single crystals*

The highly-frustrated itinerant magnetic system CaCo_2-yAs₂ exhibits A-type antiferromagnetic (AFM) order below T_N = 52 K. From the magnetization M versus temperature T, magnetic field H, and heat capacity C_p(T, H) measurements it is found that T_N decreases to 22 K with only 3% Ni substitution and is completely suppressed for x > 0.16. Magnetic susceptibility χ measurements reveal that strong ferromagnetic (FM) fluctuations develop for 0.11≤ x ≤ 0.52. The FM fluctuations for x = 0.21 and 0.31 are quasi-1D in nature, where χ_c >> χ_ab. The C_p(T) measurements further reveal that the FM spin fluctuations are quantum in nature, where a logarithmic T-dependent upturn in C_p(T )/T is observed at low T and H = 0, that is suppressed with increasing H. A reentrant spin-glass behavior arising out of competing AFM and FM interactions is also observed for x = 0.11 and 0.16 below T_N. No signature of any magnetic order or spin fluctuations is observed for x > 0.52 at T ≥ 1.8 K. Density functional theory (DFT) calculations show that the transition to nonmagnetic state occurs via a Stoner transition.