Crystallographic and magnetic properties of iron sulfides doped with 3d-transition metals Original Research Article

It is found by Mössbauer measurements on M0.025Fe0.975S (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) that the 3d-transition metal impurities profoundly affect both the crystallographic and spin-rotation transitions of iron sulfide. It is noteworthy that both V0.025Fe0.975S and Co0.025Fe0.975S have Morin transition temperatures TM which are distinctly different from that of FeS. Furthermore, the directions of changes of TM are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. A vanadium impurity of 2.5% of the metal atoms in the iron sulfide makes the crystallographic transition to take place rapidly in a narrow temperature region of about 15 K, while the α transition in FeS takes place over a wide temperature range of about 200 K. It is also found that the α transition for V0.025Fe0.975S has a hysteresis width of 5 K. It is very interesting that the crystallographic transition is independent of the lattice parameters while the spin-rotation transition is dependent on them. The purpose of this research is to report the effect of 3d-transition metal on the α and Morin (spin-flip) transitions as well as on the superexchange interactions in iron sulfides.