Abstract
Thin film magnetic heterostructures with competing interfacial coupling and Zeeman energy provide a fertile ground to study phase transition between different equilibrium states as a function of external magnetic field and temperature. A rare-earth (RE)/transition metal (TM) ferromagnetic multilayer is a classic example where the magnetic state is determined by a competition between the Zeeman energy and antiferromagnetic interfacial exchange coupling energy. Technologically, such structures offer the possibility to engineer the macroscopic magnetic response by tuning the microscopic interactions between the layers. We have performed an exhaustive study of nickel/gadolinium as a model system for understanding RE/TM multilayers using the element-specific measurement technique x-ray magnetic circular dichroism, and determined the full magnetic state diagrams as a function of temperature and magnetic layer thickness. We compare our results to a modified Stoner-Wohlfarth-based model and provide evidence of a thickness-dependent transition to a magnetic fan state which is critical in understanding magnetoresistance effects in RE/TM systems. The results provide important insight for spintronics and superconducting spintronics where engineering tunable magnetic inhomogeneity is key for certain applications.
Highlights
Modified magnetic interaction at the interfaces between different ferromagnetic materials can be utilised to engineer materials with magnetic properties that are significantly different from the bulk
Our results demonstrate the full richness of the magnetic state diagram of RE/transition metal (TM) systems and shed new light on previous work that interpreted results based on an incomplete picture of RE/TM behaviour[14,18]
Since the magnetic signal that is detected by x-ray magnetic circular dichroism (XMCD) is the projection of the magnetic moment onto the wavevector of the x-ray, the magnet coils are placed such that the applied magnetic field is parallel to the propagation direction of the x-rays
Summary
Modified magnetic interaction at the interfaces between different ferromagnetic materials can be utilised to engineer materials with magnetic properties that are significantly different from the bulk. The magnetisation of the RE decreases and a second-order phase transition to the TM-aligned state occurs in which the TM aligns parallel to the applied field and the RE aligns antiparallel to both the TM and the applied field. This simple picture was later confirmed experimentally[11,12]; the existence of a twisted state at the interface between bulk Fe and a thin layer of www.nature.com/scientificreports/. Our results demonstrate the full richness of the magnetic state diagram of RE/TM systems and shed new light on previous work that interpreted results based on an incomplete picture of RE/TM behaviour[14,18]
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