Magnetic dilution effects on morin phase transition in hematite

Abstract

Abstract Mössbauer investigations, in the range 10 to 1000 °K, in (1− x ) Fe 2 O 3 ‐ x Al 2 O 3 systems, have shown a nonlinear rapid decrease of the Morin temperature, T M , with the increasing magnetic dilution of the α‐Fe 2 O 3 lattice. The phase transition is not sharp and becomes more and more diffused as the magnetic dilution increases. An anomalous variation of the angle, θ, between the spin direction and the c ‐axis is seen for the 5.27 wt% diluted sample indicating the presence of three magnetic phases in this case. Unlike the case of undiluted α‐Fe 2 O 3 , for the 0.56 wt% diluted sample at low temperatures, outside the phase transition region, the Fe 3+ spins do not lie along the c ‐axis but are canted at an angle of about 30°. This angle, θ ≈ 30°, does not seem to change much with further increase in dilution. It is also seen that with dilution, the ratio T M / T N and the anisotropy energy, K , deduced from the temperature and concentration dependence of the hyperfine field, are decreased ( T N Néel temperature). This supports the existing anisotropy theory.