Abstract
We have carried out inelastic neutron scattering experiments to study magnetic excitations in the ordered double perovskite Ca2FeReO6. We have found a well-defined magnon mode with a bandwidth of ∼50 meV below the ferrimagnetic ordering temperature (Tc∼520 K), similar to the previously studied Ba2FeReO6. The spin excitation is gapless for most temperatures within the magnetically ordered phase. However, a spin gap of ∼10 meV opens up below ∼150 K, which is well below the magnetic ordering temperature but coincides with a previously reported metal-insulator transition and onset of structural distortion. The observed temperature dependence of the spin gap provides strong evidence for ordering of Re orbitals at ∼150 K, in accordance with an earlier proposal put forward by K. Oikawa et al. based on neutron diffraction [J. Phys. Soc. Jpn. 72, 1411 (2003)10.1143/JPSJ.72.1411] as well as recent theoretical work by Lee and Marianetti [Phys. Rev. B 97, 045102 (2018)10.1103/PhysRevB.97.045102]. The presence of separate orbital and magnetic ordering in Ca2FeReO6 suggests weak coupling between spin and orbital degrees of freedom and hints at a subdominant role played by spin-orbit coupling in describing its magnetism. In addition, we observed only one well-defined magnon band near the magnetic zone boundary, which is incompatible with simple ferrimagnetic spin waves arising from Fe and Re local moments but suggests a strong damping of the Re magnon mode.
| Original language | English |
|---|---|
| Article number | 214433 |
| Journal | Physical Review B |
| Volume | 98 |
| Issue number | 21 |
| DOIs | |
| State | Published - Dec 19 2018 |
Funding
Work at the University of Toronto was supported by the Natural Science and Engineering Research Council (NSERC) of Canada. B.C.J. and T.W.N. are supported by the Research Center Program of IBS (Institute for Basic Science) in Korea (IBS-R009-D1). B.Y. would like to acknowledge support from the Ontario Graduate Scholarship. C.W. and N.H. are supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2013R1A1A2009777). Use of the Canadian Neutron Beam Centre at Chalk River Laboratories is supported by the National Research Council (NRC) of Canada and Atomic Energy of Canada Limited (AECL). Use of the Spallation Neutron Source at Oak Ridge National Laboratory is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.