Microscopic approach to the quadrupolar-glass problem.

Abstract

We report results of the microscopic approach to the quadrupolar-glass problem in mixed molecular crystals formed by linear and spherical molecules. The temperature-concentration analysis of the orientational order parameter derived from NMR spectroscopy data is given on the two-component vector model of site-diluted ortho-para-hydrogen-type mixtures. Two features of the short-range orientational ordering, characteristically different from the spin-glass case, namely, incomplete freezing and residual ordering, respectively, at low and high temperatures are discussed. It is established that the first effect is due to spatial correlated local molecular and reaction fields and the second caused by quadrupolar intrinsic field. A zero-field freezing temperature is estimated taking into account the threshold concentration for quadrupolar glass formation. \textcopyright{} 1996 The American Physical Society.