NiBr₂⋅3H₂O, a lower dimensional antiferromagnet Available to Purchase

The trihydrate of nickelous bromide, NiBr₂⋅3H₂O, is examined magnetically for the first time. A Curie–Weiss fit, χ_M=C/(T−θ), to the susceptibility between 70 and 300 K yields g=2.31±0.01 (S=1) and θ=6.6±0.5 K. Systematic curvature in χ⁻¹ vs T is evident below 70 K. Despite the positive θ, NiBr₂⋅3H₂O appears to order antiferromagnetically at T_c=3.82±0.05 K, somewhat below a maximum in χ(T) at T(χ_max)=6.17±0.10 K, with χ_max=0.0900±0.0005 emu/mol. The ratio T_c/T(χ_max)=0.62±0.01 suggests lower magnetic dimensionality. Between 4 and 12 K an acceptable fit with a two‐dimensional Heisenberg model can be made, with g=2.58±0.01, J/k=−1.36±0.02 K (assuming Ĥ_ex=−2J∑_i≳jŜ_i⋅Ŝ_j), and a correction for interlayer exchange z′J′/k=−0.99±0.02 K. Well above T_c the susceptibility is analyzed assuming axial and rhombic crystal field distortions, i.e., D[Ŝ²_z−S(S+1)/3] and E[Ŝ²_x−Ŝ²_y] spin Hamiltonian terms, with exchange included in a mean field approximation: g=2.33±0.02, D/k=57.3±5.0 K, E/k=−24.9±3.0 K, and zJ/k=5.28±0.20 K. The parameters are provisional lacking single‐crystal data, but the zero‐field splitting is clearly quite large. Magnetization versus field isotherms depart only slightly from linearity for fields above 10 kG, and show a small hysteresis, even for temperatures above T_c. It is likely that ferromagnetically coupled NiBr₂NiBr₂Ni... chains are present, and that there are antiferromagnetic interactions between chains, such that strongly coupled layers occur, with weaker interactions between layers.