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27 Sep 1999

Volume 75, Issue 13, pp. 1821-1987

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Use of magnetocrystalline anisotropy in spin-dependent tunneling

R. A. Lukaszew, Y. Sheng, C. Uher, and R. Clarke

Appl. Phys. Lett. 75, 1941 (1999); http://dx.doi.org/10.1063/1.124878 (3 pages) | Cited 13 times

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Epitaxial growth techniques are used to impose in-plane magnetocrystalline anisotropy on a spin-polarized tunneling configuration. A Cu(100) buffer layer grown on a Si(100) substrate stabilizes epitaxial face-centered-cubic cobalt as one of the ferromagnetic electrodes. The negative magnetocrystalline constant of this metastable phase favors easy axes along Co 〈110〉 and, due to the single crystal nature of this layer, the coercivity is more than an order of magnitude larger than in the polycrystalline layers which form the second electrode. Our approach provides a way to access the high degree of spin polarization characteristic of the 3d transition metals. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.61.At Metal and metallic alloys

Spin-polarized scanning tunneling microscopy on ferromagnets

Wulf Wulfhekel and Jürgen Kirschner

Appl. Phys. Lett. 75, 1944 (1999); http://dx.doi.org/10.1063/1.124879 (3 pages) | Cited 62 times

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A straightforward approach to spin-polarized scanning tunneling microscopy based on the magnetotunnel effect between a ferromagnetic tip and a ferromagnetic sample is demonstrated. By periodically changing the magnetization of the tip in combination with a lock-in technique, topographic and spin-dependent parts of the tunnel current are separated and the topography and the magnetic structure of the sample are recorded simultaneously. Results are given for polycrystalline Ni and single crystalline Co(0001) surfaces, revealing a high spin contrast, low data acquisition times, and a resolution down to 10 nm. Potentials and limitations of this technique are discussed. © 1999 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
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
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys

Magnetic imaging of perovskite thin films by ferromagnetic resonance microscopy—La0.7Sr0.3MnO3

S. E. Lofland, S. M. Bhagat, Q. Q. Shu, M. C. Robson, and R. Ramesh

Appl. Phys. Lett. 75, 1947 (1999); http://dx.doi.org/10.1063/1.124880 (2 pages) | Cited 13 times

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We present ferromagnetic resonance scans of epitaxial thin films of La0.7Sr0.3MnO3. In most films, the resonance field indicates the presence of large stresses, the line is wide and both the field and width vary significantly with position. However, in the perpendicular geometry (field normal to the film plane) the best films show narrow lines (<20 Oe) which are relatively independent of position, indicative of magnetic homogeneity. The experiments show that this technique can be used as a contactless, nondestructive diagnostic tool for assessing the magnetic quality of colossal magnetoresistance thin films. © 1999 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.47.Gk Colossal magnetoresistance
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.80.+q Magnetomechanical effects, magnetostriction

Atomic order, electron structure, and critical parameters of epitaxial YBaCuO films

V. D. Okunev, Z. A. Samoilenko, A. Abal’oshev, P. Gierłowski, A. Klimov, and S. J. Lewandowski

Appl. Phys. Lett. 75, 1949 (1999); http://dx.doi.org/10.1063/1.124881 (3 pages) | Cited 15 times

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X-ray structural and optical methods were applied to make a detailed investigation of atomic and electronic structure of superconducting YBa2Cu3O7−δ films obtained by pulsed laser deposition. Optical transmission spectrum was found to depend not only on intraband (ℏω<1.2 eV) and interband (ℏω>1.95 eV) transitions, but also on contributions from charge transfer transitions O 2p⇒Cu 3d in the dielectric phase due to local order in a system of crystallographic (11l) planes. Superconducting properties of the films are determined by orientational structural transition (00l)+(11l)⇒(00l) and by Anderson type transition from a charge transfer O 2p⇒Cu 3d insulator to a strongly degenerate semiconductor with metallic conductivity. We show the effects of ordering on transition temperature Tc and demonstrate that at the concentration of (00l) clusters below the percolation threshold (20%) the behavior of Tc has catastrophic character. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Jb Electronic structure (photoemission, etc.)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
68.55.-a Thin film structure and morphology
74.25.Gz Optical properties
71.30.+h Metal-insulator transitions and other electronic transitions

High oxygen pressure generation of flux-pinning centers in melt-textured YBa2Cu3O7

T. Puig, J. Plain, F. Sandiumenge, X. Obradors, J. Rabier, and J. A. Alonso

Appl. Phys. Lett. 75, 1952 (1999); http://dx.doi.org/10.1063/1.124882 (3 pages) | Cited 19 times

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A strong enhancement of the critical current density, Jcab(H,T), has been generated in melt-textured YBa2Cu3O7/Y2BaCuO5 composites by means of high oxygen pressure (≈100 bar, ∼400 °C). Enhancement factors as high as 180% have been found at low temperatures leading high sample performances at 77 K (Jcab ≈ 1.2×105 A/cm2 at null field). Transmission electron microscopy studies show a high concentration of dendritic-like stacking faults generated as a consequence of the strong nonequilibrium conditions of the transformation from YBa2Cu3O7 to YBa2Cu4O8. The high concentration of 1/6〈031〉 partial dislocations within the (001) planes are proposed as point-defect pinning centers enhancing Jcab(H,T) for the H∥c configuration. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.40.Gh Other heat and thermomechanical treatments
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

High temperature c-axis resistivity of Bi2Sr2CaCu2O8+x single crystals and dependence on oxygen stoichiometry

G. Yang, J. S. Abell, and C. E. Gough

Appl. Phys. Lett. 75, 1955 (1999); http://dx.doi.org/10.1063/1.124883 (3 pages) | Cited 12 times

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The c-axis resistivity of Bi2Sr2CaCu2O8+x crystals has been measured as a function of thermal cycling in the range between 70 and 856 K in flowing oxygen and nitrogen. Hysteresis in the temperature-dependent c-axis resistivity provides evidence of thermally activated oxygen diffusion in and out of the crystal varying as D(T) = 6×107 exp(−Δ1/kT) and D(T) = 55 exp(−Δ2/kT), where Δ1 = 2.2 eV and Δ2 = 1.2 eV, respectively. Oxygen diffusion into the crystals becomes significant above T0 ∼ 595 K and out of the crystal above T1 ∼ 750 K. The implications for the stoichiometric control, superconductivity, and intrinsic high temperature dependence of the resistivity of Bi2Sr2CaCu2O8+x crystals are considered. © 1999 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
74.72.-h Cuprate superconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.Cc Kinetics of defect formation and annealing
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