Abstract
Skyrmions can be stabilized in magnetic systems with broken inversion symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions (DMI). Further, compensation of magnetic moments in ferrimagnetic materials can significantly reduce magnetic dipolar interactions, which tend to favor large skyrmions. Tuning DMI is essential to control skyrmion properties, with symmetry breaking at interfaces offering the greatest flexibility. However, in contrast to the ferromagnet case, few studies have investigated interfacial DMI in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic CoGd films by Brillouin light scattering. We demonstrate the ability to control DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic layer thickness. The DMI thickness dependence confirms its interfacial nature. In addition, magnetic force microscopy reveals the ability to tune DMI in a range that stabilizes sub-100 nm skyrmions at room temperature in zero field. Our work opens new paths for controlling interfacial DMI in ferrimagnets to nucleate and manipulate skyrmions.
Highlights
Magnetic skyrmions due to their non-trivial topology have interesting properties[1,2,3] that make them attractive for spintronic applications, such as racetrack memory and logic devices[4,5,6]
We found that as little as 10% of W in the cap layer in Pt/CoGd/Pt1-xWx thin films is sufficient to induce a Dzyaloshinskii-Moriya interactions (DMI) of about 0.15 mJ m−2, larger than the bulk DMI found in much thicker films[26]
The ferrimagnetic CoGd thin films were grown by RF magnetron co-sputtering on oxidized silicon wafers in the following sequence: W(3)/Pt(3)/Co78Gd22(t)/ Pt1-xWx(3)/Pt(3) [measure the DMI in the CoGd films (Methods)]
Summary
Magnetic skyrmions due to their non-trivial topology have interesting properties[1,2,3] that make them attractive for spintronic applications, such as racetrack memory and logic devices[4,5,6]. Compensated thin ferrimagnetic films with interfacial DMI are interesting materials due to their low stray fields, reduced sensitivity to external magnetic fields, and fast spin dynamics, which are predicted to lead to ultrasmall and ultrafast skyrmions[19,22]. Unlike in ferromagnets where fast current-induced motion of chiral textures is impeded by the Walker breakdown and domain wall pinning[13,23,24,25], high domain wall velocities––reaching 1000 m s-1––have been observed in ferrimagnetic CoGd films near the angular momentum compensation temperature[19]. Frequency (GHz) spin-wave frequency dispersion in the presence of DMI30; the asymmetry is directly related to the strength of the DMI Both techniques, domain wall dynamics and BLS, have been found to lead to similar DMI values[28,29,31]. Our findings provide insight into the key parameters that control the DMI in ferrimagnetic films toward achieving ultrasmall and ultrafast skyrmions
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