Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Magnetismus Poster: Do., 13:00–15:30 D-P226
Multiferroic DyMnO3 studied by x-ray resonant magnetic scattering
R. Feyerherm 1 , E. Dudzik 1 , N. Aliouane 2 , D. N. Argyriou 2 , O. Prokhnenko 2
1 Hahn-Meitner-Institut, c/o BESSY, Albert-Einstein-Str. 15, 12489 Berlin – 2 Hahn-
Meitner-Institut, Glienicker Str. 100, 14109 Berlin
Orthorhombic DyMnO3 exhibits incommensurate antiferromagnetic ordering of the
Mn moments below TN,Mn = 39 K with a temperature dependent propagation vector
q = 0.36 − 0.385 b ∗ . Via quadratic magnetoelastic coupling this ordering is associated
with a lattice modulation 2q. Below about Tf = 18 K, the value of q freezes in and
a spontaneous ferroelectric polarisation occurs. Below about 6 K this polarisation is
suppressed considerably [1]. In order to clarify the role of Dy in this sequence of phase
transitions, we have studied the Dy magnetic ordering using x-ray resonant magnetic
scattering at the Dy-L3 edge on a single crystal DyMnO3. Recently, we have shown that
below TN,Dy = 5 K, the Dy magnetic moments order in a commensurate structure with
propagation vector 0.5b ∗ . Simultaneous with the Dy magnetic ordering, an incommensurate
lattice modulation with propagation vector 0.905b ∗ evolves. The magnetic and
structural nature of the corresponding Bragg reflections were demonstrated empolying
linear polarisation analysis (see Figure). This behaviour was interpreted as resulting
from a strong interference of Mn and Dy induced structural distortions in DyMnO3 [2].
New measurements show that in the temperature range 5 K < T < 16 K an induced
ordered magnetic moment, significantly smaller than below 5 K, exists on the Dy with
propagation vector 0.385b ∗ , identical to the underlying Mn ordering. This temperature
range apparently coincides with the one in which the spontaneous electric polarisation
occurs, implying that the induced Dy ordering is directly related to ferroelectricity in
DyMnO3. The results are discussed in relation to neutron diffraction measurements
on an isotope enriched powder sample 162 DyMnO3 that are presented in a separate
contribution.
[1] T. Kimura et al., Nature 426 (2003) 55; Phys. Rev. B 71 (2005) 224425.
[2] R. Feyerherm et al., cond-mat/0603613, Phys. Rev B (2006), in press.
Fig. 1: Linear polarisation analysis of the Bragg
reflections (0 2.5 4) and (0 2.905 3)