  The frustrated magnet has been regarded as a system that could be a promising
host material for the quantum spin liquid (QSL). However, it is difficult to
determine the spin configuration and the corresponding mechanism in this
system, because of its geometrical frustration (i.e., crystal structure and
symmetry). Herein, we systematically investigate one of the geometrically
frustrated magnets, the TbB$_{4}$ compound. Using resonant soft x-ray
scattering (RSXS), we explored its spin configuration, as well as Tb's
quadrupole. Comprehensive evaluations of the temperature and photon energy /
polarization dependences of the RSXS signals reveal the mechanism of spin
reorientation upon cooling down, which is the sophisticated interplay between
the Tb spin and the crystal symmetry rather than its orbit (quadrupole). Our
results and their implications would further shed a light on the search for
possible realization of QSL.
