Evolution of the structural, magnetic, and electronic properties of the triple perovskite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ba</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mi>Co</mml:mi><mml:msub><mml:mi>Ir</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>9</mml:mn></mml:msub></mml:mrow></mml:math>
Charu Garg, Deepak K. Roy, Martin Lonsky, Pascal Manuel, Antonio Cervellino, Jens Müller, Mukul Kabir, Sunil Nair
Abstract
We report a comprehensive investigation of the triple perovskite iridate ${\mathrm{Ba}}_{3}\mathrm{Co}{\mathrm{Ir}}_{2}{\mathrm{O}}_{9}$. Stabilizing in the hexagonal $P{6}_{3}/mmc$ symmetry at room temperature, this system transforms to a monoclinic $C2/c$ symmetry at the magnetic phase transition. On further reduction in temperature, the system partially distorts to an even lower symmetry ($P2/c$), with both these structurally disparate phases coexisting down to the lowest measured temperatures. The magnetic structure as determined from neutron diffraction data indicates a weakly canted antiferromagnetic structure, which is also supported by first-principles calculations. Theory indicates that the ${\mathrm{Ir}}^{5+}$ carries a finite magnetic moment, which is also consistent with the neutron data. This suggests that the putative $J=0$ state is avoided. Measurements of heat capacity, electrical resistance noise, and dielectric susceptibility all point toward the stabilization of a highly correlated ground state in the ${\mathrm{Ba}}_{3}\mathrm{Co}{\mathrm{Ir}}_{2}{\mathrm{O}}_{9}$ system.