Magnetic and neutron spectroscopic properties of the tetrameric nickel compound $[M{o}_{12}{O}_{28}(\hat{I}{¼}_2-OH{)}_9(\hat{I}{¼}_3-OH{)}_3{Ni(H_{2}O{)}_3}_4]$\cdot$13H_{2}O$

Abstract

We present results of inelastic neutron scattering experiments performed for the compound Magnetic and neutron spectroscopic properties of the tetrameric nickel compound $[M{o}_{12}{O}_{28}(\hat{I}{¼}_2-OH{)}_9(\hat{I}{¼}_3-OH{)}_3{Ni(H_{2}O{)}_3}_4]$\cdot$13H_{2}O$, which is a molecular magnet with antiferromagnetically coupled Ni2+ ions forming nearly ideal tetrahedra in a diamagnetic molybdate matrix. The neutron spectroscopic data are analyzed together with high-field magnetization data (taken from the literature) which exhibit four steps at non-equidistant field intervals. The experimental data can be excellently described by antiferromagnetic Heisenberg-type exchange interactions as well as an axial single-ion anisotropy within a distorted tetrahedron of Ni2+ ions characterized by X-ray single-crystal diffraction. Our analysis contrasts to recently proposed models which are based on the existence of extremely large biquadratic (and three-ion) exchange interactions and/or on a strong field dependence of the Heisenberg coupling parameters.

39 pages, 2 tables, 12 figures