Room Temperature Paramagnetism in Chiral Metal Halide Dilute Magnetic Semiconductors—MRI Negative Contrast Agent Potential

Manipulation of spins is a key component not only in semiconductor devices but also in spintronic devices and medical applications. Various magnetic materials have been developed for spin control in applications such as magnetoresistive random-access memory (MRAM) and magnetic resonance imaging (MRI), and recently, chiral metal halide semiconductors (MHSs) have gained attention in spintronics for their ability to align charge carriers spins through chiral-induced spin-selectivity (CISS). However, conventional chiral MHSs exhibit diamagnetic properties, limiting their applicability in certain spintronic fields. Although chiral MHSs containing magnetic metals such as copper (Cu²⁺), chromium (Cr³⁺), and manganese (Mn²⁺) have been explored, practical applications have not yet been demonstrated. In this work, we introduce magnetic impurities into non-magnetic chiral MHSs using a dilute magnetic semiconductors (DMSs) strategy, resulting in the chiral metal halide DMSs (chiral MH-DMSs). Specifically, iron (Fe³⁺) ions were doped into lead-free chiral MHSs (R/S-MBA)InI₄ (MBA = methylbenzylammonium) with the formula (R/S-MBA)In_1-xFe_xI₄ (x = 0.023). These chiral MH-DMSs exhibit both room-temperature paramagnetism and chiroptical properties resulting from asymmetric interactions between chiral organic ammonium (NH₃⁺) and halides. The Fe³⁺ ions replace In³⁺ and endow paramagnetism without changing the crystal structure of P2₁ space group, as confirmed by superconducting quantum interference device–vibrating sample magnetometer (SQUID-VSM) measurements and crystallographic analysis. Furthermore, the paramagnetic behavior of (R/S-MBA)In_1-xFe_xI₄ enables their application as negative contrast agents in MRI, offering new capabilities for spintronic applications and medical imaging.
Acknowledgement
This research was supported by the Digital Research Innovation Institution Program Through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2023-00283597).