Amorphous (a-) Fe90-xCoxSc10 alloys have been produced by rapid quenching from the melt. The Curie temperature, TC, was determined using both mean field theory and Landau's theory of second-order phase transitions in zero and non-zero external fields. The dependence of TC on the atomic spacing can be explained by the empirical Bethe-Slater curve. The value of TC of a- Fe5Co85Sc10, determined by the above theoretical approaches is 1150 K, which is the highest TC ever measured for amorphous alloys. The flattening of the measured normalized magnetization, M(T)/M(0), as a function of the reduced temperature, T/TC, is explained within the framework of the Handrich- Kobe model. According to this model the fluctuation of the exchange integral is the main reason for the flattening of M(T)/M(0). In the case of a-Fe90Sc10 without Co, however, the fluctuation of the exchange integral is dominant only at zero external field, Bex = 0. At Bex = 9 T, however, the fluctuation of the exchange integral has no conspicuous effect on the reduction of the magnetization. It is shown that at Bex = 9 T the frozen magnetic clusters control the behaviour of the reduced magnetization as function of T/TC. In contrast to other ferromagnetic alloys, where the flattening of M(T)/M(0) is characteristic for an amorphous structure, the a- Fe5Co85Sc10 does not exhibit any trace of the fluctuation of the exchange integral.