Melting of chiral order in terbium manganate (TbMnO3) observed with resonant x-ray Bragg diffraction.
Resonant Bragg diffraction of soft, circularly polarized x-rays has been used to observe directly the temperature dependence of chiral-order melting in a motif of Mn ions in terbium manganate. The underlying mechanism uses the b-axis component of a cycloid, which vanishes outside the polar phase. Melting is witnessed by the first and second harmonics of a cycloid, and we explain why the observed temperature dependence differs in the two harmonics. Conclusions follow from an exact treatment of diffraction by using atomic multipoles in a circular cycloid, since a standard treatment of the diffraction, based on a single material-vector identified with the magnetic dipole, does not reproduce correctly observations at the second harmonic.
ISIS Facility, STFC Oxfordshire, UK.
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Lovesey
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Scagnoli
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Garganourakis
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Koohpayeh
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Detlefs
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Staub