Successive magnetic phase transitions at T 1 =17.5 K and T 2 =18.5 K in Gd 3 Ru 4 Al 12 , with a distorted kagome lattice of Gd ions, is studied using resonant X-ray diffraction with polarization analysis. It has been suggested that in this compound the S = 7/2 spins on the nearest-neighbor Gd-triangle form a ferromagnetic trimer and the Gd lattice can be effectively considered as an antiferromagnetic triangular lattice of S = 21/2 spin trimers [S. Nakamura et al., Phys. Rev. B 98, 054410 (2018)]. We show that the magnetic order in this system is described by an incommensurate wave vector q ∼ (0.27, 0, 0), which varies slightly with temperature. In the low temperature phase below T 1 , the experimental results are well explained by considering that the spin trimers form a helical order with both the c-axis and c-plane components. In the intermediate phase above T 1 , the c-axis component vanishes, resulting in a sinusoical structure within the c-plane. The sinusoidal-helical transition at T 1 can be regarded as an ordering of chiral degree of freedom, which is degenerate in the intermediate phase.

Anomalous quantum critical behavior of CeS under high pressure has been studied by electrical resistivity and Hall resistivity measurements up to 7.2 GPa using a Bridgman-type anvil cell. The electrical resistivity increases significantly with decreasing temperature at high pressures, which is interpreted as an enhancement in the Kondo effect. However, the increasing curve does not follow the log T dependence and it is difficult to ascribe only to the normal Kondo effect due to spin fluctuation. The increase of resistivity at low temperatures on approaching the critical pressure of 5 GPa is anomalously large in comparison with those of other inter-metallic compounds such as CeIn 3. In addition, the resistivity increases even below T N from 4.4 to 5.2 GPa, which is reminiscent of a gap opening. The measurement of Hall resistivity, however, shows no clear indication of such gap opening. We consider that a valence fluctuation, in addition to the normal spin fluctuation, plays an important role in the quantum criticality of CeS.