The magnetic P-T phase diagram of langasite Ba3TaFe3Si2O14 at high hydrostatic pressures up to 38 GPa

The langasite-type crystals with 3d ions are considered as a class of multiferroics in which ferroelectricity can be induced by the magnetic ordering. In this paper, the high-pressure magnetic states of the langasite-type powdered sample Ba3TaFe3Si2O14 have been investigated in a diamond anvil cell by the nuclear forward scattering of synchrotron radiation technique at different temperatures in hydrostatic conditions. In the pressure range of 0 < P < 19.5 GPa, an increase of the Neel temperature TN from 27 to 41 K was observed in the antiferromagnetic phase of the material. At pressures ∼19.5 GPa, a transition to another magnetic phase with huge increase in the Neel temperature to ∼120 K was found. We attribute this change to the structural transition at ∼19.5 GPa which is evidenced by a drastic change of Raman spectra at this pressure. A tentative magnetic P-T phase diagram of Ba3TaFe3Si2O14 is proposed.