Charge transfer transitions in multiferroic BiFeO3 and related ferrite insulators / Pisarev R. V.,Moskvin A. S.,Kalashnikova A. M.,Rasing Th. // PHYSICAL REVIEW B. - 2009. - V. 79, l. 23.

ISSN/EISSN:

1098-0121 / 1550-235X

Type:

Article

Abstract:

The optical response of the technologically interesting multiferroic BiFeO3 and related complex iron oxides, having high Neel or Curie temperature, is studied in the wide spectral range from 0.6 up to 5.8 eV by means of spectroscopic ellipsometry. The investigated iron oxides have different crystal symmetry with FeO6 octahedral and FeO4 tetrahedral centers distorted to a certain degree. One of the two groups of materials includes BiFeO3, ErFeO3, Y.95Bi.05FeO3, alpha-Fe2O3, Fe2-xGaxO3, and Fe3BO6 in which iron Fe3+ ions occupy only octahedral centrosymmetric or noncentrosymmetric positions and distortions range of 1-20 \%. The second group includes LiFe5O8, BaFe12O19, Sm3Fe5O12, and Ca2Fe2O5 in which Fe3+ ions occupy both octahedral and tetrahedral positions with a rising tetra/ortho ratio. We show that in the spectral range up to similar to 3.7 eV, the optical response is dominated by p-d charge transfer (CT) transitions, while at E>3.7 eV both p-d and d-d CT transitions are revealed. At variance with several previous investigations, we present a correct and unified assignment of different dipole-allowed and dipole-forbidden CT transitions. All the ferrites investigated are CT insulators with the band gap determined by a dipole-forbidden p-d CT transition t(1g) -> t(2g), forming a similar to 2.5 eV band on the tail of a strong 3.0 eV band assigned to dipole-allowed p-d CT transitions t(2u) (pi) -> t(2g) in octahedral FeO6 centers. A noticeable enhancement of the optical response in BiFeO3 at similar to 4 eV as compared with other related iron oxides is attributed to CT transitions within the Bi-O bonds. We report an observation of unexpected midinfrared CT bands in calcium ferrite Ca2Fe2O5 and an enhanced structureless spectral weight in a wide range below the main CT bands in BiFeO3 with a remarkable smearing of the fundamental absorption edge. All these anomalies are assigned to CT instabilities accompanied by a self-trapping of p-d CT excitons and nucleation of electron-hole droplets. The optical detection of this CT instability agrees with the observation of a metal-insulator transition in bismuth ferrite.

Author keywords:

IRON BORATE GDFE3(BO3)(4); ELECTRONIC-STRUCTURE; MAGNETIC-PROPERTIES; 2ND-HARMONIC GENERATION; OPTICAL-PROPERTIES; OXIDE COMPOUNDS; HIGH-PRESSURES; POLARIZATION; TEMPERATURE; FERROMAGNET

DOI:

10.1103/PhysRevB.79.235128

Web of Science ID:

ISI:000267699500055

Соавторы в МНС:

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Другие поля

Поле	Значение
Month	JUN
Publisher	AMER PHYSICAL SOC
Address	ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA
Language	English
Article-Number	235128
EISSN	1550-235X
Keywords-Plus	IRON BORATE GDFE3(BO3)(4); ELECTRONIC-STRUCTURE; MAGNETIC-PROPERTIES; 2ND-HARMONIC GENERATION; OPTICAL-PROPERTIES; OXIDE COMPOUNDS; HIGH-PRESSURES; POLARIZATION; TEMPERATURE; FERROMAGNET
Research-Areas	Physics
Web-of-Science-Categories	Physics, Condensed Matter
ResearcherID-Numbers	Rasing, Theo/D-5207-2012 Kalashnikova, Alexandra/C-7821-2014
ORCID-Numbers	Kalashnikova, Alexandra/0000-0001-5635-6186
Funding-Acknowledgement	Russian Foundation for Basic Research; Dutch Nanotechnology Network NanoNed; de Nederlandse Organisatie voor Wetenschappelijk Onderzoek NWO; INTAS; FP7 {[}N214810]
Funding-Text	We thank A. F. van Etteger and A. J. Toonen for technical support and V. V. Pavlov for the help in the data analysis. We thank A. M. Balbashov for orthoferrite single crystals and L. N. Bezmaternykh for iron borate single crystals. This work is supported by the Russian Foundation for Basic Research, the Dutch Nanotechnology Network NanoNed, de Nederlandse Organisatie voor Wetenschappelijk Onderzoek NWO, INTAS, and FP7 under the grant N214810 (FANTOMAS).
Number-of-Cited-References	85
Usage-Count-Last-180-days	8
Usage-Count-Since-2013	97
Journal-ISO	Phys. Rev. B
Doc-Delivery-Number	466XU