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8 Aug 2011

Volume 99, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 063701 (2011); http://dx.doi.org/10.1063/1.3622631 (3 pages)

Bomi Gweon, Mina Kim, Dan Bee Kim, Daeyeon Kim, Hyeonyu Kim, Heesoo Jung, Jennifer H. Shin, and Wonho Choe
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Magnetic signature of symmetry reduction in epitaxial La0.67Sr0.33MnO3 films

Radhika Barua, L. H. Lewis, and D. Heiman

Appl. Phys. Lett. 99, 062501 (2011); http://dx.doi.org/10.1063/1.3623442 (3 pages)

Online Publication Date: 8 August 2011

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The magnetic properties of epitaxially grown La0.67Sr0.33MnO3 perovskite thin films were investigated to elucidate an unexpected broken symmetry between orthogonal [100] and [010] inplane directions, resulting from the magnetostructural coupling between the film and the cubic SrTiO3 (001) substrate. The films were synthesized by molecular beam epitaxy with either complete or zero A-site cation disorder. Magnetization measured in [100] and [010] directions shows differences that signal a reduction of the in-plane cubic symmetry only for T < 290 K. The magnetization asymmetry is more robust in the film with complete A-site disorder. These results are attributed to a dominant Mn3+ character at the film-substrate interface and an associated out-of-plane bonding character with hypothesized origins in both charge imbalance and strain effects.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.at Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Origin of magnetic switching field distribution in bit patterned media based on pre-patterned substrates

B. Pfau, C. M. Günther, E. Guehrs, T. Hauet, H. Yang, L. Vinh, X. Xu, D. Yaney, R. Rick, S. Eisebitt, and O. Hellwig

Appl. Phys. Lett. 99, 062502 (2011); http://dx.doi.org/10.1063/1.3623488 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2011

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Using a combination of synchrotron radiation based magnetic imaging and high-resolution transmission electron microscopy we reveal systematic correlations between the magnetic switching field and the internal nanoscale structure of individual islands in bit patterned media fabricated by Co/Pd-multilayer deposition onto pre-patterned substrates. We find that misaligned grains at the island periphery are a common feature independent of the island switching field, while irregular island shapes and misaligned grains specifically extending into the center of an island are systematically correlated with a reduced island reversal field.
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81.05.Bx Metals, semimetals, and alloys
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.50.Ss Magnetic recording materials
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetism of covalently functionalized carbon nanotubes

Elton J. G. Santos, D. Sánchez-Portal, and A. Ayuela

Appl. Phys. Lett. 99, 062503 (2011); http://dx.doi.org/10.1063/1.3623755 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2011

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We investigate the electronic structure of carbon nanotubes functionalized by adsorbates anchored with single C-C covalent bonds. We find that despite the particular adsorbate, a spin moment with a universal value of 1.0 μB per molecule is induced at low coverage. Therefore, we propose a mechanism of bonding-induced magnetism at the carbon surface. The adsorption of a single molecule creates a dispersionless defect state at the Fermi energy, which is mainly localized in the carbon wall and presents a small contribution from the adsorbate. This universal spin moment is fairly independent of the coverage as long as all the molecules occupy the same graphenic sublattice. The magnetic coupling between adsorbates is also studied and reveals a key dependence on the graphenic sublattice adsorption site.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.20.Tx Fullerenes and related materials; intercalation compounds
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Electric control of magnon frequencies and magnetic moment of bismuth ferrite thin films at room temperature

Ashok Kumar, J. F. Scott, and R. S. Katiyar

Appl. Phys. Lett. 99, 062504 (2011); http://dx.doi.org/10.1063/1.3624845 (3 pages) | Cited 9 times

Online Publication Date: 10 August 2011

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Here, we report the tuning of room-temperature magnon frequencies from 473 GHz to 402 GHz (14%) and magnetic moment from 4 to 18 emu/cm3 at 100 Oe under the application of external electric fields (E) across interdigital electrodes in BiFeO3 (BFO) thin films. A decrease in magnon frequencies and increase in phonon frequencies were observed with Magnon and phonon Raman intensities are asymmetric with polarity, decreasing with positive E (+E) and increasing with negative E (−E) where polarity is with respect to in-plane polarization P. The magnetoelectric coupling (α) is proved to be linear and a rather isotropic α = 8.5 × 10−12 sm−1.
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75.85.+t Magnetoelectric effects, multiferroics
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films

Contribution of the easy axis orientation, anisotropy distribution and dot size on the switching field distribution of bit patterned media

Jehyun Lee, Christoph Brombacher, Josef Fidler, Barbara Dymerska, Dieter Suess, and Manfred Albrecht

Appl. Phys. Lett. 99, 062505 (2011); http://dx.doi.org/10.1063/1.3623752 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2011

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A magnetic nanostructure array was fabricated by post-patterning of a L10 ordered 5-nm-thick FePtCu film revealing a rather broad switching field distribution (SFD). The individual contributions to the SFD of the dot array were investigated by micromagnetic simulations. Based on transmission electron microscopy results, the dots show a truncated cone shape which was directly used for the finite element model. The influence of single parameters, i.e., easy axis distribution, magnetic anisotropy, and dot size, on the SFD was estimated quantitatively and compared. Furthermore, the influence of damage induced during the nanofabrication process was analyzed and correlated with experimental results.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.75.-c Magnetic properties of nanostructures
02.70.Dh Finite-element and Galerkin methods
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.-d Domain effects, magnetization curves, and hysteresis

Effect of interparticle interactions and size dispersion in magnetic nanoparticle assemblies: A static and dynamic study

Ji Sung Lee, Reasmey P. Tan, Jun Hua Wu, and Young Keun Kim

Appl. Phys. Lett. 99, 062506 (2011); http://dx.doi.org/10.1063/1.3624833 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2011

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Interparticle interactions in magnetic nanoparticles are studied by dc and ac magnetization measurements. For non-interacting nanoparticles, while the anisotropy constant of the nanoparticles Keff = 1.6 × 105 erg/cm3 is accurately determined by fitting zero-field-cooled and field-cooled measurements, we show that Keff values deduced only from time relaxation measurements must require simultaneous adjustments of the complex susceptibility by taking into account the size distribution of nanoparticles. This leads to Keff = 1.7 × 105 erg/cm3 in agreement with dc measurements. For interacting nanoparticles, comparisons with theoretical models show that energies due to magnetic dipolar interactions can only be predicted for weak and moderate interactions.
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75.75.Jn Dynamics of magnetic nanoparticles
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.78.-n Magnetization dynamics

Competitive roles of elastic and magnetic interactions in twin boundary behaviors of magnetic shape memory alloys

Yongmei M. Jin

Appl. Phys. Lett. 99, 062507 (2011); http://dx.doi.org/10.1063/1.3625428 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2011

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Domain microstructure evolutions under applied magnetic field in magnetic shape memory alloys are investigated by phase field micromagnetic microelastic modeling. The computer simulations reveal respective roles of elastic interaction, magnetic interaction, and their competition in the coupled magnetic and elastic domain processes. It is observed that different relative strengths of elastic interaction with respect to magnetic interaction lead to different domain evolution pathways and different twin boundary behaviors, including field-induced twin boundary displacement, deformation, and annihilation. Distinct twin boundary behaviors driven by magnetic field from that driven by mechanical stress are discussed.
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81.40.Lm Deformation, plasticity, and creep
62.20.dq Other elastic constants
62.20.fg Shape-memory effect; yield stress; superelasticity
75.60.Ch Domain walls and domain structure
81.40.Jj Elasticity and anelasticity, stress-strain relations

Control of spin configuration in half-metallic La0.7Sr0.3MnO3 nano-structures

J. Rhensius, C. A. F. Vaz, A. Bisig, S. Schweitzer, J. Heidler, H. S. Körner, A. Locatelli, M. A. Niño, M. Weigand, L. Méchin, F. Gaucher, E. Goering, L. J. Heyderman, and M. Kläui

Appl. Phys. Lett. 99, 062508 (2011); http://dx.doi.org/10.1063/1.3623480 (3 pages) | Cited 7 times

Online Publication Date: 11 August 2011

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We investigate the interplay between the governing magnetic energy terms in patterned La0.7Sr0.3MnO3 (LSMO) elements by direct high-resolution x-ray magnetic microscopy as a function of temperature and geometrical parameters. We show that the magnetic configurations evolve from multidomain to flux-closure states (favored by the shape anisotropy) with decreasing element size, with a thickness-dependent crossover at the micrometer scale. The flux-closure states are stable against thermal excitations up to near the Curie temperature. Our results demonstrate control of the spin state in LSMO elements by judicious choice of the geometry, which is key for spintronics applications requiring high spin-polarizations and robust magnetic states.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Wx Spin crossover
75.60.Ch Domain walls and domain structure

Substrate-dependent quasiparticle recombination time in superconducting resonators

N. Vercruyssen, R. Barends, T. M. Klapwijk, J. T. Muhonen, M. Meschke, and J. P. Pekola

Appl. Phys. Lett. 99, 062509 (2011); http://dx.doi.org/10.1063/1.3624463 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2011

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We demonstrate an increased quasiparticle recombination time in superconducting resonators on a SiNx membrane, compared to identical resonators on a SiNx/Si wafer. An interpretation is given using a thermal model of the membrane. Using an array of tunnel junctions to cool or heat the membrane, we show that the resonators on the membranes are extremely sensitive to small changes of the phonon temperature, which renders them excellent phonon thermometers with a noise level equivalent to 5μK/math. The experimental set-up is in principle an ideal platform to study the interplay of quasiparticles and phonon populations in superconductors.
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85.25.Cp Josephson devices

Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions with low critical current density

Luigi Longobardi, Davide Massarotti, Giacomo Rotoli, Daniela Stornaiuolo, Gianpaolo Papari, Akira Kawakami, Giovanni Piero Pepe, Antonio Barone, and Francesco Tafuri

Appl. Phys. Lett. 99, 062510 (2011); http://dx.doi.org/10.1063/1.3624471 (3 pages) | Cited 6 times

Online Publication Date: 11 August 2011

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High quality epitaxial NbN/MgO/NbN Josephson junctions have been realized with MgO barriers up to a thickness of d = 1 nm. The junction properties coherently scale with the size of barrier, and low critical current densities down to 3 A/cm2 have been achieved for larger barriers. In this limit, junctions exhibit macroscopic quantum phenomena for temperatures lower than 90 mK. Measurements and junction parameters support the notion of a possible use of these devices for multiphoton quantum experiments, taking advantage of the fast non equilibrium electron-phonon relaxation times of NbN.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.25.Kc Phonons
74.25.Sv Critical currents

Low frequency noise due to magnetic inhomogeneities in submicron FeCoB/MgO/FeCoB magnetic tunnel junctions

D. Herranz, A. Gomez-Ibarlucea, M. Schäfers, A. Lara, G. Reiss, and F. G. Aliev

Appl. Phys. Lett. 99, 062511 (2011); http://dx.doi.org/10.1063/1.3615798 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2011

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We report on room temperature low frequency noise due to magnetic inhomogeneities/domain walls (MI/DWs) in elliptic submicron FeCoB/MgO/FeCoB magnetic tunnel junctions with an area between 0.0245 and 0.0675 μm2. In the smaller area junctions we found an unexpected random telegraph noise (RTN1), deeply in the parallel state, possibly due to stray field induced MI/DWs in the hard layer. The second noise source (RTN2) is observed in the antiparallel state for the largest junctions. Strong asymmetry of RTN2 and of related resistance steps with current indicate spin torque acting on the MI/DWs in the soft layer at current densities below 5 × 105 A/cm2.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure

On the role of Al doping in La0.7Ca0.3MnO3: A magnetic Compton scattering study

B. L. Ahuja, Shailja Tiwari, Alpa Dashora, H. S. Mund, Jagrati Sahariya, D. M. Phase, R. J. Choudhary, A. Banerjee, M. Itou, and Y. Sakurai

Appl. Phys. Lett. 99, 062512 (2011); http://dx.doi.org/10.1063/1.3624843 (3 pages) | Cited 2 times

Online Publication Date: 12 August 2011

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Spin and orbital magnetic moments in hole doped manganite La0.7Ca0.3Mn1−xAlxO3 (x = 0, 0.02, and 0.06) have been scrutinized using experimental spin momentum densities. An analysis of magnetic Compton profiles shows that the spin moment of Mn 3d has a major contribution towards the total spin moment and its contribution decreases as we increase the concentration of Al. The present experiment along with magnetization data predict orbital moment of −0.29 ± 0.03 μB/f.u. in the parent compound (x = 0), which almost disappears on substitution of Al. The results are explained on the basis of imbalance in Mn3+ and Mn4+ charge ratio in these compounds.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.-g Interactions of particles and radiation with matter
61.72.U- Doping and impurity implantation
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