Magnetic anisotropy of hematite natural crystals: high field experiments

Hematite is one of the most important carriers of remanent magnetization in natural samples. Its strong magnetocrystalline anisotropy makes it difficult to determine one single value for the magnetic anisotropy constant and other magnetic properties. In particular, the anisotropy of hematite within its basal plane is controversial because an assumed triaxial anisotropy compatible with the crystallographic structure has not always been detected. This study presents a comparative analysis of rock magnetic properties, compositional analysis and determination of the magnetic anisotropy constant. Different models with anisotropy constant within the basal plane ranging from 0 to 13 (J m(-3)) are considered in the evaluation of the factors that control the presence or absence of a triaxial anisotropy. A linear relationship between saturation magnetization (M-s) and coercitivity (B-c) in measurements at increasing temperatures is observed in samples where anisotropy is either uniaxial or biaxial while those with significant triaxial anisotropies have a power-law relationship between M-s and B-c.