Boosting Non-Centrosymmetric Distortion and Magnetic Properties in Chiral Metal Halide Perovskites

Control of spin-polarized currents and magnetic properties in materials are important to demonstrate various spintronic applications such as MRAM and spin LEDs. In conventional semiconductors and metals, spin polarization and magnetization occur by the application of external magnetic fields or fabrication of ultra-thin (<5 nm) layer of the materials, which complicate the fabrication process and device structure. Here, we report novel materials system, hybrid chiral metal-halide perovskites (MHPs), which can control the spin polarization and magnetic properties via simple solution process. MHPs consist of three different atoms or molecules in various crystal structures (representations are ABX₃ and A₂BX₄ where A is an organic ammonium, B is a transition metal cation and X is a halide anion). First, we synthesize chiral lead (Pb)-based MHPs ((R-/S-MBA)₂PbI₄ where MBA is methylbenzylammonium) and find that R-/S-MBA cations transfer the chirality to the inorganic metal-halide octahedra (PbI₆) by the asymmetric electrostatic interaction between ammonium group in MBA and halide in inorganic octahedra. (R-/S-MBA)₂PbI₄ polycrystalline thin films show circular dichroism (CD) signals with opposite directions which are dependent on the chiral direction of MBA. Furthermore, (R-/S-MBA)₂PbI₄ show efficient spin selectivity > 80% without external magnetic fields by the chiral-induced spin selectivity (CISS) effect. Second, to solve the toxic problem in Pb-based MHPs, we synthesize Pb-free chiral MHPs that use palladium (Pd) in B site cation. Pd-based MHPs have 0-dimensional orientation of Pd-halide square-planar, where the direction of the orientation depends on the chiral direction in A-site cation, and increased CD signals when mixed halides are used in X-site (anisotropy g-factor (g_CD) = 3.3 × 10^-3 in pure chloride, 1.2 × 10^-2 in pure bromide, 1.8 × 10^-2 when Br_0.5Cl_0.5). We also measured the spin selectivity in Pd-based chiral MHPs. Third, to induce magnetic properties in MHPs in addition to the chirality, we synthesize iron (Fe)-based chiral MHPs with different Fe compositions. Fe-based chiral MHPs show CD signals in the absorption range of metal-halide tetrahedra, which clarify that R-/S-MBA transfers its chirality to the metal-halide tetrahedra. Furthermore Fe-based chiral MHPs exhibit paramagnetism at low temperature, which demonstrate the potential of future MHP materials which have both chirality and magnetic properties.