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Soft phonon mode coupled with antiferromagnetic order in incipient-ferroelectric Mott insulators Sr$$_{1-x}$$Ba$$_x$$MnO$$_3$$

Sakai, Hideaki*; Fujioka, Jun*; Fukuda, Tatsuo; Bahramy, M. S.*; Okuyama, Daisuke*; Arita, Ryotaro*; Arima, Takahisa*; Baron, A. Q. R.*; Taguchi, Yasujiro*; Tokura, Yoshinori*

Infrared optical and inelastic X-ray scattering spectra have been systematically investigated in combination with first-principles calculations for paraelectric and antiferromagnetic perovskite Sr$$_{1-x}$$Ba$$_x$$MnO$$_3$$ single crystals, which are close to a ferroelectric transition arising from off-center displacement of magnetic Mn$$^{4+}$$ ions. One optical phonon rapidly softens toward zero frequency at room temperature with increasing $$x$$. This soft-mode behavior is also reproduced by the first-principles calculations, from which we have predicted the vibration mode of all the optical phonons. Below the antiferromagnetic-transition temperature, the soft mode hardens with decreasing temperature and then resoftens toward the lowest temperature.



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Category:Materials Science, Multidisciplinary



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