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Temperature dependence of the hyperfine parameters of maghemite and Al-substituted maghemites

Author
Organization
Abstract
Synthetic aluminum-substituted maghemite samples, gamma-(AlyFe1-y)(2)O-3, with y=0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by Mossbauer spectroscopy at 8 K and in the range 80 K to 475 K at steps of 25 K. The spectra have been analysed as a superposition of two sextets composed of asymmetrical Lorentzians. The A- and B-site isomer shifts were constrained as: delta(A)=delta(B)-0.12 mm/s. From the temperature dependence of delta(B) it was possible to determine the characteristic Mossbauer temperature and the intrinsic shift. Both quantities clearly increase with increasing Al content, at least up to 10 mole%. The temperature dependence of the A-and B-sites hyperfine fields could be satisfactorily reproduced using the molecular-field theory assuming an antiparallel spin configuration. The exchange integrals were found as: J(AB)=-25 K; J(AA)=-18 K and J(BB)=-3 K. The hyperfine fields show a crossing in the vicinity of 300 K as a result of the relatively strong A-A interaction. The Curie temperature for the non-substituted sample was calculated to be 930 K and decreases to 765 K for the sample with 15 mol% Al. The gradual decrease of the saturation value of the A-site hyperfine field with increasing Al substitution and the constancy of this quantity for the B sites, suggest that the Al cations occupy the B sites.
Keywords
FIELD, SOIL, BRAZILIAN OXISOLS, IRON-OXIDES, MOSSBAUER, GAMMA-FE2O3 SMALL PARTICLES

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Chicago
de Costa, GM, Eddy De Grave, LH Bowen, PMA de Bakker, and Robert Vandenberghe. 1995. “Temperature Dependence of the Hyperfine Parameters of Maghemite and Al-substituted Maghemites.” Physics and Chemistry of Minerals 22 (3): 178–185.
APA
de Costa, GM, De Grave, E., Bowen, L., de Bakker, P., & Vandenberghe, R. (1995). Temperature dependence of the hyperfine parameters of maghemite and Al-substituted maghemites. PHYSICS AND CHEMISTRY OF MINERALS, 22(3), 178–185.
Vancouver
1.
de Costa G, De Grave E, Bowen L, de Bakker P, Vandenberghe R. Temperature dependence of the hyperfine parameters of maghemite and Al-substituted maghemites. PHYSICS AND CHEMISTRY OF MINERALS. 1995;22(3):178–85.
MLA
de Costa, GM, Eddy De Grave, LH Bowen, et al. “Temperature Dependence of the Hyperfine Parameters of Maghemite and Al-substituted Maghemites.” PHYSICS AND CHEMISTRY OF MINERALS 22.3 (1995): 178–185. Print.
@article{193464,
  abstract     = {Synthetic aluminum-substituted maghemite samples, gamma-(AlyFe1-y)(2)O-3, with y=0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by Mossbauer spectroscopy at 8 K and in the range 80 K to 475 K at steps of 25 K. The spectra have been analysed as a superposition of two sextets composed of asymmetrical Lorentzians. The A- and B-site isomer shifts were constrained as: delta(A)=delta(B)-0.12 mm/s. From the temperature dependence of delta(B) it was possible to determine the characteristic Mossbauer temperature and the intrinsic shift. Both quantities clearly increase with increasing Al content, at least up to 10 mole\%. The temperature dependence of the A-and B-sites hyperfine fields could be satisfactorily reproduced using the molecular-field theory assuming an antiparallel spin configuration. The exchange integrals were found as: J(AB)=-25 K; J(AA)=-18 K and J(BB)=-3 K. The hyperfine fields show a crossing in the vicinity of 300 K as a result of the relatively strong A-A interaction. The Curie temperature for the non-substituted sample was calculated to be 930 K and decreases to 765 K for the sample with 15 mol\% Al. The gradual decrease of the saturation value of the A-site hyperfine field with increasing Al substitution and the constancy of this quantity for the B sites, suggest that the Al cations occupy the B sites.},
  author       = {de Costa, GM and De Grave, Eddy and Bowen, LH and de Bakker, PMA and Vandenberghe, Robert},
  issn         = {0342-1791},
  journal      = {PHYSICS AND CHEMISTRY OF MINERALS},
  keyword      = {FIELD,SOIL,BRAZILIAN OXISOLS,IRON-OXIDES,MOSSBAUER,GAMMA-FE2O3 SMALL PARTICLES},
  language     = {eng},
  number       = {3},
  pages        = {178--185},
  title        = {Temperature dependence of the hyperfine parameters of maghemite and Al-substituted maghemites},
  url          = {http://dx.doi.org/10.1007/BF00202298},
  volume       = {22},
  year         = {1995},
}

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