Investigating impact demagnetization through laser impacts and SQUID microscopy

Understanding demagnetization by hypervelocity impacts is crucial for the interpretation of planetary magnetic anomalies and remanent magnetization in meteorites. We describe an innovative approach for investigating the effects of impacts on the remanent magnetization of geologic materials. It consists of the combination of pulsed laser impacts and Superconducting Quantum Interference Device (SQUID) microscopy. Laser impacts are nondestructive, create shocks with peak pressures as high as several hundred GPa, and allow well-calibrated modeling of shock wave propagation within the impacted samples. High-resolution SQUID microscopy quantitatively maps the magnetic field of room-temperature samples with an unprecedented spatial resolution of similar to 100 mu m. We present shock modeling and magnetic field data obtained for two laser impacts on a magnetite-bearing basalt sample. Magnetic measurements show a demagnetized area at the impact locations. We also show that high-resolution magnetic measurements combined with impact modeling provide a continuous relation between the demagnetization intensity and the peak pressure undergone by the sample. This promising technique will allow for the investigation of the demagnetization behavior of a variety of geological materials upon impacts, with implications for our understanding of the magnetization of extraterrestrial materials and of terrestrial impact structures.