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17 Sep 2007

Volume 91, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 123101 (2007); http://dx.doi.org/10.1063/1.2784389 (3 pages)

Thierry Laroche, Alexandre Vial, and Matthieu Roussey
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The effect of magnesium vacancies on the π intraband scattering in MgxB2 as determined by point contact Andreev reflection

K. A. Yates, Y. Miyoshi, J. Grunwell, K. Riggall, L. F. Cohen, S. K. Chen, J. L. MacManus Driscoll, and A. Serquis

Appl. Phys. Lett. 91, 122501 (2007); http://dx.doi.org/10.1063/1.2786019 (3 pages) | Cited 2 times

Online Publication Date: 17 September 2007

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In order to introduce structural defects into the π band with minimal distortions in the σ band, bulk samples of varying magnesium content were prepared. Point contact Andreev reflection measurements reveal that the density of states of the π band and the behavior of the energy gaps in field imply a relative increase of π band to σ band scattering with increasing magnesium deficiency. The results are consistent with the observed increase of the low temperature Hc2 value in magnesium deficient MgB2.
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74.25.Jb Electronic structure (photoemission, etc.)
74.50.+r Tunneling phenomena; Josephson effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

MgB2 radio-frequency superconducting quantum interference device prepared by atomic force microscope lithography

M. Gregor, T. Plecenik, M. Praščák, R. Mičunek, M. Kubinec, V. Gašparík, M. Grajcar, P. Kúš, and A. Plecenik

Appl. Phys. Lett. 91, 122502 (2007); http://dx.doi.org/10.1063/1.2779095 (3 pages) | Cited 3 times

Online Publication Date: 18 September 2007

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A new method of preparation of radio-frequency superconducting quantum interference devices on MgB2 thin films is presented. The variable-thickness bridge was prepared by a combination of optical lithography and of the scratching by an atomic force microscope. The critical current of the nanobridge was 0.35 μA at 4.2 K. Noncontact measurements of the current-phase characteristics and of the critical current versus temperature have been investigated on the authors’ structures.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Anomalous ferromagnetism in spray pyrolysis deposited multiferroic BiFeO3 films

P. K. Siwach, H. K. Singh, Jai Singh, and O. N. Srivastava

Appl. Phys. Lett. 91, 122503 (2007); http://dx.doi.org/10.1063/1.2785945 (3 pages) | Cited 9 times

Online Publication Date: 19 September 2007

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Oriented polycrystalline BiFeO3 (BFO) films are deposited on single crystal LaAlO3 (001) substrates by nebulized spray pyrolysis technique at low temperature of ∼ 300 °C. Annealing of the as deposited films in air and oxygen at ∼ 550 °C for 1 h is found to produce crystallization and BFO phase formation. X-ray diffraction results show rhombohedral disordered perovskite structure with space group R3m. As revealed by atomic force microscopy, grain size increases with oxygen annealing. Magnetic measurements show well-defined hysteretic loops at room temperature for both the films. However, oxygenation leads to dramatic increase in room temperature ferromagnetism as evidenced by large saturation magnetization of ∼ 250 emu/cm3. This enhanced magnetization is attributed to the presence of iron oxide rich nanoclusters due to oxygen annealing.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
61.66.Fn Inorganic compounds
81.15.Rs Spray coating techniques
75.50.Bb Fe and its alloys

Changing and reversing the exchange bias in a current-in-plane spin valve by means of an electric current

Xiao-Li Tang, Huai-Wu Zhang, Hua Su, Zhi-Yong Zhong, and Yu-Lan Jing

Appl. Phys. Lett. 91, 122504 (2007); http://dx.doi.org/10.1063/1.2786592 (3 pages) | Cited 13 times

Online Publication Date: 19 September 2007

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The authors show that a current flowing in a direction not perpendicular to the layer planes of an exchange-biased spin valve systematically changes the exchange bias. The direction of the exchange bias can be completely reversed when a large enough current is applied. This effect occurs only when the direction of the initial sweeping magnetic field is antiparallel to the exchange-bias field. The effect is attributed to the recently predicted current-induced torque in an antiferromagnet and provides evidence to support the prediction that the critical current is smaller in an antiferromagnet than the typical value for current switching in a ferromagnet.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
75.47.De Giant magnetoresistance

Microwave-assisted magnetization reversal in 0.36-μm-wide Permalloy wires

Y. Nozaki, K. Tateishi, S. Taharazako, M. Ohta, S. Yoshimura, and K. Matsuyama

Appl. Phys. Lett. 91, 122505 (2007); http://dx.doi.org/10.1063/1.2786593 (3 pages) | Cited 24 times

Online Publication Date: 19 September 2007

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Microwave-assisted magnetization reversal in a 0.36 μm wide Ni80Fe20 wire with a natural ferromagnetic resonance frequency of 8.42 GHz was investigated experimentally. Magnetization switching could be detected from a discontinuous change in the ferromagnetic resonance frequency of the wire. The application of microwaves with a frequency of 7.5 GHz and a power of 19.2 dBm reduced the switching field from 217 to 142 Oe. While high-power microwave-assisted switching reduced the dc switching field, it substantially broadened the switching field distribution. This is mainly attributed to inhomogeneous resonance properties of the nucleation sites in the wire.
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75.60.Jk Magnetization reversal mechanisms
75.50.Bb Fe and its alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
84.40.-x Radiowave and microwave (including millimeter wave) technology

Significant suppression of ferromagnetism by hydrostatic pressure in the diluted magnetic semiconductor Sb2−xVxTe3 with x ⩽ 0.03

J. S. Dyck, T. J. Mitchell, A. J. Luciana, P. C. Quayle, Č. Drašar, and P. Lošťák

Appl. Phys. Lett. 91, 122506 (2007); http://dx.doi.org/10.1063/1.2787881 (3 pages) | Cited 3 times

Online Publication Date: 20 September 2007

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The authors report on the hydrostatic pressure dependence of the magnetotransport properties of ferromagnetic Sb2−xVxTe3 single crystals with x = 0.02–0.03. Pressure significantly increases the free hole concentration in these compounds. In turn, the Curie temperature is suppressed by roughly 40%, which goes against many models that would predict an increase in Curie temperature with increasing carrier concentration. These results indicate that the ferromagnetism in these materials is carrier mediated and that a full Ruderman-Kittel-Kasuya-Yosida model that takes into account the oscillatory nature of the indirect exchange interaction among localized spins is needed in order to explain the data.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Superconducting thin films of heavy-fermion compound CeCoIn5 prepared by molecular beam epitaxy

M. Izaki, H. Shishido, T. Kato, T. Shibauchi, Y. Matsuda, and T. Terashima

Appl. Phys. Lett. 91, 122507 (2007); http://dx.doi.org/10.1063/1.2787969 (3 pages) | Cited 3 times

Online Publication Date: 20 September 2007

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Highly c-axis oriented thin films of Ce-based heavy-fermion superconductor CeCoIn5 were grown on Cr/MgO substrates by molecular beam epitaxy. The films consist of micrograins which are strongly oriented in c axis but are random in the film plane. Kondo temperature, superconducting transition temperature, and upper critical fields of the films are very close to those of single crystals.
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74.70.Tx Heavy-fermion superconductors
74.78.-w Superconducting films and low-dimensional structures
74.10.+v Occurrence, potential candidates
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Inverse spin Hall effect by spin injection

S. Y. Liu, Norman J. M. Horing, and X. L. Lei

Appl. Phys. Lett. 91, 122508 (2007); http://dx.doi.org/10.1063/1.2783254 (3 pages)

Online Publication Date: 20 September 2007

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Motivated by a recent experiment [ S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006) ], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering.
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72.25.Ba Spin polarized transport in metals
72.25.Hg Electrical injection of spin polarized carriers
72.15.Gd Galvanomagnetic and other magnetotransport effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Miniaturized superconducting quantum interference magnetometers for high sensitivity applications

C. Granata, A. Vettoliere, and M. Russo

Appl. Phys. Lett. 91, 122509 (2007); http://dx.doi.org/10.1063/1.2785129 (3 pages) | Cited 3 times

Online Publication Date: 20 September 2007

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A miniaturized niobium based dc superconducting quantum interference device (SQUID) magnetometer for high magnetic field sensitivity applications has been developed. The sensing coil consists of an integrated square superconducting coil with a length of 3 mm, involving a device area much smaller with respect to the standard SQUID magnetometers with a comparable magnetic field sensitivity; so it allows increasing the spatial resolution keeping the magnetic field sensitivity unaltered. Furthermore, a small pickup coil minimizes its antenna gain, reducing the radio frequency interference. At T = 4.2 K, the sensors have shown smooth and resonance free V-Φ characteristics and an intrinsic white magnetic field noise spectral density as low as 5.8 fT/Hz1/2, measured in flux locked loop configuration. The good agreement with the theoretical predictions guarantees the reliability and the controllability of the sensors. Due to their compactness and good characteristic parameters, such sensors are suitable for large multichannel systems used in biomagnetic imaging.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements

Manipulation of in-plane uniaxial anisotropy in Fe/MgO(001) films by ion sputtering

Qing-feng Zhan, Stijn Vandezande, Chris Van Haesendonck, and Kristiaan Temst

Appl. Phys. Lett. 91, 122510 (2007); http://dx.doi.org/10.1063/1.2789396 (3 pages) | Cited 7 times

Online Publication Date: 20 September 2007

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Grazing-incidence Ar+ ion sputtering has been used to produce nanoscale ripples on the surface of the Fe/Mg(001) system. This way, a uniaxial anisotropy with both controllable strength and orientation can be superimposed on top of the cubic anisotropy, resulting in Fe/MgO(001) films with unusual anisotropy symmetry. By combining longitudinal and transverse Kerr-effect measurements, different switching processes are revealed. Depending on the orientation of the external magnetic field, one-jump, two-jump, and “reverse” two-jump magnetization reversals can be observed. A simple model, which takes into account the relevant anisotropy energies, is developed to explain the experimentally observed switching fields and to evaluate the domain wall pinning energies of the sputtered sample.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys

Patterned nanoring magnetic tunnel junctions

Z. C. Wen, H. X. Wei, and X. F. Han

Appl. Phys. Lett. 91, 122511 (2007); http://dx.doi.org/10.1063/1.2786591 (3 pages) | Cited 18 times

Online Publication Date: 20 September 2007

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Patterned nanoring (NR) magnetic tunnel junctions (MTJs) with outer diameters between 100 and 400 nm and narrow ring widths between 25 and 30 nm were fabricated. The NR structure consists of CoFeB electrodes and Al-oxide barrier. The tunneling magnetoresistance (TMR) ratio in the range of 20%–50% for the NR-MTJs with the resistance-area product lower than 50 Ω μm2 were observed at room temperature. These NR-MTJs allow current-induced magnetization switching with a low switching current density of around 9×106 A/cm2. Due to the small stray field and high TMR ratio, NR-MTJs offer superior prospects for very high density magnetic random access memory, recording medium, and other spintronic devices.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.75.Dd Magnetic memory using magnetic tunnel junctions

Reversible strain effect in La0.7Sr0.3MnO3 step edge junctions

R. B. Gangineni, L. Schultz, C. Thiele, I. Mönch, and K. Dörr

Appl. Phys. Lett. 91, 122512 (2007); http://dx.doi.org/10.1063/1.2787966 (3 pages) | Cited 10 times

Online Publication Date: 21 September 2007

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The spin-polarized electric transport in ferromagnetic La0.7Sr0.3MnO3 films on piezoelectric substrates with etched steps has been investigated. The Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrate is strained reversibly by application of electric voltage. This includes strain control in film junctions formed at step edges. The film resistance (R) is very sensitive to both strain and magnetic field in a wide temperature range, 30 K<T<300 K, in contrast to the behavior of step-free films. Both R and magnetoresistance decrease (increase) significantly upon in-plane compression (expansion). In this way, strain is introduced as variable parameter for experiments on step edge grain boundaries.
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73.61.Ng Insulators
75.47.Lx Magnetic oxides
72.25.-b Spin polarized transport
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance

Remarkable enhancement of domain-wall velocity in magnetic nanostripes

Jun-Young Lee, Ki-Suk Lee, and Sang-Koog Kim

Appl. Phys. Lett. 91, 122513 (2007); http://dx.doi.org/10.1063/1.2789176 (3 pages) | Cited 20 times

Online Publication Date: 21 September 2007

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Remarkable reductions in the velocity of magnetic-field (or electric current)-driven domain-wall (DW) motions in ferromagnetic nanostripes have typically been observed under magnetic fields stronger than the Walker threshold field [ N. L. Schryer and L. R. Walker, J. Appl. Phys. 45, 5406 (1974) ]. This velocity breakdown is known to be associated with an oscillatory dynamic transformation between transverse- and antivortex (or vortex)-type DWs during their propagations. The authors propose, as the result of numerical calculations, a simple means to suppress the velocity breakdown and rather enhance the DW velocities, using a magnetic underlayer of strong perpendicular magnetic anisotropy. This underlayer plays a crucial role in preventing the nucleation of antivortex (or vortex)-type DWs at the edges of nanostripes, in the process of periodic dynamic transformations from the transverse into antivortex- or vortex-type wall. The present study not only offers a promising means of the speedup of DW propagations to levels required for their technological application to ultrafast information-storage or logic devices, but also provides insight into its underlying mechanism.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Tt Fine-particle systems; nanocrystalline materials

Nonlinear transport below TC for lateral nanoconstrictions realized in a 100 nm GaMnAs epifilm

Sung Woon Cho, Hyung Kook Choi, Joon Sue Lee, Diana Jeong, Hyung Joon Kim, Taesoon Hwang, Kee Hoon Kim, and Yun Daniel Park

Appl. Phys. Lett. 91, 122514 (2007); http://dx.doi.org/10.1063/1.2789675 (3 pages) | Cited 1 time

Online Publication Date: 21 September 2007

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Electrical transport across lateral geometrical nanoconstrictions realized in 100 nm thick GaMnAs epifilms is studied. The constrictions are patterned with the aid of chemical etching techniques, as opposed to plasma-assisted methods. Transport behavior across the constrictions, where domain walls can be formed and pinned, changes from Ohmic to non-Ohmic below temperatures corresponding to epifilm TC for junctions with high resistances. Magnetoresistance measurements across such junctions qualitatively show similar behavior to unpatterned epifilms attributable to anisotropic magnetoresistance. The experimental IV curves are in good agreement with theoretical models accounting for spin flop across a region of high resistance.
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81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
81.65.Cf Surface cleaning, etching, patterning

Epitaxial growth and electrical spin injection from Fe(1−x)Gax (001) films on AlGaAs/GaAs (001) heterostructures

O. M. J. van ‘t Erve, C. H. Li, G. Kioseoglou, A. T. Hanbicki, M. Osofsky, S.-F. Cheng, and B. T. Jonker

Appl. Phys. Lett. 91, 122515 (2007); http://dx.doi.org/10.1063/1.2789702 (3 pages) | Cited 7 times

Online Publication Date: 21 September 2007

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The authors have grown epitaxial films of Fe(1−x)Gax (0<x<0.75), a material noted for its high magnetostriction, on AlGaAs/GaAs (001) heterostructures and summarize the structure, magnetization, spin polarization, and results for electrical spin injection into AlGaAs/GaAs. The out-of-plane saturation field and magnetization decrease rapidly with Ga content, but the spin polarization determined by point contact Andreev reflection remains near that of Fe for x ⩽ 0.5 Electrical spin injection from Fe0.5Ga0.5 produces an electron spin polarization >70% in GaAs at 20 K, similar to that obtained from Fe contacts but at out-of-plane saturation fields as low as 0.36 T rather than 2.2 T.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
68.55.A- Nucleation and growth
75.80.+q Magnetomechanical effects, magnetostriction
72.25.Hg Electrical injection of spin polarized carriers
72.25.Mk Spin transport through interfaces
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