Magnetic behavior of manganese bromide hydrates including deuteration effects

Abstract The magnetic properties of previously unexamined MnBr 2 ·2H 2 O, MnBr 2 ·H 2 O, MnBr 2 ·2D 2 O and MnBr 2 ·D 2 O are studied. Curie–Weiss fits to high temperature data yield θ of −13.1, −3.9, −8.2 and −5.0 K, respectively, in χ M = C /( T − θ ). The net antiferromagnetic exchange yields susceptibility maxima at 6.34, 3.20, 2.10, and 3.40 K, with χ max of 0.197, 0.357, 0.465 and 0.348 emu/mol, respectively. Noteworthy is the contrast between dideuterate and dihydrate, the largest deuteration effect observed for hydrated transition metal halides. Antiferromagnetic ordering is estimated to occur at 5.91, 2.65, 2.00 and 2.50 K, respectively. The ratio T c / T max is 0.93, 0.83, 0.95 and 0.74 in the same order, implying low dimensional magnetism for monohydrate and monodeuterate. Heisenberg model fits to susceptibilities yield primary and secondary exchange interactions. Magnetization data at moderate fields and different temperatures are presented for each substance, and high field data to 70 kG at 2.00 K. Spin-flop transitions are estimated to occur at 45, 33 and 30 kG, respectively, for dihydrate, monohydrate and monodeuterate, but are not observable for MnBr 2 ·2D 2 O. The results are analyzed from various perspectives. A different monoclinic unit cell is determined for MnBr 2 ·2D 2 O than for MnBr 2 ·2H 2 O, with 1.3% larger volume, providing some rationale for the difference in magnetic properties.