Determination of spin Hamiltonian in the Ni${}_4$ magnetic molecule

Abstract

Magnetic excitations in a Ni${}_4$ magnetic molecule were investigated by inelastic neutron scattering and bulk susceptibility (${\chi }_{\text{bulk}}$) techniques. The magnetic excitation spectrum obtained from the inelastic neutron scattering experiments exhibits three modes at energy transfers of $\hslash \omega =0.5$, 1.35, and 1.6 meV. We show that the energy, momentum, and temperature dependences of the inelastic neutron scattering data and ${\chi }_{\text{bulk}}$ can be well reproduced by an effective spin Hamiltonian consisted of intra-molecule exchange interactions, a single-ionic anisotropy, biquadratic interactions, and Zeeman term. Under a hydrostatic pressure, the bulk magnetization decreases with increasing pressure, which along with the biquadratic term indicates spin-lattice coupling present in this system.

6 pages, 6 figures, and 2 tables