Nondipolar Interaction Between Nearest-Neighbor Neodymium Ions in the Ethyl Sulfate

Abstract

Measurements made on the EPR spectrum of a pair of interacting nearest-neighbor neodymium ions in lanthanum ethyl sulfate show that the interaction is predominantly dipolar, but that there is an additional term ${A}_{\mathrm{ij}}{S}_{\mathrm{iz}}{S}_{\mathrm{jz}}+\frac{1}{2}{B}_{\mathrm{ij}}({S}_{i+}{S}_{j\ensuremath{-}}+{S}_{i\ensuremath{-}}{S}_{j+})$, with ${A}_{\mathrm{ij}}=(+32\ifmmode\pm\else\textpm\fi{}6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and ${B}_{\mathrm{ij}}=(\ensuremath{-}3\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. A semiquantitative discussion is given of the possible origins of this nondipolar contribution including super-exchange, electric quadrupole-quadrupole, and virtual-phonon exchange interactions.