Iron spin orientation in a competing anisotropy system: Fe1-xCoxCl2

Publisher Website
Google Scholar
Abstract
The competing anisotropy system Fe1-xCoxCl2 has been studied using 57Fe Mossbauer spectroscopy. Spectra have been measured at 4.2K for single crystals across the composition range 0ex of a molecular exchange field, and have used these calculations to deduce the variation of theta ex with composition x from the Mossbauer data. At 4.2K, the phase boundaries on either side of the mixed phase region are clear. Of these boundaries, one corresponds to the ordering of a three-dimensional (3D) XY system in a random field, the other to that of a 3D Ising system in a random field. The latter boundary is not sharp, suggesting that the 3D Ising system in a random field does not undergo a true phase transition to long-range order. In the phase where the spin components perpendicular to the c axis (Sperpendicular to ) alone are ordered, a non-zero value of the spin component parallel to the c axis (S/sub ///) is observed. The authors argue that the coupling mechanism between S/sub /// and Sperpendicular to that are responsible for the generation of the non-zero local values of S/sub ///, also produce the random fields that broaden the phase transition to the mixed phase.