Antiferromagnetism of Ni(SCN)2

Abstract

The magnetic behavior of Ni(SCN)2 has been studied at low temperatures for the first time. A Curie–Weiss fit, χM=C/(T−θ), to the susceptibility between 100 and 300 K yields g=2.13±0.01 (S=1) and θ=39.8±1.4 K. Systematic curvature in χ−1 vs T is evident, however. Despite the large positive θ Ni(SCN)2 appears to order antiferromagnetically at Tc=52±1 K, slightly below a maximum in χ(T) at T(χmax)=57.2±0.5 K, with χmax=0.0331±0.0003 emu/mol. The ratio Tc/T(χmax)=0.91±0.02 does not suggest lower magnetic dimensionality. Magnetization isotherms are linear to 16 kG; some features suggesting lower temperature transitions occur. Well above Tc the susceptibility is analyzed assuming axial and rhombic crystal field distortions, i.e., D[Ŝz2−S(S+1)/3] and E[Ŝx2−Ŝy2] spin Hamiltonian terms, with exchange incorporated in a mean field approximation. An extraordinarily large ‖D/k‖≊119 K seems to emerge, a result which is very provisional lacking single crystal data. A mean field analysis of Tc and θ yields ferromagnetic intrachain exchange J1/k=8.6±0.5 K and antiferromagnetic interchain exchange J2/k=−0.76±0.4 K. It seems more likely that D is negative, but even if it is positive the exchange interaction is large enough to induce magnetic order at finite Tc in light of theories relating Tc, J, and D.