Magnetic field enhanced structural instability in EuTiO$_{3}$

EuTiO$_{3}$ undergoes a structural phase transition from cubic to tetragonal at $T_{\rm S}$ = 282 K which is not accompanied by any long range magnetic order. However, it is related to the oxygen ocathedra rotation driven by a zone boundary acoustic mode softening. Here we show that this displacive second order structural phase transition can be shifted to higher temperatures by the application of an external magnetic field (${\Delta}$$T_{\rm S}$ ${\simeq}$ 4 K for $\mu_{0}$$H$ = 9 T). This observed field dependence is in agreement with theoretical predictions based on a coupled spin-anharmonic-phonon interaction model.