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Investigation of magnetization behavior in nanoelements using the finite element method (2000)

Ridley, P. H. W. ; Roberts, G. W. ; Chantrell, R. W.

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

Journal of Applied Physics 87 (2000), S. 5523-5525

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: A model of thin film permalloy using an efficient finite element variational approach to the magnetostatic field calculation is described. The material is discretized into a nanoelement structure at the micron level which enables us to investigate material properties due to patterning. Predicted domain structures agree well with experimental data. Interactions between elements are significant and it will be shown that the domain structure in the central element differs from that of its neighbors. As expected, the addition of pointed ends stabilizes the single-domain state. Elements with two pointed ends exhibit pseudo-single-domain behavior. We have studied the single-domain/pseudo-single-domain transition for permalloy platelets, results for noninteracting platelets are given as a function of the elongation. Interactions are shown to increase or decrease the critical size depending on the geometry. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.373392

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Simulation of the micromagnetic behavior of arrays of interacting nanoelements (2002)

Ridley, P. H. W. ; Roberts, G. W.

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

Journal of Applied Physics 92 (2002), S. 1069-1077

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: In this work we investigate the behavior of small arrays of interacting permalloy particles at the submicron level. Each individual particle is termed a nanoelement and is rectangular in form with varying elongation. The interest in such structures of magnetic material is increasing, due mainly to the possible potential use in future high-density magnetic storage media applications. To carry out our investigations we have developed a dynamical micromagnetic model based on the use of the finite element method. For our results we investigate the effects of misaligned and aligned anisotropy distributions on arrays with varying size and space of nanoelement. We observe that the reversal mechanism of the arrays is very sensitive to the disorder of the intrinsic material properties. In the case of aligned uniaxial anisotropy a highly symmetric cooperative switching mechanism is observed. The larger anisotropy has the effect of stabilizing states during the reversal process, leading to distinctive switching along the hysteresis curve. A random anisotropy breaks this high symmetry sufficiently to reduce the cooperative switching, leading to a relatively random reversal of individual nanoelements. © 2002 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1487912

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Control of the behaviour of leaf-cutting ants by their ‘symbiotic’ fungus (1996)

Ridley, P. ; Howse, P. E. ; Jackson, C. W.

Springer

Cellular and molecular life sciences 52 (1996), S. 631-635

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ISSN: 1420-9071

Keywords: Atta ; symbiosis ; semiochemical ; leaf-cutting ants ; sociobiology ; fungus

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract There is an obligatory relationship between leaf-cutting ants of the generaAtta andAcromyrmex (Hymenoptera; Attini) and the fungus,Attamyces bromatificus Kreisel, for which they provide a substrate of cut plant material. We show that the ants learn to reject plant material that contains chemicals injurious to the fungus. After an initial period of acceptance, ants from laboratory nests stopped harvesting granular bait containing a fungicidal agent (cycloheximide) and orange peel. This rejection was maintained for many weeks. These colonies also rejected control bait containing no cycloheximide. Some generalisation of the response was observed; colonies rejecting orange granules also rejected grapefruit granules, although they still accepted blackcurrant granules. Rejection of fungicidal bait by colonies in the field was restricted to ants on foraging trails exposed to experimental bait. We conclude that a semiochemical from the fungus, circulated by trophallaxis and grooming, regulates the selection of plant material by foragers. The fungus gains more advantages from the symbiotic relationship than is often realised. The ants provide the fungus with housing, sanitation, defence against disease and predators, pre-selected food, and a means of dissemination, at the cost to itself of providing food for the ant brood.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01969745

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