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Booth, C. H.; Bridges, F.; Kwei, G. H.; Lawrence, J. M.; Cornelius, Andrew; Neumeier, J. J.

doi:10.1103/physrevb.57.10440

Cited by 143 publications

(166 citation statements)

References 48 publications

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“…Extensive experimental evidence exists for lattice effects in these materials. For example, anomalous increases in crystallographic Debye-Waller factors [11] and, equivalently, PDF peak-widths [12] and XAFS Debye-Waller factors [13,14] at the MI transition; an oxygen isotope dependence to T c [15,16]; thermal conductivity [17,18] and transport measurements above T c interpreted in terms of polaron dynamics [19,20]. These results can be consistently interpreted if charges localize as small polarons above T c .…”

Section: Introductionsupporting

confidence: 49%

Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure

et al. 1999

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We have measured atomic pair distribution functions (PDF) of La 1,x Ca x MnO 3 using high energy x-ray diffraction. This approach yields accurate PDFs with very high real-space resolution. It also avoids potential pitfalls from the more usual neutron measurements that magnetic scattering is present in the measurement, that the neutron scattering length of manganese is negative leading to partial cancellation of PDF peaks, and that inelasticity effects might distort the resulting PDF. We have used this to address the following questions which do not have a satisfactory answer: (1) What are the amplitudes and natures of the local Jahn-Teller and polaronic distortions in the CMR region. (2) Is the ground-state of the ferromagnetic metallic phase delocalized or polaronic. (3) As one moves away from the ground-state, by raising temperature or decreasing doping, towards the metal insulator transition, how does the state of the material evolve?

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Section: Introductionsupporting

confidence: 49%

Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure

et al. 1999

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“…Somewhat surprisingly, it is necessary to include these Mn-H paths to allow for a reasonable S 0 2 value (we use S 0 2 =0.72 from CaMnO 3 ). 48 The peak at 2.8 Å is due to 4 Mn-C's. The temperature dependence of the Fourier transforms (FTs) is very clear in the raw data, with a sharp drop in amplitude near 330 K. A comparison of the high-spin mole fractions, obtained from the relative amplitudes of the two nearneighbor Mn-C shells and from the solid state magnetism, is excellent, Figure 13.…”

Section: Methodsmentioning

confidence: 99%

Supramolecular Catalysis of Orthoformate Hydrolysis in Basic Solution: An Enzyme-Like Mechanism

2008

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Abstract. Magnetic susceptibility measurements and X-ray data confirm that tert-butyl substituted manganocenes [(Me 3 C) n C 5 H 5-n ] 2 Mn (n= 1, 2) follow the trend previously observed with the methylated manganocenes, i.e., electron donating groups attached to the Cp ring stabilize the low-spin (LS) electronic ground state relative to Cp 2 Mn and exhibit higher spin-crossover (SCO) temperatures.However, introducing three CMe 3 groups on each ring gives a temperature invariant high-spin (HS) state manganocene. The origin of the high-spin state in [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Mn is due to the significant bulk of the [1,2,4-(Me 3 C) 3 C 5 H 2 ] -ligand, which is sufficient to generate severe inter-ring steric strain that prevents the realization of the low-spin state. Interestingly, the spin transition in [1,3-(Me 3 C) 2 C 5 H 3 ] 2 Mn is accompanied by a phase transition resulting in a significant irreversible hysteresis (∆T c = 16 K). This structural transition was also observed by extended X-ray absorption fine-structure (EXAFS) measurements. Magnetic susceptibility studies and X-ray diffraction data on SiMe 3 substituted 2 manganocenes [(Me 3 Si) n C 5 H 5-n ] 2 Mn (n= 1, 2, 3) show high-spin configuration in these cases. Although tetra-and hexasubstituted manganocenes are high-spin at all accessible temperatures, the disubstituted manganocenes exhibit a small low-spin admixture at low temperature. In this respect it behaves similarily to [(Me 3 C)(Me 3 Si)C 5 H 3 ] 2 Mn, which has a constant low-spin admixture up to 90 K and then gradually converts to high-spin. Thermal spin-trapping can be observed for [(Me 3 C)(Me 3 Si)C 5 H 3 ] 2 Mn on rapid cooling.

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“…Local distortions above T¢ would inhibit hopping of charge between Mn atoms thereby increasing the resistivity. Recent local structure studies using XAFS (Booth et al, 1996;Sub'as et al, 1997;Meneghini et al, 1997;Booth et al, 1998a;Sub'as et al, 1998;Booth et al, 1998b) and neutron pair distribution analysis (Billinge et al, 1996;Louca et al, 1997) have now shown convincingly that such local distortions do exist for the range of concentrations for which CMR is observed• Here we compare data for Ca and Ba substituted LaMnOa.…”

Section: Introductionmentioning

confidence: 92%

“…Each plot is a straight line, even though the steepness of the magnetic transition is not the same for all samples. This indicates that a clear relationship exists between local structure and magnetism for both dopants, but the exact nature of this coupling is still not known Finally, the X-ray absorption edge is surprisingly sharp (Booth et al, 1998b) in view of the assumption of distinct Mn +3 and Mn +4 sites. If the localization of the e e electrons on Mn +3 changes, there should be a small edge shift but experimentally it is less than -t-0.03 eV from 50-320K for CMR samples (Fig.…”

Section: Aa2(t) (A2d(t) + A2fp) 2 = --Adat=(t)mentioning

confidence: 99%

“…The main Mn edge in these materials is sharp (,-,6eV) (Booth et al, 1998b) The edge position is often determined from the derivative peak: however for these samples the derivative peak is broad and the inflection point on the edge moves relative to the half-height energy as the composition is changed. Consequently the average edge position cannot be measured accurately this way.…”

Section: Methodsmentioning

confidence: 99%

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Temperature/magnetization-induced distortions in the local structure of substituted LaMnO₃

Bridges

Cao

Anderson

et al. 1999

J Synchrotron Radiat

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Much of the work carried out on the Colossal Magnetoresistive (CMR) materials has been interpreted using the double exchange (DE) model which assumes Mn +a and Mn +4 sites exist. In addition, to explain the large MR in films, it has recently been suggested that local distortions in the form of polarons, must also be present above the ferromagnetic transition temperature Tc; such distortions have now been observed. We present XAFS data which illustrate the magnitude of these distortions and show that the change in the Mn-O distortions correlates well with the magnetization. However the absorption edge is sharp and shows no structure indicative of two valence states, Mn +3 and Mn +4, in either the polaron regime or in the charge-ordered material.

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Lattice effects inLa1−xCaxMnO

Cited by 143 publications

References 48 publications

Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure

Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure

Supramolecular Catalysis of Orthoformate Hydrolysis in Basic Solution: An Enzyme-Like Mechanism

Temperature/magnetization-induced distortions in the local structure of substituted LaMnO₃

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Lattice effects inLa1−xCaxMnO

Cited by 143 publications

References 48 publications

Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure

Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure

Supramolecular Catalysis of Orthoformate Hydrolysis in Basic Solution: An Enzyme-Like Mechanism

Temperature/magnetization-induced distortions in the local structure of substituted LaMnO3

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Temperature/magnetization-induced distortions in the local structure of substituted LaMnO₃