Structure-property relations of Ag2-3xBixI2 have been revealed.

Room-temperature multiferroism in polycrystalline antiferromagnetic Fe perovskites is reported for the first time. In the perovskite-type oxides RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 (RE = Gd, Tb), the interplay of layered ordering of Gd(Tb), Ba, and Ca atoms with the ordering of FeO 4 -tetrahedra (T) and FeO 6 -octahedra (O) results in a polar crystal structure. The layered structure consists of the stacking sequence of RE/Ca-RE/Ca-Ba-RE/Ca layers in combination with the TOOT sequence in a unit cell. A polar moment of 33.0 μC/cm 2 for the Gd-oxide (23.2 μC/cm 2 for the Tb one) is determined from the displacements of the cations, mainly Fe, and oxygen atoms along the b-axis. These oxides present antiferromagnetic ordering doubling the c-axis, and the magnetic structure in the Tb-compound remains up to 690 K, which is one of the highest transition temperatures reported in Fe perovskites.

Optically generated excitonic states (excitons and trions) in transition metal dichalcogenides are highly sensitive to the electronic and magnetic properties of the materials underneath. Modulation and control of the excitonic states in a novel van der Waals (vdW) heterostructure of monolayer MoSe2 on double‐layered perovskite Mn oxide ((La0.8Nd0.2)1.2Sr1.8Mn2O7) is demonstrated, wherein the Mn oxide transforms from a paramagnetic insulator to a ferromagnetic metal. A discontinuous change in the exciton photoluminescence intensity via dielectric screening is observed. Further, a relatively high trion intensity is discovered due to the charge transfer from metallic Mn oxide under the Curie temperature. Moreover, the vdW heterostructures with an ultrathin h‐BN spacer layer demonstrate enhanced valley splitting and polarization of excitonic states due to the proximity effect of the ferromagnetic spins of Mn oxide. The controllable h‐BN thickness in vdW heterostructures reveals a several‐nanometer‐long scale of charge transfer as well as a magnetic proximity effect. The vdW heterostructure allows modulation and control of the excitonic states via dielectric screening, charge carriers, and magnetic spins.