A Zero-field Nuclear Magnetic Resonance Spectroscopy Study on the Structure Property Relationship in Co thin Films

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) was investigated in Co thin-films with different combinations of seeding and capping layers in previous works. The variations in the local magnetic out-of-plane (oop) anisotropy K as a function of film thickness t lead to additional contributions that make the quantification of the iDMI more challenging. These additional contributions were specifically attributed to the transition of fcc Co to hcp Co at a critical thickness tcr. In this work we clarify this issue by investigating the local structure and local magnetic stiffness and their contribution to the oop anisotropy K in two Pt/Co(t)/Ir film stacks with t = 10 nm and t = 25 nm. Zero-field nuclear magnetic resonance spectroscopy (ZF NMR) is the method of choice as it is a non-destructive and sensitive probe to examine structure and magnetic properties of nano-sized samples. We describe the evolution of the Co allotropes (fcc & hcp) and stacking fault disorder with the increase of t and illustrate the structure-property relationship between the local environments of Co and their respective magnetic stiffness.