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21 Sep 2009

Volume 95, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 95, 121104 (2009); http://dx.doi.org/10.1063/1.3231448 (3 pages)

E. H. Khoo, I. Ahmed, and E. P. Li
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Magnetic tunnel junction based microwave detector

X. Fan, R. Cao, T. Moriyama, W. Wang, H. W. Zhang, and John Q. Xiao

Appl. Phys. Lett. 95, 122501 (2009); http://dx.doi.org/10.1063/1.3231874 (3 pages) | Cited 6 times

Online Publication Date: 21 September 2009

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We investigated the tunneling magnetoresistance change in magnetic tunnel junctions in the presence of external microwaves. The changing relative angle between the free layer and the pinned layer results in a rectification of the average resistance change. Due to its miniature size and its sensitivity to the microwave magnetic field, the magnetic tunnel junction could be utilized as a microwave power sensor with the ability to detect microwave frequencies. Studying microwave power and bias current dependencies reveals desired sensor features with linear responses and enhanced signal levels.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.70.-w Magnetic devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.40.Ei Rectification

Room-temperature ferromagnetism observed in Mo-doped indium oxide films

Chang-Yup Park, Soon-Gil Yoon, Young-Hun Jo, and Sung-Chul Shin

Appl. Phys. Lett. 95, 122502 (2009); http://dx.doi.org/10.1063/1.3232243 (3 pages) | Cited 8 times

Online Publication Date: 21 September 2009

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We have investigated the magnetic properties of molybdenum-doped (0–5 wt %) indium oxide films deposited on (100) MgO substrates using pulsed-laser deposition technique. Interestingly these films were found to reveal room-temperature ferromagnetism, where the magnetization increases with Mo doping. The maximum saturation magnetization of ∼ 6.6 emu/cc was found for ∼ 5 wt % Mo doping, providing approximately five times enhancement in comparison to the undoped film. We believe that this enhancement is ascribed to the magnetic moments of Mo ions occupied in the In sites.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
75.50.Pp Magnetic semiconductors
68.55.ag Semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Hd Other semiconductors
61.72.up Other materials
75.30.Cr Saturation moments and magnetic susceptibilities

Enhanced tunneling spin polarization from ultrathin layers of amorphous CoFe

Li Gao, Xin Jiang, Philip M. Rice, and Stuart S. P. Parkin

Appl. Phys. Lett. 95, 122503 (2009); http://dx.doi.org/10.1063/1.3216050 (3 pages) | Cited 3 times

Online Publication Date: 22 September 2009

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The tunneling spin polarization of CoFe alloys is directly compared in their amorphous (< ∼ 25–30 Å) and crystalline states using superconducting tunneling spectroscopy measurements of Al95Si5/Al2O3/CoFe junctions. Ultrathin layers of normally crystalline CoFe are made amorphous by sandwiching them between amorphous alumina tunnel barriers and amorphous ferromagnetic CoFeB electrodes. The results show that the tunneling spin polarization is significantly enhanced when the CoFe alloy is made amorphous compared to when it is crystalline. We also show that a postdeposition atomic oxygen treatment of the alumina tunnel barrier significantly enhances the thermal stability of the junctions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.50.+r Tunneling phenomena; Josephson effects
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
72.25.Mk Spin transport through interfaces

Barnett effect in thin magnetic films and nanostructures

Stefan Bretzel, Gerrit E. W. Bauer, Yaroslav Tserkovnyak, and Arne Brataas

Appl. Phys. Lett. 95, 122504 (2009); http://dx.doi.org/10.1063/1.3232221 (3 pages) | Cited 2 times

Online Publication Date: 22 September 2009

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The Barnett effect refers to the magnetization induced by rotation of a demagnetized ferromagnet. We describe the location and stability of stationary states in rotating nanostructures using the Landau–Lifshitz–Gilbert equation. The conditions for an experimental observation of the Barnett effect in different materials and sample geometries are discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Tt Fine-particle systems; nanocrystalline materials

Epitaxial growth and characterization of Eu0.5Sr0.5CoO3 thin films by off-axis sputtering

Daeyoung Kwon, Youngsu Wu, Bongju Kim, Bog G. Kim, and Harold Y. Hwang

Appl. Phys. Lett. 95, 122505 (2009); http://dx.doi.org/10.1063/1.3234372 (3 pages)

Online Publication Date: 22 September 2009

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We report the epitaxial growth and physical properties of Eu0.5Sr0.5CoO3 (ESCO) thin films deposited on (001) LaAlO3 (LAO) and (001) SrTiO3 (STO) substrates by off-axis rf sputtering. The magnetic properties of a grown film are governed by the crystallinity of the thin film and strain effects due to the substrate. The temperature-dependent resistivity of an optimized ESCO thin film on a LAO substrate shows a characteristic sudden decrease near the ferromagnetic transition temperature, indicating metallic double-exchange-like behavior, while the resistivity of ESCO on a STO substrate displays insulatinglike behavior because of substrate strain. These results suggest that optimized ESCO film on LAO is ideal as a bottom electrode for strained dielectric and ferroelectric heterostructures.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
73.61.Ng Insulators

Current manipulation of a vortex confined in a micron-sized Fe19Ni81 disk

Akinobu Yamaguchi, Keiichi Motoi, Hideki Miyajima, Atsufumi Hirohata, Takehiro Yamaoka, Tsuyoshi Uchiyama, and Yuichi Utsumi

Appl. Phys. Lett. 95, 122506 (2009); http://dx.doi.org/10.1063/1.3236693 (3 pages) | Cited 5 times

Online Publication Date: 23 September 2009

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By measuring a rectifying planer Hall effect, we have manipulated a vortex core trapped in a single layered Fe19Ni81 disk dependent upon the magnitude of a dc current simultaneously applied with an rf current and a magnetic field. The observed behavior is attributed to a single vortex translational mode. The resonance frequency of the translational mode is found to be almost proportional to the magnitude of the dc current and to be governed by the shape of the energy potential well defined by the disk shape.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Current-driven transitions in ferromagnetic/insulator/superconductor narrow stripes

S. Hacohen-Gourgy, B. Almog, G. Leibovitch, R. G. Mints, and G. Deutscher

Appl. Phys. Lett. 95, 122507 (2009); http://dx.doi.org/10.1063/1.3236780 (3 pages)

Online Publication Date: 23 September 2009

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We have studied superconducting to normal state current-driven transitions in ferromagnetic Co/Co oxide/superconducting In stripes of widths ranging from 3 to 20 μm. The narrower stripes can be set up in a high or low critical current state by driving the magnetic domain structure of the thin Co film either in an almost uniform or nonuniform state of magnetization. In the latter the critical current transition is preceded by the development of normal domains, whose dynamics are determined by the Co magnetization pattern.
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74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.60.Ch Domain walls and domain structure

Highly asymmetric magnetic behavior in exchange biased systems induced by noncollinear field cooling

E. Jiménez, J. Camarero, J. Sort, J. Nogués, A. Hoffmann, F. J. Teran, P. Perna, J. M. García-Martín, B. Dieny, and R. Miranda

Appl. Phys. Lett. 95, 122508 (2009); http://dx.doi.org/10.1063/1.3236768 (3 pages) | Cited 12 times

Online Publication Date: 25 September 2009

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A detailed study of the angular dependence of the magnetization reversal in polycrystalline ferromagnetic (FM)/antiferromagnetic Co/IrMn bilayers with noncollinear FM and unidirectional anisotropies shows a peculiar asymmetric magnetic behavior. The anisotropy configuration is set via a field cooling (FC) procedure with the magnetic field misaligned with respect to the easy magnetization direction of the FM layer. Different magnetization reversal modes are observed for either positive or negative angles with respect to the FC direction. The angular dependence of both coercivity and exchange bias also clearly displays the broken symmetry of the induced noncollinearity. Our findings are reproduced with a modified Stoner–Wohlfarth model including the induced anisotropy configuration. Our results highlight the importance of the relative angle between anisotropies in exchange bias systems, opening a new path for the tailoring of their magnetic properties.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy

Low temperature hydrothermal epitaxy and Raman study of heteroepitaxial BiFeO3 film

Dibyaranjan Rout, Seung Ho Han, Kyoung-Seok Moon, Ho Gi Kim, Chae Il Cheon, and Suk-Joong L. Kang

Appl. Phys. Lett. 95, 122509 (2009); http://dx.doi.org/10.1063/1.3237160 (3 pages) | Cited 8 times

Online Publication Date: 25 September 2009

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By hydrothermal epitaxy, a heteroepitaxial BiFeO3 (BFO) film of ∼ 2.5 μm thickness was grown on a (100)-oriented single-crystalline SrTiO3 (STO) substrate at 200 °C, which is at least 250 °C lower than the conventional techniques used thus far. The x-ray diffraction pattern indicated the formation of a single-phase perovskite structure that was highly oriented along the (00l) lattice plane. Pole-figure and Φ-scan results confirmed the cube-on-cube epitaxial relationship of BFO∥STO. The Raman active vibrational modes showed anomalous changes in the vicinity of the Neel temperature (TN), which was attributed to spin-phonon coupling.
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68.55.aj Insulators
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.80.+q Magnetomechanical effects, magnetostriction
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Diffraction of spin waves from a submicrometer-size defect in a microwaveguide

Daniel R. Birt, Brian O’Gorman, Maxim Tsoi, Xiaoqin Li, Vladislav E. Demidov, and Sergej O. Demokritov

Appl. Phys. Lett. 95, 122510 (2009); http://dx.doi.org/10.1063/1.3237168 (3 pages) | Cited 8 times

Online Publication Date: 25 September 2009

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We have experimentally studied the diffraction of spin waves propagating in a Permalloy-film microwaveguide from a submicrometer-sized circular defect. For microwave excitation above the cutoff frequency of the fundamental transverse mode, the defect leads to a frequency dependent reflection of the spin wave. The efficiency of the reflection appears to be dependent on the wavelength of the incident spin wave in a nonmonotonous way. The observed two-dimensional spin wave distribution pattern after the defect can be understood based on the interference of several copropagating modes, suggesting that the defect couples the fundamental mode with higher order modes.
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84.40.Az Waveguides, transmission lines, striplines
41.20.Jb Electromagnetic wave propagation; radiowave propagation
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.30.Ds Spin waves
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