Magnetic and crystallographic properties of the mixed system (FeF3)1-x (KMnF3)x

The mixed system (FeF₃)_1-x (KMnF₃)_x with 0 ≤ x ≤ 1 has been prepared and investigated. The compounds with 0.19 ≤ x ≤ 0.22 are single phase hexagonal while the materials with 0.40 ≤ x ≤ 0.55 are single phase tetragonal. The powder samples are all light colored and at low temperatures become antiferromagnetic (with weak ferromagnetic moments.) The Néel temperatures are 111°K for the hexagonal compound with x = 0.20, and 160°K and 133°K for the tetragonal materials with x = 0.40 and 0.55, respectively. The reasons for the low ordering temperatures are examined using the generalized molecular field theory.