The Yb(2)Al(1-x)Mg(x)Si(2) series from a spin fluctuation (x = 0) to a magnetically ordered ground state (x = 1).

The structural and magnetic properties of Yb(2)Al(1-x)Mg(x)Si(2) (x = 0, 0.5 and 1), crystallizing in the tetragonal Mo(2)FeB(2)-type structure, are reported in this work. Yb(2)AlSi(2) exhibits a Pauli paramagnetic ground state arising due to spin/valence fluctuations induced by a significant Yb 4f conduction band hybridization. High-field magnetization (up to 120 kOe) indicates a nearly temperature-independent susceptibility of 8.6 × 10(-3) emu/Yb mol below 10 K. On the other hand, Yb ions in Yb(2)MgSi(2) order antiferromagnetically at a relatively high temperature T(N) of 9.5 K. The intermediate composition alloy Yb(2)Al(0.5)Mg(0.5)Si(2) is a Kondo lattice, antiferromagnet with T(N) = 5.5 K. The coefficient of the linear term of the electronic heat capacity, γ, of Yb(2)AlSi(2) is found to be 305 mJ mol(-1) K(-2), indicating a significant electronic mass enhancement due to strong electronic correlations. Below 12 K, an additional contribution to the heat capacity of the form T(3)lnT is observed. The (170)Yb Mössbauer spectra in the ordered state of Yb(2)MgSi(2) indicate a strong coupling of the 4f quadrupolar moment with the magnetic moment through a magneto-elastic coupling.