AL-27-NMR AND NQR STUDIES IN THE ANTIFERROMAGNETIC HEAVY-FERMION CEPD2AL3

Systematic measurements of the NQR spectrum and the nuclear-spin-latti ce relaxation rate, 1/T-1, of Al-27 in the heavy-fermion antiferromagn etic (AF) compound CePd2Al3 have revealed that the magnetic nature dra matically changes from showing long-range and inhomogeneous AF orderin g for annealed and as-cast polycrystals, respectively, to a disappeara nce of any type of magnetic ordering for single crystals. A close rela tionship between the magnetic ordering and the structural disorder in the Al layers isolated from the Ce-Pd layers is demonstrated. The exch ange coupling via the Al layers along the c-axis, which leads to the A F ground state, critically depends on the occupation and distribution of Al atoms as proposed by Mentink et al. It is pointed out that the r andomness remaining inevitably in the Al layers masks the intrinsic ma gnetic excitation in the AF ordered state.