Chloride Reduction of Mn³⁺ in Mild Hydrothermal Synthesis of a Charge Ordered Defect Pyrochlore, CsMn²⁺Mn³⁺F₆, a Canted Antiferromagnet with a Hard Ferromagnetic Component

Abstract

Geometrically frustrated systems play an important role in studying new physical phenomena and unconventional thermodynamics. Charge ordered defect pyrochlores AM 2+ M 3+F6 offer a convenient platform for probing the interplay between electron distribution over M 2+ and M 3+ sites and structural distortions; however, they are limited to compounds with M 2+/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.

Magnetic hourglass fermions: from exhaustive symmetry conditions to high-throughput materials predictions

“…Out of these materials, we highlight 30 which are found to demonstrate relative clear hourglass band structure near the Fermi level for reasonable values of U from LDA+SOC+U calculations [80], as listed in Table II alongside with the statistics of materials with collinear and noncollinear magnetic structures for type-I, III and IV MSGs. In the following, we showcase the hourglass band structures and detailed analysis on the topological characteristics of the hourglass BCs in magnetic materials CsMn 2 F 6 [81], NdSi [82,83] and MnCoGe [84][85][86]. Other than these three materials demonstrated in the main text, all the band structures of the calculated 175 magnetic hourglass materials are provided in Sec.…”

“…CsMn 2 F 6 [81], a recently synthesized materials with distorted pyrochlore structure, is crystallized in MSG 62.447 of type III, with orthorhombic lattice, whose BZ is shown in Fig. 2(b).…”

Excitonic transverse and amplitude fluctuations in the noncollinear and charge-ordered RbFe$^{2+}$Fe$^{3+}$F$_{6}$

“…Several compounds with similar structures have been reported in the literature. 26,27 Charge order originates from the two different iron sites which have differing valences of Fe 2+ and Fe 3+ . While the magnetic ground state of Fe 3+ is S = 5 2 with each of the five dorbitals half filled following Hund's rules and the Pauli principle, the situation for Fe 2+ is slightly more complicated with an extra electron occupying one of the t 2g states with S = 2 and an effective l=1 (which we discuss in more detail below).…”

An overview into advantages and applications of conventional and unconventional hydro(solvo)thermal approaches for novel advanced materials design

“…This way, it explores how the parameters of experimental synthesis (e.g., temperature, pressure, solvent, nature of the precursors, reaction time, and so on) affect the formation of crystalline particles leading to highly adjustable properties of a given target material [54][55][56][57][58]. In relation to the materials prepared by this strategy, we highlight the superiority in applications such as superionic conductors [28,59,60], chemical and gas sensors [29,[61][62][63][64][65], electronically conductive solids [30,[66][67][68], complex ceramic oxide and fluorides [31,32,[69][70][71][72][73][74], magnetic materials [33,[75][76][77][78], optoelectronic devices [34,[79][80][81][82], and so on. Furthermore, it is known that the kinetics of hydro(solvo)thermal reactions undergo significant changes when associating technologies such as electrochemistry, microwave, sonochemistry, and others [70,81,[83][84][85][86][87]<...…”