J B McKinnon, D Melville and E W Lee
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Abstract
The critical field required to induce this transition in
Fe-Rh alloys close to the equiatomic composition has been measured using
pulsed magnetic fields up to 280 kOe. Measurements of the thermal
expansion and high field magnetization have also been carried out. It is
found that application of Kittel's theory of exchange inversion to the
results leads to serious numerical discrepancies. A four sublattice
model is developed which indicates the importance of the excess entropy
of the ferromagnetic over the antiferromagnetic phase in exciting the
antiferromagnetic-ferromagnetic transition. The exchange iteration β
between iron sublattices is small and negative and, although its lattice
parameter dependence is large and positive, there is no suggestion of
exchange inversion corresponding to a change in sign of β at the
antiferromagnetic-ferromagnetic transition. Thus the ferromagnetic state
is stabilized by the excess entropy even in the presence of
antiferromagnetic interactions and this stability is maintained right up
to the Curie temperature.
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