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Zusammenfassung:
We present a comprehensive study on PrCaFeO4 using macroscopic methods,
neutron and x-ray diffraction, as well as inelastic neutron scattering.
One polycrystalline and two single-crystal samples were investigated
exhibiting structural phase transitions from a high-temperature
tetragonal phase to an intermediate orthorhombic phase (space group
Bmeb) at 510 degrees C (783 K). At approximately 240 K a second
structural phase transition takes place into the space group Pccn where
the tilt axis of the FeO6 octahedra changes from the [100] to the < 110
> directions. Due to strong diffuse scattering at high temperatures
neutron powder diffraction can only safely state that T-N is above 330
K. PrCaFeO4 exhibits a magnetic spin-flop phase transition where the
magnetic moments turn from the b axis to the c axis upon cooling.
However, the transition temperatures and the width of this magnetic
transition are strikingly different between the investigated samples,
suggesting a strong influence from the real structure. Indeed, a
significant difference in the oxygen content was deduced by
single-crystal x-ray diffraction. The magnon dispersion was studied by
inelastic neutron scattering revealing a nearest-neighbor interaction
comparable to that in LaSrFeO4 but with smaller anisotropy gaps. A clear
interlayer dispersion was observed resulting from the structural
distortions and the relief of geometrical frustration due to the
orthorhombic splitting.
