Shock-induced magnetic transition in iron detected by manganin gauge

Shock induced polymorphic transition of pure iron (99.5%) has been investigated experimentally using in-material self-made manganin gauges which has a shape of one-turn coil. A negative pulse is superposed on an output signal from the gauge in the pressure range above about 18GPa. The negative pulse is thought to be originated in shock-induced polymorphic transition (α-ε phase transition) because the polymorphic transition is followed by magnetic. transition (ferromagnetic to paramagnetic). The iron plate specimens between which a manganin gauge is sandwiched are magnetized in the vicinity of the gauge by constant current applied to the gauge. The polymorphic transition behind shock front reduces magnetic flux near the gauge when the shock front passes through the gauge. This flux reduction generates the negative pulse. From the negative pulse superposed on a gauge signal, information on the polymorphic transition can be obtained. Experimental data show that the negative pulse appeared in the pressure range above 18GPa and the amplitude of the pulse increased with the applied pressure. It is inferred from the discussion about experimental data that the maximum rate of transition increases with applied pressure.