© Published under licence by IOP Publishing Ltd. The magnetic properties of two Heusler compounds Fe1.3Mn1.7Si and Fe1.4Mn1.6Si are compared. Fe1.4Mn1.6Si exhibits a ferromagnetic transition at TC∼ 117 K and another transition to a phase with antiferromagnetic components at TA∼ 66 K, which is the same as the behavior of Fe2MnSi. Further, it is known that for Fe3-xMnxSi, with increasing x, TCdecreases but TAremains almost constant, and they appear to meet around x ∼1.7. The careful measurements of magnetization at various magnetic fields reveal that Fe1.3Mn1.7Si has three transitions at low fields; for instance, at 0.01 T, the transition temperatures are found to be 85 K, 67 K, and 60 K. The lowest transition at 60 K is characterized by a rapid decrease in magnetization with decreasing temperature and significant magnetic field dependence, in contrast to the transition at TA, which is relatively independent of the magnetic field, for x = 1 and 1.6. The critical field at 0 K is ∼3 T. The transition at the lowest temperature was not found for x ≤ 1.6, and it is considered a different transition from that at TA. While the transition at the highest temperature 85 K is a ferromagnetic transition, the transition at 67 K has the characteristics of the transition at TA, and it is found to be insensitive to magnetic fields. They are revealed to be the same transitions as those at TCand TAfor x ≤ 1.6.