| LiFeAs is considerably different from other iron pnictides superconductors as the magnetically ordered spin density wave state, which is suppressed upon either chemical (doping) or external pressure and is considered to be obligatory for superconductivity in all FeAs superconductors, is not present in LiFeAs. Moreover, it has been shown recently, that the substitution of Fe by Co in LiFeAs samples suppresses superconductivity quite rapidly. Calculations of the electronic structure and NMR experiments of this system may suggest that LiFeAs is a triplet p-wave superconductor. In the present study, we have grown high quality single crystals of LiFeAs and its variants with Ni by a self-flux technique. Particularly, measurements of the macroscopic susceptibility exhibit a ferromagnetic transition in Li(Fe,Ni)As. 75As Nuclear Quadrupole Resonance confirms that the ferromagnetic transition occurs in the bulk of the sample and therefore excludes that the origin of the ferromagnetism is due to parasitic effects such as Ni or Fe clusters. In summary, our results may confirm that LiFeAs is indeed close to a ferromagnetic instability. |
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