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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Superconducting π qubit with three Josephson junctions

T. Yamashita, S. Takahashi, and S. Maekawa

Appl. Phys. Lett. 88, 132501 (2006); http://dx.doi.org/10.1063/1.2189191 (3 pages) | Cited 14 times

Online Publication Date: 27 March 2006

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We propose a qubit consisting of a superconducting ring with two zero junctions and one ferromagnetic π junction. In the system, degenerate states appear in the phase space without an external magnetic field because of a competition between the zero and π states. Quantum tunneling between the degenerate states leads to a formation of bonding and antibonding states which are used as a bit. For manipulating the states, only a small magnetic field around zero is required. This feature leads to a large-scale integration and a construction of the smaller-sized qubit which is robust to the decoherence by external noises.
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03.67.Lx Quantum computation architectures and implementations
74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices

Investigations on electroresistance effect in epitaxial manganite films using field effect configurations

F. X. Hu and J. Gao

Appl. Phys. Lett. 88, 132502 (2006); http://dx.doi.org/10.1063/1.2189197 (3 pages) | Cited 15 times

Online Publication Date: 27 March 2006

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The influence of static electric field on the transport properties in La0.7A0.3MnO3 (A = Ca,Ba) epitaxial thin films was investigated by using field effect configurations (FEC). A single layer manganite film was deposited on LaAlO3 (LAO) substrate by pulsed laser deposition technique, and then a simple FEC was formed on it using the lithography technique, in which the manganite film was used as a channel, and the LAO substrate as a gate. Surprising results were achieved by employing such a FEC. The transport resistance increases with a positive gate voltage but decreases with a negative bias, which means the electroresistance (ER) effect changes sign with the field direction. The observed reduction of resistivity for the La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 channels reaches ∼ 32% and ∼ 34% upon a bias of −80  and −300 V, respectively. The films could completely return to their pristine state after the bias was removed and the ER effect could be fully reproduced.
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73.61.-r Electrical properties of specific thin films
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Magnetocaloric effect in Ni–Fe–Ga shape memory alloys

V. Recarte, J. I. Pérez-Landazábal, C. Gómez-Polo, E. Cesari, and J. Dutkiewicz

Appl. Phys. Lett. 88, 132503 (2006); http://dx.doi.org/10.1063/1.2189665 (3 pages) | Cited 22 times

Online Publication Date: 27 March 2006

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The magnetic entropy change in three different polycrystalline Ni53+xFe20−xGa27 (x = 0.5,1,2) alloys was analyzed as a function of temperature under different applied magnetic fields. The temperature dependence of the ac magnetic susceptibility (χ) and the magnetization of the alloys have been used to characterize the different structural and magnetic transformations. In spite of the different magnetic states, the alloys show comparable magnetic entropy values. For x ⩽ 1 the martensitic transformation takes place in the ferromagnetic state for measuring temperatures below room temperature, whereas the alloy with x = 2 displays the martensitic transformation above room temperature between two paramagnetic phases. Maximum values of the magnetic entropy change are correlated with the martensitic transformation, irrespective of the particular magnetic state (ferromagnetic or paramagnetic) during the transformation.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Bb Fe and its alloys
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Large magnetic anisotropy in the quasi-one-dimensional system BaCo2V2O8

Zhangzhen He, Tomoyasu Taniyama, and Mitsuru Itoh

Appl. Phys. Lett. 88, 132504 (2006); http://dx.doi.org/10.1063/1.2189913 (3 pages) | Cited 10 times

Online Publication Date: 27 March 2006

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Magnetic anisotropy in the one-dimensional spin chain system BaCo2V2O8 is investigated using magnetic susceptibility, magnetization, and heat capacity measurements. Unusual magnetic anisotropy is observed in the paramagnetic state at room temperature. The magnetic anisotropy energy of BaCo2V2O8 is estimated to be greater than 1.44(4)×107 erg/cm3 at 2 K using a simple uniaxial two-sublattice mean-field model.
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75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.20.Ck Nonmetals
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Observation of field-induced reverse transformation in ferromagnetic shape memory alloy Ni50Mn36Sn14

Keiichi Koyama, Kazuo Watanabe, Takeshi Kanomata, Ryosuke Kainuma, Katsunari Oikawa, and Kiyohito Ishida

Appl. Phys. Lett. 88, 132505 (2006); http://dx.doi.org/10.1063/1.2189916 (3 pages) | Cited 71 times

Online Publication Date: 27 March 2006

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The structural and magnetic properties of the ferromagnetic Heusler alloy Ni50Mn36Sn14 were studied by magnetization and x-ray powder diffraction measurements in fields up to 5 T. The alloy undergoes the martensitic transformation from the L21-type cubic structure with the lattice parameter ac = 0.5988 nm into an orthorhombic structure with the lattice parameters ao = 0.8617 nm, bo = 0.5702 nm and co = 0.4359 nm at Ms = 220 K with a thermal hysteresis of 40 K. The cell volume contracts by 0.37% and the magnetic moment decreases by 50% at Ms. Furthermore, we directly observed the field-induced reverse martensitic transformation.
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64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Micromagnetic investigation of the dynamics of magnetization switching induced by a spin polarized current

Kyung-Jin Lee and Bernard Dieny

Appl. Phys. Lett. 88, 132506 (2006); http://dx.doi.org/10.1063/1.2190450 (3 pages) | Cited 17 times

Online Publication Date: 27 March 2006

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Using micromagnetic modeling, we tested a prediction of single-domain spin-torque theory which switching current density depends only weakly on magnetic cell size. The switching time and current density are strongly affected by the cell size for low spin polarization. Larger samples with a small length-to-width ratio and small spin polarization can exhibit a nonmonotonous dependence of switching time on current. Excitation of incoherent spin waves caused by the circular Oersted field due to the current is responsible for this nonmonotonous dependence. However, the magnetic dynamics recovers a single-domain-like behavior when the spin polarization is high and/or the cell size is small.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport

Room-temperature ferromagnetism in Mn and Fe codoped In2O3

G. Peleckis, X. L. Wang, and S. X. Dou

Appl. Phys. Lett. 88, 132507 (2006); http://dx.doi.org/10.1063/1.2191093 (3 pages) | Cited 44 times

Online Publication Date: 28 March 2006

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The synthesis and characterization of polycrystalline room-temperature ferromagnetic semiconductor (In0.9Fe0.1−xMnx)2O3 (x = 0–0.1) oxide are reported. All of the samples with intermediate x values are ferromagnetic at room temperature. The highest saturation magnetization moment at 300 K per total amount of magnetic ion is reached in the (In0.9Fe0.04Mn0.06)2O3 sample. The lattice constant a increases linearly with increasing Mn content. Fe-only doped samples were paramagnetic, while a Mn-only doped sample was found to be ferromagnetic below TC = 46 K.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.20.Ck Nonmetals

Grain and grain-boundary critical currents in coated conductors with noncorrelating YBa2Cu3O7 and substrate grain-boundary networks

A. Palau, T. Puig, X. Obradors, R. Feenstra, A. A. Gapud, E. D. Specht, D. M. Feldmann, and T. G. Holesinger

Appl. Phys. Lett. 88, 132508 (2006); http://dx.doi.org/10.1063/1.2172737 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2006

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The superconducting grain-boundary (GB) network of coated conductors (CCs) is usually assumed to be a replica of the substrate network. In this letter, we analyze IBAD and RABITS CCs, where such replica either do or do not exist. We have analyzed the effect of GB overgrowth on the critical currents by quantifying the average superconducting grain size and determining the intragrain and grain-boundary critical current densities, JcG and JcGB. We have employed a recently developed inductive methodology enabling the simultaneous determination of these three parameters. We show that the percolative JcGB may be reduced by 50% if the GB networks do not correlate, while JcG and the grain pinning properties appear unaffected.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
61.72.Mm Grain and twin boundaries

Influence of Co addition on the magnetocaloric effect of FeCoSiAlGaPCB amorphous alloys

V. Franco, J. M. Borrego, A. Conde, and S. Roth

Appl. Phys. Lett. 88, 132509 (2006); http://dx.doi.org/10.1063/1.2188385 (3 pages) | Cited 31 times

Online Publication Date: 28 March 2006

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The FeCoSiAlGaPCB alloys can be prepared as bulk amorphous materials, with outstanding mechanical properties and increased electrical resistivity. These features can be beneficial for their application as a magnetic refrigerant. The influence of Co addition on the magnetic entropy change of the alloy has been studied. This compositional modification displaces the temperature of the peak entropy change closer to room temperature, but reduces the refrigerant capacity of the material. For the Co-free alloy, the peak entropy change is increased with respect to a Finemet alloy containing Mo, but its refrigerant capacity is not enhanced.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
81.05.Bx Metals, semimetals, and alloys

Transport properties of low angle grain boundaries in Y1−xCaxBa2Cu3O7−δ films at high magnetic fields

A. Weber, C. W. Schneider, S. Hembacher, Ch. Schiller, S. Thiel, and J. Mannhart

Appl. Phys. Lett. 88, 132510 (2006); http://dx.doi.org/10.1063/1.2190460 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2006

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The critical current density of grain boundaries and grains in Y1−xCaxBa2Cu3O7−δ films has been measured in magnetic fields up to 10 T. As a function of temperature the critical current densities across 8° [001]-tilt boundaries display a maximum at ≈ 15–20 K for 0.04 ⩽ x ⩽ 0.2 and fields of several teslas. Opposite to the behavior of large angle grain boundaries, calcium doping is found not to enhance the critical current densities of low angle grain boundaries (θ ⩽ 8°).
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Enhanced and oscillatory magnetoresistance of thin Fe(001) films

C. Martinez-Boubeta, Ll. Balcells, and A. Cebollada

Appl. Phys. Lett. 88, 132511 (2006); http://dx.doi.org/10.1063/1.2191092 (3 pages) | Cited 4 times

Online Publication Date: 29 March 2006

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We have studied the magnetoresistance of single-crystalline (001) Fe films prepared by sputtering techniques and covered by epitaxial MgO or Pt protective layers. The influence of the thickness of the magnetic layer as well as of the nature of the capping layer on the Fe anisotropic magnetoresistance was investigated by four-terminal probe, measurements performed with the current J in the [110] magnetically hard direction. We found an enhancement in the magnetoresistance value with respect to bulk and oscillations in the high field regime in MgO covered Fe/MgO(001) ultrathin films. A plausible explanation is that the enhanced magnetoresistance is due to electronic confinement effects, not present in similar Pt/Fe/MgO(001) samples.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

First-principles calculations on magnetic properties of interface-rippled Co/α-Al2O3/Co

Chiho Kim and Yong-Chae Chung

Appl. Phys. Lett. 88, 132512 (2006); http://dx.doi.org/10.1063/1.2191408 (3 pages) | Cited 3 times

Online Publication Date: 31 March 2006

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The effects of the interface fluctuations on the magnetic properties of a Co/α-Al2O3/Co magnetic tunnel junction were intensively investigated using first-principles calculations. Hybridization of Co-3d and O-2p orbitals resulted in the covalent bonds between Co and three O atoms at the interface of Co(111)/α-Al2O3(0001) and, subsequently, interfacial Co atoms became undulated as much as 34.6% of the interlayer distance measured in the z direction. The magnetic moment of Co atoms at the rippled interface was enhanced to 1.95μB, while the value of the other ferromagnetic Co atoms remained unchanged. Significantly induced minority-spin density of states at the Fermi energy of the Co-interface atoms led to a highly negative spin polarization, −52.0%, at the junction interface. Interestingly, the spin polarization value for the barrier layer was in the range of −6.3%–59.2%.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Finite-temperature magnetism of tetragonal iron

Jian-Tao Wang, Ding-Sheng Wang, and Y. Kawazoe

Appl. Phys. Lett. 88, 132513 (2006); http://dx.doi.org/10.1063/1.2191469 (3 pages) | Cited 2 times

Online Publication Date: 31 March 2006

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Based on ab initio Monte Carlo approach, finite-temperature magnetism of tetragonal Fe is studied. It is shown that the ground state magnetic structure changes from ferromagnetic to antiferromagnetic as the structure transforms from bcc to fcc. The Curie temperature (TC) or Néel temperatures (TN) are very sensitive to the lattice distortion, which decreases from bcc to fcc and then increases over the fcc range. There are a maximum of TC at the bcc and a minimum of TN around the fcc limit due to the change of the coupling distance and symmetry consideration.
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75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
64.70.K- Solid-solid transitions
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