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1

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Magnetization processes and magnetoresistance in Co/Cu multilayers as a function of the Cu layer thickness. (2000)

Aitchison, P. R. ; Chapman, J. N.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 5753-5755

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: We have studied Co(15 Å)/Cu(t) multilayers with nominal Cu spacer layer thicknesses of 7, 8, 9, and 10 Å. For multilayers with identical dimensions, transport measurements showed that the introduction of oxygen during growth increased the magnetoresistance while transmission electron microscopy revealed the effect of the oxygen bleed on the microstructure was reduced grain size, suppression of the Cohcp phase, and reduced texturing. Lorentz microscopy was used to determine the angle between magnetization vectors in adjacent magnetic layers and the values so deduced were found to correlate well with the variation of magnetoresistance within the multilayer sets. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.372511

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2

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Interactions and switching field distributions of nanoscale magnetic elements (2000)

Kirk, K. J. ; Chapman, J. N. ; McVitie, S. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 5105-5107

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Magnetic nano-elements made from NiFe and Co have been investigated using magnetic imaging in the transmission electron microscope. Nano-elements like these have possible uses for in-plane patterned media or solid state memory. In both cases the elements will need to be patterned into closely spaced arrays and magnetostatic interactions between the elements will begin to become significant. Arrays must therefore be designed so that an element's interactions with its neighbors will be small compared to its coercivity. Arrays of NiFe elements 300 nm long, 50–100 nm wide, and 26 nm thick, were fabricated by electron beam lithography and lift-off patterning. Their switching behavior and the interactions between them were studied in detail. Magnetization sequences were recorded and hysteresis loops constructed. For rows of NiFe elements with the gap between elements the same as the element width or larger, the interactions turn out to be small, suggesting that denser arrays would be possible. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.373263

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3

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Magnetization processes in Co/Cu multilayers with low magnetoresistive hysteresis (1999)

Chapman, J. N. ; Rose, J. ; Aitchison, P. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 1611-1620

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: We have used transmission electron microscopy to study magnetization processes in Co/Cu multilayers with the Cu spacer layer thickness close to 9 Å. The films show giant magnetoresistance (GMR) values (approximate)25%, saturation fields of 1–2 kOe, and very little magnetoresistive hysteresis; they are of interest as position sensors. While the Cu thickness was chosen to correspond to the first antiferromagnetic maximum, magnetic images taken throughout a magnetization cycle attest to the fact that the antiferromagnetic coupling is far from complete. Detailed analysis of image sequences and the corresponding low angle diffraction patterns suggests that the coupling is dominated by a biquadratic component. This is consistent with the relatively low value of GMR. Furthermore, the well-defined and relatively simple domain processes which are observed over the low field regime (±50 Oe) explain why little hysteresis is observed. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.370935

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4

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Correlation of domain processes and magnetoresistance changes as a function of field and number of bilayers in Co/Cu multilayers : The 41st annual conference on magnetism and magnetic materials (1997)

Aitchison, P. R. ; Chapman, J. N.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 81 (1997), S. 3775-3777

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: The understanding of the magnetization processes in Co/Cu multilayers showing substantial giant magnetoresistance (GMR) is incomplete. To gain further insight into the coupling and resultant switching characteristics, a series of Co/Cu multilayers with 3–15 bilayers has been grown by dc magnetron sputtering. Microstructural and micromagnetic studies along with MR measurements were made on the samples. Lorentz microscopy was used to directly observe the evolution of domain structures under the influence of an applied field. It appeared that dissimilar domain structures occurred in different layers. Magnetic structures were generally submicron in size although in samples with few bilayers well defined domain walls were also observed during the reversal process. Their occurrence coincided with abrupt steps in the GMR curves. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.365505

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5

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Direct observation of magnetization reversal processes in micron-sized elements of spin-valve material (1998)

Chapman, J. N. ; Aitchison, P. R. ; Kirk, K. J. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 83 (1998), S. 5321-5325

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Simple calculations suggest that when continuous films of spin-valve material are patterned into micron-sized elements the magnetic properties should change markedly, depending on the element shape and size. We have used the differential phase contrast imaging mode of transmission electron microscopy to study directly the magnetization distributions supported by such elements in zero field and when subjected to an applied field in the pinning direction. For elements whose long axis is parallel to the pinning direction a parallel alignment of the free and pinned layers is favored. When subjected to a field a complex domain structure evolves and different irreversible paths are followed as the element is taken from negative to positive saturation and back again. By contrast, when the pinning direction is parallel to the short axis an antiparallel arrangement, where the magnetostatic contribution to the energy is effectively suppressed, can be preferred and simpler reversal mechanisms, with a higher degree of reversibility, are frequently seen. © 1998 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.367358

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6

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Magnetization reversal of patterned spin–tunnel junction material: A transmission electron microscopy study (2000)

Ardhuin, H. ; Chapman, J. N. ; Aitchison, P. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 88 (2000), S. 2760-2765

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Electron beam lithography and reactive ion etching have been used to pattern micron-size magnetic elements in the free layer of spin–tunnel junctions. The magnetization reversal processes of elements with dimensions in the range from 15×1 μm2 to 1×1 μm2 have been studied using Lorentz microscopy in the transmission electron microscope. Under the application of a field parallel to the bias direction, elongated elements reverse by the growth and subsequent annihilation of a quasiperiodic domain structure which evolves from the ends of the elements. Similar processes occur in both halves of a magnetization cycle. By contrast, the reversal of square elements involves the formation of more complex domain structures which differ significantly according to the direction in which the field in applied. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1287410

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7

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Differential Phase Change at Reflexion (1950)

AITCHISON, P. M.

[s.l.] : Nature Publishing Group

Nature 166 (1950), S. 522-523

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The phase change at reflexion at a surface appears to be a function of both the material and the surface finish. From measurements made on the height of steps etched in a polished glass surface, it was found that a small differential phase-change effect occurred due to the difference in surface ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/166522b0

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8

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Diakoptics as a general approach in engineering (1987)

Aitchison, P. W.

Springer

Journal of engineering mathematics 21 (1987), S. 47-58

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ISSN: 1573-2703

Source: Springer Online Journal Archives 1860-2000

Topics: Mathematics , Technology

Notes: Abstract A method is described for reducing the solution of a matrix equation of linear equations, Mz = d, to that of a number of simpler equations. The method is one mathematical version of diakoptics, and can be used to solve engineering problems involving linear equations without specialization to each individual application. The method has the usual advantages of diakoptics: different parts of the problem can be solved on different computers (distributed computation), decreased computer storage requirements in fast storage, applicability to some types of parallel processors and decreased computation time in some circumstances. Consideration is given to reducing M to specific forms including block triangular, banded and the usual block diagonal. Consideration is also given to the case where M is not square and a new application is given to solving least-squares problems.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00127693

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