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18 Jun 2012

Volume 100, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 100, 252401 (2012); http://dx.doi.org/10.1063/1.4727909 (4 pages)

Ming Yan, Christian Andreas, Attila Kákay, Felipe García-Sánchez, and Riccardo Hertel
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Chiral symmetry breaking and pair-creation mediated Walker breakdown in magnetic nanotubes

Ming Yan, Christian Andreas, Attila Kákay, Felipe García-Sánchez, and Riccardo Hertel

Appl. Phys. Lett. 100, 252401 (2012); http://dx.doi.org/10.1063/1.4727909 (4 pages) | Cited 4 times

Online Publication Date: 18 June 2012

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Field-driven domain wall (DW) propagation in ferromagnetic nanotubes displays unusual effects, as revealed by a micromagnetic study. The left-right symmetry of the DW dynamics is broken, yielding markedly different DW mobilities for opposite propagation directions. This asymmetry arises from the tubular geometry and its impact on the DW structure. Also, the Walker breakdown field and velocity are found to be asymmetric for opposite directions. In certain cases, the breakdown can even be suppressed in one or both directions. Topological constraint requires a vortex-antivortex pair mediated breakdown, contrary to the single (anti)vortex in flat strips. This results in a higher breakdown velocity.
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75.75.-c Magnetic properties of nanostructures
61.46.Fg Nanotubes
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Electronic band gaps and transport in aperiodic graphene superlattices of Thue-Morse sequence

Tianxing Ma, Chun Liang, Li-Gang Wang, and Hai-Qing Lin

Appl. Phys. Lett. 100, 252402 (2012); http://dx.doi.org/10.1063/1.4729133 (4 pages) | Cited 7 times

Online Publication Date: 18 June 2012

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We have studied the electronic properties in aperiodic graphene superlattices of Thue-Morse sequence. Although the structure is aperiodic, an unusual Dirac point (DP) does exist and its location is exactly at the energy corresponding to the zero-averaged wave number (zero-math). Furthermore, the zero-math gap associated with the DP is robust against the lattice constants and the incident angles, and multi-DPs may appear under the suitable conditions. A resultant controllability of electronic transport in Thue-Morse sequence is predicted, which may facilitate the development of many graphene-based electronics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.22.Pr Electronic structure of graphene

Dimensionality effects on the magnetization reversal in narrow FePt nanowires

V. D. Nguyen, L. Vila, A. Marty, J. C. Pillet, L. Notin, C. Beigné, S. Pizzini, and J. P. Attané

Appl. Phys. Lett. 100, 252403 (2012); http://dx.doi.org/10.1063/1.4721672 (5 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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The magnetization reversal of 10 nm thick FePt nanowires has been studied for widths down to 30 nm. Above 500 nm, the magnetic domains grow within a dendritic structure. Below 300 nm, the reversal takes place by propagation of a single domain wall (DW), and the coercivity increases. Below 50 nm, the coercivity increase is such that a mix of nucleation and DW propagation appears. These results suggest that the reversal process is determined by the comparison of the wire dimensions with four characteristic lengths: the dendrite width, the disorder length, the mean edge roughness, and the nucleation distance.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
75.75.Cd Fabrication of magnetic nanostructures
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Effect of the interface resistance of CoFe/MgO contacts on spin accumulation in silicon

M. Ishikawa, H. Sugiyama, T. Inokuchi, K. Hamaya, and Y. Saito

Appl. Phys. Lett. 100, 252404 (2012); http://dx.doi.org/10.1063/1.4728117 (4 pages) | Cited 4 times

Online Publication Date: 18 June 2012

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We show direct evidence for importance of the interface resistance to electrically create large spin accumulation in silicon (Si). With increasing the thickness of the tunnel barrier in CoFe/MgO/n+-Si devices, a marked enhancement of spin accumulation signals can be observed in the electrical Hanle-effect measurements. To demonstrate room-temperature detection of the spin signals in three-terminal methods, the influence of the spin absorption from Si into CoFe through a tunnel barrier should be taken into account.
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85.30.-z Semiconductor devices

Magnetic anisotropy in ordered textured Co nanowires

L. G. Vivas, J. Escrig, D. G. Trabada, G. A. Badini-Confalonieri, and M. Vázquez

Appl. Phys. Lett. 100, 252405 (2012); http://dx.doi.org/10.1063/1.4729782 (4 pages) | Cited 6 times

Online Publication Date: 19 June 2012

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The magnetization reversal in ordered arrays of Co nanowires with tailored hcp-phase texture, controlled by pH synthesis and nanowires length, has been investigated. The angular dependence of coercivity has been experimentally determined for different crystal textures, and the corresponding magnetization reversal mode is interpreted by analytical modelling. The results show that reversal takes place by propagation of a transverse-like domain wall mode. The fitting of experimental and calculated data allows us the quantitative evaluation of the magnetocrystalline anisotropy constant strength whose magnetization easy direction evolves from parallel to the wires toward in-plane orientation with the change of hcp-phase texture.
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75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.75.Fk Domain structures in nanoparticles

Nondestructive two-dimensional phase imaging of embedded defects via on-chip spintronic sensor

Z. X. Cao, M. Harder, L. Fu, B. Zhang, W. Lu, G. E. Bridges, Y. S. Gui, and C.-M. Hu

Appl. Phys. Lett. 100, 252406 (2012); http://dx.doi.org/10.1063/1.4729785 (3 pages) | Cited 2 times

Online Publication Date: 19 June 2012

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A microwave near field phase imaging technique has been achieved by an on-chip spintronic sensor. The sensor directly rectifies a microwave field into a dc voltage signal by employing the spintronic principle, in which the relative phase between microwave electric and magnetic fields plays an important role. By manipulating the relative phase, the sensor can nondestructively detect embedded defects of subwavelength size.
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81.70.-q Methods of materials testing and analysis
61.72.-y Defects and impurities in crystals; microstructure

Synthesis, structure, and magnetic behavior of nanoparticles of cubic ZnMnO3

James D. Rall, S. Thota, J. Kumar, and M. S. Seehra

Appl. Phys. Lett. 100, 252407 (2012); http://dx.doi.org/10.1063/1.4729817 (4 pages) | Cited 3 times

Online Publication Date: 19 June 2012

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Synthesis and nature of magnetism in ZnMnO3 nanoparticles with cubic spinel structure (a = 8.369 Å and size D ≃ 25 nm) are reported. Magnetization M vs. H and M vs. T data yield ferrimagnetism with TN ≃ 20 K, μ/Mn = 4.46 μB, MS ≃ 18.5 emu/g, and a transition at TS ≃ 7 K. For T < TN, coercivity and exchange-bias approach zero at TN with anomaly at TS. Using magnetic data and simulations, structure of [Zn2+][Zn1/32+Mn2/33+Mn2/34+□1/3]O11/3 with antiparallel moments of Mn4+ and Mn3+ is proposed.
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75.75.Cd Fabrication of magnetic nanostructures
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Strain, spin disorder, and thickness dependence of magneto-transport in Sm0.55Sr0.45MnO3 films

M. M. Saber, M. Egilmez, F. Schoofs, O. Ofer, M. Månsson, J. W. A. Robinson, M. Blamire, K. H. Chow, and J. Jung

Appl. Phys. Lett. 100, 252408 (2012); http://dx.doi.org/10.1063/1.4728988 (5 pages) | Cited 2 times

Online Publication Date: 20 June 2012

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The correlation between the strain, spin disorder, and the thickness dependence of the magneto-transport has been investigated in as-grown and post-annealed 25-300-nm thick films of Sm0.55Sr0.45MnO3 (SSMO) deposited on SrTiO3 (STO) and LaAlO3 (LAO) substrates. In the post-annealed SSMO/LAO films, the epitaxial strain increases with a decreasing thickness; however, it is independent of the thickness of the post-annealed SSMO/STO films. In both cases, the reduction of the metal-insulator transition temperature with a decreasing thickness was observed. This behavior is attributed to an increasing compressive strain in the SSMO/LAO films and to spin disorder effects in the SSMO/STO ones.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth
71.30.+h Metal-insulator transitions and other electronic transitions

History dependence of directly observed magnetocaloric effects in (Mn, Fe)As

Milan Bratko, Kelly Morrison, Ariana de Campos, Sergio Gama, Lesley F. Cohen, and Karl G. Sandeman

Appl. Phys. Lett. 100, 252409 (2012); http://dx.doi.org/10.1063/1.4729893 (4 pages)

Online Publication Date: 20 June 2012

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We use a calorimetric technique operating in sweeping magnetic field to study the thermomagnetic history-dependence of the magnetocaloric effect (MCE) in Mn0.985Fe0.015As. We study the magnetization history for which a “colossal” MCE has been reported when inferred indirectly via a Maxwell relation. We observe no colossal effect in the direct calorimetric measurement. We further examine the impact of mixed-phase state on the MCE and show that the first order contribution scales linearly with the phase fraction. This validates various phase-fraction based methods developed to remove the colossal peak anomaly from Maxwell-based estimates.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.Pa Thermoelectric and thermomagnetic effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Ferromagnetism and manipulation of topological surface states in Bi2Se3 family by 2p light elements

Chengwang Niu, Ying Dai, Zhenkui Zhang, Yandong Ma, and Baibiao Huang

Appl. Phys. Lett. 100, 252410 (2012); http://dx.doi.org/10.1063/1.4729934 (5 pages) | Cited 2 times

Online Publication Date: 20 June 2012

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The manipulation effects by doping of 2p light elements X (X = B, C, and N) on topological surface states in V2VI3 (V = Bi and Sb, VI = Se and Te) are systemically explored. Our results unveil that X doping at anion sites can induce magnetic moments and gap opening at the Dirac point. To have a stable magnetic ground state, the dopant 2p states must be sufficiently localized, which closely depends on the X-V bond lengths. The incorporation of 2p dopants paves a promising way of tuning the properties of topological insulators and may find applications in spintronics.
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73.20.At Surface states, band structure, electron density of states
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.72.uf Ge and Si
71.20.Nr Semiconductor compounds

Vacancy mediated room temperature ferromagnetism in Co-doped Dy2O3

A. Bandyopadhyay, S. Sutradhar, B. J. Sarkar, A. K. Deb, and P. K. Chakrabarti

Appl. Phys. Lett. 100, 252411 (2012); http://dx.doi.org/10.1063/1.4729386 (5 pages) | Cited 1 time

Online Publication Date: 20 June 2012

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Nanoparticles of Co doped dysprosium oxide [Dy1.90Co0.10O3] were prepared by co-precipitating the precursor salts in presence of air and argon gas. Crystallographic phase and substitution of Co-ion in Dy2O3 were confirmed by Rietveld analysis of the x-ray diffraction patterns. Magnetic susceptibility and magnetization as a function of temperature and magnetic field were measured by Faraday and Superconducting quantum inteference device (SQUID) magnetometers, which showed that the sample synthesized in the inert atmosphere is ferromagnetic at room temperature. But no such effect has been observed in the other sample. This observation confirmed that vacancy mediated ferromagnetism can be introduced in the Co-doped dysprosium oxide.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.jd Vacancies

Bragg resonances of magnetostatic surface spin waves in a layered structure: Magnonic crystal-dielectric-metal

E. N. Beginin, Yu. A. Filimonov, E. S. Pavlov, S. L. Vysotskii, and S. A. Nikitov

Appl. Phys. Lett. 100, 252412 (2012); http://dx.doi.org/10.1063/1.4730374 (5 pages) | Cited 2 times

Online Publication Date: 21 June 2012

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It is experimentally shown that metal cladding of the surface of a one-dimensional magnonic crystal destroys the Bragg band gaps in microwave transmission spectra of propagating magnetostatic surface spin waves in magnonic crystal. This is a consequence of violating a phase synchronism condition of forward and reflected by a magnonic crystal magnetostatic surface wave. When a magnetostatic surface wave propagates in a layered structure, ferromagnetic film with a magnonic crystal-dielectric layer-metal cladding this synchronism condition can also be fulfilled, not depending on the thickness of a dielectric layer.
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75.30.Ds Spin waves
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Rf Surface magnetism
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.70.Gq Microwave and radio-frequency interactions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Reduced spin transfer torque switching current density with non-collinear polarizer layer magnetization in magnetic multilayer systems

Chun-Yeol You

Appl. Phys. Lett. 100, 252413 (2012); http://dx.doi.org/10.1063/1.4730376 (4 pages) | Cited 2 times

Online Publication Date: 22 June 2012

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Through micromagnetic simulations, it was found that the spin transfer torque (STT) switching current density is reduced with non-collinear polarizer layer magnetization. The dependence of the switching current density on the polarizer layer magnetization angle was investigated, and a typical magnetic tunneling junction structure with an exchange biased synthetic ferrimagnetic polarizer layers was considered. The easy axis of the polarizer layer was varied through controlling the exchange bias field direction in the ellipse cross-section nano-pillar structures. It was found that the switching current density was reduced by 39% when the exchange bias field was 10° from the long axis of the ellipse without the perpendicular STT. When the effect of the perpendicular STT was included, the switching current reductions were general for the non-collinear polarizer layer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
75.78.Cd Micromagnetic simulations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Exciton and carrier spin relaxations in InGaAs lattice-matched to off-cut Ge substrates

Takenori Ushimi, Hiromi Nakata, Toshihiro Ishizuka, Kazutoshi Sasayama, Shulong Lu, Jianrong Dong, and Atsushi Tackeuchi

Appl. Phys. Lett. 100, 252414 (2012); http://dx.doi.org/10.1063/1.4730386 (3 pages)

Online Publication Date: 22 June 2012

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We have investigated the exciton and carrier spin relaxations in InGaAs lattice-matched to Ge substrates. Time-resolved spin-dependent pump and probe reflectance measurements revealed a spin relaxation behavior between 10 and 300 K. The presence of the carrier density dependence of spin relaxation time at 10-200 K implies that the Bir-Aronov-Pikus process is effective. At 250-300 K, the strong temperature and weak carrier density dependences of spin relaxation time show that the D’yakonov-Perel’ process is dominant. The longest observed spin relaxation time of 2.6 ns at 77 K is explained by the decrease in the spatial overlap of electrons and holes.
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81.05.Ea III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.35.-y Excitons and related phenomena
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