FERROMAGNETIC-RESONANCE EVIDENCE FOR LONG-RANGE FERROMAGNETIC ORDERING IN AMORPHOUS FE-RICH FE100-XZRX ALLOYS

Ferromagnetic resonance (FMR) measurements have been performed on amorphous (a-) Fe100-xZrx alloys with x = 9 and 10 and on a-Co90Zr10 for horizontal-perpendicular, horizontal-parallel and vertical-parallel sample geometries at a fixed microwave frequency of about 9.3 GHz in the temperature range 77 to 500 K. In the horizontal-parallel (parallel-to h) and vertical-parallel (parallel-to v) orientations, the peak-to-peak FMR linewidth (DELTA-H(pp)) remains constant at a value of about 210 Oe (290 Oe) for Fe90Zr10(Fe91Zr9) in the temperature range 115 K less-than-or-equal-to T less-than-or-similar-to 0.8T(C) (Curie temperature), while the resonance field (H(res)) as a function of temperature increases slowly up to 0.8T(C) and for T > 0.8T(C) both DELTA-H(pp) and H(res) start increasing at a rapid rate. Values of the 'in-plane' uniaxial anisotropy field, H(k), and Gilbert damping parameter, lambda, at different temperatures T less-than-or-similar-to T(C) determined from the observed values of H(res)parallel-to v, H(res)parallel-to h and DELTA-H(pp)parallel-to v, DELTA-H(pp)parallel-to demonstrate that H(k) and lambda both scale with saturation magnetization, M(s). The temperature dependence of M(s) deduced from the FMR results conforms very well with that previously observed by us for the bulk magnetization. At T greater-than-or-similar-to T(C), a secondary resonance, whose width goes through a minimum while the resonance field increases as the temperature is increased from T congruent-to T(C) to 500 K and for which H(k) = 0. appears at low fields for the alloys with x = 9 and 10. The FMR data taken in the perpendicular geometry are consistent with those obtained for parallel-to h and parallel-to v configurations. By contrast, regardless of the sample geometry used, DELTA-H(pp) remains constant whereas H(res) exhibits a very weak dependence on temperature in the investigated temperature range (77 less-than-or-equal-to T less-than-or-equal-to 500 K) for a-Co90Zr10. The present results have been discussed in light of the existing theories.