Magnetic and resonance properties of the two-dimensional $S=1$ compound $Ni5(TeO3)4Cl2$ with frustrated geometry

The magnetic and magnetoresonance properties of a new single-crystal compound $Ni5(TeO3)4Cl2$ are studied. Measurements of the magnetization and magnetic susceptibility of the crystal in a wide temperature range $(5–300K)$ make it possible to conclude that $Ni5(TeO3)4Cl2$ is a quasi-two-dimensional antiferromagnet with the easy magnetization axis $a*$ directed perpendicular to the crystallographic plane $bc$ and a magnetic ordering temperature $TN≈21K$⁠. Resonance measurements at $4.2K$ in wide range of frequencies $(25–105GHz)$ and magnetic field (up to $200kOe$⁠) permit us to obtain the frequency-field dependence of the AFMR spectrum for a field applied along the easy magnetization axis $a*$⁠. It is shown that a magnetic field directed along the antiferromagnetic axis $(H∥a*)$ induces a magnetic phase transition of the spin-flop type, which is found to occur at $Hsf≈120kOe$⁠. The magnetic resonance experimental data are described qualitatively in the model of a biaxial antiferromagnet.