Studies of Ga NMR and NQR in SrGa4

Abstract

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).