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17 Nov 2008

Volume 93, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 93, 201101 (2008); http://dx.doi.org/10.1063/1.3025818 (3 pages)

W. Dai and C. M. Soukoulis
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Structure and magnetic properties of bulk nanocrystalline Dy metal prepared by spark plasma sintering

M. Yue, K. J. Wang, W. Q. Liu, D. T. Zhang, and J. X. Zhang

Appl. Phys. Lett. 93, 202501 (2008); http://dx.doi.org/10.1063/1.3003863 (3 pages) | Cited 4 times

Online Publication Date: 17 November 2008

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The structure and magnetic properties were studied for bulk nanocrystalline dysprosium (Dy) metal prepared by spark plasma sintering method. All the as-prepared samples have hexagonal close packed structure. A decrease in grain size results in remarkable changes in magnetic ordering temperature of the nanocrystalline Dy metal. At 5 K, the magnetization drops by 3.35%, and the coercive force increases by three times for nanocrystalline Dy compared to those of coarse-grained bulk Dy sample. These results indicate the remarkable influence of the nanostructure on the magnetism of Dy due to finite size effect.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
81.16.-c Methods of micro- and nanofabrication and processing
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Giant reversible magnetocaloric effect in cobalt hydroxide nanoparticles

X. H. Liu, W. Liu, W. J. Hu, S. Guo, X. K. Lv, W. B. Cui, X. G. Zhao, and Z. D. Zhang

Appl. Phys. Lett. 93, 202502 (2008); http://dx.doi.org/10.1063/1.3028337 (3 pages) | Cited 6 times

Online Publication Date: 17 November 2008

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The magnetocaloric effect associated with magnetic phase transitions in β-Co(OH)2 nanoparticles has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a field-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature. The large reversible magnetic-entropy change −ΔSm (20.9 J/kg K at 15 K for a field change of 7 T) indicates that β-Co(OH)2 is a potential candidate for application in magnetic refrigeration in the low-temperature range.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Mössbauer studies on structural ordering and magnetic properties of melt-spun Ni–Fe–Ga ribbons

N. V. Rama Rao, R. Gopalan, M. Manivel Raja, V. Chandrasekaran, and K. G. Suresh

Appl. Phys. Lett. 93, 202503 (2008); http://dx.doi.org/10.1063/1.3028342 (3 pages) | Cited 1 time

Online Publication Date: 18 November 2008

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Ribbons of ferromagnetic shape memory Ni2+xFe1−xGa (x = 0 and 0.12) alloys were prepared at wheel speeds of 12 and 35 m/s by melt spinning technique. The structural (site) disorder and the associated changes in the magnetic properties of the ribbons were investigated by 57Fe Mössbauer spectroscopy and magnetization measurements respectively. Mössbauer spectra of Ni2FeGa ribbon revealed the presence of both L21 order and B2-like disorder with some amount of Fe antisite atoms on Ni site. The increase in Ni content was found to decrease the TC while its effect on TM was the opposite way.
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76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.50.Bb Fe and its alloys
61.72.-y Defects and impurities in crystals; microstructure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced Jahn–Teller distortion in the orthorhombic phase of La0.15Ca0.85MnO3 and Y0.15Ca0.85MnO3

P. Tong, Bongju Kim, Daeyoung Kwon, Bog G. Kim, G. Y. Ahn, J. M. S. Park, Sung Baek Kim, and S-W. Cheong

Appl. Phys. Lett. 93, 202504 (2008); http://dx.doi.org/10.1063/1.3035249 (3 pages) | Cited 2 times

Online Publication Date: 19 November 2008

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We report the results of neutron powder diffraction experiments on La0.15Ca0.85MnO3 and Y0.15Ca0.85MnO3. After an incomplete orthorhombic-monoclinic phase transition, the residual orthorhombic phase undergoes an enhancement of Jahn–Teller distortion of MnO6 octahedra. The degree of Jahn–Teller distortion is strongly influenced by coexisting monoclinic phase. Furthermore, ferromagnetism is closely associated with this Jahn–Teller distortion, rather than the buckling effect in the orthorhombic phase. Despite the low concentration of Jahn–Teller active Mn3+ ions, our result indicates an important role of Jahn–Teller effect on physical properties of the lightly electron-doped manganites.
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64.70.K- Solid-solid transitions
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.40.Lm Deformation, plasticity, and creep
62.20.mq Buckling
72.80.Sk Insulators
75.47.Lx Magnetic oxides

Direct observation of changes to domain wall structures in magnetic nanowires of varying width

K. J. O’Shea, S. McVitie, J. N. Chapman, and J. M. R. Weaver

Appl. Phys. Lett. 93, 202505 (2008); http://dx.doi.org/10.1063/1.3023048 (3 pages) | Cited 11 times

Online Publication Date: 20 November 2008

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Lorentz microscopy has been used to explore the structure variation of domain walls in thin Permalloy nanowires in the vicinity of symmetric triangular antinotches. The antinotches present a complex potential landscape to domain walls. Walls can be trapped in front of, partly enter, or be trapped inside the antinotches according to the geometry of the latter and, in the case of vortex domain walls, the chirality. In all cases, the magnetization distribution was determined. Of particular note was the structure the wall assumed during depinning from the antinotch, complex forms extending over distances several times the wire width being observed.
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75.60.Ch Domain walls and domain structure
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)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Coherent manipulation of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As with successive optical pumping

Y. Hashimoto and H. Munekata

Appl. Phys. Lett. 93, 202506 (2008); http://dx.doi.org/10.1063/1.3030988 (3 pages) | Cited 12 times

Online Publication Date: 20 November 2008

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We report the dynamic control of magnetization precession by light alone. A ferromagnetic (Ga,Mn)As epilayer was used for experiments. Amplitude of precession was modulated to a large extent by tuning the time interval between two successive optical pump pulses, which induced torques on magnetization through a nonthermal process. Nonlinear effect in precession motion was also discussed.
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75.50.Pp Magnetic semiconductors
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds
75.50.Dd Nonmetallic ferromagnetic materials

Bloch-point-mediated magnetic antivortex core reversal triggered by sudden excitation of a suprathreshold spin-polarized current

X. J. Xing, Y. P. Yu, S. X. Wu, L. M. Xu, and S. W. Li

Appl. Phys. Lett. 93, 202507 (2008); http://dx.doi.org/10.1063/1.3033400 (3 pages) | Cited 3 times

Online Publication Date: 20 November 2008

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We report on spin dynamics of single magnetic antivortices driven by sudden excitation of a spin-polarized direct current. Using micromagnetic simulations, we find that there is a critical current density where spin dynamics transition occurs. Above the critical value, the core is switched on a time scale of ∼ 200 ps through two Bloch points injection after fully suppressed by a quadruple-vortices array, not through the well-known process involving an antivortex-vortex pair creation and annihilation. As the current density decreases, the time required to switch the core increases. The state after full relaxation depends on the current density (the excitation parameter).
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Ds Spin waves
75.60.Jk Magnetization reversal mechanisms
72.25.Hg Electrical injection of spin polarized carriers
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