Elastic softness of low-symmetry frustrated $A$Ti$_2$O$_5$ ($A$ = Co, Fe)
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| Formato: | Preprint |
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2024
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| author | Watanabe, Tadataka Takayanagi, Kazuya Nishimura, Ray Hara, Yoshiaki Prabhakaran, Dharmalingam Johnson, Roger D. Blundell, Stephen J. |
| author_facet | Watanabe, Tadataka Takayanagi, Kazuya Nishimura, Ray Hara, Yoshiaki Prabhakaran, Dharmalingam Johnson, Roger D. Blundell, Stephen J. |
| contents | Orthorhombic pseudobrookites CoTi$_2$O$_5$ and FeTi$_2$O$_5$ have a low-symmetry crystal structure comprising magnetic Co$^{2+}$/Fe$^{2+}$ ions and nonmagnetic Ti$^{4+}$ ions, where the orbital-nondegenerate Co$^{2+}$/Fe$^{2+}$ ions form one-dimensional chains running along the orthorhombic $a$ axis. These compounds undergo an antiferromagnetic phase transition at $T_N \sim$ 26 K for CoTi$_2$O$_5$ and $T_N \sim$ 40 K for FeTi$_2$O$_5$. Ultrasound velocity measurements on single crystals of CoTi$_2$O$_5$ and FeTi$_2$O$_5$ reveal that CoTi$_2$O$_5$ exhibits unusual elastic softness above $T_N$ in the symmetry-lowering elastic mode of $ac$-plane shear elastic modulus, inconsistent with the structural symmetry breaking caused by antiferromagnetic ordering at $T_N$. This suggests the presence of two distinct types of magnetostructural fluctuations above $T_N$ that should be a precursor to the symmetry-lowering lattice distortion at $T_N$. In contrast, FeTi$_2$O$_5$ exhibits either negligible or smaller elastic softness, indicating weaker spin-lattice coupling. These findings highlight CoTi$_2$O$_5$ and FeTi$_2$O$_5$ as unique spin-latticed-coupled frustrated systems with low crystal symmetry, where, while the exchange interactions are quasi-one-dimensional in nature, the frustration is released by further lowering the crystal symmetry through three-dimensional spin-lattice coupling, which is stronger in CoTi$_2$O$_5$ than in FeTi$_2$O$_5$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2408_03783 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Elastic softness of low-symmetry frustrated $A$Ti$_2$O$_5$ ($A$ = Co, Fe) Watanabe, Tadataka Takayanagi, Kazuya Nishimura, Ray Hara, Yoshiaki Prabhakaran, Dharmalingam Johnson, Roger D. Blundell, Stephen J. Strongly Correlated Electrons Materials Science Orthorhombic pseudobrookites CoTi$_2$O$_5$ and FeTi$_2$O$_5$ have a low-symmetry crystal structure comprising magnetic Co$^{2+}$/Fe$^{2+}$ ions and nonmagnetic Ti$^{4+}$ ions, where the orbital-nondegenerate Co$^{2+}$/Fe$^{2+}$ ions form one-dimensional chains running along the orthorhombic $a$ axis. These compounds undergo an antiferromagnetic phase transition at $T_N \sim$ 26 K for CoTi$_2$O$_5$ and $T_N \sim$ 40 K for FeTi$_2$O$_5$. Ultrasound velocity measurements on single crystals of CoTi$_2$O$_5$ and FeTi$_2$O$_5$ reveal that CoTi$_2$O$_5$ exhibits unusual elastic softness above $T_N$ in the symmetry-lowering elastic mode of $ac$-plane shear elastic modulus, inconsistent with the structural symmetry breaking caused by antiferromagnetic ordering at $T_N$. This suggests the presence of two distinct types of magnetostructural fluctuations above $T_N$ that should be a precursor to the symmetry-lowering lattice distortion at $T_N$. In contrast, FeTi$_2$O$_5$ exhibits either negligible or smaller elastic softness, indicating weaker spin-lattice coupling. These findings highlight CoTi$_2$O$_5$ and FeTi$_2$O$_5$ as unique spin-latticed-coupled frustrated systems with low crystal symmetry, where, while the exchange interactions are quasi-one-dimensional in nature, the frustration is released by further lowering the crystal symmetry through three-dimensional spin-lattice coupling, which is stronger in CoTi$_2$O$_5$ than in FeTi$_2$O$_5$. |
| title | Elastic softness of low-symmetry frustrated $A$Ti$_2$O$_5$ ($A$ = Co, Fe) |
| topic | Strongly Correlated Electrons Materials Science |
| url | https://arxiv.org/abs/2408.03783 |