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18 Aug 2008

Volume 93, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 93, 073101 (2008); http://dx.doi.org/10.1063/1.2970055 (3 pages)

A. J. Du, Y. Chen, G. Q. Lu, and Sean C. Smith
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Carbon nanotube Josephson junctions with Nb contacts

E. Pallecchi, M. Gaaß, D. A. Ryndyk, and Ch. Strunk

Appl. Phys. Lett. 93, 072501 (2008); http://dx.doi.org/10.1063/1.2971034 (3 pages) | Cited 11 times

Online Publication Date: 18 August 2008

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We report on the preparation of carbon nanotube Josephson junctions using superconducting electrodes made of niobium. Gate-controllable supercurrents with values of up to 30 nA are induced by the proximity effect. The IV curves are hysteretic at low temperature and the corresponding switching histograms have a width of 0.5%–2%. An on-chip resistive environment integrated in the sample layout is used to increase the switching current.
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74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Enhancement of optical and magneto-optical effects in three-dimensional opal/Fe3O4 magnetic photonic crystals

V. V. Pavlov, P. A. Usachev, R. V. Pisarev, D. A. Kurdyukov, S. F. Kaplan, A. V. Kimel, A. Kirilyuk, and Th. Rasing

Appl. Phys. Lett. 93, 072502 (2008); http://dx.doi.org/10.1063/1.2973150 (3 pages) | Cited 7 times

Online Publication Date: 18 August 2008

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Three-dimensional magnetic photonic crystals, based on an artificial opal matrix with embedded magnetite Fe3O4, were investigated in both transmission and reflection in the near-infrared and visible spectral range. A strong enhancement of the polar Kerr effect and a modification of the Faraday effect have been found near the photonic band gap at about 1.8 eV. Surprisingly the shapes of the loops of magnetic hysteresis measured by magnetic circular dichroism were found to depend on the wavelength of light. This observation has been explained using a model where two types of magnetite particles have different coercive fields.
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42.70.Qs Photonic bandgap materials
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Antiferromagnetic iridium manganese based intermediate layers for perpendicular magnetic recording media

Kumar Srinivasan, S. N. Piramanayagam, and Rachid Sbiaa

Appl. Phys. Lett. 93, 072503 (2008); http://dx.doi.org/10.1063/1.2970032 (3 pages) | Cited 5 times

Online Publication Date: 18 August 2008

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Current generation CoCrPt oxide based perpendicular magnetic recording media use two Ru-based intermediate layers in order to grow crystallographically textured, and magnetically isolated granular media. In this work, the advantage of replacing the Ru grain isolation layer with antiferromagnetic IrMn is demonstrated. Media samples using 7.5 nm thick IrMn intermediate layers show perpendicular texture with dispersion below 4°, coercivity of over 4000 Oe alongside magnetic exchange decoupling, average grain sizes of 6 nm with distributions under 14%, and thermal stability factor of 88. The IrMn layer may also help to stabilize the recording layer grains against thermal instability effects.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Exchange coupling assisted FePtC perpendicular recording media

J. F. Hu, J. S. Chen, Y. F. Ding, B. C. Lim, W. L. Phyoe, and B. Liu

Appl. Phys. Lett. 93, 072504 (2008); http://dx.doi.org/10.1063/1.2974794 (3 pages) | Cited 13 times

Online Publication Date: 19 August 2008

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Exchange coupling assisted perpendicular recording media consisting of a 10 nm magnetically hard FePtC layer with a FePtC soft overlayer of a different thickness were investigated. Both the coercivity and the saturation field of the FePtC film decreased after introducing a magnetically soft FePtC overlayer. The soft FePt grains were located on top of the underlying FePt grains and at the grain boundaries. Some of the hard and soft grains were separated by a C layer accumulated on the hard magnetic FePtC layer surface. The strength of the exchange coupling between soft and hard grains depended on the C layer thickness.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Steplike versus continuous domain propagation in Co/Pd multilayer films

C. M. Günther, F. Radu, A. Menzel, S. Eisebitt, W. F. Schlotter, R. Rick, J. Lüning, and O. Hellwig

Appl. Phys. Lett. 93, 072505 (2008); http://dx.doi.org/10.1063/1.2968305 (3 pages) | Cited 8 times

Online Publication Date: 19 August 2008

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We investigate the microscopic reversal behavior in perpendicular-anisotropy magnetic thin films using an integrated mask-sample design that allows probing a nanoscale sample region with soft x-rays. Local hysteresis loops and spectroholography images are obtained from the transmitted signal exploiting x-ray magnetic circular dichroism. Our data provide direct evidence of microscopic spin-flip avalanches, such as responsible for Barkhausen noise. In comparison with macroscopic magnetometry measurements we find evidence for the sputter pressure dependent introduction of local defects that prevent a continuous domain wall motion but are not strong enough to introduce the appearance of microscopic return point memory.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects

Tunable magnetic order of Co nanoparticles and magnetotransport in Co/ZnO nanocomposites

C. Y. Hsu, J. C. A. Huang, S. F. Chen, C. P. Liu, S. J. Sun, and Yonhua Tzeng

Appl. Phys. Lett. 93, 072506 (2008); http://dx.doi.org/10.1063/1.2959081 (3 pages) | Cited 3 times

Online Publication Date: 20 August 2008

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We demonstrate tunable magnetic order of cobalt nanoparticles in Co/ZnO nanocomposites. High-density electronic states in ZnO formed during high vacuum annealing help generate bound and free charge carriers, which in turn enable the stable magnetic ordering of Co nanoparticles in the Co/ZnO nanocomposites in a tunable manner. This is demonstrated by the following experimental observations: (i) enhanced spontaneous magnetization and coercivity, (ii) transition from semiconducting to metallic electrical-transport, and (iii) transverse magnetotransport transition from negative magnetoresistance to the anomalous Hall effect. The work explores a route to manipulate the magnetic order of magnetic nanoparticles by means of intentionally generated defects in oxides.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
73.43.Qt Magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.60.+g Mixed conductivity and conductivity transitions

Atomically smooth and single crystalline MnTiO3 thin films with a ferrotoroidic structure

H. Toyosaki, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 93, 072507 (2008); http://dx.doi.org/10.1063/1.2975373 (3 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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We report the epitaxial growth and magnetic properties of MnTiO3 thin films with an ilmenite structure. Although the lattice mismatch with sapphire substrates was as large as 8.0%, highly crystalline films with atomically flat surfaces were grown by using pulsed laser deposition. X-ray diffraction and transmission electron microscopy showed that the optimized film had almost a single crystalline structure with totally relaxed lattice parameters, inducing periodic misfit dislocations at the film/substrate interface. The magnetization curve showed an abrupt increase due to spin flopping when the magnetic field along the c-axis exceeded the critical magnetic field (μ0Hc ∼ 6 T). Due to the spin flopping, we concluded that MnTiO3 had a ferrotoroidic structure and, thus, was magnetoelectrically active.
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68.55.at Other materials
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.50.Dd Nonmetallic ferromagnetic materials
81.16.Mk Laser-assisted deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.80.+q Magnetomechanical effects, magnetostriction

Direct observation and control of the Walker breakdown process during a field driven domain wall motion

S. Glathe, R. Mattheis, and D. V. Berkov

Appl. Phys. Lett. 93, 072508 (2008); http://dx.doi.org/10.1063/1.2975181 (3 pages) | Cited 17 times

Online Publication Date: 22 August 2008

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We report the real-time study of a domain wall motion in giant magnetoresistance nanostrips. We have visualized the Walker breakdown process (WBP) [ N. L. Schryer and L. R. Walker, J. Appl. Phys. 45, 5406 (1974) ] in single shot experiments. The domain wall motion above the Walker breakdown is highly nonperiodic. Surprisingly, the time intervals of movement are equal or larger than those where the domain wall nearly stops. When an additional transversal magnetic field is applied, domain wall motion becomes more regular, enabling the study of the WBP in more detail. A sufficiently large transverse field can suppress the WBP completely.
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75.60.Ch Domain walls and domain structure
75.47.De Giant magnetoresistance

Coplanar waveguide radio frequency ferromagnetic parametric amplifier

Mingqiang Bao, Alexander Khitun, Yina Wu, Joo-Young Lee, Kang L. Wang, and Ajey P. Jacob

Appl. Phys. Lett. 93, 072509 (2008); http://dx.doi.org/10.1063/1.2975174 (2 pages) | Cited 11 times

Online Publication Date: 22 August 2008

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In this letter, we report a coplanar waveguide ferromagnetic parametric amplifier fabricated on a ferromagnetic Permalloy thin film. It shows a power gain of 4 dB at 1.15 GHz when the pump power is 11.1 dBm at the pump frequency of 2.30 GHz under the bias field of 13 Oe. This prototype ferromagnetic device can be integrated with the complementary metal-oxide semiconductor process technology and has potential applications as a spin-wave amplifier, a low noise amplifier, or an active bandpass filter.
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84.40.Az Waveguides, transmission lines, striplines
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Tunable transport in magnetically coupled MoGe/Permalloy hybrids

A. Belkin, V. Novosad, M. Iavarone, J. Fedor, J. E. Pearson, A. Petrean-Troncalli, and G. Karapetrov

Appl. Phys. Lett. 93, 072510 (2008); http://dx.doi.org/10.1063/1.2966156 (3 pages) | Cited 16 times

Online Publication Date: 22 August 2008

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We demonstrate controlled magnetotransport anisotropy of magnetically coupled superconductor-ferromagnet MoGe/Permalloy hybrids. The rotatable anisotropy Permalloy ferromagnet with stripe domain structure induces in-plane anisotropy in superconducting order parameter. We show that near the superconductor-normal state phase boundary the superconductivity in MoGe is localized in narrow mesoscopic channels just above the magnetic domain walls. Changing the in-plane direction of magnetic stripe domains it is possible to reconfigure the direction of the superconducting channels and controllably rotate the direction of the in-plane anisotropy axis in the superconductor.
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74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.47.-m Magnetotransport phenomena; materials for magnetotransport
74.78.Na Mesoscopic and nanoscale systems
75.60.Ch Domain walls and domain structure
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