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 Neel temperature (T-N). The spin reorientation temperature (T-SR) 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 alpha(T) show remarkable anomalies at T-SR and the magnetic ordering temperature (T-N). T-SR is associated with a shoulder in the linear thermal expansion and near T-N we observe invar-type of behaviour. Both effects are enhanced for the Co substituted sample, giving clear evidence for the enhanced exchange interactions. (C) 2011 Published by Elsevier Ltd.