Antiferromagnetic ordering in 2-1-4 copper oxides

Abstract
We have doped a small amount of Fe (0.5%) into the 2‐1‐4 superconducting oxides La2 CuO4−y and La1.85 Sr0.15 CuO4−y . Mössbauer measurements have indicated that the Fe dopants are in a high‐spin Fe3+ state, but sharp differences have been found for samples before and after annealing in Ar, as well as with and without Sr. An antiferromagnetic transition at 292 K in the Ar‐annealed La sample has been confirmed with both Mössbauer and magnetization measurements. The relevance of antiferromagnetism to the high‐temperature superconductivity has been addressed.