Physical properties and phase diagram of single crystal REBaMn2O6 (RE = Sm, Eu, Gd, Tb, Dy, and Y)

Abstract

We have carried out a systematic study on antiferromagnetic and charge ordering phase transitions in double-perovskite manganite compounds REBaMn2O6 (RE ​= ​Sm, Eu, Gd, Tb, Dy, and Y) by using single-crystalline samples. In YBaMn2O6, a tiny anomaly near 480 ​K as well as a first-order phase transition near 520 ​K are found in the temperature dependence of resistivity. Synchrotron x-ray single-crystal structure analysis shows that the unit cell is doubled first in the ab plane and further doubled along the c-axis as the temperature decreases. One of the most possible electronic phases between 480 ​K and 520 ​K is Zener polaron ordering. Mn atoms are paired in the ab-plane with seven 3d-electrons localized on each pair. The 3d-electron distribution in each pair begins to become asymmetric below 480 ​K. Similar two-step transitions are also observed for RE ​= ​Tb and Dy. The antiferromagnetic transition at TN ​≃ ​180 ​K is accompanied by a large hysteresis, which is attributable to a simultaneous rearrangement of charge order. The charge rearrangement temperature gradually rises with increasing the RE ionic radius. In SmBaMn2O6, the Néel temperature (TN) is 175 ​K and is lower than charge rearrangement temperature (≃ 200 ​K). These transitions are summarized in a phase diagram with respect to temperature and the ionic radius of RE3+.