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The coercivity Hc of compacts of thin (0.1?5 μ diameter) nickel wires embedded in a silver matrix has been measured as a function of the effective wire radius deff. Hc increases linearly with 1/deff2, in agreement with Aharoni's theory of magnetization reversal by curling. From the slope, δHc/gd (deff?2), upper and lower bounds for the exchange constant A of Nickel have been derived (77K): 1.5 × 10?11 Wsec/m ? 3.0 × 10?11 Wsec/m. 相似文献
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In precipitation-strengthened polycrystals, precipitate-free zones (PFZs) often form along grain boundaries. These PFZs lower the yield strength. In this investigation, thin foils of the commercial γ′-strengthened nickel-based superalloy Nimonic PE16 have been strained inside a transmission electron microscope and the relevant dislocation processes in the PFZs and in the γ′-strengthened material next to them have been observed under load. Since the PFZs are only solid solution strengthened, they are softer than the interior of the γ′-strengthened grains. Many different slip systems are activated in the PFZs even at relatively low external stresses. Multiple slip allows for compatible deformation of neighbouring grains. Extensive cross-slip and double cross-slip in the PFZs lead to a high dislocation multiplication rate. Easy creation of dislocations in the PFZs and pile-ups at the border between the PFZs and the γ′-strengthened interior of the grains enhance the propagation of slip across grain boundaries and thus lower the yield strength of the material. 相似文献
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Weber M. C. Nembach H. Blomeier S. Hillebrands B. Kaltofen R. Schumann J. Carey M. J. Fassbender J. 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(2):243-248
All-optical control of the magnetization of polycrystalline exchange bias
bilayer systems is achieved using short picosecond laser pulses. Due to the
photoexcitation, the spin temperature across the interface between the
ferromagnetic and antiferromagnetic layer is elevated, resulting in a
collapse of the interfacial exchange coupling. Thus, within the first 10 ps,
a fast reduction of both the exchange bias field and the coercive field is
observed for three different exchange bias systems comprising both different
ferromagnets and antiferromagnets. The fast thermal unpinning is followed by
a slower heat diffusion dominated relaxation process, which strongly depends
on the thermal conductivity of the used buffer layers and substrates. The
fast optical unpinning can be understood in terms of an internal anisotropy
pulse field capable of triggering ultrafast precessional magnetization
dynamics of the ferromagnetic layer, which makes heat-assisted coherent
magnetization rotation feasible. 相似文献
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Experimental evidence is presented that moving Bloch-walls decrease the flow stress of nickel single crystals. Via their strain fields, Block-walls interact with dislocations. 相似文献
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