Mn 2 FeWO 6 : A New Ni 3 TeO 6 ‐Type Polar and Magnetic Oxide

In this work, we present the high pressure and temperature (HPT) synthesis of Mn 2 FeWO 6 —a new magnetic and polar member of the A 2 BB′O 6 -type corundum derivative family, and the results of the crystal structure, SHG activity, magnetic phase diagram, and electrical/dielectric properties. First-principles calculations are also carried out to better understand its structure, polarization, complex magnetic properties, and to point to new materials design with multifunctional properties. Polycrystalline black Mn 2 FeWO 6 was prepared at 1673 K for 1 h at 8 GPa. Original lab powder X-ray diffraction (PXD, Figure S2, Supporting Information) indicates a rhombohedral cell ( a ≈ 5.3 Å, c ≈ 13.9 Å) of the main phase and a small wolframite impurity (Figure S3a,b and Table S1, Supporting Information). Figure 1 a presents the RT synchrotron powder X-ray diffraction (SPXD) patterns of Mn 2 FeWO 6 , which could correspond to any of the R 3 or R -3 structure types discussed above. However, the high-angle annular dark fi eld scanning transmission electron microscopy (HAADF-STEM) images (Figure 1 b and S4, Supporting Information) clearly show Fe/W ordering, and thus rule out IL prototype for Mn 2 FeWO 6 . Polar magnets are one of the most promising materials for multiferroics and spintronics. Recently, the A 2 BB′O 6 -type corundum derivatives have drawn much interest due to their remarkable magnetic and electronic properties with polar structures and multiferroic and second harmonic generation (SHG) behavior. [ 1–6 ] These structures are related to perovskite, but unlike perovskites, which have corner-sharing B site octahedra, in these phases, with unusually small A-site cations, both the A and B sites are octahedrally coordinated. The corner-, face-, and edge-sharing octahedra form a 3D lattice. [ 2,7 ] The A 2 BB′O 6 -type corundum derivatives can crystallize in the centrosymmetric ilmenite (IL, space group R -3), or in non-centrosymmetric LiNbO 3 (LN, R 3 c ) , or ordered ilmenite (OIL, R 3), or Ni 3 TeO 6 (NTO, R 3) structure, as shown in Figure S1 (Supporting Information). The stabilization of any one of these structures depends on the cation arrangement and their ordering/disordering degree, which are affected by the cationic size and charge differences, electron confi guration, and synthesis conditions. [ 1,8–11 ] The general structural features of A 2 BB′O 6 -type corundum derivatives with octahedral coordination of all metal sites favor the formation of practical magnetic and multiferroic/magnetoelectric materials by incorporation of magnetic transition metal ions. Recently, near room temperature (RT) ferrimagnetic (FiM) behavior of Mn 2 FeSbO 6 ( T C ≈ 270 K) [ 1 ] and antiferromagnetic (AFM) Ni 3 TeO 6 with nonhysteretic colossal magnetoelectricity [ 4 ] were reported. More recently, we reported