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12 Mar 2001

Volume 78, Issue 11, pp. 1463-1639

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Scanning Hall probe microscopy of flux penetration into a superconducting YBa2Cu3O7−δ thin film strip

A. N. Grigorenko, S. J. Bending, J. K. Gregory, and R. G. Humphreys

Appl. Phys. Lett. 78, 1586 (2001); http://dx.doi.org/10.1063/1.1352041 (3 pages) | Cited 9 times

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A high-resolution scanning Hall probe microscope has been used to measure flux profiles across one “wire” of a long YBa2Cu3O7−δ thin-film meander line as a function of both transport current density and applied magnetic field. Flux bundle penetration due to an applied current or magnetic field is demonstrated to occur at the same regions at the edge of the strip. A correlation between the surface topography of the meander line edges and the regions of penetration has been established. Penetrating flux profiles at low temperatures are in qualitative agreement with theories of dynamical instability of the order parameter. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.25.F- Transport properties

Patterning ferromagnetism in Ni80Fe20 films via Ga+ ion irradiation

W. M. Kaminsky, G. A. C. Jones, N. K. Patel, W. E. Booij, M. G. Blamire, S. M. Gardiner, Y. B. Xu, and J. A. C. Bland

Appl. Phys. Lett. 78, 1589 (2001); http://dx.doi.org/10.1063/1.1351519 (3 pages) | Cited 40 times

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We demonstrate that focused Ga+ ion irradiation can comprehensively modify the ferromagnetic properties of Ni80Fe20 thin films. Magneto-optic Kerr effect measurements at room temperature and magnetoresistance measurements at temperatures between 1.5 and 270 K characterized the irradiation effects. Irradiation steadily reduced the films’ room temperature coercivity, and a dose of 1.0×1016 ions/cm2 at 30 keV was found sufficient to cause a loss of ferromagnetism at room temperature in films of thickness up to 15.5 nm. In situ end-point detection and postirradiation atomic force microscopy confirmed that the sputtering which accompanied doses up to 1.0×1016 ions/cm2 did not compromise the protective caps on these Ni80Fe20 films. We therefore conclude that the modification of ferromagnetic properties occurred primarily because of direct Ga+ ion implantation. From these results, we speculate that focused Ga+ ion irradiation could be a convenient tool for the nanoscale patterning of magnetic properties in 3d transition metal thin films. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
61.80.Jh Ion radiation effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.82.Bg Metals and alloys
78.20.Ls Magneto-optical effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Array of nickel nanowires enveloped in polyaniline nanotubules and its magnetic behavior

Huaqiang Cao, Chenyang Tie, Zheng Xu, Jianming Hong, and Hai Sang

Appl. Phys. Lett. 78, 1592 (2001); http://dx.doi.org/10.1063/1.1354156 (3 pages) | Cited 27 times

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An array of nickel nanowires enveloped in polyaniline nanotubules was prepared by the “second-order-template” method. As the first step, an array of the polyaniline nanotubules was synthesized in the pores of an alumina membrane, then nickel nanowires were fabricated by electrochemical deposition of the nickel into the polyaniline nanotubules. The composite nanostructure was characterized by x-ray powder diffraction, and scanning electron micrography. Its magnetic properties were measured by a vibrating sample magnetometer. The coercivity and remanence are of high anisotropy with a maximum at θ=90° (parallel to the nanowires). © 2001 American Institute of Physics.
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81.07.Pr Organic-inorganic hybrid nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.De Nanotubes
82.35.Np Nanoparticles in polymers
81.15.Pq Electrodeposition, electroplating
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy
81.05.Qk Reinforced polymers and polymer-based composites

Anomalous temperature dependence of coercivity and reversal mechanism in bulk-hardened rare earth-cobalt magnets

A. M. Gabay, W. Tang, Y. Zhang, and G. C. Hadjipanayis

Appl. Phys. Lett. 78, 1595 (2001); http://dx.doi.org/10.1063/1.1354670 (3 pages) | Cited 20 times

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The “anomalous” nonmonotonic temperature dependence of coercivity, reported in Sm–Zr–Co–Cu magnets, has also been observed in bulk-hardened Y–Zr–Co–Fe–Cu alloys with a similar microstructure. The phenomenon appears to be universal for all R–Co magnets (R=rare earth) having a microstructure consisting of R2Co17 cells surrounded by the RCo5 phase. The effect of R and Cu on the temperature dependence of coercivity cannot be simply explained by traditional domain-wall pinning model based on the difference in a domain wall energy. Possibility that the coercivity is controlled by nucleation of reversed domains in magnetically isolated R2Co17 cells is discussed. © 2001 American Institute of Physics.
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75.50.Vv High coercivity materials
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure

Enhanced metal–insulator transition and magnetoresistance in melt-processed La0.67Ca0.33MnO3 and Ho-doped manganites

A. K. Pradhan, B. K. Roul, Y. Feng, Y. Wu, S. Mohanty, D. R. Sahu, and P. Dutta

Appl. Phys. Lett. 78, 1598 (2001); http://dx.doi.org/10.1063/1.1354659 (3 pages) | Cited 15 times

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We report significant enhancement of magnetoresistance (MR) in melt-processed La0.67Ca0.33MnO3 (LCM) and in Ho-doped LCM samples. The LCM system exhibits surprising enhancement of metal–insulator transition (TIM) that coincides with the Curie transition temperature (Tc), TIM ≈ Tc, illustrating the enhanced percolative transport and spin-polarization through grain boundaries. Surprisingly, 1 mol % of addition of Ho enhances Tc of ∼ 70 K with remarkable colossal MR. The nanoscale Ho distribution is consistent with the magnetic inhomogeneity-induced MR due to phase segregation in Ho-doped sample whereas charge-segregation picture is valid for undoped LCM. © 2001 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
72.60.+g Mixed conductivity and conductivity transitions
75.50.Dd Nonmetallic ferromagnetic materials
72.25.Ba Spin polarized transport in metals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.40.Rs Electrical and magnetic properties related to treatment conditions

Ballistic electron microscopy study of ultrathin oxidized aluminum barriers for magnetic tunnel junctions

W. H. Rippard, A. C. Perrella, and R. A. Buhrman

Appl. Phys. Lett. 78, 1601 (2001); http://dx.doi.org/10.1063/1.1352045 (3 pages) | Cited 19 times

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Ballistic electron emission microscopy has been used to study thin aluminum oxide tunnel junction barriers formed both by magnetron sputter deposition and thermal evaporation. We have found that the barriers made by oxidation of evaporated Al become fully formed at a significantly thinner mean deposited thickness (∼6 Å) than junctions made by sputter deposition. The effective barrier height of the aluminum oxide has been determined to be 1.22±0.05 eV and is independent of the method of deposition, thickness, and oxidation conditions. © 2001 American Institute of Physics.
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68.37.Vj Field emission and field-ion microscopy
81.15.Cd Deposition by sputtering
73.40.Gk Tunneling
81.65.Mq Oxidation
68.55.-a Thin film structure and morphology
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