Magnetic hysteresis in granular CuCo alloys

Room-temperature hysteresis loops of granular Cu100-xCox alloys (5 less than or equal to x less than or equal to 15) obtained by planar flow casting in air and submitted to proper annealing treatments have been measured up to a field of 10 kOe by means of a vibrating sample magnetometer. In major loops (\H-vert\ = 10 kOe), the reduced remanence-to-saturation ratio m(r) = M-r/M-s and the coercivity H-c measured on all studied materials appear to be related by an almost linear law of the type m(r) approximate to 1/3 (mu H-c/kT), mu being the average magnetic moment on Co particles. A similar relation is also observed on minor symmetrical loops (100 Oe less than or equal to\H-vert\ less than or equal to 9 kOe). The observed results are accounted for by a model which considers the hysteresis as originating by magnetic interactions among nearly superparamagnetic Co particles. (C) 1999 American Institute of Physics. [S0021-8979(99)51408-4]

Thermally evaporated Cu-Co top spin valve with random exchange bias

A cobalt-copper top spin valve was prepared by thermal evaporation of a stack of ferromagnetic thin films separated by thin layers of the diamagnetic metal, with a cap layer containing an antiferromagnetic AFM exchange-biasing material. A nonconventional top AFM layer was used, in order to optimize the multilayer roughness and to avoid electrical interference with metallic layers; it consists of a composite material easily processed by means of optical lithography, basically a polymeric matrix composite with a dispersion of nickel oxide microparticles. Magnetization and magnetoresistance measurements were performed from 4 to 300 K. The measurements of both quantities indicate random pinning action of the top AFM layer, resulting in a small exchange-bias field and in asymmetric magnetization and magnetoresistance curves. A simple model explains the observed physical effect

Magnetic properties and giant magnetoresistance in melt‐spun Co‐Cu alloys

Magnetic, structural, and transport properties of as‐quenched and annealed Co10Cu90 samples have been investigated using x‐ray diffraction and a SQUID magnetometer. The largest value of MR change was observed for the as‐quenched sample annealed at 450 °C for 30 min. The magnetic and transport properties closely correlate with the microstructure, mainly with Co magnetic particle size and its distribution. For thermal annealing the as‐quenched samples below 600 °C, the Co particle diameters increase from 4.0 to 6.0 nm with a magnetoresistance (MR) drop from 33.0% to 5.0% at 10 K. Comparison with the theory indicates that the interfacial electron spin‐dependent scattering mechanism correlates with GMR for Co particle diameters up to about 6.0 nm

Risonanze, ovvero piccola passeggiata in compagnia delle onde stazionarie

This chapter is devoted to a discussion of the role played by physical effects - such as standing-wave generation and the ensuing resonances which occur in acoustic resonators - on musical forms and on the design of novel, non-conventional sound generators or musical instruments. The first Section hosts a brief historical survey of the cross-fertilization between musical forms and environmental acoustics, focusing on examples which show the relation always existing between the two disciplines along the centuries. An account of the increasingly prominent role of the surrounding environment on the new musical forms explored by some contemporary musicians is given. In the second Section, the novel area of ultra-miniaturized music instruments is reviewed. The recent great advances in science and technology of the nano-world make it possible to conceive, design and fabricate harmonic or quasi-harmonic sound generators on the sub-micrometer scale. These micro- or nano-musical instruments follow the same physical laws which drive the performance of macroscopic classical instruments, although their response critically depends on the scaling down of their physical dimension

Kinetic and Structural Aspects of Magnetic Phenomena In Amorphous Soft Ferromagnets

Recent results concerning domain structure and domain-wall motion in amorphous soft ferromagnets are reviewed. The effect of the value of the saturation magnetostriction is discussed, with particular emphasis on the change in sign of λs induced in nearly-zero magnetostriction alloys by large tensile stresses. The 'fast' permeability relaxation observed during high-frequency domain-wall motion is explained in terms of a domain-wall instability under extreme velocity conditions. Finally, the unique kinetic features of the slow relaxation (after-effect) of the initial magnetic permeability will be outlined. A specific experiment, conceived to check the assumptions of the model established for this relaxation process, is proposed and discussed in detail