Magnetic and transport studies on RIrAl (R = Y, La, Ce, Pr and Nd) compounds: mixed-valent behaviour of CeIrAl

Magnetic and transport studies were carried out on RlrAI (R = Y, La, Ce, Pr and Nd) compounds which crystallize in the orthorhombic epsilon-TiNiSi-typ e structure. Magnetic susceptibility measurements reveal that CelrAl is mix ed-valent compound with a very high Kondo temperature of similar to 1300 K. Its resistivity shows no unusual behaviour reminiscent of a gap in electro nic density of states. The PrIrAl and NdIrAl compounds are found to have a ferromagnetic ground state with T(C)s of 9 and 13 K, respectively, as infer red from magnetic measurements. The electrical resistivity of these two com pounds shows a drop at about 8 and 12 K, respectively, consistent with the magnetic ordering, The Y and La analogues of this series exhibit the usual Pauli paramagnetic behaviour, with no superconducting transition down to 2 K. (C) 1999 Published by Elsevier Science Ltd.