Low Temperature Specific Heat of Amorphous (Co_<1-x>Mn_x)_<100-y>B_y Alloys

概要

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The low temperature specific heat (C_p) for the (Co_<1-x>Mn_x)_<100-y>B_y amorphous alloy series has been studied in the temperature range between 0.4 and 50K using a pumped ^3He-cryostat. Below about 10K, C_p for all the present samples can be well fitted to the ordinary expression C_p=γT+βT^3. The linearly temperature-dependent coefficient γ depends strongly on Mn concentration, that is, with increasing Mn concentration, γ values remarkably increase, for example γ of Co_<76>B_<24> is 5.9mJmol^<-1>K^<-2>, while that of (Co_<0.6>Mn_<0.4>)_<76>B_<24> is 15.6mJmol^<-1>K^<-2>. This rather large γ value cannot be explained only by the electronic term and must be attributed to the large magnetic contribution presumably due to the frustration in the spin system. The large γ values also have been obtained in the other amorphous spin glass alloys such as Fe-Ni-P-B, Fe-Zr and Co-Y. On the other hand, Mn concentration dependence of Debye temperature has a discontinuity at certain Mn concentration which corresponds to the same Co/Mn ratio at which the martensitic phase change occurs in the crystalline Co-Mn alloy. This discontinuity reflects a change in phonon behavior which must arise from substantial differences in the amorphous microstructure.
1989-03-20