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24 Dec 2001

Volume 79, Issue 26, pp. 4271-4458

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Spin-polarized scanning tunneling microscopy on half-metallic manganite thin film with half-metallic manganite tip

R. Akiyama, H. Tanaka, T. Matsumoto, and T. Kawai

Appl. Phys. Lett. 79, 4378 (2001); http://dx.doi.org/10.1063/1.1375832 (3 pages) | Cited 15 times

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Spin-polarized tunneling was demonstrated on La0.7Sr0.3MnO3 epitaxial thin film with a La0.7Sr0.3MnO3-coated PtIr tip at room temperature. A magnetic-field-dependent gap structure was found in the differential tunneling spectra due to the spin-valve effect. The spatial mapping of the differential tunneling conductance shows strongly contrasting variations, which demonstrates the presence of magnetic domains with different spin alignments. © 2001 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
72.15.Gd Galvanomagnetic and other magnetotransport effects

Quantum-well effect in magnetic tunnel junctions with ultrathin single-crystal Fe(100) electrodes

T. Nagahama, S. Yuasa, Y. Suzuki, and E. Tamura

Appl. Phys. Lett. 79, 4381 (2001); http://dx.doi.org/10.1063/1.1424068 (3 pages) | Cited 17 times

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We studied the tunnel spectra of magnetic tunnel junctions with a single-crystal ultrathin Fe(100) electrode. The tunnel spectra show oscillations of the differential conductivity and the differential tunnel magnetoresistance. The positions of the maxima of the oscillations move systematically with the change in the Fe(100) electrode’s thickness, indicating that the oscillations originate from the quantum-well states in the ultrathin Fe(100) electrode. This effect provides us with an opportunity to create voltage-controlled spin functional devices. © 2001 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Micromagnetic disorder in antiparallel biased spin valves

C. H. Marrows, G. L. Creeth, F. E. Stanley, B. J. Hickey, P. R. Aitchison, M. Crawford, and J. N. Chapman

Appl. Phys. Lett. 79, 4384 (2001); http://dx.doi.org/10.1063/1.1421641 (3 pages)

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The reorientation of antiferromagnetically coupled Co layers comprising the pinned layers of an antiparallel biased spin valve is reported. Initially, the lower Co layer is saturated in the growth field in the deposition chamber, but it reorients as the upper Co layer grows to be thicker than the lower one. We have investigated the nature of this reorientation by ex situ transport measurements and Lorentz microscopy, and found it highly inhomogeneous, leading to a complex in-plane domain pattern. This results in a reduction of the giant magnetoresistance of the spin valves close to the balance point, where the benefits of the antiparallel biasing are greatest. © 2001 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Spin-dependent tunnel junctions with ZrOx barriers

Jianguo Wang, P. P. Freitas, E. Snoeck, P. Wei, and J. C. Soares

Appl. Phys. Lett. 79, 4387 (2001); http://dx.doi.org/10.1063/1.1421232 (3 pages) | Cited 24 times

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Spin-dependent tunnel junctions with crystalline ZrOx barriers were fabricated, with tunnel magnetoresistance (TMR) reaching 20% and a resistance×area product of 24 k Ω μm2, after annealing at 260 °C. Effective barrier height and thickness are 1.6 eV and 10.6 Å, respectively. The ZrOx barriers were fabricated by rf plasma oxidation of a 5 Å thick Zr layer. High-resolution transmission electron microscopy and Rutherford backscattering spectrometry were used to characterize the as-deposited barrier. Both ZrO and ZrO2 phases are present, together with (CoFe)Ox. Upon annealing, the interfacial oxygen moves into the barrier, resulting in an increase of TMR from 2% to 19.2%, an increase of barrier height from 0.3 to 1.6 eV, and a reduction of barrier thickness from 18.5 to 10.5 Å. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.72.Cc Kinetics of defect formation and annealing

Continuous reel-to-reel measurement of critical currents of coated conductors

G. Grimaldi, M. Bauer, and H. Kinder

Appl. Phys. Lett. 79, 4390 (2001); http://dx.doi.org/10.1063/1.1428771 (3 pages) | Cited 4 times

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We demonstrate that magnetization measurements by Hall probe arrays are well suited for the reel-to-reel determination of critical currents along long lengths of coated conductors. The technique is contact-free, fast, simple, and it has a high spatial resolution. A quantitative measure of the critical current as a function of position was obtained by fitting a simple critical state model to the field distribution. The technique is demonstrated for YBa2Cu3O7 films on single-crystal substrates and then applied to samples of coated conductors. © 2001 American Institute of Physics.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena

Thermal effects in self-assembled FePt nanoparticles with partial chemical ordering

J. W. Harrell, S. Wang, D. E. Nikles, and M. Chen

Appl. Phys. Lett. 79, 4393 (2001); http://dx.doi.org/10.1063/1.1427751 (3 pages) | Cited 33 times

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We have studied the thermal stability of self-assembled FePt nanoparticles with partial chemical ordering. The magnetic viscosity was measured at zero field after partial dc demagnetization as a function of the initial remanent magnetization. The viscosity curves are in good agreement with a calculation using a noninteracting Stoner–Wohlfarth, Arrhenius–Néel model with a broad distribution of anisotropy fields and randomly oriented easy axes. The shape of the zero field viscosity curve differs from curves measured for thin film media with in-plane and perpendicular anisotropy, in which interactions are known to be important. © 2001 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Lr Magnetic aftereffects
61.46.-w Structure of nanoscale materials

Magnetic, structural, and transport properties of thin film and single crystal Co2MnSi

M. P. Raphael, B. Ravel, M. A. Willard, S. F. Cheng, B. N. Das, R. M. Stroud, K. M. Bussmann, J. H. Claassen, and V. G. Harris

Appl. Phys. Lett. 79, 4396 (2001); http://dx.doi.org/10.1063/1.1428625 (3 pages) | Cited 49 times

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The magnetic, structural, and transport properties of the Heusler alloy Co2MnSi are reported for sputtered thin films and a single crystal. X-ray diffraction reveals a phase pure L21 structure for all films grown between 573 and 773 K. Films grown at 773 K display a four-fold decrease in the resistivity relative to those grown at lower temperatures and a corresponding 30% increase in the residual resistivity ratio (ρ300 K/ρ5 K). We show that the higher growth temperature results in lattice constants, room temperature resistivities, and magnetic properties that are comparable to that of the bulk single crystal. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Effect of lattice strain and defects on the superconductivity of MgB2

A. Serquis, Y. T. Zhu, E. J. Peterson, J. Y. Coulter, D. E. Peterson, and F. M. Mueller

Appl. Phys. Lett. 79, 4399 (2001); http://dx.doi.org/10.1063/1.1428109 (3 pages) | Cited 60 times

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The influence of lattice strain and Mg vacancies on the superconducting properties of MgB2 samples has been investigated. High quality samples with sharp superconducting transitions were synthesized. The variations in lattice strain and Mg vacancy concentrations were obtained by varying the synthesis conditions. It was found that high strain (∼1%) and the presence of Mg vacancies (∼5%) resulted in lowering the Tc by only 2 K. © 2001 American Institute of Physics.
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74.62.Dh Effects of crystal defects, doping and substitution
61.72.J- Point defects and defect clusters
74.10.+v Occurrence, potential candidates
74.72.-h Cuprate superconductors

The effect of uniaxial quartic anisotropy on thermal stability of magnetic nanograins

H. Neal Bertram and Vladimir L. Safonov

Appl. Phys. Lett. 79, 4402 (2001); http://dx.doi.org/10.1063/1.1425469 (3 pages) | Cited 13 times

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The effect of quartic anisotropy (K2) for nanograins with hexagonal crystalline structure on thermal stability has been studied. For reversal field parallel to the anisotropy axis, the presence of K2 increases the energy barrier in small fields but does not change the nucleation field. The mean first passage time was calculated from the stochastic differential equation. Reversal field at a finite temperature versus field pulse time showed very little effect at short times but thermal stability at long times was significantly extended. This effect was shown to be appreciable only for fields oriented within about 15° to the anisotropy axis. © 2001 American Institute of Physics.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials

Fabrication of highly balanced directly coupled YBa2Cu3Oy gradiometers and their noise properties in an unshielded environment

A. Tsukamoto, T. Fukazawa, K. Takagi, K. Yokosawa, D. Suzuki, and K. Tsukada

Appl. Phys. Lett. 79, 4405 (2001); http://dx.doi.org/10.1063/1.1429291 (3 pages) | Cited 10 times

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We fabricated directly coupled gradiometers made of YBa2Cu3Oy thin films on bicrystal substrates. The parasitic effective area of the gradiometric pickup coil was found to be comparable with that of the superconducting quantum interference devices (SQUIDs) in each gradiometer. A gradiometer balance of below 10−3 was achieved by selecting the coupling direction of the SQUID so as to cancel the parasitic effective area of the pickup coil by the effective area of the SQUID itself. The noise of the gradiometers measured in an unshielded environment decreased in proportion to the improvement in the gradiometer balance; however, the noise of the gradiometer with a balance of 0.03% was limited by the gradient-field component of the environmental noise. © 2001 American Institute of Physics.
Show PACS
85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
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