YBNIAL - A NEW YB-BASED HEAVY-FERMION ANTIFERROMAGNET

We have investigated the compound YbNiAl, which crystallizes in the sa me structure as the well-known mixed-valent system YbCuAl, and have fo und that it is the first example of a clear cut Yb-based heavy-fermion antiferromagnet. The resistivity increases logarithmically by 25% bet ween 100 and 10 K, C/T extrapolates below 0.4 K to a gamma value of 35 0 mJ/K-2 mol and the entropy at the antiferromagnetic ordering tempera ture T-N = 3 K reaches only 0.45R In 2. We compare the properties of t his compound with those of YbPtAl, where Yb is trivalent.