Impurity effects in frustrated diamond lattice antiferromagnets
Our group has studied diamond lattice antiferromagnets in the past, motivated by various experiments on A-site spinels. You can read about some of this here and here . Classically, when only first and second neighbor Heisenberg spin interactions are present, the system can have a large ground state degeneracy consisting of a continuously varying family of spin spiral states. This degeneracy may be broken by many different perturbations.
^ TOPOur work:
In this paper we study the effect of impurities. This is interesting because on the one hand impurities break the degeneracy, reducing fluctuations and tending to the make the spins more ordered. On the other hand, their randomness can tend to disorder the spins. Here we argue very generally that sufficiently dilute impurities induce an ordered magnetic ground state, and provide a mechanism of degeneracy breaking. The states which are selected can be determined by a "swiss cheese model" analysis, which we demonstrate numerically for a particular impurity model in this case. Moreover, we present criteria for estimating the stability of the resulting ordered phase to a competing frozen (spin glass) one. The results may explain the contrasting finding of frozen and ordered ground states in CoAl2O4 and MnSc2S4, respectively. A very recent experimental paper (here) seems very much in agreement with these results.
Read the paper.
