Evidence for magnetic dimerons in the anisotropic bilayer system La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}: An EXAFS study

Journal Article · Thu Feb 01 00:00:00 EST 2007 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.75.064417· OSTI ID:20976688

O'Brien, T A; Bridges, F; Downward, L ^[1]; Mitchell, J F; Zheng, H ^[2]

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1. Physics Department, University of California, Santa Cruz, California 95064 (United States)
2. Argonne National Laboratory, Argonne, Illinois 60439 (United States)

A temperature-dependent EXAFS investigation of La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}, with x rays polarized parallel to the c axis and in the ab plane, has shown an extremely sharp and anisotropic jump in the broadening {sigma} of the Mn-O pair-distribution function (PDF) near the ferromagnetic transition temperature, T{sub c}. This jump is associated with an increase in Jahn-Teller (JT) distortions as the temperature increases through T{sub c}. The data show that changes in {sigma}{sup 2} as T is lowered below T{sub c} is linearly correlated with the sample magnetization, and that there is a break in the slope of this correlation when the sample is {approx}80% magnetized, consistent with the recently proposed dimeron model. A JT distortion clearly exists well above T{sub c} and some distortions still remain for a range of temperatures below T{sub c}. In agreement with recent work on the La{sub 1-x}Ca{sub x}MnO{sub 3} (LCMO) system, the data indicate that two types of distorted sites must occur; one is associated with the hole charge carriers (two-site polaron called a dimeron) and has a very small distortion/site; the second is associated with unpaired electron sites and has a similar distortion/site as observed for corresponding sites in LCMO. Furthermore, the broadening of the Mn-O PDF shows a second and more subtle increase above T{sub c} near T{sup *}{approx_equal}250 K, a change in structure that correlates well with features in several other experiments.

• OSTI ID: 20976688
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 75, Issue 6; Other Information: DOI: 10.1103/PhysRevB.75.064417; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
ANISOTROPY
CHARGE CARRIERS
DISTRIBUTION FUNCTIONS
ELECTRONS
FERROMAGNETIC MATERIALS
FINE STRUCTURE
JAHN-TELLER EFFECT
LANTHANUM COMPOUNDS
MAGNETIZATION
POLARONS
STRONTIUM COMPOUNDS
TEMPERATURE DEPENDENCE
TRANSITION TEMPERATURE
X RADIATION
X-RAY SPECTROSCOPY