Induced Jahn-Teller transition in DyPO$_4$ caused by a change in ground state upon level crossing

The transition caused by a change in the ground state of a rare-earth ion upon level crossing, an analogue of the induced Jahn-Teller transition in rare-earth compounds, is observed. It is shown that a jumpwise change in the Jahn-Teller interactions of $\alpha$ and $\gamma$ symmetries, caused by a change in the corresponding quadrupole moments in DyPO$_4$ upon level crossing, diminishes the critical field by $\sim20$ kOe and leads to a sharper change in magnetization $M$ and differential magnetic susceptibility $dM/dH$ near the crossover point.