We have investigated the magnetization behavior as a function of field and temperature for amorphous Fe90-xMnxZr10 alloys prepared by a single-roll melt-spinning technique. The temperature dependence of magnetization for these alloys shows the existence of antiferromagnetic couplings between Fe atoms in low fields. The magnetic parameters, obtained from the low temperature magnetization data, are consistent with the presence of mixed magnetic state. With an increase of the concentration of Mn, the Curie temperature decreases almost linearly and then the reentrant behavior is observed in all the samples. The percentage deviation of the fit from the data closely reveals that the combination of both spin wave and single-particle excitations describes the thermal demagnetization process quite well in these ferromagnetic alloys. © 2002 Elsevier Science B.V. All rights reserved.