Fluctuations of spiral spins in the double-perovskite ferrite YBaCuFeO₅

Chao-Hung Du^1,2*, Yu-Hui Liang¹, Chun-Hao Lai¹, K. C Rule³, C.-W. Wang⁴, S. Yano⁴

¹Department of Physics, Tamkang University, Tamsui Dist., Taiwan
²Research Center for X-ray Science, Tamkang University, Tamsui Dist., Taiwan
³Australian Center for Neutron Scattering, ANSTO, Australia
⁴Neutron Group, National Synchrotron Radiation Research Center, Taiwan

* Presenter:Chao-Hung Du, email:chd@gms.tku.edu.tw

The double-perovskites exhibit many fundamentally interesting chemical and physical properties; they can have electronic structures raging from insulator, metallic, halfmetallic to superconductor; they can also have different magnetic order parameters; or even simultaneously containing the multiple order parameters, such as multiferroicity. The double-perovskite ferrite YBaCuFeO₅ (YBCFO) is such a material to show a rich phase diagram. Using a modified floating zone growth method, we are able to grow the high-quality single crystal of YBCFO for the detailed studies using neutron scattering. Using neutron powder and single crystal diffraction, YBCFO was observed to show a commensurate-incommensurate magnetic transition at TN~ 175 K. This incommensurate phase develops into a spiral spin ordering with a propagating vector along c-axis. Further using neutron TOF and triple-axis spectrometers, we observed that the spiral spin ordering shows a very unusual dispersion behavior as a function of temperature, which could be the consequence of a strong coupling between the spin moments of Fe³⁺ and Cu²⁺ and their dz orbitals.

Keywords: spiral spin ordering, magnetic excitation, inelastic neutron scattering