Inhibition of Nd magnetic order in NdFe1-xCoxO3 (x ≤ 0.5)

The low-temperature specific heat of the NdFe1-x,CoxO3 (x = 0, 0.03, 0.1, 0.25, and 0.5) solid solutions has been measured in order to study the magnetic ordering of the Nd sublattice, as a function of the Co content. The experimental results show the inhibition of the Nd magnetic ordering for x >= 0.1. Bertaut's theory of spin configurations for ionic structures is used to propose a simple mean-field model which is able to explain the main features of the low-temperature heat capacity of NdFe1-xCoxO3 for x = 0, 0.03 and 0.1 in terms of the ratio between the Nd-Nd and Fe-Nd interactions. In order to properly explain the specific heat curves we find satisfactory to include a distribution of internal fields acting on the Nd3+ ions. Indeed, low-spin Co ions in NdFe1-xCoxO3 are equivalent to magnetic vacancies and the Nd atoms are polarized additionally by an internal field caused, by the Fe-Nd isotropic interaction between the non compensated Fe moments and the Nd. (c) 2005 Elsevier SAS. All rights, reserved.