A Mossbauer study of the spin-flop phase transition in some antiferromagnetic materials
The spin-flop phase transition has long been of interest to both
theoretical and experimental physicists, ever since it was first predicted
by Louis Neel in 1936. In this work spin-flop transitions in
the antiferromagnetic materials K
studied by means of Fe MBssbauer spectroscopy.
Spectra of K2FeF5 and Rb2FeF5 single crystals were recorded at 4.2K
with external magnetic fields of up to 14T applied in different modes,
providing information on the effect of misalignment on the sharpness
or 'order' of the observed transition. Directing the applied field
parallel to the easy anisotropy axis resulted in a sharp 'first-order'
transition, while misaligning the field by ~30o produced a broadened
Field-induced spin-flop transitions in a-Fe203 single crystal samples
were studied at low temperatures by applying fields of up to lOT
either parallel to or perpendicular to the easy anisotropy axis. The
observed transitions were found to be of first-order in the 'parallel'
case, and second-order in the 'perpendicular' case. The Morin transition,
a temperature driven spin-flop which occurs naturally in
at ~260K, was also studied and was found to be of first-order.
Comparison of the character of the observed transitions with the
predictions of several theoretical models of the spin-flop led to the
conclusion that the conventional mean-field theory of the transition
provides a good qualitative description of the phenomenon.