153Eu and 69,71Ga Zero-Field NMR Study of Antiferromagnetic State in EuGa4

We report ${}^{153}$Eu and ${}^{69,71}$Ga NMR under a zero magnetic field on the antiferromagnetic state of EuGa${}_4$ with $T_{\mathrm{N}}\approx 16$ K. We have successfully observed a ${}^{153}$Eu zero-field NMR signal with well-resolved nuclear quadrupole splitting in the antiferromagnetic state of EuGa${}_4$. ${}^{69,71}$Ga zero-field NMR spectra were also observed below $T_{\mathrm{N}}$. The internal field and nuclear quadrupole frequency are estimated from a simulation of the spectra by the exact diagonalization of the nuclear spin Hamiltonian matrix. The asymmetrically split zero-field NMR spectra were explained by considering a configuration of the magnetic moments of Eu${}^{2+}$ lying in the basal $ab$-plane. The temperature dependence of the internal field, which is proportional to the sublattice magnetization, can be explained by the Brillouin function with $J=S=7\mathrm{/}2$