Microspectroscopic study of the magnetic textures in a permalloy/hematite bilayer across the Morin transition

Magnetic interactions occurring at the interfaces between ferromagnetic and antiferromagnetic (FM/AFM) materials is an active research field. In the past, it has brought practical applications with industrial impact, where a reference magnetization direction is set for spintronic devices or magnetic sensors. However, interfacial interactions are not just limited to bias effects or to set a uniaxial anisotropy. More recently, several works have pointed out the importance of the distribution of the AFM magnetic domains around the FM phase, since the orientation of the AFM spins determine the orientation of those of the FM phase. The study of magnetic textures is basic to understand the emergence of special micromagnetic configurations. Skyrmions are just an example of this idea. In this context, oxides may give rise to magnetic exchange and dipolar phenomena when combined with other materials in the same structure. We have recently carried out an XMCD analysis of permalloy thin films grown on epitaxial hematite, focused on the texture of the FM domains (beamtime 2024098825 in CIRCE, see associated report). We have observed that the texture of the FM domains is qualitatively different below and above the Morin transition (MT). We propose that this is mainly due to the magnetic interactions at the AFM/FM interphase. Below MT, the AFM moments point perpendicular to the surface, while above MT the AFM moments lie along any of the 3 equivalent directions in the (0001) plane. Therefore, there is a larger and more diverse interaction with the FM moments of the Py. These interactions tend to rotate the FM moments to accommodate them into a state with lower energy. Thus, the Néel state of the AFM phase has a strong influence on the FM texture. The intention of this proposal is to complete the initiated research.