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6 Oct 2008

Volume 93, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 93, 141901 (2008); http://dx.doi.org/10.1063/1.2990662 (3 pages)

J. H. Han, K. B. Kim, S. Yi, J. M. Park, S. W. Sohn, T. E. Kim, D. H. Kim, J. Das, and J. Eckert
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Frequency modulation effect on microwave assisted magnetization switching

S. Okamoto, N. Kikuchi, and O. Kitakami

Appl. Phys. Lett. 93, 142501 (2008); http://dx.doi.org/10.1063/1.2996573 (3 pages) | Cited 10 times

Online Publication Date: 6 October 2008

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Frequency modulation (FM) effect on the microwave assisted switching (MAS) of magnetization has been studied by calculating the Landau–Lifshitz–Gilbert equation. Application of FM microwave can significantly reduce the switching field compared with constant frequency wave, mainly due to more effective microwave energy absorption by the spin system. The FM effect on the MAS is remarkable especially for smaller Gilbert damping of α ⩽ 0.02. For sufficient switching probability, the FM-MAS requires somewhat longer time of a few nanoseconds for the dc magnetic field parallel to the easy axis. The tilt dc field can effectively reduce the switching time.
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75.60.Jk Magnetization reversal mechanisms
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Spatial distribution of manganese and room temperature ferromagnetism in manganese-doped ZnO nanorods

H. L. Yan, J. B. Wang, X. L. Zhong, and Y. C. Zhou

Appl. Phys. Lett. 93, 142502 (2008); http://dx.doi.org/10.1063/1.2993354 (3 pages) | Cited 11 times

Online Publication Date: 6 October 2008

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Monochromatic cathodoluminescence image of Mn-doped ZnO nanorods shows that Mn elements are mainly distributed on the surface of nanorods. The intensity of ultraviolet luminescence decreases with the increment in Mn-doped concentration. Mn-doped ZnO nanorods exhibit a room temperature ferromagnetic characteristic with a saturation magnetization (MS) of 0.39 μB/Mn and a coercive field of 50 Oe.
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78.60.Hk Cathodoluminescence, ionoluminescence
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Subterahertz excitations and magnetoelectric effects in hexaferrite-piezoelectric bilayers

Alexey B. Ustinov and G. Srinivasan

Appl. Phys. Lett. 93, 142503 (2008); http://dx.doi.org/10.1063/1.2996585 (3 pages) | Cited 5 times

Online Publication Date: 7 October 2008

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A frequency-agile hexaferrite-piezoelectric composite for potential device applications at subterahertz frequencies is studied. The bilayer is composed of aluminum substituted barium hexagonal ferrite (BaAl2Fe10O19) and lead zirconate titanate (PZT). A dc electric field applied to PZT results in mechanical deformation of the ferrite, leading to a frequency shift in ferromagnetic resonance. The bilayer demonstrates magnetoelectric interaction coefficient of about 0.37 Oe cm/kV.
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77.65.-j Piezoelectricity and electromechanical effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.50.Gg Ferrimagnetics

Phase field modeling of magnetization processes in growth twinned Terfenol-D crystals

Yongxin Y. Huang and Yongmei M. Jin

Appl. Phys. Lett. 93, 142504 (2008); http://dx.doi.org/10.1063/1.2996586 (3 pages) | Cited 8 times

Online Publication Date: 8 October 2008

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Phase field micromagnetic microelastic modeling is used to simulate magnetization processes in growth twinned Terfenol-D crystals under external magnetic field applied along the [11math] growth direction. The simulations reveal complex domain microstructure evolution involving both magnetization rotation and domain wall motion. It is found that domains strongly interact across the (111) growth twin boundaries. The competitions among magnetostatic, elastic, and magnetocrystalline anisotropy energies are analyzed, which explains the underlying domain mechanisms responsible for the experimentally observed magnetostriction jump effect in growth twinned Terfenol-D crystals.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.72.Mm Grain and twin boundaries
75.60.Ch Domain walls and domain structure
75.80.+q Magnetomechanical effects, magnetostriction

Ferromagnetic resonance signature of metallic Co clusters in ferromagnetic ZnCoO thin films

H. J. von Bardeleben, N. Jedrecy, and J. L. Cantin

Appl. Phys. Lett. 93, 142505 (2008); http://dx.doi.org/10.1063/1.2998309 (3 pages) | Cited 5 times

Online Publication Date: 8 October 2008

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Highly Co-doped Zn0.7Co0.3O thin films that can be reproducibly grown ferromagnetic by pulsed laser deposition have been investigated by optical absorption and ferromagnetic resonance spectroscopy (FMR). The saturation magnetization depends strongly on the O2 content during the growth, the highest value being obtained for the lowest oxygen pressure conditions. Whereas the optical absorption spectra confirm the incorporation of Co as CoZn2+ in ZnO, the FMR spectra prove the additional presence of randomly oriented metallic Co nanoparticles. The angular variation in the FMR spectra allows us to determine in the most ferromagnetic film the effective magnetization, 4πM ∼ 800 G at 300 K and the g factor, g = 2.18, which is that of metallic Co. The fraction of the two species CoZn2+ and Co metal is estimated to be ∼ 3:1
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Fishtail effect and the vortex phase diagram of single crystal Ba0.6K0.4Fe2As2

Huan Yang, Huiqian Luo, Zhaosheng Wang, and Hai-Hu Wen

Appl. Phys. Lett. 93, 142506 (2008); http://dx.doi.org/10.1063/1.2996576 (3 pages) | Cited 39 times

Online Publication Date: 9 October 2008

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By measuring the magnetization hysteresis loops of superconducting Ba0.6K0.4Fe2As2 single crystals, we obtained the high upper critical field and large current carrying ability, which point to optimistic applications. The fishtail (or second peak) effect is also found in the material, and the position of the vortex pinning force shows a maximum at 1/3 of the reduced field, being consistent with the picture of vortex pinning by small size normal cores in the sample. Together with the resistive measurements, for the first time the vortex phase diagram is obtained for superconductor Ba0.6K0.4Fe2As2.
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74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Dw Superconductivity phase diagrams
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)

Room temperature anomalous Hall effect in Co doped ZnO thin films in the semiconductor regime

H. S. Hsu, C. P. Lin, H. Chou, and J. C. A. Huang

Appl. Phys. Lett. 93, 142507 (2008); http://dx.doi.org/10.1063/1.3000015 (3 pages) | Cited 8 times

Online Publication Date: 10 October 2008

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Observation of the room temperature (RT) anomalous Hall effect (AHE) and ferromagnetism in semiconducting like (carrier concentration ∼ 1019 cm−3) Co-doped ZnO samples is reported. These small AHE signals match quantitatively with the magnetic hysteresis and can be correspondent to the intrinsic diluted magnetic oxide (DMO) effect with spin polarized carriers. The contribution to the DMO effect depends on the types of carriers and how they incorporated into the electric conduction, magnetic coupling, and the coupling between them. These findings can provide useful information in the study of the origin of RT ferromagnetism in ZnO-based DMO and for further application in spintronics.
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68.55.ag Semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport

Current controlled random-access memory based on magnetic vortex handedness

Stellan Bohlens, Benjamin Krüger, André Drews, Markus Bolte, Guido Meier, and Daniela Pfannkuche

Appl. Phys. Lett. 93, 142508 (2008); http://dx.doi.org/10.1063/1.2998584 (3 pages) | Cited 37 times

Online Publication Date: 10 October 2008

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The theoretical foundation for a nonvolatile memory device based on magnetic vortices is presented. We propose a realization of a vortex random-access memory (VRAM) containing vortex cells that are controlled by alternating currents only. The proposed scheme allows to transfer the vortex into an unambiguous binary state regardless of its initial state within a subnanosecond time scale. The vortex handedness defined as the product of chirality and polarization as a bit representation allows direct mechanisms for reading and writing the bit information. The VRAM is stable at room temperature.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
84.30.Sk Pulse and digital circuits

C-axis persistent current and Cooper-pair tunneling through intrinsic Josephson junctions in a ring-shaped YBa2Cu3O7−δ film

A. I. Mansour, M. M. Saber, K. H. Chow, and J. Jung

Appl. Phys. Lett. 93, 142509 (2008); http://dx.doi.org/10.1063/1.2999627 (3 pages) | Cited 2 times

Online Publication Date: 10 October 2008

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We report the direct experimental observation of the temperature dependence of the persistent current Icj due to tunneling Cooper pairs along the c-axis intrinsic Josephson junctions integrated into YBa2Cu3O7−δ ring-shaped thin films. The measured Icj exhibits a linear temperature dependence over a wide range of temperatures well below Tc. Similar behavior was observed in different samples, confirming the reproducibility of the fabrication technique and the reliability of the results.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Large magnetic circular dichroism of Co clusters in Co-doped ZnO

Y. Fukuma, H. Asada, J. Yamamoto, F. Odawara, and T. Koyanagi

Appl. Phys. Lett. 93, 142510 (2008); http://dx.doi.org/10.1063/1.2992631 (3 pages) | Cited 4 times

Online Publication Date: 10 October 2008

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Large magnetic circular dichroism (MCD) in Co-doped ZnO films is reported. The Co-( ∼ 20%) doped ZnO films with oxygen deficiencies show ferromagnetic behavior at room temperature. While paramagnetic films exhibit a small MCD signal, broad MCD spectra with large amplitude of ∼ 20 kdeg/cm are observed for the ferromagnetic films. In the ferromagnetic films, Co cluster formation occurs, especially near the interface between the substrate and the film. The amount of the Co clusters is consistent with the spontaneous magnetization and the amplitude of the MCD.
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78.66.Hf II-VI semiconductors
78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals

Epitaxial growth of MgO and Fe/MgO/Fe magnetic tunnel junctions on (100)-Si by molecular beam epitaxy

G. X. Miao, J. Y. Chang, M. J. van Veenhuizen, K. Thiel, M. Seibt, G. Eilers, M. Münzenberg, and J. S. Moodera

Appl. Phys. Lett. 93, 142511 (2008); http://dx.doi.org/10.1063/1.2999633 (3 pages) | Cited 15 times

Online Publication Date: 10 October 2008

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Epitaxial growth of MgO barrier on Si is of technological importance due to the symmetry filtering effect of the MgO barrier in conjunction with bcc-ferromagnets. We study the epitaxial growth of MgO on (100)-Si by molecular beam epitaxy. MgO matches Si with 4:3 cell ratio, which renders Fe to be 45° rotated relative to Si, in sharp contrast to the direct epitaxial growth of Fe on Si. The compressive strains from Si lead to the formation of small angle grain boundaries in MgO below 5 nm, and also affect the transport characteristics of Fe/MgO/Fe magnetic tunnel junctions formed on top.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties
61.72.Mm Grain and twin boundaries
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