Shock-Wave Compression of 30% Ni-70% Fe Alloys: The Pressure-Induced Magnetic Transition

Abstract

Inhomogeneities of shockwave deformation in Fe32 wt.% Ni0.035 wt.% C alloyThe compressibility of 30% Ni-70% Fe (wt %) in the fcc phase is investigated from atmospheric pressure to 40 kbar with shock-wave loading techniques. The experiments are accomplished utilizing projectile impact techniques with stress profile measurements by the quartz gauge. A sharp change in compressibility indicates a second-order ferromagnetic Curie point transition at a stress of 25 kbar and a volume of 0.9807 Yo.The coefficient of Curie temperature change with pressure is found to be -5.8±0.3°C kbac 1 • The agreement of this value with previous magnetic measurements, along with the anomalously large compressibility below the transition and the large decrease in compressibility at an elevated temperature, clearly indicates that this transition is a ferromagnetic to paramagnetic transition. Values for the change of thermal expansion and specific heat at the transition are computed from the Ehrenfest relations. These values are consistent with the magnetic character of the transition and give a complete description of the thermodynamic properties of the transition. To provide more compressibility data on various types of ferromagnetic materials, a few additional measurements are reported for lnvar and 30% Ni-70% Fe in the bcc phase.

Influence of long- and short-range chemical order on spontaneous magnetization in single-crystalline Fe0.6Al0.4 compound thin films

“…Considering the importance of the average Fe-Fe nearest-neighbor distance to the spontaneous magnetization, this assumption is not perfectly valid. Although the magnetovolume effect is often associated with the isotropic volume change by, for example, hydrostatic pressure [16], anisotropic stress such as shock-wave compression [57] and tensile stress [58] can also contribute to the spontaneous magnetization change via the magnetovolume effect. From this point of view, our results conflict the anisotropic-stress-induced magnetovolume effect.…”

High strain-rate magnetoelasticity in Galfenol

“…1-3 Initial shock demagnetization studies of magnetic materials in the 1950s focused on soft ferromagnetic materials including silectron steel, deltamax, and yttrium iron garnet which are only weakly magnetoelastic. [4][5][6][7][8] Subsequently, a larger emphasis was placed on examining hard ferromagnets to increase power generation. In all of these tests, pulsed electromagnetic power was generated with an explosively driven shock wave that demagnetized the ferromagnetic sample.…”