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24 Jan 2005

Volume 86, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 86, 043106 (2005); http://dx.doi.org/10.1063/1.1853514 (3 pages)

William L. Hughes and Zhong L. Wang
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Overdamped Nb/Al–AlOx/Nb Josephson junctions

V. Lacquaniti, C. Cagliero, S. Maggi, and R. Steni

Appl. Phys. Lett. 86, 042501 (2005); http://dx.doi.org/10.1063/1.1856135 (3 pages) | Cited 13 times

Online Publication Date: 18 January 2005

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We report the fabrication and characterization of overdamped Nb/Al–AlOx/Nb superconductor–insulator–superconductor Josephson junction whose fabrication process derives from that of the well-known hysteretic junctions. These junctions are an intermediate state between the superconductor–normal metal–superconductor and the superconductor–insulator–superconductor Josephson junctions. Stable and reproducible nonhysteretic current–voltage characteristics are obtained with a proper choice of the fabrication parameters. We have measured critical current densities JC from 103 up to 2×104 A/cm2, with characteristic voltages from 80 to nearly 450 μV. The junctions are stable against time and repeated thermal cycling.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.Fk Multilayers, superlattices, heterostructures
81.05.Bx Metals, semimetals, and alloys
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
74.25.F- Transport properties
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth

Focused-ion-beam-fabricated nanoscale magnetoresistive ballistic sensors

S. Khizroev, Y. Hijazi, R. Chomko, S. Mukherjee, R. Chantrell, X. Wu, R. Carley, and D. Litvinov

Appl. Phys. Lett. 86, 042502 (2005); http://dx.doi.org/10.1063/1.1853518 (3 pages) | Cited 9 times

Online Publication Date: 19 January 2005

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In this letter, authors demonstrate magnetoresistance of the order of 18% at room temperature for a focused-ion-beam-fabricated nanoconstriction with critical dimensions of the order of 35 nm. The main purpose of this work is to show that focused ion beam (FIB)-fabricated nanoconstrictions are relatively reproducible and thus could be further developed to obtain substantially larger magnetoresistance. Magnetoresistance is expected to increase if critical dimensions of nanoconstrictions are further reduced. The proposed focused-ion-beam-fabricated nanoconstrictions could be also used as devices to study the electron “ballistic” regime in the emerging fields of Spintronics and magnetoresistive random access memory (MRAM).
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Submicrometer Hall devices fabricated by focused electron-beam-induced deposition

G. Boero, I. Utke, T. Bret, N. Quack, M. Todorova, S. Mouaziz, P. Kejik, J. Brugger, R. S. Popovic, and P. Hoffmann

Appl. Phys. Lett. 86, 042503 (2005); http://dx.doi.org/10.1063/1.1856134 (3 pages) | Cited 29 times

Online Publication Date: 19 January 2005

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Hall devices having an active area of about (500 nm)2 are fabricated by focused electron-beam-induced deposition. The deposited material consists of cobalt nanoparticles in a carbonaceous matrix. The realized devices have, at room temperature, a current sensitivity of about 1 V/AT, a resistance of a few kilo-ohms, and can be biased with a maximum current of about 1 mA. The room-temperature magnetic field resolution is about 10 μT/Hz1/2 at frequencies above 1 kHz.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Tunable magnetic anisotropy of ultrathin Co layers

S. Park, X. Zhang, A. Misra, J. D. Thompson, M. R. Fitzsimmons, S. Lee, and C. M. Falco

Appl. Phys. Lett. 86, 042504 (2005); http://dx.doi.org/10.1063/1.1850592 (3 pages) | Cited 12 times

Online Publication Date: 20 January 2005

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We prepared multilayers, consisting of an epitaxial Au/Co/Au/Cu(111) architecture on Si(111) substrates, to understand the magnetic anisotropy of an ultrathin Co layer in relation to its structure. The room-temperature magnetization of an 8-monolayer (ML)-thick Co layer is predominately either in-plane or out-of-plane depending upon the thickness of the Au underlayer. Specifically, for a Co film grown on a 2-ML-thick Au, the Co film has a distorted fcc structure and in-plane magnetic anisotropy. For a Co film grown on a 6-ML-thick Au, the Co film has a distorted hcp structure and out-of-plane magnetic anisotropy.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optical investigation of electronic states of Mn4+ ions in p-type GaN

B. Han, B. W. Wessels, and M. P. Ulmer

Appl. Phys. Lett. 86, 042505 (2005); http://dx.doi.org/10.1063/1.1853525 (3 pages) | Cited 8 times

Online Publication Date: 21 January 2005

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The electronic states of manganese in p-type GaN are investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. A series of sharp PL lines at 1.0 eV is observed in codoped GaN and attributed to the intra d-shell transition math(F)-math(F) of Mn4+ ions. PLE spectrum of the Mn4+ [math(F)-math(F)] luminescence reveals intracenter excitation processes via the excited states of Mn4+ ions. PLE peaks observed at 1.79 and 2.33 eV are attributed to the intra-d-shell math(P)-math(F) and math(F)-math(F) transitions of Mn4+, respectively. In addition to the intrashell excitation processes, a broad PLE band involving charge-transfer transition of the Mn4+/3+ deep level is observed, which is well described by the Lucovsky model. As determined from the onset of this PLE band, the position of the Mn4+/3+ deep level is 1.11 eV above the valence band maximum, which is consistent with prior theory using ab initio calculations. Our work indicates 4+ is the predominant oxidation state of Mn ions in p-type GaN:Mn when the Fermi energy is lower than 1.11 eV above the valence band maximum.
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75.50.Pp Magnetic semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
71.70.-d Level splitting and interactions
81.65.Mq Oxidation
71.15.-m Methods of electronic structure calculations

Bulk synthesis and high-temperature ferromagnetism of (In1−xFex)2O3−σ with Cu co-doping

Young K. Yoo, Qizhen Xue, Hyung-Chul Lee, Shifan Cheng, X.-D. Xiang, Gerald F. Dionne, Shifa Xu, Jun He, Yong S. Chu, S. D. Preite, Samuel E. Lofland, and Ichiro Takeuchi

Appl. Phys. Lett. 86, 042506 (2005); http://dx.doi.org/10.1063/1.1854720 (3 pages) | Cited 61 times

Online Publication Date: 21 January 2005

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The synthesis and magnetic properties of (In1−xFex)2O3−σ bulk ceramics with Cu co-doping are reported. Magnetic Fe ions are found to have high thermodynamic solubility (up to 20%) in the In2O3 host compound. The lattice constant decreases almost linearly as Fe doping concentration increases indicating the incorporation of Fe ions into the host lattice. The samples with high Fe concentration annealed under Ar reduced atmosphere were found to be ferromagnetic, and the Curie temperature is around 750 K. The extensive structural and magnetic studies rule out the possibility that the observed magnetism is derived from magnetic impurity phases.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.up Other materials
61.72.S- Impurities in crystals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Hx Magnetic impurity interactions
61.72.Cc Kinetics of defect formation and annealing
61.66.Fn Inorganic compounds

Magnetization step and spin reorientation in Pr5/8Ca3/8MnO3 manganites

Guixin Cao, Jincang Zhang, Shixun Cao, Chao Jing, and Xuechu Shen

Appl. Phys. Lett. 86, 042507 (2005); http://dx.doi.org/10.1063/1.1852710 (3 pages) | Cited 7 times

Online Publication Date: 21 January 2005

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The structural, magnetic, and transport properties of Pr5/8Ca3/8MnO3 single crystals with a phase-separated characteristic were systematically studied. One steplike charge-ordered antiferromagnetic-ferromagnetic transition was found below 60 K when a magnetic field of only several teslas was applied, and the step in the M-H curve became ultrasharp below 4.2 K. Here, the given charge/orbital ordering and spin structure indicated that the energy difference between ferromagnetic and charge ordering was small for Pr5/8Ca3/8MnO3. According to the model of spin and orbital coupling, the steps should be the result of spin reorientation under the magnetic field. Above 10 K, however, the step was not sharp, which was caused by thermal fluctuation and then affects the fluctuation rate of orbit.
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75.50.Dd Nonmetallic ferromagnetic materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.40.Mg Numerical simulation studies
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves
75.10.Dg Crystal-field theory and spin Hamiltonians
71.45.-d Collective effects
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