⁵⁵Mn and ²⁷Al NMR investigation of YMn₄Al₈ single crystals

⁵⁵Mn and ²⁷Al Nuclear magnetic resonance (NMR) measurements are performed on a single crystal of YMn₄Al₈ at 8 T down to 4 K. The NMR spectrum, Knight shift, linewidth, spin–lattice relaxation rate 1/T₁, and spin–spin relaxation rate 1/T₂ are measured as a function of temperature for the c-axis parallel and perpendicular to the magnetic field. The ⁵⁵Mn NMR spectrum exhibits five broad satellites due to nuclear quadrupole interaction for a nuclear spin of I = 5/2. The ²⁷Al NMR spectrum exhibits two different sites, Al-A and Al-B, with five satellites for each site due to nuclear quadrupole interaction for I = 5/2. Based on the broader linewidths of the Al-B spectra, the Al-B site turns out to be closer to the Mn 3d electrons. The local electronic structures at the Mn and Al sites measured by NMR are almost isotropic for the c-axis parallel and perpendicular to the magnetic field. The temperature dependence of the Knight shifts and the Korringa product 1/T₁T, as well as the magnetic susceptibility, show a large decrease at low temperature, indicating the opening of a pseudo-gap in YMn₄Al₈. The Knight shift scales with the susceptibility, from which the hyperfine coupling constant is extracted and found to be ⁵⁵A = −140 kOe/μ_B.