Magnetic properties of structure-disordered heavy fermion Ce-Mn alloys

We have measured the magnetic susceptibility χ on structure-disordered Ce_xY_80-xMn₂₀ alloys from 2 to 280 K. The χ shows a typical Curie-Weiss (CW) paramagnetic behavior above 20 K in each concentration x. In the Ce-poor region of x ≤ 51, the low-temperature χ below 15 K exhibits a spin-glass transition. The spin-glass transition temperature T_g decreases with increasing Ce-concentration. In the Ce-rich region of x ≥ 62, the spin-glass transition disappears and the CW paramagnetic behavior remains down to the low temperature limit. The Weiss temperature θ is negative for all the samples and almost constant in the Ce-poor side. However, the absolute value of θ increases with increasing Ce-concentration in the Ce-rich region. We have interpreted this fact as an increase of the antiferromagnetic c-f coupling, namely the Kondo effect, with the Ce-concentration.