Magnetic properties of metal-substituted haematite

Abstract

Mineral and isothermal magnetic properties of Al-, Mn- and Ni-substituted haematites were characterized and their relationships evaluated in order to interpret better the results of magnetic analyses of soils and recent sediments. Aluminium, manganese and nickle haematites generally behaved as single-domain (SD) particles. The influence of incorporated Al on the magnetic behavior of haematite was consistent with Al acting as a paramagnetic dilutent. Mass magnetic susceptibity (χ) and SIRM800 decreased as the level of Al substitution increased. Incorporation of Mn and Ni increased χ, which could be associated with enhancement of the spin canting effect of haematite. The stability of SIRM800 to demagnetization for Al-haematite appears to be related to a defect mechanism associated with the development of smaller crystallites arising from Al substitution. Magnetic domain rotation or flipping was probably inhibited, being blocked by structural defects during magnetization and demagnetization, and resulted in a low but stable partial SIRM (SIRM800). %IRM/SIRM800 demagnetization curves and estimated (B(o))(CR) values of ≤ 100 mT for Mn-haematite indicate pseudosingle-domain/multidomain-like behaviour despite Mn-haematite having particle and crystallite dimensions similar to Ni-haematite, which did not show this behaviour. Data indicate that parameters involving unsaturated, partial SIRM should be used with caution in magnetic studies of soils and sediments.