Effect of isothermal annealing on the magnetic behavior of amorphous ferromagnets with composition near the percolation threshold. II. In the critical region

摘要

Extensive ferromagnetic resonance (bulk magnetization) measurements have been performed on amorphous Fe90+XZr10minus;Xalloys withX=0 and 1 (X=0, 1, and 2) in the critical region, minus;0.1lsim;(Tminus;TC)/TClsim;0.1, before and after they had been subjected to isothermal annealing treatment at 400 K for durations of time,tA, ranging from 10 to 240 min (in the lsquo;lsquo;ashyphen;quenchedrsquo;rsquo; condition) with a view to study the alterations in the critical behavior as the tricritical point,Xcbartil;3, is approached along the ferromagnetic (FM)hyphen;paramagnetic (PM) transition line in the magnetic phase diagram and as the topological (TSRO) as well as chemical (CSRO) shorthyphen;range order undergo changes on account of structural relaxation. Asymptotic values of the critical exponents bgr; and ggr; and critical amplitudesm0and (m0/h0) for spontaneous magnetization and initial susceptibility have been determined for the ashyphen;quenched as well as annealed samples. Consistent with the predictions of theinfiniteFM matrix plusfinitespin clusters model and with the wellhyphen;known Harris criterion, change in CSRO and TSRO caused by altering the alloy composition and/or by isothermal annealing leaves the values of the critical exponents bgr; and ggr;, and the universal ratiom0/MS(0) unaltered from those predicted by the renormalization group theory for anorderedspin system with spatial as well as spin dimensionality ofthree. The presently determined values of the critical amplitudes reveal that the fraction of spins that actually participates in the FMhyphen;PM transition is as low as ape;10percnt; and reduces drastically asXrarr;Xcbut for a given composition, it declines slowly with increasingtA.