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1 Nov 2006

Volume 100, Issue 9, Articles (09xxxx)

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Effect of oxygen annealing on Pr0.7Ca0.3MnO3 thin film for colossal electroresistance at room temperature

D. S. Kim, C. E. Lee, Y. H. Kim, and Y. T. Kim

J. Appl. Phys. 100, 093901 (2006); http://dx.doi.org/10.1063/1.2364386 (4 pages) | Cited 10 times

Online Publication Date: 2 November 2006

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We studied an appropriate annealing condition of Pr0.7Ca0.3MnO3 (PCMO) thin film that can show good resistive switching characteristics for resistance random access memory applications and also tried to elucidate the mechanism of the resistive switching of PCMO thin film at room temperature. We could observe that crystal structure of PCMO film was changed by oxygen annealing. From x-ray photoelectron spectroscopy measurements, we can conclude that the excess of oxygen by oxygen annealing of PCMO film leads to an increase of Mn4+ content at the PCMO surface with a subsequent change in the Mn4+/Mn3+ ratio at the PCMO surface. The resistance ratio of high resistance state and low resistance state was increased by oxygen annealing of PCMO thin film. This can be explained as follows. The change of the Mn4+/Mn3+ ratio at the PCMO surface by oxygen annealing leads to the change of characteristics of Au-PCMO interface domain and therefore results in the change of the resistance ratio.
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73.61.Ng Insulators
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
79.60.Dp Adsorbed layers and thin films

Microwave characteristics of low density hollow glass microspheres plated with Ni thin-film

Z. W. Liu, L. X. Phua, Y. Liu, and C. K. Ong

J. Appl. Phys. 100, 093902 (2006); http://dx.doi.org/10.1063/1.2358824 (6 pages) | Cited 11 times

Online Publication Date: 6 November 2006

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Hollow glass microspheres coated with thin Ni films of various thicknesses (about 50–250 nm) were obtained by electroless plating technique. The resultant magnetic microspheres had very low densities ( ∼ 0.39–1.28 g cm−3) and low coercivities (<40 Oe). As-plated films comprised of nanocrystallites embedded in amorphous matrix and postannealing treatment led to a submicrocrystalline structure and an increased saturation magnetization. The high frequency properties of the composites consisting of Ni-plated microspheres and polymer were investigated. The permittivity and permeability increased with increasing microsphere content in the composite and increasing Ni film thickness. These composites had ferromagnetic resonance peak in the range of 5–12 GHz. Postannealing also had an effect on the microwave properties. The reflection loss of the composite was found dependent on the absorber material thickness, polymer:microsphere ratios, the Ni film thickness, as well as the heat treatment of the microspheres.
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78.70.Gq Microwave and radio-frequency interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Ch Permittivity (dielectric function)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.40.Gh Other heat and thermomechanical treatments
84.40.-x Radiowave and microwave (including millimeter wave) technology

Magneto-optical imaging using polarization modulation method

Takayuki Ishibashi, Zhihao Kuang, Shuta Yufune, Tetsuya Kawata, Masaru Oda, Toshiro Tani, Yasufumi Iimura, Katsuaki Sato, Yasushi Konishi, Kouich Akahane, Xiaoru Zhao, and Tetsuya Hasegawa

J. Appl. Phys. 100, 093903 (2006); http://dx.doi.org/10.1063/1.2357699 (6 pages) | Cited 8 times

Online Publication Date: 6 November 2006

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A magneto-optical (MO) microscope that uses the polarization modulation method has been developed for quantitative MO imaging. In this technique, images of MO rotation and ellipticity are reconstructed from three images for different polarization states; i.e., linear, right-circular, and left-circular polarization states. The three polarization states are generated either by rotating a quarter-wave plate or by changing the voltage applied to a liquid crystal modulator (LCM). Measurements are performed using a patterned thin film of Bi,Ga-substituted yttrium iron garnet prepared on a glass substrate. The values of MO rotation and ellipticity obtained from the images for several wavelengths between 450 and 650 nm are found to agree quantitatively with those obtained by an MO spectrometer. Hysteresis loops at any point of the image can be displayed by simply placing a pointer at the position. A real-time MO imaging with a rate of 1 frame/s is also achieved by using the LCM and a high-speed charge-coupled device camera.
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07.60.Pb Conventional optical microscopes
42.79.Ci Filters, zone plates, and polarizers
42.79.Hp Optical processors, correlators, and modulators

Effect of target power and composition on RE–Fe–B thin films with Cu and Nb buffer and cap layers

L. Castaldi, M. R. J. Gibbs, and H. A. Davies

J. Appl. Phys. 100, 093904 (2006); http://dx.doi.org/10.1063/1.2360156 (7 pages) | Cited 2 times

Online Publication Date: 7 November 2006

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We report a systematic study of the structural, morphological, and magnetic properties of RE–Fe–B (RE = rare earth) films codeposited onto thermally oxidized Si substrates. The use of Cu and Nb buffer and cap layers was investigated. The deposition of the samples was performed by magnetron sputtering with the substrates held at 470 °C and using various Fe target power densities and fixed RE:Fe:B target power density. This was done in order to vary the growth rate and the Fe content of the films. The simultaneous increase of the deposition rate and Fe content influenced the c-axis texturing of the samples. For the Cu/RE:Fe:B/Cu films, as a consequence of the good perpendicular intrinisic coercivity ( ∼ 492 kA/m at 10 W) and very high remanent polarization ( ∼ 1.51 T at 110 W), very good perpendicular energy products were obtained at 10 W ( ∼ 133 kJ/m3) and 110 W ( ∼ 136 kJ/m3). The Nb/RE:Fe:B/Nb samples had the best combination of perpendicular energy product and intrinsic coercivity, with values of 150 kJ/m3 and 800 kA/m, respectively, for an iron target power of 20 W. This high energy product was retained up to target powers of 50 W in spite of the intrinsic coercivity decreasing rapidly with increasing power beyond 20 W, because of a marked increase in remanent polarization.
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68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
75.50.Bb Fe and its alloys
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Electric field tunable ferrite-ferroelectric hybrid wave microwave resonators: Experiment and theory

A. B. Ustinov, V. S. Tiberkevich, G. Srinivasan, A. N. Slavin, A. A. Semenov, S. F. Karmanenko, B. A. Kalinikos, J. V. Mantese, and R. Ramer

J. Appl. Phys. 100, 093905 (2006); http://dx.doi.org/10.1063/1.2372575 (7 pages) | Cited 26 times

Online Publication Date: 8 November 2006

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The electric field tuning characteristics of a combined microwave resonator based on ferrite-ferroelectric layered structure have been studied in a wide range of bias magnetic fields. The combined ferrite-ferroelectric resonator was composed of two rectangular resonators fabricated from a ceramic barium strontium titanate (BST) slab and a single-crystal yttrium iron garnet (YIG) film. The in-plane dimensions for the YIG and BST resonators were chosen to be equal in order to maximize the electromagnetic coupling between their main modes and reduce spurious influence of their higher order modes. A tuning range of 100 MHz for the resonator frequency was realized at 5 GHz through the variation of magnetic permeability and dielectric permittivity of the YIG-BST structure. A theory for the hybrid wave excitations, based on a coupled-mode approach, has been developed and provides good description of the data.
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85.70.Ge Ferrite and garnet devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
41.20.-q Applied classical electromagnetism
84.40.-x Radiowave and microwave (including millimeter wave) technology
77.22.Ch Permittivity (dielectric function)

Measurement of interstrand conductance in multistrand superconducting cables

Bing Lu and Cesar Luongo

J. Appl. Phys. 100, 093906 (2006); http://dx.doi.org/10.1063/1.2363726 (10 pages)

Online Publication Date: 10 November 2006

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Multistrand superconducting cables are widely used in large scale applications to obtain large current carrying capacity. Stability is one of the key issues that ensure continuous and reliable operation of superconducting cables. Knowledge of interstrand conductance is essential for analysis of current distribution and redistribution processes that substantially influence the stability of multistrand superconducting cables. In this paper, an approach to measure interstrand conductance is developed using parametric estimation method as used in control theory. First, a distributed parameter circuit model is adopted to calculate the current and voltage distribution in superconducting cables. Then, strand voltage differences at cable ends are measured by experiment. Finally, least squares method is applied to estimate the interstrand conductance which gives the minimum error of the voltage difference at cable ends between calculated and measured data. The interstrand conductance between the subcables in different cabling stages in a cable-in-conduit conductor (CICC) has been studied under different conditions (different temperatures and different cable lengths). The results are consistent, accurate, and fit the distributed parameters circuit model well. This method provides a convenient approach to evaluate electrical coupling parameters in multistrand superconducting cables under different conditions. The estimated parameters can be used to improve the accuracy of analysis of current distribution and cable stability.
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84.71.Fk Superconducting cables

Josephson junction parameters for alternating current wave form synthesis

O. V. Karpov, V. M. Buchstaber, S. V. Sherstobitov, S. I. Tertychniy, J. Niemeyer, and O. Kieler

J. Appl. Phys. 100, 093907 (2006); http://dx.doi.org/10.1063/1.2358817 (6 pages) | Cited 1 time

Online Publication Date: 10 November 2006

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The paper discusses the dynamics of different types of overdamped Josephson junctions biased by a sinusoidal microwave current. The results clarify the theoretical background for optimizing the single junction and the junction array parameters for their use as alternating current (ac) wave form synthesizers. The determined phase lock areas demonstrate the degree of overlap for Shapiro steps [ S. Shapiro, Phys. Rev. Lett. 11, 80 (1963) ] of different orders as a function of the normalized frequency μ = 2πfωc−1, where f is the microwave frequency and ωc is the Josephson junction characteristic frequency. For μ ⩽ 0.7, which is a typical operation range for superconductor-insulator-superconductor Josephson junctions in the conventional direct current (dc) voltage standard at the bias frequency range from 10 to 100 GHz, the Shapiro steps overlap completely. For μ ≥ 1.4 [typical for superconductor-normal-superconductor junctions at the same frequency range], the steps do not overlap. This allows for ac voltage synthesis by means of binary arrays and pulse-driven systems. For 0.7 ⩽ μ ⩽ 1.4 there is a range of partially overlapping Shapiro steps, which allows a rapid switching of the Josephson dc voltages for ac synthesis by microwave power modulation. Experimentally we have achieved this range through properly designed superconductor-insulator-normal-insulator-superconductor junctions.
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74.81.Fa Josephson junction arrays and wire networks
74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices

Relation between the magnetic properties and the crystal and electronic structures of manganese spinels LiNi0.5Mn1.5O4 and LiCu0.5Mn1.5O4−δ (0<δ<0.125)

N. Biškup, J. L. Martínez, M. E. Arroyo y de Dompablo, P. Díaz-Carrasco, and J. Morales

J. Appl. Phys. 100, 093908 (2006); http://dx.doi.org/10.1063/1.2364045 (6 pages) | Cited 10 times

Online Publication Date: 13 November 2006

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The magnetic properties of LiM0.5Mn1.5O4 (M = Ni and Cu) spinels, materials of interest as electrodes for Li-ion batteries, have been studied and interpreted with the help of the first-principles calculation method. The magnetic susceptibility of the Ni compound, that behaves virtually as stoichiometric normal spinel, is consistent with the well-established magnetic model of the spinel structure that leads to ferrimagnetism. However, the Cu spinel was oxygen deficient and showed significant divergences from this model. The ferromagnetic component of this spinel was dependent on the calcining temperature and was smaller to that predicted by the magnetic model. The special crystal structure of the spinel, namely, oxygen deficiency and increased occupancy of the tetrahedral sites by Cu ions, satisfactorily explains the more complex magnetic behavior observed, further supported by the results of the first-principles electronic structure computations.
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75.30.Cr Saturation moments and magnetic susceptibilities
61.66.Fn Inorganic compounds
71.15.-m Methods of electronic structure calculations
75.50.Gg Ferrimagnetics
82.47.Aa Lithium-ion batteries
71.20.Ps Other inorganic compounds

The effect of residual strain on (001) texture evolution in FePt thin film during postannealing

Jae-Song Kim, Yang-Mo Koo, and Namsoo Shin

J. Appl. Phys. 100, 093909 (2006); http://dx.doi.org/10.1063/1.2364051 (6 pages) | Cited 10 times

Online Publication Date: 13 November 2006

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Residual strain in a Fe55Pt45 thin film was investigated in order to provide experimental support for a previous theoretical study [ J.-S. Kim et al., J. Appl. Phys. 99, 053906 (2006) ] in which a strong evolution of (001) texture during the postannealing of deposited FePt thin films was attributed to amorphous substrates. Residual strain measurements using dual diffraction peaks to analyze the strain state were used in the study. The findings show that transformation and biaxial in-plane strains coexist in annealed Fe55Pt45 films and their effect could lower the strain energy of the (001) crystal (crystal with a [001] crystallographic orientation into the surface normal) when grain growth proceeds actively. Therefore, we propose that anisotropic strain due to ordering transformations under tensile in-plane strain is a key factor that affects texture evolution. The importance of the subsequent grain growth is also discussed.
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68.60.Bs Mechanical and acoustical properties
81.40.Gh Other heat and thermomechanical treatments

Optical coatings for improved contrast in longitudinal magneto-optic Kerr effect measurements

P. R. Cantwell, U. J. Gibson, D. A. Allwood, and H. A. M. Macleod

J. Appl. Phys. 100, 093910 (2006); http://dx.doi.org/10.1063/1.2364391 (9 pages) | Cited 16 times

Online Publication Date: 14 November 2006

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We have studied the increases in the longitudinal magneto-optic Kerr effect signal contrast that can be achieved by the application of optical overlayers on magnetic films. For simple coatings, a factor of ∼ 3 improvement in signal contrast is possible. Matching the optical impedance of the magnetic material improves the raw Kerr signal and also reduces the sample reflectivity, yielding a large Kerr angle. The contrast can be optimized by increasing the rotated Kerr reflectivity component while maintaining enough of the base reflectivity Fresnel component to produce a strong signal. Calculations and experimental results are presented for single layer ZrO2 dielectric coatings on Ni along with calculations for a three-layer Au–ZrO2–Ni structure. Incidence angle effects are also presented.
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78.20.Ls Magneto-optical effects
42.70.-a Optical materials
42.79.Wc Optical coatings
78.66.Nk Insulators
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Domain wall induced modes of high-frequency response in ferromagnetic elements

Ute Queitsch, Jeffrey McCord, Andreas Neudert, Rudolf Schäfer, Ludwig Schultz, Karsten Rott, and Hubert Brückl

J. Appl. Phys. 100, 093911 (2006); http://dx.doi.org/10.1063/1.2365382 (10 pages) | Cited 9 times

Online Publication Date: 14 November 2006

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The influence of domain wall density on the magnetization dynamics of amorphous CoZrTa thin-film elements was investigated by a combination of microwave magnetometry and quasistatic plus time-resolved wide-field Kerr microscopy. In addition to domain wall motion, permeability rolloff at low frequencies occurs due to rotational processes. The dominating ferromagnetic resonance modes depend on the domain wall density due to the formation of a zone of magnetization curling at the domain walls, which results from a phase lag of domain and domain wall response. Both the amount of permeability reduction and the increase in precessional frequency, can be varied with magnetic history. All effects are avoided by lamination of the ferromagnetic films. The results demonstrate the importance of detailed domain control for the optimization of patterned films for high-frequency applications, beyond the elementary adjustment of material’s high-frequency properties.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.66.Bz Metals and metallic alloys
78.20.Ls Magneto-optical effects
78.47.-p Spectroscopy of solid state dynamics

High frequency characteristics of FeCoN thin films fabricated by sputtering at various (Ar+N2) gas flow rates

Yan Liu, Z. W. Liu, C. Y. Tan, and C. K. Ong

J. Appl. Phys. 100, 093912 (2006); http://dx.doi.org/10.1063/1.2361160 (5 pages) | Cited 13 times

Online Publication Date: 14 November 2006

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FeCoN soft magnetic thin films with various nitrogen contents were fabricated by varying the gas flow rates of the argon and nitrogen gas mixture used during reactive rf magnetron sputtering. It was found that the resistivity of FeCoN film increased up to 211 μΩ cm with increasing nitrogen content. The film produced at the gas flow rate of 7 sccm exhibited the best soft magnetic properties with small coercivity and relatively large saturation magnetization. The microstructure of the films was examined by high-resolution transmission electron microscopy and α″-FeCo phase with very high saturation magnetization was observed in the films. The high-frequency properties of the FeCoN thin films were experimentally characterized and theoretically examined. The Hoffmann’s ripple theory was used to explain the permeability spectra for the films with strong magnetization dispersion. We found that the ripple effect is responsible for the large damping in the films, and those films with larger coercivities have stronger magnetization dispersion. With the gas flow rate of the argon and nitrogen gas mixture increasing from 0 to 15 sccm, the low-frequency permeability decreased from 680 to 245 and the ferromagnetic resonance frequency increased from 2.09 to 2.99 GHz.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
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