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 Du^1,2*

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 T_N~ 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