Influence of Co substitution on magnetic properties and thermal expansion of Nd6Fe13Si intermetallic compound

We studied the effect of Co substitution in Nd6Fe13−xCoxSi (x = 0, 1) intermetallic compounds on the crystalline structure, magnetic properties and thermal expansion. The partial Co substitution reduces the lattice parameters of the tetragonal Nd6Fe13Si structure which enhance (3d–3d) exchange interaction and this causes an increase of the Néel temperature (TN). The spin reorientation temperature (TSR) of Nd6Fe12CoSi occurs at a higher temperature with respect to that of the Nd6Fe13Si compound. Both the linear thermal expansion and the linear thermal expansion coefficient α(T) show remarkable anomalies at TSR and the magnetic ordering temperature (TN). TSR is associated with a shoulder in the linear thermal expansion and near TN we observe invar-type of behaviour. Both effects are enhanced for the Co substituted sample, giving clear evidence for the enhanced exchange interactions.