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

摘要

Results of detailed ferromagnetic resonance measurements taken on amorphous (ahyphen;) Fe90+XZr10minus;Xalloys withX=0 and 1 in the horizontalhyphen;parallel and verticalhyphen;parallel sample configurations at a fixed microwave frequency of bartil;9.23 GHz in the temperature range 77 to 300 K before and after these alloys have undergone isothermal annealing treatment at 400 K for durations of time,tA, ranging from 10 to 240 min are presented and discussed. While only a single (primary) resonance is observed forTlsim;TC(the Curie temperature), an additional (secondary) resonance first appears atTbartil;TCand then gets fully resolved forTgsim;(TC+10 K). For the primary resonance (i) the lsquo;lsquo;inhyphen;planersquo;rsquo; uniaxial anisotropy field,Hk, and the Gilbert damping parameter, lgr;, bothscalewith the saturation magnetization,MS, in the temperature ranges 77 Kle;Tlsim;TCand 0.5TClsim;Tlsim;0.8TC, respectively, at alltAincludingtA=0; (ii) isothermal annealing has essentially no effect onMS(T), the lsquo;lsquo;peakhyphen;tohyphen;peakrsquo;rsquo; linewidth, Dgr;Hpp(T), Dgr;H0(the frequencyhyphen; and temperaturehyphen;independent contribution to Dgr;Hpp) and lgr;(T); (iii) withincreasingFe concentration, the value corresponding to the peak in lgr;(T)decreases, lgr;(0.5TC)increaseswhile lgr;(300 K) stays constant at 1times;108sminus;1, and (iv) isothermal annealing up to a time duration of 30 min results in an enhancement of about 1.5percnt; inTCand a reduction of nearly 40percnt; in thecharacteristictemperatureT0(which is a measure of the rehyphen;entrant transition temperature) whereas no further change occurs in bothTCandT0at higher annealing times.By contrast, for the secondary resonance, (a)Hkbartil;0 at all temperaturesTgsim;TCand values oftAcovered in the present experiments, (b) isothermal annealing leaves the resonance field unaltered, and (c) a steep decline in the value of Dgr;Hpprsquo;occurs fortAle;10 min but at higher values oftA, Dgr;Hpprsquo;remains constant forahyphen;Fe90Zr10whereas it increases at first and then saturates in the case ofahyphen;Fe91Zr9. The effect of isothermal annealing on the quantities of interest, i.e.,TC,T0, Dgr;Hpp, etc., can be qualitatively understood in terms of afinitespin clusters plus aninfiniteferromagnetic matrix model.