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20 Sep 2004

Volume 85, Issue 12, pp. 2157-2437

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 2390 (2004); http://dx.doi.org/10.1063/1.1796520 (3 pages)

Stas Polonsky and Alan Weger
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Observation of a metastable phase during solidification of undercooled Nd–Fe–B alloy melts by in situ diffraction experiments using synchrotron radiation

Thomas Volkmann, Jörn Strohmenger, Jianrong Gao, and Dieter M. Herlach

Appl. Phys. Lett. 85, 2232 (2004); http://dx.doi.org/10.1063/1.1794373 (3 pages) | Cited 7 times

Online Publication Date: 24 September 2004

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The electromagnetic levitation technique was combined with the diagnostic means at the European Synchrotron Radiation Facility in Grenoble to study in situ the phase selection during solidification of undercooled Nd–Fe–B melts. By energy dispersive diffraction experiments with synchrotron radiation on levitated Nd–Fe–B alloys complete diffraction spectra were recorded within a time interval of a few seconds. Owing to the short measuring time the primary crystallization of a metastable phase was observed that initiates the solidification of hard magnetic Nd2Fe14B1 phase. The metastable phase dissolves subsequently and cannot be detected in the as-solidified sample at the ambient temperature. By analyzing the diffraction spectra the metastable phase is identified as a ternary extension of the rhombohedral Nd2Fe17 phase being stable in binary Nd–Fe alloys.
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75.50.Ww Permanent magnets
81.30.Fb Solidification
64.70.D- Solid-liquid transitions
61.25.Mv Liquid metals and alloys

Direct evidence for strain inhomogeneity in InxGa1−xN epilayers by Raman spectroscopy

M. R. Correia, S. Pereira, E. Pereira, J. Frandon, I. M. Watson, C. Liu, E. Alves, A. D. Sequeira, and N. Franco

Appl. Phys. Lett. 85, 2235 (2004); http://dx.doi.org/10.1063/1.1791324 (3 pages) | Cited 10 times

Online Publication Date: 24 September 2004

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This contribution is focused on Raman analysis of the InxGa1−xN alloy. It presents direct evidence that both strain and composition effects must be taken into account to interpret the Raman experimental results. Raman studies have been commonly discussed in view of composition inhomogeneity only, neglecting the possible existence of strain depth variations, recently shown to occur for layers grown above the critical layer thickness. The effects of this variation on the A1(LO) phonon frequency could only be investigated by combining both structural and Raman measurements. In this letter, a set of InxGa1−xN layers has been chemically etched during different periods, allowing the depth variation of the phonon frequency to be unambiguously evidenced. Comparing the Raman spectra before and after etching, two distinct InxGa1−xN regions, differing on their strain state, are identified: a relaxed one, found near the surface region; another one, grown coherently (i.e., pseudomorphic) to the GaN buffer layer. These results are in excellent agreement with an additional reciprocal space map analysis.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.30.Fs III-V and II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Comparison of large-scale layer-relaxation simulations with experiment

K. W. Schwarz, J. Cai, and P. M. Mooney

Appl. Phys. Lett. 85, 2238 (2004); http://dx.doi.org/10.1063/1.1791332 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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Recent experiments on the strain relaxation of SiGe layers are related to basic dislocation theory via numerical calculations based on discrete dislocation dynamics. Excellent quantitative agreement is obtained, demonstrating that such technologically interesting problems can be treated on a fundamental level.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Bb Theories and models of crystal defects
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

Raman study of phonons in K2Al2B2O7 crystals

X. B. Hu, J. Y. Wang, C. Q. Zhang, X. G. Xu, Chun-Keung Loong, and Marcos Grimsditch

Appl. Phys. Lett. 85, 2241 (2004); http://dx.doi.org/10.1063/1.1786661 (3 pages) | Cited 13 times

Online Publication Date: 24 September 2004

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A Raman scattering study of the vibrational modes in K2Al2B2O7 crystals has been performed at room temperature. The vibrational modes are classified by the nuclear site group analysis method and the internal vibrational modes are assigned to vibrations of the BO3 triangle and AlO4 tetrahedron.
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42.70.Mp Nonlinear optical crystals
78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Defects induced in GaN by europium implantation

M. Mamor, V. Matias, A. Vantomme, A. Colder, P. Marie, and P. Ruterana

Appl. Phys. Lett. 85, 2244 (2004); http://dx.doi.org/10.1063/1.1797563 (3 pages) | Cited 12 times

Online Publication Date: 24 September 2004

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We have investigated structural and electrical properties of defects introduced during room temperature europium implantation into GaN. Two geometries, random and channeled implantation, were used. Rutherford backscattering and channeling analysis reveals that implantation induces a significantly lower concentration of defects, in the case of channeled implantation. These defects generate a perpendicular expansion of the GaN lattice in the implanted region, as evidenced by x-ray diffraction. From deep-level transient spectroscopy, beside intrinsic defects with energy levels below the conduction band, one additional electron trap, labeled Eu2, is observed at an energy (Ec−0.36 eV). It is believed that this defect in n‐GaN is europium related.
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81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Photoluminescence of Eu-doped GaN thin films prepared by radio frequency magnetron sputtering

Sho Shirakata, Ryo Sasaki, and Takashi Kataoka

Appl. Phys. Lett. 85, 2247 (2004); http://dx.doi.org/10.1063/1.1794868 (3 pages) | Cited 16 times

Online Publication Date: 24 September 2004

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The Eu-doped GaN thin films (GaN:Eu) were deposited on the sapphire substrate by means of the rf magnetron sputtering method. The GaN:Eu films were characterized by x-ray diffraction, scanning electron microscope, and photoluminescence (PL). Although as-grown GaN:Eu films (2 mol % Eu in target) exhibited weak broad Eu-related red PL, the annealing in NH3 atmosphere (1000°C for 1 h) led to the remarkable enhancement of Eu-related PL lines. PL spectra of such annealed GaN:Eu films exhibited a series of sharp PL lines characteristic of substitutional Eu3+ ions at Ga sites in the GaN lattice (dominant PL line is at 622 nm for the 5D0–7F2 transition). On the other hand for GaN:Eu films (5 mol % Eu in target), as-grown films are amorphous and exhibited broad Eu3+-related PL lines. The annealing led to the crystallization of the films, the elimination of Eu3+-related PL lines, and the enhancement of the near-band-edge PL. The Eu-luminescent centers are considered to be removed during the crystallization.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Effect of MnAs/GaAs(001) film accommodations on the phase-transition temperature

F. Iikawa, M. J. S. P. Brasil, O. D. D. Couto, C. Adriano, C. Giles, and L. Däweritz

Appl. Phys. Lett. 85, 2250 (2004); http://dx.doi.org/10.1063/1.1791739 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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The phase-transition temperature of MnAs epitaxial films grown by molecular-beam epitaxy on GaAs(001) with different crystalline accommodations was studied by specular and grazing incidence x-ray diffraction. The transition temperature of MnAs films with tilted hexagonal c-axis orientations with respect to the GaAs substrate is higher than the most investigated nontilted films and reaches a value above room temperature, which is more suitable for device applications.
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81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Pseudomorphic SiC alloys formed by Ge ion implantation

M. W. Dashiell, G. Xuan, E. Ansorge, X. Zhang, J. Kolodzey, G. C. DeSalvo, J. R. Gigante, W. J. Malkowski, R. C. Clarke, J. Liu, and M. Skowronski

Appl. Phys. Lett. 85, 2253 (2004); http://dx.doi.org/10.1063/1.1791741 (3 pages) | Cited 2 times

Online Publication Date: 24 September 2004

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Pseudomorphic-strained layers containing from 0.07–1.25 atomic % Ge were formed by ion implantation at 1000 °C into 4H-SiC substrates. X-ray diffraction revealed high crystalline quality and coherent interfaces for strains up to 1.4%. Infrared reflectivity indicated a phonon mode at 948 cm−1, attributed to Ge implantation disorder. Annealing above 1250 °C caused the disappearance of the 948 cm−1 disorder mode, and the strengthening of the phonon mode at 848 cm−1, associated with the 4H stacking sequence. Structural measurements of the annealed samples revealed thermally stable, coherently strained layers of the 4H polytype, without precipitation, suggesting an isoelectronic Ge alloy compatible with SiC for heterostructure strained layer engineering.
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81.05.Hd Other semiconductors
61.72.up Other materials
61.72.Nn Stacking faults and other planar or extended defects
78.30.Hv Other nonmetallic inorganics
81.40.Gh Other heat and thermomechanical treatments
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Electromodulation of photoinduced charge transfer in polyfluorene bilayer devices

A. S. Dhoot, J. A. Hogan, A. C. Morteani, and N. C. Greenham

Appl. Phys. Lett. 85, 2256 (2004); http://dx.doi.org/10.1063/1.1793337 (3 pages) | Cited 4 times

Online Publication Date: 24 September 2004

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Photoinduced charge transfer at a conjugated polymer donor-acceptor heterojunction controls the ultimate photogeneration efficiency in photovoltaic devices. We have studied this charge transfer by measurements of electric-field-induced photoluminescence (PL) modulation in polyfluorene-based bilayer devices at room and low temperatures. Depending on the field direction across the interface we observe field-induced quenching or enhancement of the PL, which we ascribe to modulation of the exciton dissociation rate through modification of the energy of the charge-transfer state formed after charge separation.
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85.60.-q Optoelectronic devices
78.66.Qn Polymers; organic compounds
78.55.Qr Amorphous materials; glasses and other disordered solids
71.55.Ht Other nonmetals
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Palladium Schottky barrier contacts to hydrothermally grown n-ZnO and shallow electron states

Ulrike Grossner, Stig Gabrielsen, Thomas Moe Børseth, Joachim Grillenberger, Andrej Yu. Kuznetsov, and Bengt G. Svensson

Appl. Phys. Lett. 85, 2259 (2004); http://dx.doi.org/10.1063/1.1790592 (3 pages) | Cited 34 times

Online Publication Date: 24 September 2004

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Schottky barrier contacts have been formed by electron beam evaporation of Pd on the (000math)-face of hydrothermally grown n-type single-crystalline ZnO. The contacts can be operated under reverse bias voltages up to −5 V and in the temperature range between 130 and 350 K. A barrier height of 0.83 eV is deducted at room temperature, which is in reasonable agreement with the value predicted by fundamental theory. The ideality factor for the current-voltage characteristics varies between 1.01 and 1.03 in the voltage range of −5.0 to +0.5 V, indicating that thermionic emission is a dominant mechanism for charge-carrier transport. Thermal admittance measurements were performed between 15 and 350 K, and two prominent levels were resolved at 0.05(1) and 0.33(2) eV below the conduction band edge, respectively. The origin of these levels is not known, but possible candidates are complexes involving hydrogen, Zn interstitials, and vacancy-oxygen centers.
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85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Coherent states in a coupled quantum dot nanocrystalline silicon transistor

M. A. H. Khalafalla, Z. A. K. Durrani, and H. Mizuta

Appl. Phys. Lett. 85, 2262 (2004); http://dx.doi.org/10.1063/1.1795974 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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We investigate the coherent coupling of electronic states in a nanocrystalline silicon quantum dot transistor. The device consists of a nanometer-scale point-contact containing only a few silicon grains. The grains form quantum dots, tunnel-coupled across thin silicon sub-oxide grain boundaries. At 4.2 K, we observe a pattern of single-electron conductance peaks versus two gate voltages, caused by electrostatic coupling between the quantum dots. Additional peaks are observed when the energy levels from two adjacent quantum dots are resonant, which may be associated with “quasi-molecular” states formed by coherent coupling of the levels. The tunnel splitting obtained from the peak separation is ∼0.4 meV, which is from a few times to an order-of-magnitude larger than reported previously in GaAs∕AlGaAs quantum dots.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.35.Gv Single electron devices
61.72.Mm Grain and twin boundaries
71.20.Mq Elemental semiconductors
73.20.At Surface states, band structure, electron density of states

Ballistic hole emission luminescence

Ian Appelbaum, K. J. Russell, I. Shalish, V. Narayanamurti, M. P. Hanson, and A. C. Gossard

Appl. Phys. Lett. 85, 2265 (2004); http://dx.doi.org/10.1063/1.1793347 (3 pages) | Cited 2 times

Online Publication Date: 24 September 2004

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Using a method complementary to ballistic electron emission luminescence (BEEL), we demonstrate tunnel-junction injection of sub-band-gap hot holes into the valence band of a semiconductor heterostructure to generate band-gap luminescence. This mechanism can be used in a scanning-probe geometry for the development of a simultaneous hole transport and luminescence microscopy of p-type Schottky devices.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
72.20.Ht High-field and nonlinear effects

Electrical activation phenomena induced by excimer laser annealing in B-implanted silicon

G. Fortunato, L. Mariucci, A. La Magna, P. Alippi, M. Italia, V. Privitera, B. Svensson, and E. Monakhov

Appl. Phys. Lett. 85, 2268 (2004); http://dx.doi.org/10.1063/1.1793352 (3 pages) | Cited 9 times

Online Publication Date: 24 September 2004

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The activation process induced by excimer laser annealing (ELA) has been investigated in 10 keV B-implanted samples. It is found that for energy densities inducing melt depths of the order or larger of the implanted region the junction depth is controlled by the melt depth, with activation approaching 100% and box-shaped carrier density distributions with abrupt junction profile. For energy densities inducing a melting shallower than the implanted region, two different activation mechanisms have been identified: the first occurring in the molten region and leading to complete B activation; the second occurring in the region immediately below the molten zone and leading to thermal activation of B, induced by the heat wave propagating into the Si wafer. This last process is characterized by an activation energy of 5 eV and is not accompanied by B diffusion. As a consequence, a deep tail of active B is produced, preventing the possibility to form abrupt and ultrashallow junctions. These results suggest that for the formation of ultrashallow junctions it is essential to combine ELA with ultralow energy ion implantation.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.70.D- Solid-liquid transitions
81.40.Gh Other heat and thermomechanical treatments
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Acceptor-bound exciton transition in Mg-doped AlN epilayer

N. Nepal, M. L. Nakarmi, K. B. Nam, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 85, 2271 (2004); http://dx.doi.org/10.1063/1.1796521 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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Mg-doped AlN epilayers grown by metalorganic chemical-vapor deposition have been studied by deep ultraviolet time-resolved photoluminescence (PL) spectroscopy. A PL emission line at 6.02 eV has been observed at 10 K in Mg-doped AlN, which is about 40 meV below the free-exciton transition in undoped AlN epilayer. Temperature dependence of the PL intensity of this emission line also reveals a binding energy of 40 meV. This transition line is believed to be due to the recombination of an exciton bound to neutral Mg acceptor (I1) with a binding energy of Ebx=40 meV. This value is also about 10% of the energy level of Mg impurity in AlN satisfying Haynes’ rule. The recombination lifetime of the I1 transition in Mg-doped AlN has been measured to be 130 ps, which is close to the expected value. The larger Ebx of the acceptor-bound exciton in AlN than that in GaN is due to large effective masses of the electrons and holes, as well as the energy level of Mg impurity.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Depletion-mode ZnO nanowire field-effect transistor

Y. W. Heo, L. C. Tien, Y. Kwon, D. P. Norton, S. J. Pearton, B. S. Kang, and F. Ren

Appl. Phys. Lett. 85, 2274 (2004); http://dx.doi.org/10.1063/1.1794351 (3 pages) | Cited 119 times

Online Publication Date: 24 September 2004

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Single ZnO nanowire metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated using nanowires grown by site selective molecular-beam epitaxy. When measured in the dark at 25°C, he depletion-mode transistors exhibit good saturation behavior, a threshold voltage of ∼−3 V, and a maximum transconductance of order 0.3 mS∕mm. Under ultraviolet (366 nm) illumination, the drain–source current increase by approximately a factor of 5 and the maximum transconductance is ∼5 mS∕mm. The channel mobility is estimated to be ∼3 cm2∕V s, which is comparable to that reported for thin film ZnO enhancement mode MOSFETs, and the on∕off ratio was ∼25 in the dark and ∼125 under UV illumination.
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85.30.Tv Field effect devices
81.07.Bc Nanocrystalline materials
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Magnetotransport in C-doped AlGaAs heterostructures

B. Grbić, C. Ellenberger, T. Ihn, K. Ensslin, D. Reuter, and A. D. Wieck

Appl. Phys. Lett. 85, 2277 (2004); http://dx.doi.org/10.1063/1.1781750 (3 pages) | Cited 15 times

Online Publication Date: 24 September 2004

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High-quality C-doped p-type AlGaAs heterostructures with mobilities exceeding 150 000 cm2∕V s are investigated by low-temperature magnetotransport experiments. We find features of the fractional quantum Hall effect as well as a highly resolved Shubnikov–de Haas oscillations at low magnetic fields. This allows us to determine the densities, effective masses, and mobilities of the holes populating the spin-split subbands arising from the lack of inversion symmetry in these structures.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ey III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

An n- to p-type conductivity transition induced by oxygen adsorption on α-Fe2O3

A. Gurlo, N. Bârsan, A. Oprea, M. Sahm, T. Sahm, and U. Weimar

Appl. Phys. Lett. 85, 2280 (2004); http://dx.doi.org/10.1063/1.1794853 (3 pages) | Cited 34 times

Online Publication Date: 24 September 2004

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The simultaneous measurements of conductance and work function changes induced by gaseous ambient have been performed on α-Fe2O3 thick film polycrystalline samples kept at 280 °C and exposed to different gaseous atmospheres. The switching from n- to p-type conductivity on α-Fe2O3 is shown to have an electronic origin, which is due to the oxygen adsorption and formation of a surface inversion layer and, therefore, to the inversion of the surface conduction type. The modeling of the n–p switching is described in terms of conductance dependence on the band bending induced by gaseous ambient.
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72.60.+g Mixed conductivity and conductivity transitions
73.25.+i Surface conductivity and carrier phenomena
68.43.Mn Adsorption kinetics
71.30.+h Metal-insulator transitions and other electronic transitions
75.50.Gg Ferrimagnetics
73.40.Cg Contact resistance, contact potential
71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
71.55.Ht Other nonmetals

Cooperative polymer gate dielectrics in organic thin-film transistors

S. Young Park, Mikyung Park, and Hong H. Lee

Appl. Phys. Lett. 85, 2283 (2004); http://dx.doi.org/10.1063/1.1794857 (3 pages) | Cited 41 times

Online Publication Date: 24 September 2004

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A concept is introduced in which two polymer dielectrics are made cooperative in acting as the gate insulator for organic thin-film transistors. The bilayer insulator consists of a thin polymer dielectric in contact with the active layer that can induce good electrical properties and a much thicker dielectric with good dielectric properties. These dielectrics are cooperative in combining the best each can offer for a high mobility and a negligible hysteresis.
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85.30.Tv Field effect devices
77.55.-g Dielectric thin films
73.61.Ng Insulators
85.65.+h Molecular electronic devices
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First principles study of transition-metal substitutions in Sm–Co permanent magnets

R. F. Sabirianov, A. Kashyap, R. Skomski, S. S. Jaswal, and D. J. Sellmyer

Appl. Phys. Lett. 85, 2286 (2004); http://dx.doi.org/10.1063/1.1792791 (3 pages) | Cited 6 times

Online Publication Date: 24 September 2004

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The microchemistry and magnetism of conventional and high-temperature Sm–Co permanent magnets are investigated by first-principles calculations. Particular emphasis is on the site preference for the substitution of Cu, Ti, and Zr in SmCo5 and Sm2Co17 compounds. Cu substitution is more favorable in the 1:5 phase, in agreement with experimental findings. Titanium and zirconium have positive solution energies for both the phases, with Ti(Zr) having slight preference for the 1:5 (2:17) phase. Some Zr may segregate to the phase boundaries because of its large solution energy. For Ti and Zr the dumbbell site of the 2:17 phase is preferred over the other three inequivalent cobalt sites. These results are used to discuss the observed cellular nanostructure of the high-temperature Sm–Co hard magnets with composition close to the 2:17 phase.
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75.50.Ww Permanent magnets
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Hx Magnetic impurity interactions
75.30.Gw Magnetic anisotropy
64.75.-g Phase equilibria

The switching properties of patterned synthetic ferrimagnetic structures

J. Janesky, N. D. Rizzo, B. N. Engel, and S. Tehrani

Appl. Phys. Lett. 85, 2289 (2004); http://dx.doi.org/10.1063/1.1792798 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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We investigated the switching properties of patterned submicrometer synthetic ferromagnetic (SF) Ni65Fe15Co20(t1 nm)∕Ru 0.8 nm∕Ni65Fe15Co20(t2 nm) tri-layers. By changing t1 and t2, the shape anisotropy field, Hksh∝∣t1−t2∣, was changed from 36 to 18 Oe, and the effective material anisotropy field, Hkeff,∝α=(t1+t2)∕∣t1−t2∣, was changed from 28 to over 60 Oe. We found that a hard axis field, Hhd, is less effective at reducing the easy axis switching field, Hsw, as α is increased, with α=3.7 requiring twice the relative magnitude of Hhd for the same relative reduction in Hsw as a single magnetic layer. In addition, by repeating the basic SF tri-layer structure in circular elements, we demonstrated improved stability against thermal activation by a factor of 2 with no associated increase in Hsw.
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68.65.Ac Multilayers
75.50.Bb Fe and its alloys
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Effect of high-frequency driving current on magnetization reversal in Co-rich amorphous microwires

A. Chizhik, A. Zhukov, J. Gonzalez, and J. M. Blanco

Appl. Phys. Lett. 85, 2292 (2004); http://dx.doi.org/10.1063/1.1792799 (3 pages) | Cited 2 times

Online Publication Date: 24 September 2004

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Influence of high frequency electric current on the magnetization reversal in Co-rich glass covered amorphous microwires has been studied. The strong correlation between the coercivity and the circular magnetization in the outer shell of the wire has been found. The change of the mechanism of magnetization reversal in the presence of high-frequency circular magnetic field, which is related with the impedance properties, is presented.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.05.Kf Glasses (including metallic glasses)
75.50.Vv High coercivity materials

Photoinduced magnetic memory effect in an iron (II) spin-crossover complex

Hongwu Liu, Akira Fujishima, and Osamu Sato

Appl. Phys. Lett. 85, 2295 (2004); http://dx.doi.org/10.1063/1.1793334 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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We report a bidirectional reversible light-induced excited spin state trapping (LIESST) effect featuring an associated memorey effect in an Fe(II) spin-crossover complex [FeL(CN)2]⋅H2O (where L is a Schiff-base macrocyclic ligand). Depending on the illumination history, bidirectional LIESST processes have been successfully observed that are induced by irradiation with the same two wavelengths. A large zero-point energy difference, strong overlapping spectra of the high-spin and low-spin bands and image internal pressure could account for this photomagnetic phenomenon.
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75.30.Wx Spin crossover
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Effects of orientation transition on exchange anisotropy of Co∕NiMn films by biorientation epitaxial Cu∕Au∕Cu underlayers

Chih-Huang Lai, Yung-Hung Wang, and R. T. Huang

Appl. Phys. Lett. 85, 2298 (2004); http://dx.doi.org/10.1063/1.1793345 (3 pages) | Cited 5 times

Online Publication Date: 24 September 2004

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A biorientation structure of Co∕NiMn films, composed of columnar (001) and (111) epitaxial grains, was developed by using Cu∕Au∕Cu underlayers on Si substrates. When the Au layer is thinner than 7.5 math, Co∕NiMn films are epitaxial (001) and show exchange fields of 50 Oe for 150 math Co. When the Au layer is thicker than 7.5 math, parts of the Co∕NiMn films change to the (111) orientation, and the (111) volume fraction increases with increasing Au thickness. The exchange field of Co∕NiMn can be manipulated by altering the relative amount of epitaxial (001) and (111) grains and the exchange field reaches 150 Oe, an enhancement of 300%, by altering the orientation from (001) to (111). The formation of (111) grains in the biorientation films may decrease (001) crystallite diameter or introduce multidomains in the NiMn films, which plausibly increase uncompensated spins or frustrated spins in NiMn films, leading to the increase in the exchange fields.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
68.65.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Modulation derived satellite peaks in x-ray reciprocal mapping on bismuth cuprate superconductor film

Satoru Kaneko, Yoshitada Shimizu, Kensuke Akiyama, Takeshi Ito, Masahiko Mitsuhashi, Seishiro Ohya, Keisuke Saito, Hiroshi Funakubo, and Mamoru Yoshimoto

Appl. Phys. Lett. 85, 2301 (2004); http://dx.doi.org/10.1063/1.1794376 (3 pages) | Cited 7 times

Online Publication Date: 24 September 2004

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X-ray reciprocal space mapping (XRSM) was employed to investigate epitaxial Bi2Sr2Ca1Cu2Ox(Bi-2212) film. Ordinal cross section XRSM (ω-2θ) and plan view XRSM (ω-ψ) clearly indicated asymmetric intensity distribution of four satellite peaks caused by supercell structure of Bi-2212 film. Modulation vector estimated by XRSM was q=0.2b*+0.9c*. The XRSM image simulated by sawtooth wave vector showed good agreement with asymmetric satellite peaks observed on epitaxial film.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.-a Thin film structure and morphology

Enhancement in ordering of FePt films by magnetic field annealing

H. Y. Wang, X. K. Ma, Y. J. He, S. Mitani, and M. Motokawa

Appl. Phys. Lett. 85, 2304 (2004); http://dx.doi.org/10.1063/1.1794380 (3 pages) | Cited 16 times

Online Publication Date: 24 September 2004

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Effect of magnetic field annealing on chemical ordering of FePt films has been investigated. It is found that the ordering rate in FePt films is enhanced by applying a magnetic field during postdeposition annealing. Measurements of the structure and magnetic properties of FePt films reveal that the disorder–order transformation starts at or below 450°C when the film is annealed in a magnetic field of 40 kOe. The possible reason for the enhancement in the ordering of FePt films by magnetic field annealing is discussed.
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75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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