Abstract
Elastic and inelastic neutron-scattering experiments have been performed on single crystals of the multiferroic ${\text{Ba}}_{3}{\text{NbFe}}_{3}{\text{Si}}_{2}{\text{O}}_{14}$. It is found that the organization of the spin clusters into true long-range ordered states occurs by the following process: (i) by 60 K, there is evidence for short-range ordered triangular Fe clusters of spins, (ii) below 40 K, the clusters begin to form long-range ordered structures as a spin-wave spectrum develops, (iii) at ${T}_{\text{N}}=26\text{ }\text{K}$, the sample exhibits coexisting long-range and short-range ordered structures, and (iv) by $T=1.5\text{ }\text{K}$, a long-range ordered structure with a well-defined spin-wave spectrum develops. The spin-wave excitation can be described by a Heisenberg Hamiltonian within a distorted triangular lattice including both the intratrimer and intertrimer interactions. Physical property measurements showing anomalies near $T=40\text{ }\text{K}$ can now be adequately explained as being due to scattering from low-energy spin fluctuations.
Published Version
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