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30 May 2011

Volume 98, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 223101 (2011); http://dx.doi.org/10.1063/1.3595266 (3 pages)

Takahiro Ohori, Yasuhide Ohno, Kenzo Maehashi, Koichi Inoue, Yutaka Hayashi, and Kazuhiko Matsumoto
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FePt L10/A1 graded media with a rough interphase boundary

Jehyun Lee, Vasilis Alexandrakis, Markus Fuger, Barbara Dymerska, Dieter Suess, Dimitris Niarchos, and Josef Fidler

Appl. Phys. Lett. 98, 222501 (2011); http://dx.doi.org/10.1063/1.3595307 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2011

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A graded media consisting of FePt L10(hard) and A1(soft) phases separated by a rough wedge-shaped interphase boundary, the “phase graded media” is suggested. The rough interface helps domain wall propagation from the soft to the hard phase, owing to the easily reversed wedge tips of the hard phase. The reversed domain expands in the hard phase with a small additional field. As a result, the switching field of the phase graded media was reduced to 13 kOe which is 16% of FePt L10 single phase (79 kOe), the reduction is comparable with the stacked graded media.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure

From positive to negative magnetoresistance in graphene with increasing disorder

Yang-Bo Zhou, Bing-Hong Han, Zhi-Min Liao, Han-Chun Wu, and Da-Peng Yu

Appl. Phys. Lett. 98, 222502 (2011); http://dx.doi.org/10.1063/1.3595681 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2011

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Artificial disorder was introduced gradually into monolayer graphene by controlling Ga+ ion irradiation and the corresponding electronic transport properties regulated by gate voltage, source-drain voltage, temperature, and magnetic field were studied experimentally. An unsaturated positive magnetoresistance (MR) up to 100% at ∼ 5 T was observed in as-fabricated graphene, while there is significant negative MR in disordered graphene. This phenomenon was attributed to the monocrystalline breaking and crystallite-boundary scattering in disordered graphene.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Wp Fullerenes and related materials
75.70.Ak Magnetic properties of monolayers and thin films
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Robust surface electronic properties of topological insulators: Bi2Te3 films grown by molecular beam epitaxy

L. Plucinski, G. Mussler, J. Krumrain, A. Herdt, S. Suga, D. Grützmacher, and C. M. Schneider

Appl. Phys. Lett. 98, 222503 (2011); http://dx.doi.org/10.1063/1.3595309 (3 pages) | Cited 5 times

Online Publication Date: 1 June 2011

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The surface electronic properties of the important topological insulator Bi2Te3 are shown to be robust under an extended surface preparation procedure, which includes exposure to atmosphere and subsequent cleaning and recrystallization by an optimized in situ sputter-anneal procedure under ultrahigh vacuum conditions. Clear Dirac-cone features are displayed in high-resolution angle-resolved photoemission spectra from the resulting samples, indicating remarkable insensitivity of the topological surface state to cleaning-induced surface roughness.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.65.Cf Surface cleaning, etching, patterning
68.55.aj Insulators

Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1−xKxFe2As2 superconductors

Lei Wang, Yanwei Ma, Qingxiao Wang, Kun Li, Xixiang Zhang, Yanpeng Qi, Zhaoshun Gao, Xianping Zhang, Dongliang Wang, Chao Yao, and Chunlei Wang

Appl. Phys. Lett. 98, 222504 (2011); http://dx.doi.org/10.1063/1.3592580 (3 pages) | Cited 11 times

Online Publication Date: 1 June 2011

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We report here an atomic resolution study of the structure and composition of the grain boundaries in polycrystalline Sr0.6K0.4Fe2As2 superconductor. A large fraction of grain boundaries contain amorphous layers larger than the coherence length, while some others contain nanometer-scale crystallites sandwiched in between amorphous layers. We also find that there is significant oxygen enrichment at the grain boundaries. Such results explain the relatively low transport critical current density (Jc) of polycrystalline samples with respect to that of bicrystal films.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
74.70.Xa Pnictides and chalcogenides
61.72.Mm Grain and twin boundaries
74.25.F- Transport properties
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
74.25.Sv Critical currents

Hybridization-induced oscillatory magnetic polarization of C60 orbitals at the C60/Fe(001) interface

T. L. A. Tran, P. K. J. Wong, M. P. de Jong, W. G. van der Wiel, Y. Q. Zhan, and M. Fahlman

Appl. Phys. Lett. 98, 222505 (2011); http://dx.doi.org/10.1063/1.3595269 (3 pages) | Cited 7 times

Online Publication Date: 2 June 2011

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We have studied the electronic and magnetic properties of the interface between C60 molecules and a Fe(001) surface. X-ray absorption spectroscopy and x-ray magnetic circular dichroism studies of C60 monolayers on Fe(001) surfaces show that hybridization between the frontier orbitals of C60 and continuum states of Fe leads to a significant magnetic polarization of C60 π∗-derived orbitals. The magnitude and also the sign of this polarization were found to depend markedly on the excitation energy. These observations underline the importance of tailoring the interfacial spin polarization at the Fermi level of ferromagnet/organic semiconductor interfaces for applications in organic spintronics.
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73.20.At Surface states, band structure, electron density of states
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra

Three-dimensional ferromagnetic architectures with multiple metastable states

F. Nasirpouri, M. A. Engbarth, S. J. Bending, L. M. Peter, A. Knittel, H. Fangohr, and M. V. Milošević

Appl. Phys. Lett. 98, 222506 (2011); http://dx.doi.org/10.1063/1.3595339 (3 pages) | Cited 1 time

Online Publication Date: 2 June 2011

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We demonstrate controllable dual-bath electrodeposition of nickel on architecture-tunable three-dimensional (3D) silver microcrystals. Magnetic hysteresis loops of individual highly faceted Ag-Ni core-shell elements reveal magnetization reversal that comprises multiple sharp steps corresponding to different stable magnetic states. Finite-element micromagnetic simulations on smaller systems show several jumps during magnetization reversal which correspond to transitions between different magnetic vortex states. Structures of this type could be realizations of an advanced magnetic data storage architecture whereby each element represents one multibit, storing a combination of several conventional bits depending on the overall number of possible magnetic states associated with the 3D core-shell shape.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
81.15.Pq Electrodeposition, electroplating
75.78.Cd Micromagnetic simulations
75.50.Cc Other ferromagnetic metals and alloys

Nanocomposite exchange-spring magnet synthesized by gas phase method: From isotropic to anisotropic

Xiaoqi Liu, Shihai He, Jiao-Ming Qiu, and Jian-Ping Wang

Appl. Phys. Lett. 98, 222507 (2011); http://dx.doi.org/10.1063/1.3597225 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2011

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The fabrication of anisotropic nanocomposite exchange-spring magnets is demonstrated experimentally by using a gas-phase nanoparticle deposition technique. High resolution transmission electron microscopy images prove the experimental easy-axis definition of embedded hard magnetic nanoparticles in soft magnetic matrix. Exchange coupling between the hard and soft phases is confirmed by measuring recoil loops and δ M-H curve of the anisotropic FePt/Fe0.8Ni0.2 nanocomposite. The magnetic energy product for the anisotropic exchange-spring magnet is 224% higher than the isotropic case.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Et Exchange and superexchange interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Rise and fall of defect induced ferromagnetism in SiC single crystals

Lin Li, S. Prucnal, S. D. Yao, K. Potzger, W. Anwand, A. Wagner, and Shengqiang Zhou

Appl. Phys. Lett. 98, 222508 (2011); http://dx.doi.org/10.1063/1.3597629 (3 pages) | Cited 7 times

Online Publication Date: 3 June 2011

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6H–SiC (silicon carbide) single crystals containing VSi–VC divacancies are investigated with respect to magnetic and structural properties. We found that an initial increase in structural disorder leads to pronounced ferromagnetic properties at room temperature. Further introduction of disorder lowers the saturation magnetization and is accompanied with the onset of lattice amorphization. Close to the threshold of full amorphization, also divacancy clusters are formed and the saturation magnetization nearly drops to zero.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.jd Vacancies
61.66.Fn Inorganic compounds

Electric field modulation of magnetoresistance in multiferroic heterostructures for ultralow power electronics

Ming Liu, Shandong Li, Ogheneyunume Obi, Jing Lou, Scott Rand, and Nian X. Sun

Appl. Phys. Lett. 98, 222509 (2011); http://dx.doi.org/10.1063/1.3597796 (3 pages) | Cited 12 times

Online Publication Date: 3 June 2011

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An energy-efficiency technique for electrically modulating magnetoresistance was demonstrated in multiferroic anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) heterostructures. A giant electric field (E-field) induced magnetic anisotropy caused by a strong magnetoelectric coupling was utilized to control the orientation of magnetization and thus dynamically manipulate magnetoresistance in AMR and GMR devices. A multiband tunable AMR field sensor was designed and developed to dramatically enhance the measurement range by 15 times. In addition, two types of E-field determination of GMR in spin-valve structures are studied. The results indicate an energy efficiency approach to controlling magnetoresistance by E-field rather than magnetic field, which shows great potential for novel low power electronic and spintronic devices.
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75.85.+t Magnetoelectric effects, multiferroics
07.55.-w Magnetic instruments and components
75.30.Gw Magnetic anisotropy
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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