Structural behavior of the kagome antiferromagnet TmBaCo{sub 4}O{sub 7} : neutron diffraction study and group-theoretical consideration.
The first-order structural phase transition at T{sub S}{approx}240K in the extended kagome antiferromagnet TmBaCo{sub 4}O{sub 7} has been studied by neutron powder diffraction. In order to comprehend the microscopic origin of the transition, a detailed symmetry analysis is performed, based on crystallographic parameters obtained by Rietveld analysis of the neutron data. The results are consistent with the P31c {yields} Pna2{sub 1} symmetry lowering and support a displacive nature of the phase transition. The complex tilting pattern of CoO{sub 4} tetrahedra in both triangular and kagome sublattices is described based on symmetry-adapted pseudovector distortion modes of the parent P6{sub 3}mc hexagonal structure. Our analysis reveals that the unusual topology of the crystal structure does not allow CoO{sub 4} tetrahedra to rotate as rigid units, resulting in their inevitable distortions, whatever the combination of rotational modes considered. A possible analogy between polyhedral distortions and spin frustration in this system is discussed.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 967954
- Report Number(s):
- ANL/MSD/JA-65644; TRN: US200924%%152
- Journal Information:
- Phys. Rev. B, Vol. 80, Issue 2009; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- ENGLISH
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