Signature of frustrated moments in quantum critical CePd_1-xNi_xAl

CePdAl with Ce 4f moments forming a distorted kagome network is one of the scarce materials exhibiting Kondo physics and magnetic frustration simultaneously. As a result, antiferromagnetic (AF) order setting in at T-N = 2.7 K encompasses only two-thirds of the Ce moments. We report measurements of the specific heat, C, and the magnetic Gruneisen parameter, Gamma(mag), on single crystals of CePd1-xNixAl with x <= 0.16 at temperatures down to 0.05 K and magnetic fields B up to 8 T. Field-induced quantum criticality for various concentrations is observed with the critical field decreasing to zero at x(c) approximate to 0.15. Remarkably, two-dimensional AF quantum criticality of Hertz-Millis-Moriya type arises for x = 0.05 and x = 0.1 at the suppression of three-dimensional magnetic order. Furthermore, Gamma(mag)(B) shows an additional contribution near 2.5 T for all concentrations, which is ascribed to correlations of the frustrated one-third of Ce moments