YbNiB4: a Kondo lattice with low-dimensional antiferromagnetic fluctuations

We have grown single crystals of YbNiB4 using a Ni60B40 flux and determined the magnetic properties of this compound by means of magnetic susceptibility, specific heat and electrical resistivity measurement. Yb ions in YbNiB4 are in a trivalent state and present a transition from a paramagnetic state to an antiferromagnetic (AF) state at TN1 = 5.4 K and a further transition towards a second AF state at TN2 = 4.0 K. Kondo type behavior in the resistivity and an enhanced Sommerfeld coefficient γ 100 mJ mol-1 K-2 provide evidence for a significant Kondo interaction. A broad maximum in χ(T) at around 8 K, well above TN1, suggests low-dimensional antiferromagnetic correlations. Both mechanisms lead to strong fluctuation in an extended temperature range above TN1, up to the characteristic energy of this system, which was estimated to be T4f = 16 K from an analysis of the entropy.