Fe_3-xInSn_xO₆(x = 0, 0.25, or 0.5): A Family of Corundum Derivatives with Sn-Induced Polarization and Above Room Temperature Antiferromagnetic Ordering

Three new double corundum derivative compounds, Fe3-xInSnxO6 (x = 0. 0.25, or 0.5), were synthesized at high pressure and temperature (6 GPa and 1400-1450 °C). All of the compounds order antiferromagnetically well above room temperature (TN = 608, 532, and 432 K for x = 0, 0.25, and 0.5, respectively). The x = 0 phase crystallizes as centrosymmetric R3¯ c, but the inclusion of closed-shell d10 Sn4+ induces x = 0.25 and 0.5 to crystallize as noncentrosymmetric R3c. Microprobe measurements indicate that for x = 0.25 and 0.5, the substitution of Sn4+ is not offset by vacancies, which implies the presence of Fe2+, as corroborated by X-ray absorption near-edge spectroscopy and single-crystal X-ray structure refinements. Neutron powder diffraction experiments on x = 0.5 indicate that these compounds are canted A-type antiferromagnets that, like Fe2O3 and InFeO3, consist of ferromagnetic layers that stack antiferromagnetically with a single magnetic transition. Weak ferromagnetic interactions persist to very high temperatures. Temperature-dependent second harmonic generation (SHG) measurements on x = 0.25 and 0.5 show a SHG response with ferroelectric-like hysteretic maxima that correspond with the respective magnetic transitions, which suggest coupling of the magnetic and polarization order. These new compounds provide more information about fine-tuning the electronic, magnetic, and structural properties of corundum-derived mutlferroics in the search for tunable high-temperature magnetoelectric materials.