The Yb2Al1−xMgxSi2 series from aspin fluctuation (x = 0) to a magnetically ordered ground state(x = 1)

Abstract

The structural and magnetic properties ofYb2Al1−xMgxSi2 (x = 0, 0.5 and 1), crystallizing in the tetragonalMo2FeB2-type structure, arereported in this work. Yb2AlSi2 exhibits a Pauli paramagnetic ground state arising due to spin/valence fluctuations inducedby a significant Yb 4f conduction band hybridization. High-field magnetization(up to 120 kOe) indicates a nearly temperature-independent susceptibility of8.6 × 10−3 emu/Yb mol below 10 K. On the other hand, Yb ions inYb2MgSi2 order antiferromagnetically at a relatively high temperatureTN of 9.5 K. The intermediate composition alloyYb2Al0.5Mg0.5Si2 is a Kondo lattice,antiferromagnet with TN = 5.5 K. The coefficient of the linear term of the electronic heat capacity,γ, ofYb2AlSi2 is foundto be 305 mJ mol−1 K−2, indicating a significant electronic mass enhancement due to strong electroniccorrelations. Below 12 K, an additional contribution to the heat capacity of the formT3lnT is observed. The170Yb Mössbauer spectra inthe ordered state of Yb2MgSi2 indicate a strong coupling of the 4f quadrupolar moment with the magnetic momentthrough a magneto-elastic coupling.