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13 Dec 1999

Volume 75, Issue 24, pp. 3739-3886

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Inverse giant magnetoresistance at room temperature in antiparallel biased spin valves and application to bridge sensors

C. H. Marrows, F. E. Stanley, and B. J. Hickey

Appl. Phys. Lett. 75, 3847 (1999); http://dx.doi.org/10.1063/1.125476 (3 pages) | Cited 12 times

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We report a spin-engineering scheme whereby the sign of the giant magnetoresistance in an antiparallel biased spin valve may be selected by varying only layer thicknesses within the structure. The antiferromagnetic coupling in the biased layers leads to either positive exchange bias or positive magnetoresistance in the response of the structure. Hence, spin valves may be fabricated with either positive or negative sensitivities to applied fields in the same sense. When two spin valves of each type are connected in the appropriate Wheatstone bridge configuration, a sensor with four active legs may be constructed. The bias may be set by either the growth field, or by application of uniform field to the entire sensor structure in a single postprocessing anneal step. © 1999 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Et Exchange and superexchange interactions

Structure and magnetic properties of Pr2Co17−xMnx compounds

Zhi-gang Sun, Hong-wei Zhang, Jing-yun Wang, and Bao-gen Shen

Appl. Phys. Lett. 75, 3850 (1999); http://dx.doi.org/10.1063/1.125477 (3 pages) | Cited 6 times

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The structure and magnetic properties of Pr2Co17−xMnx (x = 0–14) compounds were studied. A single phase with the rhombohedral Th2Zn17-type structure was obtained from x-ray diffraction patterns for x = 0–11. The unit-cell volumes were found to increase linearly at a rate of about 5.7 Å3 per Mn atom. Both the Curie temperature and saturation magnetic moment at 5 K decrease monotonously with increasing Mn concentration. The spin reorientation was found in Pr2Co17−xMnx compounds for x = 1–5. The magnetic phase diagram of the compounds was given. A transition from ferromagnetic to antiferromagnetic for x = 8–9 was observed due to the Mn substitution. At high Mn concentration (x = 12,13,14), a rare-earth intermetallic 3:29 phase was found. This kind of 3:29 phase shows a paramagnetic character when the temperature is above 5 K. © 1999 American Institute of Physics.
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75.50.Ww Permanent magnets
75.50.Cc Other ferromagnetic metals and alloys
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.20.En Metals and alloys

Enhanced intergrain tunneling magnetoresistance in double perovskite Sr2FeMoO6 polycrystals with nanometer-scale particles

C. L. Yuan, S. G. Wang, W. H. Song, T. Yu, J. M. Dai, S. L. Ye, and Y. P. Sun

Appl. Phys. Lett. 75, 3853 (1999); http://dx.doi.org/10.1063/1.125478 (3 pages) | Cited 61 times

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Polycrystalline ordered double perovskite Sr2FeMoO6 bulk samples with grain size in the range of 29–45 nm have been synthesized at temperatures from 900 to 1000 °C, using a sol-gel method. We find that the intergrain magnetoresistance is closely correlated with the grain size. The sample with the grain size of 29 nm shows large magnetoresistance Δρ/ρ0, 30%–20% at a low magnetic field of 4 kG over a wide temperature range from 20 to 300 K. The results can be explained in terms of spin-dependent intergrain tunneling model. © 1999 American Institute of Physics.
Show PACS
75.47.Gk Colossal magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.50.Dd Nonmetallic ferromagnetic materials
75.45.+j Macroscopic quantum phenomena in magnetic systems
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure

Enhancement of magnetic coercivity and macroscopic quantum tunneling in monodispersed Co/CoO cluster assemblies

D. L. Peng, K. Sumiyama, T. Hihara, and S. Yamamuro

Appl. Phys. Lett. 75, 3856 (1999); http://dx.doi.org/10.1063/1.125479 (3 pages) | Cited 12 times

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Magnetic properties have been measured for monodisperse-sized Co/CoO cluster assemblies prepared by a plasma-gas-condensation-type cluster beam deposition technique. The clear correlation obtained between exchange bias field and coercivity suggests the enhancement of uniaxial anisotropy owing to the exchange coupling between the ferromagnetic Co core and antiferromagnetic CoO shell, and magnetic disorder at the core–shell interface. A nonthermal magnetic relaxation observed below 8 K, being referred to as macroscopic quantum tunneling of the magnetization, is ascribed to the enhanced uniaxial anisotropy. © 1999 American Institute of Physics.
Show PACS
75.50.Tt Fine-particle systems; nanocrystalline materials
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics

Spin-wave quantization and dynamic coupling in micron-size circular magnetic dots

J. Jorzick, S. O. Demokritov, B. Hillebrands, B. Bartenlian, C. Chappert, D. Decanini, F. Rousseaux, and E. Cambril

Appl. Phys. Lett. 75, 3859 (1999); http://dx.doi.org/10.1063/1.125480 (3 pages) | Cited 39 times

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We report on the observation of spin-wave quantization in square arrays of micron-size circular magnetic Ni80Fe20 dots by means of Brillouin light-scattering spectroscopy. For a large wave-vector interval several discrete, dispersionless modes with a frequency splitting of up to 2.5 GHz were observed. The modes are identified as magnetostatic surface spin waves laterally quantized due to in-plane confinement in each single dot. The frequencies of the lowest observed modes decrease with increasing distance between the dots, thus indicating an essential dynamic magnetic dipole interaction between the dots at small interdot distances. © 1999 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
75.70.Rf Surface magnetism

Fundamental limits to magnetic-field sensitivity of flux-gate magnetic-field sensors

R. H. Koch, J. G. Deak, and G. Grinstein

Appl. Phys. Lett. 75, 3862 (1999); http://dx.doi.org/10.1063/1.125481 (3 pages) | Cited 12 times

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In this letter we determine the theoretical limit of the magnetic-field sensitivity of the flux-gate magnetometer. In order to do so, we have developed a model for the white noise of a flux gate based on the fundamental dynamics of the magnetic material forming the flux-gate core. Solving this model, we predict that the white noise of a physically realizable flux gate with a volume of 2×10−8 m3 is less than 100 fT/math. The white noise varies with the lossy susceptibility of the core and inversely with the volume. We also compare the measured white noise of a thin-film flux gate with the predictions of our model and find that the measured and predicted noise agree reasonably well. © 1999 American Institute of Physics.
Show PACS
07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Ay Magnetic device characterization, design, and modeling

Absolute measurement of penetration depth in a superconducting film by the two-coil technique

R. F. Wang, S. P. Zhao, G. H. Chen, and Q. S. Yang

Appl. Phys. Lett. 75, 3865 (1999); http://dx.doi.org/10.1063/1.125482 (3 pages) | Cited 4 times

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A two-coil mutual-inductance apparatus that is optimized to allow for the measurement of the absolute value of penetration depth λ in superconducting films is described. Nb films with thickness d ranging from 20 to 90 nm are used to illustrate the measurement. For a 70-nm-thick Nb film at 4.2 K, with d/λ ∼ 0.6, the uncertainty in the measured λ is about ±2.3%. From the results on the Nb film series, we show that a satisfactory determination of the absolute value of λ is possible for these films with d/λ<0.95. © 1999 American Institute of Physics.
Show PACS
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
07.55.-w Magnetic instruments and components
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