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1 Aug 1999

Volume 86, Issue 3, pp. 1177-1776

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Electrodynamic properties of coplanar waveguides made from high-temperature superconducting YBa2Cu3O7−δ electrodes on nonlinear dielectric SrTiO3 substrates

A. T. Findikoglu, D. W. Reagor, K. Ø. Rasmussen, A. R. Bishop, N. Grønbech-Jensen, Q. X. Jia, Y. Fan, C. Kwon, and L. A. Ostrovsky

J. Appl. Phys. 86, 1558 (1999); http://dx.doi.org/10.1063/1.370967 (11 pages) | Cited 8 times

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We present a comprehensive study of broadband (0–2 GHz) electrodynamic properties of coplanar waveguides made from high-temperature superconducting thin-film YBa2Cu3O7−δ electrodes on nonlinear dielectric single-crystal SrTiO3 substrates. The waveguides exhibit strong dielectric nonlinearities, in addition to temperature-, dc-bias-, and frequency-dependent dissipation and refractive index. By using parameters determined from small-signal (linear) transmission characteristics of the waveguides as a function of dc bias, we develop a model equation that successfully predicts and describes large-signal (nonlinear) behavior. © 1999 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
85.25.Am Superconducting device characterization, design, and modeling

Current transfer at superconducting Bi2Sr2CaCu2O8+δ–Ag joints

A. Kuršumović, R. P. Baranowski, B. A. Glowacki, and J. E. Evetts

J. Appl. Phys. 86, 1569 (1999); http://dx.doi.org/10.1063/1.370929 (5 pages) | Cited 10 times

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Composite reaction textured Bi2Sr2CaCu2O8+δ superconducting samples were made by partial melt processing, with aligned MgO fibers as seeding and texturing interfaces. The electric contacts were in situ processed thick silver tapes of the same width as the sample. The voltage drop at the metal–superconductor joint was measured in liquid nitrogen during continuous current ramp in self fields and applied fields. The contact resistivity and current transfer length were estimated by applying a transmission line model for current transport across the joint. The calculated and estimated transfer length, corresponding to >95% current transfer, occurs over only 0.75 mm of the contact in the case of a 0.125-mm-thick Ag current lead. At currents, I, below critical, IC, this approach was satisfactory. However, at higher currents nonohmic behavior is observed. The apparent contact resistance increased with increasing current, and with applied magnetic field. This contribution to the contact resistance arises from flux flow effects in the superconductor and is shown to vary nonlinearly with both increasing current and increasing applied field. Consequently the current transfer length increased progressively over the whole contact, approaching a rather uniform current distribution at about I ∼ 12IC. The results are compared with a nonlinear finite element model of current flow in an in situ current element; the agreement of the model with experiment is good. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.F- Transport properties
02.70.Dh Finite-element and Galerkin methods

Origin of a magnetic easy axis in pipeline steel

L. Clapham, C. Heald, T. Krause, D. L. Atherton, and P. Clark

J. Appl. Phys. 86, 1574 (1999); http://dx.doi.org/10.1063/1.370930 (7 pages) | Cited 7 times

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Oil and gas pipelines are generally magnetically anisotropic, with a magnetic easy axis in the pipe axial direction. This is of interest because magnetic flux leakage tools are commonly used for the detection and sizing of defects. In the present study we investigate the origin of this magnetic easy axis, using an angular magnetic Barkhausen noise technique to characterize the magnetic anisotropy. The texture, microstructure, and residual stress are examined as possible causes of the easy axis, using x-ray pole figure analysis and microstructural examination along with high and low temperature annealing treatments. Our results indicate that plastic deformation and residual stress are responsible for the magnetic easy axis, since an elimination of the residual stresses through low temperature “stress relief” heat treatment produces a magnetically isotropic structure without altering the texture or microstructure. X-ray pole figure analysis supports the conclusion that magnetic anisotropy is not related to texture in these materials. We conclude that the axial magnetic easy axis is due to a compressive residual hoop stress resulting from the cold bending and cold expansion of the pipe during processing. © 1999 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
81.30.Bx Phase diagrams of metals, alloys, and oxides
75.50.Bb Fe and its alloys

Magnetization hystereses in trilayer systems with an in-plane component defect

Takehiko Yorozu and Xiao Hu

J. Appl. Phys. 86, 1581 (1999); http://dx.doi.org/10.1063/1.370931 (15 pages) | Cited 2 times

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Hystereses loops during magnetization reversal processes are calculated numerically for systems of trilayer magnetic materials having an in-plane anisotropy defect between two perpendicular anisotropy layers. The shape of the hysteresis loop depends critically on the magnetic parameters and the thickness of the in-plane layer. The sum of anisotropy, exchange and Zeeman energy is also pursued in accordance with the reversal processes. When the energy required for the magnetization reversal is plotted as a function of the defect layer thickness, the energy accumulated in the defect indicates maximum value where the nucleation field bifurcates from the field necessary for the entire magnetization reversal. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions

Magneto-optical properties of chromium-alloyed manganese bismuth thin films

Prabhakar R. Bandaru, Timothy D. Sands, Dieter Weller, and Ernesto E. Marinero

J. Appl. Phys. 86, 1596 (1999); http://dx.doi.org/10.1063/1.370932 (8 pages) | Cited 5 times

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MnBi thin films have been considered for short-wavelength rewritable optical recording media due to the very large magneto-optic Kerr rotation and perpendicular anisotropy (Ku) of the hexagonal magnetic low-temperature MnBi phase. However, coincident structural and magnetic transformations near the Curie temperature (360 °C) result in poor thermal cycling behavior, preventing the application of MnBi as rewritable media. We have previously hypothesized that the substitution of Cr for Mn would reduce the ferromagnetic coupling along the c axis, thereby lowering the Curie temperature and possibly decoupling the magnetic and structural transitions. Preliminary experimental data reported earlier [P. R. Bandaru et al., Appl. Phys. Lett. 72, 2337 (1998)] supported this hypothesis. In this article, the effects of Cr substitution are further explored and the feasibility of Mn1−xCrxBi (0<x<0.15) films for magneto-optical recording applications analyzed. It is shown that 5% Cr is sufficient for decoupling the phase transitions with no significant loss in the magneto-optic figure of merit. Transmission electron microscopy studies indicate a small grain size (∼50 nm) for the Cr-alloyed films, which could be beneficial for reducing media noise. © 1999 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.50.Ss Magnetic recording materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.70.Sq Magnetooptical devices
75.30.Gw Magnetic anisotropy

Effect of Fe doping on magnetic properties and magnetoresistance in La1.2Sr1.8Mn2O7

Jun Zhang, Fangwei Wang, Panlin Zhang, and Qiwei Yan

J. Appl. Phys. 86, 1604 (1999); http://dx.doi.org/10.1063/1.370933 (3 pages) | Cited 22 times

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We report the effect of Fe doping on magnetic properties and magnetoresistance (MR) in the layered perovskite La1.2Sr1.8Mn2O7. Fe doping results in the weakening of ferromagnetic (FM) ordering, and the occurrence of a low-temperature spin-glass state in La1.2Sr1.8Mn2−xFexO7. Resistivity increases sharply with increasing Fe concentration. The metal–insulator transition disappears at a very low doping level (x = 0.01), but the low-temperature MR effect is enhanced. These effects result from the replacement of Mn3+ by the doped Fe ions, which interrupts the path of double–exchange interaction and destroys the FM metallic state. Due to the anisotropic interaction in the layered perovskite, the magnetic properties and MR effect are more sensitive to Fe doping than those in ABO3-type perovskites. © 1999 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.50.Lk Spin glasses and other random magnets
75.50.Dd Nonmetallic ferromagnetic materials

Atomic structure, magnetism, and transport properties of damaged La0.67Ca0.33MnO3−δ processed via high-energy ball milling

Michael B. Liou, Shaheen Islam, D. J. Fatemi, V. M. Browning, D. J. Gillespie, and V. G. Harris

J. Appl. Phys. 86, 1607 (1999); http://dx.doi.org/10.1063/1.370934 (4 pages) | Cited 2 times

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A La0.67Ca0.33MnO3−δ alloy was produced via a low-temperature solid state reaction in a high-energy ball mill. The milled alloy is found to exhibit the paramagnetic-to-ferromagnetic (P–F) transition at 150 K. However, the widely reported insulator-to-metal (I–M) transition that usually accompanies the P–F transition is totally suppressed. Anneals at 500–1000 °C in air (t = 8 h) are found to lower the resistivity but not restore the I–M transition. The suppression of the I–M transition is attributed to anion defects in the structure that have not been annihilated during heat treatments. Extended x-ray absorption fine structure is employed to track the evolution of the atomic structure around the Mn cations at various stages of processing. © 1999 American Institute of Physics.
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61.66.Fn Inorganic compounds
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.60.+g Mixed conductivity and conductivity transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Cc Kinetics of defect formation and annealing
71.30.+h Metal-insulator transitions and other electronic transitions

Magnetization processes in Co/Cu multilayers with low magnetoresistive hysteresis

J. N. Chapman, J. Rose, P. R. Aitchison, H. Holloway, and D. J. Kubinski

J. Appl. Phys. 86, 1611 (1999); http://dx.doi.org/10.1063/1.370935 (10 pages) | Cited 6 times

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We have used transmission electron microscopy to study magnetization processes in Co/Cu multilayers with the Cu spacer layer thickness close to 9 Å. The films show giant magnetoresistance (GMR) values ≈25%, saturation fields of 1–2 kOe, and very little magnetoresistive hysteresis; they are of interest as position sensors. While the Cu thickness was chosen to correspond to the first antiferromagnetic maximum, magnetic images taken throughout a magnetization cycle attest to the fact that the antiferromagnetic coupling is far from complete. Detailed analysis of image sequences and the corresponding low angle diffraction patterns suggests that the coupling is dominated by a biquadratic component. This is consistent with the relatively low value of GMR. Furthermore, the well-defined and relatively simple domain processes which are observed over the low field regime (±50 Oe) explain why little hysteresis is observed. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

The role of S passivation on magnetic properties of Fe overlayers grown on GaAs(100)

F. P. Zhang, P. S. Xu, E. D. Lu, H. Z. Guo, F. Q. Xu, and X. Y. Zhang

J. Appl. Phys. 86, 1621 (1999); http://dx.doi.org/10.1063/1.370936 (4 pages) | Cited 4 times

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We have produced epitaxial Fe overlayers on sulfur-passivated GaAs(100) surfaces by CH3CSNH2 treatment, and investigated the correlation between magnetic properties of the overlayers and surface chemical structure of GaAs(100) surfaces by ferromagnetic resonance and synchrotron radiation photoemission. The surface chemical properties were modified by changing the annealing temperature of the surfaces prior to the growth. The results show that the magnetization of Fe overlayers is crucially determined by the presence of Ga–S chemical bonds and excess As after the anneals. A comparative investigation of the magnetization has been made on both S passivated and clean GaAs(100). It is confirmed that S passivation on the GaAs surface can effectively eliminate the magnetization deficiency previously attributed to interdiffusion of As into the Fe overlayer. © 1999 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
81.65.Rv Passivation
73.20.Hb Impurity and defect levels; energy states of adsorbed species
75.70.Rf Surface magnetism
73.40.Ns Metal-nonmetal contacts
75.50.Bb Fe and its alloys
79.60.Dp Adsorbed layers and thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

A theoretical investigation of the effect of the oblique anisotropy axis on the ferromagnetic resonance linewidth

A. Layadi

J. Appl. Phys. 86, 1625 (1999); http://dx.doi.org/10.1063/1.370937 (5 pages) | Cited 8 times

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The effect of the oblique anisotropy axis on the ferromagnetic resonance (FMR) linewidth in a thin film is studied theoretically. The angular dependence of the frequency linewidth is investigated in the plane containing the anisotropy axis and in the film plane. The effect of the tilt angle on the frequency linewidth is shown. Some unusual broadening of the lines in the FMR spectra and certain features of the variation of the frequency linewidth Δf with field orientation and field intensity could be interpreted as being due to the fact that the magnetocrystalline anisotropy axis, i.e., the easy or hard direction of the magnetization, is tilted from the normal with an angle δ. The tilt angle δ as well as the Gilbert damping coefficient α can be deduced from experimental data through this analysis. © 1999 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
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