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VOLUME 105 | ISSUE 1 | PAGE 28
Magnetic phase separation and strong enhancement of the Neel temperature at high pressures in a new multiferroic Ba3TaFe3Si2O14
The high pressure properties of a new multiferroic of the langasite family Ba3TaFe3Si2O14 were investigated in diamond-anvil cells (DAC) in the temperature range of 4.2-295 K by a new method of synchrotron Mossbauer spectroscopy. Strong enhancement of the Neel temperature TN was observed at pressures above 20 GPa associated with the structural transformation. The highest value of TN is about 130 K which is almost five times larger than the value at ambient pressure (about 27 K). It was suggested that the high value of TN appears due to redistribution of Fe ions over 3f and 2d tetrahedral sites of the langasite structure. In this case, the short Fe-O distances and favorable Fe-O-Fe bond angles create conditions for strong superexchange interactions between iron ions, and effective two-dimensional (2D) magnetic ordering appears in the (ab) plane. The separation of the sample into two magnetic phases with different TN values of about 50 and 130 K was revealed, which can be explained by the strong two dimensional 2D magnetic ordering in the (ab) plane and 3D ordering involving inter-plane interaction.