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arXiv · 1504.03792

Acoustic study for dynamical molecular-spin state without undergoing magnetic phase transition in spin-frustrated ZnFe$_2$O$_4$

Tadataka Watanabe·Shota Takita·Keisuke Tomiyasu·Kazuya Kamazawa
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Abstract

Ultrasound velocity measurements were performed on a single crystal of spin-frustrated ferrite spinel ZnFe$_2$O$_4$ from 300 K down to 2 K. In this cubic crystal, all the symmetrically-independent elastic moduli exhibit softening with a characteristic minimum with decreasing temperature below $\sim$100 K. This elastic anomaly suggests a coupling between dynamical lattice deformations and molecular-spin excitations. In contrast, the elastic anomalies, normally driven by the magnetostructural phase transition and its precursor, are absent in ZnFe$_2$O$_4$, suggesting that the spin-lattice coupling cannot play a role in relieving frustration within this compound. The present study infers that, for ZnFe$_2$O$_4$, the dynamical molecular-spin state evolves at low temperatures without undergoing precursor spin-lattice fluctuations and spin-lattice ordering. It is expected that ZnFe$_2$O$_4$ provides the unique dynamical spin-lattice liquid-like system, where not only the spin molecules but also the cubic lattice fluctuate spatially and temporally.

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Tadataka Watanabe, Shota Takita, Keisuke Tomiyasu, Kazuya Kamazawa. 2015-10-16. Acoustic study for dynamical molecular-spin state without undergoing magnetic phase transition in spin-frustrated ZnFe$_2$O$_4$. https://doi.org/10.1103/physrevb.92.174420

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