FERROMAGNETISM OF NI(SCN)2(C2H5OH)2

The magnetic properties of Ni(SCN)2(C2H5OH)2 have been studied, the first Ni(II) system in the general family of compounds M(SCN)2(ROH)2 (where M = divalent Mn, Fe, Co, or Ni and R = CH3, C2H5, i- or n-C3H7) to be examined at low temperatures. In contrast to previously studied Mn(II) and Co(II) members of this family, which exhibit predominant antiferromagnetism, the present compound is ferromagnetic. The susceptibility of a polycrystalline sample is of Curie-Weiss from only above 75 K, with gBAR = 2.17(5) +/- 0.01 and S = 1 and with theta = 24.1 +/- 1.0 K. The initial susceptibility is well accounted for by an asymptotic critical law, chi-0 = GAMMA[T/T(c) - 1]-gamma, in the reduced temperature range 0.147-0.013, with T(c) = 13.08(1) +/- 0.01 K, gamma = 1.35(4) +/- 0.02, and GAMMA = 0.092(5) +/- 0.003 emu/mol. The gamma value is between 3D-XY and 3D-Heisenberg model predictions. The susceptibility in the paramagnetic regime well above T(c) is analyzed including the effects of axial and rhombic crystal field distortions, represented by D[S triple-over-dot z2 - S(S + 1)/3] and E[S triple-over-dot x2 - S triple-over-dot y2] terms in the spin Hamiltonian, and incorporating exchange interactions in a mean-field approximation. An excellent fit is obtained with g = 2.175, D/k = -64.3 +/- 5 K, E/k = 23.1 +/- 4 K, and zJ/k = 19.4 +/- 1 K. The magnitude of D is the largest we know of in a Ni(II) compound. The three spin states of the 3A crystal field ground term are strongly split, probably contributing to the relatively low value of T(c) compared to zJ/K. Some two-dimensional character in the exchange, as has been found for other members of this family of compounds, may also contribute.