Paramagnetic anisotropy of a natural kaolinite and its modification by chemical reduction

Substitutional iron in natural layered kaolinite shows an unusual response to external magnetic fields. DC magnetization as well as susceptibility measurements using a SQUID magnetometer show paramagnetic behavior with strong anisotropy depending on the relative direction of layer planes and magnetic field. Additional anisotropic electron paramagnetic resonance measurements show the several paramagnetic centers in this mineral. The anisotropy in mutually perpendicular magnetizations reaches 20% at 1.8 K and can be explained by the Van Vleck paramagnetism of Fe2+ impurities in this natural kaolinite. (C) 2002 Elsevier Science B.V. All rights reserved.