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18 Sep 2000

Volume 77, Issue 12, pp. 1741-1913

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Reliability of normal-state current–voltage characteristics as an indicator of tunnel-junction barrier quality

B. J. Jönsson-Åkerman, R. Escudero, C. Leighton, S. Kim, Ivan K. Schuller, and D. A. Rabson

Appl. Phys. Lett. 77, 1870 (2000); http://dx.doi.org/10.1063/1.1310633 (3 pages) | Cited 67 times

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We demonstrate that one of the most commonly used criteria to ascertain that tunneling is the dominant conduction mechanism in magnetic tunnel junctions—fits of current–voltage (I–V) data—is far from reliable. Using a superconducting electrode and measuring the differential conductance below Tc, we divide samples into junctions with an integral barrier and junctions having metallic shorts through the barrier. Despite the clear difference in barrier quality, equally reasonable fits to the I–V data are obtained above Tc. Our results further suggest that the temperature dependence of the zero-bias resistance is a more solid criterion, which could therefore be used to rule out possible pinholes in the barrier. © 2000 American Institute of Physics.
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75.45.+j Macroscopic quantum phenomena in magnetic systems
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Gk Tunneling

Magnetoresistance effect and interlayer coupling of (Ga, Mn)As trilayer structures

D. Chiba, N. Akiba, F. Matsukura, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 77, 1873 (2000); http://dx.doi.org/10.1063/1.1310626 (3 pages) | Cited 69 times

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We have investigated the magnetic and magnetotransport properties of (Ga, Mn)As/(Al, Ga)As/(Ga, Mn)As semiconductor-based magnetic trilayer structures. We observe a weak ferromagnetic interlayer coupling between the two ferromagnetic (Ga, Mn)As layers as well as magnetoresistance effects due to spin-dependent scattering and to spin-dependent tunneling. Both the coupling strength and the magnetoresistance ratio decrease with the increase of temperature and/or the increase of Al composition of the nonmagnetic (Al, Ga)As layer. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Pp Magnetic semiconductors
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Particle sizing of magnetite-based magnetic fluid using atomic force microscopy: A comparative study with electron microscopy and birefringence

B. M. Lacava, R. B. Azevedo, L. P. Silva, Z. G. M. Lacava, K. Skeff Neto, N. Buske, A. F. Bakuzis, and P. C. Morais

Appl. Phys. Lett. 77, 1876 (2000); http://dx.doi.org/10.1063/1.1311320 (3 pages) | Cited 21 times

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Atomic force microscopy (AFM), transmission electron microscopy (TEM), and static magnetic birefringence (SMB) were used to unfold the particle size polydispersity profile of a magnetite-based magnetic fluid sample. The data obtained from different techniques were curve fitted using the lognormal distribution function, from which the mean particle diameter (Dm) and the standard deviation (σ) were obtained. In comparison to the TEM data, the AFM data show a reduction of Dm (about 20%) and an increase of σ (about 15%). In contrast, close agreement between the TEM and SMB data was found. © 2000 American Institute of Physics.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
75.50.Mm Magnetic liquids
07.79.Lh Atomic force microscopes
78.20.Ls Magneto-optical effects
02.60.Ed Interpolation; curve fitting

A giant magnetoresistance sensor for high magnetic field measurements

F. B. Mancoff, J. Hunter Dunn, B. M. Clemens, and R. L. White

Appl. Phys. Lett. 77, 1879 (2000); http://dx.doi.org/10.1063/1.1311316 (3 pages) | Cited 29 times

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We used giant magnetoresistance in a magnetic field sensor able to measure large fields of up to several kG. We deposit spin valves with a magnetic multilayer with perpendicular anisotropy as one ferromagnet and a material with in-plane anisotropy as the other ferromagnet. For magnetic fields along the film normal, the multilayer’s magnetization is fixed perpendicular while the magnetic layer with in-plane anisotropy is rotated towards out-of-plane magnetization. The device response is nearly linear with applied field and determines both the magnitude and sign of the field, making it attractive for measuring large magnetic fields. © 2000 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy

Sensitive Josephson magnetometry of flux quantization in a normal conducting hole in a narrow YBa2Cu3O7 line

H.-J. Barthelmess, S. Krey, S. Ostertun, and M. Schilling

Appl. Phys. Lett. 77, 1882 (2000); http://dx.doi.org/10.1063/1.1290493 (3 pages)

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A small YBa2Cu3O7 Josephson junction on a 24° symmetric SrTiO3 bicrystal is used as a sensitive magnetometer with micrometer spatial resolution in magnetic fields of up to 1 mT. The dependence of its critical current on the external magnetic flux is used to measure the local magnetic field. In the narrow line of 4 μm width leading to the Josephson junction we prepared a normal conducting area of about 2.5 μm diameter. This was achieved by heating the YBa2Cu3O7 locally with a focused laser beam to lower the oxygen content and thus suppress superconductivity at 77 K. We investigate the flux quantization in this normal conducting “hole” by cooling the whole device in different magnetic fields, reducing this external field to zero, and measuring the resulting flux. This way, superconducting properties of a hole in a superconducting film have been determined, which are important for the operation of hole-patterned magnetometers based on direct current superconducting quantum interference devices in static magnetic fields. © 2000 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
07.55.Ge Magnetometers for magnetic field measurements
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
74.25.Sv Critical currents
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