Abstract
Quaternary oxychlorides derived from Ruddlesden–Popper 3d transition metal oxides offer a route to cleavable crystals with bulk antiferromagnetic ordering temperatures reaching at least 550 K. Here, we study the magnetic, optical, and mechanical behavior of Sr2FeO3Cl, Ca2FeO3Cl, Ca3Fe2O5Cl2, and Sr3Fe2O5Cl2. Through optical absorption measurements, we show that these antiferromagnetic semiconductors have optical band gaps of ≈2.1(1) eV. The magnetic ordering symmetries and temperatures were probed by neutron powder diffraction and Mössbauer spectroscopy on polycrystalline samples, demonstrating Néel temperatures (TN) near room temperature in the single layer Sr2FeO3Cl (TN ≈ 311 K) and Ca2FeO3Cl (TN ≈ 360 K), and the double-layer compound Sr3Fe2O5Cl2 has TN ≈ 545 K. The high-spin moments of Fe3+ lie within the basal plane and the magnetic structures are compensated within each magnetic layer and characterized by magnetic propagation vectors k = ( 1/2 1/2 0). Magnetization results demonstrate the quasi-2D nature of the magnetism, with a broad maximum in the susceptibility near 2TN for Sr2FeO3Cl. Scotch tape tests and mechanical exfoliation onto SiO2 confirm the micaceous nature of these crystals with cleavage down to a single unit cell (two magnetic layers) achieved for Sr3Fe2O5Cl2. This paper highlights strong antiferromagnetic interactions, semiconducting band gaps, and cleavability of quaternary Fe-based oxychlorides and motivates future work on crystals and exfoliated flakes of these and related oxyhalide systems.
