The effects of interfacial structure on the Dzyaloshinskii–Moriya interaction in magnetic thin film heterostructures.

The interfacial Dzyaloshinskii–Moriya interaction (DMI) plays a key role in generating, stabilizing, and manipulating skyrmions. Factors like layer sequencing in multilayers, magnetic inhomogeneities, interface mixing and roughness significantly impact DMI strength. Controlling interfacial quality and magnetic properties is crucial for stabilizing skyrmions for spintronics applications. Ta/CoFeB/TaOx structures show magnetization switching without an external field via spin-orbit torque (SOT) as well as the presence of room temperature skyrmions. High-frequency surface acoustic waves (SAW) on magnetic skyrmions using polar magneto-optical Kerr effect microscopy in Cr/Ta/Pt/CoFeB/Pt indicate an increase in skyrmion density, an effect we attribute to the effects of strain on the numerous pinning sites

We are interested in investigating skyrmion responses to SAW in the absence of strong pinning. To that end, we have grown three families of samples, on 128 Y -cut LiNbO3 substrates: Cr/Ta/Pt/CoFeB/Pt, Cr/Ta/Pt/CoFeB/Ta, and Cr/Ta/CoFeB/Ta. In the first sample, strong PMA was observed at a CoFeB thickness of 0.7 nm. In the second sample, the Pt thickness influences PMA; as the Pt thickness increases from 1 nm to 2 nm, the samples switch from in-plane to out-of-plane. In the third sample, no discernible magnetic signal was detected for the same 0.7 nm CoFeB thickness, likely due to the formation of a magnetic dead-layer at the CoFeB/Ta interface, possibly caused by naturally oxidized Ta migration and B diffusion. We will present TEM and XPS results, correlating magnetic and structural properties with the aim of maximizing the DMI. TEM structural analysis can show the presence of an interfacial layer at the CoFeB/Ta interface, and XPS will show the chemical and electronic states of that layer. The effects of increased diffusion between layers via annealing of samples will also be discussed.