Magneto-optical study of the magnetic phase diagram of the dilute metamagnet Fe_pMg_1-pCl₂

Abstract

The mixed phase region of the magnetic phase diagram of FepMg1-pCl2 (p=1.00-0.71) has been mapped by a direct optical method. The tricritical temperature falls with increasing dilution by magnesium and is extrapolated to zero at p approximately 0.6, close to the percolation limit for a plane triangular lattice rather than the three-dimensional analogue, despite the essential three-dimensional nature of the metamagnetic transition. In contrast, the tricritical field tends to a finite value as p decreases.