4f spin driven ferroelectric-ferromagnetic multiferroicity in PrMn₂O₅ under a magnetic field

In contrast to all other members of the RMn₂O₅ family with nonzero 4 f electrons (R = Nd to Lu), PrMn₂O₅ does not show any spin driven ferroelectricity in the magnetically ordered phase. By means of high-field electric polarization measurements up to 45 T, we have found that this exceptional candidate undergoes a spin driven multiferroic phase under magnetic field. X-ray magnetic circular dichroism studies up to 30 T at the Pr L₂ edge show that this ferroelectricity originates from and directly couples to the ferromagnetic component of the Pr³⁺spins. Experimental observations along with our generalized gradient-approximation+U calculations reveal that this exotic ferroelectric-ferromagnetic combination stabilizes through the exchange-striction mechanism solely driven by a 3d-4f-type coupling, as opposed to the other RMn₂O₅ members with 3d-3d driven ferroelectric-antiferromagnetic-type conventional type-II multiferroicity.