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

Abstract

We have studied a mosaic of 1T -CrSe 2 single crystals using β-detected nuclear magnetic resonance of 8 Li 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 instead exhibits a broad minimum with a remarkable absence of strong features in the vicinity of structural and magnetic transitions between 150 and 200 K. Together, the results suggest 8 Li + site occupation within the van der Waals gap between CrSe 2 trilayers. Possible origins of the two environments are discussed.

Local electronic and magnetic properties of the doped topological insulators Bi$_{2}$Se$_{3}$:Ca and Bi$_{2}$Te$_{3}$:Mn investigated using ion-implanted $^{8}$Li $β$-NMR

“…Apart from the quadrupolar component, another contribution at the resonance "centre", with no resolved splitting is discernible, analogous that observed in other vdW materials. 5,56,83 Unlike the more common case encountered for the spin I = 3/2 7 Li nucleus, there is no m ±1/2 ↔ m ∓1/2 main line transition that is unshifted in first-order by the quadrupolar interaction. The absence of any peaks interlacing the m ±2 ↔ m ±1 transitions suggest this "cen- 8 Li + implanted in BSC calculated using the SRIM Monte Carlo code.…”

“…Above 200 K, the activated increase in 1/T 1 may indicate the onset of diffusive 8 Li + motion, similar to the nonmagnetic analogs, with the additional effect that the local magnetic field from the Mn spins is also modulated by 8 Li hopping (not just the EFG), similar to the ordered magnetic vdW layered CrSe 2 . 83 However, it may instead mark the onset of thermal excitation of electrons across the bandgap that is narrowed by Mn doping. 13 Thermally excited carriers may also explain the increase in 1/T 1 at comparable temperatures in Ga 1-x Mn x As, 54 a very different medium for Li + diffusion.…”

The Site and High Field βNMR Properties of 8Li+ Implanted in α-Al2O3

“…The relaxation in sapphire is so slow that it can be used to accurately determine the total experimental asymmetry. This useful calibration allows for identification of a missing fraction such as shown in the magnetic CrSe 2 [34]. In Figure 5 the relaxation is seen to be considerably faster in rutile TiO 2 and deuterated polystyrene (PS-d8).…”