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11 Oct 1999

Volume 75, Issue 15, pp. 2163-2335

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Magnetotransport and magnetic domain structure in compressively strained colossal magnetoresistance films

Yan Wu, Y. Suzuki, U. Rüdiger, J. Yu, A. D. Kent, T. K. Nath, and C. B. Eom

Appl. Phys. Lett. 75, 2295 (1999); http://dx.doi.org/10.1063/1.124995 (3 pages) | Cited 69 times

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We have studied the magnetoresistance (MR) of compressively strained La0.7Sr0.3MnO3 (LSMO) films in various magnetic states in order to understand the role of magnetic domain structure on magnetotransport. In thin films of LSMO on (100) LaAlO3, the perpendicular magnetic anisotropy results in perpendicularly magnetized domains with fine scale ∼200 nm domain subdivision, which we image directly at room temperature using magnetic force microscopy. The main MR effects can be understood in terms of bulk colossal MR and anisotropic MR. We also find evidence for a small domain wall contribution to the MR, which is an order of magnitude larger than expected from a double exchange model. © 1999 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
75.47.Gk Colossal magnetoresistance

Effect of magnetocrystalline anisotropy on the magnetic properties of Fe-rich R–Fe–B nanocomposite magnets

T. Zhao, Q. F. Xiao, Z. D. Zhang, M. Dahlgren, R. Grössinger, K. H. J. Buschow, and F. R. de Boer

Appl. Phys. Lett. 75, 2298 (1999); http://dx.doi.org/10.1063/1.124996 (3 pages) | Cited 13 times

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Nanocomposite ribbons consisting of hard-magnetic R2Fe14B (R=rare-earth) and soft-magnetic Fe3B phases were produced by melt spinning and subsequent heat treatment. Alloys of composition Nd4−xSmxFe77.5B18.5, with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 all showing strong remanence enhancement, were selected to investigate the effect of the magnetocrystalline anisotropy of the R2Fe14B-type phase on the exchange coupling with the soft-magnetic phase in the nanocomposite magnets. An enhancement of exchange coupling due to anisotropy reduction was found, as expected on the basis of the model of Kneller and Hawig. A maximum of the energy product (BH)max was achieved for x = 0.2 after annealing at 700 °C. The thermomagnetic behavior also changes upon substitution of Sm for Nd. © 1999 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Gw Magnetic anisotropy
75.50.Ww Permanent magnets
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Highly balanced long-baseline single-layer high-Tc superconducting quantum interference device gradiometer

A. Eulenburg, E. J. Romans, C. Carr, A. J. Millar, G. B. Donaldson, and C. M. Pegrum

Appl. Phys. Lett. 75, 2301 (1999); http://dx.doi.org/10.1063/1.124997 (3 pages) | Cited 18 times

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We describe a direct-current superconducting quantum interference device (SQUID) first-order gradiometer fabricated from a single layer of YBa2Cu3O7 on a 30×10 mm2 bicrystal substrate. The device has a baseline of 13 mm and an intrinsic balance of ∼ 10−3. The gradient sensitivity at 77 K and 1 kHz is 50 fT/(cmmath) in magnetic shielding and 260 fT/(cmmath) when operated unshielded in our laboratory. An antiparallel two-SQUID coupling scheme is employed to optimize the device’s balance to at least 3×10−5. © 1999 American Institute of Physics.
Show PACS
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Tuning exchange bias

P. Miltényi, M. Gierlings, M. Bamming, U. May, G. Güntherodt, J. Nogués, M. Gruyters, C. Leighton, and Ivan K. Schuller

Appl. Phys. Lett. 75, 2304 (1999); http://dx.doi.org/10.1063/1.124998 (3 pages) | Cited 68 times

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The exchange bias shift of the hysteresis loop, HE, in antiferromagnetic/ferromagnetic layer systems can be easily controlled (within certain limits) by cooling in zero field from different magnetization states above the antiferromagnetic Néel temperature, TN. This indicates that for moderate cooling fields, HE is determined by the magnetization state of the ferromagnet at TN, and not by the strength of the cooling field. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.-s Critical-point effects, specific heats, short-range order
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced magnetoresistance effect in layered systems

M. S. Ferreira, J. d’Albuquerque e Castro, R. B. Muniz, and Murielle Villeret

Appl. Phys. Lett. 75, 2307 (1999); http://dx.doi.org/10.1063/1.124999 (3 pages) | Cited 8 times

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Magnetoresistance ratios several orders of magnitude higher than those of conventional multilayers may be obtained with much smaller saturation fields in magnetic layers separated by a periodically modulated structure. Conditions for the occurrence of such effect, as well as the possible use of these systems as spin-filter devices and magnetic logical gates, are discussed. © 1999 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.-w Magnetic devices

Harmonic frequency mixing in Bi2Sr2CaCu2O8+X intrinsic Josephson junctions

H. B. Wang, Y. Aruga, T. Tachiki, Y. Mizugaki, J. Chen, K. Nakajima, T. Yamashita, and P. H. Wu

Appl. Phys. Lett. 75, 2310 (1999); http://dx.doi.org/10.1063/1.125000 (3 pages) | Cited 7 times

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In a c-axis junction stack (10 μm×10 μm in a-b plane) patterned on a Bi2Sr2CaCu2O8+X single crystal, we performed harmonic mixings between a 100 GHz signal and up to the 98th harmonic of a local oscillator at about 1 GHz. The dependence of PIF on V, where PIF is the mixing output at the intermediate frequency and V is the dc voltage across the junction stack, was strongly affected by the local oscillator power levels. For low values of local oscillator power, the optimum operation point where PIF became maximum was around zero bias, and typical multi-branch structure of PIF vs V curves were observed. For high values of local oscillator power, the optimum operation point moved to the high-voltage region. In both cases, interesting oscillations occurred on the PIF vs V curves. Our experimental results led us to believe that intrinsic Josephson junctions can be good candidates for high frequency applications and the harmonic mixing may be a useful probe to investigate plasma phenomena in the layered superconductors. © 1999 American Institute of Physics.
Show PACS
85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
74.72.-h Cuprate superconductors
84.40.Dc Microwave circuits
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