Searching for a Quantum Critical Point in Rh doped ferromagnetic Ce_2.15Pd_1.95In_0.9

Low temperature magnetic and thermal (C_m) properties of the ferromagnetic (FM) alloys Ce_2.15(Pd_1−xRh_x)_1.95In_0.9 were investigated in order to explore the possibility for tuning towards a quantum critical point (QCP) by doping Pd with Rh. As expected, the magnetic transition decreases from T = 4.1K at x = 0 with increasing Rh concentration. However, the phase boundary splits into two transitions, the upper being antiferromagnetic (AF) whereas the lower FM. The AF phase boundary extrapolates to T_N= 0 for x_cr ≈ 0.65 whereas the first order FM transition vanishes at x ≈ 0.3. The quantum critical character of the T_N → 0 point is inferred from the divergent T dependence of the tail of C_m/T observed in the x = 0.5 and 0.55 alloys, and the tendency to saturation of the maximum of C_m (T_N)/T currently observed in exemplary Ce compounds when T_N → 0. Beyond the critical concentration the unit cell volume deviates from the Vegard's law in coincidence with a strong increase of the Kondo temperature.