27Al-NMR and NQR studies in the antiferromagnetic heavy fermion CePd2Al3

Systematic measurements of the NQR spectrum and the nuclear-spin-lattice relaxation rate, 1/T1, of 27Al in the heavy-fermion antiferromagnetic (AF) compound CePd2Al3 have revealed that the magnetic nature dramatically changes from showing long-range and inhomogeneous AF ordering for annealed and as-cast polycrystals, respectively, to a disappearance of any type of magnetic ordering for single crystals. A close relationship between the magnetic ordering and the structural disorder in the Al layers isolated from the Ce-Pd layers is demonstrated. The exchange coupling via the Al layers along the c-axis, which leads to the AF ground state, critically depends on the occupation and distribution of Al atoms as proposed by Mentink et al. It is pointed out that the randomness remaining inevitably in the Al layers masks the intrinsic magnetic excitation in the AF ordered state. (author)