Open AccessCation Diffusion Processes and Self‐reversal of Thermoremanent Magnetization in the Ilmenite‐Haematite Solid Solution Series
Author(s) -
Hoffman Kenneth A.
Publication year - 1975
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1975.tb05485.x
Subject(s) - ilmenite , thermoremanent magnetization , solvus , nucleation , curie temperature , condensed matter physics , phase (matter) , diffusion , materials science , phase transition , solid solution , range (aeronautics) , magnetization , thermodynamics , mineralogy , geology , chemistry , physics , microstructure , metallurgy , ferromagnetism , remanence , superalloy , organic chemistry , quantum mechanics , magnetic field , composite material
Summary Synthesized x FeTiO 3 ‐ (1‐ x )Fe 2 O 3 specimens having compositions near the centre of the solid solution series indicate that nucleation of cation‐ordered clusters may occur several hundred degrees above the order‐disorder transition temperature T c(o‐d) , a finding in conflict with theory. In addition, the ‘ x ‐phase’ is shown to have at most a narrow range of blocking temperatures about 100° above the Curie point of the ordered phase, a result incompatible with the model developed by Ishikawa & Syono. The following model, which well explains the experimental data, is proposed: At temperatures above T c(o‐d) but below the top of the solvus, short‐range unmixing occurs with small ilmenite‐rich and haematite‐rich regions forming throughout the specimen. Upon cooling, the ilmeniterich regions order first and act as the ‘nuclei’ for further ordering. The haematite‐rich regions, on the other hand, are the x ‐phase. It is argued that when these disordered haematite‐rich regions are in contact with ordered material, self‐reversal occurs.