EVIDENCE FOR A SURFACE FERROMAGNETIC LAYER IN AMORPHOUS YFE2

Spin resonance measurement on bulk samples of a-YFe2, grown by d.c. sputtering, and a thin film of Y0.30Fe0.70, grown by co-evaporation, are reported. In agreement with our earlier reports, we observed a multi-line spectrum in which one line has a frequency and angular dependence expected from a thin ferromagnetic layer with (4πM)eff≳6 kOe at 300 K despite the fact that a-YFe2 is known to have no long range order at this temperature. Rutherford back-scattering, chemical etching studies, and temperature dependence of (4πM)eff lead us to conclude that the ferromagnetic layer is not a consequence of segregation, surface contamination or locally crystallized material. We propose that it arises from some kind of an atomic rearrangement which is initiated at the surface and progresses inward on a time scale of weeks.