Search Results - (Author, Cooperation:R. Cochrane)

2018-03-06

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

2018-01-19

Wiley-Blackwell

0022-3417

1096-9896

Medicine

2015-05-15

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2015-06-27

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1471-0528

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have studied the effect of annealing on the magnetic and structural properties of sputtered Si/Re50 A(ring) [Co20 A(ring)/RexA(ring)]40 superlattices with xRe=3,5,7,10 A(ring). Annealing the samples for 1 h at 300 °C causes a slight increase in interfacial mixing and a contraction of lattice spacing d(002) owing to interdiffusion and structural relaxation, as indicated by the x-ray diffraction data. In addition, the subsequent room-temperature magnetoresistance (MR) increases for samples with antiferromagnetic (AF) coupling, by up to 20% for xRe=5 A(ring), providing strong experimental evidence for the spin-dependent scattering mechanism which predicts an increasing MR with increasing diffuse interface scattering. A further 1 h anneal at 525 °C provokes dramatic interdiffusion between the Co and Re layers, which is accompanied by a considerable decrease of the MR, indicating a disappearance of the interlayer AF coupling.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have studied the magnetoresistance (MR) properties of sputtered Si/Re 50A(ring)[Co 20 A(ring)/Re x A(ring)]40 superlattices with xRe=3–32 A(ring). Transverse and longitudinal MR exhibit oscillation of the interlayer coupling as a function of Re layer thickness with a period of (approximately-equal-to)12 A(ring) and a maximum transverse MR of (approximately-equal-to)1.2% for xRe=5 A(ring) at 4.2 K. The saturation magnetic field Bs and MR magnitude ΔR/R for samples with xRe=5 and 7 A(ring) are nearly constant up to 40 K, above which they decrease approximately linearly with increasing temperature. In addition, the perpendicular MR in magnetic fields up to 1 T changes sign from negative for samples with xRe≤7 A(ring) (strong antiferromagnetic coupling) to positive for those with xRe≥10 A(ring).

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The growth of heteroepitaxial GaxIn1−xP on InP for 0〈x〈0.25 has been carried out by low-pressure metalorganic chemical vapor deposition and characterized by high-resolution x-ray diffraction and low-temperature photoluminescence measurements. The x-ray data indicate that the epilayers are under biaxial tensile strain and that, for samples with x〈0.05, the lattice mismatch is accommodated almost completely by tetragonal distortions. From photoluminescence measurements, the energy band gap is found to vary monotonically with the Ga concentration; it also shifts linearly with the elastic strain in the layer. The calculated value of 0.99×104 meV per unit strain is in good agreement with that predicted from elasticity theory.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We describe the effects of 1 MeV Si+ ion-beam irradiation on a sputtered Co/Ag multilayer with layer thicknesses of 5 Å for Co and 25 Å for Ag, thicknesses for which the magnetoresistance is maximum in the as-deposited sample. X-ray diffraction, magnetization, and magnetoresistance measurements all point to the conclusion that the Co is initially dispersed through the Ag and segregates completely upon ion-beam bombardment. Throughout the process both Ag and Co grains maintain a high degree of texture, essentially face centered cubic (111). The magnetization behavior evolves from superparamagnetic to mixed superparamagnetic–ferromagnetic with ion dose whereas the room-temperature magnetoresistance decreases from 12% to 1.5% upon irradiation up to 5×1016 Si+/cm2. Simple models taking into account the size distribution of the Co particles have been used to analyze these phenomena in order to quantify the particle size distribution. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The structural, magnetic and transport properties of rf sputtered Co/Ag multilayers with Co-layer thicknesses ranging from 1 to 14 Å have been studied by a combination of x-ray diffraction, magnetic and transport measurements. The magnetoresistance at room temperature has a maximum value of more than 12% for a Co-layer thickness around 5 Å. Magnetic measurements demonstrate that samples near this Co-layer thickness are in the transition region from superparamagnetic to ferromagnetic behavior. X-ray analysis indicates that, during deposition, a significant quantity of Co is dispersed throughout a highly textured Ag matrix. Upon irradiation with 1 MeV Si+ ions up to a dose of 5×1016 Si+/cm2, an initial demixing of the Co is followed by segregation into grains with the same texture as the Ag. The resulting changes in the magnetization and magnetoresistance are characterized on the basis of a log-normal distribution of the volume of the magnetic particles. As the particle sizes increase, a systematic evolution towards ferromagnetic behavior for films initially in the superparamagnetic and transition regions results. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Longitudinal magnetization curves and giant magnetoimpedance (GMI) analyses are combined to investigate the anisotropy and magnetization processes of dc-current-self-annealed Co68.15Fe4.35Se12.5B15 wires. The magnetization curves show an almost anhysteretic behavior with small Barkhausen jumps occurring at a critical field H*. This unusual shape is in very good agreement with the high resolution GMI response to the field, which reflects the circumferential bias permeability. Magnetization curves yield information on the bulk properties, while GMI allows the investigation of the surface region of the sample. The anisotropy constant is calculated using initial-magnetization curves and the resonance condition, yielding interesting conclusions concerning the inhomogeneity of the wires. © 1999 American Institute of Physics.

Electronic Resource

1471-0528

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We present a study of sputtered Ni/Fe multilayers in order to examine the effect of interfacial mixing and interdiffusion on the magnetic and transport properties. The multilayer structure has been examined by low-angle x-ray reflectivity, which reveals interface mixing of about two monolayers. The magnetization measurements show differences in the anisotropy of multilayers for which the thickness ratio of nickel to iron is changed from 1:1 to 3:1. With the 1:1 composition, multilayers show high permeability with a longitudinal easy axis, while samples with 3:1 composition show lower permeability and a rotated easy axis. By fitting the resistivity and magnetoresistance thickness variation with a semiclassical model, we have determined an interface contribution to the resistivity and a possible contribution to the magnetoresistance. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Polarized neutron reflectometry measurements were carried out on a thin-film Co-Re multilayer sample with Re thickness of 6 A(ring) which is at the peak of the first oscillation of the magnetoresistance. Antiferromagnetic coupling between successive Co layers is observed at in-plane magnetic fields below 0.1 T. Towards the low field end of this regime, the axes of the antiferromagnetic domains are distributed relatively uniformly in the sample plane but at ∼0.1 T the moments flop perpendicular to the applied field. As the field is increased further, the Co moments are pulled into the field direction producing a partial ferromagnetic alignment. At 0.5 T, the highest field where the measurements have been made, the antiferromagnetic to ferromagnetic transition was found to be only ∼50% complete, indicating that the saturation field required for Co-Re system is much higher than that for Co-Cu multilayers of similar layer spacing.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A detailed investigation of the structural and optoelectronic properties of thick GaInP epilayers on sulfur-doped InP substrates is reported. Significant variations of the optical absorption and photoluminescence transition energies from light- and heavy-hole states are observed as a function of the epilayer composition as well as of the degree of relaxation of the misfit strain. High-resolution x-ray measurements were used to determine the Ga concentrations and the strains and indicate significant anisotropic relaxation in several films. Even small relaxations result in a significant increase in the optical linewidths and a rapid drop in the transition intensities. A model with no free parameters based on the strain Hamiltonian of Pikus and Bir provides excellent agreement with the transition energies and serves to identify unambiguously the transitions observed in the optical spectra. Within this model, isotropic in-plane relaxation produces a shift of both light- and heavy-hole energies whereas anisotropic in-plane relaxation contributes only negligibly.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Results for the temperature and magnetic-field dependence of melt-spun Cu87Co13 are presented and discussed. The magnetoresistance of the as-spun sample exhibits superparamagnetic behavior with a magnetoresistance of 18% at 0.4 K and in a field of 80 kOe. The magnetic-field dependence of the magnetoresistance is approximately proportional to the Langevin function. The microstructure of the sample was investigated by transmission electron microscopy and it appears that the giant magnetoresistance is due to the presence of small Co precipitates with an approximate mean diameter of 12 A(ring) and a mean separation of 35 A(ring).

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Structural properties of sputtered Si/Re 50 A(ring)/(Co 20 A(ring)/Re x A(ring))40 superlattices have been investigated in detail by low- and high-angle x-ray-diffraction measurements. The low-angle x-ray reflectivity data have been analyzed using an optical model and the high-angle data have been treated on the basis of a trapezoidal model. The fitted results indicate that the films with small xRe=3, 5, and 7 A(ring) are essentially composed of pure Co layers and Re rich alloy (∼80%) interfaces about 3–5 monolayers thick. The magnetoresistance (MR) data of the antiferromagnetically coupled films have been analyzed using a semiclassical MR model of interfacial spin-dependent scattering.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Structural and magnetoresistance results on annealed sputtered (Ni81Fe19, Ni66Fe16Co18)/Ag granular multilayers are presented. Structural evolution has shown that highly (111) textured, discontinuous layered structures can persist on annealing up to 400 °C. The average magnetic particle size is controlled by the annealing temperature and the initial magnetic layer thickness. No giant magnetoresistance was observed in the as-deposited films, while significant MR was found after annealing between 300 °C and 400 °C. Magnetoresistance over 30%, together with a small saturation field, was found at 4.2 K for a starting magnetic thickness of 4 A(ring). Increasing the magnetic layer thickness to 20 A(ring) greatly improves the magnetic thermal stability, and leads to high magnetoresistive sensitivities of up to 0.35%/Oe in a field of 10 Oe at room temperature. The magnetization hysteresis, anisotropy, and magnetic interaction in such a granular multilayer are also discussed.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We present the effect of deposition temperature (Ts) on the structural and magnetic properties of sputtered Ni/Fe multilayers. As Ts increases above room temperature, a systematic change in texture from (111) to (200) and an increase in grain size are observed. Superlattice modulations are clearly visible in low-angle x-ray reflectivity measurements for all the multilayers deposited up to 250 °C. However, superlattice peaks intensities decrease with increasing Ts indicating enhanced mixing of Ni and Fe across interfaces. Nonmonotonic variations in electrical resistivity (ρs) and coercivity (Hc) with Ts are seen and explained in terms of the interplay between the increase in grain size and alloying at the interfaces. The total anisotropic magnetoresistance (AMR) as well as its field sensitivity increase with Ts. © 1997 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We present an analysis of the stability of a dendrite against a small perturbation to the tip velocity. We find that dendritic growth in pure metals and alloys will become unstable above some upper critical undercooling ΔT2*. In alloys above a critical concentration, dendritic growth may also become unstable below a lower critical undercooling, ΔT1*. In the example systems studied, Ni–Cu and Ag–O, the location of these unstable regions shows remarkably close agreement with the onset of spontaneous grain refinement. We obtain values of ΔT2* for Ni and Ag of 195 K and 160 K, respectively, in good agreement with the observed values of 170 K and 133–153 K. © 1997 American Institute of Physics.

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