Abstract The magnetic properties of amorphous Fe90-xMnxZr10 (X = 0, 4, 6, 10, 15) alloys prepared by the drum spinning technique are reported. The dependence of the average magnetic moment per atom μ and Curie temperature Tc on Mn content and the behaviour of the quasi-spin glass in these amorphous alloys are discussed. The magnetic phase diagram of amorphous FeMnZr alloys has been obtained. It is observed that the thermomagnetic curves show a irreversible variance in crystallized Fe84Mn6Zr10 alloy. This phenomenon may be originated from the α→γ phase and γ→α phase transformations at high and low temperatures, respectively.