Magnetic behavior of manganese bromide hydrates including deuteration effects

• The magnetic properties of Mn(II) bromide dihydrate and monohydrate are studied.
• The effects of replacing H2O by D2O are examined for both hydration states.
• For monohydrate the change in magnetic behavior on deuteration is small.
• For dihydrate the change in magnetic behavior on deuteration is large.
• The unit cell of MnBr2·2D2O is different from and slightly larger than for MnBr2·2H2O.

The magnetic properties of previously unexamined MnBr2·2H2O, MnBr2·H2O, MnBr2·2D2O and MnBr2·D2O are studied. Curie–Weiss fits to high temperature data yield θ of −13.1, −3.9, −8.2 and −5.0 K, respectively, in χM=C/(T−θ). The net antiferromagnetic exchange yields susceptibility maxima at 6.34, 3.20, 2.10, and 3.40 K, with χmax 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 Tc/Tmax 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 MnBr2·2D2O. The results are analyzed from various perspectives. A different monoclinic unit cell is determined for MnBr2·2D2O than for MnBr2·2H2O, with 1.3% larger volume, providing some rationale for the difference in magnetic properties.