Quadrupole Splittings and Paramagnetic Shifts in the NMR of 27Al in Rare Earth Aluminum Garnets

Abstract

The nuclear magnetic resonance of ²⁷Al at both the a and d aluminum sites of dysprosium aluminum garnet (DAG), terbium aluminum garnet (TbAG), and ytterbium aluminum garnet (YbAG) have been measured at several temperatures between 4° and 290°K. The quadrupole coupling constants e²qQ/ℏ in MHz for the d and the a sites were temperature independent and equal to 5.731 and 0.320 in TbAG, 5.873 and 0.447 in DAG, and 6.300 and 1.053 in YbAG. The increase of the effective internal magnetic field at an aluminum nucleus expressed as a percentage of the externally applied field (the paramagnetic shift) which reaches values of 2% at 4.2°K for YbAG was calculated for YbAG assuming only magnetic dipole interaction and shown to be in excellent agreement with experiment at temperatures between 4.2°K and 290°K. For DAG and TbAG in which the paramagnetic shift reaches 4.8% at 100°K and 6.2% at 77°K, respectively, a similar calculation must await more accurate wavefunctions for the excited states of the magnetic ions.