Magnetic interactions in praseodymium ruthenate Pr3RuO7 with fluorite-related structure

Add time:08/02/2019    Source:sciencedirect.com

Solid solutions Pr3(Ru1-xTax)O7 (0≤x≤1.0) and (Pr1-xYx)3RuO7 (0≤x≤0.7) were obtained as a single phase compound. They crystallize in an orthorhombic superstructure derived from that of the cubic fluorite with space group Cmcm. The results of the Rietveld analysis for X-ray diffraction profiles of Pr3(Ru1-xTax)O7 showed that Ru and Ta atoms are randomly situated at the six-coordinate 4b site. For (Pr1-xYx)3RuO7, with increasing the concentration of Y ions (x value), the smaller Y ions occupy selectively the seven-coordinate 8g site rather than the eight-coordinate 4a site.Through magnetic susceptibility measurements for Pr3(Ru1-xTax)O7, the antiferromagnetic transition temperatures decrease linearly with increasing x value, and at x=0.75 no magnetic ordering was found down to 1.8 K, indicating the magnetic interaction is not one-dimensional, but three-dimensional. On the other hand, the antiferromagnetic transition temperature for (Pr1-xYx)3RuO7 decreases with increasing x value, but above x≥0.50 it becomes constant (~12 K). This result indicates that Pr3+ ions at the seven-coordinate site greatly contribute to the antiferromagnetic interactions observed in (Pr1-xYx)3RuO7.Density functional calculations of Pr3RuO7 demonstrate that the electronic structure gives insulating character and that oxygen 2p orbitals hybridize strongly with Ru 4d orbitals in the valence band (VB). Near the top of VB, the Pr 4 f orbitals at the seven-coordinated site also show a weak hybridization with the O(1) 2p orbitals. The Ru-O(1)-Pr superexchange pathway take part in three-dimensional magnetic interaction and play an important role in an enhancement of long-range magnetic ordering.

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