Charge and spin coupling in magnetoresistive oxygen-vacancy strontium ferrate SrFeO3–δ

Lee, S.H.; Frawley, T.W.; Yao, C.H.; Lai, Y.C.; Du, Chao-Hung; Hatton, P.D.; Wang, M.J.; Chou, F.C.; Huang, D.J.

Abstract

Using magnetization, conductivity and x-ray scattering measurements, we demonstrate that the giant magnetoresistance of the oxygen-deficient ferrite SrFeO2.875±0.02 is a consequence of the coupling between the charge and spin order parameters and the tetragonal to monoclinic structural distortion. Upon cooling the sample at T sime 120 K we find a shoulder in both field-cool and zero field cool magnetization data and the simultaneous appearance of incommensurate structural satellites observed using x-ray diffraction. These satellites are shown to be due to incommensurate charge ordering with the high temperature delocalized Fe${}^{3.5+}$ ions becoming localized with a charge disproportion forming an incommensurate charge-ordered phase. Strong resonant enhancement of these satellites at the Fe L III absorption edge confirms that this charge ordering is occurring at the Fe(2) sites. Further cooling increases the charge order correlation until T sime 62 K where there is a full structural transition from the tetragonal phase to a mononclinic phase. This causes a jump in the charge order wavevector from an incommensurate value of 0.610 to a commensurate ground state position of 5/8. This first-order structural transition displays considerable hysteresis as well as dramatic reductions in the magnetization, resistivity and magnetoresistance. The transition also causes an antiferromagnetic spin-ordering with a doubled unit cell along the c-axis. Well as observing new commensurate magnetic reflections at the FeIII edge we also observed resonant enhancement at the oxygen K-edge showing considerable hybridization between the Fe 3d and oxygen 2p states at low temperatures. Our results show that the formation of a magnetic long-rage ordered ground state drives the charge ordering from an incommensurate ordering to a commensurate ground state. This is evidence of a strong coupling between the magnetic and charge order parameters which is the basis for the unusual magnetoresistive effects observed at the transition.

Citation

Lee, S., Frawley, T., Yao, C., Lai, Y., Du, C., Hatton, P., …Huang, D. (2016). Charge and spin coupling in magnetoresistive oxygen-vacancy strontium ferrate SrFeO3–δ. New Journal of Physics, 18(9), Article 093033. https://doi.org/10.1088/1367-2630/18/9/093033

• Journal Article Type: Article
• Acceptance Date: Sep 5, 2016
• Online Publication Date: Sep 20, 2016
• Publication Date: Sep 20, 2016
• Deposit Date: Oct 28, 2017
• Publicly Available Date: Dec 11, 2017
• Journal: New Journal of Physics
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 18
• Issue: 9
• Article Number: 093033
• DOI: https://doi.org/10.1088/1367-2630/18/9/093033
• Public URL: https://durham-repository.worktribe.com/output/1345379