Critical behavior in a Kondo-screening partially-ordered antiferromagnet CePdAl

A rare-earth compound CePdAl is a good example of the Kondo-screening partially-ordered antiferromagnet below TN = 2.7 K. In this compound, the formation of the Kondo-singlet state is realized as a new route of the relief of the frustration. The spin dynamics of CePdAl are, however, still controversial. In order to further investigate the spin dynamics of CePdAl, we have performed 27Al-NMR and specific heat single crystal measurements and reanalysed published powder neutron diffraction data. NMR intensities decrease with decreasing temperature in the ordered state suggesting the slow spin fluctuations below TN = 2.7 K, while the intensity of magnetic Bragg peak measured by neutron diffraction increases monotonously in the same temperature range. The critical exponents derived from the neutron diffraction and the specific heat measurements are not coincident with those of known universality classes. An unconventional magnetic order parameter or a charge degree of freedom originated from the coexistence of frustration and the Kondo effect may influence the critical behavior.