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28 Jul 2008

Volume 93, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 93, 043101 (2008); http://dx.doi.org/10.1063/1.2963352 (3 pages)

Xin Fu, Jun Jiang, Wenzheng Zhang, and Jun Yuan
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Controlled rotation of the exchange-bias direction in IrMn/Cu/Co via ion irradiation

D. Schafer, J. Geshev, S. Nicolodi, L. G. Pereira, J. E. Schmidt, and P. L. Grande

Appl. Phys. Lett. 93, 042501 (2008); http://dx.doi.org/10.1063/1.2961032 (3 pages) | Cited 9 times

Online Publication Date: 28 July 2008

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Co/Cu/IrMn films were irradiated with 40 keV  He+ ions varying the fluence and the current, with magnetic field applied at 120° with respect to the original exchange-bias direction. The angular variations of the exchange-bias field of the irradiated samples were compared with those of the as-made and the thermally annealed films. Gradual deviation of the exchange-bias direction with the fluence increase was observed. Complete reorientation of the easy axes of both ferromagnet and antiferromagnet toward that of the field applied during irradiation was achieved for fluences higher than 1×1015 ions/cm2, accompanied with a significant enhancement of the exchange-bias field.
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75.30.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.80.Jh Ion radiation effects
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ferromagnetism in CuO–ZnO multilayers

C. Sudakar, K. Padmanabhan, R. Naik, G. Lawes, B. J. Kirby, Sanjiv Kumar, and V. M. Naik

Appl. Phys. Lett. 93, 042502 (2008); http://dx.doi.org/10.1063/1.2959186 (3 pages) | Cited 8 times

Online Publication Date: 28 July 2008

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We investigated the magnetic properties of CuO–ZnO heterostructures to elucidate the origin of the ferromagnetic signature in Cu doped ZnO. The CuO and ZnO layer thickness were varied from 15 to 150 nm and from 70 to 350 nm, respectively. Rutherford backscattering experiments showed no significant diffusion of either Cu in ZnO or Zn in CuO layers. Magnetic measurements indicate ferromagnetism at 300 K, which depends on the CuO particle size, but not on the CuO–ZnO interfacial area. Polarized neutron reflectometry measurements show that the observed magnetization cannot be accounted for solely by spins localized near the CuO–ZnO interface or in the CuO layer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Voltage from mechanical stress in type-II superconductors: Depinning of the magnetic flux by moving dislocations

Jaroslav Albert and E. M. Chudnovsky

Appl. Phys. Lett. 93, 042503 (2008); http://dx.doi.org/10.1063/1.2960337 (3 pages)

Online Publication Date: 28 July 2008

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Mechanical stress causes motion of defects in solids. We show that in a type-II superconductor, a moving dislocation generates a pattern of current that exerts a depinning force on the surrounding vortex lattice. The concentration of dislocations and the mechanical stress needed to produce critical depinning currents are shown to be within practical range. When external magnetic field and transport current are present, this effect generates voltage across the superconductor. Thus a superconductor can serve as an electrical sensor of the mechanical stress.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation

An optimal tunable Josephson element for quantum computing

F. Chiarello, M. G. Castellano, G. Torrioli, S. Poletto, C. Cosmelli, P. Carelli, D. V. Balashov, M. I. Khabipov, and A. B. Zorin

Appl. Phys. Lett. 93, 042504 (2008); http://dx.doi.org/10.1063/1.2960338 (3 pages) | Cited 2 times

Online Publication Date: 28 July 2008

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We introduce a three-junction superconducting quantum interference device (SQUID) that can be used as an optimal tunable element in Josephson quantum computing applications. This device can replace the simple dc SQUID generally used as a tunable element in this kind of applications, with a series of advantages concerning the coherence time and the tolerance to small errors. We study the device both theoretically and experimentally at 4.2 K, obtaining a good agreement between the results.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Field driven ferromagnetic phase nucleation and propagation in antiferromagnetically coupled multilayer films with perpendicular anisotropy

T. Hauet, C. M. Günther, O. Hovorka, A. Berger, M.-Y. Im, P. Fischer, T. Eimüller, and O. Hellwig

Appl. Phys. Lett. 93, 042505 (2008); http://dx.doi.org/10.1063/1.2961001 (3 pages) | Cited 4 times

Online Publication Date: 28 July 2008

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We investigate the reversal process in {[Co/Pt]X−1Co/Ru}×16/[Co/Pt]X multilayer films by magnetometry and magnetic transmission x-ray microscopy. After demagnetization, a stable one-dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick sample (X = 7) is imaged, while metastable sharp antiferromagnetic domain walls are observed in the remanent state for a thinner stack sample (X = 6). When applying an external magnetic field the sharp domain walls of the thinner sample gradually transform into the FM phase via separate nucleation of many isolated FM domains all along the domain boundary. We present energy calculations that reveal the underlying energetics driving the overall reversal mechanism.
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75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms

Wide-range characterization of current conduction in high-Tc coated conductors

J. R. Thompson, Ö. Polat, D. K. Christen, D. Kumar, P. M. Martin, and J. W. Sinclair

Appl. Phys. Lett. 93, 042506 (2008); http://dx.doi.org/10.1063/1.2964195 (3 pages) | Cited 4 times

Online Publication Date: 28 July 2008

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The conduction of supercurrents in a short-segment state-of-the-art coated conductor prototype has been studied over ∼ 8 decades of dissipation. A combination of conventional transport methods, magnetometry in a swept magnetic field, and “flux creep” measurements was used to obtain current density J versus electric field E characteristics over a span E ∼ 10−5–10−13 V/cm. The inductive measurements allow facile exploration of current conduction over a wide range of temperatures, magnetic fields, and dissipation levels where future applications are envisioned.
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74.25.F- Transport properties
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors

The structure and local surrounding of Fe in Co2−xFe1+xSi

Verena Jung, Benjamin Balke, Gerhard H. Fecher, and Claudia Felser

Appl. Phys. Lett. 93, 042507 (2008); http://dx.doi.org/10.1063/1.2965463 (3 pages) | Cited 1 time

Online Publication Date: 28 July 2008

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This work reports on the magnetostructural properties of Co2−xFe1+xSi with 0<x<1. The Heusler compound Co2FeSi is a half-metallic ferromagnet with high Curie temperature and was suggested as candidate for a high tunneling magnetoresistance. Changing the Fe content allows to tune its magnetic properties. It is demonstrated that the solid solution series Co2−xFe1+xSi is perfectly ordered. 57Fe Mössbauer spectroscopy was used to determine the local hyperfine magnetic fields of the Fe atoms. Two different hyperfine magnetic fields are detected in samples with x>0. Changes in the relative intensities indicate the well ordered substitution of Co by Fe atoms.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.50.Bb Fe and its alloys

Do thermal fluctuations influence the recoil loops of nanocomposite magnets?

Chuan-bing Rong, Yuzi Liu, and J. Ping Liu

Appl. Phys. Lett. 93, 042508 (2008); http://dx.doi.org/10.1063/1.2956392 (3 pages) | Cited 9 times

Online Publication Date: 29 July 2008

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An exchange-coupled FePt/Fe3Pt nanocomposite system with well defined hard/soft two-phase morphology was prepared by reducing chemically synthesized FePt/Fe3O4 bimagnetic nanoparticles. It was interesting to observe that the recoil loop openness is strongly dependent on the sweep rate of applied fields. A quantitative analysis shows a linear relation between the openness of recoil loops and the reciprocal activation volume, indicating that the recoil loops are intimately related to thermal fluctuation. The large open area of the recoil loops for nanocomposite magnets compared to that of single phase magnets is attributed to the unstable magnetic moments in the soft phase.
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75.30.Et Exchange and superexchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Mössbauer study on martensite phase in Ni50Mn36.557Fe0.5Sn13 metamagnetic shape memory alloy

R. Y. Umetsu, R. Kainuma, Y. Amako, Y. Taniguchi, T. Kanomata, K. Fukushima, A. Fujita, K. Oikawa, and K. Ishida

Appl. Phys. Lett. 93, 042509 (2008); http://dx.doi.org/10.1063/1.2960551 (3 pages) | Cited 28 times

Online Publication Date: 29 July 2008

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Magnetic and differential scanning calorimetric measurements and Mössbauer examination were carried out to clarify the magnetic features of Ni50Mn36.557Fe0.5Sn13. The magnetic field cooling effects were observed in the thermomagnetization curves below 235 K and the Curie temperature of the parent phase was near the martensitic transformation temperature. The Mössbauer spectra taken from the parent+martensite two-phase state at 312 K and from the martensite single-phase state at 264 K were both singlets, showing a typical paramagnetic feature. On the other hand, the Mössbauer spectra taken from the martensite phase at 199 and 80 K were complicated, including some magnetic components.
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76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
75.50.Bb Fe and its alloys

Flux-driven Josephson parametric amplifier

T. Yamamoto, K. Inomata, M. Watanabe, K. Matsuba, T. Miyazaki, W. D. Oliver, Y. Nakamura, and J. S. Tsai

Appl. Phys. Lett. 93, 042510 (2008); http://dx.doi.org/10.1063/1.2964182 (3 pages) | Cited 22 times

Online Publication Date: 31 July 2008

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We have developed a Josephson parametric amplifier comprising a superconducting coplanar-waveguide resonator terminated by a dc superconducting quantum interference device (SQUID). An external field (the pump, ∼ 20 GHz) modulates the flux threading of the dc SQUID and, therefore, the resonant frequency of the cavity field (the signal, ∼ 10 GHz), which leads to the parametric signal amplification. We operated the amplifier at different band centers and observed amplification (17 dB at maximum) and deamplification depending on the relative phase between the pump and the signal. The noise temperature is estimated to be less than 0.87 K.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.40.Az Waveguides, transmission lines, striplines

Distinct spins of substituent Co in polycrystalline Co- and Cu-codoped ZnO magnetic semiconductors

Y. B. Zhang and S. Li

Appl. Phys. Lett. 93, 042511 (2008); http://dx.doi.org/10.1063/1.2966143 (3 pages) | Cited 15 times

Online Publication Date: 31 July 2008

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Polycrystalline Zn0.938Co0.062O and Zn0.928Co0.062Cu0.01O oxides have been synthesized by solid state reaction. A single-phase wurtzite structure was formed in the polycrystalline samples with substituent Co and Cu in oxidation states of +2 and +1, respectively. The magnetization can be fitted with a paramagnetic Curie term, an antiferromagnetic Curie–Weiss term, and a diamagnetic constant. The results show that the substitution of Co at the Zn site does not occur randomly but Co ions appear to have a tendency to group, while the substitution of Cu at the Zn can reduce Co’s grouping tendency, resulting in more isolated free Co ions.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Pp Magnetic semiconductors
75.20.Ck Nonmetals
61.72.uj III-V and II-VI semiconductors

Magnetic properties of the insulating ferromagnetic phase in strained Pr0.6Ca0.4MnO3 thin films

T. Mertelj, R. Yusupov, M. Filippi, W. Prellier, and D. Mihailovic

Appl. Phys. Lett. 93, 042512 (2008); http://dx.doi.org/10.1063/1.2966364 (3 pages) | Cited 8 times

Online Publication Date: 31 July 2008

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Bulk magnetization in Pr0.6Ca0.4MnO3 thin films with tensile (SrTiO3) and compressive (LaAlO3) substrate-induced strain is compared to the magneto-optical Kerr effect (MOKE) measurements. In the absence of an external magnetic field, in both films, a stable ferromagnetic insulating majority phase coexists with an antiferromagnetic insulating phase below ∼ 120 K. The MOKE measurements indicate that at 5 K a metastable ferromagnetic metallic (FM) phase is formed at the surface of the stretched film in a magnetic field below 1.1 T already; while in the bulk the FM phase starts to form in the field above ∼ 4 T in both films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.66.Nk Insulators

Analytical model of spin-polarized semiconductor lasers

Christian Gøthgen, Rafał Oszwałdowski, Athos Petrou, and Igor Žutić

Appl. Phys. Lett. 93, 042513 (2008); http://dx.doi.org/10.1063/1.2967739 (3 pages) | Cited 14 times

Online Publication Date: 31 July 2008

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We formulate an analytical model for semiconductor lasers with injection (pump) of spin-polarized electrons, allowing us to systematically investigate different operating regimes. We demonstrate that the maximum threshold reduction by electrically pumped spin-polarized carriers is larger than previously thought possible and, surprisingly, can be enhanced by ultrafast spin relaxation of holes. We reveal how different modes of carrier recombination directly affect the threshold reduction. Neither spin-up nor spin-down electron populations are separately clamped (pinned) near the threshold, where such lasers can act as effective nonlinear filters of circularly polarized light, owing to their spin-dependent gain.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Inducing ferromagnetism in ZnO through doping of nonmagnetic elements

Y. W. Ma, J. B. Yi, J. Ding, L. H. Van, H. T. Zhang, and C. M. Ng

Appl. Phys. Lett. 93, 042514 (2008); http://dx.doi.org/10.1063/1.2966360 (3 pages) | Cited 10 times

Online Publication Date: 1 August 2008

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In this work, Zn, Al, Pt, Ag, and Au nonmagnetic metallic films were deposited on the surface of ZnO film, followed by high vacuum annealing at different temperatures. Results showed that (Zn,Al,Pt)/ZnO films possessed room temperature ferromagnetism (RTF) after the vacuum annealing, while (Ag,Au)/ZnO films did not. Our detailed structural investigations (transmission electron microscopy and x-ray photoelectron spectroscopy) revealed that this RTF was associated with the presence of metal clusters. The RTF disappeared in Al/ZnO after a subsequent annealing in air, as metal clusters were oxidized. Pt/ZnO remained ferromagnetic, as the metal cluster structure was stable subjected to the air annealing.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Evidence for Griffiths phase in La0.4Ca0.6MnO3 film with strip-domain inclusions

Y. H. Hyun, J. S. Park, T. W. Eom, G. H. Kim, Y. S. Lee, Y. P. Lee, V. G. Prokhorov, and V. L. Svetchnikov

Appl. Phys. Lett. 93, 042515 (2008); http://dx.doi.org/10.1063/1.2967189 (3 pages) | Cited 5 times

Online Publication Date: 1 August 2008

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The microstructure and the magnetic properties of La0.4Ca0.6MnO3 film, prepared by rf magnetron sputtering on a LaAlO3 substrate, have been investigated. The electron microscopy study reveals the presence of strip-domain phase with a periodic spacing of about 3c for the orthorhombic symmetry. The magnetic measurements show that in addition to the expected antiferromagnetic transition at TN ≃ 120 K with decreasing temperature, the film manifests the Griffiths phase behavior in a wide temperature range.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
68.55.-a Thin film structure and morphology

Manipulation of paramagnetic particles using a nanoscale asymmetric magnetic potential

L. E. Helseth, T. H. Johansen, and T. M. Fischer

Appl. Phys. Lett. 93, 042516 (2008); http://dx.doi.org/10.1063/1.2967729 (3 pages)

Online Publication Date: 1 August 2008

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We report how one-dimensional nanomagnets can be used to manipulate paramagnetic particles located in liquid systems. It is shown that by using an asymmetric magnetic potential well, single particles can be efficiently sorted out from a one-dimensional array and moved along the phase boundary confining the array.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
81.16.Dn Self-assembly
82.70.Dd Colloids
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