  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.
