Magnetic and neutron spectroscopic properties of the tetrameric nickel compound $[Mo_{12}O_{28}(\mu_2-OH)_9(\mu_3-OH)_3{Ni(H_2O)_3}_4] $\cdot$ 13H_2O$

TL;DR

This study investigates the magnetic and spectroscopic properties of a tetrameric nickel compound using neutron scattering and magnetization data, revealing antiferromagnetic interactions and anisotropy consistent with Heisenberg models.

Contribution

The paper provides a detailed analysis of neutron and magnetization data showing that the compound's behavior is well described by Heisenberg exchange and anisotropy, challenging models with large biquadratic interactions.

Findings

Neutron scattering and magnetization data are consistent with Heisenberg exchange.

The compound exhibits antiferromagnetic coupling with anisotropy.

Data contradicts models requiring large biquadratic exchange interactions.

Abstract

We present results of inelastic neutron scattering experiments performed for the compound Magnetic and neutron spectroscopic properties of the tetrameric nickel compound $[Mo_{12}O_{28}(\mu_2-OH)_9(\mu_3-OH)_3{Ni(H_2O)_3}_4] $\cdot$ 13H_2O$, 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.