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12 Dec 2005

Volume 87, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 243101 (2005); http://dx.doi.org/10.1063/1.2147713 (3 pages)

Y.-S. Choi, K. Hennessy, R. Sharma, E. Haberer, Y. Gao, S. P. DenBaars, S. Nakamura, E. L. Hu, and C. Meier
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Change in photovoltage due to an external magnetic field in a manganite-based heterojunction

Z. G. Sheng, B. C. Zhao, W. H. Song, Y. P. Sun, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 87, 242501 (2005); http://dx.doi.org/10.1063/1.2140878 (3 pages) | Cited 20 times

Online Publication Date: 5 December 2005

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The effect of magnetic field on the photovoltaic effect (PVE) has been investigated for a manganite-based heterojunction composed of a La0.7Ce0.3MnO3 film and a 0.5 wt % Nb-doped SrTiO3 substrate. A linear decrease in the photovoltage (Voc) with magnetic fields is observed and the relative variation of Voc [defined as 1−Voc(H)/Voc(0)] is larger than 10% under a field of 0.5 T at a temperature T = 16.5 K. There is a proportional relation between ΔVoc and the magnetoresistance of the heterojunction. We attribute the modulation of PVE to variation of magnetization and resistance of depletion layer by external magnetic fields.
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73.50.Pz Photoconduction and photovoltaic effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance

Growth and characterization of CaCu2Mn5O12 thin films deposited on CaCu3Ti4O12-buffered LaAlO3 substrates

S. Autier-Laurent, B. Mercey, and Ch. Simon

Appl. Phys. Lett. 87, 242502 (2005); http://dx.doi.org/10.1063/1.2140879 (3 pages) | Cited 1 time

Online Publication Date: 5 December 2005

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Thin films of perovskitelike CaCu2Mn5O12 have been grown by pulsed laser deposition. These films are ferromagnetic with a Curie temperature (TC) of 292 K which is very close to that expected for the bulk material (TC = 310 K). Increasing the oxygen pressure during cooling does not markedly affect the out-of-plane lattice parameter (c) or TC of the films, but enhances the magnetization at low temperature. Transport properties of films exhibit metallic behavior in the temperature range of 10–360 K. The most important difference between these films and the bulk material was observed in their magnetotransport characteristics. The magnetoresistance effect is important at low temperatures for the bulk material, while for the thin films, this effect is large (−8%) close to TC, as expected for a regular ferromagnetic material.
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75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Characterization of growth and crystallization processes in CoFeB/MgO/CoFeB magnetic tunnel junction structure by reflective high-energy electron diffraction

Shinji Yuasa, Yoshishige Suzuki, Toshikazu Katayama, and Koji Ando

Appl. Phys. Lett. 87, 242503 (2005); http://dx.doi.org/10.1063/1.2140612 (3 pages) | Cited 72 times

Online Publication Date: 5 December 2005

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We performed reflective high-energy electron diffraction observations to investigate the growth and crystallization processes of Co60Fe20B20/MgO/Co60Fe20B20 magnetic tunnel junction structures. A MgO layer grown on an amorphous CoFeB layer has an amorphous structure up to the MgO thickness (tMgO) of 4 monoatomic layers (ML) and begins to crystallize with (001) preferred orientation when tMgO ≥ 5 ML. By annealing, an amorphous CoFeB layer grown on MgO(001) crystallizes in a body-centered-cubic structure with (001) orientation because MgO(001) acts as a template to crystallize CoFeB. The results give important information for understanding the mechanism of giant tunneling magnetoresistance effect in CoFeB/MgO/CoFeB MTJs.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.Ac Multilayers
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
64.70.D- Solid-liquid transitions
75.47.De Giant magnetoresistance
75.47.Np Metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
81.40.Gh Other heat and thermomechanical treatments

Using exchange bias to extend the temperature range of square loop behavior in [Pt/Co] multilayers with perpendicular anisotropy

J. Sort, F. Garcia, S. Auffret, B. Rodmacq, B. Dieny, V. Langlais, S. Suriñach, J. S. Muñoz, M. D. Baró, and J. Nogués

Appl. Phys. Lett. 87, 242504 (2005); http://dx.doi.org/10.1063/1.2139840 (3 pages) | Cited 6 times

Online Publication Date: 6 December 2005

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The temperature dependence of the magnetic properties of [Pt/Co] multilayers (ML), exhibiting perpendicular anisotropy, with and without exchange biasing with an antiferromagnet (AFM) has been investigated. Upon heating, a loss of the out-of-plane anisotropy and, consequently, of the remanence to saturation ratio is observed in these systems. However, such effect occurs at higher temperatures in the [Pt/Co] ML exchange coupled to the AFM than for the unbiased ML. This is attributed to the additional anisotropy induced to the ML by the ferromagnetic-antiferromagnetic exchange coupling.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Voltage-controlled tunneling anisotropic magnetoresistance of a ferromagnetic p++-(Ga,Mn)As/n+-GaAs Zener-Esaki diode

R. Giraud, M. Gryglas, L. Thevenard, A. Lemaître, and G. Faini

Appl. Phys. Lett. 87, 242505 (2005); http://dx.doi.org/10.1063/1.2137903 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2005

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The large tunneling anisotropic magnetoresistance of a ferromagnetic p++-(Ga,Mn)As/n+-GaAs Zener-Esaki diode is shown in a perpendicular magnetic field over a large temperature and voltage range. Under an applied bias, the tunnel junction transparency is modified, allowing one to continuously tune anisotropic transport properties between the tunneling and the ohmic regimes. Furthermore, an asymmetric bias dependence of the tunneling anisotropic magnetoresistance is also observed: A reverse bias highlights the full (Ga,Mn)As valence-band states contribution, whereas a forward bias only probes part of the density of states and reveals opposite contributions from two valence subbands.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Characterization of off-axis MgB2 epitaxial thin films for planar junctions

M. Iavarone, G. Karapetrov, A. Menzel, V. Komanicky, H. You, W. K. Kwok, P. Orgiani, V. Ferrando, and X. X. Xi

Appl. Phys. Lett. 87, 242506 (2005); http://dx.doi.org/10.1063/1.2140473 (3 pages) | Cited 7 times

Online Publication Date: 6 December 2005

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Using scanning tunneling spectroscopy, we perform a full mapping of the quasiparticle density of states of magnesium diboride (MgB2) epitaxial thin films grown on (110) yttrium stabilized zirconia (YSZ) by hybrid physical-chemical vapor deposition. The films have critical temperatures of 40 K. X-ray measurements show an epitaxial MgB2 growth having the c-axis tilted by 32° with respect to the normal to the substrate, consistent with the atomic force microscopy images of the sample. Scanning tunneling spectroscopy clearly finds that the spectroscopic peak associated to the π gap is reduced on most of the film surface and the feature representative of the σ gap is present, with different intensity, on the majority of the sample’s surface, which is consistent with x-ray measurements.
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74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.F- Transport properties
74.25.Jb Electronic structure (photoemission, etc.)
68.55.-a Thin film structure and morphology

Step-induced uniaxial magnetic anisotropy of La0:67Sr0:33MnO3 thin films

Mercy Mathews, Ferry M. Postma, J. Cock Lodder, R. Jansen, Guus Rijnders, and Dave H. A. Blank

Appl. Phys. Lett. 87, 242507 (2005); http://dx.doi.org/10.1063/1.2143136 (3 pages) | Cited 34 times

Online Publication Date: 8 December 2005

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The magnetic anisotropy of epitaxial La0.67Sr0.33MnO3 (LSMO) thin films on vicinal, TiO2-terminated SrTiO3 substrates is investigated. Atomic force microscopy shows a regular step-terrace structure on the LSMO surface which is a replication of the surface of the substrate. The films show in-plane uniaxial magnetic anisotropy at room temperature, with the easy axis along the step direction. At low temperature the films show biaxial crystalline anisotropy with easy axes along [110], and hard axes along the [100] direction of LSMO.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Gh Oxide surfaces

Magnetic hyperfine fields in the room-temperature dilute magnetic semiconducting alloy Fe:Sb1−xSex

D. R. S. Somayajulu, Mukesh Chawda, Narendra Patel, Mitesh Sarkar, K. C. Sebastian, K. Venugopalan, and A. Gupta

Appl. Phys. Lett. 87, 242508 (2005); http://dx.doi.org/10.1063/1.2137875 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2005

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A dilute quantity of Fe (0.008) was doped into V-VI (Sb1−xSex) for X = 0 to 0.50 alloys based on Sb semimetal. Hall measurements showed that the materials were n-type semiconductors for X = 0.01 to 0.10 and the charge carrier densities increased from 4.2×1019 cm−3 to 1.142×1021 cm−3 in this region. For higher concentration of Se (X = 0.50), the charge carrier densities decreased dramatically to 2.1×1015. For X = 0, Fe showed no magnetic moment. For X = 0.01 to 0.1 two magnetic sites (A and B) were observed at room temperature by Mossbauer measurement. Site A appears to be an SeFeSb, type ternary alloy. p-d interaction and carrier-induced polarization seem to be responsible for the magnetic interaction at this site (A). Tc (for Site A) was measured to be ∼ 573 K. Similar behavior was observed for Fe(0.002). Site B Mossbauer parameters coincide with those of Fe7Se8.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Cr Saturation moments and magnetic susceptibilities
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

Annealing-induced changes of the magnetic anisotropy of (Ga,Mn)As epilayers

V. Stanciu and P. Svedlindh

Appl. Phys. Lett. 87, 242509 (2005); http://dx.doi.org/10.1063/1.2123380 (3 pages) | Cited 11 times

Online Publication Date: 9 December 2005

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The dependence of the magnetic anisotropy of As-capped (Ga,Mn)As epilayers on the annealing parameters—temperature and time—has been investigated. A uniaxial magnetic anisotropy is evidenced, whose orientation with respect to the crystallographic axes changes upon annealing from [math10] for the as-grown samples to [110] for the annealed samples. Both cubic and uniaxial anisotropies are tightly linked to the magnetic transition temperature, and hence, to the concentration of charge carriers, the magnitude of which is controlled by the annealing process.
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75.50.Pp Magnetic semiconductors
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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