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24 Jun 2002

Volume 80, Issue 25, pp. 4687-4873

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Buried superconducting layers comprised of magnesium diboride nanocrystals formed by ion implantation

H. Y. Zhai, H. M. Christen, C. W. White, J. D. Budai, D. H. Lowndes, and A. Meldrum

Appl. Phys. Lett. 80, 4786 (2002); http://dx.doi.org/10.1063/1.1488695 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2002

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Superconducting layers of MgB2 were formed on Si substrates using techniques that are widely used and accepted in the semiconductor industry. Mg ions were implanted into boron films deposited on Si or Al2O3 substrates. After a thermal processing step, buried superconducting layers comprised of MgB2 nanocrystals were obtained which exhibit the highest Tc reported so far for MgB2 on silicon (Tconset ≈ 33.6 K, ΔTc = 0.5 K, as measured by current transport). These results show that our approach is clearly applicable to the fabrication of superconducting devices that can be operated at much higher temperatures ( ≈ 20 K) than the current Nb technology ( ≈ 6 K) while their integration with silicon structures remains straight-forward. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
61.72.up Other materials
81.07.Bc Nanocrystalline materials
74.62.-c Transition temperature variations, phase diagrams
74.72.-h Cuprate superconductors
61.46.-w Structure of nanoscale materials

Magnetization reversal and configurational anisotropy of dense permalloy dot arrays

Xiaobin Zhu, P. Grütter, V. Metlushko, and B. Ilic

Appl. Phys. Lett. 80, 4789 (2002); http://dx.doi.org/10.1063/1.1489720 (3 pages) | Cited 25 times

Online Publication Date: 17 June 2002

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Electron beam patterned permalloy circular dots of 700 nm diameter with small separations were studied by magnetic force microscopy (MFM) in the presence of an in situ magnetic field. Images in the demagnetized state show that the dot is in a vortex state with a vortex core (singularity) in the center. Local hysteresis loops, measured by cantilever frequency shift in an external field, indicate that the magnetization reversal of individual disks is a vortex nucleation and annihilation process. By carefully doing MFM, nucleation and annihilation fields without MFM tip stray field distortions are obtained. Configurational anisotropy originated from magnetostatic coupling is found through hysteresis loops. © 2002 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.)
75.50.Ww Permanent magnets
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
68.37.Rt Magnetic force microscopy (MFM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High-resolution magnetic Co supertips grown by a focused electron beam

I. Utke, P. Hoffmann, R. Berger, and L. Scandella

Appl. Phys. Lett. 80, 4792 (2002); http://dx.doi.org/10.1063/1.1489097 (3 pages) | Cited 50 times

Online Publication Date: 17 June 2002

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We present a technique for local growth of high-resolution, high-aspect-ratio magnetic tips and thin adherent magnetic cap coatings on top of batch fabricated scanning force microscopy silicon tips. A focused electron beam of a scanning electron microscope is used for decomposition of a directed cobalt carbonyl vapor flux. Exposure parameters determine the tip geometry and tip length. Deposits consist of cubic Co clusters of 2–5 nm in size dispersed in a stabilizing carbonaceous matrix. Magnetic force microscope sensors having magnetic tip apex diameters between 50 and 240 nm were produced. Tracks of magnetic transitions written in recording media of hard disks were used to characterize tip performance. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.70.Ak Magnetic properties of monolayers and thin films

Influence of the magnetic tip in ferromagnetic resonance force microscopy

V. Charbois, V. V. Naletov, J. Ben Youssef, and O. Klein

Appl. Phys. Lett. 80, 4795 (2002); http://dx.doi.org/10.1063/1.1489475 (3 pages) | Cited 10 times

Online Publication Date: 17 June 2002

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We compare mechanically detected ferromagnetic resonance spectra for different separations h between the magnetic tip and sample surface. When the bias field generated by the tip is smaller than a few hundred gauss, the prominent changes are shifts of the entire spectrum (without line shape distortions) to higher frequency as h decreases. These results are in agreement with the Damon and Eshbach model for spin waves propagating in a potential perturbed by the additional field of the probe magnet. It is used to predict the spatial resolution limit for magnetostatic modes bounded by the stray field of the tip. The answer is ∼ 4 μm for yttrium iron garnet. © 2002 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.37.Rt Magnetic force microscopy (MFM)
07.79.Pk Magnetic force microscopes
75.30.Ds Spin waves

Anomalous magnetotransport properties of epitaxial full Heusler alloys

M. S. Lund, J. W. Dong, J. Lu, X. Y. Dong, C. J. Palmstrøm, and C. Leighton

Appl. Phys. Lett. 80, 4798 (2002); http://dx.doi.org/10.1063/1.1489081 (3 pages) | Cited 32 times

Online Publication Date: 17 June 2002

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We report the magnetotransport properties of epitaxial films of the full Heusler alloys Ni2MnGa, Ni2MnGe, and Ni2MnAl, grown by molecular beam epitaxy on (001) GaAs. The ferromagnetic alloys (Ni2MnGa,Ni2MnGe) exhibit an anomalous temperature dependence of the resistivity and a negative magnetoresistance peaking near the Curie temperature due to spin disorder scattering. Considering the absolute values of the resistivity, the anomalous high temperature behavior and an upturn in the resistivity below 20 K, we suggest that these Heusler alloys rather than being conventional metals are in fact strongly disordered electronic systems. © 2002 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Cc Other ferromagnetic metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.At Metal and metallic alloys
72.15.Qm Scattering mechanisms and Kondo effect
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