Negative Thermal Expansion And Itinerant Ferromagnetism In Mn1.4fe3.6si3

We report the thermal expansion, critical behavior, magnetocaloric effect (MCE), and magnetoresistance (MR) on the polycrystalline Mn1:4Fe3:6Si3 compound around the ferromagnetic transition. A large negative volume thermal expansion (alpha(V) similar to -20 x 10(-6) K-1) is observed across the transition temperature with a strong anisotropic variation of lattice parameters in the ab-plane. The anisotropic magnetoelasticity arises from the competition between magnetic ordering and structural deformation that could be responsible for the large MCE (Delta S-m similar or equal to -6 J/Kg K) across the magnetic transition in this compound. The large and negative MR (similar to-3% in 80 kOe) is also observed at the transition temperature which can be attributed to the suppression of spin disorder. Furthermore, the Rhodes-Wolfarth ratio (RWR > 1) and identical field dependence of MR and MCE isotherms indicate the itinerant character of the 3d electrons. The critical exponents determined from the analysis of magnetization and MCE are consistent with the quasi-two-dimensional (2D) Ising model with long range exchange interactions that decays as J(r) similar to r(similar to 3:41). This unconventional quasi-2D Ising character with long-range interactions can be ascribed to strong ab-plane anisotropy and the delocalized 3d electrons in the studied compound. Published under an exclusive license by AIP Publishing.