Both spin-liquid and magnetically ordered phases of both half-integer and integer low-spin quantum magnets are of interest, since the magnetic structures found in the latter case usually have no classical counterparts. Such a magnetic structure was found in a combined experimental and theoretical study of the integer spin system $\mathrm{Ni}{(\mathrm{NO}}_3{)}_2$. Our thermodynamic measurements have revealed a magnetically ordered phase with small spontaneous magnetization at $T_{\mathrm{C}} = 5.5\mathrm{K}$. The magnetization saturation of about $2{\mu }_{\mathrm{B}}$ at low temperatures corresponds to the high-spin state ($S = 1$) of ${\mathrm{Ni}}^{2+}$ ions evidenced in $L_{2,3}$ edges in x-ray absorption spectroscopy spectra. We show that a consistent description of the available data is possible within a noncollinear umbrella-type ferrimagnetic ground state model for which both intra- and interlayer magnetic interactions should be antiferromagnetic. Such a scenario is suggested by the first-principles and model calculations.

• Received 26 January 2014
• Revised 16 August 2014

DOI:https://doi.org/10.1103/PhysRevB.90.134407