Intrinsic low-temperature magnetic properties on the ultra-clean UTe${}_2$ with $T_{\mathrm{c}}$ = 2.1 K revealed by ${}^{125}$Te NMR

To investigate the intrinsic magnetic properties of UTe${}_2$, we performed ${}^{125}$Te-NMR measurements on the ultra-clean single-crystalline UTe${}_2$ with superconducting transition temperature $T_{\mathrm{c}}$ = 2.1~K and compared the results with those of the $T_{\mathrm{c}}$ = 1.6~K sample. The broadening of the linewidth of the NMR spectrum in the $a$-axis magnetic field and the low-temperature magnetic fluctuations observed in the 1.6~K sample are suppressed in the ultra-clean sample, indicating that such magnetic properties originate from a tiny amount of U deficiency. The present results suggest that the magnetic properties in UTe${}_2$ are sensitive to the U deficiency. We also observed a peculiar angular dependence of the NMR quantities due to large magnetic anisotropy with the $a$-axis as the magnetic easy axis.