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10 Nov 2008

Volume 93, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 93, 192501 (2008); http://dx.doi.org/10.1063/1.3013857 (3 pages)

O. Hellwig, A. Moser, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher, J. D. Risner-Jamtgaard, D. Yaney, and E. E. Fullerton
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Suppression of magnetic trench material in bit patterned media fabricated by blanket deposition onto prepatterned substrates

O. Hellwig, A. Moser, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher, J. D. Risner-Jamtgaard, D. Yaney, and E. E. Fullerton

Appl. Phys. Lett. 93, 192501 (2008); http://dx.doi.org/10.1063/1.3013857 (3 pages) | Cited 11 times

Online Publication Date: 10 November 2008

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An attractive approach for bit patterned media fabrication is the blanket deposition of magnetic material onto prepatterned substrates with elevated pillars and recessed trench areas. One issue with this method is the residual magnetic material in the trenches that causes disturbing stray fields during writing and readback. Here we present a technique to suppress the magnetic moment in the trenches with an additional annealing step by using prepatterned substrates consisting of SiN pillars on a Si wafer. The annealing triggers an interdiffusion process between the magnetic media and the Si in the trenches that results in the formation of a nonmagnetic silicide, while the magnetic moment on top of the SiN pillars remains substantially unaltered.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
66.30.Ny Chemical interdiffusion; diffusion barriers
75.30.Cr Saturation moments and magnetic susceptibilities
61.72.Cc Kinetics of defect formation and annealing
75.50.Ss Magnetic recording materials

Microstructure analysis of a SmCo/Fe exchange spring bilayer

Yuzi Liu, Y. Q. Wu, M. J. Kramer, Y. Choi, J. S. Jiang, Z. L. Wang, and J. P. Liu

Appl. Phys. Lett. 93, 192502 (2008); http://dx.doi.org/10.1063/1.2978325 (3 pages) | Cited 8 times

Online Publication Date: 10 November 2008

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The microstructure of a magnetron sputtered Cr(20 nm)/Sm–Co(20 nm)/Fe(20 nm)/Cr(5 nm) exchange spring magnet was studied using an advanced analytical transmission electron microscopy to better understand the relationship between its chemistry and structure to enhance the energy product. It is shown that the Fe atoms diffuse into the well textured Sm–Co layer, causing a transition from the stoichiometric Sm2Co7 near the Sm–Co/Cr interface to a defected Sm(Co,Fe)5 in the Sm–Co–Fe intermixed area. The graded intermixed layer between Sm–Co and pure Fe gives rise to a compositionally enhanced energy product.
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66.30.Lw Diffusion of other defects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
64.70.K- Solid-solid transitions

Room-temperature ferromagnetism in MgO nanocrystalline powders

Jifan Hu, Zhongli Zhang, Ming Zhao, Hongwei Qin, and Minhua Jiang

Appl. Phys. Lett. 93, 192503 (2008); http://dx.doi.org/10.1063/1.3021085 (3 pages) | Cited 56 times

Online Publication Date: 10 November 2008

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MgO nanocrystalline powders prepared by sol-gel method present room-temperature ferromagnetism, whereas MgO bulk exhibits diamagnetism. The vacuum annealing of MgO nanocrystalline powders reduces ferromagnetism. The observed room-temperature ferromagnetism in MgO nanocrystalline powders possibly originates from Mg vacancies at/near the surfaces of nanograins. Mg vacancies can induce local magnetic moments. Large concentrations of Mg vacancies at the surfaces of nanograins possibly establish magnetic percolation.
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81.16.-c Methods of micro- and nanofabrication and processing
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
61.72.jd Vacancies

Improvement and protection of niobium surface superconductivity by atomic layer deposition and heat treatment

T. Proslier, J. Zasadzinski, J. Moore, M. Pellin, J. Elam, L. Cooley, C. Antoine, J. Norem, and K. E. Gray

Appl. Phys. Lett. 93, 192504 (2008); http://dx.doi.org/10.1063/1.2995996 (3 pages) | Cited 3 times

Online Publication Date: 11 November 2008

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A method to treat the surface of Nb is described, which potentially can improve the performance of superconducting rf cavities. We present tunneling and x-ray photoemission spectroscopy measurements at the surface of cavity-grade niobium samples coated with a 3 nm alumina overlayer deposited by atomic layer deposition. The coated samples baked in ultrahigh vacuum at low temperature degraded superconducting surface. However, at temperatures above 450 C, the tunneling conductance curves show significant improvements in the superconducting density of states compared with untreated surfaces.
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74.62.Yb Other effects
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.50.+r Tunneling phenomena; Josephson effects
74.25.Gz Optical properties
74.70.-b Superconducting materials other than cuprates
74.25.Jb Electronic structure (photoemission, etc.)

Fractional order Shapiro steps in superconducting nanowires

R. C. Dinsmore, III, Myung-Ho Bae, and A. Bezryadin

Appl. Phys. Lett. 93, 192505 (2008); http://dx.doi.org/10.1063/1.3012360 (3 pages) | Cited 3 times

Online Publication Date: 11 November 2008

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We expose superconducting nanowires to microwave radiation in order to study phase lock-in effects in quasi-one-dimensional superconductors. For sufficiently high microwave powers a resistive branch with Shapiro steps appears in the voltage-current characteristics. At frequencies in the range of 0.9–4 GHz these steps are of integer order only. At higher frequencies steps of 1/2, 1/3, 1/4, and even 1/6 order appear. We numerically model this behavior using a multivalued current-phase relationship for nanowires.
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74.50.+r Tunneling phenomena; Josephson effects

The magnetoelectric domains and cross-field switching in multiferroic BiFeO3

L. J. Li, J. Y. Li, Y. C. Shu, and J. H. Yen

Appl. Phys. Lett. 93, 192506 (2008); http://dx.doi.org/10.1063/1.3025843 (3 pages) | Cited 24 times

Online Publication Date: 11 November 2008

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BiFeO3 is an exciting multiferroic material because of its room temperature multiferrocity, excellent ferroelectric properties, and recently demonstrated electric control of antiferromagnetic domains. In this letter we report a theoretical study on the structure and evolution of magnetoelectric domains in BiFeO3. We not only observed the coupled ferroelectric and antiferromagnetic domains and demonstrated the electric control of antiferromagnetic ordering, both in consistency with experiments, but also revealed the switching of antiferromagnetic domains by mechanical stress that is yet to be explored in experiments.
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75.80.+q Magnetomechanical effects, magnetostriction
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena

Space-charge trap mediated conductance blockade in tunnel junctions with half-metallic electrodes

J. F. Feng, T.-H. Kim, X. F. Han, X.-G. Zhang, Y. Wang, J. Zou, D. B. Yu, H. Yan, and A. P. Li

Appl. Phys. Lett. 93, 192507 (2008); http://dx.doi.org/10.1063/1.3025851 (3 pages) | Cited 4 times

Online Publication Date: 11 November 2008

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A conductance blockade effect has been observed in the magnetic tunnel junction consisting of La0.7Sr0.3MnO3 electrodes and a SrTiO3 barrier. The blockade effect is correlated with the space-charge trap states in the barrier. The blockade threshold eVB = 128 meV is significantly greater than Coulomb charging energy EC = 11 meV. The blockade can be lifted with a magnetic field, accompanied by a very large magnetoresistance up to 10 000%. The intriging blockade behavior is distinctly different from the conventional Coulomb blockade effect, showing a unique spin-dependent tunneling process mediated by the localized charge trap states.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Lx Magnetic oxides
77.22.Jp Dielectric breakdown and space-charge effects
73.23.Hk Coulomb blockade; single-electron tunneling
72.25.-b Spin polarized transport

Thermal coercivity mechanism in Fe nanoribbons and stripes

F. Garcia-Sanchez and O. Chubykalo-Fesenko

Appl. Phys. Lett. 93, 192508 (2008); http://dx.doi.org/10.1063/1.3026172 (3 pages) | Cited 1 time

Online Publication Date: 11 November 2008

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We investigate the influence of thermally activated process on coercivity values of long Fe nanostripes. By means of the Lagrangian multiplier technique and the micromagnetic approach, we evaluate energy barriers separating the two magnetization states of long Fe nanostripes, varying their width from 30 to 250 nm. As the width of nanostripes decreases, the reversal time, evaluated through the Arrhenius–Neel law, becomes comparable to the measurement time scale (characteristic for typical magnetometer) for fields below the values obtained through zero-temperature micromagnetic approach. We found appreciable variation of the coercivity due to thermal activation for stripe widths below 100 nm.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys

Competing interactions and complex magnetism at SrRuO3/SrMnO3 interfaces

Y. Choi, Y. C. Tseng, D. Haskel, D. E. Brown, D. Danaher, and O. Chmaissem

Appl. Phys. Lett. 93, 192509 (2008); http://dx.doi.org/10.1063/1.3013333 (3 pages)

Online Publication Date: 12 November 2008

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The coupled interfacial Mn and Ru spin configurations in a SrRuO3(SRO)/SrMnO3(SMO) superlattice are investigated with x-ray resonant techniques. With an out-of-plane applied field H, a net Mn moment is induced opposite to (along) H below (above) SRO Curie temperature TC, due to changes in interfacial antiferromagnetic Ru–Mn coupling. In comparison with the Mn moment induced along an out-of-plane field below TC, the Mn moment induced along an in-plane field is five (three) times smaller below (above) TC, due to frustration in the Ru–Mn coupling. Despite its in-plane anisotropy, the G-type antiferromagnetic SMO favors out-of-plane over in-plane canting of Mn moments.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ee Antiferromagnetics

Ab initio study of electron-phonon coupling in boron-doped SiC

E. R. Margine and X. Blase

Appl. Phys. Lett. 93, 192510 (2008); http://dx.doi.org/10.1063/1.3023073 (3 pages) | Cited 8 times

Online Publication Date: 14 November 2008

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Density functional theory calculations have been used to study the electronic structure, lattice dynamics, and electron-phonon coupling in boron-doped silicon carbide in the cubic phase. Our results provide evidence that the recently discovered superconducting transition in boron-doped silicon carbide can be explained within a standard phonon-mediated mechanism. For the same doping rate, the coupling constant λ in B-doped SiC is very close to that of doped diamond and twice as large as that of B-doped silicon. However, doped silicon carbide differs from its diamond counterpart as most of the electron-phonon coupling originates from low energy vibrational modes.
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63.20.kd Phonon-electron interactions
74.25.Kc Phonons
74.25.Jb Electronic structure (photoemission, etc.)
74.62.Dh Effects of crystal defects, doping and substitution
61.72.up Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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