Fluctuations of spiral spins in the double-perovskite ferrite YBaCuFeO₅
Yu-Hui Liang1, Chun-Hao Lai1, K. C Rule3, C.-W. Wang4, S. Yano4, F.-C. Chou5, Chao-Hung Du1,2*
1Physics, Tamkang University, New Taipei City, Taiwan
2Research Center for X-ray Science, Tamkang University, New Taipei City, Taiwan
3Australian Center for Neutron Scattering, ANSTO, NSW, Australia
4Neutron Group, National Synchrotron Radiation Research Center, Taiwan
5Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
* Presenter:Chao-Hung Du, email:chd0312@gmail.com
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. This finding also calls for the analytically modeling for the further understanding the mechanism behind.

Keywords: Inelastic neutron scattering, spiral magnetism, magnon dispersion