scholarly journals Structural and Magnetic States in Layered Manganites: An Expanding View of the Phase Diagram

1999 ◽  
Vol 602 ◽  
Author(s):  
J.F. Mitchell ◽  
J.E. Millburn ◽  
C. Ling ◽  
D.N. Argyriou ◽  
H. N. Bordallo
Keyword(s):  
Degrees Of Freedom ◽  
Hole Concentration ◽  
Charge Ordering ◽  
Perovskite Manganites ◽  
Electronic Interactions ◽  
Colossal Magnetoresistive ◽  
Reduced Dimensions ◽  
Incommensurate Magnetic Structure ◽  
Extreme Sensitivity ◽  
Magnetic States

AbstractColossal 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 La2−2xSr1+2xMn2O7 series in the Mn4+-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 Mn3+/Mn4+ sites.

Electron Incoherent Scattering from Nanometer-Sized Charge Ordering in Colossal Magnetoresistive La2/3ca1/3mnO3

2001 ◽  
Vol 7 (S2) ◽  
pp. 434-435
Author(s):  
J. M. Zuo
Keyword(s):  
Phase Separation ◽  
Electron Diffraction ◽  
Degrees Of Freedom ◽  
Complex Oxides ◽  
Charge Ordering ◽  
Phase Separations ◽  
Length Scales ◽  
Colossal Magnetoresistive ◽  
Electronic Phase Separation ◽  
Electronic Phase

Electronic phase separation is known to occur in complex oxides ranging from high-Tc superconductors to colossal magnetoresisitive (CMR) manganites. Accumulating experimental evidences show regions of temperature dependent conducting and insulating regions, whose exact origin is unknown. Theoretically, it is has been shown that these systems are unstable from the strong interplay between the lattice, charge and spin degrees of freedom.The key to understand the electronic phase separation in complex oxides is the structure. Electron diffraction is the only probe that covers the length scales from angstroms to microns. Characterization at these length scales is critical (electronic phase separations are typically about nanometers in sizes). Traditionally, electron diffraction has been played important roles in discovering the new types of phase separations, but has contributed little to the quantitative understanding. The reason is the strong interaction of electrons with matter, which gives both strong inelastic background and multiple scattering.

Effects of Localized Holes on Charge Transport, Local Structure and Spin Dynamics in the Metallic State of CMR La1-xCaxMnO3

1997 ◽  
Vol 494 ◽  
Author(s):  
R. H. Heffner ◽  
M. F. Hundley ◽  
C. H. Booth
Keyword(s):  
Degrees Of Freedom ◽  
Spin Dynamics ◽  
Muon Spin ◽  
Functional Dependence ◽  
Spatial Inhomogeneity ◽  
Metallic State ◽  
Colossal Magnetoresistive ◽  
Spatially Inhomogeneous ◽  
Inhomogeneous Spin ◽  
X Ray Absorption

ABSTRACTWe review resistivity, x-ray-absorption fine-structure (XAFS) and muon spin relaxation (μSR) data which provide clear evidence for localized holes causing polaron distortion and unusual spin dynamics below Tc in “colossal magnetoresistive” (CMR) La1-xCaxMnO3. Resistivity measurements for x=0.33 under an applied field H have shown that ln[ρ(H,T)] α -M, where M is the magnetization. The XAFS data show a similar functional dependence for the polaron distortions on M. The data from these two measurements are interpreted in terms of some fraction of the available holes x remaining localized and some increasing fraction becoming delocalized with increasing M. Finally, this polaron-induced spatial inhomogeneity yields anomalously slow, spatially inhomogeneous spin dynamics below Tc, as shown in the μSR data. These experiments individually probe the charge, lattice and spin degrees of freedom in this CMR system and suggest that the polarons retain some identity even at temperatures significantly below Tc.

Pressure effects on charge-ordering transitions in Perovskite manganites

1997 ◽  
Vol 55 (12) ◽  
pp. 7549-7556 ◽  
Author(s):  
Y. Moritomo ◽  
H. Kuwahara ◽  
Y. Tomioka ◽  
Y. Tokura
Keyword(s):  
Charge Ordering ◽  
Pressure Effects ◽  
Perovskite Manganites ◽  
Ordering Transitions

Magnetic dynamics in colossal magnetoresistive perovskite manganites

1998 ◽  
Vol 356 (1742) ◽  
pp. 1563-1575 ◽  
Author(s):  
T. G. Perring ◽  
G. Aeppli ◽  
S. M. Hayden ◽  
Y. Tokura ◽  
Y. Moritomo ◽  
...  
Keyword(s):  
Perovskite Manganites ◽  
Magnetic Dynamics ◽  
Colossal Magnetoresistive

The Charge Ordering Behavior of Colossal Magnetoresistive (CMR) Layered Compounds La2-2xSr1+2xMn2O7 (x = 0.5 ∼ 0.6)

2001 ◽  
Vol 7 (S2) ◽  
pp. 410-411
Author(s):  
Z. P. Luo ◽  
D. J. Miller ◽  
J. F. Mitchell
Keyword(s):  
Physical Properties ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Charge Ordering ◽  
Layered Compounds ◽  
Hole Doping ◽  
Ion Milling ◽  
Colossal Magnetoresistive ◽  
Cold Stage

In colossal magnetoresistive (CMR) materials, large changes in physical properties stem from the interplay between charge ordering (CO) coupled with orbital and magnetic orderings. Thus detailed microstructural studies are important in understanding these changes in physical properties. In-situTEM observation is a very useful approach to study CO transitions in these CMR compounds. We have recently studied the CO behavior of the three-dimensional perovskite Nd1/2Sr1+2xMnO3. in this work, we report the CO of two-dimensional naturally layered compounds La2-2xSr1+2xMn2O7 (327 phase), where x is the hole doping level and varies from 0.5 to 0.6 in this work.Thin foil TEM specimens were prepared from polycrystalline bulk samples by conventional thinning and ion milling method at liquid N2 temperature. The in-situ TEM work was carried out in the Electron Microscopy Center at Argonne National Laboratory using a Philips CM30 with a liquid N2 cold stage, and a Hitachi H-9000 with liquid He cold stage.

Twinning Mlcrostructure and Charge Ordering in the Colossal Magnetoresistive Manganite Nd1/2Sr1/2MnO3

2000 ◽  
Vol 6 (S2) ◽  
pp. 404-405
Author(s):  
Z. P. Luo ◽  
D. J. Miller ◽  
J. F. Mitchell
Keyword(s):  
Microstructural Characterization ◽  
Thin Foil ◽  
High Resistance State ◽  
Charge Ordering ◽  
Ion Milling ◽  
Colossal Magnetoresistive ◽  
Superlattice Structure ◽  
Resistance State ◽  
A Charge ◽  
Ordered State

Charge ordering (C.O.) in the colossal magnetoresistive (CMR) manganites gives rise to an insulating, high-resistance state. This charge ordered state can be melted into a low-resistance metallic-like state by the application of magnetic field. Thus, the potential to attain high values of magnetoresistance with the application of small magnetic fields may be aided by a better understanding of the charge-ordering phenomenon. This study focused on microstructural characterization in Nd1/2Sr1/2MnO3. In Nd1/2Sr1/2MnO3, the nominal valence of Mn is 3.5+. On cooling, charge can localize and lead to a charge ordering between Mn 3+ and Mn 4+. The ordering of charge results in a superlattice structure and a reduction in symmetry.Thin foil specimens were prepared from bulk samples by conventional thinning and ion milling (at LN2 temperature) methods. The TEM work was carried out in a Philips CM30 at 300 kV with a Gatan LN2 cold stage, and a JEM 4000EX with a resolution of 0.17 nm at 400 kV for HREM observation.

Probing the underlying charge ordering: Ruthenium-doped Sm1−xSrxMnO3 perovskite manganites

2001 ◽  
Vol 89 (4) ◽  
pp. 2232-2236 ◽  
Author(s):  
A. Maignan ◽  
C. Martin ◽  
M. Hervieu ◽  
B. Raveau ◽  
J. Hejtmanek
Keyword(s):  
Charge Ordering ◽  
Perovskite Manganites
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