FERROMAGNETIC-RESONANCE INVESTIGATION OF MAGNETISM IN FE-RICH FE100-XTIX SPUTTERED AMORPHOUS-ALLOYS

Fe-rich Fe100-xTix alloys in the Ti concentration range 9 less than or equal to x less than or equal to 11 have been successfully prepared i n the amorphous state for the first time using the DC co-sputtering me thod. Exhaustive ferromagnetic resonance (FMR) measurements were perfo rmed on these alloys at a fixed microwave-field frequency of about 9.2 3 GHz in the temperature range 77-300 K. In this temperature range, a single resonance is observed for the alloys with x = 10 and 11 as agai nst two resonances (primary and secondary), having different propertie s, in the case of a-Fe91Ti9. For the primary (single) resonance in a-F e91Ti9 (the alloys with x = 10 and 11), the 'in-plane' uniaxial anisot ropy field H-K (T, x) scales with the saturation magnetization Ms(T, x ). This result suggests that the anisotropy energy is of dipolar origi n. By contrast, the relation H-K proportional to M(S) breaks down in t he case of secondary resonance. The primary and secondary resonances t hus characterize two distinctly different amorphous magnetic phases wh ich widely differ in their chemical as well as geometrical short-range orders. For all the alloys in question, thermal demagnetization is ma inly due to spin-wave (SW) excitations, and the SW stiffness D decreas es with increasing x. SW modes soften at T less than or equal to T-RE. (the so-called re-entrant transition temperature) and D possesses a r educed value for T < T-RE. The existence of a re-entrant state at low temperatures is also vindicated by the rapid increase in the magnitude of the peak;to-peak FMR linewidth Delta H-pp below a certain temperat ure. The temperature at which an upturn occurs in Delta H-pp(T) shifts to lower temperatures as the Fe concentration is decreased, indicatin g that the re-entrant behaviour is progressively suppressed with incre asing x.