Structural chemistry and electronic properties of the n = 3 Ruddlesden-Popper phases Ca{sub 4}Mn{sub 2}FeO{sub 9.75} and Sr{sub 4}Mn{sub 2}FeO{sub 9.80}
- Univ. of Oxford (United Kingdom)
The room-temperature crystal structures of the n = 3 Ruddlesden-Popper phases Ca/{sub 4}-Mn{sub 2}FeO{sub 9.75} and Sr{sub 4}Mn{sub 2}FeO{sub 9.80} have been refined from neutron and X-ray powder diffraction data. Both adopt space group I4/mmm with (a,c) = (Ca, 3.73683(1), 27.0860(1) {angstrom}), (Sr, 3.83393(1), 27.8148(1) {angstrom}). In both compounds the cation site at the center of the perovskite blocks is preferentially occupied by Fe (Ca, Mn:Fe = 0.424:0.576(4)), and the anion vacancies are found around this site. The occupied anion sites show static disorder in Ca{sub 4}Mn{sub 2}FeO{sub 9.75} but not in Sr{sub 4}Mn{sub 2}FeO{sub 9.80}. Both compounds are electrical insulators which order antiferromagnetically at T{sub N} = 75 K (Ca) or 90 K (Sr). Susceptibility and M(H) data suggest that not all the Mn and Fe cations take part in the long-range magnetic ordering, and there is evidence of a spin glass transition in both compounds at {approximately}11 K. The magnetic structure of Ca{sub 4}Mn{sub 2}FeO{sub 9.75} at 5 K has been determined by neutron diffraction. No ordered moment was detected on the Mn/Fe site at the center of the perovskite blocks; 0.74(1) {micro}{sub B} per transition metal cation was measured at the sites on the block edges. Possible causes of magnetic frustration in this crystal structure are considered. Ca{sub 4}Mn{sub 2}FeO{sub 9.75} has a magnetoresistance of {minus}4% at 137 K in a 14 T field.
- OSTI ID:
- 338384
- Journal Information:
- Chemistry of Materials, Vol. 11, Issue 3; Other Information: PBD: Mar 1999
- Country of Publication:
- United States
- Language:
- English
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