STRONG FRUSTRATION AND DILUTION-ENHANCED ORDER IN A QUASI-2D SPIN-GLASS

The interactions in the magnetoplumbite isomorph SrCr8Ga4O19 are highly frustrated. Thermodynamic data are presented and show the existence of a transition from paramagnetic to spin-glass ordering but only at Tc=3.3 K, despite the high Curie-Weiss temperature of 515 K. Other unusual properties include a low-temperature specific heat varying as T2 and an inverse relationship of Tc to magnetic-ion concentration for a set of differently prepared crystals. This result is conjectured to arise from competition between 2D frustration and a tendency toward 3D order, controlled by preferential site substitution. © 1990 The American Physical Society.