Magnetism and magnetic properties of Ti-rich titanomagnetite and its tendency for alteration in favour of titanomaghemite

Abstract

The study of the Ti-rich titanomagnetite (Ti-Mt) and the low-temperature
oxidized Ti-Mt bearing basalts has been undertaken. High magnetic susceptibility of the
Ti-rich Ti-Mt basalts does not correspond to high spontaneous magnetization. The decrease
of spontaneous magnetization with increasing content of ulv¨ospinel is evidenced.
The spontaneous magnetization in ferromagnetics and ferrimagnetics originate in the magnetic
domains, but the domain structure in the Ti-rich larger Ti-Mt grain sizes is rarely
developed. The cause of high magnetic susceptibility of the Ti-rich Ti-Mt stems probably
from the molecular field of the two sub-lattice structure of the Ti-Mt.
Alternative explanation: In the low magnetic fields, the permeability of the mixed
ferrites increases with increasing temperature and reaches the extreme maximum at the
temperature closely below the Curie temperature of material. Similar behaviour have
been shown also by the Ti-rich Ti-Mt-es. Rapid decrease of the magnetic crystalographic
anisotropy with temperature and the decrease in intensity of the exchange interactions
are responsible for this effect. So, the increase of Ti4+ ions in the titanomagnetite results
in the increase of magnetic susceptibility of the Ti-rich Ti-Mt-es.
The problem of the extremely low magnetic susceptibility in the basalts with lowtemperature
oxidized phase consists in the following: along with the low-temperature oxidation
of Fe2+ to Fe3+ ion and the formation of vacancies in creating titanomaghemite,
the rearrangement of magnetic moments in initial Ti-rich Ti-Mt has taken place. The
initial state had a more anti-ferromagnetic arrangement with high content of ulv¨ospinel
of high non-collinearity. High magnetism of the initial Ti-Mt was due to the action of
the molecular field. During the above-mentioned process this original state was broken
down, and the magnetic susceptibility was rapidly decreased. A completely new ferrimagnnetic
arrangement of magnetic moments of the sub-lattices has been established in
the titanomaghemite.