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24 Jan 2000

Volume 76, Issue 4, pp. 397-519

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Explicit and closed-form expressions for describing magnetic behaviors of uniaxial anisotropy materials

Jeen Hur, Mun Cheol Paek, Kyoung-Ik Cho, and Sung-Chul Shin

Appl. Phys. Lett. 76, 472 (2000); http://dx.doi.org/10.1063/1.125791 (3 pages) | Cited 2 times

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We present explicit, analytic, and closed-form expressions for describing magnetic behaviors of materials having the magnetic anisotropy energy of K sin2 θ. The functional forms of the expressions depend on the ratio of an applied field to an anisotropy field and the ratio of the lowest critical field, for a domain wall to nucleate or move, to the anisotropy field. The present expressions for functions of experimentally measurable quantities gave an elegant method of fitting the quantities to the torque measurement. Furthermore, they may be useful to analyze the ferromagnetic resonance experiment and to measure the distribution of magnetic properties of magnetic aggregates. © 2000 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
02.60.Ed Interpolation; curve fitting
02.30.Ks Delay and functional equations

Appearance of superparamagnetism on heating nanosize Mn0.65Zn0.35Fe2O4

Chandana Rath, N. C. Mishra, S. Anand, R. P. Das, K. K. Sahu, Chandan Upadhyay, and H. C. Verma

Appl. Phys. Lett. 76, 475 (2000); http://dx.doi.org/10.1063/1.125792 (3 pages) | Cited 32 times

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Nanosize particles (average size ∼12 nm) of mixed ferrite Mn0.65Zn0.35Fe2O4 were prepared by the hydrothermal precipitation route and studied using x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, magnetization measurements, and Mössbauer spectroscopy. The as-prepared sample was largely ferrimagnetic and, as the sample was annealed at temperatures above 250 °C, it gradually became superparamagnetic. This unexpected behavior is explained by assuming that the cation distribution in the nanosize as-prepared sample is in a metastable state and, as the sample is heated, this distribution changes to a more stable state while the grain size remains nearly the same. © 2000 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Exchange-biased La2/3Ca1/3(Sr1/3)MnO3 ultrathin films

K. R. Nikolaev, I. N. Krivorotov, W. K. Cooley, A. Bhattacharya, E. Dan Dahlberg, and A. M. Goldman

Appl. Phys. Lett. 76, 478 (2000); http://dx.doi.org/10.1063/1.125793 (3 pages) | Cited 15 times

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Exchange-induced unidirectional anisotropy in trilayers consisting of a thin conductive ferromagnetic layer of La2/3Ca1/3(Sr1/3)MnO3 sandwiched between two antiferromagnetic layers of La1/3Ca2/3MnO3 has been demonstrated through studies of magnetization, magnetoresistance, and in-plane anisotropy of magnetoresistance. The structures were grown by ozone-assisted molecular beam epitaxy and were characterized by a number of techniques. The possibility for the development of exchange-biased magnetic tunnel junctions using these nonclassic double-exchange ferromagnets is discussed. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Gk Colossal magnetoresistance
75.30.Gw Magnetic anisotropy
75.45.+j Macroscopic quantum phenomena in magnetic systems

Current perpendicular to plane giant magnetoresistance of multilayered nanowires electrodeposited in anodic aluminum oxide membranes

P. R. Evans, G. Yi, and W. Schwarzacher

Appl. Phys. Lett. 76, 481 (2000); http://dx.doi.org/10.1063/1.125794 (3 pages) | Cited 57 times

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Co–Ni–Cu/Cu multilayered nanowires were prepared by electrodeposition using nanoporous aluminum oxide membranes rather than the more usual track-etched polycarbonate membranes as templates. Very large values of the current perpendicular to plane giant magnetoresistance (CPP-GMR) were recorded: 55% at room temperature and 115% at 77 K. The use of aluminum oxide membranes also made possible a study of the effects of annealing on the CPP-GMR. © 2000 American Institute of Physics.
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73.61.At Metal and metallic alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Pq Electrodeposition, electroplating

Local modification of the thin YBa2Cu3O7−y microstrips by the voltage-biased atomic force microscope tip

B. M. Kim, I. S. Song, J. H. Sok, I. H. Song, Y. S. Min, M. K. Kim, and J. W. Lee

Appl. Phys. Lett. 76, 484 (2000); http://dx.doi.org/10.1063/1.125795 (3 pages) | Cited 4 times

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The atomic force microscope (AFM) tip biased at around −15 V is found to be capable of locally modifying the entire thickness of 40-nm-thick semiconducting or superconducting YBa2Cu3O7−y microstrips in air. We show, using combined electrical and AFM measurements, that the local regions underneath the surface of the semiconducting or superconducting YBa2Cu3O7−y microstrips are transformed into either nonconducting or nonsuperconducting regions, respectively, upon applying the negatively biased AFM tip. The conductance of the nonsuperconducting regions is also found to be comparable to that of the superconducting regions before modification at 298 K. © 2000 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
84.40.Az Waveguides, transmission lines, striplines
85.25.-j Superconducting devices

Coupling superconducting-ferromagnetic point contacts by Andreev reflections

Guy Deutscher and Denis Feinberg

Appl. Phys. Lett. 76, 487 (2000); http://dx.doi.org/10.1063/1.125796 (3 pages) | Cited 110 times

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The properties of a device made of two point contacts between normal (N) or ferromagnetic (F) tips, and a superconductor (S), are discussed as a function of the spin polarization and the distance L between the contacts. When L is smaller than the superconductor coherence length ξ, nonlocal Andreev reflections occur: for opposite spin polarizations of the contacts, “mixed” Cooper pairs made of electrons coming one from each tip can be injected into the superconductor. This leads to unusual properties, for instance, the parallel resistance of two S/F contacts goes from infinity for full and equal polarizations, to a finite Andreev value for opposite ones. © 2000 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.20.Fg BCS theory and its development
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Properties of BaFe12O19 films prepared by laser deposition with in situ heating and post annealing

Y. F. Lu and W. D. Song

Appl. Phys. Lett. 76, 490 (2000); http://dx.doi.org/10.1063/1.125797 (3 pages) | Cited 16 times

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BaFe12O19 films on (001) sapphire substrates are prepared by laser deposition with in situ heating and postannealing. The properties of the films are analyzed by x-ray diffractometry, vibrating sample magnetometer, atomic force microscopy, and Raman spectroscopy. The relationship among the coercivity, crystalline orientation, and grain shape and size is discussed. The film with coercivity of 5.1 kOe has been obtained by laser deposition with postannealing. The film with a preferential c-axis orientation normal to the film plane and the grains having good crystallinity with hexagonal symmetry have been obtained by laser deposition with in situ heating. © 2000 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ss Magnetic recording materials
81.15.Fg Pulsed laser ablation deposition
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
68.55.-a Thin film structure and morphology
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Reduction of the interfacial Si displacement of ultrathin SiO2 on Si(100) formed by atmospheric-pressure ozone

Akira Kurokawa, Ken Nakamura, Shingo Ichimura, and Dae Won Moon

Appl. Phys. Lett. 76, 493 (2000); http://dx.doi.org/10.1063/1.125798 (3 pages) | Cited 19 times

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We examined the structure around the interface of SiO2 and Si using medium-energy ion scattering spectroscopy (MEIS) to investigate the interfacial Si displacement of an ultrathin silicon dioxide formed by oxidation of a Si(100) substrate with atmospheric-pressure ozone at a substrate temperature of 375 °C. A thermally grown oxide with the same thickness as an ozone-formed oxide was also measured with MEIS for comparison. The ozone-formed oxide exhibited considerably less Si displacement in the oxide layers near the interface than a thermally grown oxide, which indicates that an ozone oxide is homogenous. These results explain well our previous findings that an ozone oxide exhibits a constant HF etching rate of silicon dioxide while a thermally grown oxide slows the etching rate near the interface. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning

Influence of Pt heterostructure bottom electrodes on SrBi2Ta2O9 thin film properties

Seung-Hyun Kim, D. J. Kim, J.-P. Maria, A. I. Kingon, S. K. Streiffer, J. Im, O. Auciello, and A. R. Krauss

Appl. Phys. Lett. 76, 496 (2000); http://dx.doi.org/10.1063/1.125799 (3 pages) | Cited 23 times

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The properties of SrBi2Ta2O9 (SBT) films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films grown on stable Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibit high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films synthesized on Pt/Ti/SiO2/Si. It is shown that severe diffusion of Ti from the Ti interlayer onto the surface of the Pt bottom electrode and the increased surface roughness of this electrode stack play key roles in degradation of SBT properties. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.80.Dj Domain structure; hysteresis
73.61.Ng Insulators
66.30.Ny Chemical interdiffusion; diffusion barriers
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

First principles study of Pb vacancies in PbTiO3

S. Pöykkö and D. J. Chadi

Appl. Phys. Lett. 76, 499 (2000); http://dx.doi.org/10.1063/1.125800 (3 pages) | Cited 31 times

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Electronic and ionic structures of lead vacancies in PbTiO3 were studied using an ab initio approach. Even though the lead vacancy is found to be an acceptor with stable charge states ranging from 2- to 4- it does not form a tightly bound defect pair with a double donor oxygen vacancy. The formation of distant and nearby lead-vacancy–oxygen-vacancy pairs is shown to be exothermic under certain growth conditions. © 2000 American Institute of Physics.
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71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Electrical properties of ZrO2 gate dielectric on SiGe

T. Ngai, W. J. Qi, R. Sharma, J. Fretwell, X. Chen, J. C. Lee, and S. Banerjee

Appl. Phys. Lett. 76, 502 (2000); http://dx.doi.org/10.1063/1.125801 (3 pages) | Cited 2 times

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We report the electrical properties of a high dielectric constant (high-k) material, ZrO2, deposited directly on SiGe, without the use of a Si buffer layer or a passivation barrier. ZrO2 thin films of equivalent oxide thickness (EOT) down to 16.5 Å were deposited on strained SiGe layers by reactive sputtering. Results indicate that ZrO2 films on SiGe have good interfacial properties and low leakage currents. Sintering in forming gas at 350 °C for 1 h could further improve the film quality. Although threshold voltage stability and dielectric dispersion become a concern for thick ZrO2 films, thin ZrO2 films of EOT less than 20 Å exhibit excellent electrical properties making them a good candidate for SiGe applications. © 2000 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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Demonstration of III–V semiconductor-based nonvolatile memory devices

Zhongwei Pan and Kai Shum

Appl. Phys. Lett. 76, 505 (2000); http://dx.doi.org/10.1063/1.125802 (3 pages) | Cited 4 times

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Using the concept for nonvolatile memories recently proposed by K. Shum, J. Q. Zhou, W. Zhang, L. F. Zeng, and M. C. Tamargo [Appl. Phys. Lett. 71, 2487 (1997)], a promising nonvolatile memory device has been designed and demonstrated using a III–V semiconductor quantum structure. Preliminary data on the device’s stability and reliability reveals that further improvements are possible on the cycling endurance and retention time. © 2000 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
85.30.Hi Surface barrier, boundary, and point contact devices
84.30.Sk Pulse and digital circuits

Micromachined convective accelerometers in standard integrated circuits technology

Veljko Milanović, Edwin Bowen, Mona E. Zaghloul, Nim H. Tea, John S. Suehle, Beverly Payne, and Michael Gaitan

Appl. Phys. Lett. 76, 508 (2000); http://dx.doi.org/10.1063/1.125803 (3 pages) | Cited 18 times

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This letter describes an implementation of micromachined accelerometers in standard complimentary metal–oxide–semiconductor technology. The devices operate based on heat convection and consist of microheaters and thermocouple or thermistor temperature sensors separated by a gap which measure temperature difference between two sides of the microheater caused by the effect of acceleration on free gas convection. The devices show a small linearity error of <0.5% under tilt conditions (±90°), and <2% under acceleration to 7g(g ≡ 9.81 m/s2). Sensitivity of the devices is a nearly linear function of heater power. For operating power of ∼ 100 mW, a sensitivity of 115 μV/g was measured for thermopile configuration and 25 μV/g for thermistor configurations. Both types of devices are operable up to frequencies of several hundred Hz. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.10.Cm Micromechanical devices and systems
06.30.Gv Velocity, acceleration, and rotation
07.20.Dt Thermometers
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Photoenhanced wet oxidation of gallium nitride

L.-H. Peng, C.-H. Liao, Y.-C. Hsu, C.-S. Jong, C.-N. Huang, J.-K. Ho, C.-C. Chiu, and C.-Y. Chen

Appl. Phys. Lett. 76, 511 (2000); http://dx.doi.org/10.1063/1.125804 (3 pages) | Cited 28 times

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We investigate the photo-oxidation process and the corresponding passivation effects on the optical properties of unintentionally doped n-type gallium nitride (GaN). When illuminated with a 253.7 nm mercury line source, oxidation of GaN is found to take place in aqueous phosphorus acid solutions with pH values ranging from 3 to 4. At room temperature, the photo-oxidation process is found reaction-rate limited and has a peak value of 224 nm/h at pH=3.5. Compared with the as-grown GaN layers, threefold enhancement in the photocurrent and photoluminescence response are observed on the oxidized GaN surfaces. These results are attributed to the surface passivation effects due to the deep ultraviolet-enhanced wet oxidation on GaN. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
81.65.Rv Passivation
81.05.Ea III-V semiconductors
82.50.-m Photochemistry
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.55.Cr III-V semiconductors

Picosecond photoacoustics using common-path interferometry

Mehrdad Nikoonahad, Shing Lee, and Haiming Wang

Appl. Phys. Lett. 76, 514 (2000); http://dx.doi.org/10.1063/1.125805 (3 pages) | Cited 5 times

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A pump-probe technique based on the detection of optical phase changes at the surface is described. A common-path interferometer in which the reference and probe pulses interrogate the surface immediately (∼500 ps) before and after the pump pulse is demonstrated. The primary application of this system is film thickness measurement in integrated circuit processing. Pulses 60 to 100 fs wide, from a Ti-sapphire laser at 800 nm, are brought to a 5 μm focus on the surface, resulting in picosecond acoustic pulses in the film. Echoes from film interfaces, upon arrival at the surface, lead to a phase change in the probe beam which is measured. Results from tungsten, aluminum, and copper film structures are presented. © 2000 American Institute of Physics.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
07.60.Ly Interferometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Microtip-assisted metal–insulator transition in a layered chalcogenide

W. Yamaguchi, O. Shiino, T. Endo, K. Kitazawa, and T. Hasegawa

Appl. Phys. Lett. 76, 517 (2000); http://dx.doi.org/10.1063/1.125806 (3 pages) | Cited 1 time

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The layered compound 1T–TaS1.7Se0.3 forms a nanoscale domain structure, separated by mesh-like domain walls, above its bulk metal–insulator transition temperature TMI of ∼ 180 K. Scanning tunneling microscopy and spectroscopy of the compound demonstrated that each metallic domain can be converted to insulating one by successive scans of the probe tip just above TMI. This tip-assisted phenomenon is consistently explained by assuming that the domain structure arises from irregular distortion of charge density waves, and that the stacking pattern of charge density waves plays an essential role in the metal–insulator transition. © 2000 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
71.45.Lr Charge-density-wave systems
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
61.46.-w Structure of nanoscale materials
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