Nuclear exchange spin couplings in metal trihydrides: A tight binding approximation

Abstract

A multiband tight binding model of the metal trihydrides, including on-site repulsion and exchange, is examined. By linearly coupling the system to a harmonic bath we show that the multiband model yields an effective temperature dependent Heisenberg spin Hamiltonian. This system exhibits a temperature dependent competition between ferro- and antiferromagnetic exchange spin couplings. The resulting spin spectrum is consistent with observed anomalous isotope dependent metal trihydride H-N.M.R. spectra.