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20 Dec 2010

Volume 97, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 97, 252101 (2010); http://dx.doi.org/10.1063/1.3525588 (3 pages)

Wei Pan, Stephen W. Howell, Anthony Joseph Ross, III, Taisuke Ohta, and Thomas A. Friedmann
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Quantitative evaluation of defect-models in superconducting phase qubits

J. H. Cole, C. Müller, P. Bushev, G. J. Grabovskij, J. Lisenfeld, A. Lukashenko, A. V. Ustinov, and A. Shnirman

Appl. Phys. Lett. 97, 252501 (2010); http://dx.doi.org/10.1063/1.3529457 (3 pages)

Online Publication Date: 20 December 2010

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We use high-precision spectroscopy and detailed theoretical modeling to determine the form of the coupling between a superconducting phase qubit and a two-level defect. Fitting the experimental data with our theoretical model allows us to determine all relevant system parameters. We observe a strong qubit-defect coupling with a nearly vanishing longitudinal component. We quantitatively compare several existing theoretical models for the microscopic origin of two-level defects.
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74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
03.67.Lx Quantum computation architectures and implementations
03.67.Mn Entanglement measures, witnesses, and other characterizations
61.72.-y Defects and impurities in crystals; microstructure

Magnetostructural influences of thin Mg insert layers in crystalline CoFe(B)/MgO/CoFe(B) magnetic tunnel junctions

A. T. Hindmarch, V. Harnchana, D. Ciudad, E. Negusse, D. A. Arena, A. P. Brown, R. M. D. Brydson, and C. H. Marrows

Appl. Phys. Lett. 97, 252502 (2010); http://dx.doi.org/10.1063/1.3527939 (3 pages) | Cited 2 times

Online Publication Date: 20 December 2010

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It is common to find a thin ( ∼ 0.5 nm) layer of Mg deposited prior to the MgO tunnel barrier in crystalline CoFe(B)/MgO/CoFe(B) magnetic tunnel junctions, due to the improved device performance that results. However, despite their common usage, the reasons why such layers are effective are unclear. We use structures that model the lower electrode of such devices to show that a suitably thick Mg insert layer enhances the crystal quality of both MgO and CoFe(B), permits interfacial oxides to reduce back to a metallic ferromagnetic state, and hence improves magnetic switching of the CoFe(B) electrode, properties which are inextricably linked to device performance.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Aging of magnetic properties in MgO films

Ll. Balcells, J. I. Beltrán, C. Martínez-Boubeta, Z. Konstantinović, J. Arbiol, and B. Martínez

Appl. Phys. Lett. 97, 252503 (2010); http://dx.doi.org/10.1063/1.3527963 (3 pages) | Cited 3 times

Online Publication Date: 21 December 2010

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In this work we report on the magnetic behavior of MgO thin films prepared by sputtering. A severe aging process of the ferromagnetic properties is detected in magnetic samples exposed to ambient atmosphere. However, ferromagnetism can be successively switched on again by annealing samples in vacuum. We suggest this behavior reflects the key role played by defects in stabilizing ferromagnetism in MgO films and is likely to be closely related to the hydrogen-driven instability of V-type centers in this material.
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68.55.A- Nucleation and growth
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
61.72.jn Color centers

Enhancement of the spin pumping efficiency by spin wave mode selection

C. W. Sandweg, Y. Kajiwara, K. Ando, E. Saitoh, and B. Hillebrands

Appl. Phys. Lett. 97, 252504 (2010); http://dx.doi.org/10.1063/1.3528207 (3 pages) | Cited 9 times

Online Publication Date: 21 December 2010

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The spin pumping efficiency of standing spin wave modes in a rectangular Y3Fe5O12/Pt sample has been investigated by means of inverse spin-Hall effect (ISHE). Standing spin waves drive spin pumping, the generation of spin currents from magnetization precession, into the Pt layer which is converted into a detectable voltage due to the ISHE. We discovered that the spin pumping efficiency is significantly higher for standing surface spin waves, hybridized with thickness modes, rather than for volume spin wave modes. The results suggest that the use of higher-mode surface spin waves allows for the fabrication of an efficient spin-current injector.
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72.25.Pn Current-driven spin pumping
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.76.+j Spin transport effects
72.20.My Galvanomagnetic and other magnetotransport effects

Monopolelike probes for quantitative magnetic force microscopy: Calibration and application

S. Vock, F. Wolny, T. Mühl, R. Kaltofen, L. Schultz, B. Büchner, C. Hassel, J. Lindner, and V. Neu

Appl. Phys. Lett. 97, 252505 (2010); http://dx.doi.org/10.1063/1.3528340 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2010

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A local magnetization measurement was performed by magnetic force microscopy (MFM) to determine magnetization in domains of an exchange coupled [Co/Pt]/Co/Ru multilayer with predominant perpendicular anisotropy. The quantitative MFM measurements were conducted with an iron-filled carbon nanotube tip, which is shown to behave like a monopole. As a result we determined an additional in-plane magnetization component of the multilayer, which is explained by estimating the effective permeability of the sample within the μ∗-method.
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07.79.Pk Magnetic force microscopes
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Gigantic enhancement of spin Seebeck effect by phonon drag

Hiroto Adachi, Ken-ichi Uchida, Eiji Saitoh, Jun-ichiro Ohe, Saburo Takahashi, and Sadamichi Maekawa

Appl. Phys. Lett. 97, 252506 (2010); http://dx.doi.org/10.1063/1.3529944 (3 pages) | Cited 6 times

Online Publication Date: 23 December 2010

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We investigate both theoretically and experimentally a gigantic enhancement of the spin Seebeck effect in a prototypical magnet LaY2Fe5O12 at low temperatures. Our theoretical analysis sheds light on the important role of phonons; the spin Seebeck effect is enormously enhanced by nonequilibrium phonons that drag the low-lying spin excitations. We further argue that this scenario gives a clue to understand the observation of the spin Seebeck effect that is unaccompanied by a global spin current, and predict that the substrate condition affects the observed signal.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
72.20.Pa Thermoelectric and thermomagnetic effects
63.20.kd Phonon-electron interactions

Magnetoimpedance sensitive to dc bias current in amorphous microwires

M. Ipatov, V. Zhukova, A. Zhukov, and J. Gonzalez

Appl. Phys. Lett. 97, 252507 (2010); http://dx.doi.org/10.1063/1.3529946 (3 pages) | Cited 5 times

Online Publication Date: 23 December 2010

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We have investigated the impedance dependence of magnetically soft microwire on the internal circumferential magnetic field HB created by the dc bias current IB and theoretically and experimentally demonstrated that in a conductor with helical magnetic anisotropy, the high frequency impedance depends on the dc bias current IB (or the corresponding bias field HB) and this dependence is hysteretic. We have experimentally observed a change of impedance more than 35% upon changing the bias current. The possible applications of the dc current-driven magnetoimpedance effect are discussed.
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75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials

Large converse magnetoelectric coupling effect at room temperature in CoPd/PMN-PT (001) heterostructure

Ju-Hyun Kim, Kwang-Su Ryu, Jae-Woo Jeong, and Sung-Chul Shin

Appl. Phys. Lett. 97, 252508 (2010); http://dx.doi.org/10.1063/1.3531648 (3 pages) | Cited 2 times

Online Publication Date: 23 December 2010

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We report a large converse magnetoelectric (CME) effect at room temperature in a multiferroic heterostructure formed from thin layers of perpendicularly magnetized CoxPd1-x alloys deposited on a piezoelectric single-crystal of lead magnesium niobate-lead titanate PMN-PT(001). The CME results from a strain-induced reorientation of the CoPd magnetization. By varying the composition and thickness of the CoxPd1-x film, a large converse magnetoelectric coupling constant, α = 8×10−7 s/m, at room temperature was found for 10 nm Co0.25Pd0.75. This large CME effect results from combining a highly magnetostrictive CoPd alloy with highly piezoelectric PMN-PT.
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75.80.+q Magnetomechanical effects, magnetostriction
77.65.Ly Strain-induced piezoelectric fields
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics
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