Quantum magnetization plateau and sign change of the magnetocaloric effect in a ferrimagnetic spin chain.

The magnetocaloric effect in the $(5∕2,1)$ ferrimagnetic chain is investiagted using a finite-cluster solver with central spin selection to reduce finite-size effects. We found that an enhanced magnetocaloric effect occurs at the boundary of the ground-state magnetization plateau. The calculated magnetic Gr\"uneisen parameter ΓH exhibits strong signatures of a field-induced quantum phase transition at the critical magnetic field Hc destroying the plateau. We obtain the characteristic increase ΓH~T^-1∕νz near Hc and the sign change ΓH≈-Gᵣ∕(H-Hc), in accordance with scaling theory predictions.