Temperature dependence of the Dzyaloshinskii-Moriya interaction in ultrathin films

Abstract

The temperature dependence of magnetic properties in thin films are important for understanding the underlying physics and enabling the creation of novel devices. Whilst the temperature dependence of saturation magnetization Ms, exchange stiffness A and anisotropy K have been widely investigated [1, 2, 3], research on the interfacial Dzyaloshinskii–Moriya interaction (DMI) remains limited [4]. The DMI exists in perpendicularly magnetized ultrathin films with interfaces to heavy metals and is critical to the formation of magnetic skyrmions. We present a study of the temperature dependence of DMI in a Ta/Pt/CoFeB/Ru/Pt/CoFeb/Ru/Pt heterostructure hosting skyrmions, based on extensive characterization by bulk magnetometry and x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). Ms, anisotropy field Hk, zero-field domain width W and skyrmion radius R are extracted directly from the measurements. Through Ms and Hk, the strength of uniaxial anisotropy Ku is determined. Then, we adapt the bulk Bloch law to the thin film geometry to extract A from the temperature dependence of Ms (Fig. 1). Furthermore, we combine Ms, W, R, Ku and A in the static multilayer domain energy model [5] and the static skyrmion size model [6], where the DMI values are calculated at different temperatures (Fig. 2). We find a large spatial variation of the DMI strength between the one derived by the spatial domains and that at skyrmion sites. Besides, the DMI value shows a linear correlation with A and Ku. The possible physical origins are discussed. Finally, according to our results, we argue that the skyrmion size should remain constant over an extensive temperature range [7].