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20 Aug 2001

Volume 79, Issue 8, pp. 1073-1217

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Coercivity and squareness enhancement in ball-milled hard magnetic–antiferromagnetic composites

J. Sort, J. Nogués, S. Suriñach, J. S. Muñoz, M. D. Baró, E. Chappel, F. Dupont, and G. Chouteau

Appl. Phys. Lett. 79, 1142 (2001); http://dx.doi.org/10.1063/1.1392308 (3 pages) | Cited 28 times

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The room-temperature coercivity, HC, and squareness, MR/MS (remanence/saturation magnetizations), of permanent magnet, SmCo5 powders have been enhanced by ball milling with antiferromagnetic NiO (with Néel temperature, TN = 590 K). This enhancement is observed in the as-milled state. However, when the milling of SmCo5 is carried out with an antiferromagnet with TN below room temperature (e.g., for CoO, TN = 290 K), the coercivity enhancement is only observed at low temperatures after field cooling through TN. The ferromagnetic–antiferromagnetic exchange coupling induced either by local heating during milling (SmCo5+NiO) or field cooling (SmCo5+CoO) is shown to be the origin of the HC increase. © 2001 American Institute of Physics.
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75.50.Ww Permanent magnets
75.50.Ee Antiferromagnetics
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Stacked Josephson junctions in view of macroscopic quantum experiments

C. Granata, V. Corato, A. Monaco, B. Ruggiero, M. Russo, and P. Silvestrini

Appl. Phys. Lett. 79, 1145 (2001); http://dx.doi.org/10.1063/1.1391238 (3 pages) | Cited 16 times

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We present Nb/AlOx/Nb–Al/AlOx/Nb stacked Josephson junctions which we propose as three-terminal elements to control the quantum behavior of Josephson complex systems. A bias current can be independently injected in the “top” junction, providing a fine control of the critical current of the “bottom” junction. The reported characterization of the device refers to data in the classical limit including measurements of the switching dynamics between metastable states of the system at different temperatures and bias conditions. At low temperature, the effective dissipation of the bottom junction remains substantially unchanged when different injection currents flow in the top junction. These results are interesting to project new configurations of macroscopic quantum experiments. © 2001 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.25.Sv Critical currents
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Intermartensitic transformation and magnetic-field-induced strain in Ni52Mn24.5Ga23.5 single crystals

W. H. Wang, G. H. Wu, J. L. Chen, S. X. Gao, W. S. Zhan, G. H. Wen, and X. X. Zhang

Appl. Phys. Lett. 79, 1148 (2001); http://dx.doi.org/10.1063/1.1396820 (3 pages) | Cited 37 times

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We have found a complete thermoelastic intermartensitic transformation between modulated and unmodulated martensite in single-crystal Ni52Mn24.5Ga23.5. This intermartensitic transformation provides a much larger strain than that of the martensitic transformation. A giant switching-like strain of ±5.0% can be achieved by a small magnetic field of 0.2 T upon the intermartensitic transformation. In the modulated martensite, a large recoverable magnetic-field-induced strain of up to 1.2% has been obtained. © 2001 American Institute of Physics.
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64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
75.50.Cc Other ferromagnetic metals and alloys
75.80.+q Magnetomechanical effects, magnetostriction

Magnetic patterning of chemically-ordered CrPt3 films

Olav Hellwig, Dieter Weller, A. J. Kellock, J. E. E. Baglin, and Eric E. Fullerton

Appl. Phys. Lett. 79, 1151 (2001); http://dx.doi.org/10.1063/1.1394722 (3 pages) | Cited 19 times

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We report magnetic patterning of ferrimagnetic CrPt3 films by locally suppressing the magnetic order using ion-beam irradiation. Chemically-ordered CrPt3 films grown on MgO(110) single-crystal and amorphous SiNx substrates are ferrimagnetic and exhibit strain-induced uniaxial magnetic anisotropy. X-ray diffraction confirms the formation of the L12 phase and magneto-optical Kerr effect spectroscopy reveals the theoretically expected dependence of Kerr rotation and ellipticity on photon energy. Irradiation of the films with 700 keV N+ ions at doses ≳6×1016 ions/cm2 transforms the chemically-ordered CrPt3 ferrimagnetic alloy into the chemically-disordered nonmagnetic fcc phase. As a result, ordered CrPt3 layers can be patterned into magnetic and nonmagnetic regions and are candidate material for ion-beam-patterned magnetic recording media. © 2001 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys

High critical current density of MgB2 bulk superconductor doped with Ti and sintered at ambient pressure

Y. Zhao, Y. Feng, C. H. Cheng, L. Zhou, Y. Wu, T. Machi, Y. Fudamoto, N. Koshizuka, and M. Murakami

Appl. Phys. Lett. 79, 1154 (2001); http://dx.doi.org/10.1063/1.1396629 (3 pages) | Cited 100 times

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Ti-doped MgB2 superconductors with different doping levels were prepared by solid-state reaction at ambient pressure. The density, diamagnetic signal, and Jc of the samples change significantly with the doping level, with the best result achieved at x = 0.1. At 5 K, the Jc reaches 2×106 A/cm2 in the self-field and 5×104 A/cm2 in 5 T. At 20 K, the Jc is still as high as 1.3×106 A/cm2 in the self-field and 9.4×104 A/cm2 in 2 T. It is observed that partial melting occurs in the Ti-doped samples, resulting in an excellent grain connection and extremely high density. In addition, some fine particles (with sizes from 10 to 100 nm) of the second phases induced by Ti doping are distributed in the MgB2 matrix, and this may play an important role in flux pinning enhancement. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
64.70.D- Solid-liquid transitions
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Spin-valve transistor with an Fe/Au/Fe(001) base

R. Sato and K. Mizushima

Appl. Phys. Lett. 79, 1157 (2001); http://dx.doi.org/10.1063/1.1397257 (3 pages) | Cited 47 times

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A spin-valve transistor with an epitaxial Fe/Au/Fe(001) base was formed on n-GaAs, the characteristics of which were examined under a magnetic field for emitter voltages up to 3 V. The transfer ratio of the transistor, i.e., the ratio of collector-to-emitter current exceeded 10−3 at 3 V, preserving the magnet current ratio, i.e., the ratio of collector current in the parallel-to-antiparallel magnetic configuration well above 100%. It was suggested that the transfer ratio would be further enhanced by improving the flatness of the tunnel junction for injecting electrons from the emitter into the base, as well as by increasing the electron transmittance at the base/collector interface. © 2001 American Institute of Physics.
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85.75.Hh Spin polarized field effect transistors
75.47.De Giant magnetoresistance
75.75.-c Magnetic properties of nanostructures
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