15,401 research outputs found
Geometric Aspects of the Dipolar Interaction in Lattices of Small Particles
The hysteresis curves of systems composed of small interacting magnetic
particles, regularly placed on stacked layers, are obtained with Monte Carlo
simulations. The remanence as a function of temperature, in interacting
systems, presents a peak that separates two different magnetic states. At low
temperatures, small values of remanence are a consequence of antiferromagnetic
order due to the dipolar interaction. At higher values of temperature the
increase of the component normal to the lattice plane is responsible for the
small values of remanence. The effect of the number of layers, coordination
number and distance between particles are investigated.Comment: 5 pages, 7 figure
Orientation of Demagnetized Bees
The orientation of honey bee dances is affected by the earth's magnetic field. Honey bees possess localized, well-oriented, stable and superparamagnetic domains of magnetite. Four lines of evidence suggest that the superparamagnetic domains of bees are more likely to be involved in magnetic field detectors than the stable domains. (1) Although the stable domains vary widely in size and number between bees, approximately 2×10^8 superparamagnetic domains are found reliably in all bees, and are restricted to there latively narrow size range of 300–350 Å. This suggests that the superparamagnetic domains are more likely to have a biological function. (2) Behavioural observations of dances in null fields are difficult to reconcile with astable-domain detector but are clearly predicted by many superparamagnetic detector models. (3) When honey bees are demagnetized, their ability to orient to the earth's field is unaffected. This suggests that the detector either utilizes the super paramagnetic domains or depends on aligned anisotropic stable domains processed without regard to magneticpolarity. (4) Bees that have only superparamagnetic domains are able nevertheless to orient to the earth's magnetic field, a phenomenon which indicates that permanent domains may not be required for detection
Magnetic remanence of Josephson junction arrays
In this work we study the magnetic remanence exhibited by Josephson junction
arrays in response to an excitation with an AC magnetic field. The effect,
predicted by numerical simulations to occur in a range of temperatures, is
clearly seen in our tridimensional disordered arrays. We also discuss the
influence of the critical current distribution on the temperature interval
within which the array develops a magnetic remanence. This effect can be used
to determine the critical current distribution of an array.Comment: 8 pages, 4 figures, Talk to be presented on 44th Annual Conference on
Magnetism & Magnetic Materials, San Jose, CA, USA Accepted to be published in
Journal of Applied Physic
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