ANTIFERROMAGNETISM OF NI(SCN)2

The magnetic behavior of Ni(SCN)2 has been studied at low temperatures for the first time. A Curie-Weiss fit, chi(M)=C/(T-theta), to the sus ceptibility between 100 and 300 K yields g = 2.13 +/- 0.01 (S = 1) and theta = 39.8 +/- 1.4 K. Systematic curvature in chi-1 vs T is evident , however. Despite the large positive theta Ni (SCN) 2 appears to orde r antiferromagnetically at T(c) = 52 +/- 1 K, slightly below a maximum in chi(T) at T(chi(max)) = 57.2 +/- 0.5 K, with chi(max) = 0.0331 +/- 0.0003 emu/mol. The ratio T(c)/T(chi(max)) = 0.91 +/- 0.02 does not s uggest lower magnetic dimensionality. Magnetization isotherms are line ar to 16 kG; some features suggesting lower temperature transitions oc cur. Well above T(c) the susceptibility is analyzed assuming axial and rhombic crystal field distortions, i.e., D[S(z)2-S(S + 1)/3] and E[S( x)2-S(y)2] spin Hamiltonian terms, with exchange incorporated in a mea n field approximation. An extraordinarily large \D/k\ almost-equal-to 1 19 K seems to emerge, a result which is very provisional lacking sin gle crystal data. A mean field analysis of T(c) and theta yields ferro magnetic intrachain exchange J1/k = 8.6 +/- 0.5 K and antiferromagneti c interchain exchange J2/k = - 0.76 +/- 0.4 K. It seems more likely th at D is negative, but even if it is positive the exchange interaction is large enough to induce magnetic order at finite T(c) in light of th eories relating T(c) J, and D.