Low-temperature magnetic transitions in Fe2MnSi Heusler alloys prepared in bulk and ribbon form

Microstructural and magnetic properties of the Fe₂MnSi Heusler alloys in the bulk and ribbon form have been investigated from a viewpoint of technology of their production. The bulk alloys were prepared by arc and induction melting while for the ribbon-type samples the planar flow casting technology was used. X-ray diffraction has confirmed a presence of the L2₁ cubic phase in both polished 500 µm thick discs cut from a button and cylinder type ingots of the same chemical composition and in the 20 μm thick and 2 mm wide ribbon. Values of lattice parameters (0.560–0.571 nm) obtained for discs and both ribbon sides were almost independent on technology, which, on the other hand, has markedly influenced the microstructure yielding the large size of grains and grain boundaries in the disc samples in comparison to about two orders of magnitude smaller grains in the ribbon sample. From the magnetic viewpoint all alloys were paramagnetic at a room temperature contrary to their magnetic behaviour at low temperatures. The slight excess of Mn at the expense of Fe in the chemical composition of the ribbon sample detected by the energy dispersive X-ray spectroscopy has contributed to a marked positive shift of the Curie temperature (T_c ≈ 270 K and 215–230 K for ribbon and bulk samples, respectively). The second magnetic transition of a magnetic moment re-orientation observed at about 69 K was similar for all kinds of samples.