Possible magnetic structure with a tilted helical plane in SmBe₁₃ probed by ⁹ Be-NMR study

⁹Be-NMR measurements were performed using single crystalline SmBe₁₃ in order to investigate a magnetic structure of a low-temperature ordering state microscopically. We observed a spectral broadening in the ordered state, and the broadened spectral shape depends on the magnetic field directions. By comparing the experimentally obtained and simulated NMR spectra for magnetic fields along the cubic [001] and [011] directions, we argue a helical structure with a basal plane tilted from the (001) plane in low-field ordering region under the assumption of a helical with a propagation vector of (0, 0, 1/3) found in other RBe₁₃ compounds (R = rare earths). Such a tilted helical structure is explained by a combination of an ellipse helical in the (001) plane and a longitudinal magnetic density wave along the [001] direction. Considering a magnetic easy axis parallel to [001] revealed by the magnetization measurements, the peculiar helical structure in SmBe₁₃ may be built on delicate balance among exchange interactions, dipole-dipole interaction, and single-ion magnetic anisotropy due to the crystalline electric field. (author)