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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Spin-torque transfer in batch-fabricated spin-valve magnetic nanojunctions (invited)

J. Z. Sun, D. J. Monsma, T. S. Kuan, M. J. Rooks, D. W. Abraham, B. Oezyilmaz, A. D. Kent, and R. H. Koch

J. Appl. Phys. 93, 6859 (2003); http://dx.doi.org/10.1063/1.1538170 (5 pages) | Cited 35 times

Online Publication Date: 9 May 2003

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A two terminal spin-injection device is fabricated using a nanostencil process with a Co–Cu–Co stack. The stack can be deposited both by sputtering and by electron-beam evaporation. A better edge definition is observed in evaporation-deposited films under cross section transmission electron microscopy. Both methods succeeded in producing junctions with sub-100 nm lateral dimensions and show spin-injection-induced magnetic switching. © 2003 American Institute of Physics.
Show PACS
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.75.-c Magnetic properties of nanostructures
81.16.Nd Micro- and nanolithography
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
75.60.Jk Magnetization reversal mechanisms
75.47.Np Metals and alloys
75.47.De Giant magnetoresistance

High-resolution giant magnetoresistance on-chip arrays for magnetic imaging

C. H. Smith, R. W. Schneider, and A. V. Pohm

J. Appl. Phys. 93, 6864 (2003); http://dx.doi.org/10.1063/1.1558248 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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Arrays of micrometer-sized giant magnetoresistance (GMR) magnetic sensors with corresponding micrometer-sized spacing on a single chip are being used to detect very small magnetic fields with high spatial resolution. These very small magnetic fields, or changes in magnetic fields, are associated with magnetic biosensors, nondestructive evaluation, precision position sensing, document validation including currency and magnetic tape, and other magnetic imaging. By using a silicon substrate, the signal conditioning and logic capability of integrated circuits can be incorporated to optimize system performance. This integrated technique reduces the effect of noise and simplifies the sensor/signal-processing interface. GMR sensor arrays with sensor spacing as small as 5 micrometers as well as single-chip arrays with 128 sensors covering a 4 mm width have been constructed. The GMR sensors are made of multilayer material consisting of FeCo/Cu layers with 8% to 20% GMR and maximum sensitivities of 1.0 mV/V/G (100 nV/nT @10 V). The sensor elements are photolithographically patterned with 1.5 to 2 μm wide stripes for high resistance and directional sensitivity. These on-chip magnetic arrays are being applied to various forms of magnetic media as well as work with biosensors and nondestructive test. © 2003 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.75.Ss Magnetic field sensors using spin polarized transport
07.55.-w Magnetic instruments and components
75.50.Bb Fe and its alloys

High speed signal transmission with magneto-couplers

S. Ganzer, G. Bayreuther, J. Hauch, and G. Rieger

J. Appl. Phys. 93, 6867 (2003); http://dx.doi.org/10.1063/1.1558249 (3 pages)

Online Publication Date: 9 May 2003

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Couplers in general serve for galvanically isolated signal transmission between sensitive equipment. Standard opto-couplers are generally limited to a bandwidth of 25 MHz. However, with ever-increasing data transfer rates the need for couplers with much higher bandwidth is steadily growing. For this purpose magneto-couplers are very promising because their bandwidth is expected to be limited only by the Larmor precession of the magnetic moments with frequencies in the range of 1–10 GHz. In magneto-couplers the signal to be transmitted is converted into a current through a micro-coil. The resulting magnetic field is detected by a giant magnetoresistance (GMR) sensor element separated by an isolation layer. In the present case this element is a Wheatstone bridge consisting of four spin valves. The voltage across the bridge resulting from the magnetization change of the soft layers due to the field pulses is detected with a 1 GHz storage oscilloscope. Present experiments indicate a bandwidth larger than 500 MHz. After proper termination of the signal paths and applying a dc-bias field the rise time of the input signal of less than 1 ns is not increased by the coupler. Furthermore we show that the driving pulse may be completely reproduced in shape by applying external dc-bias fields. It will also be discussed how capacitive and inductive crosstalk between the coil and the spin valves and nonideal termination of the signal paths affect the achievable bandwidth. © 2003 American Institute of Physics.
Show PACS
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
84.32.Dd Connectors, relays, and switches

Magnetoresistive signal isolators employing linear spin-valve sensing resistors

Zhenghong Qian, Dexin Wang, Jim Daughton, Mark Tondra, Erik Lange, Cathy Nordman, Anthony Popple, John Myers, and Jim Schuetz

J. Appl. Phys. 93, 6870 (2003); http://dx.doi.org/10.1063/1.1541635 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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Feasibility of fabricating low power, high-speed, magnetoresistive signal isolators employing linear spin-valve resistors as sensing elements has been demonstrated. In the fabricated prototype digital isolators, linear spin-valve resistors are physically isolated from an on-chip coil by an 11 μm BCB isolation barrier, which provides the galvanic isolation with a breakdown voltage larger than 2000 V. The devices are high speed (>50 MHz), small size, and low power consumption. Only a 4.5 mA coil driving current is required for the device to be fully functional. The power consumption is estimated to be ∼1/6 of NVE’s present isolator products, which requires a 50 mA coil driving current. Besides digital signal isolators, linear spin-valve resistors can also be used in analog signal isolators. The response of the linear spin-valve resistors to the current passing through the coil has been demonstrated to have a very good linearity, with a linearity error less than 0.05%. © 2003 American Institute of Physics.
Show PACS
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.Ss Magnetic field sensors using spin polarized transport
07.55.-w Magnetic instruments and components
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
07.68.+m Photography, photographic instruments; xerography

RC-coupled ferromagnetic single-electron transistors

Jun-ichi Shirakashi and Yasushi Takemura

J. Appl. Phys. 93, 6873 (2003); http://dx.doi.org/10.1063/1.1539073 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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We study quantitatively the operation of ferromagnetic single-electron transistors coupled to the controlling gate potential by the gate resistance and gate capacitance in series. In this type of the device, several metastable charge states are possible within the range of Coulomb blockade. The enhancement and hysteresis of tunnel magnetoresistance on the drain and gate voltages are predicted. The inelastic macroscopic quantum tunneling of charge and the existence of several charge states play an important role in the unique behavior of tunnel magnetoresistance. This implies that RC-coupled ferromagnetic single-electron transistors have a functionality as novel magnetoresistive nanostructure devices. © 2003 American Institute of Physics.
Show PACS
85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
73.23.Hk Coulomb blockade; single-electron tunneling
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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