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9 Jun 2003

Volume 82, Issue 23, pp. 4011-4195

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4160 (2003); http://dx.doi.org/10.1063/1.1580641 (3 pages)

Eva M. Höhberger, Tomas Krämer, Werner Wegscheider, and Robert H. Blick
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Investigation on intergrain exchange coupling of nanocrystalline permanent magnets by Henkel plot

Hong-wei Zhang, Chuan-bing Rong, Xiao-bo Du, Jian Zhang, Shao-ying Zhang, and Bao-gen Shen

Appl. Phys. Lett. 82, 4098 (2003); http://dx.doi.org/10.1063/1.1576291 (3 pages) | Cited 40 times

Online Publication Date: 2 June 2003

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In a real magnet, the relation between isothermal remanence Jr(H) and dc demagnetization remanence Jd(H) is expressed as δm(H) = [Jd(H)−Jr(∞)+2Jr(H)]/J(∞). It is believed that nonzero δm is due to the interactions between particles in the magnet. Using Pr2Fe14B as a sample, the relation is examined by the micromagnetic finite element method. The positive value of δm is primarily caused by intergrain exchange coupling. The decrease of intergrain exchange coupling results in the drop of the maximum value of δm. However, the variation of anisotropy in grain boundaries produces no change in the maximum value of δm. A Henkel plot is suggested to be effective for checking intergrain exchange coupling in magnets. © 2003 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ww Permanent magnets
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Effect of Li doping on the magnetotransport properties of La0.7Ca0.3−yLiyMnO3 system: Decrease of metal–insulator transition temperature

Sayani Bhattacharya, R. K. Mukherjee, B. K. Chaudhuri, and H. D. Yang

Appl. Phys. Lett. 82, 4101 (2003); http://dx.doi.org/10.1063/1.1580650 (3 pages) | Cited 18 times

Online Publication Date: 2 June 2003

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With increasing the Li doping level in La0.7Ca0.3−yLiyMnO3 (0 ⩽ y ⩽ 0.3), the system is driven from a higher-conductivity regime to a lower-conductivity regime, which is in sharp contrast with the behavior of Na or K doping. Compared to those of K or Na, the ionic radius of Li is much smaller than that of Ca. Therefore, substitution of Ca by Li results in a smaller average A-site radius, narrowing the bandwidth and hence enhancing the band gap and resistivity. The effect of random disorder of La3+ and A2+ also plays an important role leading to charge localization. © 2003 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
75.47.Lx Magnetic oxides
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena

Elastic properties of hot-isostatically-pressed magnesium diboride

V. F. Nesterenko and Y. Gu

Appl. Phys. Lett. 82, 4104 (2003); http://dx.doi.org/10.1063/1.1579566 (3 pages) | Cited 7 times

Online Publication Date: 2 June 2003

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Magnesium diboride was hot-isostatically pressed using three qualitatively different cycles: dense material cooled under pressure (DMCUP), “standard” cycle with pressure and temperature simultaneously reduced, and isothermal pressure release. Elastic properties of dense MgB2 were measured at normal conditions using resonant ultrasound spectroscopy method. The highest values of elastic moduli correspond to the sample processed using DMCUP cycle. The data for fully dense samples are in satisfactory agreement with theoretical predictions based on quantum mechanics calculations. The effect of lower density on elastic constants is consistent with a theoretical approach based on elasticity theory taking into account effect of porosity. © 2003 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Vw Pressure treatment
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Spin valves with spin-engineered domain-biasing scheme

Z. Q. Lu and G. Pan

Appl. Phys. Lett. 82, 4107 (2003); http://dx.doi.org/10.1063/1.1581977 (3 pages) | Cited 1 time

Online Publication Date: 2 June 2003

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Synthetic spin-filter spin valves with spin-engineered biasing scheme sub/Ta/NiFe/IrMn/NiFe/NOL/Cu1/CoFe/Cu2/CoFe/Ru/CoFe/IrMn/Ta were developed. In the structure, the orthogonal magnetic configuration for biasing and pinning field was obtained by one-step magnetic annealing process by means of spin flop, which eliminated the need for two antiferromagnetic materials with distinctively different blocking temperatures and two-step magnetic annealing as in conventional exchange biasing scheme. The longitudinal domain biasing of spin valves was achieved by using interlayer coupling field through Cu1 spacer. By adjusting the thickness of the Cu1 layer, the interlayer coupling biasing field can provide domain stabilization and was sufficiently strong to constrain the magnetization in coherent rotation. This can prevent Barkhausen noises associated with magnetization reversal. We report here a proof of concept study of such a domain-biasing scheme, which has its important technological applications in nanoscale spin valve and magnetic tunneling junction read heads and other spintronic devices. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
72.25.Ba Spin polarized transport in metals
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.30.Et Exchange and superexchange interactions
75.40.-s Critical-point effects, specific heats, short-range order
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.47.Np Metals and alloys
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.75.-c Magnetic properties of nanostructures

Vortex nucleation in submicrometer ferromagnetic disks

M. Rahm, M. Schneider, J. Biberger, R. Pulwey, J. Zweck, D. Weiss, and V. Umansky

Appl. Phys. Lett. 82, 4110 (2003); http://dx.doi.org/10.1063/1.1581363 (3 pages) | Cited 29 times

Online Publication Date: 2 June 2003

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We investigate both experimentally and by means of micromagnetic calculations magnetic states preceding vortex formation in permalloy nanodisks. In experiment, we used micro-Hall sensors fabricated from GaAs/AlGaAs heterojunction material to measure stray field hysteresis loops of individual disks. Micromagnetic calculations involving different micromagnetic codes allowed us to interpret the experimental results. Both calculations and experiments suggest that vortex formation can be reached via different precursor states. © 2003 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Jk Magnetization reversal mechanisms

High critical current density in iron-clad MgB2 tapes

H. Fang, S. Padmanabhan, Y. X. Zhou, and K. Salama

Appl. Phys. Lett. 82, 4113 (2003); http://dx.doi.org/10.1063/1.1582358 (3 pages) | Cited 51 times

Online Publication Date: 2 June 2003

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Iron-clad MgB2 superconducting tapes with a MgB2 core cross-section area of 1.07×10−3 cm2 were fabricated using the standard powder-in-tube method. The starting precursor was ultrafine Mg and B mixture powder prepared by high-energy ball milling. Very good grain connections as well as grain refinement were obtained in tapes annealed at 850 °C. Under a 1.5-T external magnetic field, Jc is 1.07×105 and 6.54×103 A/cm2 at 20 and 30 K, respectively. An extrapolation to zero field at 20 K gives a Jc of 3.0×105 A/cm2. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
81.40.Gh Other heat and thermomechanical treatments
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Cooperative versus superparamagnetic behavior of dense magnetic nanoparticles in Co80Fe20/Al2O3 multilayers

S. Sahoo, O. Petracic, W. Kleemann, S. Stappert, G. Dumpich, P. Nordblad, S. Cardoso, and P. P. Freitas

Appl. Phys. Lett. 82, 4116 (2003); http://dx.doi.org/10.1063/1.1581002 (3 pages) | Cited 32 times

Online Publication Date: 2 June 2003

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Spin glasslike cooperative freezing is evidenced at low temperatures in a magnetic nanoparticle system prepared as a discontinuous metal–insulator multilayer [Co80Fe20(0.9 nm)/Al2O3(3 nm)]10. The relaxational behavior clearly deviates from Arrhenius–Néel–Brown-type and rather hints at collective freezing into a spin glass phase below Tg ≃ 61 K. Holelike memory imprinting during a stop-and-wait magnetization procedure corroborates the collective nature of the frozen state. Consequences for future magnetic terabit storage devices are briefly discussed. © 2003 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Lk Spin glasses and other random magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys

Current–voltage characteristics of Pb and Sn granular superconducting nanowires

Sébastien Michotte, Stefan Mátéfi-Tempfli, and Luc Piraux

Appl. Phys. Lett. 82, 4119 (2003); http://dx.doi.org/10.1063/1.1582356 (3 pages) | Cited 30 times

Online Publication Date: 2 June 2003

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Arrays of granular superconducting Pb and Sn nanowires (40–55 nm in diameter and 22 or 50 μm long) have been prepared by electrodeposition in nanoporous membranes. A simple technique has been developed to perform electrical transport measurement on a single nanowire. By sweeping the dc current inside the nanowire, we observed the formation of phase-slip-centers far below the critical temperature. In contrast, in voltage-driven experiments, an interesting S-shaped behavior has been observed in the nucleation region of these phase-slip-centers. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.F- Transport properties
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