Magnetic and transport properties of single crystal YbIrGe

The magnetic and transport properties of YbIrGe and LuIrGe have been investigated. YbIrGe with the TiNiSi-type orthorhombic structure is an antiferromagnet with TN=2.4K. Magnetic susceptibility χ(T) of YbIrGe shows a strong anisotropy which changes from the easy-plane type within the ab-plane above 100 K to the easy-axis type along the b-axis at lower temperatures. χ(T) along the a-axis makes a kink at TN in contrast to T-independence of χ(T) along b- and c-axis below TN. We propose that the Yb magnetic moments couple antiparallel in the direction of the a-axis as a magnetic structure below TN. The magnetic entropy gain at TN was released by 85% of the expected value of Rln 2 at the maximum. Therefore, YbIrGe may not be classified as a typical heavy fermion compound.