Mössbauer study of magnetically ordered states in Heusler compounds Fe₃₋ₓMnₓSi

It has been known that the Heusler compound Fe ₃₋ₓ Mn ₓ Si has a complex magnetic phase diagram. For 0.75 ≤ x ≤ 1.75, it exhibits a ferromagnetic transition at TC , and at a lower temperature TA , another transition to a phase with both ferromagnetic and antiferromagnetic components. Recently, however, magnetization and specific heat measurements revealed that for $$x=$$ 1.7, yet another transition occurs at a temperature lower than TA , i.e., there are three transitions at zero magnetic field. In our previous study, the nature of the ordered phases and transitions for $$x =$$ 1.7 and 1.68 were investigated using Mössbauer spectroscopy, and the existence of a hyperfine field Bₕf was confirmed. This demonstrates that the low temperature phases are magnetically ordered phases. In this study, to further investigate the ordered phases and transitions in Fe ₃₋ₓ Mn ₓ Si, we measure Mössbauer spectra for x = 1.8 and 1.9, where only a single antiferromagnetic transition appears to exist as judged from magnetization measurements, and the transition temperature is defined as TA2' . The spectra show that Bₕf is present for $$x=$$ 1.8 and 1.9 at low temperatures, and the values of Bₕf are comparable with that for x = 1.7. With increasing temperature T, Bₕf decreases smoothly, and at T>TA2' the spectrum becomes a singlet and Bₕf is zero. These results confirm the existence of magnetic order for x = 1.8 and 1.9.