A detailed ‘‘zero‐field’’ Mo¨ssbauer and ferromagnetic resonance (FMR) study of a‐Fe90−xCoxZr10alloys with 0≤x≤10 reveals that (i) alloys withx≤2 exhibit at low temperatures properties that are reminiscent of reentrant spin glass behavior (ii) for such alloys, the hyperfine field distributionP(H) isbimodaland comprises two Gaussian distributions and the peak‐to‐peak FMR linewidth, &Dgr;Hpp, diverges exponentially forT<TC(iii) forx≥4, the low‐field Gaussian component inP(H) and the divergence in &Dgr;Hppat low temperatures both get completely suppressed. These observations imply that the reentrant behavior gets progressively suppressed with partial replacement of Fe with Co. All the diverse aspects of the present results have been interpreted in terms of the ferromagnetic matrix plus finite spin clusters model.