Ferromagnetic Interactions in Highly Stable,Partially Reduced TiO2: The S=2 State in Anatase

We report direct evidence for quintuplet spin states in a particular kind of reduced TiO₂ anatase obtained by the mild oxidation of TiB₂ under hydrothermal conditions. Continuous‐wave and pulse EPR spectroscopy at X and Q band frequencies provide compelling evidence for the presence of S= 2 states, stable in a wide range of temperatures up to room temperature. A tentative model, corroborated by spin‐polarized DFT calculations, is proposed, which consists of four ferromagnetically interacting Ti³⁺ ions with distances ranging from 0.5 nm to 0.8 nm and tetrahedral arrangement.     

Reversible Thermochromism and Strong Ferromagnetism in Two-Dimensional Hybrid Perovskites

Two-dimensional (2D) hybrid perovskites have shown many attractive properties associated with their soft lattices and multiple quantum well structure. Herein, we report the synthesis and characterization of two new multifunctional 2D hybrid perovskites, (PED)CuCl₄ and (BED)₂CuCl₆, which show reversible thermochromic behavior, dramatic temperature-dependent conductivity change, and strong ferromagnetism. Upon temperature change, the (PED)CuCl₄ and (BED)₂CuCl₆ crystals exhibit a reversible color change between yellow and red-brown. The associated structural changes were monitored by in situ temperature-dependent powder X-ray diffraction (PXRD). The (BED)₂CuCl₆ exhibits superior thermal stability, with a thermochromic working temperature up to 443 K. The conductivity of (BED)₂CuCl₆ changes over six orders of magnitude upon temperature change. The 2D perovskites exhibit ferromagnetic properties with Curie temperatures around 13 K.