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25 Apr 2011

Volume 98, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 98, 171102 (2011); http://dx.doi.org/10.1063/1.3582035 (3 pages)

Shigeru Nakayama, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa
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Room-temperature spin-dependent tunneling through molecules

S. Wang, F. J. Yue, J. Shi, Y. J. Shi, A. Hu, Y. W. Du, and D. Wu

Appl. Phys. Lett. 98, 172501 (2011); http://dx.doi.org/10.1063/1.3583585 (3 pages) | Cited 3 times

Online Publication Date: 25 April 2011

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We have fabricated assemblies of molecular junctions comprised of superparamagnetic Fe3O4 nanoparticles self-assembled with alkane molecules of different lengths as the spacer. The electrical resistance increases exponentially over nearly two decades as the molecular length varies from 0.7 to 2.5 nm, indicating that electrons tunnel through the molecules that are chemically bonded with Fe3O4 nanoparticles. Up to ∼ 21% room-temperature magnetoresistance is observed. Remarkably, the tunneling magnetoresistance ratio stays nearly independent of molecular length, which entails room-temperature spin-conserving transport in organic molecules.
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85.75.Mm Spin polarized resonant tunnel junctions
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.Lx Magnetic oxides
72.25.-b Spin polarized transport

[Co/Pd]–NiFe exchange springs with tunable magnetization tilt angle

T. N. Anh Nguyen, Y. Fang, V. Fallahi, N. Benatmane, S. M. Mohseni, R. K. Dumas, and Johan Åkerman

Appl. Phys. Lett. 98, 172502 (2011); http://dx.doi.org/10.1063/1.3580612 (3 pages) | Cited 7 times

Online Publication Date: 26 April 2011

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We investigate exchange coupled [Co/Pd]5–NiFe thin films. Due to competition between the in-plane shape anisotropy of the NiFe and strong perpendicular magnetic anisotropy of the [Co/Pd]5 multilayer, unique magnetic configurations are achievable. In particular, we explore the out-of-plane magnetization tilt angle of the NiFe layer. Experimental results, based on conventional magnetometry, ferromagnetic resonance, and magnetic force microscopy, agree well with one-dimensional micromagnetic simulations. We find that the tilt angle is highly tunable (0°–60°) over a small range of NiFe thicknesses (4.8–8 nm). Potential applications for high power, zero-field operation spin torque oscillators are discussed.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Bb Fe and its alloys

Ferrimagnetic stripe domain formation in antiferromagnetically-coupled Co/Pt–Co/Ni–Co/Pt multilayers studied via soft x-ray techniques

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

Appl. Phys. Lett. 98, 172503 (2011); http://dx.doi.org/10.1063/1.3583454 (3 pages)

Online Publication Date: 27 April 2011

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We investigate the macroscopic and microscopic magnetic reversal in perpendicular anisotropy antiferromagnetically (AF) coupled [Co/Pt]N−1/Co–Ru–[Co/Ni]M−1/Co–Ru–[Co/Pt]N−1/Co multilayers (ML) using soft x-ray spectroholography and local, as well as area-integrated, soft x-ray hysteresis loop techniques. For N = 25⪢M = 3 we find ferrimagnetic stripe domains in remanence due to the combination of strong dipolar fields from the thick Co/Pt MLs with a strong AF-interlayer exchange coupling of the thin Co/Ni ML in the center, which reverses its polarity three times during a magnetic field reversal. Furthermore, local hysteresis loops reveal distinct random spin-flip avalanches, thus indicating the existence of local magnetic pinning sites due to the insertion of the center Co/Ni stack.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
78.70.-g Interactions of particles and radiation with matter
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optimized design of a low-resistance electrical conductor for the multimegahertz range

André Kurs, Morris Kesler, and Steven G. Johnson

Appl. Phys. Lett. 98, 172504 (2011); http://dx.doi.org/10.1063/1.3569141 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2011

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We propose a design for a conductive wire composed of several mutually insulated coaxial conducting shells. With the help of numerical optimization, it is possible to obtain electrical resistances significantly lower than those of a heavy-gauge copper wire or litz wire in the 2–20 MHz range. Moreover, much of the reduction in resistance can be achieved for just a few shells; in contrast, litz wire would need to contain ∼ 104 strands to perform comparably in this frequency range.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
02.60.Pn Numerical optimization

Tuning magnetocaloric effect with nanocrystallite size

S. P. Mathew and S. N. Kaul

Appl. Phys. Lett. 98, 172505 (2011); http://dx.doi.org/10.1063/1.3584018 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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We demonstrate that the average nanocrystallite size and size distribution can be used as control parameters to respectively tune the peak value and the width-at-half-maximum of the isothermal magnetic entropy change or the adiabatic temperature change during the magnetization process (magnetocaloric effect) such that a reasonably large relative cooling power, conducive to magnetic refrigeration, is achieved.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Influence of ion irradiation on switching field and switching field distribution in arrays of Co/Pd-based bit pattern media

T. Hauet, O. Hellwig, S.-H. Park, C. Beigné, E. Dobisz, B. D. Terris, and D. Ravelosona

Appl. Phys. Lett. 98, 172506 (2011); http://dx.doi.org/10.1063/1.3581896 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2011

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We have used ion irradiation to tune switching field and switching field distribution (SFD) in polycrystalline Co/Pd multilayer-based bit pattern media. Light He+ ion irradiation strongly decreases perpendicular magnetic anisotropy amplitude due to Co/Pd interface intermixing, while the granular structure, i.e., the crystalline anisotropy, remains unchanged. In dot arrays, the anisotropy reduction leads to a decrease in coercivity (HC) but also to a strong broadening of the normalized SFD/HC (in percentage), since the relative impact of misaligned grains is enhanced. Our experiment thus confirms the major role of misorientated grains in SFD of nanodevice arrays.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.80.Jh Ion radiation effects

Electric-field control of phase separation and memory effect in Pr0.6Ca0.4MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

Q. P. Chen, J. J. Yang, Y. G. Zhao, S. Zhang, J. W. Wang, M. H. Zhu, Y. Yu, X. Z. Zhang, Zhu Wang, Bin Yang, D. Xie, and T. L. Ren

Appl. Phys. Lett. 98, 172507 (2011); http://dx.doi.org/10.1063/1.3584025 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2011

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Heterostructures were fabricated by growing Pr0.6Ca0.4MnO3 (PCMO) films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the magnetizations of the samples can be tuned dramatically by electric fields via piezostrain and the effect is dominated by the change in phase separation. More interestingly, the electric-field control of magnetization is nonvolatile, manifesting a memory effect of strain. The results were discussed by considering the effect of electric-field-induced strain on the energy landscape of PCMO and the resultant change in phase separation. This work is helpful for exploring the evolution of phase separation with well-controlled strains and the magnetoelectric coupling effect.
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77.55.Nv Multiferroic/magnetoelectric films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.85.+t Magnetoelectric effects, multiferroics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Observation of spin wave modes depending on a tunable periodic magnetic field

Lihui Bai, Makoto Kohda, and Junsaku Nitta

Appl. Phys. Lett. 98, 172508 (2011); http://dx.doi.org/10.1063/1.3584032 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2011

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Excited spin waves in Ni0.8Fe0.2 strips are studied by detecting electrical signals with the use of a spin rectification effect. Through a meander control line, a periodic magnetic field is applied on the strips. Spin wave modes strongly depends on the periodic magnetic field. In a short period sample, we find spin wave coupling effect controlled by the periodic magnetic field, which can be used as a tunable spin wave filter.
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75.76.+j Spin transport effects
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Giant reversible anisotropic magnetocaloric effect in an antiferromagnetic EuFe2As2 single crystal

M. S. Kim, N. H. Sung, Yoonkook Son, M. S. Ko, and B. K. Cho

Appl. Phys. Lett. 98, 172509 (2011); http://dx.doi.org/10.1063/1.3579254 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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Here, we report the characterization of a giant reversible anisotropic magnetocaloric effect in a EuFe2As2 single crystal. The magnetic properties of EuFe2As2 single crystals are quite interesting; they display a small magnetic hysteresis, anisotropy, and a first-order magnetic phase transition. The maximum magnetic entropy change in in-plane magnetic-field direction was 14.6 J/kg K around 20 K and out-of-plane was 10.3 J/kg K around 20 K as a result of changing the magnetic field from 0 to 5 T. These results suggest the possibility of using EuFe2As2 single crystals in magnetic refrigeration applications.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Single crystal silicon capacitors with low microwave loss in the single photon regime

S. J. Weber, K. W. Murch, D. H. Slichter, R. Vijay, and I. Siddiqi

Appl. Phys. Lett. 98, 172510 (2011); http://dx.doi.org/10.1063/1.3583449 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2011

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We have fabricated superconducting microwave resonators in a lumped element geometry using single crystal silicon dielectric parallel plate capacitors with C>2 pF. Aluminum devices with resonant frequencies between 4.0 and 6.5 GHz exhibited an average internal quality factor Qi of 2×105 in the single photon excitation regime at T = 20 mK. Attributing the observed loss solely to the capacitive element, our measurements place an upper bound on the loss tangent of the silicon dielectric layer of tan δi = 5×10−6. This level of loss is an order of magnitude lower than is currently observed in structures incorporating amorphous dielectric materials, thus making single crystal silicon capacitors an attractive, robust route for realizing long-lived quantum circuits.
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85.25.Am Superconducting device characterization, design, and modeling
84.40.Az Waveguides, transmission lines, striplines
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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