Investigation of ionic and anomalous magnetic behavior in CrSe₂ using ⁸Li β-NMR

We have studied a mosaic of 1T-CrSe₂ single crystals using β-detected nuclear magnetic resonance of ⁸Li from 4 to 300 K. We identify two broad resonances that show no evidence of quadrupolar splitting, indicating two magnetically distinct environments for the implanted ion. We observe stretched exponential spin lattice relaxation and a corresponding rate (1/T ₁) that increases monotonically above 200 K, consistent with the onset of ionic diffusion. A pronounced maximum in 1/T ₁ is observed at the low temperature magnetic transition near 20 K. Between these limits, 1/T ₁ exhibits a broad minimum with an anomalous absence of strong features in the vicinity of structural and magnetic transitions between 150 and 200 K. Together, the results suggest ⁸Li⁺ site occupation within the van der Waals gap between CrSe₂ trilayers. Possible origins of the two environments are discussed.