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17 Jun 2002

Volume 80, Issue 24, pp. 4483-4665

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Large low-field magnetoresistance and TC in polycrystalline (Ba0.8Sr0.2)2−xLaxFeMoO6 double perovskites

D. Serrate, J. M. De Teresa, J. Blasco, M. R. Ibarra, L. Morellón, and C. Ritter

Appl. Phys. Lett. 80, 4573 (2002); http://dx.doi.org/10.1063/1.1485119 (3 pages) | Cited 48 times

Online Publication Date: 10 June 2002

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Large low-field magnetoresistance (LFMR) together with high Curie temperatures (TC) are requirements for some applications in magnetoelectronics. In order to optimize both parameters, we have investigated double perovskites (Ba0.8Sr0.2)2−xLaxFeMoO6 (0 ⩽ x ⩽ 0.4). High-temperature neutron diffraction measurements indicate a strong increase in TC with La doping (from ≈345 K for x = 0 to ≈405 K for x = 0.4). The LFMR is very large for x = 0 (at 10 KOe ≈ 27% at 10 K and ≈7% at 290 K) and decreases with La doping. This decrease cannot be attributed to a substantial enhancement of Fe/Mo antisite disorder, which is small as tracked by means of x-ray and high-resolution neutron diffraction, but to grain boundaries modifications. © 2002 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Mm Grain and twin boundaries

Orthogonal pinning of two ferromagnetic layers in a synthetic spin valve

Robert S. Beach, Jeffrey McCord, Patrick Webb, and Daniele Mauri

Appl. Phys. Lett. 80, 4576 (2002); http://dx.doi.org/10.1063/1.1485106 (3 pages) | Cited 5 times

Online Publication Date: 10 June 2002

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A method for pinning synthetic antiferromagnet (SAF) based spin valves is presented, which allows pinning to be established perpendicular to the setting field H. As the SAF(AP1/Ru/AP2) magnetizes, its layer moments undergo a spin–flop transition for a magnetic field H = HSF and align with H for H = HSat. The magnetization of layer AP1 is perpendicular to H for a field H = HGold. This field corresponds to the maximum giant magnetoresistance GMR on HSF<H<HSat for an unpinned SAF spin valve. SAF-pinned samples [antiferromagnet/AP1/Ru/AP2] set using H = HGold are mixed domain, with AP1 magnetized in two directions perpendicular to H, corresponding to left- and right-handed flopping. The spin–flop handedness may be controlled for a viable process. The technique offers substantial advantages to sensor stabilization schemes that rely on additional pinned ferromagnet/antiferromagnet layers, because these layers may be pinned orthogonal to the SAF without regard to the blocking temperatures of the respective antiferromagnets. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Mg Numerical simulation studies
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.75.-c Magnetic properties of nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced transparency ramp-type Josephson contacts through interlayer deposition

Henk-Jan H. Smilde, Hans Hilgenkamp, Guus Rijnders, Horst Rogalla, and Dave H. A. Blank

Appl. Phys. Lett. 80, 4579 (2002); http://dx.doi.org/10.1063/1.1485305 (3 pages) | Cited 23 times

Online Publication Date: 10 June 2002

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A thin interlayer is incorporated in ramp-type Josephson junctions to obtain an increased transparency. The interlayer restores the surface damaged by ion milling and has the advantage of an all in situ barrier deposition between two superconductors, leading to clean and well-defined interfaces. The method has been applied to Josephson junctions between high (YBa2Cu3O7−δ) and low temperature (Nb) superconductors, separated by a Au barrier. Transmission electron microscopy images of these junctions reveal crystalline YBa2Cu3O7−δ up to the interface with the Au barrier. The junctions have improved critical current density values exceeding 20 kA/cm2, normal state resistances of 3×10−8 Ω cm2 and IcRn products of 0.7 mV at 4.2 K. Furthermore, the junction properties can be controlled by varying the Au barrier thickness. © 2002 American Institute of Physics.
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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
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Spin polarized tunneling through single-crystal GaAs(001) barriers

S. Kreuzer, J. Moser, W. Wegscheider, D. Weiss, M. Bichler, and D. Schuh

Appl. Phys. Lett. 80, 4582 (2002); http://dx.doi.org/10.1063/1.1486044 (3 pages) | Cited 29 times

Online Publication Date: 10 June 2002

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We investigate spin-dependent transport through an epitaxial GaAs(001) barrier sandwiched between polycrystalline iron films. Electron transport through the barrier is dominated by quantum mechanical tunneling, demonstrated by a nonlinear I–V characteristic, an exponential dependence of the tunneling current on the barrier thickness and the temperature dependence of the current. Though small a clear tunneling magnetoresistance effect proves spin-dependent transport through the Fe–GaAs interface. The small size of the effect and the high-field magnetoresistance suggest that spin–flip scattering plays a decisive role in transport. © 2002 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
73.40.Sx Metal-semiconductor-metal structures
81.05.Ea III-V semiconductors
81.05.Bx Metals, semimetals, and alloys
73.61.Ey III-V semiconductors
75.45.+j Macroscopic quantum phenomena in magnetic systems
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
85.75.Mm Spin polarized resonant tunnel junctions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

Single-flux-quantum pump based on a three-junction superconducting quantum interference device

Yoshinao Mizugaki, Jian Chen, Satoshi Nishikata, Keiji Sugi, Kensuke Nakajima, and Tsutomu Yamashita

Appl. Phys. Lett. 80, 4585 (2002); http://dx.doi.org/10.1063/1.1485308 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2002

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We demonstrate the operation of a single-flux-quantum (SFQ) pump that is electromagnetically dual to the single-electron pump. The circuit is composed of a three-junction superconducting quantum interference device with three control lines. By applying two phase-shifted rf signals magnetically, the SFQ-pump transfers one SFQ per one cycle of the rf signals even at zero- and negatively-biased condition. The circuit was fabricated using a Nb/AlOx/Nb Josephson junction technology. When we fed rf signals of 4.5 GHz, we observed a Shapiro step crossing the zero-current axis. Periodic dependence of voltage at the zero-biasing state upon dc offset flux was also confirmed. © 2002 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Current-induced dendritic magnetic instability in superconducting MgB2 films

A. V. Bobyl, D. V. Shantsev, T. H. Johansen, W. N. Kang, H. J. Kim, E. M. Choi, and S. I. Lee

Appl. Phys. Lett. 80, 4588 (2002); http://dx.doi.org/10.1063/1.1485304 (3 pages) | Cited 21 times

Online Publication Date: 10 June 2002

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Magneto-optical imaging reveals that in superconducting films of MgB2 a pulse of transport current creates avalanche-like flux dynamics where highly branching dendritic patterns are formed. The instability is triggered when the current exceeds a threshold value, and the superconductor, shaped as a long strip, is initially in the critical state. The instability exists up to 19 K, which is a much wider temperature range than in previous experiments, where dendrites were formed by a slowly varying magnetic field. The instability is believed to be of thermomagnetic origin indicating that thermal stabilization may become crucial in applications of MgB2. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
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.F- Transport properties
74.25.Gz Optical properties
78.20.Ls Magneto-optical effects
68.60.Dv Thermal stability; thermal effects
74.25.Bt Thermodynamic properties

Spin-filter diode based on ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures

Yong Guo, Xin-Yi Chen, Feng Zhai, Bing-Lin Gu, and Yoshiyuki Kawazoe

Appl. Phys. Lett. 80, 4591 (2002); http://dx.doi.org/10.1063/1.1485121 (3 pages) | Cited 20 times

Online Publication Date: 10 June 2002

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We propose and demonstrate a spin-filter diode based on semimagnetic semiconductor ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures. It is found that the degree of spin polarization greatly depends on the electric field direction and its magnitude. There is significant difference of the spin polarization between under forward bias and under reverse bias. It is also found that the spin polarization will reverse under relatively small magnetic field, which is originated from resonant enhancement effect for spin-up electrons tunneling through effective steplike potential of the corresponding structure. © 2002 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
72.25.Mk Spin transport through interfaces
75.50.Pp Magnetic semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
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