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Magnetismus Poster: Do., 13:00–15:30 D-P256
Orbital correlations and magnetism in single layered manganites
D. Senff 1 , O. Schumann 1 , F. Krüger 2 , Y. Sidis 3 , P. Link 4 , K. Hradil 5 , A.
Schneidewind 6 , K. Habicht 7 , W. Schmidt 8 , M. Braden 1
1 II. Physikalisches Institut, Universität Köln – 2 Instituut Lorentz, Universitait Leiden
– 3 Laboratoire Leon Brillouin, Saclay/France – 4 FRM II, TU München – 5 Institut
für Physikalische Chemie, Universität Göttingen – 6 Institut für Festkörperphysik, TU
Dresden – 7 Hahn Meitner Institut, Berlin – 8 Institut Laue Langevin, Grenoble/France
The stable tetragonal crystal structure and the reduced electronic dimensionality in
single layered manganites La1−xSr1+xMnO4 open the way to a detailed study of the
complex interplay of several degrees of freedom being relevant for all manganite-oxides
[1] and which in the 3d perovskite manganites results in the colossal depression of the
electric resistivity under magnetic field.
The most studied compound of this family is the half-doped system La0.5Sr1.5MnO4
with an equal ratio of three- and four-valent Mn-ions, leading to a complex ordering of
charges and orbitals below TCOO. At lowest temperatures this ordering is accompanied
by an AFM ordering of the spins of the so-called CE-type, which is characterized by an
AFM ordering of FM zigzag chains. Here we present our results of an inelastic neutron
scattering study on the magnetic excitations of this complex ordered ground state [2].
We find a very anisotropic magnon spectrum with a steep dispersion along the direction
of the FM zig-zag chains and only a weak AFM coupling between adjacent chains. We
discus the observed spectrum in terms of linear spinwave theory, and based on a strong
next-nearest neighbour exchange we stress the similarity of the magnetic excitation
spectrum of the CE-type ordering with that in FM metallic perovskite manganites.
To weaken the AFM interchain-coupling and the CE-type structure we studied the doping
dependence of the CE-ordering in the region 0.4 ≤ x ≤ 0.6. For the underdoped
compound x = 0.4 enhanced diffuse magnetic scattering indeed points to a pertubation
of the magnetic coupling between adjacent chains. Although the sample remains
insulating a strong FM response of 1.5µB/Mn at fields of 14T seems to somehow
connect the single layered manganites with the 3d CMR-perovskites. Upon overdoping
with Sr (x > 0.5), we do not observe a significant softening of the interchain coupling,
but instead both the charge/orbital and the magnetic ordering get incommensurable,
oncemore resembling the observations in the perovskite manganites.
[1] D. Senff et al., Phys. Rev. B 71, 024425 (2005).
[2] D. Senff et al., cond-mat 0512305, submitted to PRL.