Structural and magnetic states in layered manganites: An expanding view of the phase diagram Page: 4 of 15
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STRUCTURAL AND MAGNETIC STATES IN LAYERED MANGANITES:
AN EXPANDING VIEW OF THE PHASE DIAGRAM
J.F. MITCHELL, J.E. MILLBURN, C. LING, D.N. ARGYRIOU AND H. N. BORDALLO*
Materials Science Division, Argonne National Laboratory, Argonne, IL 60439
*Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL 60439
Colossal magnetoresistive (CMR) manganites display a spectacular range of structural,
magnetic, and electronic phases as a function of hole concentration, temperature, magnetic field,
etc. Although the bulk of research has concentrated on the 3-D perovskite manganites, the
ability to study anisotropic magnetic and electronic interactions made available in reduced
dimensions has accelerated interest in the layered Ruddlesden-Popper (R-P) phases of the
manganite class. The quest for understanding the coupling among lattice, spin, and electronic
degrees of freedom (and dimensionality) is driven by the availability of high quality materials.
In this talk, we will present recent results on synthesis and magnetic properties of layered
manganites from the La2,,Sr+2XMn207 series in the Mn"*-rich regime x > 0.5. This region of the
composition diagram is populated by antiferromagnetic structures that evolve from the A-type
layered order to G-type "rocksalt" order as x increases. Between these two regimes is a wide
region (0.7 < x < 0.9) where an incommensurate magnetic structure is observed. The IC
structure joins spin canting and phase separation as a mode for mixed-valent manganites to
accommodate FM/AF competition. Transport in these materials is dominated by highly
insulating behavior, although a region close to x = 0.5 exhibits metal-nonmetal transitions and an
extreme sensitivity to oxygen content. We suggest two possible explanations for this transport
behavior at doping just above x=0.5: localization by oxygen defects or charge ordering of
Colossal magnetoresistive oxides have captured the interest of condensed matter
scientists because of their strong coupling among spin, lattice, and charge degrees of freedom.
The delicate balance of energy scales among these three aspects of manganite physics gives rise
to the dramatic properties observed in the manganites, including insulator-metal (IM) transitions,
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Mitchell, J. F.; Millburn, J. E.; Ling, C.; Argyriou, D. N. & Bordallo, H. N. Structural and magnetic states in layered manganites: An expanding view of the phase diagram, article, January 5, 2000; Illinois. (digital.library.unt.edu/ark:/67531/metadc703211/m1/4/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.