Directional dependence of magnetization and coercivity in hematite ore experimentally deformed in torsion

Rock-magnetic properties are widely used to resolve the composition, concentration, size, shape and alignment of iron oxides in rock samples. Although anisotropy of magnetic susceptibility is measured routinely, acquisition of remanent magnetization as well as hysteresis loops are usually measured in one direction only. This may lead to biased interpretation of the results. In our study, observation of strong directional dependence of remanence acquisition curves and hysteresis loops in experimentally deformed samples of hematite ore is reported. While the original undeformed hematite ore sample exhibited magnetic properties practically independent of the direction, the specimens which experienced deformation in torsion showed significant anisotropy. For example, the anisotropy of saturation magnetization reached several tens of percent. Our results suggest that experimental deformation resulted in neoformation of magnetite nanoparticles, as well as shift of the original hematite coercivity spectra towards lower values. These findings have significant impact on the remanent and induced magnetization measurement protocols and interpretation of the data. Anisotropy of these parameters should be checked at least in cases when hematite is assumed to be present in the samples, or the samples underwent creep deformation.