Investigation of the magnetic ground state of a halide perovskite heterostructure.

The halide perovskite heterostructure (CuCl4)2(MTPA)4Cu3Cl6 (Cu_Cu; MTPA = 3-(methylthio)-propylammonium) forms from solution as single crystals consisting of alternating layers of 2D CuII-Cl perovskite and 1D CuII-Cl diamond–chain intergrowth. Using magnetometry, heat capacity, and electron paramagnetic resonance measurements, we have interrogated the magnetic ordering of the 2D perovskite layer and the 1D intergrowth layer at temperatures down to 55 mK. No long–range magnetic ordering event in the intergrowth is evident, suggesting that, due to the geometric constraints imposed by the perovskite framework, individual diamond chains in the intergrowth of Cu_Cu are magnetically isolated from one another. In contrast, comparable motifs in well–studied diamond spin chain materials such as azurite do not show magnetic 1D character at low temperatures due to interchain contacts in the solid state. As such, Cu_Cu provides an ideal platform for studying isolated, anisotropic spin chains. This material illustrates the capability of halide perovskite heterostructures to serve as vehicles for the scalable synthesis of complex multi–layered magnetic materials. A heat capacity anomaly at 0.3 K suggests some local spin pairing in Cu_Cu. We aim to use muon spin relaxation measurements above and below this temperature to conclusively demonstrate a lack of long-range magnetic ordering, which would be consistent with our proposal of a 1D Heisenberg spin chain ground state in the intergrowth.