Sign Reversal of the Mn-O Bond Compressibility in La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} below {ital T}{sub {ital C}}: Exchange Striction in the Ferromagnetic State
- Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Center for Material Science and Engineering, ECT 9.102, University of Texas at Austin, Austin, Texas 78712-1063 (United States)
The crystal structure of the layered perovskite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} has been studied under hydrostatic pressure up to {approximately}6kbar, in the paramagnetic and ferromagnetic states, with neutron powder diffraction. The compressibility of the Mn-O apical bonds in the double layer of MnO{sub 6} octahedra changes sign from the paramagnetic insulator (PI) to the ferromagnetic metal (FM) state; in the FM state the Mn-O-Mn linkage between MnO{sub 2} planes expands under applied pressure, whereas they contract in the PI state. This counterintuitive behavior is interpreted in terms of {ital exchange striction,} which reflects the competition between super and double exchange. An increase of the Mn moment with applied pressure in the FM state is consistent with a positive dT{sub C}/dP, as well as a cant angle {theta}{sub 0} between the magnetizations of neighboring MnO{sub 2} sheets that decreases with pressure. {copyright} {ital 1997} {ital The American Physical Society}
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 502720
- Journal Information:
- Physical Review Letters, Vol. 78, Issue 8; Other Information: PBD: Feb 1997
- Country of Publication:
- United States
- Language:
- English
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