Interplay of spin and orbital ordering in the layered colossal magnetoresistance manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}(0.5{<=}x{le}1.0)
The crystallographic and magnetic phase diagram of the n=2 layered manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} in the region x{>=}0.5 has been studied using temperature-dependent neutron powder diffraction. The magnetic phase diagram reveals a progression of ordered magnetic structures generally paralleling that of three-dimensional (3D) perovskites with similar electronic doping: A (0.5{<=}x{le}0.66){yields}C (0.75{<=}x{le}0.90){yields}G (0.90{<=}x{le}1.0). However, the quasi-2D structure amplifies this progression to expose features of manganite physics uniquely accessible in the layered systems: (i) a ''frustrated'' region between the A and C regimes where no long-range magnetic order is observed; (ii) magnetic polytypism arising from weak interbilayer magnetic exchange in the type-C regime; and (iii) a tetragonal-to-orthorhombic phase transition whose temperature evolution directly measures ordering of d{sub 3y{sup 2}-r{sup 2}} orbitals in the a-b plane. This orbital-ordering transition is precursory to type-C magnetic ordering, where ferromagnetic rods lie parallel to the b axis. These observations support the notion that e{sub g} orbital polarization is the driving force behind magnetic spin ordering. Finally, in the crossover region between type-C and type-G states, we see some evidence for the development of local type-C clusters embedded in a type-G framework, directly addressing proposals of similar short-range magnetic ordering in highly doped La{sub 1-x}Ca{sub x}MnO{sub 3} perovskites.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40205663
- Journal Information:
- Physical Review B, Vol. 62, Issue 22; Other Information: Othernumber: PRBMDO000062000022015096000001; 017045PRB; PBD: 1 Dec 2000; ISSN 0163-1829
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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