μSR and Mossbauer studies of transverse spin freezing

Partially frustrated ferromagnets exhibit two magnetic transitions. T,, marks the ordering of transverse spin degrees of freedom in the plane perpendicular to the axis defined by ferromagnetic order established at T(c) Zero-field muon spin relaxation (ZF-muSR) is sensitive both to the increase in static order that occurs at T,, as the transverse spin components order, and also to the fluctuations associated with that ordering. The dynamic and static signatures coincide, confirming all of the features expected to be associated with the transition. We have used ZF-muSR to establish detailed phase diagrams for two bond-frustrated systems: a-Fe(x)Zr(100-x) and a-Fe(90-x)Ru(x)Zr(10), and a-(Fe(100-x)Mn(x))(78)Si(8)B(14), a site-frustrated system. In addition, we have used selective excitation double Mossbauer (SEDM) spectroscopy to probe the dynamics at T(xy) and confirm that ZF-muSR yields the same values, both for T(xy), and, more significantly, for the fluctuation rates. (C) 2002 Elsevier Science B.V. All rights reserved.