Chloride Reduction of Mn<sup>3+</sup> in Mild Hydrothermal Synthesis of a Charge Ordered Defect Pyrochlore, CsMn<sup>2+</sup>Mn<sup>3+</sup>F<sub>6</sub>, a Canted Antiferromagnet with a Hard Ferromagnetic Component
Vladislav V. Klepov, Kristen A. Pace, Anna A. Berseneva, Justin B. Felder, Stuart Calder, Gregory Morrison, Qiang Zhang, Melanie Kirkham, David Parker, Hans‐Conrad zur Loye
Abstract
Geometrically frustrated systems play an important role in studying new physical phenomena and unconventional thermodynamics. Charge ordered defect pyrochlores AM2+M3+F6 offer a convenient platform for probing the interplay between electron distribution over M2+ and M3+ sites and structural distortions; however, they are limited to compounds with M2+/3+ = V, Fe, Ni, and Cu due to difficulties in the simultaneous stabilization of other 3d elements in the +2 and +3 oxidation states. Herein, we employ Cl– anions under hydrothermal conditions for the mild reduction of Mn2O3 in concentrated HF to obtain the CsMn2+Mn3+F6 composition as a phase pure sample and study its properties. The magnetism of CsMn2F6 was characterized by measuring the magnetic susceptibility and isothermal magnetization data, and a magnetic transition to a canted antiferromagnet state was found at 24.1 K. We determined the magnetic structure of CsMn2F6 using powder neutron diffraction, which revealed successive long-range ordering of the Mn2+ and Mn3+ sites that is accompanied by a second transition. The role and strength of magnetic exchange interactions were characterized using DFT calculations.