ); the semiconductor mobility; and the introduction of an intermediate region at the semiconductormetal interface in order to simulate a contact resistance. In order to obtain a large EMR effect the conductivity ratio ( σ M / σ S ) is required to be larger than two orders of magnitude; below this critical value the resultant magnetoresistance effect is dramatically reduced. Large mobility semiconductors exhibit larger EMR values for a given field (below saturation) and reduce the magnetic field required to produce saturation of the magnetoresistance. This is due to a larger Hall angle produced at a given magnetic field and is consistent with the mechanism of the EMR effect. Since practical magnetic field sensors are required to operate at low magnetic fields, high mobility semiconductors are required in the production of more sensitive EMR sensors. The formation of a Schottky barrier at the semiconductor-metal interface has been modelled with the introduction of a contact resistance at the semiconductor-metal interface. Increasing values of contact resistance are found to reduce the EMR effect with it disappearing altogether for large values. This has been shown explicitly by looking at the current flow in the system and is consistent with the mechanism of the EMR effect. The interface resistance was used to fit the simulated model to existing experimental data. The best fit occurred with an interface with resistivity of 1.55×10-4 m (overestimate). The EMR effect holds great potential with regard to its future application to magnetic field sensors. The design of any such devices should incorporate high mobility materials (such as graphene

  11. On-Chip Magnetic Bead Manipulation and Detection Using a Magnetoresistive Sensor-Based Micro-Chip: Design Considerations and Experimental Characterization.

    PubMed

    Gooneratne, Chinthaka P; Kodzius, Rimantas; Li, Fuquan; Foulds, Ian G; Kosel, Jürgen

    2016-08-26

    The remarkable advantages micro-chip platforms offer over cumbersome, time-consuming equipment currently in use for bio-analysis are well documented. In this research, a micro-chip that includes a unique magnetic actuator (MA) for the manipulation of superparamagnetic beads (SPBs), and a magnetoresistive sensor for the detection of SPBs is presented. A design methodology, which takes into account the magnetic volume of SPBs, diffusion and heat transfer phenomena, is presented with the aid of numerical analysis to optimize the parameters of the MA. The MA was employed as a magnetic flux generator and experimental analysis with commercially available COMPEL™ and Dynabeads(®) demonstrated the ability of the MA to precisely transport a small number of SPBs over long distances and concentrate SPBs to a sensing site for detection. Moreover, the velocities of COMPEL™ and Dynabead(®) SPBs were correlated to their magnetic volumes and were in good agreement with numerical model predictions. We found that 2.8 μm Dynabeads(®) travel faster, and can be attracted to a magnetic source from a longer distance, than 6.2 μm COMPEL™ beads at magnetic flux magnitudes of less than 10 mT. The micro-chip system could easily be integrated with electronic circuitry and microfluidic functions, paving the way for an on-chip biomolecule quantification device.

  12. On-Chip Magnetic Bead Manipulation and Detection Using a Magnetoresistive Sensor-Based Micro-Chip: Design Considerations and Experimental Characterization

    PubMed Central

    Gooneratne, Chinthaka P.; Kodzius, Rimantas; Li, Fuquan; Foulds, Ian G.; Kosel, Jürgen

    2016-01-01

    The remarkable advantages micro-chip platforms offer over cumbersome, time-consuming equipment currently in use for bio-analysis are well documented. In this research, a micro-chip that includes a unique magnetic actuator (MA) for the manipulation of superparamagnetic beads (SPBs), and a magnetoresistive sensor for the detection of SPBs is presented. A design methodology, which takes into account the magnetic volume of SPBs, diffusion and heat transfer phenomena, is presented with the aid of numerical analysis to optimize the parameters of the MA. The MA was employed as a magnetic flux generator and experimental analysis with commercially available COMPEL™ and Dynabeads® demonstrated the ability of the MA to precisely transport a small number of SPBs over long distances and concentrate SPBs to a sensing site for detection. Moreover, the velocities of COMPEL™ and Dynabead® SPBs were correlated to their magnetic volumes and were in good agreement with numerical model predictions. We found that 2.8 μm Dynabeads® travel faster, and can be attracted to a magnetic source from a longer distance, than 6.2 μm COMPEL™ beads at magnetic flux magnitudes of less than 10 mT. The micro-chip system could easily be integrated with electronic circuitry and microfluidic functions, paving the way for an on-chip biomolecule quantification device. PMID:27571084

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

    SciTech Connect

    Dey, Rik Pramanik, Tanmoy; Roy, Anupam; Rai, Amritesh; Guchhait, Samaresh; Sonde, Sushant; Movva, Hema C. P.; Register, Leonard F.; Banerjee, Sanjay K.; Colombo, Luigi

    2014-06-02

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

  14. Origin of the extremely large magnetoresistance in the semimetal YSb

    NASA Astrophysics Data System (ADS)

    Xu, J.; Ghimire, N. J.; Jiang, J. S.; Xiao, Z. L.; Botana, A. S.; Wang, Y. L.; Hao, Y.; Pearson, J. E.; Kwok, W. K.

    2017-08-01

    Electron-hole (e -h ) compensation is a hallmark of multiband semimetals with extremely large magnetoresistance (XMR) and has been considered to be the basis for XMR. Recent spectroscopic experiments, however, reveal that YSb with nonsaturating magnetoresistance is uncompensated, questioning the e -h compensation scenario for XMR. Here we demonstrate with magnetoresistivity and angle-dependent Shubnikov-de Haas (SdH) quantum oscillation measurements that YSb does have nearly perfect e -h compensation, with a density ratio of ˜0.95 for electrons and holes. The density and mobility anisotropy of the charge carriers revealed in the SdH experiments allow us to quantitatively describe the magnetoresistance with an anisotropic multiband model that includes contributions from all Fermi pockets. We elucidate the role of compensated multibands in the occurrence of XMR by demonstrating the evolution of calculated magnetoresistances for a single band and for various combinations of electron and hole Fermi pockets.

  15. Using magnetoresistance to probe reversal asymmetry in exchange biased bilayers

    SciTech Connect

    Leighton, C.; Song, M.; Nogues, J.; Cyrille, M. C.; Schuller, Ivan K.

    2000-07-01

    We have measured the anisotropic magnetoresistance of Fe films exchange coupled to antiferromagnetic MnF{sub 2} layers. Exchange bias and coercivity obtained from magnetoresistance are in close agreement with superconducting quantum interference device magnetometry data. In addition the magnetoresistance reveals an asymmetry in the magnetization reversal process, despite the fact that the magnetization hysteresis loops show little shape asymmetry. These results correlate well with an earlier study of magnetization reversal asymmetry by polarized neutron reflectometry. The data imply that the magnetization reverses by coherent rotation on one side of the loop and by nucleation and propagation of domain walls on the other. (c) 2000 American Institute of Physics.

  16. Colossal Magnetoresistive Manganite Based Fast Bolometric X-ray Sensors for Total Energy Measurements of Free Electron Lasers

    SciTech Connect

    Yong, G J; Kolagani, R M; Adhikari, S; Mundle, R M; Cox, D W; Davidson III, A L; Liang, Y; Drury, O B; Hau-Riege, S P; Gardner, C; Ables, E; Bionta, R M; Friedrich, S

    2008-12-17

    Bolometric detectors based on epitaxial thin films of rare earth perovskite manganites have been proposed as total energy monitors for X-ray pulses at the Linac Coherent Light Source free electron laser. We demonstrate such a detector scheme based on epitaxial thin films of the perovskite manganese oxide material Nd{sub 0.67}Sr{sub x0.33}MnO{sub 3}, grown by pulsed laser deposition on buffered silicon substrates. The substrate and sensor materials are chosen to meet the conflicting requirements of radiation hardness, sensitivity, speed and linearity over a dynamic range of three orders of magnitude. The key challenge in the material development is the integration of the sensor material with Si. Si is required to withstand the free electron laser pulse impact and to achieve a readout speed three orders of magnitude faster than conventional cryoradiometers for compatibility with the Linac Coherent Light Source pulse rate. We discuss sensor material development and the photoresponse of prototype devices. This Linac Coherent Light Source total energy monitor represents the first practical application of manganite materials as bolometric sensors.

  17. Study of anisotropic magnetoresistance in the thermodynamic fluctuation regime of single crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}

    SciTech Connect

    Heine, G.; Lang, W. |; Wang, Xiao-Lin

    1996-11-01

    Measurements of the in-plane and out-of-plane magnetoresistance in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} single crystals with a critical temperature T{sub c} = 93 K are reported for temperatures between T{sub c} and 200 K and in magnetic fields up to 13 T. Both the transverse and the longitudinal in-plane magnetoresistance are positive and originate entirely from the suppression of superconducting fluctuations by the magnetic field. The longitudinal out-of-plane magnetoresistance is negative at all temperatures and magnetic fields. As possible origins two recent models are discussed, the reduction of the quasiparticle density of states due to condensation into superconducting fluctuations and thermally activated transport over an interplane pseudogap.

  18. Frequency dependence of organic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Wang, Fujian; Rybicki, James; Lin, Ran; Hutchinson, Kent; Hou, Jia; Wohlgenannt, Markus

    2011-03-01

    Organic magnetoresistive (OMAR) devices show a large enough magnetoresistive response (typically 10%) for potential applications as magnetic field sensors. However, applications often require sensing high frequency magnetic fields, and the examination of the frequency-dependent magnetoresistive response is therefore required. Analysis of time constants that limit the frequency response may also shed light on the mechanism behind the OMAR effect, because different OMAR mechanisms occur at different time scales In our experiments, the AC magnetic field is supplied by a coil with a ferrite core which is driven by a function generator The AC magnet shows a frequency response that is almost flat up to 1MHz. We found that the OMAR frequency limit is about 10 kHz for a typical organic semiconductor device and at least 100 kHz for devices made from a doped polymer film. We also performed capacitance and conductance vs. frequency measurements to understand the origin of the observed limit frequencies. This work was supported by Army MURI under GrantNo. W911NF-08-1-0317 and NSF under Grant No. ECS 0725280.

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

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

    PubMed

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

    2017-08-23

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

  1. An in-depth noise model for giant magnetoresistance current sensors for circuit design and complementary metal–oxide–semiconductor integration

    SciTech Connect

    Roldán, A. Roldán, J. B.; Reig, C.; Cardoso, S.; Cardoso, F.; Ferreira, R.; Freitas, P. P.

    2014-05-07

    Full instrumentation bridges based on spin valve of giant magnetoresistance and magnetic tunnel junction devices have been microfabricated and experimentally characterized from the DC and noise viewpoint. A more realistic model of these devices was obtained in this work, an electrical and thermal model previously developed have been improved in such a way that noise effects are also included. We have implemented the model in a circuit simulator and reproduced the experimental measurements accurately. This provides a more realistic and complete tool for circuit design where magnetoresistive elements are combined with well-known complementary metal–oxide–semiconductor modules.

  2. Magnetoresistance in nanostructured Tb/Ti and Tb/Si multilayers

    SciTech Connect

    Svalov, A. V.; Kurlyandskaya, G. V.; Vas'kovskiy, V. O.; Sorokin, A. N.; Diercks, D.

    2011-01-15

    Magnetic, magnetoresistive and structural properties were studied for [Tb/Ti]{sub n} and [Tb/Si]{sub n} multilayers which were prepared by rf-sputtering. The thickness of the Tb layers varied from 1.5 to 12 nm. The thickness of 2 nm nonmagnetic spacers of Ti or Si was kept constant. Both anisotropic and isotropic magnetoresistance was observed in [Tb/Ti]{sub n} and [Tb/Si]{sub n} multilayers. A decrease in the thickness of the terbium layers led to a decrease in the anisotropic contribution to the total magnetoresistance. The negative isotropic magnetoresistanse in [Tb/Ti]{sub n} and [Tb/Si]{sub n} multilayers can be attributed to the giant magnetoresistance (GMR) and/or high field isotropic magnetoresistance. The structure of the samples of both types enabled the existence of the GMR effect.

  3. Theory of organic magnetoresistance in disordered organic semiconductors

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas J.; Flatté, Michael E.

    2012-10-01

    The understanding of spin transport in organics has been challenged by the discovery of large magnetic field effects on properties such as conductivity and electroluminescence in a wide array of organic systems. To explain the large organic magnetoresistance (OMAR) phenomenon, we present and solve a model for magnetoresistance in positionally disordered organic materials using percolation theory. The model describes the effects of singlettriplet spin transitions on hopping transport by considering the role of spin dynamics on an effective density of hopping sites. Faster spin transitions open up `spin-blocked' pathways to become viable conduction channels and hence produce magnetoresistance. We concentrate on spin transitions under the effects of the hyperfine (isotropic and anisotropic), exchange, and dipolar interactions. The magnetoresistance can be found analytically in several regimes and explains several experimental observations

  4. A detection system based on giant magnetoresistive sensors and high-moment magnetic nanoparticles demonstrates zeptomole sensitivity: potential for personalized medicine.

    PubMed

    Srinivasan, Balasubramanian; Li, Yuanpeng; Jing, Ying; Xu, YunHao; Yao, Xiaofeng; Xing, Chengguo; Wang, Jian-Ping

    2009-01-01

    Zeptomole detector: A highly sensitive giant-magnetoresistive chip and FeCo nanoparticles can be used to linearly detect 600-4500 copies of streptavidin. Under unoptimized conditions, this system also detects human IL-6 with a sensitivity 13-times higher than that of standard ELISA techniques.

  5. Technology Trend of Sputtering System for Magnetoresistive Devices

    NASA Astrophysics Data System (ADS)

    Tsunekawa, Koji

    Magnetoresistive films used for read-heads of hard disc drives, magnetic random access memory devices, and magnetic sensors are fabricated by magnetron sputtering method. Since giant magnetoresistive and tunnel magnetoresistive films are composed of multilayered films, in which the thickness of each layer is in the nanometer range, high accuracy in thickness control and thickness uniformity is required for the sputtering systems. Film properties are also influenced by the quality of the vacuum during the fabrication process. This article addresses such issues on the deposition of magnetoresistive films, and introduces mass-production sputtering technologies capable of fabricating high quality multilayers. Furthermore, fabrication methods of the tunnel barrier in tunnel magnetoresistive devices are also described.

  6. Low frequency noise of anisotropic magnetoresistors in DC and AC-excited metal detectors

    NASA Astrophysics Data System (ADS)

    Vyhnanek, J.; Janosek, M.; Ripka, P.

    2013-06-01

    Magnetoresistors can replace induction sensors in applications like non-destructive testing and metal detection, where high spatial resolution or low frequency response is required. Using an AC excitation field the magnetic response of eddy currents is detected. Although giant magnetoresistive (GMR) sensors have higher measuring range and sensitivity compared to anisotropic magnetoresistors (AMR), they show also higher hysteresis and noise especially at low frequencies. Therefore AMR sensors are chosen to be evaluated in low noise measurements with combined processing of DC and AC excitation field with respect to the arrangement of processing electronics. Circuit with a commercial AMR sensor HMC1001 and AD8429 preamplifier using flipping technique exhibited 1-Hz noise as low as 125 pT/. Without flipping, the 1-Hz noise increased to 246 pT/.

  7. Magnetoresistive waves in plasmas

    NASA Astrophysics Data System (ADS)

    Felber, F. S.; Hunter, R. O., Jr.; Pereira, N. R.; Tajima, T.

    1982-10-01

    The self-generated magnetic field of a current diffusing into a plasma between conductors can magnetically insulate the plasma. Propagation of magnetoresistive waves in plasmas is analyzed. Applications to plasma opening switches are discussed.

  8. A flexible anisotropic self-powered piezoelectric direction sensor based on double sided ZnO nanowires configuration

    NASA Astrophysics Data System (ADS)

    Nour, E. S.; Chey, C. O.; Willander, M.; Nur, O.

    2015-03-01

    We have successfully synthesized highly dense and well aligned zinc oxide nanowires (NWs) on the two sides of a PEDOT: PSS substrate by a single step low temperature hydrothermal method. The grown sample was used to fabricate a double sided piezoelectric nanogenerator (NG). The maximum harvested output power density from the fabricated double sided NG configuration was about 4.44 mW cm-2. The results obtained from the present double sided NG were approximately double the output from a single side. In addition to that, the voltage polarity of the harvested voltage from the two sides of the NG has been investigated. The results showed that upon bending, an anisotropic voltage polarity is generated on the two sides. Indicating that, this double sided NG can be used as a self-powered voltage polarity based direction sensor. The results of the present flexible double sided NG is very promising for harvesting energy from irregular mechanical energy sources in the surrounding environment. In addition, the fabricated configuration showed stability for sensing and can be used in surveillance and security applications.

  9. Reversible and irreversible magnetoresistance of quasisingle domain permalloy microstructures

    NASA Astrophysics Data System (ADS)

    Steiner, M.; Pels, C.; Meier, G.

    2004-06-01

    Permalloy microstructures are investigated by magnetoresistance measurements at 2.0 K and by magnetic-force microscopy at room temperature. While the reversible anisotropic magnetoresistance is determined to be 2.4% at saturation fields of Bsat=1020 mT, the irreversible switching yields a resistance change of the order of 0.05% at 13 mT. By tilting the external magnetic field relative to the easy axis of the quasi single-domain microstructures insight in the reversal process is gained. Comparison with an analytical model provides evidence for magnetization reversal by curling.

  10. Using anisotropic diffusion for efficient extraction of sensor noise in camera identification.

    PubMed

    van Houten, Wiger; Geradts, Zeno

    2012-03-01

    Each digital camera has an intrinsic fingerprint that is unique to each camera. This device fingerprint can be extracted from an image and can be compared with a reference device fingerprint to determine the device origin. The complexity of the filters proposed to accomplish this is increasing. In this note, we use a relatively simple algorithm to extract the sensor noise from images. It has the advantages of being easy to implement and parallelize, and working faster than the wavelet filter that is common for this application. In addition, we compare the performance with a simple median filter and assess whether a previously proposed fingerprint enhancement technique improves results. Experiments are performed on approximately 7500 images originating from 69 cameras, and the results are compared with this often used wavelet filter. Despite the simplicity of the proposed method, the performance exceeds the common wavelet filter and reduces the time needed for the extraction. © 2012 American Academy of Forensic Sciences.

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

    PubMed

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

    2016-06-17

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

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

    PubMed Central

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

    2016-01-01

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

  13. Magnetoresistive Flux Focusing Eddy Current Flaw Detection

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  14. Magnetoresistive flux focusing eddy current flaw detection

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  15. Anomalous electronic structure and magnetoresistance in TaAs2

    PubMed Central

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

    2016-01-01

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

  16. Anomalous electronic structure and magnetoresistance in TaAs2

    DOE PAGES

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

    2016-01-01

    We report that the change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. In conclusion, density functional calculations find that TaAs2 is a new topological semimetal [Z2 invariant (0;111)] withoutmore » Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.« less

  17. Electronic structure basis for the extraordinary magnetoresistance in WTe2

    DOE PAGES

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

    2014-11-19

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

  18. Systematic Angular Study of Magnetoresistance in Permalloy Connected Kagome Artificial Spin Ice

    NASA Astrophysics Data System (ADS)

    Park, Jungsik; Le, Brian; Watts, Justin; Leighton, Chris; Samarth, Nitin; Schiffer, Peter

    Artificial spin ices are nanostructured two-dimensional arrays of ferromagnetic elements, where frustrated interactions lead to unusual collective magnetic behavior. Here we report a room-temperature magnetoresistance study of connected permalloy (Ni81Fe19) kagome artificial spin ice networks, wherein the direction of the applied in-plane magnetic field is systematically varied. We measure both the longitudinal and transverse magnetoresistance in these structures, and we find certain transport geometries of the network show strong angular sensitivity - even small variations in the applied field angle lead to dramatic changes of the magnetoresistance response. We also investigate the magnetization reversal of the networks using magnetic force microscopy (MFM), demonstrating avalanche behavior in the magnetization reversal. The magnetoresistance features are analyzed using an anisotropic magnetoresistance (AMR) model. Supported by the US Department of Energy. Work at the University of Minnesota was supported by Seagate Technology, NSF MRSEC, and a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme.

  19. Enhanced magnetoresistance and pinning-depinning processes of vortex domain walls in ferromagnetic nanowires

    NASA Astrophysics Data System (ADS)

    Soledade, P. R.; Brandão, J.; Mello, A.; Sampaio, L. C.

    2017-02-01

    We have investigated the pinning-depinning processes of vortex domain walls (VDW) in Permalloy nanowires with asymmetric triangular notches by means of magnetoresistance measurements and micromagnetic simulations. Through a model based on the anisotropic magnetoresistance (AMR) and the magnetization structure obtained from simulations, the magnetoresistance when the VDW passes stretched through the notch was calculated. Besides the depinning field, as it is known, also the magnetoresistance drop depends on the domain wall chirality. Measurements show that the resistance drop for clockwise (CW) chirality is  ≈180 m Ω (38%) larger than for the counterclockwise (CCW) chirality. From the VDW resistance calculations it becomes clear which domain wall parameters, like domain wall structure, chirality and wall width, play a role on the magnetoresistance. These results offer an additional route to better controlling the VDW motion, which can be beneficial to applications.

  20. Magnetoresistance of heavy and light metal/ferromagnet bilayers

    SciTech Connect

    Avci, Can Onur; Garello, Kevin; Mendil, Johannes; Ghosh, Abhijit; Blasakis, Nicolas; Gabureac, Mihai; Trassin, Morgan; Fiebig, Manfred; Gambardella, Pietro

    2015-11-09

    We studied the magnetoresistance of normal metal (NM)/ferromagnet (FM) bilayers in the linear and nonlinear (current-dependent) regimes and compared it with the amplitude of the spin-orbit torques and thermally induced electric fields. Our experiments reveal that the magnetoresistance of the heavy NM/Co bilayers (NM = Ta, W, and Pt) is phenomenologically similar to the spin Hall magnetoresistance (SMR) of YIG/Pt, but has a much larger anisotropy of the order of 0.5%, which increases with the atomic number of the NM. This SMR-like behavior is absent in light NM/Co bilayers (NM = Ti and Cu), which present the standard anisotropic magnetoresistance expected from polycrystalline FM layers. In the Ta, W, and Pt/Co bilayers, we find an additional magnetoresistance directly proportional to the current and to the transverse component of the magnetization. This so-called unidirectional SMR, of the order of 0.005%, is largest in W and correlates with the amplitude of the antidamping spin-orbit torque. The unidirectional SMR is below the accuracy of our measurements in YIG/Pt.

  1. Features of the electric-field distribution in anisotropic semiconductor wafers in a transverse magnetic field

    SciTech Connect

    Filippov, V. V.; Bormontov, E. N.

    2013-07-15

    A macroscopic model of the Hall effects and magnetoresistance in anisotropic semiconductor wafers is developed. The results obtained by solving the electrodynamic boundary problem allow the potential and eddy currents in anisotropic semiconductors to be calculated at different current-contact locations, depending on the parameters of the sample material's anisotropy. The results of this study are of great practical importance for investigating the physical properties of anisotropic semiconductors and simulating the electron-transport phenomena in devices based on anisotropic semiconductors.

  2. Advanced giant magnetoresistance technology for measurement applications

    NASA Astrophysics Data System (ADS)

    Weiss, Roland; Mattheis, Roland; Reiss, Günter

    2013-08-01

    Giant magnetoresistance (GMR) sensors are considered one of the first real applications of nanotechnology. They consist of nm-thick layered structures where ferromagnetic metals are sandwiched by nonmagnetic metals. Such multilayered films produce a large change in resistance (typically 10 to 20%) when subjected to a magnetic field, compared with a maximum change of a few per cent for other types of magnetic sensors. This technology has been intensively used in read heads for hard disk drives and now increasingly finds applications due to the high sensitivity and signal-to-noise ratio. Additionally these sensors are compatible with miniaturization and thus offer a high spatial resolution combined with a frequency range up to the 100 MHz regime and simple electronic conditioning. In this review, we first discuss the basics of the underlying magnetoresistance effects in layered structures and then present three prominent examples for future applications: in the field of current sensing the new GMR sensors offer high bandwidth and good accuracy in a space-saving open loop measurement configuration. In rotating systems they can be used for multiturn angle measurements, and in biotechnology the detection of magnetic particles enables the quantitative measurement of biomolecule concentrations.

  3. Magnetoresistance of Au films

    SciTech Connect

    Zhang, D. L.; Song, X. H.; Zhang, X.; Zhang, Xiaoguang

    2014-12-10

    Measurement of the magnetoresistance (MR) of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler s rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms.

  4. Magnetoresistance of Au films

    DOE PAGES

    Zhang, D. L.; Song, X. H.; Zhang, X.; ...

    2014-12-10

    Measurement of the magnetoresistance (MR) of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler s rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms.

  5. Magnetoresistive Emulsion Analyzer

    PubMed Central

    Lin, Gungun; Baraban, Larysa; Han, Luyang; Karnaushenko, Daniil; Makarov, Denys; Cuniberti, Gianaurelio; Schmidt, Oliver G.

    2013-01-01

    We realize a magnetoresistive emulsion analyzer capable of detection, multiparametric analysis and sorting of ferrofluid-containing nanoliter-droplets. The operation of the device in a cytometric mode provides high throughput and quantitative information about the dimensions and magnetic content of the emulsion. Our method offers important complementarity to conventional optical approaches involving ferrofluids, and paves the way to the development of novel compact tools for diagnostics and nanomedicine including drug design and screening. PMID:23989504

  6. Negative magnetoresistivity in holography

    NASA Astrophysics Data System (ADS)

    Sun, Ya-Wen; Yang, Qing

    2016-09-01

    Negative magnetoresistivity is a special magnetotransport property associated with chiral anomaly in four dimensional chiral anomalous systems, which refers to the transport behavior that the DC longitudinal magnetoresistivity decreases with increasing magnetic field. We calculate the longitudinal magnetoconductivity in the presence of back-reactions of the magnetic field to gravity in holographic zero charge and axial charge density systems with and without axial charge dissipation. In the absence of axial charge dissipation, we find that the quantum critical conductivity grows with increasing magnetic field when the backreaction strength is larger than a critical value, in contrast to the monotonically decreasing behavior of quantum critical conductivity in the probe limit. With axial charge dissipation, we find the negative magnetoresistivity behavior. The DC longitudinal magnetoconductivity scales as B in the large magnetic field limit, which deviates from the exact B 2 scaling of the probe limit result. In both cases, the small frequency longitudinal magnetoconductivity still agrees with the formula obtained from the hydrodynamic linear response theory, even in the large magnetic field limit.

  7. Planar Hall magnetoresistive aptasensor for thrombin detection.

    PubMed

    Sinha, B; Ramulu, T S; Kim, K W; Venu, R; Lee, J J; Kim, C G

    2014-09-15

    The use of aptamer-based assays is an emerging and attractive approach in disease research and clinical diagnostics. A sensitive aptamer-based sandwich-type sensor is presented to detect human thrombin using a planar Hall magnetoresistive (PHR) sensor in cooperation with superparamagnetic labels. A PHR sensor has the great advantages of a high signal-to-noise ratio, a small offset voltage and linear response in the low-field region, allowing it to act as a high-resolution biosensor. In the system presented here, the sensor has an active area of 50 µm × 50 µm with a 10-nm gold layer deposited onto the sensor surface prior to the binding of thiolated DNA primary aptamer. A polydimethylsiloxane well of 600-µm radius and 1-mm height was prepared around the sensor surface to maintain the same specific area and volume for each sensor. The sensor response was traced in real time upon the addition of streptavidin-functionalized magnetic labels on the sensor. A linear response to the thrombin concentration in the range of 86 pM-8.6 µM and a lower detection limit down to 86 pM was achieved by the proposed present method with a sample volume consumption of 2 µl. The proposed aptasensor has a strong potential for application in clinical diagnosis.

  8. Monte Carlo simulation of multilayer magnetic structures and calculation of the magnetoresistance coefficient

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskii, D. E.

    2015-11-01

    The Monte Carlo study of three-layer and spin-valve magnetic structures with giant magnetoresistance effects has been performed with the application of the Heisenberg anisotropic model to the description of the magnetic properties of thin ferromagnetic films. The dependences of the magnetic characteristics on the temperature and external magnetic field have been obtained for the ferromagnetic and antiferromagnetic configurations of these structures. A Monte Carlo method for determining the magnetoresistance coefficient has been developed. The magnetoresistance coefficient has been calculated for three-layer and spin-valve magnetic structures at various thicknesses of ferromagnetic films. It has been shown that the calculated temperature dependence of the magnetoresistance coefficient is in good agreement with experimental data obtained for the Fe(001)/Cr(001) multilayer structure and the CFAS/Ag/CFAS/IrMn spin valve based on the Co2FeAl0.5Si0.5 (CFAS) Heusler alloy.

  9. Theory of magnetoresistance due to lattice dislocations in face-centred cubic metals

    NASA Astrophysics Data System (ADS)

    Bian, Q.; Niewczas, M.

    2016-06-01

    A theoretical model to describe the low temperature magneto-resistivity of high purity copper single and polycrystals containing different density and distribution of dislocations has been developed. In the model, magnetoresistivity tensor is evaluated numerically using the effective medium approximation. The anisotropy of dislocation-induced relaxation time is considered by incorporating two independent energy bands with different relaxation times and the spherical and cylindrical Fermi surfaces representing open, extended and closed electron orbits. The effect of dislocation microstructure is introduced by means of two adjustable parameters corresponding to the length and direction of electron orbits in the momentum space, which permits prediction of magnetoresistance of FCC metals containing different density and distribution of dislocations. The results reveal that dislocation microstructure influences the character of the field-dependent magnetoresistivity. In the orientation of the open orbits, the quadratic variation in magnetoresistivity changes to quasi-linear as the density of dislocations increases. In the closed orbit orientation, dislocations delay the onset of magnetoresistivity saturation. The results indicate that in the open orbit orientations of the crystals, the anisotropic relaxation time due to small-angle dislocation scattering induces the upward deviation from Kohler's rule. In the closed orbit orientations Kohler's rule holds, independent of the density of dislocations. The results obtained with the model show good agreement with the experimental measurements of transverse magnetoresistivity in deformed single and polycrystal samples of copper at 2 K.

  10. Hybrid Molecular and Spin Dynamics Simulations for Ensembles of Magnetic Nanoparticles for Magnetoresistive Systems.

    PubMed

    Teich, Lisa; Schröder, Christian

    2015-11-13

    The development of magnetoresistive sensors based on magnetic nanoparticles which are immersed in conductive gel matrices requires detailed information about the corresponding magnetoresistive properties in order to obtain optimal sensor sensitivities. Here, crucial parameters are the particle concentration, the viscosity of the gel matrix and the particle structure. Experimentally, it is not possible to obtain detailed information about the magnetic microstructure, i.e., orientations of the magnetic moments of the particles that define the magnetoresistive properties, however, by using numerical simulations one can study the magnetic microstructure theoretically, although this requires performing classical spin dynamics and molecular dynamics simulations simultaneously. Here, we present such an approach which allows us to calculate the orientation and the trajectory of every single magnetic nanoparticle. This enables us to study not only the static magnetic microstructure, but also the dynamics of the structuring process in the gel matrix itself. With our hybrid approach, arbitrary sensor configurations can be investigated and their magnetoresistive properties can be optimized.

  11. Noncontact vibration measurements using magnetoresistive sensing elements

    NASA Astrophysics Data System (ADS)

    Tomassini, R.; Rossi, G.

    2016-06-01

    Contactless instrumentations is more and more used in turbomachinery testing thanks to the non-intrusive character and the possibility to monitor all the components of the machine at the same time. Performances of blade tip timing (BTT) measurement systems, used for noncontact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor characteristics and processing methods. The sensors used for BTT generate pulses, used for precise measurements of turbine blades time of arrival. Nowadays proximity sensors used in this application are based on optical, capacitive, eddy current and microwave measuring principle. Pressure sensors has been also tried. This paper summarizes the results achieved using a novel instrumentation based on the magnetoresistive sensing elements. The characterization of the novel probe has been already published. The measurement system was validated in test benches and in a real jet-engine comparing different sensor technologies. The whole instrumentation was improved. The work presented in this paper focuses on the current developments. In particular, attention is given to the data processing software and new sensor configurations.

  12. Magnetoresistance of Au films

    SciTech Connect

    Zhang, D. L. Song, X. H.; Zhang, X.; Zhang, X.-G.

    2014-12-14

    Classical magnetoresistance (MR) in nonmagnetic metals are conventionally understood in terms of the Kohler rule, with violation usually viewed as anomalous electron transport, in particular, as evidence of non-Fermi liquid behavior. Measurement of the MR of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms. Consequently, the Kohler rule should not be used to distinguish normal and anomalous electron transport in solids.

  13. Tunnel magnetoresistance of diamondoids

    NASA Astrophysics Data System (ADS)

    Matsuura, Yukihito

    2016-10-01

    Tunnel magnetoresistance (TMR) of diamondoids has been predicted by first principles density functional theory. Diamantane was used as a basic molecular proxy for diamondoids because hydrogen atoms in the apical position are easily substituted for a thiol group. The pristine diamantane exhibited a low TMR ratio of 7%, and boron-substitution considerably decreased the TMR ratio. Conversely, nitrogen-substitution enhanced the TMR ratio by up to 20%. Heteroatom-substitution changes the tunneling probabilities by varying the molecular bond lengths. Furthermore, when the spins of the electrodes are parallel, the heteroatoms resulted in transmittance probabilities at an energy range near the Fermi level. Consequently, heteroatom-substitution can control the TMR ratios of diamondoids very well.

  14. Anomalous magnetoresistance in Fibonacci multilayers.

    SciTech Connect

    Machado, L. D.; Bezerra, C. G.; Correa, M. A.; Chesman, C.; Pearson, J. E.; Hoffmann, A.

    2012-01-01

    We theoretically investigated magnetoresistance curves in quasiperiodic magnetic multilayers for two different growth directions, namely, [110] and [100]. We considered identical ferromagnetic layers separated by nonmagnetic layers with two different thicknesses chosen based on the Fibonacci sequence. Using parameters for Fe/Cr multilayers, four terms were included in our description of the magnetic energy: Zeeman, cubic anisotropy, bilinear coupling, and biquadratic coupling. The minimum energy was determined by the gradient method and the equilibrium magnetization directions found were used to calculate magnetoresistance curves. By choosing spacers with a thickness such that biquadratic coupling is stronger than bilinear coupling, unusual behaviors for the magnetoresistance were observed: (i) for the [110] case, there is a different behavior for structures based on even and odd Fibonacci generations, and, more interesting, (ii) for the [100] case, we found magnetic field ranges for which the magnetoresistance increases with magnetic field.

  15. Transversal magnetoresistance in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Klier, J.; Gornyi, I. V.; Mirlin, A. D.

    2015-11-01

    We explore theoretically the magnetoresistivity of three-dimensional Weyl and Dirac semimetals in transversal magnetic fields within two alternative models of disorder: (i) short-range impurities and (ii) charged (Coulomb) impurities. Impurity scattering is treated using the self-consistent Born approximation. We find that an unusual broadening of Landau levels leads to a variety of regimes of the resistivity scaling in the temperature-magnetic field plane. In particular, the magnetoresistance is nonmonotonous for the white-noise disorder model. For H →0 the magnetoresistance for short-range impurities vanishes in a nonanalytic way as H1 /3. In the limits of strongest magnetic fields H , the magnetoresistivity vanishes as 1 /H for pointlike impurities, while it is linear and positive in the model with Coulomb impurities.

  16. Scattering anisotropy and giant magnetoresistance in magnetic multilayers

    SciTech Connect

    Binder, J.; Zahn, P.; Mertig, I.

    2001-06-01

    We present full ab initio calculations of giant magnetoresistance (GMR) in Co/Cu (001) multilayers including self-consistent impurity scattering potentials. Starting from density functional theory the electronic structure of the multilayer and the scattering at impurities are described by means of a new Green function method. It will be demonstrated that impurity scattering in magnetic multilayers is strongly anisotropic in comparison to impurity scattering in bulk systems. Concerning transport the anisotropy of scattering leads to a formation of highly conducting channels which give rise to short circuits and cause strong variation of GMR as a function of the impurity position in the multilayer. {copyright} 2001 American Institute of Physics.

  17. Magnetoresistive smart fluid (marsonpol) and devices

    NASA Astrophysics Data System (ADS)

    Reji, John; Suresh, G.; Narayanadas, D. J.

    2003-10-01

    Magnetorheological fluid, Electrorheological fluid and ferro fluids are the smart fluids known today. These fluids are either electrically conductive or non conductive. They do not exhibit variable electrical resistance or switching behavior. Of recent interest to researchers has been the development of new types of magnetoresistive materials. Such materials can be of large practical importance, as they will change their electrical resistance in the presence of a magnetic field. However, most materials only exhibit appreciable magnetoresistance under extreme conditions, such as high magnetic fields or low temperatures. A smart fluid whose electrical resistance can be varied by several orders of magnitude under nominal level of magnetic field is reported in this paper (designated MARSONPOL). In the absence of a magnetic field the fluid is an insulator having electrical resistance in the order of 108 ohm-meter and in the presence of a magnetic field the resistance of the material reduces to less than 1 ohm-meter, at room temperature of 30°C. The sharp and reversible change in resistivity makes the material transform from an insulator to conductor, rendering properties characteristic of either state, within a fraction of a second. Fluids with such characteristics are not reported in the literature making this development a breakthrough and opening up potentials for the development of several smart devices. One such device is the magnetic field sensor probe currently under development at NPOL. A capsule of MARSONPOL forms the basic sensor element. Depending on the strength of the Magnetic field, the electrical resistivity of the capsule undergoes changes. The present paper will discuss details of the smart fluid as well as features of the magnetic field sensor.

  18. Origin of the extremely large magnetoresistance in the semimetal YSb

    DOE PAGES

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

    2017-08-29

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

  19. Anomalous magnetoresistance in the spinel superconductor LiTi2O4

    NASA Astrophysics Data System (ADS)

    Jin, K.; He, G.; Zhang, X.; Maruyama, S.; Yasui, S.; Suchoski, R.; Shin, J.; Jiang, Y.; Yu, H. S.; Yuan, J.; Shan, L.; Kusmartsev, F. V.; Greene, R. L.; Takeuchi, I.

    2015-05-01

    LiTi2O4 is a unique compound in that it is the only known spinel oxide superconductor. The lack of high quality single crystals has thus far prevented systematic investigations of its transport properties. Here we report a careful study of transport and tunnelling spectroscopy in epitaxial LiTi2O4 thin films. An unusual magnetoresistance is observed which changes from nearly isotropic negative to prominently anisotropic positive as the temperature is decreased. We present evidence that shows that the negative magnetoresistance likely stems from the suppression of local spin fluctuations or spin-orbit scattering centres. The positive magnetoresistance suggests the presence of an orbital-related state, also supported by the fact that the superconducting energy gap decreases as a quadratic function of magnetic field. These observations indicate that the spin-orbital fluctuations play an important role in LiTi2O4 in a manner similar to high-temperature superconductors.

  20. Anomalous magnetoresistance in the spinel superconductor LiTi2O4.

    PubMed

    Jin, K; He, G; Zhang, X; Maruyama, S; Yasui, S; Suchoski, R; Shin, J; Jiang, Y; Yu, H S; Yuan, J; Shan, L; Kusmartsev, F V; Greene, R L; Takeuchi, I

    2015-05-20

    LiTi2O4 is a unique compound in that it is the only known spinel oxide superconductor. The lack of high quality single crystals has thus far prevented systematic investigations of its transport properties. Here we report a careful study of transport and tunnelling spectroscopy in epitaxial LiTi2O4 thin films. An unusual magnetoresistance is observed which changes from nearly isotropic negative to prominently anisotropic positive as the temperature is decreased. We present evidence that shows that the negative magnetoresistance likely stems from the suppression of local spin fluctuations or spin-orbit scattering centres. The positive magnetoresistance suggests the presence of an orbital-related state, also supported by the fact that the superconducting energy gap decreases as a quadratic function of magnetic field. These observations indicate that the spin-orbital fluctuations play an important role in LiTi2O4 in a manner similar to high-temperature superconductors.

  1. Anomalous electronic structure and magnetoresistance in TaAs2

    SciTech Connect

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

    2016-01-01

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

  2. Monte Carlo simulation of magnetic multilayered structures with giant magnetoresistance effects

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskiy, D. E.

    2016-02-01

    Description of giant magnetoresistance effects in magnetic multilayered structures with the use of the anisotropic Heisenberg model for determination of magnetic properties of thin ferromagnetic films forming these structures is given. Monte Carlo simulations of magnetic properties for structures, which are constructed from two ferromagnetic films divided by nonmagnetic film, are carried out. The temperature and magnetic field dependencies are considered for ferromagnetic and antiferromagnetic configurations of these structures. The calculation of the magnetoresistance is carried out for different thicknesses of the ferromagnetic films. It was shown, that the obtained temperature dependence for the magnetoresistance is agreed very well with experimental results, measured for the magnetic multilayered structures similar to structures, which are considered in our investigations.

  3. Tunneling magnetoresistance in Si nanowires

    NASA Astrophysics Data System (ADS)

    Montes, E.; Rungger, I.; Sanvito, S.; Schwingenschlögl, U.

    2016-11-01

    We investigate the tunneling magnetoresistance of small diameter semiconducting Si nanowires attached to ferromagnetic Fe electrodes, using first principles density functional theory combined with the non-equilibrium Green’s functions method for quantum transport. Silicon nanowires represent an interesting platform for spin devices. They are compatible with mature silicon technology and their intrinsic electronic properties can be controlled by modifying the diameter and length. Here we systematically study the spin transport properties for neutral nanowires and both n and p doping conditions. We find a substantial low bias magnetoresistance for the neutral case, which halves for an applied voltage of about 0.35 V and persists up to 1 V. Doping in general decreases the magnetoresistance, as soon as the conductance is no longer dominated by tunneling.

  4. Origin of nonsaturating linear magnetoresistivity

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  5. Bipolaron mechanism for organic magnetoresistance.

    PubMed

    Bobbert, P A; Nguyen, T D; van Oost, F W A; Koopmans, B; Wohlgenannt, M

    2007-11-23

    We present a mechanism for the recently discovered magnetoresistance in disordered pi-conjugated materials, based on hopping of polarons and bipolaron formation, in the presence of the random hyperfine fields of the hydrogen nuclei and an external magnetic field. Within a simple model we describe the magnetic field dependence of the bipolaron density. Monte Carlo simulations including on-site and longer-range Coulomb repulsion show how this leads to positive and negative magnetoresistance. Depending on the branching ratio between bipolaron formation or dissociation and hopping rates, two different line shapes in excellent agreement with experiment are obtained.

  6. Bipolaron Mechanism for Organic Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Bobbert, P. A.; Nguyen, T. D.; van Oost, F. W. A.; Koopmans, B.; Wohlgenannt, M.

    2007-11-01

    We present a mechanism for the recently discovered magnetoresistance in disordered π-conjugated materials, based on hopping of polarons and bipolaron formation, in the presence of the random hyperfine fields of the hydrogen nuclei and an external magnetic field. Within a simple model we describe the magnetic field dependence of the bipolaron density. Monte Carlo simulations including on-site and longer-range Coulomb repulsion show how this leads to positive and negative magnetoresistance. Depending on the branching ratio between bipolaron formation or dissociation and hopping rates, two different line shapes in excellent agreement with experiment are obtained.

  7. Magnetoresistance of multiwall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Lu, Li; Kang, N.; Kong, W. J.; Hu, J. S.; Pan, Z. W.; Xie, S. S.

    2002-03-01

    We have investigated the magnetoresistance of multiwall carbon nanotubes bundles. At temperatures above 15 K, the magnetoresistance was found to follow exactly a scaling law as predicted by the theory of two-dimensional (2D) weak localization. Below 15 K, the 2D weak localization behavior is modified due to the formation of a Coulomb gap. This modification does not fit to those theories which treat electron-electron interaction as a perturbation. Altshular-Aronov-Spivak (AAS) resistance oscillation was observed in milli-Kelvin temperature range. The results will be discussed in terms of the interplay between electron-electron interaction and disorder scattering in multiwall carbon nanotube.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  9. 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.

  10. Pure spin-Hall magnetoresistance in Rh/Y3Fe5O12 hybrid

    PubMed Central

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

    2015-01-01

    We report an investigation of anisotropic magnetoresistance (AMR) and anomalous Hall resistance (AHR) of Rh and Pt thin films sputtered on epitaxial Y3Fe5O12 (YIG) ferromagnetic insulator films. For the Pt/YIG hybrid, large spin-Hall magne toresistance (SMR) along with a sizable conventional anisotropic magnetoresistance (CAMR) and a nontrivial temperature dependence of AHR were observed in the temperature range of 5–300 K. In contrast, a reduced SMR with negligible CAMR and AHR was found in Rh/YIG hybrid. Since CAMR and AHR are characteristics for all ferromagnetic metals, our results suggest that the Pt is likely magnetized by YIG due to the magnetic proximity effect (MPE) while Rh remains free of MPE. Thus the Rh/YIG hybrid could be an ideal model system to explore physics and devices associated with pure spin current. PMID:26639108

  11. Mobility controlled linear magnetoresistance with 3D anisotropy in a layered graphene pallet

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Li, Peng; He, Xin; Li, Jun; Wen, Yan; Ren, Wencai; Cheng, Hui-ming; Yang, Yang; Al-Hadeethi, Yas F.; Zhang, Xixiang

    2016-10-01

    A bulk sample of pressed graphene sheets was prepared under hydraulic pressure (~150 MPa). The cross-section of the sample demonstrates a layered structure, which leads to 3D electrical transport properties with anisotropic mobility. The electrical transport properties of the sample were measured over a wide temperature (2-400 K) and magnetic field (-140 ~\\text{kOe}≤slant H≤slant 140 ~\\text{kOe} ) range. The magnetoresistance measured at a fixed temperature can be described by R≤ft(H,θ \\right)=R≤ft({{\\varepsilon}θ}H,0\\right) with {{\\varepsilon}θ}={≤ft({{\\cos}2}θ +{{γ-2}{{\\sin}2}θ \\right)}1/2} , where γ is the mobility anisotropy constant and θ is the angle between the normal of the sample plane and the magnetic field. The large linear magnetoresistance (up to 36.9% at 400 K and 140 kOe) observed at high fields is ascribed to a classical magnetoresistance caused by mobility fluctuation ( Δ μ ). The magnetoresistance value at 140 kOe was related to the average mobility ≤ft(< μ > \\right) because of the condition Δ μ << μ > . The carrier concentration remained constant and the temperature-dependent resistivity was proportional to the average mobility, as verified by Kohler’s rule. Anisotropic dephasing length was deduced from weak localization observed at low temperatures.

  12. CPP magnetoresistance of magnetic multilayers: A critical review

    NASA Astrophysics Data System (ADS)

    Bass, Jack

    2016-06-01

    review is designed to provide a history of how knowledge of CPP-MR parameters grew, to give credit for discoveries, to explain how combining theory and experiment has enabled extraction of quantitative information about these parameters, but also to make clear that progress was not always direct and to point out where disagreements still exist. To limit its length, the review considers only collinear orientations of the moments of adjacent F-layers. To aid readers looking for specific information, we have provided an extensive table of contents and a detailed summary. Together, these should help locate over 100 figures plus 17 tables that collect values of individual parameters. In 1997, CIP-MR replaced anisotropic MR (AMR) as the sensor in read heads of computer hard drives. In principle, the usually larger CPP-MR was a contender for the next generation read head sensor. But in 2003, CIP-MR was replaced by the even larger Tunneling MR (TMR), which has remained the read-head sensor ever since. However, as memory bits shrink to where the relatively large specific resistance AR of TMR gives too much noise and too large an R to impedance match as a read-head sensor, the door is again opened for CPP-MR. We will review progress in finding techniques and F-alloys and F/N pairs to enhance the CPP-MR, and will describe its present capabilities.

  13. Geometrically enhanced extraordinary magnetoresistance in semiconductor-metal hybrids

    NASA Astrophysics Data System (ADS)

    Hewett, T. H.; Kusmartsev, F. V.

    2010-12-01

    Extraordinary magnetoresistance (EMR) arises in hybrid systems consisting of semiconducting material with an embedded metallic inclusion. We have investigated such systems with the use of finite-element modeling, with our results showing good agreement to existing experimental data. We show that this effect can be dramatically enhanced by over four orders of magnitude as a result of altering the geometry of the conducting region. The significance of this result lies in its potential application to EMR magnetic field sensors utilizing more familiar semiconducting materials with nonoptimum material parameters, such as silicon. Our model has been extended further with a geometry based on the microstructure of the silver chalcogenides, consisting of a randomly sized and positioned metallic network with interspersed droplets. This model has shown a large and quasilinear magnetoresistance analogous to experimental findings.

  14. Optimization of magneto-resistive response of ion-irradiated exchange biased films through zigzag arrangement of magnetization

    SciTech Connect

    Trützschler, Julia; Sentosun, Kadir; McCord, Jeffrey; Langer, Manuel; Fassbender, Jürgen; Mönch, Ingolf; Mattheis, Roland

    2014-03-14

    Exchange coupled ferromagnetic-antiferromagnetic Ni{sub 81}Fe{sub 19}/Ir{sub 23}Mn{sub 77} films with a zigzag alignment of magnetization are prepared by local ion irradiation. The anisotropic magneto-resistive behavior of the magnetic thin film structures is correlated to the magnetic structure and modeled. A unique uniaxial field sensitivity along the net magnetization alignment is obtained through the orthogonally modulated and magnetic domain wall stabilized magnetic ground state. Controlling local thin film magnetization distributions and, thus, the overall magnetization response opens unique ways to tailor the magneto-resistive sensitivity of functional magnetic thin film devices.

  15. Giant magnetoresistance materials for magnetic recording technology

    SciTech Connect

    Heffner, R.H.; Adams, C.D.; Brosha, E.L.

    1997-12-01

    This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work focused on a class of transition-metal-oxide (TMO) materials (LaMnO{sub 3} doped with Ca, Ba, or Sr) that exhibits an insulator-to-metal transition near a ferromagnetic phase transition temperature. This yields a very large magnetoresistance; thus these materials may have important uses as magnetic sensors in a variety of applications, ranging from automobiles to read heads for magnetic storage. In addition, the transport current in the ferromagnetic state is likely to be very highly polarized, which means that additional device applications using the phenomena of spin-polarized tunneling can be envisioned. Use of these materials as magnetic sensors depends upon learning to control the synthesis parameters (principally temperature, pressure and composition) to achieve a specific carrier concentration and/or mobility. A second challenge is the high magnetic fields ({ge}1 Tesla) currently required to achieve a large change in resistance. The authors began an investigation of two novel approaches to this field-sensitivity problem, involving the development of multilayer structures of the TMO materials. Finally, they began to explore the use of epitaxial strain as a means of changing the transport properties in thin-film multilayers.

  16. Giant tunneling magnetoresistance in silicene

    SciTech Connect

    Wang, Yu; Lou, Yiyi

    2013-11-14

    We have theoretically studied ballistic electron transport in silicene under the manipulation of a pair of ferromagnetic gate. Transport properties like transmission and conductance have been calculated by the standard transfer matrix method for parallel and antiparallel magnetization configurations. It is demonstrated here that, due to the stray field-induced wave-vector filtering effect, remarkable difference in configuration-dependent transport gives rise to a giant tunneling magnetoresistance. In combination with the peculiar buckled structure of silicene and its electric tunable energy gap, the receiving magnetoresistance can be efficiently modulated by the externally-tunable stray field, electrostatic potential, and staggered sublattice potential, providing some flexible strategies to construct silicene-based nanoelectronic device.

  17. Magnetoresistance behavior of UNiGe

    SciTech Connect

    Nakotte, H.; Lacerda, A.; Purwanto, A.; Havela, L.; Sechovsky, V.; Prokes, K.; Brueck, E.; Boer, F.R. de; Torikachvili, M.S.

    1995-05-01

    The authors have measured the temperature dependences of the magnetoresistance of single-crystalline UNiGe for both parallel (i//B//c-axis) and perpendicular configurations (i//a-axis, B//c-axis) in magnetic fields up to 18 T. Both configurations yield similar magnetoresistance behavior, which emphasizes the strong magnetic contribution to the resistivity in all directions. Crossing magnetic-phase boundaries causes anomalies in the magnetoresistance, which allowed a completion of the previously proposed magnetic phase diagram.

  18. Giant magnetoresistance in silicene nanoribbons.

    PubMed

    Xu, Chengyong; Luo, Guangfu; Liu, Qihang; Zheng, Jiaxin; Zhang, Zhimeng; Nagase, Shigeru; Gao, Zhengxiang; Lu, Jing

    2012-05-21

    By performing first-principle quantum transport calculations, we predict a giant magnetoresistance in zigzag silicene nanoribbons (ZSiNRs) connecting two semi-infinite silicene electrodes through switch of the edge spin direction of ZSiNRs. Spin-filter efficiency of both the antiferromagnetic and ferromagnetic ZSiNRs is sign-changeable with the bias voltage. Therefore, potential application of silicene in spintronics devices is suggested.

  19. Anisotropic universe with anisotropic sources

    SciTech Connect

    Aluri, Pavan K.; Panda, Sukanta; Sharma, Manabendra; Thakur, Snigdha E-mail: sukanta@iiserb.ac.in E-mail: snigdha@iiserb.ac.in

    2013-12-01

    We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union 2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.

  20. Anisotropic magnetotransport in Dirac-Weyl magnetic junctions

    NASA Astrophysics Data System (ADS)

    Ominato, Yuya; Kobayashi, Koji; Nomura, Kentaro

    2017-02-01

    We theoretically study the anisotropic magnetotransport in Dirac-Weyl magnetic junctions where a doped ferromagnetic Weyl semimetal is sandwiched between doped Dirac semimetals. We calculate the conductance using the Landauer formula and find that the system exhibits extraordinarily large anisotropic magnetoresistance (AMR). The AMR depends on the ratio of the Fermi energy to the strength of the exchange interaction. The origin of the AMR is the shift of the Fermi surface in the Weyl semimetal, and the mechanism is completely different from the conventional AMR originating from the spin dependent scattering and the spin-orbit interaction.

  1. Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip.

    PubMed

    Hua, J; Xiao, Z L; Imre, A; Yu, S H; Patel, U; Ocola, L E; Divan, R; Koshelev, A; Pearson, J; Welp, U; Kwok, W K

    2008-08-15

    We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R(theta,H) = R(H/Hctheta) where Hctheta =Hc0(cos2theta + gamma(-2)sin2theta)(-1/2) is the angular dependent critical field, gamma is the width to thickness ratio, and Hc0 is the critical field in the thickness direction at theta=0 degrees . The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.

  2. Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip.

    SciTech Connect

    Hua, J.; Xiao, Z. L.; Imre, A.; Yu, S. H.; Patel, U.; Ocola, L. E.; Divan, R.; Koshelev, A.; Pearson, J.; Welp, U.; Kwok, W. K.; Northern Illinois Univ.

    2008-01-01

    We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R({theta},H) = R(H/H{sub c{theta}}) where H{sub c{theta}} = H{sub c0}(cos{sup 2} {theta} + {gamma}{sup -2} sin{sup 2}{theta}){sup -1/2} is the angular dependent critical field, {gamma} is the width to thickness ratio, and H{sub c0} is the critical field in the thickness direction at {theta} = 0{sup o}. The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.

  3. Magnetic-proximity-induced magnetoresistance on topological insulators

    NASA Astrophysics Data System (ADS)

    Chiba, Takahiro; Takahashi, Saburo; Bauer, Gerrit E. W.

    2017-03-01

    We theoretically study the magnetoresistance (MR) of two-dimensional massless Dirac electrons as found on the surface of three-dimensional topological insulators (TIs) that are capped by a ferromagnetic insulator (FI). We calculate charge and spin transport by Kubo and Boltzmann theories, taking into account the ladder-vertex correction and the in-scattering due to normal and magnetic disorder. The induced exchange splitting is found to generate an electric conductivity that depends on the magnetization orientation, but its form is very different from both the anisotropic and the spin Hall MR. The in-plane MR vanishes identically for nonmagnetic disorder, while out-of-plane magnetizations cause a large MR ratio. On the other hand, we do find an in-plane MR and planar Hall effect in the presence of magnetic disorder aligned with the FI magnetization. Our results may help us understand recent transport measurements on TI |FI systems.

  4. Magic angle effects and angular magnetoresistance oscillations as dimensional crossovers.

    PubMed

    Lebed, A G; Bagmet, N N; Naughton, M J

    2004-10-08

    Interference effects between velocity and density of states, which occur as electrons move along open orbits in the extended Brillouin zone in anisotropic conductors, result in a change of wave functions' dimensionality at magic angle (MA) directions of a magnetic field. In particular, these 1D-->2D dimensional crossovers result in the appearance of sharp minima in a resistivity component rho perpendicular (H,alpha), perpendicular to conducting layers. This explains the main qualitative features of MA and angular magnetoresistance oscillations' phenomena observed due to the existence of quasi-one-dimensional sheets of Fermi surface in (TMTSF)2X, (DMET-TSeF)2X, and kappa-(ET)2Cu(NCS)(2) conductors.

  5. Giant Magnetoresistive Biochips for Biomarker Detection and Genotyping: An Overview

    NASA Astrophysics Data System (ADS)

    Wang, Shan X.

    2008-06-01

    Giant magnetoresistive biochips based on spin valve sensor arrays and magnetic nanoparticle labels have been successfully applied to the detection of biological events in the form of both protein and DNA assays with great speed, sensitivity, selectivity and economy. The technology is highly scalable to deep multiplex detection of biomarkers in a complex disease, and amenable to integration of microfluidics and CMOS electronics for portable applications. The results suggest that a magneto-nano biochip holds great promises in biomedicine, particularly for point of care molecular diagnostics of cancer, infectious diseases, radiation injury, cardiac and other diseases.

  6. Magnetoresistance of galfenol-based magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Panaccione, G.; Eddrief, M.; Marangolo, M.; Torelli, P.

    2015-12-01

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe1-xGax) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  7. Development of High Resolution Eddy Current Imaging Using an Electro-Mechanical Sensor (Preprint)

    DTIC Science & Technology

    2011-11-01

    7], Magneto-Resistance (MR) and Giant Magneto-Resistance (GMR) [8-10] sensors, Flux Gate sensors [11-12], SQUID sensors [13,14] etc. In all these...IOS Press, Amsterdam, 1995), pp. 115–124. 8. T. Dogaru and S. T. Smith, “ Giant Magnetoresistance-Based Eddy-Current Sensor,” in IEEE Transactions...on Magnetics, Vol. 37, No. 4, pp.2790-2793 (2001). 9. Buzz Wincheski and Min Namkung, ‘Deep flaw detection with giant magnetoresistive (GMR) based

  8. Quantum criticality and DBI magneto-resistance

    NASA Astrophysics Data System (ADS)

    Kiritsis, Elias; Li, Li

    2017-03-01

    We use the DBI action from string theory and holography to study the magneto-resistance at quantum criticality with hyperscaling violation. We find and analyze a rich class of scaling behaviors for the magneto-resistance. A special case describes the scaling results found in pnictides by Hayers et al in 2014 (arXiv:1412.6484).

  9. Development and Testing of Prototype Giant Magnetoresistive (GMR) Rotating Probe System

    NASA Astrophysics Data System (ADS)

    Wincheski, Buzz; Simpson, John; Namkung, Min; Perey, Dan; Callahan, John

    2003-03-01

    Continued development of the giant magnetoresistive based rotating probe system has resulted in the fabrication of a fieldable prototype instrument. The system, designed for the detection of deeply buried flaws under installed fasteners, utilizes a giant magnetoresistive sensor within the self-nulling probe design for improved low frequency capabilities. The prototype unit incorporates a new probe design for deep penetration and reduced edge effects along with new electronics and system software. Testing of the prototype system has been performed at SANDIA National Laboratories Aging Aircraft NDI Validation Center. The complete system configuration along with field testing results are presented.

  10. Spin Hall magnetoresistance in Co2FeSi/Pt thin films: dependence on Pt thickness and temperature

    NASA Astrophysics Data System (ADS)

    Huang, Xiufeng; Dai, Zhiwen; Huang, Lin; Lu, Guangduo; Liu, Min; Piao, Hongguang; Kim, Dong-Hyun; Yu, Seong-cho; Pan, Liqing

    2016-11-01

    We have investigated the temperature and the Pt layer thickness dependence of the magnetoresistances (MRs) in Co2FeSi/Pt thin films. Based on the field dependent measurements, it can be seen that the spin-current-induced spin Hall magnetoresistance (SMR) plays the dominant role in the MRs in the Co2FeSi/Pt bilayers in the whole temperature range. Meanwhile, a quite small part of anisotropic magnetoresistance (AMR) existed in the MRs. It proved to be originated from magnetic proximity effect (MPE) by measuring the Pt thickness and temperature dependence of the AMR. Moreover, the Co2FeSi layer thickness has much weaker effect on the SMR and AMR compared to the Pt layer thickness. These results indicate that the Co2FeSi/Pt interface is beneficial to be used in the spin-current-induced physical phenomena.

  11. Magnetoresistance in relativistic hydrodynamics without anomalies

    NASA Astrophysics Data System (ADS)

    Baumgartner, Andrew; Karch, Andreas; Lucas, Andrew

    2017-06-01

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

  12. Rashba-Edelstein Magnetoresistance in Metallic Heterostructures

    NASA Astrophysics Data System (ADS)

    Nakayama, Hiroyasu; Kanno, Yusuke; An, Hongyu; Tashiro, Takaharu; Haku, Satoshi; Nomura, Akiyo; Ando, Kazuya

    2016-09-01

    We report the observation of magnetoresistance originating from Rashba spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein (RE) magnetoresistance. We show that the simultaneous action of the direct and inverse RE effects in a Bi /Ag /CoFeB trilayer couples current-induced spin accumulation to the electric resistance. The electric resistance changes with the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, despite the fact that bulk SOC is not responsible for the magnetoresistance. We further found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system.

  13. Static Magnetic Properties of Films Measured by Means of Angular Perturbative Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Oliveira, Alexandre; Melo, Abner; da Costa, Ricardo; Chesman, Carlos

    In this work we introduced a new technique to measure magnetic anisotropies and magnetoelectrical properties, such as Anisotropic Magnetoresistance (AMR) and Giant Magnetoresistance (GMR) amplitudes. The Perturbative Magnetoresistance (PMR) consist of a regular collinear four probe magnetoresistance set up with an AC magnetic field (hac) applied perpendicular to the DC (Hdc) one. hac amplitude is about 1.0 Oe and oscillate at 270 Hz. We successfully interpreted the signal response from the voltage measured by lock-in amplifier and proposed a model based on energy minimization to extract magnetic anisotropies, AMR and GMR amplitudes. Measuring the in-plane angular dependency of PMR signal we were able to identify the usual magnetic anisotropy, such as uniaxial, unidirectional and cubic. Taking into account the perturbative nature of this technique (small hac amplitude and low frequency), we argue that angular PMR can be used to investigate some dynamic magnetic effects where static technique can not provide such information. A distinct feature of angular PMR is the capability to be used in saturated and non-saturated regime, so revealing magnetic properties dependency on applied field strength. We addressed the Rotatable Anisotropy as an example in this work.

  14. Enhanced Magnetoresistance in Molecular Junctions by Geometrical Optimization of Spin-Selective Orbital Hybridization.

    PubMed

    Rakhmilevitch, David; Sarkar, Soumyajit; Bitton, Ora; Kronik, Leeor; Tal, Oren

    2016-03-09

    Molecular junctions based on ferromagnetic electrodes allow the study of electronic spin transport near the limit of spintronics miniaturization. However, these junctions reveal moderate magnetoresistance that is sensitive to the orbital structure at their ferromagnet-molecule interfaces. The key structural parameters that should be controlled in order to gain high magnetoresistance have not been established, despite their importance for efficient manipulation of spin transport at the nanoscale. Here, we show that single-molecule junctions based on nickel electrodes and benzene molecules can yield a significant anisotropic magnetoresistance of up to ∼200% near the conductance quantum G0. The measured magnetoresistance is mechanically tuned by changing the distance between the electrodes, revealing a nonmonotonic response to junction elongation. These findings are ascribed with the aid of first-principles calculations to variations in the metal-molecule orientation that can be adjusted to obtain highly spin-selective orbital hybridization. Our results demonstrate the important role of geometrical considerations in determining the spin transport properties of metal-molecule interfaces.

  15. Frequency dependence of organic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Wagemans, W.; Janssen, P.; van der Heijden, E. H. M.; Kemerink, M.; Koopmans, B.

    2010-09-01

    To identify the microscopic mechanisms of organic magnetoresistance (OMAR), the dependency on the frequency of the applied magnetic field is explored, which consists of a dc and ac component. The measured magnetoconductance decreases when the frequency is increased. The decrease is stronger for lower voltages, which is shown to be linked to the presence of a negative capacitance, as measured with admittance spectroscopy. The negative capacitance disappears when the frequency becomes comparable to the inverse transit time of the minority carriers. These results are in agreement with recent interpretations that magnetic field effects on minority carrier mobility dominate OMAR.

  16. Large linear magnetoresistance in a transition-metal stannide β-RhSn4

    NASA Astrophysics Data System (ADS)

    Xing, X. Z.; Xu, C. Q.; Zhou, N.; Li, B.; Zhang, Jinglei; Shi, Z. X.; Xu, Xiaofeng

    2016-09-01

    Materials exhibiting large magnetoresistance may not only be of fundamental research interest, but also can lead to wide-ranging applications in magnetic sensors and switches. Here we demonstrate a large linear-in-field magnetoresistance, Δρ/ρ reaching as high as ˜600% at 2 K under a 9 T field, in the tetragonal phase of a transition-metal stannide β-RhSn4. Detailed analyses show that its magnetic responses are overall inconsistent with the classical model based on the multiple electron scattering by mobility fluctuations in an inhomogenous conductor, but rather in line with the quantum effects due to the presence of Dirac-like dispersions in the electronic structure. Our results may help guiding the future quest for quantum magnetoresistive materials into the family of stannides, similar to the role played by PtSn4 with topological node arcs.

  17. Room Temperature Giant and Linear Magnetoresistance in Topological Insulator Bi2Te3 Nanosheets

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi2Te3 topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

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

    PubMed

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

    2012-06-29

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

  19. Magnetotransport in metal/insulating-ferromagnet heterostructures: Spin Hall magnetoresistance or magnetic proximity effect

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Ma, L.; Shi, Z.; Fan, W. J.; Zheng, Jian-Guo; Evans, R. F. L.; Zhou, S. M.

    2015-08-01

    We study the anomalous Hall-like effect (AHLE) and the effective anisotropic magnetoresistance (EAMR) in antiferromagnetic γ -IrMn3/Y3Fe5O12(YIG ) and Pt/YIG heterostructures. For γ -IrMn3/YIG , the EAMR and the AHLE resistivity change sign with temperature due to the competition between the spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE) induced by the interfacial antiferromagnetic uncompensated magnetic moment. In contrast, for Pt/YIG, the AHLE resistivity changes sign with temperature whereas no sign change is observed in the EAMR. This is because the MPE and the SMR play a dominant role in the AHLE and the EAMR, respectively. As different types of galvanomagnetic properties, the AHLE and the EAMR have proved vital in disentangling the MPE and the SMR in metal/insulating-ferromagnet heterostructures.

  20. Route towards huge magnetoresistance in doped polymers

    NASA Astrophysics Data System (ADS)

    Kersten, S. P.; Meskers, S. C. J.; Bobbert, P. A.

    2012-07-01

    Room-temperature magnetoresistance of the order of 10% has been observed in organic semiconductors. We predict that even larger magnetoresistance can be realized in suitably synthesized doped conjugated polymers. In such polymers, ionization of dopants creates free charges that recombine with a rate governed by a competition between an applied magnetic field and random hyperfine fields. This leads to a spin-blocking effect that depends on the magnetic field. We show that the combined effects of spin blocking and charge blocking, the fact that two free charges cannot occupy the same site, lead to a magnetoresistance of almost two orders of magnitude. This magnetoresistance occurs even at vanishing electric field and is therefore a quasiequilibrium effect. The influences of the dopant strength, energetic disorder, and interchain hopping are investigated. We find that the dopant strength and energetic disorder have only little influence on the magnetoresistance. Interchain hopping strongly decreases the magnetoresistance because it can lift spin-blocking and charge-blocking configurations that occur in strictly one-dimensional transport. We provide suggestions for realization of polymers that should show this magnetoresistance.

  1. Advanced Magnetoresistance Sensing of Rotation Rate for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Avram, Marioara; Volmer, Marius; Avram, Andrei

    2008-06-01

    We propose to build a non-Newtonian fluids viscosimeter, in order to measure the viscosity of biological fluids such as blood. The system is based on a rotating microgear wheel and a magnetoresistive sensor with a non-contacting transduction mechanism to transform the rotor rotation rate into an electrical signal. As the rotor turns, the field from this microscopic magnet will modulate the resistance of a bar of a low coercitivity material such as Permalloy, with an in-plane uniaxial magnetization, placed nearby, close to the rotor flanges. The change in resistivity provides an electrical signal with frequency proportional to the rotation rate, and hence the fluid velocity. The rotor is fabricated from polysilicon and coated with a soft magnetic material. The magnetoresistive sensor is formed of two Wheatstone bridges orientated on the X and Y axes. As the microgear wheel rotates, a tooth passing by the sensing GMR of the Wheatstone bridge changes the magnetic field, thus enabling us to measure the velocity of the gear wheel. The gear wheel has the outer diameter of 200 μm and is obtained by using the cut and refill technique. The basis for fabrication of movable parts is the use of sacrificial layers that act both as spacers and also to keep the parts attached to the silicon wafer during fabrication.

  2. 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.

  3. Tunneling magnetoresistance of silicon chains

    SciTech Connect

    Matsuura, Yukihito

    2016-05-28

    The tunneling magnetoresistance (TMR) of a silicon chain sandwiched between nickel electrodes was examined by using first-principles density functional theory. The relative orientation of the magnetization in a parallel-alignment (PA) configuration of two nickel electrodes enhanced the current with a bias less than 0.4 V compared with that in an antiparallel-alignment configuration. Consequently, the silicon chain-nickel electrodes yielded good TMR characteristics. In addition, there was polarized spin current in the PA configuration. The spin polarization of sulfur atoms functioning as a linking bridge between the chain and nickel electrode played an important role in the magnetic effects of the electric current. Moreover, the hybridization of the sulfur 3p orbital and σ-conjugated silicon 3p orbital contributed to increasing the total current.

  4. Competing Mechanisms in Organic Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Koopmans, Bert

    2013-03-01

    A surprisingly large ``organic magnetoresistance'' (OMAR) has been found in both polymers and small molecule organic semiconductors at relatively small applied magnetic fields (~ 5 mT) and at room temperature. Unlike spin-injection devices, where the occurrence of a finite spin polarization of the current is essential for measuring a finite magnetoresistance, OMAR is generally considered to be due to spin correlations between spin carrying particles in the organic material. Although the microscopic mechanisms of hyperfine field induced spin mixing are relatively well understood, it is still intensively debated which particles are involved and how they can affect the current in such a drastic manner. In this presentation recent developments and new insights as to the underlying physics are discussed. Quantitative models will be introduced, based on different pairs of particles and mechanisms, and giving rise to effects at a variety of field scales. It will be discussed how specific device physics causes a non-trivial relation between microscopic spin-dependent reactions and macroscopic device behaviour. Finally, it will be shown how comprehensive studies on especially engineered organic systems, including polymer-fullerene blends and molecular doping, can be used to pinpoint the relevance of different mechanisms in the complementary regimes. The experimentally observed linewidth, sign and amplitude of both ``high-field'' (>100 mT) and ``low-field'' (~ 5 mT) effects, as well as their bias voltage dependence display very pronounced features as a function of fullerene doping. They provide unique fingerprints for which mechanism is of relevance. After careful analysis, this allows for identification of three earlier proposed mechanisms, involving exciton-charge, electron-hole and bipolaron (polarons of like charge) reactions. Present activities are aiming at using this insight for tailoring OMAR response by design.

  5. Viscous magnetoresistance of correlated electron liquids

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  6. Magnetoresistance in inhomogeneous graphene/metal hybrids

    NASA Astrophysics Data System (ADS)

    Moktadir, Zakaria; Mizuta, Hiroshi

    2013-02-01

    We investigate extraordinary magnetoresistance (EMR) of inhomogeneous graphene-metal hybrids using finite element modelling. Inhomogeneous graphene is a binary system made of electron and hole puddles. Two geometries of the embedded metallic structure were considered: circular and fishbone geometries. We found that the breaking of graphene into charge puddles weakens the magnetoresistance of the hybrid system compared to a homogeneous graphene-metal system. For a fixed value of the magnetic field, the magnetoresistance increases with decreasing area fraction occupied by electrons puddles. Fishbone geometry showed an enhanced magnetoresistance compared to circular geometry. The EMR is also investigated as a function of the contact resistance for the fishbone geometry where it was found that a minimal contact resistance is essential to obtain enhanced EMR in graphene-metal hybrid devices.

  7. Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane

    NASA Technical Reports Server (NTRS)

    Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

    2001-01-01

    A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

  8. Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Li, Huan-Huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-Tao; Tian, Yu-Feng; Yan, Shi-Shen; Lin, Zhao-Jun; Kang, Shi-Shou; Chen, Yan-Xue; Liu, Guo-Lei; Mei, Liang-Mo

    2015-09-01

    Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

  9. Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions

    PubMed Central

    Zhang, Kun; Li, Huan-huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-tao; Tian, Yu-feng; Yan, Shi-shen; Lin, Zhao-jun; Kang, Shi-shou; Chen, Yan-xue; Liu, Guo-lei; Mei, Liang-mo

    2015-01-01

    Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices. PMID:26387967

  10. Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions.

    PubMed

    Zhang, Kun; Li, Huan-Huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-Tao; Tian, Yu-Feng; Yan, Shi-Shen; Lin, Zhao-Jun; Kang, Shi-Shou; Chen, Yan-Xue; Liu, Guo-Lei; Mei, Liang-Mo

    2015-09-21

    Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

  11. Organic magnetoresistance based on hopping theory

    NASA Astrophysics Data System (ADS)

    Yang, Fu-Jiang; Xie, Shi-Jie

    2014-09-01

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

  12. Giant magnetoresistance through a single molecule.

    PubMed

    Schmaus, Stefan; Bagrets, Alexei; Nahas, Yasmine; Yamada, Toyo K; Bork, Annika; Bowen, Martin; Beaurepaire, Eric; Evers, Ferdinand; Wulfhekel, Wulf

    2011-03-01

    Magnetoresistance is a change in the resistance of a material system caused by an applied magnetic field. Giant magnetoresistance occurs in structures containing ferromagnetic contacts separated by a metallic non-magnetic spacer, and is now the basis of read heads for hard drives and for new forms of random access memory. Using an insulator (for example, a molecular thin film) rather than a metal as the spacer gives rise to tunnelling magnetoresistance, which typically produces a larger change in resistance for a given magnetic field strength, but also yields higher resistances, which are a disadvantage for real device operation. Here, we demonstrate giant magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope. We measure the magnetoresistance to be 60% and the conductance to be 0.26G(0), where G(0) is the quantum of conductance. Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  14. Frequency dependence of magnetoresistance in MEH-PPV

    NASA Astrophysics Data System (ADS)

    Kamdem Djidjou, Thaddee; Nguyen, Tho; Valy Vardeny, Z.; Rogachev, Andrey

    2012-02-01

    The organic magnetoresistance (OMAR) in organic light emitting diodes (OLED) made of MEH-PPV was investigated by means of DC transport and the admittance spectroscopy in the range of 1 Hz to 10 MHz at room temperature. The measurements were carried out on unipolar and bipolar OLEDs made of pristine MEH-PPV as well as MEH-PPV with traps introduced by the UV light irradiation. We found that in bipolar, UV-exposed OLEDs, the magnitude of magnetoresistance effect in real part of admittance increases with DC bias, reaches very high value of 35 % (in the field 30mT) at bias 4.8 V and decreases at higher bias voltages. Also, we observed that the cutoff frequency of OMAR effect monotonically increases with DC bias voltage. The cutoff has extrinsic origin and is likely caused by a dissipative process related to the reorientation of permanent dipoles. At the highest tested bias voltage 6.7 V, we were able to detect the OMAR at the highest frequency of our system, 10 MHz. We have found that imaginary part of the admittance is also affected by magnetic field. The effect of magnetic field on dynamical capacitance of the device at low frequencies is very strong and opens up a possibility of using these devices as magnetic field sensors.

  15. Development of High Resolution Eddy Current Imaging Using an Electro-Mechanical Sensor (Postprint)

    DTIC Science & Technology

    2011-08-01

    coil and detecting the magnetic field using sensors like Hall Effect (HE) [5-7], Magneto-Resistance (MR) and Giant Magneto-Resistance (GMR) [8-10...sensors, Flux Gate sensors [11,12], SQUID sensors [13,14] etc. In all these methods, large electromagnetic coils are used to generate eddy currents in...Bowler and K. Miya, (IOS Press, Amsterdam, 1995), pp. 115–124. 8. T. Dogaru and S. T. Smith, “ Giant Magnetoresistance-Based Eddy-Current Sensor,” in

  16. Magnetoresistance Behavior of Conducting Filaments in Resistive-Switching NiO with Different Resistance States.

    PubMed

    Zhao, Diyang; Qiao, Shuang; Luo, Yuxiang; Chen, Aitian; Zhang, Pengfei; Zheng, Ping; Sun, Zhong; Guo, Minghua; Chiang, Fu-Kuo; Wu, Jian; Luo, Jianlin; Li, Jianqi; Kokado, Satoshi; Wang, Yayu; Zhao, Yonggang

    2017-03-29

    The resistive switching (RS) effect in various materials has attracted much attention due to its interesting physics and potential for applications. NiO is an important system and its RS effect has been generally explained by the formation/rupture of Ni-related conducting filaments. These filaments are unique since they are formed by an electroforming process, so it is interesting to explore their magnetoresistance (MR) behavior, which can also shed light on unsolved issues such as the nature of the filaments and their evolution in the RS process, and this behavior is also important for multifunctional devices. Here, we focus on MR behavior in NiO RS films with different resistance states. Rich and interesting MR behaviors have been observed, including the normal and anomalous anisotropic magnetoresistance and tunneling magnetoresistance, which provide new insights into the nature of the filaments and their evolution in the RS process. First-principles calculation reveals the essential role of oxygen migration into the filaments during the RESET process and can account for the experimental results. Our work provides a new avenue for exploration of the conducting filaments in resistive switching materials and is significant for understanding the mechanism of RS effect and multifunctional devices.

  17. Temperature-Dependent Three-Dimensional Anisotropy of the Magnetoresistance in WTe_{2}.

    PubMed

    Thoutam, L R; Wang, Y L; Xiao, Z L; Das, S; Luican-Mayer, A; Divan, R; Crabtree, G W; Kwok, W K

    2015-07-24

    Extremely large magnetoresistance (XMR) was recently discovered in WTe_{2}, triggering extensive research on this material regarding the XMR origin. Since WTe_{2} is a layered compound with metal layers sandwiched between adjacent insulating chalcogenide layers, this material has been considered to be electronically two-dimensional (2D). Here we report two new findings on WTe_{2}: (1) WTe_{2} is electronically 3D with a mass anisotropy as low as 2, as revealed by the 3D scaling behavior of the resistance R(H,θ)=R(ϵ_{θ}H) with ϵ_{θ}=(cos^{2}θ+γ^{-2}sin^{2}θ)^{1/2}, θ being the magnetic field angle with respect to the c axis of the crystal and γ being the mass anisotropy and (2) the mass anisotropy γ varies with temperature and follows the magnetoresistance behavior of the Fermi liquid state. Our results not only provide a general scaling approach for the anisotropic magnetoresistance but also are crucial for correctly understanding the electronic properties of WTe_{2}, including the origin of the remarkable "turn-on" behavior in the resistance versus temperature curve, which has been widely observed in many materials and assumed to be a metal-insulator transition.

  18. Temperature Dependent Three-dimensional Anisotropy of the Magnetoresistance in WTe{sub 2}.

    SciTech Connect

    Thoutam, L. R.; Wang, Y. L.; Xiao, Z. L.; Das, S.; Luican-Mayer, A.; Divan, R.; Crabtree, G. W.; Kwok, W. K.

    2015-07-22

    Extremely large magnetoresistance (XMR) was recently discovered in WTe2, triggering extensive research on this material regarding the XMR origin. Since WTe2 is a layered compound with metal layers sandwiched between adjacent insulating chalcogenide layers, this material has been considered to be electronically two-dimensional (2D). Here we report two new findings on WTe2: (1) WTe2 is electronically 3D with a mass anisotropy as low as 2, as revealed by the 3D scaling behavior of the resistance R(H20) = R(e0H) with e0=(cos 20+y-2 sin2 0)1/2, 0 being the magnetic field angle with respect to c-axis of the crystal and (r) being the mass anisotropy; (2) the mass anisotropy (r) varies with temperature and follows the magnetoresistance behavior of the Fermi liquid state when the temperature is lowered. Our results not only provide a general scaling approach for the anisotropic magnetoresistance but also are crucial for correctly understanding the electronic properties of WTe2, including the origin of the remarkable ‘turn-on’ behavior in the resistance versus temperature curve, which has been widely observed in many materials and assumed to be a metal-insulator transition.

  19. Tunneling magnetoresistive heads for magnetic data storage.

    PubMed

    Mao, Sining

    2007-01-01

    Spintronics is emerging to be a new form of nanotechnologies, which utilizes not only the charge but also spin degree of freedom of electrons. Spin-dependent tunneling transport is one of the many kinds of physical phenomena involving spintronics, which has already found industrial applications. In this paper, we first provide a brief review on the basic physics and materials for magnetic tunnel junctions, followed more importantly by a detailed coverage on the application of magnetic tunneling devices in magnetic data storage. The use of tunneling magnetoresistive reading heads has helped to maintain a fast growth of areal density, which is one of the key advantages of hard disk drives as compared to solid-state memories. This review is focused on the first commercial tunneling magnetoresistive heads in the industry at an areal density of 80 approximately 100 Gbit/in2 for both laptop and desktop Seagate hard disk drive products using longitudinal media. The first generation tunneling magnetoresistive products utilized a bottom stack of tunnel junctions and an abutted hard bias design. The output signal amplitude of these heads was 3 times larger than that of comparable giant magnetoresistive devices, resulting in a 0.6 decade bit error rate gain over the latter. This has enabled high component and drive yields. Due to the improved thermal dissipation of vertical geometry, the tunneling magnetoresistive head runs cooler with a better lifetime performance, and has demonstrated similar electrical-static-discharge robustness as the giant magnetoresistive devices. It has also demonstrated equivalent or better process and wafer yields compared to the latter. The tunneling magnetoresistive heads are proven to be a mature and capable reader technology. Using the same head design in conjunction with perpendicular recording media, an areal density of 274 Gbit/in2 has been demonstrated, and advanced tunneling magnetoresistive heads can reach 311 Gbit/in2. Today, the

  20. Classical and quantum routes to linear magnetoresistance

    NASA Astrophysics Data System (ADS)

    Hu, Jingshi

    The transverse, positive magnetoresistance of suitably doped silver chalcogenides and indium antimonides changes linearly with magnetic field by thousands of percent, with no sign of saturation up to MegaGauss. A precise characterization of these unexpected observations has led to two very different, yet equally interesting magnetotransport mechanisms: the classical inhomogeneity-induced current jetting, and quantum linear magnetoresistance. The inhomogeneous distribution of excess/deficient silver atoms lies behind the anomalous magnetoresistive response of silver chalcogenides, introducing spatial conductivity fluctuations with length scales independent of the cyclotron radius. We show that a systematic investigation of the resistivity tensor in longitudinal field could be used to identify the spatial inhomogeneities and determine the associated length scale of the current distortion. By contrast, the linear magnetoresistance observed in single-crystalline InSb presents a spectacular manifestation of magnetotransport in the extreme quantum limit, when only one Landau band is partially filled. Harnessing both the classical and quantum effects opens the gate to artificial fabrication of conducting networks with micron scale unit size for enhanced magnetoresistive sensitivity.

  1. Angle-dependent magnetoresistance and quantum oscillations in high-mobility semimetal LuPtBi.

    PubMed

    Xu, Guizhou; Hou, Zhipeng; Wang, Yue; Zhang, Xiaoming; Zhang, Hongwei; Liu, Enke; Xi, X; Xu, Feng; Wu, Guangheng; Zhang, Xixiang; Wang, Wenhong

    2017-03-14

    The recent discovery of ultrahigh mobility and large positive magnetoresistance in topologically non-trivial Half-Heusler semimetal LuPtBi provides a unique playground for studying exotic physics and significant perspective for device applications. As an fcc-structured electron-hole-compensated semimetal, LuPtBi theoretically exhibits six symmetrically arranged anisotropic electron Fermi pockets and two nearly-spherical hole pockets, offering the opportunity to explore the physics of Fermi surface with a simple angle-related magnetotransport properties. In this work, through the angle-dependent transverse magnetoresistance measurements, in combination with high-field SdH quantum oscillations, we achieved to map out a Fermi surface with six anisotropic pockets in the high-temperature and low-field regime, and furthermore, identify a possible magnetic field driven Fermi surface change at lower temperatures. Reasons account for the Fermi surface change in LuPtBi are discussed in terms of the field-induced electron evacuation due to Landau quantization.

  2. Spin Hall magnetoresistance at high temperatures

    SciTech Connect

    Uchida, Ken-ichi; Qiu, Zhiyong; Kikkawa, Takashi; Iguchi, Ryo; Saitoh, Eiji

    2015-02-02

    The temperature dependence of spin Hall magnetoresistance (SMR) in Pt/Y{sub 3}Fe{sub 5}O{sub 12} (YIG) bilayer films has been investigated in a high temperature range from room temperature to near the Curie temperature of YIG. The experimental results show that the magnitude of the magnetoresistance ratio induced by the SMR monotonically decreases with increasing the temperature and almost disappears near the Curie temperature. We found that, near the Curie temperature, the temperature dependence of the SMR in the Pt/YIG film is steeper than that of a magnetization curve of the YIG; the critical exponent of the magnetoresistance ratio is estimated to be 0.9. This critical behavior of the SMR is attributed mainly to the temperature dependence of the spin-mixing conductance at the Pt/YIG interface.

  3. Magnetic and magnetoresistance studies of nanometric electrodeposited Co films and Co/Cu layered structures: Influence of magnetic layer thickness

    NASA Astrophysics Data System (ADS)

    Zsurzsa, S.; Péter, L.; Kiss, L. F.; Bakonyi, I.

    2017-01-01

    The magnetic properties and the magnetoresistance behavior were investigated for electrodeposited nanoscale Co films, Co/Cu/Co sandwiches and Co/Cu multilayers with individual Co layer thicknesses ranging from 1 nm to 20 nm. The measured saturation magnetization values confirmed that the nominal and actual layer thicknesses are in fairly good agreement. All three types of layered structure exhibited anisotropic magnetoresistance for thick magnetic layers whereas the Co/Cu/Co sandwiches and Co/Cu multilayers with thinner magnetic layers exhibited giant magnetoresistance (GMR), the GMR magnitude being the largest for the thinnest Co layers. The decreasing values of the relative remanence and the coercive field when reducing the Co layer thickness down to below about 3 nm indicated the presence of superparamagnetic (SPM) regions in the magnetic layers which could be more firmly evidenced for these samples by a decomposition of the magnetoresistance vs. field curves into a ferromagnetic and an SPM contribution. For thicker magnetic layers, the dependence of the coercivity (Hc) on magnetic layer thickness (d) could be described for each of the layered structure types by the usual equation Hc=Hco+a/dn with an exponent around n=1. The common value of n suggests a similar mechanism for the magnetization reversal by domain wall motion in all three structure types and hints also at the absence of coupling between magnetic layers in the Co/Cu/Co sandwiches and Co/Cu multilayers.

  4. Magnetoresistance of galfenol-based magnetic tunnel junction

    SciTech Connect

    Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Eddrief, M.; Marangolo, M.

    2015-12-15

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe{sub 1-x}Ga{sub x}) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  5. Anomalous Magnetoresistance in Dirty Magnetic Quantum Wells

    NASA Astrophysics Data System (ADS)

    Jaroszyński, J.; Andrearczyk, T.; Karczewski, G.; Wojtowicz, T.; Wróbel, J.; Popović, Dragana; Dietl, T.

    2006-09-01

    We report on magnetotransport in a 2D modulation doped (Cd,Mn)Te diluted magnetic semiconductor (DMS). The quantum Hall effect is observed in applied perpendicular magnetic fields, as one would expect in a high mobility 2D system. It is surprising, however, that the application of an in-plane B reveals features commonly observed in colossal magnetoresistant (CMR) materials, such as a strong negative magnetoresistance as well as dramatic and nonmonotonic changes in the zero-field resistance which coincide with the ferromagnetic ordering. These analogies suggest that the phenomena observed in DMS and manganites have a common origin — the formation of microscopic clusters.

  6. Current-perpendicular-to-the-plane giant magnetoresistance in spin-valves with AgSn alloy spacers

    SciTech Connect

    Read, J. C.; Nakatani, T. M.; Smith, Neil; Choi, Y.-S.; York, B. R.; Brinkman, E.; Childress, J. R.

    2015-07-28

    We investigate the use of AgSn alloys as the spacer layer in current-perpendicular-to-the-plane magnetoresistance devices. Alloying with Sn increases resistivity but results in a reasonably long (>10 nm) spin-diffusion length, so large magnetoresistance can be achieved with thin AgSn spacers. Compared to Ag thin films, AgSn forms smaller grain sizes, reduced roughness, and exhibits less interdiffusion upon annealing, resulting in decreased interlayer magnetic coupling in exchange biased spin-valves. AgSn also shows improved corrosion resistance compared to Ag, which is advantageous for nanofabrication, including magnetic recording head sensors. Combining a AgSn spacer with Co-based Heusler alloy ferromagnet in an exchange biased, polycrystalline trilayer thinner than 12 nm results in magnetoresistance values up to 15% at room temperature.

  7. Giant magnetoresistance in granular FeSiO 2 films

    NASA Astrophysics Data System (ADS)

    Zhao, B.; Yan, X.

    1997-02-01

    We studied resistivity, magnetoresistivity and magnetization in granular FeSiO 2 films. In the hopping region, magnetoresistance was found to be as large as -5%, and is isotropic for different measurement geometry, which is the signature of giant magnetoresistance due to a spin-dependent conduction process. Temperature dependence of magnetoresistance could be described qualitatively but not quantitatively by two specific spin-dependent tunnelling models. We found that resistivity ϱ changes five orders of magnitude by altering measurement temperature, annealing temperature or metal volume fraction, and that magnetoresistivity -Δϱ increases with ϱ monotonously.

  8. Dynamic Vehicle Detection via the Use of Magnetic Field Sensors

    PubMed Central

    Markevicius, Vytautas; Navikas, Dangirutis; Zilys, Mindaugas; Andriukaitis, Darius; Valinevicius, Algimantas; Cepenas, Mindaugas

    2016-01-01

    The vehicle detection process plays the key role in determining the success of intelligent transport management system solutions. The measurement of distortions of the Earth’s magnetic field using magnetic field sensors served as the basis for designing a solution aimed at vehicle detection. In accordance with the results obtained from research into process modeling and experimentally testing all the relevant hypotheses an algorithm for vehicle detection using the state criteria was proposed. Aiming to evaluate all of the possibilities, as well as pros and cons of the use of anisotropic magnetoresistance (AMR) sensors in the transport flow control process, we have performed a series of experiments with various vehicles (or different series) from several car manufacturers. A comparison of 12 selected methods, based on either the process of determining the peak signal values and their concurrence in time whilst calculating the delay, or by measuring the cross-correlation of these signals, was carried out. It was established that the relative error can be minimized via the Z component cross-correlation and Kz criterion cross-correlation methods. The average relative error of vehicle speed determination in the best case did not exceed 1.5% when the distance between sensors was set to 2 m. PMID:26797615

  9. Dynamic Vehicle Detection via the Use of Magnetic Field Sensors.

    PubMed

    Markevicius, Vytautas; Navikas, Dangirutis; Zilys, Mindaugas; Andriukaitis, Darius; Valinevicius, Algimantas; Cepenas, Mindaugas

    2016-01-19

    The vehicle detection process plays the key role in determining the success of intelligent transport management system solutions. The measurement of distortions of the Earth's magnetic field using magnetic field sensors served as the basis for designing a solution aimed at vehicle detection. In accordance with the results obtained from research into process modeling and experimentally testing all the relevant hypotheses an algorithm for vehicle detection using the state criteria was proposed. Aiming to evaluate all of the possibilities, as well as pros and cons of the use of anisotropic magnetoresistance (AMR) sensors in the transport flow control process, we have performed a series of experiments with various vehicles (or different series) from several car manufacturers. A comparison of 12 selected methods, based on either the process of determining the peak signal values and their concurrence in time whilst calculating the delay, or by measuring the cross-correlation of these signals, was carried out. It was established that the relative error can be minimized via the Z component cross-correlation and Kz criterion cross-correlation methods. The average relative error of vehicle speed determination in the best case did not exceed 1.5% when the distance between sensors was set to 2 m.

  10. Alkanethiol capping-induced changes in the magnetoresistance of Co

    NASA Astrophysics Data System (ADS)

    Knaus, Brad; Garzon, Samir; Crawford, Thomas M.

    2008-03-01

    We demonstrate that chemisorption of a ˜ 1 nm thick dodecanethiol (C12H25SH) self-assembled monolayer on the surface of an Au film alters the magnetotransport of an underlying Co film. Giant paramagnetism has been previously detected in Au thin films and nanoparticles capped with alkanethiols via SQUID magnetometry. By observing the impact of Au-thiol magnetism on a ferromagnetic thin film we avoid background subtraction and the influence of impurities. After thiolation, significant changes are observed in the anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) from Co/Au bilayers (30 nm/5-60 nm) patterned into 1 x 5 mm^2 bars. Driven with nearly perpendicular external fields, we observed domain nucleation shifts of ˜0.65 T and changes in the FWHM of the AMR. We have also measured differences in the MR as a function of ambient exposure time presumably due to oxidation effects known to occur in alkanethiols. Effects of surface scattering were eliminated with the introduction of a 12nm Al2O3 insulation barrier between Co and Au. We have calculated that the effects of magnetostriction are too small by more than two orders of magnitude to explain our observations. We therefore hypothesize that Au-thiol magnetization acts as a source of magnetic field which biases the underlying Co film.

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

    DOEpatents

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

    2001-01-01

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

  12. Strong anisotropic thermal conductivity of monolayer WTe2

    NASA Astrophysics Data System (ADS)

    Ma, Jinlong; Chen, Yani; Han, Zheng; Li, Wu

    2016-12-01

    Tungsten ditelluride (WTe2) has attracted increasing attention due to its large magnetoresistance and pressure-induced superconductivity. In this work, we investigate the thermal conductivity (κ) of monolayer WTe2 by performing first-principles calculations, and find strong anisotropic κ with predicted room-temperature values of 9 and 20 W m-1 K-1 along two principal lattice directions, respectively. Such strong anisotropy suggests the importance of orientation when engineering thermal-related applications based on WTe2. The anisotropy of κ is attributed to the in-plane linear acoustic phonon branches, while the out-of-plane quadratic acoustic phonon branch is almost isotropic. The size dependence of κ shows that the size effect can persists up to 10 μm, and the anisotropy decreases with decreasing sample size due to the suppression of low-frequency anisotropic phonons by boundary scattering.

  13. Giant Magnetoresistive Biochip for DNA Detection and HPV Genotyping

    PubMed Central

    Xu, Liang; Yu, Heng; Akhras, Michael S.; Han, Shu-Jen; Osterfeld, Sebastian; White, Robert L.; Pourmand, Nader; Wang, Shan X.

    2008-01-01

    A giant magnetoresistive (GMR) biochip based on spin valve sensor array and magnetic nanoparticle labels was developed for inexpensive, sensitive and reliable DNA detection. The DNA targets detected in this experiment were PCR products amplified from Human Papillomavirus (HPV) plasmids. The concentrations of the target DNA after PCR were around 10 nM in most cases, but concentrations of 10 pM were also detectable, which is demonstrated by experiments with artificial DNA samples. A mild but highly specific surface chemistry was used for probe oligonucleotide immobilization. Double modulation technique was used for signal detection in order to reduce the 1/f noise in the sensor. Twelve assays were performed with an accuracy of approximately 90%. Magnetic signals were consistent with particle coverage data measured with Scanning Electron Microscopy. More recent research on microfluidics showed the potential of reducing the assay time below one hour. This is the first demonstration of magnetic DNA detection using plasmid-derived samples. This study provides a direct proof that GMR sensors can be used for biomedical applications. PMID:18457945

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

    PubMed

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

    2007-04-01

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

  15. Electromotive force and huge magnetoresistance in magnetic tunnel junctions.

    PubMed

    Pham, Nam Hai; Ohya, Shinobu; Tanaka, Masaaki; Barnes, Stewart E; Maekawa, Sadamichi

    2009-03-26

    The electromotive force (e.m.f.) predicted by Faraday's law reflects the forces acting on the charge, -e, of an electron moving through a device or circuit, and is proportional to the time derivative of the magnetic field. This conventional e.m.f. is usually absent for stationary circuits and static magnetic fields. There are also forces that act on the spin of an electron; it has been recently predicted that, for circuits that are in part composed of ferromagnetic materials, there arises an e.m.f. of spin origin even for a static magnetic field. This e.m.f. can be attributed to a time-varying magnetization of the host material, such as the motion of magnetic domains in a static magnetic field, and reflects the conversion of magnetic to electrical energy. Here we show that such an e.m.f. can indeed be induced by a static magnetic field in magnetic tunnel junctions containing zinc-blende-structured MnAs quantum nanomagnets. The observed e.m.f. operates on a timescale of approximately 10(2)-10(3) seconds and results from the conversion of the magnetic energy of the superparamagnetic MnAs nanomagnets into electrical energy when these magnets undergo magnetic quantum tunnelling. As a consequence, a huge magnetoresistance of up to 100,000 per cent is observed for certain bias voltages. Our results strongly support the contention that, in magnetic nanostructures, Faraday's law of induction must be generalized to account for forces of purely spin origin. The huge magnetoresistance and e.m.f. may find potential applications in high sensitivity magnetic sensors, as well as in new active devices such as 'spin batteries'.

  16. Angular dependence of the magnetoresistance below T c of epitaxial Bi 2Sr 2CuO y thin films

    NASA Astrophysics Data System (ADS)

    Rifi, H.; Li, Z. Z.; Megtert, S.; Raffy, H.; Laborde, O.; Monceau, P.

    1994-12-01

    Magnetoresistance of high quality epitaxial Bi 2Sr 2CuO y thin films has been measured for temperatures below T c (1.5Kanisotropic Bi 2Sr 2CaCu 2O y phase. The behavior with the magnetic field perpendicular to the CuO 2 planes is briefly discussed.

  17. Magnetoresistive system with concentric ferromagnetic asymmetric nanorings

    SciTech Connect

    Avila, J. I. Tumelero, M. A.; Pasa, A. A.; Viegas, A. D. C.

    2015-03-14

    A structure consisting of two concentric asymmetric nanorings, each displaying vortex remanent states, is studied with micromagnetic calculations. By orienting in suitable directions, both the asymmetry of the rings and a uniform magnetic field, the vortices chiralities can be switched from parallel to antiparallel, obtaining in this way the analogue of the ferromagnetic and antiferromagnetic configurations found in bar magnets pairs. Conditions on the thickness of single rings to obtain vortex states, as well as formulas for their remanent magnetization are given. The concentric ring structure enables the creation of magnetoresistive systems comprising the qualities of magnetic nanorings, such as low stray fields and high stability. A possible application is as contacts in spin injection in semiconductors, and estimations obtained here of magnetoresistance change for a cylindrical spin injection based device show significant variations comparable to linear geometries.

  18. Dirac State in Giant Magnetoresistive Materials

    NASA Astrophysics Data System (ADS)

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

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

  19. An analytic approach to tunnelling magnetoresistance

    NASA Astrophysics Data System (ADS)

    Eames, M. E.; Inkson, J. C.

    2009-08-01

    We present an analytic model for the barrier transmission coefficient that can be used to calculate the tunnelling magnetoresistance (TMR) for metal-insulator-metal systems. It removes the approximations inherent in the Simmons' and Brinkman models currently used to fit experimental systems that give much lower predictions of the barrier height than would be expected. The model is accurate enough to directly relate to the experiment and hence device optimisation by predicting junction parameters that are in line with bulk properties.

  20. Large hysteretic magnetoresistance of silicide nanostructures

    NASA Astrophysics Data System (ADS)

    Kim, T.; Naser, B.; Chamberlin, R. V.; Schilfgaarde, M. V.; Bennett, P. A.; Bird, J. P.

    2007-11-01

    We demonstrate a large (as much as 100%) and strongly hysteretic magnetoresistance (MR) in nominally nonferromagnetic silicide films and nanowires. This unusual MR is quenched above a few kelvins, where conventional behavior due to weak antilocalization is recovered. The dynamic characteristics of this effect are suggestive of weakly interacting, localized paramagnetic moments that form at the surface oxide of the silicide nanostructures, with dramatic consequences for transport when the system size is reduced to the nanoscale.

  1. Anisotropic Artificial Impedance Surfaces

    NASA Astrophysics Data System (ADS)

    Quarfoth, Ryan Gordon

    Anisotropic artificial impedance surfaces are a group of planar materials that can be modeled by the tensor impedance boundary condition. This boundary condition relates the electric and magnetic field components on a surface using a 2x2 tensor. The advantage of using the tensor impedance boundary condition, and by extension anisotropic artificial impedance surfaces, is that the method allows large and complex structures to be modeled quickly and accurately using a planar boundary condition. This thesis presents the theory of anisotropic impedance surfaces and multiple applications. Anisotropic impedance surfaces are a generalization of scalar impedance surfaces. Unlike the scalar version, anisotropic impedance surfaces have material properties that are dependent on the polarization and wave vector of electromagnetic radiation that interacts with the surface. This allows anisotropic impedance surfaces to be used for applications that scalar surfaces cannot achieve. Three of these applications are presented in this thesis. The first is an anisotropic surface wave waveguide which allows propagation in one direction, but passes radiation in the orthogonal direction without reflection. The second application is a surface wave beam shifter which splits a surface wave beam in two directions and reduces the scattering from an object placed on the surface. The third application is a patterned surface which can alter the scattered radiation pattern of a rectangular shape. For each application, anisotropic impedance surfaces are constructed using periodic unit cells. These unit cells are designed to give the desired surface impedance characteristics by modifying a patterned metallic patch on a grounded dielectric substrate. Multiple unit cell geometries are analyzed in order to find the setup with the best performance in terms of impedance characteristics and frequency bandwidth.

  2. Anisotropic Nanoparticles and Anisotropic Surface Chemistry.

    PubMed

    Burrows, Nathan D; Vartanian, Ariane M; Abadeer, Nardine S; Grzincic, Elissa M; Jacob, Lisa M; Lin, Wayne; Li, Ji; Dennison, Jordan M; Hinman, Joshua G; Murphy, Catherine J

    2016-02-18

    Anisotropic nanoparticles are powerful building blocks for materials engineering. Unusual properties emerge with added anisotropy-often to an extraordinary degree-enabling countless new applications. For bottom-up assembly, anisotropy is crucial for programmability; isotropic particles lack directional interactions and can self-assemble only by basic packing rules. Anisotropic particles have long fascinated scientists, and their properties and assembly behavior have been the subjects of many theoretical studies over the years. However, only recently has experiment caught up with theory. We have begun to witness tremendous diversity in the synthesis of nanoparticles with controlled anisotropy. In this Perspective, we highlight the synthetic achievements that have galvanized the field, presenting a comprehensive discussion of the mechanisms and products of both seed-mediated and alternative growth methods. We also address recent breakthroughs and challenges in regiospecific functionalization, which is the next frontier in exploiting nanoparticle anisotropy.

  3. Gate tunable magneto-resistance of ultra-thin W Te2 devices

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Zhang, Zhiran; Cai, Chaoyi; Tian, Shibing; Kushwaha, Satya; Lu, Hong; Taniguchi, Takashi; Watanabe, Kenji; Cava, Robert J.; Jia, Shuang; Chen, Jian-Hao

    2017-06-01

    In this work, the magneto-resistance (MR) of ultra-thin WTe2/BN heterostructures far away from electron-hole equilibrium is measured. The change of MR of such devices is found to be determined largely by a single tunable parameter, i.e. the amount of imbalance between electrons and holes. We also found that the magnetoresistive behavior of ultra-thin WTe2 devices is well-captured by a two-fluid model. According to the model, the change of MR could be as large as 400 000%, the largest potential change of MR among all materials known, if the ultra-thin samples are tuned to neutrality when preserving the mobility of 167 000 cm2 V-1 s-1 observed in bulk samples. Our findings show the prospects of ultra-thin WTe2 as a variable magnetoresistance material in future applications such as magnetic field sensors, information storage and extraction devices, and galvanic isolators. The results also provide important insight into the electronic structure and the origin of the large MR in ultra-thin WTe2 samples.

  4. Magnetoresistance and Anti-Ferromagnetic Coupling in FM-Graphene-FM Trilayers

    NASA Astrophysics Data System (ADS)

    Cobas, Enrique D.; van't Erve, Olaf M. J.; Cheng, Shu-Fan; Jonker, Berend T.

    Both high-magnetoresistance(MR) minority spin filtering and anti-ferromagnetic (AFM) coupling have been predicted for FM|Graphene|FM vertical heterostructures. Our previous experiments demonstrated ordinary magnetoresistance in NiFe-Graphene-Co heterostructures and no evident AFM coupling. Here we present experimental results that confirm both MR minority spin filtering and AFM coupling in high-quality FM|Graphene|FM heterostructures. The heterostructures were fabricated by a combination of sputtering, chemical vapor deposition and electron beam evaporation. The stack was patterned into symmetric cross-bar structures using Ar ion milling. Measurements show negative magnetoresistance in excess of 10 percent, confirming spin-filtering, and weak anti-ferromagnetic coupling throughout the temperature range 15K to 300K. The temperature dependence of the MR was studied and found consistent with thermal excitation of spin waves in the ferromagnetic electrodes. Junction resistance-area products are in the range of 10 Ωcm2. These heterostructures provide a fast and low-power magnetic field sensor in the sub-100 Oe range and are a step towards high-MR low RA-product MRAM junctions.

  5. Linear magnetoresistance in n-type silicon due to doping density fluctuations

    PubMed Central

    Porter, Nicholas A.; Marrows, Christopher H.

    2012-01-01

    We report the observation of a large linear magnetoresistance in the ohmic regime in commonplace commercial n-type silicon wafer with a P dopant density of (1.4±0.1) ×1015 cm–3, and report measurements of it in the temperature range 30–200 K. It arises from the deformation of current paths, which causes a part of the Hall field to be detected at the voltage probes. In short, wide samples we found linear magnetoresistance as large as 4707% in an 8 tesla field at 35 K. Sample geometry effects like these are commonplace in commercial Hall sensors. However, we found that the effect persisted in long, thin samples where the macroscopic current flow should be uniform between the voltage probes: we observed a magnetoresistance of 445% under the same conditions as above. We interpret this result as arising due to spatial fluctuations in the donor density, in the spirit of the Herring model. PMID:22876340

  6. Fe/Bi2Te3/Fe Tunneling Magneto-Resistance with topological insulator barrier

    NASA Astrophysics Data System (ADS)

    Salomon, Vallery; Seifu, Dereje

    2014-03-01

    Thin film tri-layer structure Fe/Bi2Te3/Fe was synthesized using magnetron DC / RF sputtering. This sample was synthesized at a substrate temperature of 100 °C. It was studied using in-house built magneto-optic Kerr effect (MOKE) instrument. The operating principles of MOKE consist of measuring changes in polarization of light reflected from a magnetic sample. The bulk magnetization was measured using vibrating sample magnetometer (VSM) and torque magneto meter (TMM). Topographic structure and magnetic domains were studied using atomic force microscope (AFM) and magnetic force microscope (MFM). Tunnel magneto-resistance (TMR) effect occurs in a structure that is composed of two conductors separated by a thin insulator of the order of few nanometers, the insulator barrier in this case is a well known topological insulator, Bi2Te3. In this structure, electrons tunnel from one of the conductors to the other through the insulating barrier. This is a forbidden process in classical physics, tunnel magneto-resistance is a purely quantum mechanical effect which is key in developing magneto-resistive random access memory (MRAM), magnetic sensors, and novel logic devices. We would like to acknowledge the support by ARL #W911NF-12-2-0041 and by NSF #MRI -DMR-1337339.

  7. Hybrid magnetoresistance in the proximity of a ferromagnet

    NASA Astrophysics Data System (ADS)

    Chien, Chia-Ling

    2014-03-01

    A new type of magnetoresistance (MR) effect has recently been observed in nominally nonmagnetic metal (Pt) thin films in contact with either a ferromagnetic (FM) insulator such as yttrium iron garnet (YIG), or a FM metal, such as permalloy (Py). The resistivities with in-plane magnetic fields parallel (ρ∥) and transverse (ρT) to a current and a perpendicular field (ρ⊥) at room temperature show the behavior of ρ⊥ ~ρ∥ >ρT, distinctively different from all other known MR effects, including the well-known anisotropic MR in FMs of ρ∥>ρT ~ρ⊥ . The key question is whether the new MR is the proposed spin Hall MR (SMR) based on spin current conversion in Pt, or due to magnetic proximity effects (MPE), for which Pt is highly susceptible when in contact with a FM. Recent experiments show that the characteristics of ρ⊥ ~ρ∥ >ρT, for which the SMR theory accounts, do not hold at low temperatures nor at different magnetic fields. Furthermore, the new MR persists even after altering the Pt/YIG interface thereby blocking the spin current. The feature of new MR can also be reproduced when Pt is in contact with a non-magnetic insulator doped with a few percent of Fe impurities. These results show that the new MR is probably due to both spin current and MPE. Through tuning the YIG surface and the insertion of other layers between Pt and YIG, we are able to separate the two contributions of spin current and MPE of the new hybrid MR. This work, in collaboration with S. Y. Huang, D. Qu (JHU) B. F. Miao (JHU and Nanjing University), Y. M. Lu and J. W. Cai (Institute of Physics, Chinese Academy of Sciences), has been supported in part by NSF DMR1262253. H. Nakayama et al.,Phys. Rev. Lett. 110, 206601(2013).

  8. Magnetoresistance in antiferromagnet-based spin tunnel junctions

    NASA Astrophysics Data System (ADS)

    Jungwirth, Tomas

    2012-02-01

    To date spintronics research and applications of magnetically ordered systems have focused on ferromagnets (FMs). There are, however, fundamental physical limitations for FM materials which may make them impractical to realize the full potential of spintronics. Metal FMs offer high temperature operation but the large magnetic stray fields make them unfavorable for high-density integration and metals are unsuitable for transistor and information processing applications. FM semiconductors on the other hand do not allow for high-temperature operation. We present a concept in which these limitations are circumvented in spintronics based on antiferromagnets. The concept is based on relativistic magnetic and magneto-transport anisotropy effects in nanodevices whose common characteristics is that they are an even function of the microscopic magnetic moment vector, i.e., can be equally strong in AFMs as in FMs. As a demonstration we present our experimental observation of >100% tunneling anisotropic magnetoresistance in a device with an IrMn AFM tunnel electrode [1]. We will also discuss candidate materials for high-temperature AFM semiconductor spintronics [2].[4pt] [1] B. G. Park, J.Wunderlich, X.Marti, V.Holy, Y.Kurosaki, M.Yamada, H.Yamamoto, A.Nishide, J.Hayakawa, H.Takahashi, A.B.Shick, T.Jungwirth, Nature Mat. 10, 347 (2011). [0pt] [2] T.Jungwirth, V.Nov'ak, X.Marti, M.Cukr, F.M'aca, A.B. Shick, J.Masek, P.Horodysk'a, P.Nemec, V.Hol'y, et al., Phys. Rev. B 83, 035321 (2011).

  9. Anisotropic ray trace

    NASA Astrophysics Data System (ADS)

    Lam, Wai Sze Tiffany

    Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3x3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for

  10. Study of the magnetic microstructure of Ni/NiO nanogranular samples above the electric percolation threshold by magnetoresistance measurements.

    PubMed

    Del Bianco, L; Spizzo, F; Tamisari, M; Calbucci, M; Allia, P

    2012-08-01

    Magnetoresistance measurements have been exploited to gain information on the magnetic microstructure of two Ni/NiO nanogranular materials consisting of Ni nanocrystallites (mean size of the order of 10 nm) embedded in a NiO matrix and differing in the amount of metallic Ni, ~33 and ~61 vol%. The overall conductance of both samples is metallic in character, indicating that the Ni content is above the percolation threshold for electric conductivity; the electric resistivity is two orders of magnitude smaller in the sample with higher Ni fraction (10(-5) Ωm against 10(-3) Ωm). An isotropic, spin-dependent magnetoresistance has been measured in the sample with lower Ni content, whereas both isotropic and anisotropic magnetoresistance phenomena coexist in the other material. This study, associated with magnetization loop measurements and the comparison with the exchange bias effect, allows one to conclude that in the sample with lower Ni content neither the physical percolation of the Ni nanocrystallites nor the magnetic percolation (i.e., formation of a homogeneous ferromagnetic network) are achieved; in the other sample physical percolation is reached while magnetic percolation is still absent. In both behaviors, a key role is played by the NiO matrix, which brings about a magnetic nanocrystallite/matrix interface exchange energy term and rules both the direct exchange interaction among Ni nanocrystallites and the magnetotransport properties of these nanogranular materials.

  11. Magneto-thermopower and magnetoresistance of single Co-Ni alloy nanowires

    NASA Astrophysics Data System (ADS)

    Böhnert, Tim; Vega, Victor; Michel, Ann-Kathrin; Prida, Victor M.; Nielsch, Kornelius

    2013-08-01

    The magneto-thermopower is measured and correlated to the anisotropic magnetoresistance of Co-Ni alloyed nanowires with varying composition. The highest absolute and relative variation of the Seebeck coefficient in perpendicularly applied magnetic fields at room temperature is determined to be 1.5 μVK-1 for Co0.24Ni0.76 and 8.1% for Co0.39Ni0.61 nanowires. Power factors of 3.7 mW/mK2 have been achieved, which is competitive with common thermoelectric materials like Bi2Te3. For Co-Ni nanowires containing up to 39% Co, a linear relationship between the magnetic field dependent change of the Seebeck coefficient and the electrical conductivity is found.

  12. Polarization dependent asymmetric magneto-resistance features in nanocrystalline diamond films

    SciTech Connect

    Bhattacharyya, Somnath

    2014-08-18

    Polar angle-dependence of magneto-resistance (AMR) in heavily nitrogen-incorporated ultra-nanocrystalline diamond (UNCD) films is recorded by applying high magnetic fields, which shows strong anisotropic features at low temperatures. The temperature-dependence of MR and AMR can reveal transport in the weak-localization regime, which is explained by using a superlattice model for arbitrary values of disorder and angles. While a propagative Fermi surface model explains the negative MR features for low degree of disorder the azimuthal angle-dependent MR shows field dependent anisotropy due to the aligned conducting channels on the layers normal to film growth direction. The analysis of MR and AMR can extract the temperature dependence of dephasing time with respect to the elastic scattering time which not only establishes quasi-two dimensional features in this system but also suggests a potential application in monitoring the performance of UNCD based quantum devices.

  13. Distortion of Magnetic Domain Wall Measured by Magneto-Resistance Changes in a Co Nanoring.

    PubMed

    Nam, Chunghee

    2015-01-01

    The electrical anisotropic magneto-resistance (AMR) measurements were performed to see the formation of a 360 degree magnetic domain wall (360 DW) and distortion of the magnetic moments in a Co nanoring structure. Since the 360 DW is consisted of two 180 degree DWs, a decrease of the resistance was found in the switching process from the vortex to reverse onion state by the AMR effects, which is consistent with micromagnetic simulations. In addition, a decrease of the resistance in the switching process from the onion to vortex state was observed by the distortion of the local magnetic moments due to an applied magnetic field. The stochastic behavior in the switching process is caused by thermally induced magnetic moments changes.

  14. Towards sub-200 nm nano-structuring of linear giant magneto-resistive spin valves by a direct focused ion beam milling process

    SciTech Connect

    Riedmüller, Benjamin; Huber, Felix; Herr, Ulrich

    2014-02-14

    In this work, we present a detailed investigation of a focused ion beam (FIB) assisted nano-structuring process for giant magneto-resistive (GMR) spin valve sensors. We have performed a quantitative study of the dependence of the GMR ratio as well as the sensor resistance on the ion dose, which is implanted in the active region of our sensors. These findings are correlated with the decrease of magneto-resistive properties after micro- and nano-structuring by the FIB and reveal the importance of ion damage which limits the applicability of FIB milling to GMR devices in the low μm range. Deposition of a protective layer (50 nm SiO{sub 2}) on top of the sensor structure before milling leads to a preservation of the magneto-resistive properties after the milling procedure down to sensor dimensions of ∼300 nm. The reduction of the sensor dimensions to the nanometer regime is accompanied by a shift of the GMR curves, and a modification of the saturation behavior. Both effects can be explained by a micromagnetic model including the magnetic interaction of free and pinned layer as well as the effect of the demagnetizing field of the free layer on the sensor behavior. The results demonstrate that the FIB technology can be successfully used to prepare spintronic nanostructures.

  15. Tuning quantum corrections and magnetoresistance in ZnO nanowires by ion implantation.

    PubMed

    Zeng, Y J; Pereira, L M C; Menghini, M; Temst, K; Vantomme, A; Locquet, J-P; Van Haesendonck, C

    2012-02-08

    Using ion implantation, the electrical as well as the magnetotransport properties of individual ZnO nanowires (NWs) can be tuned. The virgin NWs are configured as field-effect transistors which are in the enhancement mode. Al-implanted NWs reveal a three-dimensional metallic-like behavior, for which the magnetoresistance is well described by a semiempirical model that takes into account the presence of doping induced local magnetic moments and of two conduction bands. On the other hand, one-dimensional electron transport is observed in Co-implanted NWs. At low magnetic fields, the anisotropic magnetoresistance can be described in the framework of weak electron localization in the presence of strong spin-orbit scattering. From the weak localization, a large phase coherence length is inferred that reaches up to 800 nm at 2.5 K. The temperature-dependent dephasing is shown to result from a one-dimensional Nyquist noise-related mechanism. At the lowest temperatures, the phase coherence length becomes limited by magnetic scattering.

  16. Tuning giant magnetoresistance in rolled-up Co-Cu nanomembranes by strain engineering.

    PubMed

    Müller, Christian; Bof Bufon, Carlos Cesar; Makarov, Denys; Fernandez-Outon, Luis E; Macedo, Waldemar A A; Schmidt, Oliver G; Mosca, Dante Homero

    2012-11-21

    Compact rolled-up Co-Cu nanomembranes of high quality with different numbers of windings are realized by strain engineering. A profound analysis of magnetoresistance (MR) is performed for tubes with a single winding and a varied number of Co-Cu bilayers in the stack. Rolled-up nanomembranes with up to 12 Co-Cu bilayers are successfully fabricated by tailoring the strain state of the Cr bottom layer. By carrying out an angular dependent study, we ruled out the contribution from anisotropic MR and confirm that rolled-up Co-Cu multilayers exhibit giant magnetoresistance (GMR). No significant difference of MR is found for a single wound tube compared with planar devices. In contrast, MR in tubes with multiple windings is increased at low deposition rates of the Cr bottom layer, whereas the effect is not observable at higher rates, suggesting that interface roughness plays an important role in determining the GMR effect of the rolled-up nanomembranes. Furthermore, besides a linear increase of the MR with the number of windings, the self-rolling of nanomembranes substantially reduces the device footprint area.

  17. Rectification of radio-frequency current in a giant-magnetoresistance spin valve

    NASA Astrophysics Data System (ADS)

    Zietek, Sławomir; Ogrodnik, Piotr; Frankowski, Marek; Checiński, Jakub; Wiśniowski, Piotr; Skowroński, Witold; Wrona, Jerzy; Stobiecki, Tomasz; Żywczak, Antoni; Barnaś, Józef

    2015-01-01

    We report on a highly efficient spin diode effect in exchange-biased spin-valve giant-magnetoresistance (GMR) strips. In such multilayer structures, the symmetry of the current distribution along the vertical direction is broken and, as a result, a noncompensated Oersted field acting on the magnetic free layer appears. This field in turn is a driving force of magnetization precessions. Due to the GMR effect, the resistance of the strip oscillates following the magnetization dynamics. This leads to rectification of the applied radio-frequency current and induces a direct-current voltage Vdc. We present a theoretical description of this phenomenon and calculate the spin diode signal Vdc as a function of frequency, external magnetic field, and angle at which the external field is applied. Satisfactory quantitative agreement between theoretical predictions and experimental data has been achieved. Finally, we show that the spin diode signal in GMR devices is significantly stronger than in the anisotropic magnetoresistance permalloy-based devices.

  18. Photonic Magnetic Field Sensor

    DTIC Science & Technology

    2007-11-02

    reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical ( GMO ) or Faraday...Squids are those based upon the giant magneto-optical ( GMO ) effect in ferrimagnetic materials or YIG garnets and the giant magneto-resistance (GMR...effect in manganese based compounds. The development of the GMO material was mostly motivated by the need for compact, in-line fiber optical

  19. Spin dependent magnetoresistance at ferromagnet/superconductor/ferromagnet La{sub 0.7}Ca{sub 0.3}MnO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7-delta}/La{sub 0.7}Ca{sub 0.3}MnO{sub 3} trilayers.

    SciTech Connect

    Visani, C.; Pena, V.; Garcia-Barriocanal, J.; Arias, D.; Sefrioui, Z.; Leon, C.; Santamaria, J.; Nemes, N. M.; Garcia-Hernandez, M.; Martinez, J. L.; te Velthuis, S.G.E; Hoffmann, A.; Materials Science Division; Univ. Complutense de Madrid; Inst. de Ciencia de Materiales de Madrid

    2007-01-01

    We report on large magnetoresistance in ferromagnet/superconductor/ferromagnet trilayer structures made of La{sub 0.7}Ca{sub 0.3}MnO{sub 3} and YBa{sub 2}Cu{sub 3}O{sub 7}. We find that the shape and height of the magnetoresistance peaks are not modified when the relative orientation of current and magnetic field is changed from parallel to perpendicular. Furthermore, we find that the temperature shift of the resistance curves is independent of current and of the sweep rate of the magnetic field. These observations favor the view that the magnetoresistance phenomenon originates in the spin dependent transport of quasiparticles transmitted from the ferromagnetic electrodes into the superconductor, and rule out interpretations in terms of spontaneous vortices or anisotropic magnetoresistance of the ferromagnetic layers.

  20. Superficial magnetic imaging by an xy-scanner of three magnetoresistive channels.

    PubMed

    Cano, M E; Pacheco, A H; Cordova, T; Mazon, E E; Barrera, A

    2012-03-01

    A scanning system developed for planar magnetic surfaces composed of a moving line of three magnetoresistive ultrasensitive transducers, complemented by a signal conditioning circuit is presented. After the calibration of the sensors, it was used to determine magnetized surface images with different shapes to evaluate the sensitivity of the device, and the images are represented in gray levels on a scale from 0 to 255 intensities, to get a visual representation of the magnetic field strength. The device is shown to be sensitive enough to detect gradients homogeneities and discontinuities in the magnetic field maps and images of magnetic susceptibility.

  1. Dramatically decreased magnetoresistance in non-stoichiometric WTe2 crystals

    NASA Astrophysics Data System (ADS)

    Lv, Yang-Yang; Zhang, Bin-Bin; Li, Xiao; Pang, Bin; Zhang, Fan; Lin, Da-Jun; Zhou, Jian; Yao, Shu-Hua; Chen, Y. B.; Zhang, Shan-Tao; Lu, Minghui; Liu, Zhongkai; Chen, Yulin; Chen, Yan-Feng

    2016-05-01

    Recently, the layered semimetal WTe2 has attracted renewed interest owing to the observation of a non-saturating and giant positive magnetoresistance (~105%), which can be useful for magnetic memory and spintronic devices. However, the underlying mechanisms of the giant magnetoresistance are still under hot debate. Herein, we grew the stoichiometric and non-stoichiometric WTe2 crystals to test the robustness of giant magnetoresistance. The stoichiometric WTe2 crystals have magnetoresistance as large as 3100% at 2 K and 9-Tesla magnetic field. However, only 71% and 13% magnetoresistance in the most non-stoichiometry (WTe1.80) and the highest Mo isovalent substitution samples (W0.7Mo0.3Te2) are observed, respectively. Analysis of the magnetic-field dependent magnetoresistance of non-stoichiometric WTe2 crystals substantiates that both the large electron-hole concentration asymmetry and decreased carrier mobility, induced by non-stoichiometry, synergistically lead to the decreased magnetoresistance. This work sheds more light on the origin of giant magnetoresistance observed in WTe2.

  2. Hall effect and magnetoresistivity in the ternary molybdenum sulfides

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Haugland, E. J.; Alterovitz, S. A.

    1978-01-01

    The Hall coefficient and magnetoresistance of sputtered films of Cu(x)Mo6S8 and PbMo6S8 have been measured, as well as the magnetoresistance in sintered samples of the same materials. Assuming a single band model, net carrier densities and mean mobilities are determined

  3. Hall effect and magnetoresistivity in the ternary molybdenum sulfides

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Haugland, E. J.; Alterovitz, S. A.

    1978-01-01

    The Hall coefficient and magnetoresistance of sputtered films of Cu(x)Mo6S8 and PbMo6S8 have been measured, as well as the magnetoresistance in sintered samples of the same materials. Assuming a single band model, net carrier densities and mean mobilities are determined

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

    SciTech Connect

    Wu, Di-Cheng; Pan, You-Wei; Lin, Shih-Wei; Lin, Sheng-Di; Wu, Jenq-Shinn

    2016-04-25

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

  5. Application of magnetic sensors in automation control

    NASA Astrophysics Data System (ADS)

    Hou, Chunhong; Qian, Zhenghong

    2011-01-01

    Controls in automation need speed and position feedback. The feedback device is often referred to as encoder. Feedback technology includes mechanical, optical, and magnetic, etc. All advance with new inventions and discoveries. Magnetic sensing as a feedback technology offers certain advantages over other technologies like optical one. With new discoveries like GMR (Giant Magneto-Resistance), TMR (Tunneling Magneto-Resistance) becoming feasible for commercialization, more and more applications will be using advanced magnetic sensors in automation. This paper offers a general review on encoder and applications of magnetic sensors in automation control.

  6. Large magnetoresistance in oxide based ferromagnet/superconductor spin switches.

    SciTech Connect

    Pena, V.; Nemes, N.; Visani, C.; Garcia-Barriocanal, J.; Bruno, F.; Arias, D.; Sefrioui, Z.; Leon, C.; te Velthuis, S. G. E.; Hoffmann, A.; Garcia-Hernandez, M.; Santamaria, J.; Materials Science Division; Univ. Complutense de Madrid; Inst. de Ciencia de Materiales de Madrid

    2006-01-01

    We report large magnetoresistance (in excess of 1000%) in ferromagnet / superconductor / ferromagnet structures made of La{sub 0.7}Ca{sub 0.3}MnO{sub 3} and YBa{sub 2}Cu{sub 3}O{sub 7} in the current in plane (CIP) geometry. This magnetoresistance has many of the ingredients of the giant magnetoresistance of metallic superlattices: it is independent on the angle between current and magnetic field, depends on the relative orientation of the magnetization in the ferromagnetic layers, and takes very large values. The origin is enhanced scattering at the F/S interface in the anti parallel configuration of the magnetizations. Furthermore, we examine the dependence of the magnetoresistance effect on the thickness of the superconducting layer, and show that the magnetoresistance dies out for thickness in excess of 30 nm, setting a length scale for the diffusion of spin polarized quasiparticles.

  7. Extraordinary Magnetoresistance in Hybrid Semiconductor-Metal Systems

    NASA Astrophysics Data System (ADS)

    Hewett, T. H.; Kusmartsev, F. V.

    We show that extraordinary magnetoresistance (EMR) arises in systems consisting of two components; a semiconducting ring with a metallic inclusion embedded. The important aspect of this discovery is that the system must have a quasi-two-dimensional character. Using the same materials and geometries for the samples as in experiments by Solin et al.1,2, we show that such systems indeed exhibit a huge magnetoresistance. The magnetoresistance arises due to the switching of electrical current paths passing through the metallic inclusion. Diagrams illustrating the flow of the current density within the samples are utilised in discussion of the mechanism responsible for the magnetoresistance effect. Extensions are then suggested which may be applicable to the silver chalcogenides. Our theory offers an excellent description and explanation of experiments where a huge magnetoresistance has been discovered2,3.

  8. Extraordinary Magnetoresistance in Hybrid Semiconductor-Metal Systems

    NASA Astrophysics Data System (ADS)

    Hewett, T. H.; Kusmartsev, F. V.

    2010-12-01

    We show that extraordinary magnetoresistance (EMR) arises in systems consisting of two components; a semiconducting ring with a metallic inclusion embedded. The important aspect of this discovery is that the system must have a quasi-two-dimensional character. Using the same materials and geometries for the samples as in experiments by Solin et al.1,2, we show that, such systems indeed exhibit a huge magnetoresistance. The magnetoresistance arises due to the switching of electrical current paths passing through the metallic inclusion. Diagrams illustrating the flow of the current density within the samples are utilised in discussion of the mechanism responsible for the magnetoresistance effect. Extensions are then suggested which may be applicable to the silver chalcogenides. Our theory offers an excellent description and explanation of experiments where a huge magnetoresistance has been discovered2,3.

  9. Large magnetoresistance effect in nitrogen-doped silicon

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Yang, Zhaolong; Wang, Wei; Si, Mingsu; Yang, Dezheng; Liu, Huiping; Xue, Desheng

    2017-05-01

    In this work, we reported a large magnetoresistance effect in silicon by ion implantation of nitrogen atoms. At room temperature, the magnetoresistance of silicon reaches 125 % under magnetic field 1.7 T and voltage bias -80 V. By applying an alternating magnetic field with a frequency (f) of 0.008 Hz, we find that the magnetoresistance of silicon is divided into f and 2f two signal components, which represent the linear and quadratic magnetoresistance effects, respectively. The analysis based on tuning the magnetic field and the voltage bias reveals that electric-field-induced space-charge effect plays an important role to enhance both the linear and quadratic magnetoresistance effects. Observation as well as a comprehensive explanation of large MR in silicon, especially based on semiconductor CMOS implantation technology, will be an important progress towards magnetoelectronic applications.

  10. Diluted magnetic semiconductor nanowires exhibiting magnetoresistance

    DOEpatents

    Yang, Peidong; Choi, Heonjin; Lee, Sangkwon; He, Rongrui; Zhang, Yanfeng; Kuykendal, Tevye; Pauzauskie, Peter

    2011-08-23

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

  11. Giant magnetoresistance in organic spin valves

    SciTech Connect

    Sun, Da-Li; Yin, Lifeng; Sun, Chengjun; Guo, Hangwen; Gai, Zheng; Zhang, Xiaoguang; Ward, Thomas Z; Cheng, Zhaohua; Shen, Jian

    2010-01-01

    Interfacial diffusion between magnetic electrodes and organic spacer layers is a serious problem in the organic spintronics which complicates attempts to understand the spin-dependent transport mechanism and hurts the achievement of a desirably high magnetoresistance (MR). We deposit nanodots instead of atoms onto the organic layer using buffer layer assist growth. Spin valves using this method exhibit a sharper interface and a giant MR of up to {approx}300%. Analysis of the current-voltage characteristics indicates that the spin-dependent carrier injection correlates with the observed MR.

  12. Giant magnetoresistance in bilayer graphene nanoflakes

    NASA Astrophysics Data System (ADS)

    Farghadan, Rouhollah; Farekiyan, Marzieh

    2016-09-01

    Coherent spin transport through bilayer graphene (BLG) nanoflakes sandwiched between two electrodes made of single-layer zigzag graphene nanoribbon was investigated by means of Landauer-Buttiker formalism. Application of a magnetic field only on BLG structure as a channel produces a perfect spin polarization in a large energy region. Moreover, the conductance could be strongly modulated by magnetization of the zigzag edge of AB-stacked BLG, and the junction, entirely made of carbon, produces a giant magnetoresistance (GMR) up to 100%. Intestinally, GMR and spin polarization could be tuned by varying BLG width and length. Generally, MR in a AB-stacked BLG strongly increases (decreases) with length (width).

  13. Active Damping Using Distributed Anisotropic Actuators

    NASA Technical Reports Server (NTRS)

    Schiller, Noah H.; Cabell, Randolph H.; Quinones, Juan D.; Wier, Nathan C.

    2010-01-01

    A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.

  14. Three-dimensional Anisotropy and Kohler's Rule Scaling of the Magnetoresistance in WTe2

    NASA Astrophysics Data System (ADS)

    Wang, Yong-Lei

    Tungsten ditelluride (WTe2) was recently discovered to have extremely large magnetoresistance (XMR) at low temperatures and exhibits a transformative 'turn-on' temperature behavior: when the applied magnetic field H is above a certain value, the resistivity versus temperature ρ (T) curve shows a minimum at a field dependent temperature T* (H) . Since WTe2 is a layered compound with metal layers sandwiched between adjacent insulating chalcogenide layers, it is typically considered to be a two dimensional (2D) material, whereby the anisotropic magnetoresistance is attributed only to the perpendicular component of the magnetic field. Moreover, the 'turn-on' temperature behavior has been interpreted as a magnetic-field-driven metal-insulator transition or attributed to an electronic structure change. In this talk I will report on two scaling behaviors of the magnetoresistance in WTe2. The first shows that the angle dependence of the magnetoresistance follows a conventional 3D anisotropy scaling and hence reveals the electrical 3D nature of WTe2. The second demonstrates that the ρ (T , H) curves, including those with 'turn-on' temperature behavior, can be scaled with Kohler's rule. The observed Kohler's rule scaling excludes the possible existence of a magnetic-field-driven metal-insulator transition or significant contribution of an electronic structure change to the low-temperature XMR in WTe2. It indicates that both the XMR and the 'turn-on' behavior originate from the high mobilities of the charge carriers, which are strongly temperature dependent in WTe2. We also derived quantitative expressions for the magnetic field dependence of the 'turn-on' temperature T* (H) and for the temperature dependence of the resistivity ρ (T* , H) at the onset of the XMR behavior. In collaboration with L. R. Thoutam, Z. L. Xiao, J. Hu, S. Das, Z. Q. Mao, J. Wei, R. Divan, A. Luican-Mayer, G. W. Crabtree, and W. K. Kwok This work was supported by the U.S. DOE, Office of Science, BES

  15. Anisotropic contrast optical microscope

    NASA Astrophysics Data System (ADS)

    Peev, D.; Hofmann, T.; Kananizadeh, N.; Beeram, S.; Rodriguez, E.; Wimer, S.; Rodenhausen, K. B.; Herzinger, C. M.; Kasputis, T.; Pfaunmiller, E.; Nguyen, A.; Korlacki, R.; Pannier, A.; Li, Y.; Schubert, E.; Hage, D.; Schubert, M.

    2016-11-01

    An optical microscope is described that reveals contrast in the Mueller matrix images of a thin, transparent, or semi-transparent specimen located within an anisotropic object plane (anisotropic filter). The specimen changes the anisotropy of the filter and thereby produces contrast within the Mueller matrix images. Here we use an anisotropic filter composed of a semi-transparent, nanostructured thin film with sub-wavelength thickness placed within the object plane. The sample is illuminated as in common optical microscopy but the light is modulated in its polarization using combinations of linear polarizers and phase plate (compensator) to control and analyze the state of polarization. Direct generalized ellipsometry data analysis approaches permit extraction of fundamental Mueller matrix object plane images dispensing with the need of Fourier expansion methods. Generalized ellipsometry model approaches are used for quantitative image analyses. These images are obtained from sets of multiple images obtained under various polarizer, analyzer, and compensator settings. Up to 16 independent Mueller matrix images can be obtained, while our current setup is limited to 11 images normalized by the unpolarized intensity. We demonstrate the anisotropic contrast optical microscope by measuring lithographically defined micro-patterned anisotropic filters, and we quantify the adsorption of an organic self-assembled monolayer film onto the anisotropic filter. Comparison with an isotropic glass slide demonstrates the image enhancement obtained by our method over microscopy without the use of an anisotropic filter. In our current instrument, we estimate the limit of detection for organic volumetric mass within the object plane of ≈49 fg within ≈7 × 7 μm2 object surface area. Compared to a quartz crystal microbalance with dissipation instrumentation, where contemporary limits require a total load of ≈500 pg for detection, the instrumentation demonstrated here improves

  16. Anisotropic contrast optical microscope.

    PubMed

    Peev, D; Hofmann, T; Kananizadeh, N; Beeram, S; Rodriguez, E; Wimer, S; Rodenhausen, K B; Herzinger, C M; Kasputis, T; Pfaunmiller, E; Nguyen, A; Korlacki, R; Pannier, A; Li, Y; Schubert, E; Hage, D; Schubert, M

    2016-11-01

    An optical microscope is described that reveals contrast in the Mueller matrix images of a thin, transparent, or semi-transparent specimen located within an anisotropic object plane (anisotropic filter). The specimen changes the anisotropy of the filter and thereby produces contrast within the Mueller matrix images. Here we use an anisotropic filter composed of a semi-transparent, nanostructured thin film with sub-wavelength thickness placed within the object plane. The sample is illuminated as in common optical microscopy but the light is modulated in its polarization using combinations of linear polarizers and phase plate (compensator) to control and analyze the state of polarization. Direct generalized ellipsometry data analysis approaches permit extraction of fundamental Mueller matrix object plane images dispensing with the need of Fourier expansion methods. Generalized ellipsometry model approaches are used for quantitative image analyses. These images are obtained from sets of multiple images obtained under various polarizer, analyzer, and compensator settings. Up to 16 independent Mueller matrix images can be obtained, while our current setup is limited to 11 images normalized by the unpolarized intensity. We demonstrate the anisotropic contrast optical microscope by measuring lithographically defined micro-patterned anisotropic filters, and we quantify the adsorption of an organic self-assembled monolayer film onto the anisotropic filter. Comparison with an isotropic glass slide demonstrates the image enhancement obtained by our method over microscopy without the use of an anisotropic filter. In our current instrument, we estimate the limit of detection for organic volumetric mass within the object plane of ≈49 fg within ≈7 × 7 μm(2) object surface area. Compared to a quartz crystal microbalance with dissipation instrumentation, where contemporary limits require a total load of ≈500 pg for detection, the instrumentation demonstrated here improves

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

    SciTech Connect

    Schneider, J. M.; Chitta, V. A.; Oliveira, N. F.; Peres, M. L. Castro, S. de; Soares, D. A. W.; Wiedmann, S.; Zeitler, U.; Abramof, E.; Rappl, P. H. O.; Mengui, U. A.

    2014-10-20

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

  18. Nonlocal Magnetoresistance Mediated by Spin Superfluidity.

    PubMed

    Takei, So; Tserkovnyak, Yaroslav

    2015-10-09

    The electrical response of two diffusive metals is studied when they are linked by a magnetic insulator hosting a topologically stable (superfluid) spin current. We discuss how charge currents in the metals induce a spin supercurrent state, which in turn generates a magnetoresistance that depends on the topology of the electrical circuit. This magnetoresistance relies on phase coherence over the entire magnet and gives direct evidence for spin superfluidity. We show that driving the magnet with an ac current allows coherent spin transport even in the presence of U(1)-breaking magnetic anisotropy that can preclude dc superfluid transport. Spin transmission in the ac regime shows a series of resonance peaks as a function of frequency. The peak locations, heights, and widths can be used to extract static interfacial properties, e.g., the spin-mixing conductance and effective spin Hall angle, and to probe dynamic properties such as the spin-wave dispersion. Thus, ac transport may provide a simpler route to realizing nonequilbrium coherent spin transport and a useful way to characterize the magnetic system, serving as a precursor to the realization of dc superfluid spin transport.

  19. High-performance magnetic sensorics for printable and flexible electronics.

    PubMed

    Karnaushenko, Daniil; Makarov, Denys; Stöber, Max; Karnaushenko, Dmitriy D; Baunack, Stefan; Schmidt, Oliver G

    2015-02-04

    High-performance giant magnetoresistive (GMR) sensorics are realized, which are printed at predefined locations on flexible circuitry. Remarkably, the printed magnetosensors remain fully operational over the complete consumer temperature range and reveal a giant magnetoresistance up to 37% and a sensitivity of 0.93 T(-1) at 130 mT. With these specifications, printed magnetoelectronics can be controlled using flexible active electronics for the realization of smart packaging and energy-efficient switches.

  20. Non-local magnetoresistance in YIG/Pt nanostructures

    SciTech Connect

    Goennenwein, Sebastian T. B. Pernpeintner, Matthias; Gross, Rudolf; Huebl, Hans; Schlitz, Richard; Ganzhorn, Kathrin; Althammer, Matthias

    2015-10-26

    We study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet. The local magnetoresistive response, inferred from the voltage drop measured along one given Pt strip upon current-biasing it, shows the characteristic magnetization orientation dependence of the spin Hall magnetoresistance. We simultaneously also record the non-local voltage appearing along a second, electrically isolated, Pt strip, separated from the current carrying one by a gap of a few 100 nm. The corresponding non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process, confirming the results recently put forward by Cornelissen et al. [“Long-distance transport of magnon spin information in a magnetic insulator at room temperature,” Nat. Phys. (published online 14 September 2015)]. Our magnetotransport data, taken at a series of different temperatures as a function of magnetic field orientation, rotating the externally applied field in three mutually orthogonal planes, show that the mechanisms behind the spin Hall and the non-local magnetoresistance are qualitatively different. In particular, the non-local magnetoresistance vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance prevails.

  1. Nanotesla magnetoresistance in π-conjugated polymer devices

    NASA Astrophysics Data System (ADS)

    Klemm, Philippe; Bange, Sebastian; Pöllmann, Agnes; Boehme, Christoph; Lupton, John M.

    2017-06-01

    We demonstrate submicrotesla sensitivity of organic magnetoresistance in thin-film diodes made of the conducting polymer poly(styrene sulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS). The magnetoresistance sensitivity is shown to be better than 20 parts per billion (ppb). As for other conjugated polymers, magnetoresistance can be separated into two regimes of field strength: the nonmonotonic ultrasmall magnetic field effect on magnetic field scales below 2 mT, and the monotonic intermediate magnetic field effect on scales over several tens of mT. The former gives the PEDOT:PSS magnetoresistance curve a characteristic W-shaped functionality, with inverted turning points compared to those found in conventional organic light-emitting diode (OLED) devices. We succeed in resolving the ultrasmall magnetic field effect of the PEDOT:PSS layer incorporated within an OLED structure, which is responsible for an additional magnetoresistive feature on the ppm scale. Such a device shows unprecedented complexity in magnetoresistance with a total of four extrema within a field range of ±1 mT. We propose that these unique characteristics arise from spin-spin interactions in the weakly bound carrier pairs responsible for the spin-dependent recombination probed in magnetoresistance.

  2. Anisotropic eddy viscosity models

    NASA Technical Reports Server (NTRS)

    Carati, D.; Cabot, W.

    1996-01-01

    A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.

  3. Magnetoresistive immunosensor for the detection of Escherichia coli O157:H7 including a microfluidic network.

    PubMed

    Mujika, M; Arana, S; Castaño, E; Tijero, M; Vilares, R; Ruano-López, J M; Cruz, A; Sainz, L; Berganza, J

    2009-01-01

    A hand held device has been designed for the immunomagnetic detection and quantification of the pathogen Escherichia coli O157:H7 in food and clinical samples. In this work, a technology to manufacture a Lab on a Chip that integrates a 3D microfluidic network with a microfabricated biosensor has been developed. With this aim, the sensing film optimization, the design of the microfluidic circuitry, the development of the biological protocols involved in the measurements and, finally, the packaging needed to carry out the assays in a safe and straightforward way have been completed. The biosensor is designed to be capable to detect and quantify small magnetic field variations caused by the presence of superparamagnetic beads bound to the antigens previously immobilized on the sensor surface via an antibody-antigen reaction. The giant magnetoresistive multilayer structure implemented as sensing film consists of 20[Cu(5.10nm)/Co(2.47 nm)] with a magnetoresistance of 3.20% at 235Oe and a sensitivity up to 0.06 Omega/Oe between 150Oe and 230Oe. Silicon nitride has been selected as optimum sensor surface coating due to its suitability for antibody immobilization. In order to guide the biological samples towards the sensing area, a microfluidic network made of SU-8 photoresist has been included. Finally, a novel packaging design has been fabricated employing 3D stereolithographic techniques. The microchannels are connected to the outside using standard tubing. Hence, this packaging allows an easy replacement of the used devices.

  4. Spin-tunneling magnetoresistive elements based on multilayered nanostructures

    NASA Astrophysics Data System (ADS)

    Amelichev, V. V.; Belyakov, P. A.; Vasil'ev, D. V.; Zhukov, D. A.; Kazakov, Yu. V.; Kostyuk, D. V.; Orlov, E. P.; Kasatkin, S. I.; Krikunov, A. I.

    2017-08-01

    The results of studies of characteristics of spin-tunneling magnetoresistive (STMR) elements fabricated from multilayered nanostructures using a mask technique have been considered. The parameters of magnetic annealing of STMR elements have experimentally been obtained. The results of these experiments have shown that a magnitude of the magnetoresistive effect can increase by four to five or more times. The test samples of STMR elements, which have a magnitude of the giant magnetoresistive effect up to 50% and a resistance of 30-35 kΩ, have been studied in the absence of a magnetic field.

  5. Magnetoresistance and Hall resistivity of semimetal WTe2 ultrathin flakes

    NASA Astrophysics Data System (ADS)

    Luo, Xin; Fang, Chi; Wan, Caihua; Cai, Jialin; Liu, Yong; Han, Xiufeng; Lu, Zhihong; Shi, Wenhua; Xiong, Rui; Zeng, Zhongming

    2017-04-01

    This article reports the characterization of WTe2 thin flake magnetoresistance and Hall resistivity. We found it does not exhibit magnetoresistance saturation when subject to high fields, in a manner similar to their bulk characteristics. The linearity of Hall resistivity in our devices confirms the compensation of electrons and holes. By relating experimental results to a classic two-band model, the lower magnetoresistance values in our samples is demonstrated to be caused by decreased carrier mobility. The dependence of mobility on temperature indicates the main role of optical phonon scattering at high temperatures. Our results provide more detailed information on carrier behavior and scattering mechanisms in WTe2 thin films.

  6. Large magnetoresistance of insulating silicon films with superconducting nanoprecipitates

    NASA Astrophysics Data System (ADS)

    Heera, V.; Fiedler, J.; Skorupa, W.

    2016-10-01

    We report on large negative and positive magnetoresistance in inhomogeneous, insulating Si:Ga films below a critical temperature of about 7 K. The magnetoresistance effect exceeds 300 % at temperatures below 3 K and fields of 8 T. The comparison of the transport properties of superconducting samples with that of insulating ones reveals that the large magnetoresistance is associated with the appearance of local superconductivity. A simple phenomenological model based on localized Cooper pairs and hopping quasiparticles is able to describe the temperature and magnetic field dependence of the sheet resistance of such films.

  7. Magnetoresistance and Hall resistivity of semimetal WTe2 ultrathin flakes.

    PubMed

    Luo, Xin; Fang, Chi; Wan, Caihua; Cai, Jialin; Liu, Yong; Han, Xiufeng; Lu, Zhihong; Shi, Wenhua; Xiong, Rui; Zeng, Zhongming

    2017-04-07

    This article reports the characterization of WTe2 thin flake magnetoresistance and Hall resistivity. We found it does not exhibit magnetoresistance saturation when subject to high fields, in a manner similar to their bulk characteristics. The linearity of Hall resistivity in our devices confirms the compensation of electrons and holes. By relating experimental results to a classic two-band model, the lower magnetoresistance values in our samples is demonstrated to be caused by decreased carrier mobility. The dependence of mobility on temperature indicates the main role of optical phonon scattering at high temperatures. Our results provide more detailed information on carrier behavior and scattering mechanisms in WTe2 thin films.

  8. Direct visualization of lead corona and its nanomolar colorimetric detection using anisotropic gold nanoparticles.

    PubMed

    Dwivedi, Charu; Chaudhary, Abhishek; Gupta, Abhishek; Nandi, Chayan K

    2015-03-11

    The study presents dithiothreitol (DTT) functionalized anisotropic gold nanoparticles (GNP) based colorimetric sensor for detection of toxic lead ions in water. Our results demonstrate the selectivity and sensitivity of the developed sensor over various heavy metal ions with detection limit of ∼9 nM. The mechanism of sensing is explained on the basis of unique corona formation around the DTT functionalized anisotropic GNP.

  9. Spin-transfer torque in ferromagnetic bilayers generated by anomalous Hall effect and anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Grollier, Julie; Stiles, M. D.

    2016-10-01

    We propose an experimental scheme to determine the spin-transfer torque efficiency excited by the spin-orbit interaction in ferromagnetic bilayers from the measurement of the longitudinal magnetoresistace. Solving a diffusive spin-transport theory with appropriate boundary conditions gives an analytical formula of the longitudinal charge current density. The longitudinal charge current has a term that is proportional to the square of the spin-transfer torque efficiency and that also depends on the ratio of the film thickness to the spin diffusion length of the ferromagnet. Extracting this contribution from measurements of the longitudinal resistivity as a function of the thickness can give the spin-transfer torque efficiency.

  10. Spin-transfer torque in ferromagnetic bilayers generated by anomalous Hall effect and anisotropic magnetoresistance.

    PubMed

    Taniguchi, Tomohiro; Grollier, Julie; Stiles, M D

    2016-01-01

    We propose an experimental scheme to determine the spin-transfer torque efficiency excited by the spin-orbit interaction in ferromagnetic bilayers from the measurement of the longitudinal magnetoresistace. Solving a diffusive spin-transport theory with appropriate boundary conditions gives an analytical formula of the longitudinal charge current density. The longitudinal charge current has a term that is proportional to the square of the spin-transfer torque efficiency and that also depends on the ratio of the film thickness to the spin diffusion length of the ferromagnet. Extracting this contribution from measurements of the longitudinal resistivity as a function of the thickness can give the spin-transfer torque efficiency.

  11. Spin-transfer torque in ferromagnetic bilayers generated by anomalous Hall effect and anisotropic magnetoresistance

    PubMed Central

    Taniguchi, Tomohiro; Grollier, Julie; Stiles, M. D.

    2016-01-01

    We propose an experimental scheme to determine the spin-transfer torque efficiency excited by the spin-orbit interaction in ferromagnetic bilayers from the measurement of the longitudinal magnetoresistace. Solving a diffusive spin-transport theory with appropriate boundary conditions gives an analytical formula of the longitudinal charge current density. The longitudinal charge current has a term that is proportional to the square of the spin-transfer torque efficiency and that also depends on the ratio of the film thickness to the spin diffusion length of the ferromagnet. Extracting this contribution from measurements of the longitudinal resistivity as a function of the thickness can give the spin-transfer torque efficiency. PMID:28057977

  12. Sound localization in an anisotropic plate using electret microphones.

    PubMed

    Hoseini Sabzevari, S Amir; Moavenian, Majid

    2017-01-01

    Acoustic source localization without knowing the velocity profile in anisotropic plates is still one of the most challenging areas in this field. The current time-of-flight based approaches for localization in anisotropic media, are based on using six high sampling sensors. The number of sensors and the corresponding large amount of data, would make those methods inefficient in practical applications. Although there are many different non-time-of-flight based approaches such as machine learning, or soft computing based methods that can be used for localization with a less number of sensors, they are not as accurate as time-of-flight based techniques. In this article, a new approach which requires only four low sampling rate sensors to localize acoustic source in an anisotropic plate is proposed. In this technique, four electret low sampling rate sensors in two clusters are installed on the plate surface. The presented method uses attenuation analysis in a suitable frequency band to decrease the number of sensors. The approach is experimentally tested and verified on an airplane composite nose by applying artificially generated acoustic emissions (Hsu-Nielsen source). The results reveal that the accuracy of proposed technique depends on distinction of dominant frequency band. A stethoscope as a physical filter is employed to reduce the sensitivity of the technique and delineation of frequency band. The suggested technique improves the accuracy of localization prediction. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Passive wireless strain measurement based upon the Villari effect and giant magnetoresistance

    NASA Astrophysics Data System (ADS)

    Windl, Roman; Bruckner, Florian; Abert, Claas; Huber, Christian; Vogler, Christoph; Huber, Thomas; Oezelt, Harald; Suess, Dieter

    2016-12-01

    A passive wireless radio frequency-identification (RFID) stress/strain sensor is presented. Stress is transformed into a change of magnetic field by utilizing an amorphous metal ribbon. This magnetic field change is measured by a giant magnetoresistance magnetic field sensor and converted into a digital value with a RFID chip for wireless access. Standard metal foil strain gauges have a gauge factor GF from around 2 to 5 and suffer from the disadvantage of a physically connected power supply and measurement equipment. For the presented sensor, a strain range of -10 μm/m to 190 μm/m results in a linear sensor response, a gauge factor of GF ≈ 245, and a detectivity of 4.10 nm/m 1/√{Hz } . The detectivity of the presented sensor is similar to the detectivity of a reference metal foil strain gauge. Due to low power consumption and easy signal analysis, this sensor is well suited for long term strain measurement inside closed spaces. RFID adds features like multiple tag detection, wireless passive operation and a user data storage.

  14. Experimental and theoretical investigation of the precise transduction mechanism in giant magnetoresistive biosensors.

    PubMed

    Lee, Jung-Rok; Sato, Noriyuki; Bechstein, Daniel J B; Osterfeld, Sebastian J; Wang, Junyi; Gani, Adi Wijaya; Hall, Drew A; Wang, Shan X

    2016-01-05

    Giant magnetoresistive (GMR) biosensors consisting of many rectangular stripes are being developed for high sensitivity medical diagnostics of diseases at early stages, but many aspects of the sensing mechanism remain to be clarified. Using e-beam patterned masks on the sensors, we showed that the magnetic nanoparticles with a diameter of 50 nm located between the stripes predominantly determine the sensor signals over those located on the sensor stripes. Based on computational analysis, it was confirmed that the particles in the trench, particularly those near the edges of the stripes, mainly affect the sensor signals due to additional field from the stripe under an applied field. We also demonstrated that the direction of the average magnetic field from the particles that contributes to the signal is indeed the same as that of the applied field, indicating that the particles in the trench are pivotal to produce sensor signal. Importantly, the same detection principle was validated with a duplex protein assay. Also, 8 different types of sensor stripes were fabricated and design parameters were explored. According to the detection principle uncovered, GMR biosensors can be further optimized to improve their sensitivity, which is highly desirable for early diagnosis of diseases.

  15. Experimental and theoretical investigation of the precise transduction mechanism in giant magnetoresistive biosensors

    PubMed Central

    Lee, Jung-Rok; Sato, Noriyuki; Bechstein, Daniel J. B.; Osterfeld, Sebastian J.; Wang, Junyi; Gani, Adi Wijaya; Hall, Drew A.; Wang, Shan X.

    2016-01-01

    Giant magnetoresistive (GMR) biosensors consisting of many rectangular stripes are being developed for high sensitivity medical diagnostics of diseases at early stages, but many aspects of the sensing mechanism remain to be clarified. Using e-beam patterned masks on the sensors, we showed that the magnetic nanoparticles with a diameter of 50 nm located between the stripes predominantly determine the sensor signals over those located on the sensor stripes. Based on computational analysis, it was confirmed that the particles in the trench, particularly those near the edges of the stripes, mainly affect the sensor signals due to additional field from the stripe under an applied field. We also demonstrated that the direction of the average magnetic field from the particles that contributes to the signal is indeed the same as that of the applied field, indicating that the particles in the trench are pivotal to produce sensor signal. Importantly, the same detection principle was validated with a duplex protein assay. Also, 8 different types of sensor stripes were fabricated and design parameters were explored. According to the detection principle uncovered, GMR biosensors can be further optimized to improve their sensitivity, which is highly desirable for early diagnosis of diseases. PMID:26728870

  16. A 256 pixel magnetoresistive biosensor microarray in 0.18μm CMOS

    PubMed Central

    Hall, Drew A.; Gaster, Richard S.; Makinwa, Kofi; Wang, Shan X.; Murmann, Boris

    2014-01-01

    Magnetic nanotechnologies have shown significant potential in several areas of nanomedicine such as imaging, therapeutics, and early disease detection. Giant magnetoresistive spin-valve (GMR SV) sensors coupled with magnetic nanotags (MNTs) possess great promise as ultra-sensitive biosensors for diagnostics. We report an integrated sensor interface for an array of 256 GMR SV biosensors designed in 0.18 μm CMOS. Arranged like an imager, each of the 16 column level readout channels contains an analog front- end and a compact ΣΔ modulator (0.054 mm2) with 84 dB of dynamic range and an input referred noise of 49 nT/√Hz. Performance is demonstrated through detection of an ovarian cancer biomarker, secretory leukocyte peptidase inhibitor (SLPI), spiked at concentrations as low as 10 fM. This system is designed as a replacement for optical protein microarrays while also providing real-time kinetics monitoring. PMID:24761029

  17. A 256 pixel magnetoresistive biosensor microarray in 0.18μm CMOS.

    PubMed

    Hall, Drew A; Gaster, Richard S; Makinwa, Kofi; Wang, Shan X; Murmann, Boris

    2013-05-01

    Magnetic nanotechnologies have shown significant potential in several areas of nanomedicine such as imaging, therapeutics, and early disease detection. Giant magnetoresistive spin-valve (GMR SV) sensors coupled with magnetic nanotags (MNTs) possess great promise as ultra-sensitive biosensors for diagnostics. We report an integrated sensor interface for an array of 256 GMR SV biosensors designed in 0.18 μm CMOS. Arranged like an imager, each of the 16 column level readout channels contains an analog front- end and a compact ΣΔ modulator (0.054 mm(2)) with 84 dB of dynamic range and an input referred noise of 49 nT/√Hz. Performance is demonstrated through detection of an ovarian cancer biomarker, secretory leukocyte peptidase inhibitor (SLPI), spiked at concentrations as low as 10 fM. This system is designed as a replacement for optical protein microarrays while also providing real-time kinetics monitoring.

  18. Toward a system to measure action potential on mice brain slices with local magnetoresistive probes

    SciTech Connect

    Amaral, J.; Cardoso, S.; Freitas, P. P.; Sebastiao, A. M.

    2011-04-01

    This work combines an electrophysiological system with a magnetoresistive chip to measure the magnetic field created by the synaptic/action potential currents. The chip, with 15 spin valve sensors, was designed to be integrated in a recording chamber for submerged mice brain slices used for synaptic potential measurements. Under stimulation (rectangular pulses of 0.1 ms every 10 s) through a concentric electrode placed near the CA3/CA1 border of the hippocampus, the spin valve sensor readout signals with 20 {mu}V amplitude and a pulse length of 20 to 30 ms were recorded only in the pyramidal cell bodies region and can be interpreted as being derived from action potentials/currents.

  19. Toward a system to measure action potential on mice brain slices with local magnetoresistive probes

    NASA Astrophysics Data System (ADS)

    Amaral, J.; Cardoso, S.; Freitas, P. P.; Sebastião, A. M.

    2011-04-01

    This work combines an electrophysiological system with a magnetoresistive chip to measure the magnetic field created by the synaptic/action potential currents. The chip, with 15 spin valve sensors, was designed to be integrated in a recording chamber for submerged mice brain slices used for synaptic potential measurements. Under stimulation (rectangular pulses of 0.1 ms every 10 s) through a concentric electrode placed near the CA3/CA1 border of the hippocampus, the spin valve sensor readout signals with 20 μV amplitude and a pulse length of 20 to 30 ms were recorded only in the pyramidal cell bodies region and can be interpreted as being derived from action potentials/currents.

  20. Giant magnetoresistive biosensors for molecular diagnosis: surface chemistry and assay development

    NASA Astrophysics Data System (ADS)

    Yu, Heng; Osterfeld, Sebastian J.; Xu, Liang; White, Robert L.; Pourmand, Nader; Wang, Shan X.

    2008-08-01

    Giant magnetoresistive (GMR) biochips using magnetic nanoparticle as labels were developed for molecular diagnosis. The sensor arrays consist of GMR sensing strips of 1.5 μm or 0.75 μm in width. GMR sensors are exquisitely sensitive yet very delicate, requiring ultrathin corrosion-resistive passivation and efficient surface chemistry for oligonucleotide probe immobilization. A mild and stable surface chemistry was first developed that is especially suitable for modifying delicate electronic device surfaces, and a practical application of our GMR biosensors was then demonstrated for detecting four most common human papillomavirus (HPV) subtypes in plasmids. We also showed that the DNA hybridization time could potentially be reduced from overnight to about ten minutes using microfluidics.

  1. Sensors for noncontact vibration diagnostics in rotating machinery

    NASA Astrophysics Data System (ADS)

    Procházka, Pavel

    2016-06-01

    The paper deals with electromagnetic sensors for noncontact vibration diagnostics in rotating machinery. The sensors were designed for operational measurements in turbomachinery by means of the tip-timing method. The main properties of eddy-current, Hall effect, induction and magnetoresistive sensors are described and compared. Possible arrangements of the experimental systems for static and dynamic calibration of the sensors are suggested and discussed.

  2. Evaluation of Magnetoresistive RAM for Space Applications

    NASA Technical Reports Server (NTRS)

    Heidecker, Jason

    2014-01-01

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

  3. Magnetic mesocrystal-assisted magnetoresistance in manganite.

    PubMed

    Yang, Jan-Chi; He, Qing; Zhu, Yuan-Min; Lin, Jheng-Cyuan; Liu, Heng-Jui; Hsieh, Ying-Hui; Wu, Ping-Chun; Chen, Yen-Lin; Lee, Shang-Fan; Chin, Yi-Ying; Lin, Hong-Ji; Chen, Chien-Te; Zhan, Qian; Arenholz, Elke; Chu, Ying-Hao

    2014-11-12

    Mesocrystal, a new class of crystals as compared to conventional and well-known single crystals and polycrystalline systems, has captured significant attention in the past decade. Recent studies have been focused on the advance of synthesis mechanisms as well as the potential on device applications. In order to create further opportunities upon functional mesocrystals, we fabricated a self-assembled nanocomposite composed of magnetic CoFe2O4 mesocrystal in Sr-doped manganites. This combination exhibits intriguing structural and magnetic tunabilities. Furthermore, the antiferromagnetic coupling of the mesocrystal and matrix has induced an additional magnetic perturbation to spin-polarized electrons, resulting in a significantly enhanced magnetoresistance in the nanocomposite. Our work demonstrates a new thought toward the enhancement of intrinsic functionalities assisted by mesocrystals and advanced design of novel mesocrystal-embedded nanocomposites.

  4. Low field magnetoresistance of gadolinium nanowire

    SciTech Connect

    Chakravorty, Manotosh Raychaudhuri, A. K.

    2014-02-07

    We report low field (μ{sub 0}H < 0.2 T) magnetoresistance (MR) studies on a single Gd nanowire patterned from a nano-structured film (average grain size ∼ 35 nm) by focused ion beam. For comparison, we did similar MR measurements on a polycrystalline sample with large crystallographic grains (∼4 μm). It is observed that in the low field region where the MR is due to motion of magnetic domains, the MR in the large grained sample shows a close relation to the characteristic temperature dependent magnetocrystalline anisotropy including a sharp rise in MR at the spin reorientation transition at 235 K. In stark contrast, in the nanowire, the MR shows complete suppression of the above behaviours and it shows predominance of the grain boundary and spin disorder controlling the domain response.

  5. Antiferromagnetic anisotropy determination by spin Hall magnetoresistance

    NASA Astrophysics Data System (ADS)

    Wang, Hua; Hou, Dazhi; Qiu, Zhiyong; Kikkawa, Takashi; Saitoh, Eiji; Jin, Xiaofeng

    2017-08-01

    An electric method for measuring magnetic anisotropy in antiferromagnetic insulators (AFIs) is proposed. When a metallic film with strong spin-orbit interactions, e.g., platinum (Pt), is deposited on an AFI, its resistance should be affected by the direction of the AFI Néel vector due to the spin Hall magnetoresistance (SMR). Accordingly, the direction of the AFI Néel vector, which is affected by both the external magnetic field and the magnetic anisotropy, is reflected in resistance of Pt. The magnetic field angle dependence of the resistance of Pt on AFI is calculated by considering the SMR, which indicates that the antiferromagnetic anisotropy can be obtained experimentally by monitoring the Pt resistance in strong magnetic fields. Calculations are performed for realistic systems such as Pt/Cr2O3, Pt/NiO, and Pt/CoO.

  6. Negative Magnetoresistance in Amorphous Indium Oxide Wires

    PubMed Central

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

    2016-01-01

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

  7. Negative Magnetoresistance in Amorphous Indium Oxide Wires

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  8. A new class of magnetoresistive compounds ^1

    NASA Astrophysics Data System (ADS)

    Xu, R.; Husmann, A.; Rosenbaum, T. F.; Saboungi, M.-L.; Enderby, J. E.; Price, D. L.

    1997-03-01

    We have measured a significant magnetoresistance (MR) in some silver selenide and silver telluride compounds from 4.5 K up to room termperature; the composition is such that these compounds are narrow gap self-doped degenerate n-type semiconductors. Our results show no evidence of saturation up to at least 5.5 T for transverse MR and the field dependences are rather linear ^2. A comparison is being made with that of other traditional and novel materials. Studies are under way to determine the origin of this phenomenom and the physical factors which may further enhance the MR. Supported by NSF-MRSEC at Chicago and by U.S.DOE contrac W-31-109-ENG-38 at ANL. R. Xu, A. Husmann, T.F. Rosenbaum, M.-L. Saboungi, D.L. Price, J.E. Enderby, in preparation.

  9. Hyperfine interaction and magnetoresistance in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Sheng, Y.; Nguyen, T. D.; Veeraraghavan, G.; Mermer, Ö.; Wohlgenannt, M.; Qiu, S.; Scherf, U.

    2006-07-01

    We explore the possibility that hyperfine interaction causes the recently discovered organic magnetoresistance (OMAR) effect. We deduce a simple fitting formula from the hyperfine Hamiltonian that relates the saturation field of the OMAR traces to the hyperfine coupling constant. We compare the fitting results to literature values for this parameter. Furthermore, we apply an excitonic pair mechanism model based on hyperfine interaction, previously suggested by others to explain various magnetic-field effects in organics, to the OMAR data. Whereas this model can explain a few key aspects of the experimental data, we uncover several fundamental contradictions as well. By varying the injection efficiency for minority carriers in the devices, we show experimentally that OMAR is only weakly dependent on the ratio between excitons formed and carriers injected, likely excluding any excitonic effect as the origin of OMAR.

  10. Molecular hyperfine fields in organic magnetoresistance devices

    NASA Astrophysics Data System (ADS)

    Giro, Ronaldo; Rosselli, Flávia P.; dos Santos Carvalho, Rafael; Capaz, Rodrigo B.; Cremona, Marco; Achete, Carlos A.

    2013-03-01

    We calculate molecular hyperfine fields in organic magnetoresistance (OMAR) devices using ab initio calculations. To do so, we establish a protocol for the accurate determination of the average hyperfine field Bhf and apply it to selected molecular ions: NPB, TPD, and Alq3. Then, we make devices with precisely the same molecules and perform measurements of the OMAR effect, in order to address the role of hole-transport layer in the characteristic magnetic field B0 of OMAR. Contrary to common belief, we find that molecular hyperfine fields are not only caused by hydrogen nuclei. We also find that dipolar contributions to the hyperfine fields can be comparable to the Fermi contact contributions. However, such contributions are restricted to nuclei located in the same molecular ion as the charge carrier (intramolecular), as extramolecular contributions are negligible.

  11. Anomalous magnetoresistance in magnetized topological insulator cylinders

    SciTech Connect

    Siu, Zhuo Bin; Jalil, Mansoor B. A.

    2015-05-07

    The close coupling between the spin and momentum degrees of freedom in topological insulators (TIs) presents the opportunity for the control of one to manipulate the other. The momentum can, for example, be confined on a curved surface and the spin influenced by applying a magnetic field. In this work, we study the surface states of a cylindrical TI magnetized in the x direction perpendicular to the cylindrical axis lying along the z direction. We show that a large magnetization leads to an upwards bending of the energy bands at small |k{sub z}|. The bending leads to an anomalous magnetoresistance where the transmission between two cylinders magnetized in opposite directions is higher than when the cylinders are magnetized at intermediate angles with respect to each other.

  12. Spin-controlled negative magnetoresistance resulting from exchange interactions

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  13. Magnetoresistive properties of nanostructured magnetic metals, manganites, and magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Solin, N. I.; Romashev, L. N.; Naumov, S. V.; Saranin, A. A.; Zotov, A. V.; Olyanich, D. A.; Kotlyar, V. G.; Utas, O. A.

    2016-02-01

    We consider methods for controlling magnetoresistive parameters of magnetic metal superlattices, manganites, and magnetic semiconductors. By reducing the thickness of ferromagnetic layers in superlattices (e.g., Fe layers in Fe/Cr superlattices), it is possible to form superparamagnetic clustered-layered nanostructures with a magnetoresistance weakly depending on the direction of the external magnetic field, which is very important for applications of such type of materials. Producing Mn vacancies and additionally annealing lanthanum manganites in the oxygen atmosphere, it is possible to increase their magnetoresistance by more than four orders of magnitude. By changing the thickness of p- n junction in the structure of ferromagnetic semiconductors, their magnetoresistance can be increased by 2-3 orders of magnitude.

  14. Linear magnetoresistance in a topological insulator Ru2Sn3

    NASA Astrophysics Data System (ADS)

    Shiomi, Y.; Saitoh, E.

    2017-03-01

    We have studied magnetotransport properties of a topological insulator material Ru2Sn3. Bulk single crystals of Ru2Sn3 were grown by a Bi flux method. The resistivity is semiconducting at high temperatures above 160 K, while it becomes metallic below 160 K. Nonlinear field dependence of Hall resistivity in the metallic region shows conduction of multiple carriers at low temperatures. In the high-temperature semiconducting region, magnetoresistance exhibits a conventional quadratic magnetic-field dependence. In the low-temperature metallic region, however, high-field magnetoresistance is clearly linear with magnetic fields, signaling a linear dispersion in the low-temperature electronic structure. Small changes in the magnetoresistance magnitude with respect to the magnetic field angle indicate that bulk electron carriers are responsible mainly for the observed linear magnetoresistance.

  15. Effect of quantum tunneling on spin Hall magnetoresistance

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  16. High speed magneto-resistive random access memory

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    A high speed read MRAM memory element is configured from a sandwich of magnetizable, ferromagnetic film surrounding a magneto-resistive film which may be ferromagnetic or not. One outer ferromagnetic film has a higher coercive force than the other and therefore remains magnetized in one sense while the other may be switched in sense by a switching magnetic field. The magneto-resistive film is therefore sensitive to the amplitude of the resultant field between the outer ferromagnetic films and may be constructed of a high resistivity, high magneto-resistive material capable of higher sensing currents. This permits higher read voltages and therefore faster read operations. Alternate embodiments with perpendicular anisotropy, and in-plane anisotropy are shown, including an embodiment which uses high permeability guides to direct the closing flux path through the magneto-resistive material. High density, high speed, radiation hard, memory matrices may be constructed from these memory elements.

  17. Effect of quantum tunneling on spin Hall magnetoresistance.

    PubMed

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

    2017-02-22

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

  18. Fractures in anisotropic media

    NASA Astrophysics Data System (ADS)

    Shao, Siyi

    Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The

  19. Parallel Anisotropic Tetrahedral Adaptation

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Darmofal, David L.

    2008-01-01

    An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.

  20. Graphene magnetoresistance device in van der Pauw geometry.

    PubMed

    Lu, Jianming; Zhang, Haijing; Shi, Wu; Wang, Zhe; Zheng, Yuan; Zhang, Ting; Wang, Ning; Tang, Zikang; Sheng, Ping

    2011-07-13

    We have fabricated extraordinary magnetoresistance (EMR) device, comprising a monolayer graphene with an embedded metallic disk, that exhibits large room temperature magnetoresistance (MR) enhancement of up to 55,000% at 9 T. Finite element simulations yield predictions in excellent agreement with the experiment and show possibility for even better performance. Simplicity, ease of implementation and high sensitivity of this device imply great potential for practical applications.

  1. Sign control of magnetoresistance through chemically engineered interfaces.

    PubMed

    Ciudad, David; Gobbi, Marco; Kinane, Christy J; Eich, Marius; Moodera, Jagadeesh S; Hueso, Luis E

    2014-12-03

    Chemically engineered interfaces are shown to produce inversions of the magnetoresistance in spintronic devices including lithium fluoride interlayers. This behavior is explained by the formation of anti-ferromagnetic difluoride layers. By changing the order of deposition of the different materials, the sign of the magnetoresistance can be deterministically controlled both in organic spin valves and in inorganic magnetic tunnel junctions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. A two-site bipolaron model for organic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Wagemans, W.; Bloom, F. L.; Bobbert, P. A.; Wohlgenannt, M.; Koopmans, B.

    2008-04-01

    The recently proposed bipolaron model for large "organic magnetoresistance" (OMAR) at room temperature is extended to an analytically solvable two-site scheme. It is shown that even this extremely simplified approach reproduces some of the key features of OMAR, viz., the possibility to have both positive and negative magnetoresistance, as well as its universal line shapes. Specific behavior and limiting cases are discussed. Extensions of the model, to guide future experiments and numerical Monte Carlo studies, are suggested.

  3. Anisotropic Total Variation Filtering

    SciTech Connect

    Grasmair, Markus; Lenzen, Frank

    2010-12-15

    Total variation regularization and anisotropic filtering have been established as standard methods for image denoising because of their ability to detect and keep prominent edges in the data. Both methods, however, introduce artifacts: In the case of anisotropic filtering, the preservation of edges comes at the cost of the creation of additional structures out of noise; total variation regularization, on the other hand, suffers from the stair-casing effect, which leads to gradual contrast changes in homogeneous objects, especially near curved edges and corners. In order to circumvent these drawbacks, we propose to combine the two regularization techniques. To that end we replace the isotropic TV semi-norm by an anisotropic term that mirrors the directional structure of either the noisy original data or the smoothed image. We provide a detailed existence theory for our regularization method by using the concept of relaxation. The numerical examples concluding the paper show that the proposed introduction of an anisotropy to TV regularization indeed leads to improved denoising: the stair-casing effect is reduced while at the same time the creation of artifacts is suppressed.

  4. SAW imaging in anisotropic media

    NASA Astrophysics Data System (ADS)

    Clark, M.; Sharples, S. D.; Somekh, M. G.

    2000-05-01

    We have developed a non-contact laser ultrasound SAW microscope operating at 82 MHz and harmonics thereof, which is capable of rapid image acquisition. Conventional acoustic microscopy is largely immune to the effects of aberration because of the very short acoustic path length that is imposed by the presence of the couplant. The couplant also limits the sensitivity of contacting acoustic microscopy. In laser ultrasound systems the absence of couplant means that longer path lengths are possible but the anisotropy and grain structure of the material can aberrate the passage of the acoustic wave limiting the performance of the system and producing acoustic speckle. We show that even weakly aberrating materials (e.g. aluminum) can produce significant speckle effects. We present experimental non-contacting imaging results on isotropic and textured anisotropic samples; together with simulated images. The results demonstrate that the speckle statistics of the experimental and simulated results agree well; thus demonstrating the cause of the speckle in the experimental images. We demonstrate how a wavefront sensor and adaptation of the optical excitation profile offers a solution to the problem of texture in non-contacting SAW imaging. Finally, we discuss how some material properties may be inferred from the speckle.

  5. Colossal magnetoresistivity in manganese-based perovskites (invited) (abstract)

    NASA Astrophysics Data System (ADS)

    Ramesh, R.; Venkatesan, T.; Ogale, S. B.; Greene, R. L.; Bhagat, S. M.

    1996-04-01

    Magnetoresistivity values of the order of 106% (and in some cases even higher) have been obtained in epitaxial AxB1-xMnO3-y (A=La,Nd; B=Ca,Sr,Ba) thin films grown by pulsed laser deposition. Ferromagnetic resonance experiments suggest a granular-type behavior with conducting ferromagnetic regions (Rcond<10 mΩ cm) in a less conducting matrix (Rinsulazting≳100.Rcond). Ion channeling experiments over a range of temperatures clearly reveal the existence of structural distortion at the peak resistivity temperature TP. Systematic studies of samples prepared under a variety of oxygenation conditions show that the resistivity above TP can be modeled with a single functional form: Rcond≊eΔ/kT, where Δ, the activation energy, is of the order of 50-200 meV. This suggests that these different samples represent the same basic material in a semiconducting matrix, with differing volume fractions of the two components which depends on the processing conditions. These ``colossal'' values of MR have been obtained at temperatures lower than room temperature and at fields of the order of a few Teslas, both of which are impediments to the development of viable MR sensor and nonvolatile storage technologies. We are therefore addressing the critical scientific and technological issues through a variety of materials integration approaches. Using structural chemistry and lattice matching as fundamental guiding principles, we are growing epitaxial heterostructure superlattices consisting of the CMR oxides interleaved with magnetic perovskites such as La-Sr-Co-O (metallic ferromagnet), rare earth-Fe-O (ferromagnetic insulator). We are also exploring the possibility of using the semiconducting properties of these materials in an all-perovskite field effect transistor device. In this presentation, we will describe our progress to date on these studies to enhance the field and temperature dependence of the MR properties and explore new device architectures that utilize the inherently

  6. Anisotropic Weyl symmetry and cosmology

    SciTech Connect

    Moon, Taeyoon; Oh, Phillial; Sohn, Jongsu E-mail: ploh@skku.edu

    2010-11-01

    We construct an anisotropic Weyl invariant theory in the ADM formalism and discuss its cosmological consequences. It extends the original anisotropic Weyl invariance of Hořava-Lifshitz gravity using an extra scalar field. The action is invariant under the anisotropic transformations of the space and time metric components with an arbitrary value of the critical exponent z. One of the interesting features is that the cosmological constant term maintains the anisotropic symmetry for z = −3. We also include the cosmological fluid and show that it can preserve the anisotropic Weyl invariance if the equation of state satisfies P = zρ/3. Then, we study cosmology of the Einstein-Hilbert-anisotropic Weyl (EHaW) action including the cosmological fluid, both with or without anisotropic Weyl invariance. The correlation of the critical exponent z and the equation of state parameter ω-bar provides a new perspective of the cosmology. It is also shown that the EHaW action admits a late time accelerating universe for an arbitrary value of z when the anisotropic conformal invariance is broken, and the anisotropic conformal scalar field is interpreted as a possible source of dark energy.

  7. On the relativistic anisotropic configurations

    NASA Astrophysics Data System (ADS)

    Shojai, F.; Kohandel, M.; Stepanian, A.

    2016-06-01

    In this paper we study anisotropic spherical polytropes within the framework of general relativity. Using the anisotropic Tolman-Oppenheimer-Volkov equations, we explore the relativistic anisotropic Lane-Emden equations. We find how the anisotropic pressure affects the boundary conditions of these equations. Also we argue that the behavior of physical quantities near the center of star changes in the presence of anisotropy. For constant density, a class of exact solution is derived with the aid of a new ansatz and its physical properties are discussed.

  8. Resistivity dependence of magnetoresistance in Co/ZnO films.

    PubMed

    Quan, Zhi-Yong; Zhang, Li; Liu, Wei; Zeng, Hao; Xu, Xiao-Hong

    2014-01-06

    We report the dependence of magnetoresistance effect on resistivity (ρ) in Co/ZnO films deposited by magnetron sputtering at different sputtering pressures with different ZnO contents. The magnitude of the resistivity reflects different carrier transport regimes ranging from metallic to hopping behaviors. Large room-temperature magnetoresistance greater than 8% is obtained in the resistivity range from 0.08 to 0.5 Ω · cm. The magnetoresistance value decreases markedly when the resistivity of the films is less than 0.08 Ω · cm or greater than 0.5 Ω · cm. When 0.08 Ω · cm < ρ < 0.5 Ω · cm, the conduction contains two channels: the spin-dependent tunneling channel and the spin-independent second-order hopping (N = 2). The former gives rise to a high room-temperature magnetoresistance effect. When ρ > 0.5 Ω · cm, the spin-independent higher-order hopping (N > 2) comes into play and decreases the tunneling magnetoresistance value. For the samples with ρ < 0.08 Ω · cm, reduced magnetoresistance is mainly ascribed to the formation of percolation paths through interconnected elongated metallic Co particles. This observation is significant for the improvement of room-temperature magnetoresistance value for future spintronic devices.

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

    SciTech Connect

    Wang, Dali; Jin, Guojun

    2013-12-21

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

  10. Anisotropic multiple bounce models

    NASA Astrophysics Data System (ADS)

    Bacalhau, Anna Paula; Peter, Patrick; Vitenti, Sandro D. P.

    2017-07-01

    We analyze the Galileon ghost condensate implementation of a bouncing cosmological model in the presence of a non-negligible anisotropic stress. We exhibit its structure, which we find to be far richer than previously thought. In particular, even restricting attention to a single set of underlying microscopic parameters, we obtain, numerically, many qualitatively different regimes: depending on the initial conditions on the scalar field leading the dynamics of the Universe, the contraction phase can evolve directly towards a singularity, avoid it by bouncing once, or even bounce many times before settling into an ever-expanding phase. We clarify the behavior of the anisotropies in these various situations.

  11. High anisotropic pitch

    SciTech Connect

    Dickakian, G. B.

    1985-11-05

    An improved process for preparing an optically anisotropic pitch which comprises heating a pitch feed material at a temperature within the range of about 350/sup 0/ C. to 450/sup 0/ C. while passing an inert gas therethrough at a rate of at least 2.5 SCFH/lb of pitch feed material and agitating said pitch feed material at a stirrer rate of from about 500 to 600 rpm to obtain an essentially 100% mesophase pitch product suitable for carbon production.

  12. Anisotropic spinfoam cosmology

    NASA Astrophysics Data System (ADS)

    Rennert, Julian; Sloan, David

    2014-01-01

    The dynamics of a homogeneous, anisotropic universe are investigated within the context of spinfoam cosmology. Transition amplitudes are calculated for a graph consisting of a single node and three links—the ‘Daisy graph’—probing the behaviour a classical Bianchi I spacetime. It is shown further how the use of such single node graphs gives rise to a simplification of states such that all orders in the spin expansion can be calculated, indicating that it is the vertex expansion that contains information about quantum dynamics.

  13. Linear unsaturating magnetoresistance in disordered systems

    NASA Astrophysics Data System (ADS)

    Lai, Ying Tong; Lara, Silvia; Love, Cameron; Ramakrishnan, Navneeth; Adam, Shaffique

    Theoretical works have shown that disordered systems exhibit classical magnetoresistance (MR). In this talk, we examine a variety of experimental systems that observe linear MR at high magnetic fields, including silver chalcogenides, graphene, graphite and Weyl semimetals. We show that a careful analysis of the magnitude of the MR, as well as the field strength at which the MR changes from quadratic to linear, reveal important properties of the system, such as the ratio of the root-mean-square fluctuations in the carrier density and the average carrier density. By looking at other properties such as the zero-field mobility, we show that this carrier density inhomogeneity is consistent with what is known about the microscopic impurities in these experiments. The application of this disorder-induced MR to a variety of different experimental scenarios underline the universality of these theoretical models. This work is supported by the Singapore National Research Foundation (NRF-NRFF2012-01) and the Singapore Ministry of Education and Yale-NUS College through Grant Number R-607-265-01312.

  14. Giant magnetoresistance of copper/permalloy multilayers

    NASA Astrophysics Data System (ADS)

    Holody, P.; Chiang, W. C.; Loloee, R.; Bass, J.; Pratt, W. P., Jr.; Schroeder, P. A.

    1998-11-01

    Current perpendicular (CPP) and current in-plane (CIP) magnetoresistances (MR) have been measured on sputtered Cu/Py (Py=Permalloy) multilayers at 4.2 K. The CPP-MR is several times larger than the CIP-MR. For fixed Py layer thickness, tPy=1.5 nm, both the CPP and CIP MR's show oscillations with increasing tCu with a period similar to that previously reported for the CIP-MR. The CPP data for Cu thicknesses large enough that exchange interactions between Py layers are small are analyzed using the two spin-current model for both infinite and finite spin-diffusion length in Py. The very low coercive field of Py leads to a larger than usual uncertainty in the derived parameters, because of the uncertainty in the degree of antiparallel alignment required for the analysis. Three alternative analyses give bulk and interface spin-dependent anisotropy parameters, β, and γ, of comparable size, so that both must be considered in determining the CPP-MR. Our preferred values, based upon an assumed IPysf=5.5+/-1 nm, are β=0.65+/-0.1 and γ=0.76+/-0.1. These values produce good fits to the CPP-MR's of Co/Cu/Py/Cu multilayers.

  15. Positive magnetoresistance in Ca-doped cobaltites

    SciTech Connect

    Zhou, S. M. Li, Y.; Guo, Y. Q.; Zhao, J. Y.; Shi, L.

    2014-12-08

    Transport properties of polycrystalline La{sub 1−x}Ca{sub x}CoO{sub 3} (0.10 ≤ x ≤ 0.25) are systemically studied in this work. Three types of magnetoresistance (MR) effects are found in the Ca-doped cobaltites. Two negative MRs appear around high-temperature ferromagnetic transition and at low temperatures, which correspond to the conventional MR due to the field-induced suppression of spin-disorder scattering and the intergranular giant-MR due to spin-dependent transport between the ferromagnetic clusters, respectively. More interestingly, another exotic positive MR emerges at intermediate temperature region, which had not been previously reported in Sr- and Ba-doped cobaltites. It is found that this positive MR is associated with an abnormally magnetic transition and increases with the increase of x. For x = 0.25, the MR at low temperatures is dominated by the positive one, which is isotropic and nearly linear with the magnetic field. The possible origin of the positive MR in the Ca-doped cobaltites is discussed.

  16. Controlling organic magnetoresistance via interface engineering

    NASA Astrophysics Data System (ADS)

    Richter, C. A.; Jang, H.-J.; Pookpanratana, S. J.; Basham, J. I.; Hacker, C. A.; Kirillov, O. A.; Kline, R. J.; Jurchescu, O. D.; Gundlach, D. J.

    2014-03-01

    We present the results of experiments in which we manipulate organic magnetoresistance (OMAR) in devices based on Alq3 (tris-(8-hydroxyquinoline) aluminum) and TPD (N,N '-Bis(3-methylphenyl)-N,N '-diphenylbenzidine) by adding a self-assembled monolayer (SAM). The results of OMAR measurements on this OLED-like architecture are correlated with impedance spectroscopy results to elucidate charge carrier transport and accumulation. We observe competing OMAR mechanisms in these devices, the relative strength of which can be tuned by adding SAMs at electrode interfaces. To determine how the interfacial and structural properties of these organic devices effect the OMAR, we obtained a complete picture of the interfacial, topological, and crystalline properties of these devices by performing UPS (Ultraviolet Photoelectron Spectroscopy), XPS (X-ray PS), XRD (X-ray diffraction), and AFM (atomic force microscopy). To verify our understanding of how interfacial changes affect OMAR, we characterized simple Alq3-only devices: one with a SAM and one without it. Despite having the same current density at room temperature, the latter shows a negative MR while the former displays a positive MR.

  17. Organic magnetoresistance under resonant ac drive

    NASA Astrophysics Data System (ADS)

    Roundy, R. C.; Raikh, M. E.

    2013-09-01

    Motivated by a recent experiment, we develop a theory of organic magnetoresistance (OMAR) in the presence of a resonant ac drive. To this end, we perform a thorough analysis of the dynamics of ac-driven electron-hole polaron pair in magnetic field, which is a sum of external and random hyperfine fields. Resonant ac drive affects the OMAR by modifying the singlet content of the eigenmodes. This, in turn, leads to the change of recombination rate, and ultimately, to the change of the spin-blocking that controls the current. Our analysis demonstrates that, upon increasing the drive amplitude, the blocking eigenmodes of the triplet type acquire a singlet admixture and become unblocking. Most surprisingly, the opposite process goes in parallel: new blocking modes emerge from nonblocking precursors as the drive increases. These emergent blocking modes are similar to subradiant modes in the Dicke effect. A nontrivial evolution of eigenmodes translates into a nontrivial behavior of OMAR with the amplitude of the ac drive: it is initially linear, then passes through a maximum, drops, and finally saturates.

  18. Hopping magnetoresistance in ion irradiated monolayer graphene

    NASA Astrophysics Data System (ADS)

    Shlimak, I.; Zion, E.; Butenko, A. V.; Wolfson, L.; Richter, V.; Kaganovskii, Yu.; Sharoni, A.; Haran, A.; Naveh, D.; Kogan, E.; Kaveh, M.

    2016-02-01

    Magnetoresistance (MR) of ion irradiated monolayer graphene samples with a variable-range hopping (VRH) mechanism of conductivity was measured at temperatures down to T=1.8 K in magnetic fields up to B=8 T. It was observed that in perpendicular magnetic fields, hopping resistivity R decreases, which corresponds to negative MR (NMR), while parallel magnetic field results in positive MR (PMR) at low temperatures. NMR is explained on the basis of the "orbital" model in which perpendicular magnetic field suppresses the destructive interference of many paths through the intermediate sites in the total probability of the long-distance tunneling in the VRH regime. At low fields, a quadratic dependence (| ΔR / R | ∼ B2) of NMR is observed, while at B > B*, the quadratic dependence is replaced by the linear one. It was found that all NMR curves for different samples and different temperatures could be merged into common dependence when plotted as a function of B/B*. It is shown that B* ∼ T1/2 in agreement with predictions of the "orbital" model. The obtained values of B* also allowed us to estimate the localization radius ξ of charge carriers for samples with a different degree of disorder. PMR in parallel magnetic fields is explained by suppression of hopping transitions via double occupied states due to alignment of electron spins.

  19. Anomalous Magnetoresistance Phenomena in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Bergeson, Jeremy D.; Lincoln, Derek M.; Shima Edelstein, Ruth; Prigodin, Vladimir N.; Epstein, Arthur J.

    2006-03-01

    We report magnetoresistance (MR) phenomena with temperature and bias dependence in organic semiconductor thin films with either nonmagnetic or magnetic contacts through high field reaching 9T. For nonmagnetic organic thin films such as Alq3 we find a low field MR up to 15%. A similar magnetic field effect has been reported earlier^1 but, as noted, the mechanism remains unclear. We propose a model of the anomalous MR where charge transport is space-charge limited. The current is determined by the e-h recombination rate. The recombination rate is field dependent, analogous to the chemical yield for radical pairs^2. Using an organic- based magnetic semiconductor^3, V[TCNE]x, and Co as magnetic contacts, with a nonmagnetic organic semiconductor (α-6T) leads to an order-of-magnitude broader zero-centered MR peak superimposed on a spin-valve effect. Possible origins of this broader MR will be discussed. 1. Francis, et al., New J. Phys. 6 185 (2004); Frankevich, et al., Phys. Rev. B 53 4498 (1996) 2. Steiner and Ulrich, Chem. Rev. 89 51 (1989) 3. Pokhodnya, et al., Adv. Mater. 12 410 (2000); Prigodin, et al., Adv. Mater. 14 1230 (2002); Shima Edelstein, et al., Mater. Res. Soc. Symp. Proc. 871E I7.3 (2005)

  20. Tunneling magnetoresistance phenomenon utilizing graphene magnet electrode

    SciTech Connect

    Hashimoto, T.; Kamikawa, S.; Haruyama, J.; Soriano, D.; Pedersen, J. G.; Roche, S.

    2014-11-03

    Using magnetic rare-metals for spintronic devices is facing serious problems for the environmental contamination and the limited material-resource. In contrast, by fabricating ferromagnetic graphene nanopore arrays (FGNPAs) consisting of honeycomb-like array of hexagonal nanopores with hydrogen-terminated zigzag-type atomic structure edges, we reported observation of polarized electron spins spontaneously driven from the pore edge states, resulting in rare-metal-free flat-energy-band ferromagnetism. Here, we demonstrate observation of tunneling magnetoresistance (TMR) behaviors on the junction of cobalt/SiO{sub 2}/FGNPA electrode, serving as a prototype structure for future rare-metal free TMR devices using magnetic graphene electrodes. Gradual change in TMR ratios is observed across zero-magnetic field, arising from specified alignment between pore-edge- and cobalt-spins. The TMR ratios can be controlled by applying back-gate voltage and by modulating interpore distance. Annealing the SiO{sub 2}/FGNPA junction also drastically enhances TMR ratios up to ∼100%.

  1. Nodal Quasiparticle in Pseudogapped Colossal Magnetoresistive Manganites

    SciTech Connect

    Mannella, N.

    2010-06-02

    A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the d-wave symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite Fermi arcs. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.

  2. Magnetoresistance in paramagnetic heavy fermion metals.

    PubMed

    Parihari, D; Vidhyadhiraja, N S

    2009-10-07

    A theoretical study of magnetic field (h) effects on single-particle spectra and the transport quantities of heavy fermion metals in the paramagnetic phase is carried out. We have employed a non-perturbative local moment approach (LMA) to the asymmetric periodic Anderson model within the dynamical mean field framework. The lattice coherence scale ω(L), which is proportional within the LMA to the spin-flip energy scale, and has been shown in earlier studies to be the energy scale at which crossover to single-impurity physics occurs, increases monotonically with increasing magnetic field. The many body Kondo resonance in the density of states at the Fermi level splits into two, with the splitting being proportional to the field itself. For h≥0, we demonstrate adiabatic continuity from the strongly interacting case to a corresponding non-interacting limit, thus establishing Fermi liquid behaviour for heavy fermion metals in the presence of a magnetic field. In the Kondo lattice regime, the theoretically computed magnetoresistance is found to be negative in the entire temperature range. We argue that such a result could be understood at [Formula: see text] by field-induced suppression of spin-flip scattering and at [Formula: see text] through lattice coherence. The coherence peak in the heavy fermion resistivity diminishes and moves to higher temperatures with increasing field. Direct comparison of the theoretical results to the field dependent resistivity measurements in CeB(6) yields good agreement.

  3. Unusual magnetoresistance in cubic B20 Fe0.85Co0.15Si chiral magnets

    DOE PAGES

    Huang, S. X.; Chen, Fei; Kang, Jian; ...

    2016-06-24

    The B20 chiral magnets with broken inversion symmetry and C4 rotation symmetry have attracted much attention. The broken inversion symmetry leads to the Dzyaloshinskii–Moriya that gives rise to the helical and Skyrmion states.Wereport the unusual magnetoresistance (MR) of B20 chiral magnet Fe0.85Co0.15Si that directly reveals the broken C4 rotation symmetry and shows the anisotropic scattering by Skyrmions with respect to the current directions. The intimacy between unusual MR and broken symmetry is well confirmed by theoretically studying an effective Hamiltonian with spin–orbit coupling. In conclusion, the unusual MR serves as a transport signature for the Skyrmion phase.

  4. Effect of NiO inserted layer on spin-Hall magnetoresistance in Pt/NiO/YIG heterostructures

    SciTech Connect

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

    2016-07-18

    We investigate spin-current transport with an antiferromagnetic insulator NiO thin layer by means of the spin-Hall magnetoresistance (SMR) over a wide range of temperature in Pt/NiO/Y{sub 3}Fe{sub 5}O{sub 12} (Pt/NiO/YIG) heterostructures. The SMR signal is comparable to that without the NiO layer as long as the temperature is near or above the blocking temperature of the NiO, indicating that the magnetic fluctuation of the insulating NiO is essential for transmitting the spin current from the Pt to YIG layer. On the other hand, the SMR signal becomes negligibly small at low temperature, and both conventional anisotropic magnetoresistance and the anomalous Hall resistance are extremely small at any temperature, implying that the insertion of the NiO has completely suppressed the Pt magnetization induced by the YIG magnetic proximity effect (MPE). The dual roles of the thin NiO layer are, to suppress the magnetic interaction or MPE between Pt and YIG, and to maintain efficient spin current transmission at high temperature.

  5. Inhomogeneous anisotropic cosmology

    NASA Astrophysics Data System (ADS)

    Kleban, Matthew; Senatore, Leonardo

    2016-10-01

    In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.

  6. Inhomogeneous anisotropic cosmology

    SciTech Connect

    Kleban, Matthew; Senatore, Leonardo

    2016-10-12

    In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with “flat” (including toroidal) and “open” (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are “flat” or “open”. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with “flat” or “open” topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.

  7. Inhomogeneous anisotropic cosmology

    DOE PAGES

    Kleban, Matthew; Senatore, Leonardo

    2016-10-12

    In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here in this paper, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with "flat'' (including toroidal) and "open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarilymore » large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are "flat" or "open". Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with "flat'' or "open" topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.« less

  8. Inhomogeneous anisotropic cosmology

    SciTech Connect

    Kleban, Matthew; Senatore, Leonardo

    2016-10-12

    In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here in this paper, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with "flat'' (including toroidal) and "open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are "flat" or "open". Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with "flat'' or "open" topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.

  9. Anisotropic Particles in Turbulence

    NASA Astrophysics Data System (ADS)

    Voth, Greg A.; Soldati, Alfredo

    2017-01-01

    Anisotropic particles are common in many industrial and natural turbulent flows. When these particles are small and neutrally buoyant, they follow Lagrangian trajectories while exhibiting rich orientational dynamics from the coupling of their rotation to the velocity gradients of the turbulence field. This system has proven to be a fascinating application of the fundamental properties of velocity gradients in turbulence. When particles are not neutrally buoyant, they experience preferential concentration and very different preferential alignment than neutrally buoyant tracer particles. A vast proportion of the parameter range of anisotropic particles in turbulence is still unexplored, with most existing research focusing on the simple foundational cases of axisymmetric ellipsoids at low concentrations in homogeneous isotropic turbulence and in turbulent channel flow. Numerical simulations and experiments have recently developed a fairly comprehensive picture of alignment and rotation in these cases, and they provide an essential foundation for addressing more complex problems of practical importance. Macroscopic effects of nonspherical particle dynamics include preferential concentration in coherent structures and drag reduction by fiber suspensions. We review the models used to describe nonspherical particle motion, along with numerical and experimental methods for measuring particle dynamics.

  10. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

    PubMed

    Stamopoulos, D; Aristomenopoulou, E

    2015-08-26

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

  11. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers

    PubMed Central

    Stamopoulos, D.; Aristomenopoulou, E.

    2015-01-01

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

  12. The Effects of Fringe Fields on Organic Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas; Macià, Ferran; Wang, Fujian; Wohlgenannt, Markus; Kent, Andrew; Flatté, Michael

    2013-03-01

    The importance of random hyperfine fields is now widely acknowledged as a vital ingredient for the phenomena of organic magnetoresistance (OMAR). Recent experiments (Phys. Rev. X 2 021013 (2012)) have shown that another type of random field - fringe fields due to a nearby ferromagnet - can also dramatically affect magnetoconductivity. A theoretical analysis of the fringe field OMAR is challenging due to the different properties of the fringe fields when compared to the hyperfine fields. For instance, the range of fringe field strengths is 1-2 orders of magnitude larger than that of the hyperfine couplings. The correlation length between fringe fields is also larger by the same degree. We use a recent theory of OMAR that is well-suited to numerically calculate the magnetoresistance with both hyperfine and fringe fields present. We find agreement with key features of experimental fringe-field magnetoresistance dependences on applied magnetic field, including the field values of extrema of the magnetoresistance, the region of large magnetoresistance effects from the fringe fields, and the sign of the effect. This work was supported by an ARO MURI.

  13. Anisotropic power-law inflation

    SciTech Connect

    Kanno, Sugumi; Soda, Jiro; Watanabe, Masa-aki E-mail: jiro@tap.scphys.kyoto-u.ac.jp

    2010-12-01

    We study an inflationary scenario in supergravity model with a gauge kinetic function. We find exact anisotropic power-law inflationary solutions when both the potential function for an inflaton and the gauge kinetic function are exponential type. The dynamical system analysis tells us that the anisotropic power-law inflation is an attractor for a large parameter region.

  14. Read/write head having a GMR sensor biased by permanent magnets located between the GMR and the pole shields

    DOEpatents

    Yuan, Samuel W.; Rottmayer, Robert Earl; Carey, Matthew J.

    1999-01-01

    A compact read/write head having a biased giant magnetoresistive sensor. Permanent magnet films are placed adjacent to the giant magnetoresistive sensor operating in the current-perpendicular-to the-plane (Cpp) mode and spaced with respect to the sensor by conducting films. These permanent magnet films provide a magnetic bias. The bias field is substantial and fairly uniform across sensor height. Biasing of the giant magnetoresistive sensor provides distinguishable response to the rising and falling edges of a recorded pulse on an adjacent recording medium, improves the linearity of the response, and helps to reduce noise. This read/write head is much simpler to fabricate and pattern and provides an enhanced uniformity of the bias field throughout the sensor.

  15. Magnetic Nanoparticle Sensors

    PubMed Central

    Koh, Isaac; Josephson, Lee

    2009-01-01

    Many types of biosensors employ magnetic nanoparticles (diameter = 5–300 nm) or magnetic particles (diameter = 300–5,000 nm) which have been surface functionalized to recognize specific molecular targets. Here we cover three types of biosensors that employ different biosensing principles, magnetic materials, and instrumentation. The first type consists of magnetic relaxation switch assay-sensors, which are based on the effects magnetic particles exert on water proton relaxation rates. The second type consists of magnetic particle relaxation sensors, which determine the relaxation of the magnetic moment within the magnetic particle. The third type is magnetoresistive sensors, which detect the presence of magnetic particles on the surface of electronic devices that are sensitive to changes in magnetic fields on their surface. Recent improvements in the design of magnetic nanoparticles (and magnetic particles), together with improvements in instrumentation, suggest that magnetic material-based biosensors may become widely used in the future. PMID:22408498

  16. Stripe sensor tomography.

    PubMed

    Barbic, Mladen; Vltava, Lvcian; Barrett, Christopher P; Emery, Teresa H; Scherer, Axel

    2008-03-01

    We introduce a general concept of tomographic imaging for the case of an imaging sensor that has a stripelike shape. We first show that there is no difference, in principle, between two-dimensional tomography using conventional electromagnetic or particle radiation and tomography where a stripe sensor is mechanically scanned over a sample at a sequence of different angles. For a single stripe detector imaging, linear motion and angular rotation are required. We experimentally demonstrate single stripe sensor imaging principle using an elongated inductive coil detector. By utilizing an array of parallel stripe sensors that can be individually addressed, two-dimensional imaging can be performed with rotation only, eliminating the requirement for linear motion, as we also experimentally demonstrate with parallel coil array. We conclude that imaging with a stripe-type sensor of particular width and thickness (where the width is much larger than the thickness) is resolution limited only by the thickness (smaller parameter) of the sensor. We give examples of multiple sensor families where this imaging technique may be beneficial such as magnetoresistive, inductive, superconducting quantum interference device, and Hall effect sensors, and, in particular, discuss the possibilities of the technique in the field of magnetic resonance imaging.

  17. Very low field magnetic resonance imaging with spintronic sensors

    NASA Astrophysics Data System (ADS)

    Herreros, Q.; Dyvorne, H.; Campiglio, P.; Jasmin-Lebras, G.; Demonti, A.; Pannetier-Lecoeur, M.; Fermon, C.

    2013-09-01

    A very low field magnetic resonance imaging (MRI) setup based on magnetoresistive-superconducting mixed sensors is presented. A flux transformer is used to achieve coupling between the sample to image and the mixed sensor. The novel detector was implemented in a spin echo MRI experiment, exposing the mixed sensor to RF pulses without use of any RF switch. The performance of the novel detector is given in terms of signal-to-noise ratio and is compared with classical tuned coils.

  18. Huge positive magnetoresistance in antiferromagnetic double perovskite metals

    NASA Astrophysics Data System (ADS)

    Nand Singh, Viveka; Majumdar, Pinaki

    2014-07-01

    Metals with large positive magnetoresistance are rare. We demonstrate that antiferromagnetic metallic states, as have been predicted for the double perovskites, are excellent candidates for huge positive magnetoresistance. An applied field suppresses long range antiferromagnetic order leading to a state with short range antiferromagnetic correlations and strong electronic scattering. The field induced resistance ratio can be more than tenfold, at moderate field, in a structurally ordered system, and continues to be almost twofold even in systems with ˜25% antisite disorder. Although our explicit demonstration is in the context of a two- dimensional spin-fermion model of the double perovskites, the mechanism we uncover is far more general, complementary to the colossal negative magnetoresistance process, and would operate in other local moment metals that show a field driven suppression of non-ferromagnetic order.

  19. Magnetoresistive junctions based on epitaxial graphene and h-BN

    NASA Astrophysics Data System (ADS)

    Yazyev, Oleg; Pasquarello, Alfredo

    2009-03-01

    Using a first-principles approach, we investigate the structural, magnetic and transport properties of interfaces based on epitaxially grown monolayer graphene and hexagonal boron nitride (h-BN) in combination with ferromagnetic transition metals (Fe, Co and Ni). Such structurally well defined interfaces based on (111) fcc or (0001) hcp transition metals can be produced using simple manufacturing processes. Our calculations predict magnetoresistance ratios over 100% for certain junction compositions. In addition, such systems feature strong antiparallel (Fe and Co) and parallel (Ni) exchange coupling across the interface combined with low junction resistance. The predicted properties position such magnetoresistive junctions as an interesting alternative to the currently used giant and tunneling magnetoresistance systems and make them suitable for practical applications.

  20. Huge positive magnetoresistance in antiferromagnetic double perovskite metals.

    PubMed

    Singh, Viveka Nand; Majumdar, Pinaki

    2014-07-23

    Metals with large positive magnetoresistance are rare. We demonstrate that antiferromagnetic metallic states, as have been predicted for the double perovskites, are excellent candidates for huge positive magnetoresistance. An applied field suppresses long range antiferromagnetic order leading to a state with short range antiferromagnetic correlations and strong electronic scattering. The field induced resistance ratio can be more than tenfold, at moderate field, in a structurally ordered system, and continues to be almost twofold even in systems with ∼ 25% antisite disorder. Although our explicit demonstration is in the context of a two- dimensional spin-fermion model of the double perovskites, the mechanism we uncover is far more general, complementary to the colossal negative magnetoresistance process, and would operate in other local moment metals that show a field driven suppression of non-ferromagnetic order.

  1. Large linear magnetoresistance in a GaAs/AlGaAs heterostructure

    SciTech Connect

    Aamir, Mohammed Ali Goswami, Srijit Ghosh, Arindam; Baenninger, Matthias; Farrer, Ian; Ritchie, David A.; Tripathi, Vikram; Pepper, Michael

    2013-12-04

    We report non-saturating linear magnetoresistance (MR) in a two-dimensional electron system (2DES) at a GaAs/AlGaAs heterointerface in the strongly insulating regime. We achieve this by driving the gate voltage below the pinch-off point of the device and operating it in the non-equilibrium regime with high source-drain bias. Remarkably, the magnitude of MR is as large as 500% per Tesla with respect to resistance at zero magnetic field, thus dwarfing most non-magnetic materials which exhibit this linearity. Its primary advantage over most other materials is that both linearity and the enormous magnitude are retained over a broad temperature range (0.3 K to 10 K), thus making it an attractive candidate for cryogenic sensor applications.

  2. Anisotropic Kepler and anisotropic two fixed centres problems

    NASA Astrophysics Data System (ADS)

    Maciejewski, Andrzej J.; Przybylska, Maria; Szumiński, Wojciech

    2017-02-01

    In this paper we show that the anisotropic Kepler problem is dynamically equivalent to a system of two point masses which move in perpendicular lines (or planes) and interact according to Newton's law of universal gravitation. Moreover, we prove that generalised version of anisotropic Kepler problem as well as anisotropic two centres problem are non-integrable. This was achieved thanks to investigation of differential Galois groups of variational equations along certain particular solutions. Properties of these groups yield very strong necessary integrability conditions.

  3. Thermodynamics of anisotropic branes

    NASA Astrophysics Data System (ADS)

    Ávila, Daniel; Fernández, Daniel; Patiño, Leonardo; Trancanelli, Diego

    2016-11-01

    We study the thermodynamics of flavor D7-branes embedded in an anisotropic black brane solution of type IIB supergravity. The flavor branes undergo a phase transition between a `Minkowski embedding', in which they lie outside of the horizon, and a `black hole embedding', in which they fall into the horizon. This transition depends on the black hole temperature, its degree of anisotropy, and the mass of the flavor degrees of freedom. It happens either at a critical temperature or at a critical anisotropy. A general lesson we learn from this analysis is that the anisotropy, in this particular realization, induces similar effects as the temperature. In particular, increasing the anisotropy bends the branes more and more into the horizon. Moreover, we observe that the transition becomes smoother for higher anisotropies.

  4. Structural and giant magnetoresistance characterization of Ag sbnd Co multilayers

    NASA Astrophysics Data System (ADS)

    Angelakeris, M.; Poulopoulos, P.; Valassiades, O.; Stoemenos, J.; Kalogirou, O.; Niarchos, D.; Flevaris, N. K.

    1997-01-01

    Ag sbnd Co multilayers were prepared on various substrates (Si, polyimide and glass) by e-beam evaporation under ultra high vacuum. X-ray diffraction and high resolution electron microscopy studies showed a deterioration of multilayer structure upon reducing the individual Co-layer thickness to 0.5 nm. Furthermore, the saturation field in the parallel field geometry increases, as SQUID magnetometry revealed, while magnetoresistance reaches 16% at room temperature and exceeds 30% at 30 K. Magnetoresistance values were found to depend strongly on individual layer thicknesses as well as on the total film thickness.

  5. Magnetoresistance oscillations in superconducting granular niobium nitride nanowires.

    SciTech Connect

    Patel, U.; Xiao, Z. L.; Gurevich, A.; Avci, S.; Hua, J.; Divan, R.; Welp, U.; Kwok, W. K.; Northern Illinois Univ.; National High Magnetic Field Lab.

    2009-01-01

    We report on magnetoresistance oscillations in superconducting NbN{sub x} nanowires synthesized through ammonia gas annealing of NbSe{sub 3} precursor nanostructures. Even though the transverse dimensions of the nanowires are much larger than the superconducting coherence length, the voltage-current characteristics of these nanowires at low temperatures are reminiscent of one-dimensional superconductors where quantum phase slips are associated with the origin of dissipation. We show that both the magnetoresistance oscillations and voltage-current characteristics observed in this work result from the granular structure of our nanowires.

  6. Rectification magnetoresistance device: Experimental realization and theoretical simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Huang, Qikun; Yan, Yi; Wang, Xiaolin; Wang, Jing; Kang, Shishou; Tian, Yufeng

    2016-11-01

    A unique technique has been proposed to realize rectification magnetoresistance (RMR) by combining a commercial diode and a magnetoresistance component in parallel. The observed RMR could be greatly tuned in a wide range by applying direct current and alternating current simultaneously to the device. Moreover, a quantitative theoretical model has been established, which well explained both the observed RMR and the electrical manipulation behavior. The highly tunable RMR and the correlated magnetoelectric functionalities provide an alternative route for developing multi-functional spintronics devices.

  7. Analytical theory and method for longitudinal magneto-optical Kerr effect of optically anisotropic magnetic film

    NASA Astrophysics Data System (ADS)

    Wang, Xiao; Lian, Jie; Li, Ping; Xu, XiJin; Li, MengMeng

    2017-01-01

    The Fresnel equations are solved to analyze the reflection and propagation properties of the ordinary and extraordinary light of the optically anisotropic magnetic film. Using the boundary and propagation matrix, the longitudinal magneto-optical Kerr rotation expression is derived. After that, simulations are performed on optically anisotropic and isotropic Co/SiO2 film. Results show that for Co material in the thin-film limit, the anisotropic Co can provide larger max rotations than the isotropic Co in the visible region. This is because that the refractive index discrepancy of optically anisotropic Co film reduces the Fresnel reflective coefficient rpp, which improves the Kerr rotation. This makes the optically anisotropic Co film more effective in magneto optical sensor design and device fabrication.

  8. Prediction of the point of impact in an anisotropic plate

    NASA Astrophysics Data System (ADS)

    Koabaz, M.; Hajzargarbashi, T.; Kundu, T.; Deschamps, M.

    2011-01-01

    Locating the point of impact of a foreign object in a plate is important for continuous health monitoring of structures. A new method based on an optimization scheme has been recently proposed to locate the point of impact in anisotropic plates by analyzing the times of arrival of the ultrasonic signals at the passive sensors attached to the plate. Following this optimization based technique, in this paper the impact point on an anisotropic plate is predicted from the acoustic emission data. Experiments are carried out with a carbon-epoxy plate where the impact point is modeled by an acoustic source. A Parallel Pre-stressed Actuator (PPA) is used as the acoustic source and the acoustic signals at different locations are received by adhesively bonded acoustic sensors. The source point is then predicted and compared with its actual location. Related theory is also presented in the paper.

  9. Optical trapping of anisotropic nanocylinder

    NASA Astrophysics Data System (ADS)

    Bareil, Paul B.; Sheng, Yunlong

    2013-09-01

    The T-matrix method with the Vector Spherical Wave Function (VSWF) expansions represents some difficulties for computing optical scattering of anisotropic particles. As the divergence of the electric field is nonzero in the anisotropic medium and the VSWFs do not satisfy the anisotropic wave equations one questioned whether the VSWFs are still a suitable basis in the anisotropic medium. We made a systematic and careful review on the vector basis functions and the VSWFs. We found that a field vector in Euclidean space can be decomposed to triplet vectors {L, M, N}, which as non-coplanar. Especially, the vector L is designed to represent non-zero divergence component of the vector solution, so that the VSWF basis is sufficiently general to represent the solutions of the anisotropic wave equation. The mathematical proof can be that when the anisotropic wave equations is solved in the Fourier space, the solution is expanded in the basis of the plan waves with angular spectrum amplitude distributions. The plane waves constitute an orthogonal and complete set for the anisotropic solutions. Furthermore, the plane waves are expanded into the VSWF basis. These two-step expansions are equivalent to the one-step direct expansion of the anisotropic solution to the VSWF basis. We used direct VSWF expansion, along with the point-matching method in the T-matrix, and applied the boundary condition to the normal components displacement field in order to compute the stress and the related forces and torques and to show the mechanism of the optical trap of the anisotropic nano-cylinders.

  10. Room temperature electrically tunable rectification magnetoresistance in Ge-based Schottky devices

    NASA Astrophysics Data System (ADS)

    Huang, Qi-Kun; Yan, Yi; Zhang, Kun; Li, Huan-Huan; Kang, Shishou; Tian, Yu-Feng

    2016-11-01

    Electrical control of magnetotransport properties is crucial for device applications in the field of spintronics. In this work, as an extension of our previous observation of rectification magnetoresistance, an innovative technique for electrical control of rectification magnetoresistance has been developed by applying direct current and alternating current simultaneously to the Ge-based Schottky devices, where the rectification magnetoresistance could be remarkably tuned in a wide range. Moreover, the interface and bulk contribution to the magnetotransport properties has been effectively separated based on the rectification magnetoresistance effect. The state-of-the-art electrical manipulation technique could be adapt to other similar heterojunctions, where fascinating rectification magnetoresistance is worthy of expectation.

  11. Room temperature electrically tunable rectification magnetoresistance in Ge-based Schottky devices

    PubMed Central

    Huang, Qi-kun; Yan, Yi; Zhang, Kun; Li, Huan-huan; Kang, Shishou; Tian, Yu-feng

    2016-01-01

    Electrical control of magnetotransport properties is crucial for device applications in the field of spintronics. In this work, as an extension of our previous observation of rectification magnetoresistance, an innovative technique for electrical control of rectification magnetoresistance has been developed by applying direct current and alternating current simultaneously to the Ge-based Schottky devices, where the rectification magnetoresistance could be remarkably tuned in a wide range. Moreover, the interface and bulk contribution to the magnetotransport properties has been effectively separated based on the rectification magnetoresistance effect. The state-of-the-art electrical manipulation technique could be adapt to other similar heterojunctions, where fascinating rectification magnetoresistance is worthy of expectation. PMID:27876868

  12. Studies of current-perpendicular-to-plane (CPP) magnetoresistance

    NASA Astrophysics Data System (ADS)

    Eid, Khalid Fatthi

    2002-09-01

    Scientifically, measurements of Giant Magnetoresistance (GMR) in ferromagnetic/nonmagnetic (F/N) metal multilayers with Current flow Perpendicular to the layer Planes (CPP-MR) are of interest because they can provide unique insights into the physical phenomena underlying GMR. Technologically, the CPP-MR is of growing interest because it may be able to provide the larger MRs needed for next generation devices. Most CPP-MR data have been reasonably well described by two simple models, the two-current series-resistor (2CSR) model, in which the only lengths are the thicknesses of the F- and N-metals, t F and tN, and the Valet-Fert extension to when spin-flipping occurs, where the characteristic lengths are the spin-flipping (or spin-diffusion) lengths lFSF and lNSF . This thesis consists of several experiments that test and/or use these models. (1) Recently, new data were claimed to be evidence that there are additional length scales in the CPP-MR, the mean-free-paths for elastic scattering, lambdaN and lambdaF (actually two lengths in the F-metal). After reproducing the reported results, we extended them in three different ways to test the claimed interpretation. We conclude that the mean-free-paths are not responsible for the behavior of the data; rather we propose spin-memory-loss at the F/N interfaces as the primary explanation. (2) The CPP-MR would be more competitive for devices if the total specific resistance, area times resistance, AR, the change in AR with magnetic field, ADeltaR, or both can be increased. We investigated three potential ways to increase them: (a) by alloying the F metal layer with an impurity expected to produce a large change in resistivity without decreasing the anisotropic scattering that is fundamental to GMR, (b) by creating additional interfaces within individual ferromagnetic layers, and (c) by inserting a source of strong spin-flipping, in hopes of reducing the contribution of contact or lead resistances to ADeltaR. (3) Ruthenium (Ru

  13. Hybrid magnetoresistance in Pt-based multilayers: Effect originated from strong interfacial spin-orbit coupling

    PubMed Central

    Meng, Kangkang; Xiao, Jiaxing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Zhao, Jianhua; Jiang, Yong

    2016-01-01

    The hybrid magnetoresistance (MR) behaviors in Pt/Co90Fe10/Pt, Mn1.5Ga/Pt and Mn1.5Ga/Pt/Co90Fe10/Pt multilayers have been investigated. Both planer Hall effect (PHE) and angle-dependent MR in Pt/Co90Fe10/Pt revealed the combination of spin Hall MR (SMR) and normal anisotropic MR (AMR), indicating the large contribution of strong spin-orbit coupling (SOC) at the interfaces. When Pt contacted with perpendicular magnetic anisotropy (PMA) metal Mn1.5Ga, the strong interfacial SOC modified the effective anomalous Hall effect. The MR in Mn1.5Ga/Pt/Co90Fe10/Pt is not a simple combination of SMR and AMR, but ascribed to the complicated domain wall scattering and strong interfacial SOC when Pt is sandwiched by the in-plane magnetized Co90Fe10 and the PMA Mn1.5Ga. PMID:26843035

  14. Effect of thermal deformation on giant magnetoresistance of flexible spin valves grown on polyvinylidene fluoride membranes

    NASA Astrophysics Data System (ADS)

    Luping, Liu; Qingfeng, Zhan; Xin, Rong; Huali, Yang; Yali, Xie; Xiaohua, Tan; Run-wei, Li

    2016-07-01

    We fabricated flexible spin valves on polyvinylidene fluoride (PVDF) membranes and investigated the influence of thermal deformation of substrates on the giant magnetoresistance (GMR) behaviors. The large magnetostrictive Fe81Ga19 (FeGa) alloy and the low magnetostrictive Fe19Ni81 (FeNi) alloy were selected as the free and pinned ferromagnetic layers. In addition, the exchange bias (EB) of the pinned layer was set along the different thermal deformation axes α 31 or α 32 of PVDF. The GMR ratio of the reference spin valves grown on Si intrinsically increases with lowering temperature due to an enhancement of spontaneous magnetization. For flexible spin valves, when decreasing temperature, the anisotropic thermal deformation of PVDF produces a uniaxial anisotropy along the α 32 direction, which changes the distribution of magnetic domains. As a result, the GMR ratio at low temperature for spin valves with EB∥ α 32 becomes close to that on Si, but for spin valves with EB∥ α 31 is far away from that on Si. This thermal effect on GMR behaviors is more significant when using magnetostrictive FeGa as the free layer. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374312, 51401230, 51522105, and 51471101) and the Ningbo Science and Technology Innovation Team, China (Grant No. 2015B11001).

  15. Hybrid magnetoresistance in Pt-based multilayers: Effect originated from strong interfacial spin-orbit coupling.

    PubMed

    Meng, Kangkang; Xiao, Jiaxing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Zhao, Jianhua; Jiang, Yong

    2016-02-04

    The hybrid magnetoresistance (MR) behaviors in Pt/Co90Fe10/Pt, Mn1.5Ga/Pt and Mn1.5Ga/Pt/Co90Fe10/Pt multilayers have been investigated. Both planer Hall effect (PHE) and angle-dependent MR in Pt/Co90Fe10/Pt revealed the combination of spin Hall MR (SMR) and normal anisotropic MR (AMR), indicating the large contribution of strong spin-orbit coupling (SOC) at the interfaces. When Pt contacted with perpendicular magnetic anisotropy (PMA) metal Mn1.5Ga, the strong interfacial SOC modified the effective anomalous Hall effect. The MR in Mn1.5Ga/Pt/Co90Fe10/Pt is not a simple combination of SMR and AMR, but ascribed to the complicated domain wall scattering and strong interfacial SOC when Pt is sandwiched by the in-plane magnetized Co90Fe10 and the PMA Mn1.5Ga.

  16. Hybrid magnetoresistance in Pt-based multilayers: Effect originated from strong interfacial spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Meng, Kangkang; Xiao, Jiaxing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Zhao, Jianhua; Jiang, Yong

    2016-02-01

    The hybrid magnetoresistance (MR) behaviors in Pt/Co90Fe10/Pt, Mn1.5Ga/Pt and Mn1.5Ga/Pt/Co90Fe10/Pt multilayers have been investigated. Both planer Hall effect (PHE) and angle-dependent MR in Pt/Co90Fe10/Pt revealed the combination of spin Hall MR (SMR) and normal anisotropic MR (AMR), indicating the large contribution of strong spin-orbit coupling (SOC) at the interfaces. When Pt contacted with perpendicular magnetic anisotropy (PMA) metal Mn1.5Ga, the strong interfacial SOC modified the effective anomalous Hall effect. The MR in Mn1.5Ga/Pt/Co90Fe10/Pt is not a simple combination of SMR and AMR, but ascribed to the complicated domain wall scattering and strong interfacial SOC when Pt is sandwiched by the in-plane magnetized Co90Fe10 and the PMA Mn1.5Ga.

  17. Spin-induced anomalous magnetoresistance at the (100) surface of hydrogen-terminated diamond

    NASA Astrophysics Data System (ADS)

    Takahide, Yamaguchi; Sasama, Yosuke; Tanaka, Masashi; Takeya, Hiroyuki; Takano, Yoshihiko; Kageura, Taisuke; Kawarada, Hiroshi

    2016-10-01

    We report magnetoresistance measurements of hydrogen-terminated (100)-oriented diamond surfaces wherein an ionic-liquid-gated field-effect-transistor technique was used to make hole carriers accumulate. Unexpectedly, the observed magnetoresistance is positive within the range of 2 magnetoresistance previously detected for similar devices with (111)-oriented diamond surfaces. Furthermore, we find that (1) the magnetoresistance is orders of magnitude larger than that of the classical orbital magnetoresistance; (2) the magnetoresistance is nearly independent of the direction of the applied magnetic field; and (3) for the in-plane field, the magnetoresistance ratio, defined as [ρ (B )-ρ (0 )]/ρ (0 ) , follows a universal function of B /T . These results indicate that the spin degree of freedom of hole carriers plays an important role in the surface conductivity of hydrogen-terminated (100) diamond.

  18. Giant Magnetoresistance-based Biosensor for Detection of Influenza A Virus

    PubMed Central

    Krishna, Venkatramana D.; Wu, Kai; Perez, Andres M.; Wang, Jian-Ping

    2016-01-01

    We have developed a simple and sensitive method for the detection of influenza A virus based on giant magnetoresistance (GMR) biosensor. This assay employs monoclonal antibodies to viral nucleoprotein (NP) in combination with magnetic nanoparticles (MNPs). Presence of influenza virus allows the binding of MNPs to the GMR sensor and the binding is proportional to the concentration of virus. Binding of MNPs onto the GMR sensor causes change in the resistance of sensor, which is measured in a real time electrical readout. GMR biosensor detected as low as 1.5 × 102 TCID50/mL virus and the signal intensity increased with increasing concentration of virus up to 1.0 × 105 TCID50/mL. This study showed that the GMR biosensor assay is relevant for diagnostic application since the virus concentration in nasal samples of influenza virus infected swine was reported to be in the range of 103 to 105 TCID50/mL. PMID:27065967

  19. Vortex dynamics in anisotropic traps

    SciTech Connect

    McEndoo, S.; Busch, Th.

    2010-07-15

    We investigate the dynamics of linear vortex lattices in anisotropic traps in two dimensions and show that the interplay between the rotation and the anisotropy leads to a rich but highly regular dynamics.

  20. Cracking on anisotropic neutron stars

    NASA Astrophysics Data System (ADS)

    Setiawan, A. M.; Sulaksono, A.

    2017-07-01

    We study the effect of cracking of a local anisotropic neutron star (NS) due to small density fluctuations. It is assumed that the neutron star core consists of leptons, nucleons and hyperons. The relativistic mean field model is used to describe the core of equation of state (EOS). For the crust, we use the EOS introduced by Miyatsu et al. [1]. Furthermore, two models are used to describe pressure anisotropic in neutron star matter. One is proposed by Doneva-Yazadjiev (DY) [2] and the other is proposed by Herrera-Barreto (HB) [3]. The anisotropic parameter of DY and HB models are adjusted in order the predicted maximum mass compatible to the mass of PSR J1614-2230 [4] and PSR J0348+0432 [5]. We have found that cracking can potentially present in the region close to the neutron star surface. The instability due cracking is quite sensitive to the NS mass and anisotropic parameter used.

  1. Magnetoresistance, electrical conductivity, and Hall effect of glassy carbon

    SciTech Connect

    Baker, D.F.

    1983-02-01

    These properties of glassy carbon heat treated for three hours between 1200 and 2700/sup 0/C were measured from 3 to 300/sup 0/K in magnetic fields up to 5 tesla. The magnetoresistance was generally negative and saturated with reciprocal temperature, but still increased as a function of magnetic field. The maximum negative magnetoresistance measured was 2.2% for 2700/sup 0/C material. Several models based on the negative magnetoresistance being proportional to the square of the magnetic moment were attempted; the best fit was obtained for the simplest model combining Curie and Pauli paramagnetism for heat treatments above 1600/sup 0/C. Positive magnetoresistance was found only in less than 1600/sup 0/C treated glassy carbon. The electrical conductivity, of the order of 200 (ohm-cm)/sup -1/ at room temperature, can be empirically written as sigma = A + Bexp(-CT/sup -1/4) - DT/sup -1/2. The Hall coefficient was independent of magnetic field, insensitive to temperature, but was a strong function of heat treatment temperature, crossing over from negative to positive at about 1700/sup 0/C and ranging from -0.048 to 0.126 cm/sup 3//coul. The idea of one-dimensional filaments in glassy carbon suggested by the electrical conductivity is compatible with the present consensus view of the microstructure.

  2. Tuning spin transport properties and molecular magnetoresistance through contact geometry

    SciTech Connect

    Ulman, Kanchan; Narasimhan, Shobhana; Delin, Anna

    2014-01-28

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

  3. Low temperature magnetoresistance measurements on bismuth nanowire arrays.

    PubMed

    Kaiser, Ch; Weiss, G; Cornelius, T W; Toimil-Molares, M E; Neumann, R

    2009-05-20

    We present low temperature resistance R(T) and magnetoresistance measurements for Bi nanowires with diameters between 100 and 500 nm, which are close to being single-crystalline. The nanowires were fabricated by electrochemical deposition in pores of polycarbonate membranes. R(T) varies as T(2) in the low temperature range 1.5 Kmagnetoresistance. The transverse magnetoresistance of all samples shows a clear B(1.5) variation. Its size depends strongly on the diameter of the wires but only weakly on temperature. Finally, a steplike increase in the magnetoresistance of our sample with a wire diameter of 100 nm was found and this might be attributed to a transition from one-dimensional to three-dimensional localization.

  4. Actuation performances of anisotropic gels

    NASA Astrophysics Data System (ADS)

    Nardinocchi, P.; Teresi, L.

    2016-12-01

    We investigated the actuation performances of anisotropic gels driven by mechanical and chemical stimuli, in terms of both deformation processes and stroke-curves, and distinguished between the fast response of gels before diffusion starts and the asymptotic response attained at the steady state. We also showed as the range of forces that an anisotropic hydrogel can exert when constrained is especially wide; indeed, changing fiber orientation allows us to induce shear as well as transversely isotropic extensions.

  5. Microfluidic multiplexed partitioning enables flexible and effective utilization of magnetic sensor arrays.

    PubMed

    Bechstein, Daniel J B; Ng, Elaine; Lee, Jung-Rok; Cone, Stephanie G; Gaster, Richard S; Osterfeld, Sebastian J; Hall, Drew A; Weaver, James A; Wilson, Robert J; Wang, Shan X

    2015-11-21

    We demonstrate microfluidic partitioning of a giant magnetoresistive sensor array into individually addressable compartments that enhances its effective use. Using different samples and reagents in each compartment enables measuring of cross-reactive species and wide dynamic ranges on a single chip. This compartmentalization technique motivates the employment of high density sensor arrays for highly parallelized measurements in lab-on-a-chip devices.

  6. Anisotropic assembly and pattern formation

    NASA Astrophysics Data System (ADS)

    von Brecht, James H.; Uminsky, David T.

    2017-01-01

    We investigate the role of anisotropy in two classes of individual-based models for self-organization, collective behavior and self-assembly. We accomplish this via first-order dynamical systems of pairwise interacting particles that incorporate anisotropic interactions. At a continuum level, these models represent the natural anisotropic variants of the well-known aggregation equation. We leverage this framework to analyze the impact of anisotropic effects upon the self-assembly of co-dimension one equilibrium structures, such as micelles and vesicles. Our analytical results reveal the regularizing effect of anisotropy, and isolate the contexts in which anisotropic effects are necessary to achieve dynamical stability of co-dimension one structures. Our results therefore place theoretical limits on when anisotropic effects can be safely neglected. We also explore whether anisotropic effects suffice to induce pattern formation in such particle systems. We conclude with brief numerical studies that highlight various aspects of the models we introduce, elucidate their phase structure and partially validate the analysis we provide.

  7. Permanent-Magnet Free Biasing of MR Sensors with Tunable Sensitivity

    NASA Astrophysics Data System (ADS)

    Halloran, Sean; Dasilva, Fabio; Pappas, David

    2007-03-01

    Exchange coupling^1 has been previously observed in a trilayer structure of ferromagnet (FM)/non-magnetic/antiferromagnet (AFM) and the exchange bias was found to be a function of the thickness of the buffer layer.^2,3,4 This unique coupling is used as a stabilizing bias for the sense layer with the additional ability to tailor the magnetic gain of the sensor for various applications. The elimination of permanent magnet bias results in the elimination of one patterning and one deposition step. Ruthenium (Ru) is used as the buffer layer and is self aligned with the FM and AFM layers and the thickness is varied to change the slope of the transfer curve in the linear region. Sensor devices are fabricated with a bipolar output, a medium sensitivity, and a wide field range. The results show that this biasing scheme is well suited for barber pole and soft adjacent layer (SAL) anisotropic magnetoresistance (AMR) stripes used in magnetic field sensors with a FM layer of Permalloy (NiFe) and an AFM layer of Iridium-Manganese (IrMn). Applications include a 256 channel read head used for magnetic forensics. 1N.J. Gokemeijer, T. Ambrose, C.L. Chien, N. Wang and K.K. Fung, J. Appl. Phys. 81 (8), 4999, 15 April 1997. 2W.H. Meiklejohn and C.P. Bean, Phys. Rev. 102, 1413 1956; 105, 904, 1957. 3L. Thomas, A.J. Kellock and S.S.P. Parkin, J. Appl. Phys. 87 (9), 5061, 1 May 2000. 4D. Wang, J. Daughton, C. Nordman, P. Eames and J. Fink, J. Appl. Phys. 99, 2006.

  8. Anisotropic artificial substrates for microwave applications

    NASA Astrophysics Data System (ADS)

    Shahvarpour, Attieh

    The perfect electromagnetic conductor (PEMC) boundary is a novel fundamental electromagnetic concept. It is a generalized description of the electromagnetic boundary conditions including the perfect electric conductor (PEC) and the perfect magnetic conductor (PMC) and due to its fundamental properties, it has the potential of enabling several electromagnetic applications. However, the PEMC boundaries concept had remained at the theoretical level and has not been practically realized. Therefore, motivated by the importance of this electromagnetic fundamental concept and its potential applications, the first contribution of this thesis is focused on the practical implementation of the PEMC boundaries by exploiting Faraday rotation principle and ground reflection in the ferrite materials which are intrinsically anisotropic. As a result, this thesis reports the first practical approach for the realization of PEMC boundaries. A generalized scattering matrix (GSM) is used for the analysis of the grounded-ferrite PEMC boundaries structure. As an application of the PEMC boundaries, a transverse electromagnetic (TEM) waveguide is experimentally demonstrated using grounded ferrite PMC (as particular case of the PEMC boundaries) side walls. Perfect electromagnetic conductor boundaries may find applications in various types of sensors, reflectors, polarization convertors and polarization-based radio frequency identifiers. Leaky-wave antennas perform as high directivity and frequency beam scanning antennas and as a result they enable applications in radar, point-to-point communications and MIMO systems. The second contribution of this thesis is introducing and analysing a novel broadband and highly directive two-dimensional leaky-wave antenna. This antenna operates differently in the lower and higher frequency ranges. Toward its lower frequencies, it allows full-space conical-beam scanning while at higher frequencies, it provides fixed-beam radiation (at a designable angle

  9. Light propagation through anisotropic turbulence.

    PubMed

    Toselli, Italo; Agrawal, Brij; Restaino, Sergio

    2011-03-01

    A wealth of experimental data has shown that atmospheric turbulence can be anisotropic; in this case, a Kolmogorov spectrum does not describe well the atmospheric turbulence statistics. In this paper, we show a quantitative analysis of anisotropic turbulence by using a non-Kolmogorov power spectrum with an anisotropic coefficient. The spectrum we use does not include the inner and outer scales, it is valid only inside the inertial subrange, and it has a power-law slope that can be different from a Kolmogorov one. Using this power spectrum, in the weak turbulence condition, we analyze the impact of the power-law variations α on the long-term beam spread and scintillation index for several anisotropic coefficient values ς. We consider only horizontal propagation across the turbulence cells, assuming circular symmetry is maintained on the orthogonal plane to the propagation direction. We conclude that the anisotropic coefficient influences both the long-term beam spread and the scintillation index by the factor ς(2-α).

  10. Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  11. Anisotropic lattice models of electrolytes

    NASA Astrophysics Data System (ADS)

    Kobelev, Vladimir; Kolomeisky, Anatoly B.

    2002-11-01

    Systems of charged particles on anisotropic three-dimensional lattices are investigated theoretically using Debye-Huckel theory. It is found that the thermodynamics of these systems strongly depends on the degree of anisotropy. For weakly anisotropic simple cubic lattices, the results indicate the existence of order-disorder phase transitions and a tricritical point, while the possibility of low-density gas-liquid coexistence is suppressed. For strongly anisotropic lattices this picture changes dramatically: The low-density gas-liquid phase separation reappears and the phase diagram exhibits critical, tricritical, and triple points. For body-centered lattices, the low-density gas-liquid phase coexistence is suppressed for all degrees of anisotropy. These results show that the effect of anisotropy in lattice models of electrolytes amounts to reduction of spatial dimensionality.

  12. Fluctuation relations for anisotropic systems

    NASA Astrophysics Data System (ADS)

    Villavicencio-Sanchez, R.; Harris, R. J.; Touchette, H.

    2014-02-01

    Currents of particles or energy in driven non-equilibrium steady states are known to satisfy certain symmetries, referred to as fluctuation relations, determining the ratio of the probabilities of positive fluctuations to negative ones. A generalization of these fluctuation relations has been proposed recently for extended non-equilibrium systems of dimension greater than one, assuming, crucially, that they are isotropic (Hurtado P. I., Pérez-Espigares C., del Pozo J. J. and Garrido P. L., Proc. Natl. Acad. Sci. U.S.A., 108 (2011) 7704). Here we relax this assumption and derive a fluctuation relation for d-dimensional systems having anisotropic bulk driving rates. We test the validity of this anisotropic fluctuation relation by calculating the particle current fluctuations in the 2d anisotropic zero-range process, using both exact and fluctuating hydrodynamic approaches.

  13. Anisotropically structured magnetic aerogel monoliths

    NASA Astrophysics Data System (ADS)

    Heiligtag, Florian J.; Airaghi Leccardi, Marta J. I.; Erdem, Derya; Süess, Martin J.; Niederberger, Markus

    2014-10-01

    Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. Electronic supplementary information (ESI) available: Digital photographs of dispersions and gels with different water-to-ethanol ratios; magnetic measurements of an anatase aerogel containing 0.25 mol% Fe3O4 nanoparticles; XRD patterns of the iron oxide and

  14. Magnetoresistance in organic light-emitting diode structures under illumination

    NASA Astrophysics Data System (ADS)

    Desai, P.; Shakya, P.; Kreouzis, T.; Gillin, W. P.

    2007-12-01

    We have investigated the effect of illumination on the organic magnetoresistance (OMR) in organic light-emitting diode (OLED) structures. The results show that it is possible to obtain OMR at voltages below “turn-on,” where no OMR was visible for devices operated in the dark. The photoinduced OMR has a field dependence that is identical to that obtained for OLEDs containing very thin layers, where triplet dissociation at the cathode was a major component of the OMR. At voltages around the open circuit voltage, where the current through the device is very small, very large OMRs of ˜300% can be observed. The results support our proposed model for organic magnetoresistance as being caused in part by the interaction of free carriers with triplet excitons within the device. The results suggest that the introduction of a low field magnet could provide a simple means of improving the efficiency of organic photovoltaic cells.

  15. Giant magnetoresistance in the variable-range hopping regime

    SciTech Connect

    Ioffe, L. B.; Spivak, B. Z.

    2013-09-15

    We predict the universal power-law dependence of the localization length on the magnetic field in the strongly localized regime. This effect is due to the orbital quantum interference. Physically, this dependence shows up in an anomalously large negative magnetoresistance in the hopping regime. The reason for the universality is that the problem of the electron tunneling in a random media belongs to the same universality class as the directed polymer problem even in the case of wave functions of random sign. We present numerical simulations that prove this conjecture. We discuss the existing experiments that show anomalously large magnetoresistance. We also discuss the role of localized spins in real materials and the spin polarizing effect of the magnetic field.

  16. Large magnetoresistance and Fermi surface topology of PrSb

    NASA Astrophysics Data System (ADS)

    Wu, F.; Guo, C. Y.; Smidman, M.; Zhang, J. L.; Yuan, H. Q.

    2017-09-01

    We report magnetotransport measurements of PrSb in high magnetic fields. Our results show that PrSb exhibits large magnetoresistance at low temperatures. Meanwhile angle-dependent magnetoresistance measurements were used to probe the Fermi surface via Shubnikov-de Haas oscillations. We found that the angular dependence of the oscillation frequency of the α branch can be explained well by a model for a two-dimensional-like Fermi surface, whereas the effective mass of this branch as a function of angle shows a fourfold signature. The evolution of the Fermi surface with increasing magnetic field also was studied up to 32 T. A continuous increase in the oscillation frequency up to 14 T is observed before it becomes constant at higher fields. Meanwhile our analysis of the residual Landau index from the high-field data reveals a zero Berry phase and therefore trivial topology of the Fermi surface.

  17. Separating Positive and Negative Magnetoresistance in Organic Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Bloom, F. L.; Wagemans, W.; Kemerink, M.; Koopmans, B.

    2007-12-01

    We study the transition between positive and negative organic magnetoresistance (OMAR) in tris-(8 hydroxyquinoline) aluminium (Alq3), in order to identify the elementary mechanisms governing this phenomenon. We show how the sign of OMAR changes as function of the applied voltage and temperature. The transition from negative to positive magnetoresistance (MR) is found to be accompanied by an increase in slope of log⁡(I) versus log⁡(V). ac admittance measurements show this transition coincides with the onset of minority charge (hole) injection in the device. All these observations are consistent with two simultaneous contributions with opposite sign of MR, which may be assigned to holes and electrons having different magnetic field responses.

  18. Coexistence of tunneling magnetoresistance and Josephson effects in SFIFS junctions

    NASA Astrophysics Data System (ADS)

    Vávra, O.; Soni, R.; Petraru, A.; Himmel, N.; Vávra, I.; Fabian, J.; Kohlstedt, H.; Strunk, Ch.

    2017-02-01

    We demonstrate an integration of tunneling magnetoresistance and the Josephson effects within one tunneling junction. Several sets of Nb-Fe-Al-Al2O3-Fe-Nb wafers with varying Al and Fe layers thickness were prepared to systematically explore the competition of TMR and Josephson effects. A coexistence of the critical current IC(dFe) and the tunneling magnetoresistance ratio T M R(dFe) is observed for iron layer dFe thickness range 1.9 and 2.9 nm. Further optimization such as thinner Al2O3 layer leads to an enhancement of the critical current and thus to an extension of the coexistence regime up to dFe≃3.9 nm Fe.

  19. Enhancing magnetoresistance in tetrathiafulvalene carboxylate modified iron oxide nanoparticle assemblies

    NASA Astrophysics Data System (ADS)

    Lv, Zhong-Peng; Luan, Zhong-Zhi; Cai, Pei-Yu; Wang, Tao; Li, Cheng-Hui; Wu, Di; Zuo, Jing-Lin; Sun, Shouheng

    2016-06-01

    We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO-) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications.We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO-) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications. Electronic supplementary information (ESI) available: Experimental details; supplementary figures and tables. See DOI: 10.1039/c6nr03311c

  20. Anomalies of magnetoresistance in Ce-based heavy fermion compounds

    NASA Astrophysics Data System (ADS)

    Sluchanko, N. E.; Bogach, A. V.; Anisimov, M. A.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Chistyakov, O. D.; Burkhanov, G. S.; Gabani, S.; Flachbart, K.

    2015-12-01

    Magnetoresistance Δρ(H,T) of several heavy-fermion compounds, CeAl2, CeAl3 and CeCu6, substitutional solid solutions with quantum critical behavior CeCu6-xAux (x = 0.1, 0.2) and alloys with magnetic ground state Ce(Al1-xMx)2 (M = Co, Ni, x ≤ 0.8) was studied in a wide range of temperatures (1.8-40 K) in magnetic fields up to 80 kOe. It was shown that a consistent interpretation of the field dependences of the resistance for both non-magnetic and magnetically ordered cerium-based intermetallic compounds with strong electron correlations can be achieved within the framework of an approach that accounts for scattering of charge carriers by localized magnetic moments in a metal matrix. Within this approach, three different components of the magnetoresistance of cerium intermetallic compounds were identified: the negative Brillouin contribution proportional to the local magnetization ( -Δρ/ρ˜Mloc2 ), the alternating linear contribution ( Δρ/ρ˜H ) and the magnetic component, saturating in magnetic fields below 15 kOe. In the framework of the Yosida model for the cerium alloys under study, estimates of the local magnetic susceptibility χloc(H, T0) were obtained from the magnetoresistance data. Numerical differentiation of the magnetoresistance with respect to the magnetic field and analysis of the obtained d (Δρ/ρ)/d H =f (H ,T ) dependences allowed us to reconstruct the H-T magnetic phase diagrams of the strongly correlated electron systems under study as well as to examine the effects of spin polarization and renormalization of the electronic states on charge transport both in the regime of quantum critical behavior and in the magnetically ordered state.

  1. Magnetoresistance and magnetic properties in amorphous Fe-based wires

    NASA Astrophysics Data System (ADS)

    Bordin, G.; Buttino, G.; Cecchetti, A.; Poppi, M.

    2001-06-01

    The longitudinal and transverse magnetoresistances in amorphous Fe 77.5Si 7.5B 15 wires are studied at different values of the DC-bias currents in order to clarify the mechanism of the magnetization according to a 'core-shell' domain model. The role of closure domain structures in the magnetization process of the wires is analysed. Moreover, the effects of the Joule heating on the internal stresses, introduced during the rapid quenching in the sample preparation, are examined.

  2. Negative huge magnetoresistance in high-mobility 2D electron gases: DC-current dependence

    NASA Astrophysics Data System (ADS)

    Iñarrea, J.; Bockhorn, L.; Haug, R. J.

    2016-07-01

    Two-dimensional electron gases with very high mobility show a huge or giant negative magnetoresistance at low temperatures and low magnetic fields. We present an experimental and theoretical work on the influence of the applied current on the negative huge magnetoresistance of these systems. We obtain an unexpected and strong nonlinear behavior consisting in an increase of the negative huge magnetoresistance with increasing current, in other words, for increasing current the magnetoresistance collapses at small magnetic fields. This nonlinearity is explained by the subtle interplay of elastic scattering within Landau levels and between Landau levels.

  3. Magnetoresistance Associated with Antiferromagnetic Interlayer Coupling Spaced by a Semiconductor in Fe /Si Multilayers

    NASA Astrophysics Data System (ADS)

    Inomata, K.; Yusu, K.; Saito, Y.

    1995-03-01

    Multilayer Fe/Si films with constant Fe thickness (2.6 nm) and variable Si thickness are investigated. Negative magnetoresistance is observed and two different temperature dependences are found as a function of Si thickness. For tSi = 1.2 nm, the magnetoresistance decreases with temperature decrease. For tSi>1.5 nm, the magnetoresistance increases (weakly) with temperature decrease. The magnetoresistance is attributed to spin-dependent scattering caused by antiferromagnetic layer coupling across a semiconducting spacer: narrow gap iron silicide for thin Si spacer layers and amorphous Si for thicker spacer layers.

  4. Flat magnetic exchange springs as mechanism for additional magnetoresistance in magnetic nanoisland arrays

    NASA Astrophysics Data System (ADS)

    Boltaev, A. P.; Pudonin, F. A.; Sherstnev, I. A.; Egorov, D. A.; Kozmin, A. M.

    2017-04-01

    Process of magnetization and magnetoresistance have been studied in nanoisland bilayer systems of FeNi-Co. Hysteresis loops show characteristic features (steps) most clearly observed in certain orientations of the sample in a magnetic field. To explain these features the concept of flat magnetic exchange spring has been introduced for nanoisland bilayers. It has been proposed that additional magnetoresistance can be the result of spin-dependent scattering of electrons in the area of flat magnetic exchange spring. Magnetoresistance studies of bilayer systems has shown that additional magnetoresistance occurs at the same magnetic fields as steps on hysteresis loops.

  5. Low-temperature magnetoresistance of GaSb whiskers

    NASA Astrophysics Data System (ADS)

    Druzhinin, A.; Ostrovskii, I.; Khoverko, Yu.; Liakh-Kaguy, N.

    2017-06-01

    Transverse and longitudinal magnetoresistancies in n-type GaSb whiskers with different doping concentration (Te) in the vicinity to the metal-insulator transition (MIT) from metal side of the transition were studied in the temperature range 1.5-60 K and magnetic field 0-14 T. Shubnikov-de Haas oscillations in GaSb whiskers at low temperatures were revealed in magnetic field range 2-12 T. The oscillation period 0.025T-1 was found at various doping concentration in GaSb whiskers. The effective mass of electrons mc = 0.041m0 and Dingle temperature of about 7.5 K were found in GaSb whiskers with impurity concentration in the vicinity to MIT. The presence of negative magnetoresistance in GaSb whiskers with the impurity concentration in the nearest approximation to MIT with resistivity ρ300 K = 0.0053 Ω cm was observed and associated with weak localization. Besides for the whiskers a resistance minimum was observed at temperature about 16 K that is connected with Kondo effect. Magnetoresistance studies of n-type conductivity for GaSb whiskers revealed the crossover from weak localization to antilocalization in the temperature range of 1.4-4.2 K and magnetic fields below 1 T.

  6. Negative magnetoresistance in Dirac semimetal Cd3As2

    NASA Astrophysics Data System (ADS)

    Li, Hui; He, Hongtao; Lu, Hai-Zhou; Zhang, Huachen; Liu, Hongchao; Ma, Rong; Fan, Zhiyong; Shen, Shun-Qing; Wang, Jiannong

    2016-01-01

    A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 1017 cm-3 at 300 K to 2.2 × 1016 cm-3 below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed.

  7. Negative magnetoresistance in Dirac semimetal Cd3As2

    PubMed Central

    Li, Hui; He, Hongtao; Lu, Hai-Zhou; Zhang, Huachen; Liu, Hongchao; Ma, Rong; Fan, Zhiyong; Shen, Shun-Qing; Wang, Jiannong

    2016-01-01

    A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 1017 cm−3 at 300 K to 2.2 × 1016 cm−3 below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed. PMID:26744088

  8. Preparation and magnetoresistance of silver and copper chalcogenide thin films

    NASA Astrophysics Data System (ADS)

    Chuprakov, Ilya; Watts, Steven; Wirth, Steffen; von Molnár, Stephan; Dahmen, Klaus-Hermann

    1998-03-01

    An unexpected giant positive magnetoresitance was recently discovered in non-stoichiometric crystals of Ag_2Te and Ag_2Se [1]. There, a linear magnetoresistance effect as high as 120% was observed in fields of 4 T at room temperature. Here we report on thin films of copper and silver chalcogenides prepared by a vapor phase transport method. A prefered grain orientation is found in the films after annealing. Resistance, magnetoresistance and Hall effect were measured. Typically, the resistivity is temperature independent below 70 K with a value of 1 mΩ cm. As in the crystals, there is a large positive magnetoresistance, but the field dependence is non-linear with a typical value of 50% at room temperature and 200% at temperatures below 100 K for applied fields of 6 T. Variations of the deposition techniques are explored in order to establish the relationship between the deposition conditions and transport properties. [0.25cm] [1] R. Xu, A. Husmann, T.F. Rosenbaum, M.-L. Saboungi, E.J. Enderby and P.B. Littlewood, Nature 390, 57 (1997).

  9. Giant magnetoresistance of manganese oxides with a layered perovskite structure

    NASA Astrophysics Data System (ADS)

    Moritomo, Y.; Asamitsu, A.; Kuwahara, H.; Tokura, Y.

    1996-03-01

    MANGANESE oxides with the cubic perovskite structure (typified by LaMnO3) have stimulated considerable interest because of their magnetoresistive properties1-9 they exhibit extremely large changes in electrical resistance in response to applied magnetic fields, a property that is of technological relevance for the development of magnetic memory and switching devices. But for such applications to be viable, great improvements will be needed in both the sensitivity and temperature dependence of the magnetoresistive response. One approach under consideration for optimizing these properties is chemical substitution10. Here we demonstrate an alternative strategy, in which we synthesize layered variants of the cubic perovskite parent compounds that have a controlled number of MnO2 sheets per unit cell. This strategy is structurally analogous to that employed for the systematic exploration of the high-transition-temperature copper oxide superconductors11. We find that the magneto-resistive properties of these materials depend sensitively on the dimensionality of the manganese oxide lattice. Although the properties of our materials are still far from optimal, further exploration of this series of layered perovskites may prove fruitful.

  10. Detection of BCG bacteria using a magnetoresistive biosensor: A step towards a fully electronic platform for tuberculosis point-of-care detection.

    PubMed

    Barroso, Teresa G; Martins, Rui C; Fernandes, Elisabete; Cardoso, Susana; Rivas, José; Freitas, Paulo P

    2017-09-06

    Tuberculosis is one of the major public health concerns. This highly contagious disease affects more than 10.4 million people, being a leading cause of morbidity by infection. Tuberculosis is diagnosed at the point-of-care by the Ziehl-Neelsen sputum smear microscopy test. Ziehl-Neelsen is laborious, prone to human error and infection risk, with a limit of detection of 10(4) cells/mL. In resource-poor nations, a more practical test, with lower detection limit, is paramount. This work uses a magnetoresistive biosensor to detect BCG bacteria for tuberculosis diagnosis. Herein we report: i) nanoparticle assembly method and specificity for tuberculosis detection; ii) demonstration of proportionality between BCG cell concentration and magnetoresistive voltage signal; iii) application of multiplicative signal correction for systematic effects removal; iv) investigation of calibration effectiveness using chemometrics methods; and v) comparison with state-of-the-art point-of-care tuberculosis biosensors. Results present a clear correspondence between voltage signal and cell concentration. Multiplicative signal correction removes baseline shifts within and between biochip sensors, allowing accurate and precise voltage signal between different biochips. The corrected signal was used for multivariate regression models, which significantly decreased the calibration standard error from 0.50 to 0.03log10 (cells/mL). Results show that Ziehl-Neelsen detection limits and below are achievable with the magnetoresistive biochip, when pre-processing and chemometrics are used. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. Room temperature magnetoresistance and exchange bias in "314-type" oxygen-vacancy ordered SrCo0.85Fe0.15O2.62

    NASA Astrophysics Data System (ADS)

    Mohanty, Prachi; Marik, Sourav; Singh, Deepak; Singh, Ravi P.

    2017-07-01

    Herein, we report the magneto-transport and exchange bias effect in a "314-type" oxygen vacancy ordered material with composition SrCo0.85Fe0.15O2.62. This material exhibits a ferrimagnetic transition above room temperature, at 315 K. The negative magnetoresistance starts to appear from room temperature (-1.3% at 295 K in 70 kOe) and reaches a sizable value of 58% at 4 K in 70 kOe. A large exchange bias effect is observed below 315 K when the sample is cooled in the presence of a magnetic field. The coexistence of nearly compensated and ferrimagnetic regions in the layered structure leads to a magnetoresistance and an exchange bias in this sample. The appearance of a sizable magnetoresistance and a giant exchange bias effect, especially near room temperature, indicates that "314-type" cobaltates are a promising class of material systems for the exploration of materials with potential applications as magnetic sensors or in the area of spintronics.

  12. Large low-field positive magnetoresistance in nonmagnetic half-Heusler ScPtBi single crystal

    NASA Astrophysics Data System (ADS)

    Hou, Zhipeng; Wang, Yue; Liu, Enke; Zhang, Hongwei; Wang, Wenhong; Wu, Guangheng

    2015-11-01

    High-quality nonmagnetic half-Heusler ScPtBi single crystals were synthesized by a Bi self-flux method. This compound was revealed to be a hole-dominated semimetal with a large low-field magnetoresistance up to 240% at 2 K in a magnetic field of 1 T. Magneto-transport measurements demonstrated that the large low-field magnetoresistance effect resulted from the coexistence of field-induced metal-semiconductor transition and weak-antilocalization effect. Moreover, Hall measurements indicated that ScPtBi single crystal showed a high mobility over a wide temperature region even up to room temperature (4050 cm2V-1s-1 at 2 K-2016 cm2V-1s-1 at 300 K). These findings not only suggest the nonmagnetic ScPtBi semimetal a potential material candidate for applications in high-sensitivity magnetic sensors but also are of great significance to comprehensively understand the rare-earth based half-Heusler compounds.

  13. Frequency-dependence of the linear-polarization-angle phase-shift in the microwave radiation-induced magnetoresistance oscillations

    NASA Astrophysics Data System (ADS)

    Liu, Han-Chun; Samaraweera, Rasanga; Wegscheider, Werner; Mani, Ramesh

    High-mobility GaAs/AlGaAs heterojunctions subjected to microwave photoexcitation in the perpendicular magnetic field configuration exhibit ¼-cycle phase-shifted oscillatory magnetoresistance and zero-resistance states at low magnetic fields or high filling factors. Recent studies showed that the amplitude of oscillatory magnetoresistance is polarization-angle sensitive and can be described by a fitting formula, Rxx(θ) = A+/-Ccos2(θ- θ0) with diagonal resistance, Rxx, polarization angle θ, and the extracted phase shift, θ0. Previous works have demonstrated that θ0 is frequency-dependent by investigating some specific frequencies. Here, we examine the continuous variation of θ0 with frequency over the bands, 36-40 GHz and 45-49 GHz. Surprisingly, the results indicate dissimilar θ0 variation within the two frequency bands. A comparison of θ0(f) with the microwave polarization reported by an in-situ polarization sensor suggests that the frequency variation of θ0 might be caused by two different mechanisms in the two examined bands.

  14. A review of magnetic sensors

    NASA Astrophysics Data System (ADS)

    Lenz, James E.

    1990-06-01

    Eleven of the most common technologies used for magnetic field sensing are described and compared. These are the search coil, flux-gate, optically pumped, nuclear precession, SQUID, Hall-effect, magnetoresistive, magnetodiode, magnetotransistor, fiber optic, and magnetooptic technologies. The use of these sensors in relation to working with or around the earth's magnetic field is addressed. Three classes of applications and a specific application from each are examined: low-sensitivity (noncontact switching), medium-sensitivity (magnetic anomaly detection and magnetic compassing), and high-sensitivity (brain-function mapping).

  15. Extremely large magnetoresistance in the type-II Weyl semimetal Mo Te2

    NASA Astrophysics Data System (ADS)

    Chen, F. C.; Lv, H. Y.; Luo, X.; Lu, W. J.; Pei, Q. L.; Lin, G. T.; Han, Y. Y.; Zhu, X. B.; Song, W. H.; Sun, Y. P.

    2016-12-01

    We performed the angle dependent magnetoresistance (MR), Hall effect measurements, the temperature dependent magneto-thermoelectric power (TEP) S (T ) measurements, and the first-principles calculations to study the electronic properties of orthorhombic phase Mo Te2 (Td-Mo Te2) , which was proposed to be electronically two dimensional (2D). There are some interesting findings about Td-Mo Te2 . (1) A scaling approach ɛθ=(sin2θ +γ-2co s2θ ) 1 /2 is applied, where θ is the magnetic field angle with respect to the c axis of the crystal and γ is the mass anisotropy. Unexpectedly, the electronically three-dimensional (3D) character with γ as low as 1.9 is observed in Td-Mo Te2 . (2) The possible Lifshitz transition and the following electronic structure change can be verified around T ˜150 K and T ˜60 K , which is supported by the evidence of the slope changing of the temperature dependence of TEP, the carrier density extracted from Hall resistivity, and the onset temperature of γ obtained from the MR measurements. The extremely large MR effect in Td-Mo Te2 could originate from the combination of the electron-hole compensation and a particular orbital texture on the electron pocket, which is supported by the calculations of electronic structure. Our results may provide a general scaling relation for the anisotropic MR and help to recognize the origins of the MR effect in other systems, such as the Weyl semimetals and the Dirac ones.

  16. Synthesis and anisotropic magnetic and transport properties of cubic SrCoO3 single crystal

    NASA Astrophysics Data System (ADS)

    Long, Youwen; Kaneko, Yoshio; Ishiwata, Shintaro; Taguchi, Yasujiro; Tokura, Yoshinori

    2011-03-01

    Solid state oxides containing transition metals with unusually high valence states exhibit interesting physical properties. However, due to the unstableness of these high valence states, high pressure is often needed to stabilize such high valence states. We were successful in growing a large-size SrCo O3 single crystal by using high-pressure technique. This material shows good metallic behavior with high ferromagnetic Curie temperature about 305 K, and the easy magnetization axis is 111 > direction . ThespinmomentofCo 4+ ionmeasuredat 2 Kand 7 Tisabout 2.50 μB , suggesting an spin configuration as predicted by theoretical calculations. Although SrCoO3 has a highly symmetric cubic crystal structure (Pm-3m), it exhibits significant anisotropic magnetoresistance at low temperatures.

  17. Multiband superconductivity in Ta4Pd3Te16 with anisotropic gap structure.

    PubMed

    Jiao, Wen-He; Liu, Yi; Li, Yu-Ke; Xu, Xiao-Feng; Bao, Jin-Ke; Feng, Chun-Mu; Li, S Y; Xu, Zhu-An; Cao, Guang-Han

    2015-08-19

    We carried out measurements of the magnetoresistance, magnetic susceptibility and specific heat on crystals of the low-dimensional transition metal telluride Ta4Pd3Te16. Our results indicate that Ta4Pd3Te16 is an anisotropic type-II superconductor in the clean limit with the extracted Ginzburg-Landau parameter KGL = 84. The upper critical field Hc2(T) shows an anomalous temperature dependence at low temperatures and the anisotropy of Hc2(T) is strongly T-dependent, both of which indicate a multiband scenario. The electronic specific heat Cel(T) can be consistently described by a two-gap (s   +   d waves) model from the base temperature T/Tc ~ 0.12 up to Tc. Our results suggest nodal and multiband superconductivity in Ta4Pd3Te16.

  18. Effectis of Lattice Distortion, Polaron Sonduction and Double-Exchange Interaction on the Physical Properties of Magnetoresistive Manganites and Cobaltites

    NASA Technical Reports Server (NTRS)

    Yeh, N. C.; Vasquez, R. P.; Wei, J. Y. T.; Fu, C. C.; Beach, G.; Huynh, J.; Samoilov, A. V.; Boris, A. V.; Kovaleva, N. N.; Bazhenov, A. V.

    1997-01-01

    The relevance of lattice distortion, polaron conduction, and double-exchange interaction to the occurrence of colossal magnetoresistance (SMR) is investigated by comparing the physical properties of magnetoresistive manganites and cobaltites.

  19. Signature of enhanced spin-orbit interaction in the magnetoresistance of LaTiO3/SrTiO3 interfaces on δ doping

    NASA Astrophysics Data System (ADS)

    Das, Shubhankar; Hossain, Z.; Budhani, R. C.

    2016-09-01

    We present a study of modulation of spin-orbit interaction (SOI) at the interface of LaTiO3/SrTiO3 by δ doping with an isostructural ferromagnetic perovskite LaCoO3. The sheet carrier density at the interface decreases exponentially with δ -doping thickness. We have explored that the spin-orbit scattering time (τs o) can be decreased by nearly three orders of magnitude, whereas the inelastic scattering time (τi) remains almost constant with δ -doping thickness. We have also observed that the τi varies almost inversely proportional to temperature and τs o remains insensitive to temperature, which suggest that the spin relaxation in these interfaces follows D'yakonov-Perel mechanism. The observed in-plane anisotropic magnetoresistance is attributed to the mixing of the spin-up and spin-down states of the d band at the Fermi level due to SOI.

  20. Unusual magnetoresistance in cubic B20 Fe0.85Co0.15Si chiral magnets

    SciTech Connect

    Huang, S. X.; Chen, Fei; Kang, Jian; Zang, Jiadong; Shu, G. J.; Chou, F. C.; Chien, C. L.

    2016-06-24

    The B20 chiral magnets with broken inversion symmetry and C4 rotation symmetry have attracted much attention. The broken inversion symmetry leads to the Dzyaloshinskii–Moriya that gives rise to the helical and Skyrmion states.Wereport the unusual magnetoresistance (MR) of B20 chiral magnet Fe0.85Co0.15Si that directly reveals the broken C4 rotation symmetry and shows the anisotropic scattering by Skyrmions with respect to the current directions. The intimacy between unusual MR and broken symmetry is well confirmed by theoretically studying an effective Hamiltonian with spin–orbit coupling. In conclusion, the unusual MR serves as a transport signature for the Skyrmion phase.