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3 Oct 2005

Volume 87, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 87, 143902 (2005); http://dx.doi.org/10.1063/1.2077839 (3 pages)

Kaustubh D. Bhalerao, Edward Eteshola, Matthew Keener, and Stephen C. Lee
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Linear magnetic flux amplifier

D. S. Golubović and V. V. Moshchalkov

Appl. Phys. Lett. 87, 142501 (2005); http://dx.doi.org/10.1063/1.2077855 (3 pages) | Cited 5 times

Online Publication Date: 26 September 2005

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By measuring the critical current versus the applied magnetic field Ic(Φ) of an Al superconducting loop enclosing a soft Permalloy magnetic dot, we demonstrate that it is feasible to design a linear magnetic flux amplifier for applications in superconducting quantum interference devices. The selected dimensions of a single-domain Permalloy dot provide that the preferential orientation of the magnetization is rotated from the perpendicular direction. By increasing an applied magnetic field, the magnetization of the dot coherently rotates toward the out-of-plane direction, thus providing a flux gain and an enhancement of the sensitivity. As a result of a pronounced shape anisotropy, the flux gain generated by the dot can be tuned by adjusting the dimensions of the dot.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Spin-dependent tunneling spectroscopy in single-crystal Fe/MgO/Fe tunnel junctions

Y. Ando, T. Miyakoshi, M. Oogane, T. Miyazaki, H. Kubota, K. Ando, and S. Yuasa

Appl. Phys. Lett. 87, 142502 (2005); http://dx.doi.org/10.1063/1.2077861 (3 pages) | Cited 32 times

Online Publication Date: 27 September 2005

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We report a detailed spin-dependent tunneling spectroscopy in single-crystal Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs) that show a giant tunnel magnetoresistance effect. Spectra for antiparallel magnetic configurations show asymmetry because of extrinsic electron scatterings caused by structural defects at the barrier/electrode interfaces. Surprisingly, spectra for parallel magnetic configurations exhibit a complex oscillatory structure that has never been observed in conventional MTJs with an aluminum-oxide tunnel barrier. The complex spectra reflect the tunneling process via interface resonant states. These results provide some information that helps to elucidate the physics of spin-dependent electron tunneling and to further enhance magnetoresistance.
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75.47.De Giant magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Ultrafast direct writing scheme with unipolar field pulses for synthetic antiferromagnetic magnetic random access memory cells

H. T. Nembach, C. Bayer, H. Schultheiss, M. C. Weber, P. Martin Pimentel, P. A. Beck, B. Leven, and B. Hillebrands

Appl. Phys. Lett. 87, 142503 (2005); http://dx.doi.org/10.1063/1.2043236 (3 pages) | Cited 5 times

Online Publication Date: 27 September 2005

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A writing scheme is presented for Savtchenko-type magnetic random access memory (MRAM) cells, which allows for ultrafast direct writing with high stability against half select switching, using two orthogonally oriented unipolar magnetic field pulses with time delay, which allows for backswitching by reversing the temporal sequence of the two pulses. The numerical simulations are based on the Stoner–Wohlfarth model and a Runge Kutta integration of the Landau–Lifshitz and Gilbert equation.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
84.30.Sk Pulse and digital circuits

Ferromagnetism of MnO and Mn3O4 nanowires

Chan Woong Na, Doo Suk Han, Dae Sung Kim, Jeunghee Park, Yoon Tae Jeon, Gangho Lee, and Myung-Hwa Jung

Appl. Phys. Lett. 87, 142504 (2005); http://dx.doi.org/10.1063/1.2061849 (3 pages) | Cited 18 times

Online Publication Date: 27 September 2005

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Mixture of single-crystalline MnO and Mn3O4 nanowires was synthesized by thermal evaporation of MnCl2 powders. The diameter is 50–100 nm, the length is about 20 μm, and the growth direction is uniformly [100] for both cubic MnO and tetragonal Mn3O4 nanowires. The temperature-dependent magnetization and magnetic hysteresis curves suggest the Curie temperature of 12 and 43 K for the MnO and Mn3O4 nanowires, respectively.
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75.50.Dd Nonmetallic ferromagnetic materials
81.07.Bc Nanocrystalline materials
68.65.La Quantum wires (patterned in quantum wells)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.-w Structure of nanoscale materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
61.66.Fn Inorganic compounds

Spin-glass behavior in CeCu2-type uranium compound U2AuGa3

D. X. Li, T. Yamamura, S. Nimori, K. Yubuta, and Y. Shiokawa

Appl. Phys. Lett. 87, 142505 (2005); http://dx.doi.org/10.1063/1.2081130 (3 pages) | Cited 6 times

Online Publication Date: 27 September 2005

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We present the results of ac and dc susceptibility, magnetization, magnetic relaxation, specific heat, and electrical resistivity measurements on U2AuGa3, an orthorhombic CeCu2-type nonmagnetic atom disorder system. These data clearly indicate that U2AuGa3 undergoes a spin glass phase transition at a static freezing temperature Ts = 23.6 K, in spite of the lack of triangular magnetic structure. It is observed that the variation of the characteristic temperature Tir (the bifurcation point between field-cooled and zero-field-cooled susceptibilities) with applied field H for U2AuGa3 is not consistent with the “AT line,” but follows a Tir∝−H2/5 law. The observed spin glass behavior and the formation of frustrated magnetic interactions in U2AuGa3 are discussed in a magnetic cluster model.
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75.50.Lk Spin glasses and other random magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Superconducting NbSe2 nanowires and nanoribbons converted from NbSe3 nanostructures

Y. S. Hor, U. Welp, Y. Ito, Z. L. Xiao, U. Patel, J. F. Mitchell, W. K. Kwok, and G. W. Crabtree

Appl. Phys. Lett. 87, 142506 (2005); http://dx.doi.org/10.1063/1.2072847 (3 pages) | Cited 11 times

Online Publication Date: 27 September 2005

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We describe the synthesis of superconducting NbSe2 nanowires and nanoribbons by the nondestructive removal of Se from one-dimensional NbSe3 nanostructure precursors. We report scanning electron microscopy imaging, x-ray diffraction, and transmission electron microscopy analyses of the morphology, composition, and crystallinity of the converted NbSe2 nanostructures. Transport measurements on individual nanowires/ribbons confirm their superconductivity with Tc ∼ 7.2 K, and the appearance of current-induced resistance steps is attributed to localized phase slip centers, akin to those reported in other superconducting nanostructures.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.10.+v Occurrence, potential candidates
68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials

Magnetic domain structure of wires studied by using the magneto-optical indicator film method

Yu. Kabanov, A. Zhukov, V. Zhukova, and J. Gonzalez

Appl. Phys. Lett. 87, 142507 (2005); http://dx.doi.org/10.1063/1.2077854 (3 pages) | Cited 12 times

Online Publication Date: 28 September 2005

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Experimental studies of the magnetic domain structure of amorphous wires with positive (Fe-rich) and negative (Co-rich) magnetostriction by using the magneto-optical indicator film method have been performed. The following main results have been obtained. (i) Fe-rich wires possess unclosed 180° surface domain structures with magnetization perpendicular to the wire surface, i.e., without closure domains previously assumed for such materials. Such results have been attributed to the large magnetolastic anisotropy induced by the fabrication process. (ii) Domain structures of Co-rich wires consist of rather big (as-compared with Fe-rich wires) circular domains.
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75.60.Ch Domain walls and domain structure
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy

Structural, magnetic, and electronic properties of (110)-oriented epitaxial thin films of the bilayer manganite La1.2Sr1.8Mn2O7

Yayoi Takamura, Jostein K. Grepstad, Rajesh V. Chopdekar, Yuri Suzuki, Ann F. Marshall, Hong Zheng, and John F. Mitchell

Appl. Phys. Lett. 87, 142508 (2005); http://dx.doi.org/10.1063/1.2077850 (3 pages) | Cited 5 times

Online Publication Date: 28 September 2005

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We have synthesized (110)-oriented epitaxial thin films of the bilayer (n = 2) manganite, La1.2Sr1.8Mn2O7, with the metallic/ferromagnetic a-b planes lying perpendicular to the substrate surface and the c-axis aligned in the plane of the film. X-ray diffraction and transmission electron microscopy confirm the alignment of the a-b planes along the [1math0] substrate direction. The films consist primarily of the n = 2 phase with a minor component of the n = 1 (La,Sr)2MnO4 and n = ∞ (La,Sr)MnO3 phases. A resistivity maximum coincides with a ferromagnet/paramagnet transition at a reduced Tc ∼ 90 K (versus 120 K for bulk), indicative of the effects of epitaxial strain. The films display similar anisotropic properties to their bulk counterpart with the magnetically easy direction confined to the a-b planes and 20–200 times lower resistivity for current flowing along the a-b planes compared to the c-axis.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Lp Transmission electron microscopy (TEM)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.-a Thin film structure and morphology

Huge magnetoresistance in ultrathin La0.7Ca0.3MnO3 films: The role of superparamagnetic clusters and domain walls

J. M. Colino and A. de Andrés

Appl. Phys. Lett. 87, 142509 (2005); http://dx.doi.org/10.1063/1.2081139 (3 pages) | Cited 7 times

Online Publication Date: 30 September 2005

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The magnetic behavior of epitaxial La0.7Ca0.3MnO3 (LCMO) films grown on SrTiO3, with thickness down to 2.4 nm, has been analyzed and correlated to the magnetoresistance (MR). Below about 10 nm the canonical ferromagnetic order switches to a distribution of superparamagnetic clusters. These ultrathin films show a huge MR (4000%) at Tc and, at 5 K, the MR is 300 times that of the ferromagnetic films’ value. Metallic conductivity is observed below Tc down to the blocking temperature (TB ≈ 65 K) but a strong upturn appears below TB. These findings can be explained by the ordering of uncoupled superparamagnetic clusters and their blocking at lower temperature, together with the collapse of the magnetic domain walls which are substituted by very small Mn magnetic clusters (few Mn) probably localized at the structural domain boundaries.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
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)
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
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