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Title: Hybrid excitations due to crystal field, spin-orbit coupling, and spin waves in LiFePO 4

Here, we report on the spin waves and crystal field excitations in single crystal LiFePO 4 by inelastic neutron scattering over a wide range of temperatures, below and above the antiferromagnetic transition of this system. In particular, we find extra excitations below T N = 50 K that are nearly dispersionless and are most intense around magnetic zone centers. Furthermore, we show that these excitations correspond to transitions between thermally occupied excited states of Fe 2 + due to splitting of the S = 2 levels that arise from the crystal field and spin-orbit interactions. These excitations are further amplified by the highly distorted nature of the oxygen octahedron surrounding the iron atoms. Above T N , magnetic fluctuations are observed up to at least 720 K, with an additional inelastic excitation around 4 meV, which we attribute to single-ion effects, as its intensity weakens slightly at 720 K compared to 100 K, which is consistent with the calculated cross sections using a single-ion model. This theoretical analysis, using the MF-RPA model, provides both detailed spectra of the Fe d shell and estimates of the average ordered magnetic moment and T N . By applying the MF-RPA model to amore » number of existing spin-wave results from other Li M PO 4 ( M = Mn , Co, and Ni), we are able to obtain reasonable predictions for the moment sizes and transition temperatures.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [1]
  1. Iowa State Univ., Ames, IA (United States). Dept. of Materials Science and Engineering (DMSE)
  2. Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab., ISIS Neutron Source
  3. Helmholtz-Zentrum Berlin (HZB), (Germany). German Research Centre for Materials and Energy
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division
Publication Date:
Report Number(s):
IS-J 9306
Journal ID: ISSN 2469-9950; PRBMDO; TRN: US1702604
Grant/Contract Number:
AC02-07CH11358; AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 95; Journal Issue: 10; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Ames Laboratory (AMES), Ames, IA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1355753
Alternate Identifier(s):
OSTI ID: 1346433; OSTI ID: 1361313