Mn²⁺EPR study of the phase transition in langbeinite Cd₂(NH₄)₂(SO₄)₃

Abstract

The phase transition in the langbeinite Cd2(NH4)2(SO4)3 has been studied via the EPR of Mn2+. The phase transition temperature has been determined to be Tc=94.5+or-0.5K. The spin-Hamiltonian parameters have been computed using a rigorous least-squares fitting procedure, numerically diagonalising the spin Hamiltonian and simultaneously fitting a large number of EPR line positions obtained for several orientations of the external magnetic field on a digital computer. It is suggested that the phase transition below Tc is due to the freezing of (SO4)2- rotations.