ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The trihydrate of nickelous bromide, NiBr2⋅3H2O, is examined magnetically for the first time. A Curie–Weiss fit, χM=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 Tc=3.82±0.05 K, somewhat below a maximum in χ(T) at T(χmax)=6.17±0.10 K, with χmax=0.0900±0.0005 emu/mol. The ratio Tc/T(χmax)=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 Hˆex=−2J∑i(approximately-greater-than)jSˆi⋅Sˆj), and a correction for interlayer exchange z′J′/k=−0.99±0.02 K. Well above Tc the susceptibility is analyzed assuming axial and rhombic crystal field distortions, i.e., D[Sˆ2z−S(S+1)/3] and E[Sˆ2x−Sˆ2y] 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 Tc. 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. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.361651
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