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1 Oct 2007

Volume 91, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 91, 143101 (2007); http://dx.doi.org/10.1063/1.2789812 (3 pages)

Hyun S. Kim, Hua Qin, and Robert H. Blick
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Nuclear magnetic resonance on room temperature samples in nanotesla fields using a two-stage dc superconducting quantum interference device sensor

R. Körber, A. Casey, A. Shibahara, M. Piscitelli, B. P. Cowan, C. P. Lusher, J. Saunders, D. Drung, and Th. Schurig

Appl. Phys. Lett. 91, 142501 (2007); http://dx.doi.org/10.1063/1.2794028 (3 pages) | Cited 6 times

Online Publication Date: 1 October 2007

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We describe a compact system for pulsed nuclear magnetic resonance at ultralow magnetic fields on small liquid samples ( ∼ 0.14 ml) at room temperature. The broadband spectrometer employs an integrated two-stage superconducting quantum interference device current sensor with a coupled energy sensitivity of 50h, in the white noise limit. Environmental noise is screened using a compact arrangement of mu-metal and a superconducting shield. Proton signals in water have been observed down to 93 nT (a Larmor frequency of 4.0 Hz), with a minimum linewidth of 0.16 Hz measured at ∼ 40 Hz. Two-component free induction decays were observed from oil/water mixtures between 275 and 300 K.
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76.60.Jx Effects of internal magnetic fields

Symmetric and asymmetric domain wall diodes in magnetic nanowires

M. T. Bryan, T. Schrefl, and D. A. Allwood

Appl. Phys. Lett. 91, 142502 (2007); http://dx.doi.org/10.1063/1.2794030 (3 pages) | Cited 18 times

Online Publication Date: 1 October 2007

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Micromagnetic simulations reveal how transverse domain walls couple with triangular diodes in magnetic nanowires. For symmetric diodes, the coupling explains the observed differences in the magnetic field required to depin domain walls traveling in opposite directions. In asymmetric diodes, the wall-triangle interaction can lead to order-of-magnitude differences in the depinning fields of oppositely magnetized walls traveling in the same direction. The asymmetric structures therefore combine the diode function of the symmetric structures with domain wall chirality filtering. We also show how two back-to-back diodes may be used to trap a domain wall and form a memory element.
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75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Mg Numerical simulation studies

Finite-size-induced stability of a permanent magnet levitating over a superconductor in the Meissner state

Jose Luis Perez-Diaz and Juan Carlos Garcia-Prada

Appl. Phys. Lett. 91, 142503 (2007); http://dx.doi.org/10.1063/1.2794408 (3 pages) | Cited 6 times

Online Publication Date: 1 October 2007

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The force between a magnetic dipole and a finite superconductor in the Meissner state (H<Hc1) is calculated by using an expression based on London’s and Maxwell’s equations. It demonstrates the existence of attractiveness and stability. The finiteness of a piece of superconductor therefore suffices to explain a stability for the levitation of a magnet over it or even the suspension of one of them under the other one. This does not contradict the existence of flux penetration. However, this makes the flux penetration not necessary to explain both stability and attractiveness, as has been assumed until now.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Reduction of hysteresis loss and large magnetic entropy change in the NaZn13-type LaPrFeSiC interstitial compounds

J. Shen, B. Gao, H. W. Zhang, F. X. Hu, Y. X. Li, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 91, 142504 (2007); http://dx.doi.org/10.1063/1.2794412 (3 pages) | Cited 25 times

Online Publication Date: 1 October 2007

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Magnetic properties and magnetic entropy change of the NaZn13-type La0.5Pr0.5Fe11.5Si1.5Cx compounds have been investigated. Both the lattice parameter and the Curie temperature increase linearly with increasing carbon concentration. The maximum hysteresis loss at TC reduces remarkably from 94.8 J/kg for x = 0 to 23.1 J/kg for x = 0.3 because of the weakening of the itinerant electron metamagnetic transition. However, the magnetic entropy change remains at the large values of 32.4 J/kg K for x = 0 and 27.6 J/kg K for x = 0.3 under a field change of 0–5 T, which implies that a large magnetocaloric effect and a small hysteresis loss have been simultaneously achieved in the La0.5Pr0.5Fe11.5Si1.5Cx carbides.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
65.40.G- Other thermodynamical quantities
75.10.Lp Band and itinerant models
75.30.Sg Magnetocaloric effect, magnetic cooling

Enhanced Curie temperature and spin polarization in Mn4FeGe3

T. Y. Chen, C. L. Chien, and C. Petrovic

Appl. Phys. Lett. 91, 142505 (2007); http://dx.doi.org/10.1063/1.2794425 (3 pages) | Cited 5 times

Online Publication Date: 1 October 2007

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Intermetallic ferromagnetic compound Mn5Ge3, with Curie temperature TC = 296 K, a spin polarization of P = 42%, and a good lattice match to semiconductors, is a potential spin injector for spintronics. We report the enhanced magnetic properties and spin polarization of Mn4FeGe3. By replacing one Mn atom in Mn5Ge3 with Fe, the TC of Mn4FeGe3 has been enhanced to 319.50 K, while still maintaining the same crystal structure, high electrical conductivity, and a high residual resistivity ratio of 5.33. More importantly, the spin polarization in excess of 60% of Mn4FeGe3, much higher than that of Mn5Ge3, has been realized.
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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.)
72.25.-b Spin polarized transport
61.66.Dk Alloys
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Bb Fe and its alloys

Improving ion irradiated high Tc Josephson junctions by annealing: The role of vacancy-interstitial annihilation

M. Sirena, S. Matzen, N. Bergeal, J. Lesueur, G. Faini, R. Bernard, J. Briatico, and D. G. Crété

Appl. Phys. Lett. 91, 142506 (2007); http://dx.doi.org/10.1063/1.2783227 (3 pages) | Cited 6 times

Online Publication Date: 3 October 2007

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The authors have studied the annealing effect in the transport properties of high Tc Josephson junctions (JJs) made by ion irradiation. Low temperature annealing (80 °C) increases the JJ coupling temperature (TJ) and the IcRn product, where Ic is the critical current and Rn the normal resistance. They have found that the spread in JJ characteristics can be reduced by sufficient long annealing times, increasing the reproducibility of ion irradiated Josephson junctions. The characteristic annealing time and the evolution of the spread in the JJ characteristics can be explained by a vacancy-interstitial annihilation process rather than by an oxygen diffusion one.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.25.F- Transport properties
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
74.25.Sv Critical currents

Locally resolved ferromagnetic resonance in Co stripes

Ralf Meckenstock, I. Barsukov, O. Posth, J. Lindner, A. Butko, and D. Spoddig

Appl. Phys. Lett. 91, 142507 (2007); http://dx.doi.org/10.1063/1.2794026 (3 pages) | Cited 9 times

Online Publication Date: 3 October 2007

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Microwave excitations of Co stripes of 100×1.5×0.025 μm3 were investigated by angular dependent ferromagnetic resonance (FMR) and by locally resolved scanning thermal microscopy based (SThM) FMR, offering a lateral resolution of <100 nm and a sensitivity of 106 spins. Besides the uniform excitation, backward volume modes and a rim resonance were identified by SThM-FMR imaging. Micromagnetic simulations (OOMMF) confirm the experimentally observed lateral confinement of these modes. The magnetic parameters of the Co stripes correspond to the ones of Co bulk with a surface anisotropy Ks = 0.5 mJ/m2.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy

Sub-6-nm grain size control in polycrystalline thin films using synthetic nucleation layer

S. N. Piramanayagam and K. Srinivasan

Appl. Phys. Lett. 91, 142508 (2007); http://dx.doi.org/10.1063/1.2795329 (3 pages) | Cited 10 times

Online Publication Date: 3 October 2007

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A key objective in the design of recording media for hard disk drives is to tailor the grain size. A fourfold increase in the recording density from the current levels demands that the mean grain diameter be reduced from 7 to about 5.5 nm, and distribution to below 15%. Traditional techniques involving dopants can realize small grain sizes but also deteriorate the structural and magnetic properties. In this study, the utility of an extremely thin synthetic nucleation layer in reducing the grain size and distribution of the recording media is demonstrated, with significant implications for other applications too.
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75.50.Ss Magnetic recording materials
68.55.-a Thin film structure and morphology
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films

Thermopower and Co K-edge studies of potassium sodium cobalt oxyhydrates Na0.33K0.02(H2O)1.33CoO2−δ and Na0.07K0.21(H2O)0.63CoO2−δ

Chia-Jyi Liu, Chia-Yuan Liao, Jung-Sheng Wang, Pradipta K. Nayak, Zhi-Ru Lin, and Hwo-Shuenn Sheu

Appl. Phys. Lett. 91, 142509 (2007); http://dx.doi.org/10.1063/1.2789786 (3 pages) | Cited 2 times

Online Publication Date: 4 October 2007

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We report measurements of the thermopower and Co K-edge x-ray absorption spectroscopy on bilayer and monolayer (Na,K)x(H2O)yCoO2−δ. According to the Co K-edge x-ray absorption spectra, the Co oxidation number for bilayer hydrate Na0.33K0.02(H2O)1.33CoO2−δ is higher than that of monolayer hydrate Na0.07K0.21(H2O)0.63CoO2−δ with a chemical shift of 3.5 eV, which is in sharp contrast with Co K-edge x-ray absorption spectroscopy and cerimetric titration results for Nax(H2O)yCoO2−δ, where there is essentially no difference of the oxidation number of Co between bilayer and monolayer sodium cobalt oxyhydrates. According to thermopower analysis, band narrowing is observed when γ-Na0.7CoO2 is transformed to potassium sodium cobalt oxyhydrates.
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72.20.Pa Thermoelectric and thermomagnetic effects
78.70.Dm X-ray absorption spectra
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
76.60.Cq Chemical and Knight shifts

Spin polarized tunneling in a ferromagnetic Zener diode

E. Comesaña and G. A. Gehring

Appl. Phys. Lett. 91, 142510 (2007); http://dx.doi.org/10.1063/1.2795335 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2007

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Calculations of the tunneling current as a function of voltage for a Zener diode where both sides are ferromagnetic have been performed. The current is evaluated as a function of the voltage and of the magnetization on each side of the diode. The tunneling magnetoresistance is analyzed. Two cases are considered, one that corresponds to Mn doped GaAs in which the ferromagnetism is stronger on the p side of the diode and the other that corresponds to ZnO where there are likely to be many more carriers on the n side of the diode.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Magnetic patterning of (Ga,Mn)As by hydrogen passivation

L. Thevenard, A. Miard, L. Vila, G. Faini, A. Lemaître, N. Vernier, J. Ferré, and S. Fusil

Appl. Phys. Lett. 91, 142511 (2007); http://dx.doi.org/10.1063/1.2795790 (3 pages) | Cited 6 times

Online Publication Date: 4 October 2007

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We present a method to create magnetic patterns in thin layers of (Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the hole density, and thereby locally suppress the carrier-mediated ferromagnetic phase. The sample surface is thus maintained continuous, and the minimal structure size is of about 200 nm. In micron-sized ferromagnetic dots fabricated by hydrogen passivation on perpendicularly magnetized layers, the switching fields can be maintained closer to the continuous film coercivity, compared to dots made by usual dry etch techniques.
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81.65.Rv Passivation
72.20.-i Conductivity phenomena in semiconductors and insulators
75.50.Vv High coercivity materials

Critical behavior in Ti-doped manganites LaMn1−xTixO3 (0.05 ⩽ x ⩽ 0.2)

J. Yang and Y. P. Lee

Appl. Phys. Lett. 91, 142512 (2007); http://dx.doi.org/10.1063/1.2795796 (3 pages) | Cited 7 times

Online Publication Date: 4 October 2007

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The critical properties of the ferromagnetic insulating system LaMn1−xTixO3 (0.05 ⩽ x ⩽ 0.2) are investigated based on the static magnetization measurements around Curie temperature TC. The values of critical exponents, derived from the magnetic data using the Kouvel-Fisher method, yield 0.359 ⩽ β ⩽ 0.378, 1.24 ⩽ γ ⩽ 1.29, and 4.11 ⩽ δ ⩽ 4.21 with a TC of 95–173 K. The exponent values are close to those expected for three-dimensional Heisenberg ferromagnets with short-range interactions, and the magnetic transition is understood in the context of Griffiths phase, arising from the random-temperature effects.
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75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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