Abstract
In general, fluctuations suppress order in “conventional” many body systems. Here we present results of an experimental study intended to test recent ideas about how quantum, thermal and quenched noise may induce ordering in highly frustrated magnets. Our model system, the garnet Fe2Ca3Ge3O12, is an antiferromagnet with a continuously degenerate Neel ground state. We report combined magnetization- and neutron diffraction studies on the dilution series (FexGa1-x)2Ca3Ge3O12 (0≤x≤1). We propose a complex magnetic phase diagram with a spin glass phase around x=0.5. Within a wide concentration range, we observe a micro-domain state, where true long range order is never established. The correlation lengths lie between some 300 A for x=0.4 and ≥900, A for x≥0.8. We relate our findings to recent theories about how fluctuations select a definite spin structure in highly frustrated antiferromagnets. This leads us to propose two different spin structures for the pure and the diluted samples: our observations are in accordance with a stabilization of a collinear structure via quantum and thermal fluctuations, while quenched stoichiometric disorder lifts the ground state degeneracy but favours a canted spin arrangement.
Published Version
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