Onset of negative magnetic heat capacity due to spin-vibrational coupling in quantum spin clusters

We examine the effect of spin-vibrational coupling on the thermodynamic and inelastic neutron scattering of a quantum spin-1/2 dimer and trimer. Through an exact diagonalization approach, we modulate the exchange interaction between spin-1/2 ions using coupling between a Heisenberg interaction and a harmonic oscillator to determine the exact analytical solutions for the energy eigenstates. Using these solutions, we determine energy excitations and thermodynamic responses. In an analysis of the exchange modulation, we find that a second-order effect of the oscillation of exchange interaction produces a distinct negative heat capacity. These effects have the potential to provide improved understanding in the areas of spintronics and quantum information applications.