Source Of Magnetostriction Research Articles

Beyond a phenomenological description of magnetostriction

Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction—the underlying magnetoelastic stress—can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the sub-picosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.

The magnetoelastic paradox in [formula omitted] and [formula omitted

For isotropic systems the only source of magnetostriction is believed to be the exchange striction (ES). In many cases large magnetostrictive effects have been observed in Gd 3 + based systems ( S = 7 2 , L = 0 ), but in no case a significant symmetry breaking lattice distortion has been found. For ferromagnetic (fm) order this is in line with the ES model. However, for antiferromagnetic (afm) large symmetry breaking distortions of the lattice are expected from theory. This contrasts to all available experimental data on several Gd-based antiferromagnets. We demonstrate examples for this magnetoelastic paradox and discuss in detail experimental evidence for GdAg 2 and GdRu 2 Si 2 .

An Ocean Acoustic Tomography System with a 200 Hz Giant Magnetostrictive Source

This paper describes tomography equipment for measuring ocean phenomena in a 1000 km2 area. A 200 Hz giant magnetostrictive source was developed to increase the transmitting level and decrease the source size. Five 200 Hz transceiver systems were constructed with these sources. These systems have surface buoys for real-time data transmission via the INMARSAT-C. Sea tests of the five transceiver systems were conducted east of the Izu-Ogasawara Trench to observe the Kuroshio Extension during July and September 1997.

Low frequency sound sources: statement of problem and some possible solutions

The main stumbling block in a project to measure the backscattering cross-section (target strength) of commercial fish at frequencies in the band 300 Hz to 3000 Hz has been that of providing a suitable sound source. The spectrum level requirement of this source is + 70 dB relative to 1 μbar (0.1 N/m2) at 1 m per Hz across the band, or about 100 W peak power during a 10 ms pulse at any frequency. The general problem of radiating this power level into water at these frequencies is considered. Several sources employing various principles of transduction including sparkers, boomers, explosives, hydroacoustic, electrodynamic, piezoelectric and magnetostrictive sources, are considered in terms of a common parameter—the maximum output spectrum level—as well as efficiency.

The Effect of High Intensity Sound on Smokes and Other Aerosols

When smoke or other aerosols are placed in a resonance tube driven by a strongly vibrating source the particles are aggregated rapidly. In the investigation reported at this time magnetostrictive sources of frequencies 11.3 to 22 kilocycles per second were placed at the lower end of a vertical resonance tube into which either water vapor, cigarette smoke, or titanium tetrachloride smoke was introduced. The aggregated particles which are suspended at certain stationary positions in the tube, form large “disks” and “thimbles.” Some of the “disks” are oriented horizontally, while others have vertical orientation. The vertical “disks” are formed in sets of three equally spaced about the axis of the resonance tube. The process of aggregation is illustrated by means of motion pictures.