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4 Oct 2004

Volume 85, Issue 14, pp. 2679-2983

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 2860 (2004); http://dx.doi.org/10.1063/1.1799245 (3 pages)

Priya Mahadevan and Alex Zunger
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MgB2 films with very high critical current densities due to strong grain boundary pinning

H. Kitaguchi, A. Matsumoto, H. Kumakura, T. Doi, H. Yamamoto, K. Saitoh, H. Sosiati, and S. Hata

Appl. Phys. Lett. 85, 2842 (2004); http://dx.doi.org/10.1063/1.1805195 (3 pages) | Cited 83 times

Online Publication Date: 14 October 2004

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MgB2 superconductor has a great potential for applications because of its high Tc and Bc2, exceeding those of any Nb-base superconductors at any temperature. It is now important to understand its flux pinning so as to raise Jc to high values over a wide field range. We show that nanometer-sized columnar-grain structure can produce Jc exceeding 5×106 A∕cm2. The angular dependence of Jc indicates that the strongest pinning occurs when the field is aligned parallel to the grain boundaries. Our results confirm earlier deductions that grain boundaries in MgB2 act as effective pinning centers like those in Nb3Sn.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Yb Other effects
61.72.Mm Grain and twin boundaries

Temperature-dependent magnetic interface location in interdiffused exchange biased bilayers

M. S. Lund, M. R. Fitzsimmons, S. Park, and C. Leighton

Appl. Phys. Lett. 85, 2845 (2004); http://dx.doi.org/10.1063/1.1799250 (3 pages) | Cited 7 times

Online Publication Date: 14 October 2004

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Antiferromagnetic (AF) binary alloys are attractive choices for exchange pinning of ferromagnets (F) in applications. Unfortunately, inducing AF ordering in these alloys often requires annealing which leads to interdiffusion at the AF∕F interface and a subsequent, and poorly understood, reduction in exchange bias. We report a study of the effects of interdiffusion in epitaxial NiMn∕Ni bilayers. Using polarized neutron reflectometry, we deduce that the competition between AF and F interactions in the interdiffused region leads to a temperature-dependent magnetic interface location, “glassy” behavior, memory effects, and low-temperature training. The results have important implications for the understanding of the temperature dependence of the exchange bias in these materials.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
66.30.Ny Chemical interdiffusion; diffusion barriers
75.30.Et Exchange and superexchange interactions
81.40.Gh Other heat and thermomechanical treatments

Domain wall diodes in ferromagnetic planar nanowires

D. A. Allwood, Gang Xiong, and R. P. Cowburn

Appl. Phys. Lett. 85, 2848 (2004); http://dx.doi.org/10.1063/1.1802388 (3 pages) | Cited 53 times

Online Publication Date: 14 October 2004

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We demonstrate a lithographically defined magnetic structure through which domain walls from planar magnetic nanowires propagate in one direction only, under an appropriate magnetic field. This domain wall diode is of the form of an isosceles triangle, with one nanowire emanating from its apex and one from its base. A domain wall arriving at the triangle apex, under an applied magnetic field, is able to overcome minor pinning through the diode and continue through the opposite nanowire. However, a domain wall arriving at the triangle base is unable to overcome the significant pinning energy presented by the sudden change in track width. Domain wall diodes are of potential use in controlling domain wall propagation for fundamental investigations and technological applications.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.60.Ch Domain walls and domain structure
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
61.46.-w Structure of nanoscale materials
78.20.Ls Magneto-optical effects

Superconductivity in diamond thin films well above liquid helium temperature

Yoshihiko Takano, Masanori Nagao, Isao Sakaguchi, Minoru Tachiki, Takeshi Hatano, Kensaku Kobayashi, Hitoshi Umezawa, and Hiroshi Kawarada

Appl. Phys. Lett. 85, 2851 (2004); http://dx.doi.org/10.1063/1.1802389 (3 pages) | Cited 119 times

Online Publication Date: 14 October 2004

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We report unambiguous evidence for superconductivity in a heavily boron-doped diamond thin film grown by microwave plasma-assisted chemical vapor deposition (MPCVD). An advantage of the MPCVD-deposited diamond is that it can contain boron at high concentration, especially in (111)-oriented films. Superconducting transition temperatures are determined by transport measurements to be 7.4 K for TC onset and 4.2 K for zero resistance. The upper critical field is estimated to be 7 T. Magnetization as a function of magnetic fields shows typical type-II superconducting properties.
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81.05.Cy Elemental semiconductors
74.78.-w Superconducting films and low-dimensional structures
73.61.Cw Elemental semiconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.10.+v Occurrence, potential candidates
74.25.F- Transport properties

Coevaporation of CoPt nanoparticles

L. Castaldi, K. Giannakopoulos, A. Travlos, and D. Niarchos

Appl. Phys. Lett. 85, 2854 (2004); http://dx.doi.org/10.1063/1.1802378 (3 pages) | Cited 13 times

Online Publication Date: 14 October 2004

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Co50Pt50 nanoparticles were codeposited on thermally oxidized Si substrates by electron beam evaporation, at a temperature of the substrate of 700 to 750 °C. The codeposition led to a perfect mixture of the Co and Pt elements within the three-dimensional nanoislands, which exhibit a mean diameter between ∼18 and ∼20 nm. The postannealing treatment of the CoPt nanograins resulted in the progressive crystallization of the L10 ordered phase and, consequently, in the progressive magnetic hardening of the samples with a maximum coercivity of ∼5.6 kOe.
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81.07.Bc Nanocrystalline materials
81.07.Wx Nanopowders
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
64.70.Nd Structural transitions in nanoscale materials
75.70.Ak Magnetic properties of monolayers and thin films
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Gh Other heat and thermomechanical treatments
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Spin dynamics of the antiferromagnetic-to-ferromagnetic phase transition in FeRh on a sub-picosecond time scale

Jan-Ulrich Thiele, Matthias Buess, and Christian H. Back

Appl. Phys. Lett. 85, 2857 (2004); http://dx.doi.org/10.1063/1.1799244 (3 pages) | Cited 25 times

Online Publication Date: 14 October 2004

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The antiferromagnetic-to-ferromagnetic phase transition in FeRh films induced by heating with a femtosecond laser pulse was investigated using the time-resolved magneto-optical Kerr effect. An initial rise time of the magneto-optical signal of about 500 fs is found as the FeRh is heated through the transition. The data offer a complementary view to previous pump–probe experiments on “simple” ferromagnetic materials and allow a glimpse at the complex interplay between lattice, electron and spin dynamics governing the first-order antiferromagnetic-to-ferromagnetic phase transition of FeRh.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Trends in ferromagnetism, hole localization, and acceptor level depth for Mn substitution in GaN, GaP, GaAs, and GaSb

Priya Mahadevan and Alex Zunger

Appl. Phys. Lett. 85, 2860 (2004); http://dx.doi.org/10.1063/1.1799245 (3 pages) | Cited 36 times

Online Publication Date: 14 October 2004

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We examine the intrinsic mechanism of ferromagnetism in dilute magnetic semiconductors by analyzing the trends in the electronic structure as the host is changed from GaN to GaSb, keeping the transition metal impurity fixed. In contrast with earlier interpretations which depended on the host semiconductor, it is found that a single mechanism is sufficient to explain the ferromagnetic stabilization energy for the entire series.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
71.55.Eq III-V semiconductors
75.30.Hx Magnetic impurity interactions
73.20.At Surface states, band structure, electron density of states

Planar thin film YBa2Cu3O7−δ Josephson junction pairs and arrays via nanolithography and ion damage

Ke Chen, Shane A. Cybart, and R. C. Dynes

Appl. Phys. Lett. 85, 2863 (2004); http://dx.doi.org/10.1063/1.1803620 (3 pages) | Cited 12 times

Online Publication Date: 14 October 2004

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We have fabricated in-plane high-Tc Josephson junction pairs and series arrays using our established nanolithography and ion damage process. Junctions in a pair showed nearly identical electrical properties. The ten-junction array exhibited current–voltage characteristics that can be described by the resistively shunted junction model at 78 K. Flat giant Shapiro steps were observed in both cases. We believe that the ion-damaged high-Tc superconducting Josephson junction is a good candidate to form large numbers of junctions in series arrays that can function above 77 K for quantum voltage standards and other applications.
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74.81.Fa Josephson junction arrays and wire networks
74.72.-h Cuprate superconductors
74.25.F- Transport properties
68.55.A- Nucleation and growth
74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
81.65.Cf Surface cleaning, etching, patterning

Radiation of spin waves by a single micrometer-sized magnetic element

Vladislav E. Demidov, Sergej O. Demokritov, Burkard Hillebrands, Markus Laufenberg, and Paulo P. Freitas

Appl. Phys. Lett. 85, 2866 (2004); http://dx.doi.org/10.1063/1.1803621 (3 pages) | Cited 43 times

Online Publication Date: 14 October 2004

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Dynamic magnetic properties of a single micrometer-sized magnetic element consisting of a permalloy and a partially patterned CoFe layer separated by an intervening Cu spacer layer have been studied by means of a micro-focus Brillouin light scattering setup, which allows for local measurements of the magnetization dynamics on the submicrometer scale. It is shown that quantized spin-wave modes excited in the magnetic element act as radiation sources for spin waves in the surrounding magnetic film. It is found that the intensities of spin waves excited by different quantized modes follow different distance laws when traveling away from the region of excitation.
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75.50.Bb Fe and its alloys
68.65.Ac Multilayers
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Extremely surface-sensitive hysteresis loop measurement with a spin-polarized metastable helium atom beam

M. Kurahashi, T. Suzuki, and Y. Yamauchi

Appl. Phys. Lett. 85, 2869 (2004); http://dx.doi.org/10.1063/1.1800279 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2004

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The sample current induced by the deexcitation of He* atoms on a ferromagnetic surface was found to depend on the He* spin direction. This spin dependence was used for measuring the hysteresis loop of an Fe film on Cu(100). The hysteresis loop is extremely surface specific because the spin dependence is due to the electron emission via the He* deexcitation that occurs on the vacuum side of the topmost surface layer. The hysteresis loop for a 2.2 ML Fe film on Cu(100) has been found to agree well with that measured with the surface magneto-optic Kerr effect.
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67.25.bh Films and restricted geometries
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Rf Surface magnetism
61.80.Fe Electron and positron radiation effects
61.82.Bg Metals and alloys

Anisotropy and magnetotransport in ordered magnetic antidot arrays

F. J. Castaño, K. Nielsch, C. A. Ross, J. W. A. Robinson, and R. Krishnan

Appl. Phys. Lett. 85, 2872 (2004); http://dx.doi.org/10.1063/1.1800281 (3 pages) | Cited 30 times

Online Publication Date: 14 October 2004

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Magnetic films containing ordered arrays of holes (“antidots”) with period ∼200 nm have been prepared using porous anodic alumina substrates with square and hexagonal symmetries. Large area (∼cm2) single-layer CoFe ordered antidot arrays show well-defined in-plane magnetic anisotropy related to the symmetry of the arrays, and the anisotropic magnetoresistance is smaller than that of a continuous film. For NiFe∕Cu∕CoFe antidot arrays, the giant magnetoresistance ratio of the patterned films is of similar magnitude to that of the unpatterned film, and shares the symmetry of the substrate. This behavior is attributed to the geometry of the antidots, which confine the magnetization of each layer parallel to the current flow.
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75.50.Bb Fe and its alloys
68.65.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Antiferromagnetic coupling in ferromagnetic oxide trilayer films composed of Sr0.7Ca0.3RuO3 and La0.6Sr0.4MnO3

Y. Uozu, T. Nakajima, M. Nakamura, Y. Ogimoto, M. Izumi, and K. Miyano

Appl. Phys. Lett. 85, 2875 (2004); http://dx.doi.org/10.1063/1.1800284 (3 pages) | Cited 4 times

Online Publication Date: 14 October 2004

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Magnetic and transport properties of trilayer films composed of ferromagnetic metals Sr0.7Ca0.3RuO3 (SCRO) and La0.6Sr0.4MnO3 (LSMO) on SrTiO3 (001) substrate were studied. Decrease in magnetization below Curie temperature of SCRO indicates antiferromagnetic coupling between SCRO and LSMO layers resulting from superexchange interaction. Resistivity is found to be lower in antiparallel magnetic configuration, which is due to negative spin polarization of SCRO.
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75.50.Dd Nonmetallic ferromagnetic materials
68.65.Ac Multilayers
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Vv High coercivity materials
68.55.-a Thin film structure and morphology
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Lx Magnetic oxides
75.47.Pq Other materials
75.50.Ee Antiferromagnetics

Domain structure of sintered SmCo5 magnets studied by magnetic force microscopy

Witold Szmaja, Jarosław Grobelny, and Michał Cichomski

Appl. Phys. Lett. 85, 2878 (2004); http://dx.doi.org/10.1063/1.1801165 (3 pages) | Cited 10 times

Online Publication Date: 14 October 2004

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The domain structure of sintered SmCo5 permanent magnets at the surface perpendicular to the alignment axis was investigated by magnetic force microscopy (MFM). The main domains forming a maze pattern of typically 3–5 μm in width and surface reverse spikes of typically 1–2 μm in size are observed. This coarse domain structure is similar to those present in sufficiently thick uniaxial crystals with strong magnetocrystalline anisotropy, reported in earlier investigations performed by Bitter pattern method or magneto-optic Kerr microscopy. In addition to the coarse domain structure, a complicated system of the fine surface domains of 10–200 nm in width is observed. The thickness of the zone below the surface filled with these fine scale domains is estimated to be 100 nm and their presence is related to the reduction of the magnetostatic energy close to the specimen surface. Practically no correlation between the magnetic domain structure and the surface topography, the latter revealed by atomic force microscopy, was observed. The high spatial resolution and high surface sensitivity of the MFM technique are demonstrated.
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75.60.Ch Domain walls and domain structure
75.50.Ww Permanent magnets
75.70.Rf Surface magnetism
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
68.37.Ps Atomic force microscopy (AFM)

Unusual diamagnetic response in PrAlNiCuFe metallic glass

Y. T. Wang, M. X. Pan, D. Q. Zhao, W. H. Wang, and W. L. Wang

Appl. Phys. Lett. 85, 2881 (2004); http://dx.doi.org/10.1063/1.1801174 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2004

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An unusual diamagnetic response is observed in a Pr60Al10Ni10Cu16Fe4 bulk metallic glass (BMG) during the zero-field-cooled (ZFC) magnetization measurement. The ZFC magnetization of the BMG is found to reverse its direction at low temperature and becomes diamagnetic, whereas the field-cooled branch remains positive. This apparent diamagnetism is ascribed to the specific couple between the ferromagnetic nanoparticles and the amorphous matrix in low fields. Besides, in superconductors, a giant diamagnetic response is unusual in magnetic materials. Therefore, it may simulate scientific and technological interest.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.20.En Metals and alloys
75.60.Jk Magnetization reversal mechanisms
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Nanocrystallization of FeCoZrB alloys studied by 59Co nuclear magnetic resonance

E. Jędryka, M. Wójcik, P. Švec, and I. Škorvánek

Appl. Phys. Lett. 85, 2884 (2004); http://dx.doi.org/10.1063/1.1797553 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2004

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59Co nuclear magnetic resonance spectroscopy was used to monitor structural modifications of Fe44.5Co44.5Zr7B4 amorphous ribbon induced by heat treatment at 510 and 560 °C. A precipitation of highly ordered (B2 phase) nanocrystalline Co45Fe55 particles has been evidenced upon annealing. Within the amorphous matrix a preferential clustering of Co78Zr22-like local environments occurs, leading to the compositionally modulated structure.
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81.07.Bc Nanocrystalline materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
61.46.-w Structure of nanoscale materials
81.30.Mh Solid-phase precipitation
76.60.Lz Spin echoes
81.40.Gh Other heat and thermomechanical treatments

An approach for electrical self-stabilization of high-temperature superconducting wires for power applications

T. Aytug, M. Paranthaman, H. Y. Zhai, A. A. Gapud, K. J. Leonard, P. M. Martin, A. Goyal, J. R. Thompson, and D. K. Christen

Appl. Phys. Lett. 85, 2887 (2004); http://dx.doi.org/10.1063/1.1794848 (3 pages) | Cited 11 times

Online Publication Date: 14 October 2004

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Electrical and thermal stability of high-temperature superconducting (HTS) wires∕tapes are essential in applications involving efficient production, distribution, and storage of electrical energy. We have developed a conductive buffer layer structure composed of bilayer La0.7Sr0.3MnO3∕Ir on a textured Ni–W alloy metal tape to functionally shunt the HTS layer to the underlying substrate. The key feature is the Ir layer, which serves as a barrier to both inward diffusion of oxygen and outward diffusion of metal substrate cations during fabrication. Electrical and microstructural property characterizations of YBa2Cu3O7-δ films on short prototype conductors demonstrate self-field critical current density values, Jc, exceeding 2×106 A∕cm2 at 77 K and excellent electrical coupling to the underlying metal substrate, with no unwanted insulating oxide interfaces. Implementing this approach in power technologies would significantly increase the engineering current density of the conductor and reduce overall process costs.
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84.71.Mn Superconducting wires, fibers, and tapes
74.78.-w Superconducting films and low-dimensional structures
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Sv Critical currents
74.25.F- Transport properties
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
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