Y. Tanaka et al., MICROSTRUCTURES AND MAGNETIC-PROPERTIES OF FE-PT PERMANENT-MAGNETS, Journal of magnetism and magnetic materials, 170(3), 1997, pp. 289-297
We have investigated the magnetic properties of Fe-38.5Pt, Fe-39.5Pt a
nd Fe-50.0Pt (at %) alloys after various heat treatment conditions usi
ng a vibrating sample magnetometer, and correlated these properties wi
th the microstructures of the alloys by transmission electron microsco
py. The Fe-50Pt ahoy shows poor magnetic hardness regardless of the he
at treatment conditions. The magnetic hardness of the Fe-39.5Pt alloy
shows a maximum value after annealing for 10 h at 873 K, while it mono
tonically decreases after annealing at 1073 K. The alloy with the high
est coercivity was composed of a single phase gamma(1) with an average
domain size of approximately 10 nm. The electron diffraction results
indicate that the alloy is frustrated with accumulated stress, induced
by a cubic --> tetragonal transformation which occurs without twinnin
g. On the other hand, when stress is relieved by twin formation after
prolonged aging, the coercivity decreases. By annealing at 1073 K, the
well known polytwin structure evolves. However, only poor hard magnet
ic properties are observed when this polytwin structure appears, Hence
, the highest coercivity is attributed to the formation of nanoscale L
1(0) ordered antiphase domains which is expected to be a highly anisot
ropic single domain magnetic particle.