Pushing magnetic spirals beyond room temperature by reducing the uniaxial pyramidal elongation in layered Cu/Fe perovskites

Abstract

The impact of a 3d divalent substitution for Cu using M^{2+} ions not presenting elongated MO_{5} pyramids has been explored in YBaCuFeO_{5} as a new strategy to upgrade the magnetic properties of this high-temperature spiral magnet and potential multiferroic. In this work we investigate the incidence of the Cu^{2+} with Co^{2+} substitution in YBa(Cu_{1−x}Co_{x})FeO_{5} compounds in which B-site disorder is kept invariant (disorder n_{d}≈36%). The study validates the reduction of the uniaxial elongation distortion at Cu sites as an efficient alternative way to disorder that enables one to enhance the thermal stability of the spiral order. In addition, the rotation plane of the helix is reoriented by the Cu/Co substitution and nearby the triple point (when T_{S} is maximal) the spiral order adopts an almost complete cycloidal magnetic configuration. These results lay the foundation of a new mechanism to tune the stability of the magnetic spirals in layered perovskites based on reducing the uniaxial elongation associated to the (4+1)-coordination of Cu^{2+} ions in square CuO_{5} pyramids.