Spin susceptibility and low-frequency dynamics of uranium $5f$ electrons have been investigated by nuclear magnetic resonance (NMR) on the ${}^{14}\mathrm{N}$ nuclei in paramagnetic and magnetically ordered phases for single crystalline and polycrystalline samples of uranium mononitride (UN). NMR spectra, shifts of the ${}^{14}\mathrm{N}$ NMR lines, and the spin-lattice relaxation times $T_1$ have been obtained in the temperature range $T=10–760\mathrm{K}$ in magnetic field $B=92.8\mathrm{kOe}$. It is shown that in the UN paramagnetic phase, temperature dependence of the ${}^{14}\mathrm{N}$ NMR line shift is proportional to the spin susceptibility of the uranium $5f$ electrons. Joint analysis of NMR and magnetic susceptibility data allows us to determine temperature dependence of spin fluctuation energy ${\mathrm{\Gamma }}_{\mathrm{nmr}}\left(T\right)$ of the uranium $5f$ electrons and to demonstrate that its temperature variation is close to $\mathrm{\Gamma }\left(T\right)\propto T^{0.5}$ dependence which is characteristic of the concentrated Kondo systems above the coherent state formation temperature. In the magnetically ordered UN phase the ${}^{14}\mathrm{N}$ NMR spectra consist of several lines that can be explained in terms of the model of type $I$ antiferromagnetic order corresponding to $1k$ structure in the presence of magnetic domains.

• Received 12 December 2020
• Revised 11 August 2021
• Accepted 30 September 2021

DOI:https://doi.org/10.1103/PhysRevB.104.155148