EFFECT OF MAGNETIC-FIELD ON EARLY-STAGE O F ORDERING PROCESS OF FEPD ALLOYS

With a disorder-order transition of FePd alloys from A1 to L1(0), char acteristic micro-twin structures are formed, and marked uniaxial magne tic anisotropy is revealed, and much work has been done regarding the relation between microstructures and magnetic properties of the alloys . Few work, however, has been reported as to the effect of magnetic fi eld on the morphology change at the beginning of order reactions of th e alloys. The present study has been carried out to examine microstruc ture changes of an early stage of ordering of FePd alloys with heating at various temperatures near the magnetic Curie temperature under mag netic fields by transmission electron microscopy. The results are summ arized as follows: (1) By in-situ transmission electron microscope obs ervations with a standard objective pole piece particular variant doma ins grow preferentially, while every variant domain nucleates homogene ously with an anti-magnetic objective pole piece. (2) Under a magnetic field parallel to the specimen surface, a variant crystal with c-axis near the direction of the magnetic field starts to grow from grain bo undaries, and {011} macrotwins are formed as accommodation defects. (3 ) Magneto-heat treatment effect is present in a certain temperature ra nge of ferromagnetic short range order just above the magnetic Curie t emperature. (4) Magnetostriction calculated from elastic constants is an order of 10(-5), which seems small but still plays an important rol e in the initiation of variant domains.