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16 Sep 2002

Volume 81, Issue 12, pp. 2145-2305

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Superconducting properties of MgB2 thin films prepared on flexible plastic substrates

Peter Kúš, Andrej Plecenik, Leonid Satrapinsky, Ying Xu, and Roman Sobolewski

Appl. Phys. Lett. 81, 2199 (2002); http://dx.doi.org/10.1063/1.1507828 (3 pages) | Cited 14 times

Online Publication Date: 9 September 2002

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Superconducting MgB2 thin films were prepared on 50-μm-thick, flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B precursors with nominal thickness of about 100 nm and a subsequent ex situ rapid annealing process in an Ar or vacuum atmosphere. In the optimal annealing process, the Mg–B films were heated to approximately 600 °C, but, at the same time, the backside of the structures was attached to a water-cooled radiator to avoid overheating of the plastic substrate. The resulting MgB2 films were amorphous with the onset of the superconducting transition at Tc,on ≈ 29 K and a transition width of approximately 3 K. The critical current density was >7×105 A/cm2 at 4.2 K, and its temperature dependence indicated a granular film composition with a network of intergranular weak links. The films could be deposited on large-area foils (up to 400 cm2) and, after processing, cut into any shape (e.g., strips) with scissors, or bent multiple times, without any observed degradation of their superconducting properties. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Batch-fabricated spin-injection magnetic switches

J. Z. Sun, D. J. Monsma, D. W. Abraham, M. J. Rooks, and R. H. Koch

Appl. Phys. Lett. 81, 2202 (2002); http://dx.doi.org/10.1063/1.1506794 (3 pages) | Cited 96 times

Online Publication Date: 9 September 2002

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A method is developed for the fabrication of sub-100 nm current-perpendicular spin-valve junctions with low contact resistance. The approach is to use a batch-fabricated trilayer template with the junction features defined by a metal stencil layer and an undercut in the insulator. The spin-valve thin film stack is deposited afterwards into the stencil, with the insulator undercut providing the necessary magnetic isolation. Using this approach, reproducible spin-current-induced magnetic switching is demonstrated for junctions down to 50 nm×100 nm in size. © 2002 American Institute of Physics.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Mk Spin transport through interfaces
75.47.De Giant magnetoresistance
75.60.Jk Magnetization reversal mechanisms

Detection of coherent and incoherent spin dynamics during the magnetic switching process using vector-resolved nonlinear magneto-optics

T. J. Silva, P. Kabos, and M. R. Pufall

Appl. Phys. Lett. 81, 2205 (2002); http://dx.doi.org/10.1063/1.1508163 (3 pages) | Cited 27 times

Online Publication Date: 9 September 2002

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It is usually assumed that magnetic switching proceeds via coherent rotation under conditions of high symmetry. There is no a priori reason to expect an inhomogeneous response when a uniform magnetic torque is applied to a homogeneous ferromagnet. We test this assumption using vector- and time-resolved nonlinear magneto-optic measurements on a continuous Ni–Fe film. While coherent dynamics are observed when the magnetization M is initially oriented along the easy axis (the preferred axis of M in the absence of external fields), we find evidence for inhomogeneous spin dynamics when M is initially oriented perpendicular to the easy axis, which suggests the generation of incoherent spin waves during the magnetic reorientation process. The inhomogeneity is sufficient to reduce the spatially averaged magnetic moment within the measured area by almost 50%.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Ds Spin waves
75.30.Cr Saturation moments and magnetic susceptibilities
78.66.Bz Metals and metallic alloys
78.47.-p Spectroscopy of solid state dynamics

Dependence of physical properties and giant magnetoresistance ratio on substrate position during rf sputtering of NiO and α-Fe2O3 for bottom spin valves

Seongtae Bae, Jack H. Judy, P. J. Chen, and W. F. Egelhoff

Appl. Phys. Lett. 81, 2208 (2002); http://dx.doi.org/10.1063/1.1508161 (3 pages) | Cited 2 times

Online Publication Date: 9 September 2002

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The dependence of composition, crystalline orientation texture, surface roughness, and giant magnetoresistance (GMR) ratio on substrate position during rf reactive sputtering of antiferromagnetic NiO and α-Fe2O3 films for dc magnetron sputtered Co/Cu/Co bottom spin valves have been investigated. For substrate positions from the center to edge of the target, the GMR ratio increased from 13.5% to 19.8% for NiO and from 9.8% to 13% for α-Fe2O3. These significant enhancements of GMR ratio was found to correlate with a decrease of surface roughness, increase in crystalline texture, and a nearly bulk stoichiometry of the NiO and α-Fe2O3 thin films. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Ee Antiferromagnetics
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
68.35.B- Structure of clean surfaces (and surface reconstruction)

Detection of a micron-sized magnetic sphere using a ring-shaped anisotropic magnetoresistance-based sensor: A model for a magnetoresistance-based biosensor

M. M. Miller, G. A. Prinz, S.-F. Cheng, and S. Bounnak

Appl. Phys. Lett. 81, 2211 (2002); http://dx.doi.org/10.1063/1.1507832 (3 pages) | Cited 120 times

Online Publication Date: 9 September 2002

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We have fabricated micron-sized NiFe ring-shaped sensors that show localized detection of the radial component of the dipolar fringing field from a single, partially magnetized, micron-sized NiFe sphere. Specifically, the anisotropic magnetoresistance response to this fringing field is strongly peaked when the sphere is directly above the center of the ring and rapidly decreases to zero when the sphere is outside the ring. Such a device is a model system for a proposed biosensor array architecture that could operate similarly to high-density random access computer memory.
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85.75.Ss Magnetic field sensors using spin polarized transport
87.80.-y Biophysical techniques (research methods)
75.47.De Giant magnetoresistance
85.75.Bb Magnetic memory using giant magnetoresistance

Reduced temperature and bias-voltage dependence of the magnetoresistance in magnetic tunnel junctions with Hf-inserted Al2O3 barrier

Byong Guk Park and Taek Dong Lee

Appl. Phys. Lett. 81, 2214 (2002); http://dx.doi.org/10.1063/1.1508413 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2002

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A modified tunnel barrier structure for the magnetic tunnel junction (MTJ) was fabricated by inserting a Hf layer in the middle of the Al2O3 tunnel barrier. MTJs with the Hf-inserted barrier show a higher tunnel mangnetoresistance (TMR) ratio and weaker temperature and bias-voltage dependence of TMR compared to the MTJs with a conventional Al2O3 barrier. The enhancement of the TMR ratio and the reduction of the temperature and bias-voltage dependence were attributed to the reduction of defects in the barrier. © 2002 American Institute of Physics.
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73.40.Gk Tunneling
75.45.+j Macroscopic quantum phenomena in magnetic systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
72.15.Gd Galvanomagnetic and other magnetotransport effects

Monte Carlo simulation on the indirect exchange interactions of Co-doped ZnO film

Abraham F. Jalbout, Hanning Chen, and Scott L. Whittenburg

Appl. Phys. Lett. 81, 2217 (2002); http://dx.doi.org/10.1063/1.1508168 (3 pages) | Cited 42 times

Online Publication Date: 9 September 2002

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Monte Carlo simulations using a three-dimensional lattice model studied the Ruderman–Kittel–Kasuya–Yosida (RKKY) indirect exchange interaction of doped magnetic Co ions in ZnO films. The results of the calculations show that the RKKY interaction in Co-doped ZnO is long ranged and its magnitude is proportional to R−1 (inverse of the distance R from a central Co2+ ion). The sign oscillates with a frequency that depends on the concentration of the carrier. The long-distance sum of the RKKY indirect exchange energies is positive indicating that these materials are ferromagnetic, in direct correlation with previously reported results. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
75.40.Mg Numerical simulation studies
75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
75.70.Ak Magnetic properties of monolayers and thin films

Structural studies of L10 FePt nanoparticles

T. J. Klemmer, N. Shukla, C. Liu, X. W. Wu, E. B. Svedberg, O. Mryasov, R. W. Chantrell, D. Weller, M. Tanase, and D. E. Laughlin

Appl. Phys. Lett. 81, 2220 (2002); http://dx.doi.org/10.1063/1.1507837 (3 pages) | Cited 53 times

Online Publication Date: 9 September 2002

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We have studied the lattice parameter changes of L10 FePt nanoparticles annealed to near equilibrium as a function of composition by x-ray diffraction. We have found that the (111) diffraction peak shifts linearly with composition, however, the c parameter mostly changes in the Pt rich compositions and the a parameter mostly changes in the Fe rich compositions with respect to the equiatomic composition. This causes the tetragonality of the L10 structure to be maximized near the Fe 50%/Pt 50% composition. The magnetic properties were measured at room temperature and at 5 K and are correlated to the structural changes occurring as a function of composition. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
61.66.Dk Alloys
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