Studies of Ga NMR and NQR in SrGa₄

In order to microscopically investigate the properties in SrGa₄, the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of ^69&71Ga (a nuclear spin I = 3/2) in the powder sample of SrGa₄ do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the ⁶⁹Ga NQR in SrGa₄. The Knight shifts of the ⁶⁹Ga(I) and ⁶⁹Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the ⁶⁹Ga(I) and ⁶⁹Ga(II) are 0.01 and –0.11 % at 4.2 K, and 0.09 and –0.08 % at 300 K, respectively. The values of the 1/ T₁T of the NMR of both ⁶⁹Ga(I) and ⁶⁹Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s ⁻¹K⁻¹ at ⁶⁹Ga(I) and 0.12 s ⁻¹K⁻¹ at ⁶⁹Ga(II), while the 1/ T₁T slightly increase above 100K with increasing temperature. The value of T₁ of ⁶⁹Ga(I) is one order of magnitude less than that of ⁶⁹Ga(II).