Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

Abstract

We studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite‐bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature‐dependent magnetic susceptibility, magnetic hysteresis and low‐temperature saturation isothermal remanent magnetization. Structural properties of magnetite were analyzed using X‐ray diffraction, high‐resolution scanning electron microscopy and synchrotron‐assisted X‐ray absorption spectroscopy. The shock‐induced changes include magnetic domain size reduction due to brittle and ductile deformation features and an increase in Verwey transition temperature due to lattice distortion. After heating, the crystal lattice is relaxed and apparent crystallite size is increased suggesting a recovery of lattice defects documented by a mosaic recrystallization texture. The structural changes correlate with modifications in magnetic domain state recorded by temperature‐dependent magnetic susceptibility, hysteresis properties and low‐temperature saturation isothermal remanent magnetization. These alterations in both, magnetic and structural properties of magnetite can be used to assess impact‐related magnetic anomalies in impact structures with a high temperature overprint.

Demagnetization Energy and Internal Stress in Magnetite From Temperature‐Dependent Hysteresis Measurements

“…Shock‐induced magnetic hardening refers to an increased magnetic coercivity observed after impact shock (Cisowski & Fuller, 1978; Pohl et al., 1975), but also shock‐induced bulk coercivity decreases have been reported (Bezaeva et al., 2010). Improving the quantification of stress in such observations by the SRW method promises substantial progress (Bezaeva et al., 2016; Gattacceca et al., 2007; Kontny et al., 2018; Sato et al., 2021).…”

Domain State and Temperature Dependence of Pressure Remanent Magnetization in Synthetic Magnetite: Implications for Crustal Remagnetization

“…Similar increases in coercivity by pressure cycling were reported in earlier studies (Gilder & Le Goff, ; Reznik et al, ). The more SD‐like behavior is usually attributed to the introduction of stacking faults and dislocations in the magnetite grains, which act as new pinning sites for domain walls (Kontny et al, ; Lindquist et al, ). Consequently, the increased dislocation density increases the coercivity as well as the remanence efficiency of the sample (Dunlop & Özdemir, ).…”

Shock‐induced formation of wüstite and fayalite in a magnetite‐quartz target rock

“…Our recent investigations of a laboratory-shocked magnetite-quartz ore demonstrate that increasing shock pressure causes variations in magnetic and structural properties of magnetite (Reznik et al 2016a), as well as structural modifications in quartz, biotite, and amphibole (Reznik et al 2016b). However, possible structural and phase transformations occurring at the interfacial regions between minerals like magnetite and quartz were not within the scope of our previous studies (Reznik et al 2016a(Reznik et al , 2016bKontny et al 2018), and we did not concentrate on interactions between the ARMCO iron container and the target rock.…”

“…, ; Kontny et al. ), and we did not concentrate on interactions between the ARMCO iron container and the target rock.…”