Mineral magnetism of synthetic microcrystalline and nanophase iron oxides and iron oxyhydroxides

A suite of well-characterized synthetic microcrystalline hematite samples, 2-line and 6-line ferrihydrite samples and nanohematite samples are studied through magnetization-field curves measured at room temperature. The single-domain microcrystalline hematite samples are analyzed through basic hysteresis parameters providing sample characteristics such as magnetic anisotropy information, the effect of annealing on the origin of the magnetization and the relatively constant intrinsic high field susceptibility. The application of a magnetic granulometry method on the magnetic data of the superparamagnetic nanohematite and ferrihydrite samples provides fundamental information such as the intrinsic mass magnetization and estimated particle size. Additionally, it gives insight into possible moment formation mechanisms within the superparamagnetic particles. The observed differences between the magnetic properties of the magnetically blocked and the superparamagnetic samples considered are also discussed.