Low-temperature specific heat study of amorphous Fe1-xBxalloys

Abstract

The low-temperature specific heats of amorphous Fe_1-xB_x alloys (x = 0.14, 0.16, 0.18 and 0.20) have been measured over the temperature range 1.5-6K. The results are well represented by the equation C = gammaT + alphaT³ + sigmaT^3/2 and the electronic specific heat coefficient gamma , Debye temperature Theta_D and spin-wave stiffness constant D are determined. Both gamma and Theta_D values are found to decrease rapidly with increasing B concentration. The largest gamma value is twice as large as that for the pure BCC Fe. The value of Theta_D is also very high, compared with the other metal-metalloid amorphous alloys. Such high values are attributed to the existence of the covalent bond between Fe and B atoms. The present results are also discussed from the point of view of Invar characteristics particularly in comparison with a typical Invar Fe_0.65Ni_0.35 alloy. The large gamma and low D values are observed in both alloy systems, while the high Theta_D in amorphous Fe-B alloys is in sharp contrast with the lattice softening phenomena in Fe-Ni alloy, which is believed to be one of the characteristic features of an Invar alloy.