Magnetocaloric effect and Grüneisen parameter of quantum magnets with a spin gap
Аннотация
We obtained, within a path-integral formalism (mean-field variational Gaussian approximation), analytical expressions for thermodynamic quantities such as magnetization, heat capacity, and the magnetic Gr\"uneisen parameter ${\mathrm{\ensuremath{\Gamma}}}_{H}$ of the system of triplons in spin gapped quantum magnets. Near the critical temperature ${\mathrm{\ensuremath{\Gamma}}}_{H}$ is discontinuous and changes its sign upon the Bose-Einstein condensation (BEC) of triplons. We predict that in the limit of low temperature $T$ and near the critical magnetic field ${H}_{c},\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Gamma}}}_{H}$ diverges as ${\mathrm{\ensuremath{\Gamma}}}_{H}\ensuremath{\sim}1/{T}^{2}$, while it scales as ${\mathrm{\ensuremath{\Gamma}}}_{H}\ensuremath{\sim}1/(H\ensuremath{-}{H}_{c})$ as the magnetic field approaches ${H}_{c}$.