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Square lattice antiferromagnets (NO)M(NO3)3 (M = Co, Ni): Effects of anisotropy
Two novel transition metal nitrates (NO)M(NO3)3 (M = Co, Ni) have been characterized in thermodynamic measurements. The structure of these compounds provides a unique opportunity for accommodation of Jahn – Teller cation with odd number of electrons Co2+ (3d7), and non – Jahn - Teller one with even number of electrons Ni2+ (3d8), in similar crystallographic position. Both compounds order antiferromagnetically at TNCo = 12.8 K and TNNi = 23.8 K. The single ion anisotropies of Co2+ D = 7.2 K and Ni2+ D = 2 K ensure qualitatively different behavior under external magnetic field. The cobalt nitrate demonstrates sharp metamagnetic transition at BM = 2.2 T while the nickel nitrate evidences smooth deflection at spin-flop transition BSF ∼ 6 T. To gain microscopic understanding of the magnetic properties of (NO)M(NO3)3 the first principles density functional theory calculations have been performed.