Experimental realization of a helical magnetic structure at Ni/Gd interfaces at room temperature

Rare earth (RE) metals in proximity to transition metals (TMs) normally exhibit a strong antiferromagnetic exchange interaction and thus show an increase in the Curie temperature and twisted magnetic structures. Here, we performed depth profiling of the structure and magnetic properties of a Ni/Gd multilayer at room temperature using polarized neutron reflectivity (PNR) measurements, suggesting intermixing and long-range ordered magnetism at interfaces. We observed different spin-dependent PNR profiles for the multilayer upon reflecting neutrons from front and back surfaces. The analysis of the observed PNR profiles can be explained by the twisted magnetic phase at interfaces due to strong antiferromagnetic exchange interaction between Ni (TM) and Gd (RE). Diffuse PNR measurements indicate that the structural and magnetic roughnesses at the interfaces are not correlated. The depth-dependent experimental techniques were supported by a simple one-dimensional (1D) spin-based model calculation for the existence of a magnetic helical (twisted) phase at the interfaces in this system at room temperature. The twisted phase may contribute significantly to modifying the temperature-dependent magnetic properties. This work demonstrates the realization of a twisted phase at room temperature in the RE/TM system, paving a pathway to manipulate the magnetic properties of all-optical electronics for future magnetic memory applications.