Coupling of Lattice Dynamics to Spin Transitions in La1-xSrxCoO3

2002 ◽  
Vol 718 ◽  
Author(s):  
Despina Louca ◽  
J. L. Sarrao
Keyword(s):  
Function Analysis ◽  
Dynamic Structure ◽  
Spin Configuration ◽  
Spin Lattice ◽  
Intermediate Spin ◽  
Pair Density ◽  
Variable Spin ◽  
Local Lattice ◽  
Jahn Teller ◽  
Spin Transitions

AbstractLa1-xSrxCoO3 is distinct because of its unique spin transitions subjecting the system to variable spin-lattice coupling. Pair density function analysis provided strong evidence for local lattice distortions associated with a Jahn-Teller active mode that is directly correlated to the change in the magnetic/conductive states of this system. The presence of Jahn-Teller distortions also serves as an indication for the intermediate spin configuration. Measurements of the dynamic structure function, S(Q, ω), showed that several phonon peaks fluctuate with carrier density and temperature. Such changes were not seen in an otherwise identical structure, LaAlO3. These phonon peaks are quite unusual and are most likely due to localized modes that appear to be dispersionless.

Evidence for a Jahn-Teller Distortion in the CMR Layered Manganite La1.4Sr1.6Mn2O7

1997 ◽  
Vol 494 ◽  
Author(s):  
Despina Louca ◽  
G. H. Kwei ◽  
J. F. Mitchell
Keyword(s):  
Function Analysis ◽  
Layered Compounds ◽  
Crystallographic Structure ◽  
Teller Distortion ◽  
Atomic Pair ◽  
Pair Density ◽  
Jahn Teller ◽  
Pulsed Neutron ◽  
Jahn Teller Distortion ◽  
Comparable Magnitude

ABSTRACTThe changes with temperature in the crystallographic structure of the two-layered La1.4Sr1.6Mn2O7, are on average quite small but the atomic pair density function analysis of pulsed neutron diffraction data shows that the lattice is locally distorted in accordance with the change in the transport properties. In particular, while no Jahn-Teller (JT) distortion is expected in the layered compounds because the octahedral bilayers are almost cubic, lattice distortions attributed to a large JT effect are present and are of comparable magnitude as in the cubic perovskite system. This could in turn explain the similarity in their properties. The number of the JT distorted sites is reduced with temperature concomitantly with the decrease in resistivity of the ab-plane.

Theory of Tunneling Assisted Electron Spin–Lattice Relaxation

1971 ◽  
Vol 49 (12) ◽  
pp. 1620-1629 ◽  
Author(s):  
K. P. Lee ◽  
D. Walsh
Keyword(s):  
Lattice Relaxation ◽  
Zeeman Splitting ◽  
Spin Lattice Relaxation ◽  
Phonon Coupling ◽  
Orbital State ◽  
Strongly Coupled ◽  
Practical Applications ◽  
Spin Lattice ◽  
Jahn Teller ◽  
Temperature Relaxation

It is shown for an Eg orbital state and a tunneling splitting which is small compared with the Zeeman splitting that a strong Jahn–Teller coupling can lead to an enhancement of the direct spin–phonon coupling by several orders of magnitude. By comparing the theory with low temperature relaxation measurements on Cu2+ in a double nitrate the magnitude of several of the significant parameters associated with the Jahn–Teller problem is derived. A T2g orbital state strongly coupled to t2g modes of vibration can also have a strong spin–phonon coupling; the corresponding situation is briefly discussed.The strong coupling of the vibronic states to the lattice and the considerable range in the strength of this coupling have a number of practical applications.

Local Order in Amorphous Fe-alloys

2002 ◽  
Vol 754 ◽  
Author(s):  
Despina Louca ◽  
Kyungsoo Ahn ◽  
V. Ponnambalam ◽  
S. J. Poon
Keyword(s):  
Atomic Structure ◽  
Short Range ◽  
Function Analysis ◽  
Local Order ◽  
Ferromagnetic Coupling ◽  
Volume Contraction ◽  
Glass Forming ◽  
Structure Changes ◽  
Pair Density ◽  
Fe Alloys

ABSTRACTThe pair density function analysis of neutron diffraction data of Fe-based metallic glasses of the Zr and Mo series shows how the local atomic structure changes by chemical substitution. The results provide evidence for short-range chemical reorganization accompanied by a volume contraction that could in turn be associated with stronger glass forming ability. While the existence of chemical short-range topological ordering is enhanced in both systems by alloying with a transition metal such as Mn, locally, the atomic structure changes in a way that corresponds to an increase in bonding interactions. The shortening of bonds is also related to volume contraction that can in turn be associated with a reduction of the ferromagnetic coupling of the Fe sublattice and to a lower Curie transition temperature.

scholarly journals Real-Space Description of Dynamics of Liquids

2018 ◽  
Vol 2 (4) ◽  
pp. 22 ◽  
Author(s):  
Takeshi Egami
Keyword(s):  
Materials Science ◽  
Inelastic Neutron Scattering ◽  
Spin Dynamics ◽  
Dynamic Structure ◽  
Real Space ◽  
Inelastic Neutron ◽  
Superfluid 4He ◽  
Complex Materials ◽  
Pair Density ◽  
Space Description

In strongly disordered matter, such as liquids and glasses, atomic and magnetic excitations are heavily damped and partially localized by disorder. Thus, the conventional descriptions in terms of phonons and magnons are inadequate, and we have to consider spatially correlated atomic and spin dynamics in real-space and time. Experimentally this means that the usual representation of dynamics in terms of the dynamic structure factor, S(Q, E), where Q and E are the momentum and energy exchanges in scattering, is insufficient. We propose a real-space description in terms of the dynamic pair-density function (DyPDF) and the Van Hove function (VHF) as an alternative, and discuss recent results on superfluid 4He by inelastic neutron scattering and water by inelastic X-ray scattering. Today much of the objects of research in condensed-matter physics and materials science are highly complex materials. To characterize the dynamics of such complex materials, the real-space approach is likely to become the mainstream method of research.

The Local Atomic Structure of Lal-xSrxCoO3: Effects Induced by The Spin-State and Non-Metal to Metal Transitions

1997 ◽  
Vol 494 ◽  
Author(s):  
Despina Louca ◽  
J. L. Sarrao ◽  
G. H. Kwei
Keyword(s):  
Bond Length ◽  
Charge Carriers ◽  
Thermal Excitation ◽  
Metallic State ◽  
Structural Effects ◽  
Spin Configuration ◽  
Bond Lengths ◽  
Structural Distortions ◽  
Pair Density ◽  
Pulsed Neutron

ABSTRACTThe pair density function (PDF) used in the analysis of pulsed neutron diffraction data of La1-xSrxCoO3 revealed new structural effects which are correlated to the susceptibility and transport transitions. The transition in the spin configuration of the Co ions from the low-spin (LS) to the high-spin (HS) state in the Co perovskite oxides can potentially induce structural distortions due to the coupling of the spin to the lattice and charge. The ground state of the pure compound, LaCoO3, is in the LS state and is non-magnetic. A transition occurs to the HS state at ∼ 50 K as indicated from the susceptibility measurements due to the thermal excitation of electrons to the eg level. The CoLSO6 octahedra associated with the Co ions in the LS configuration are distinguished from the CoHSO6 octahedra with the Co in the HS configuration because the CoLS-O bond length is shorter than the CoHS-O distance due to the different size of the corresponding Co ions. Such bond lengths are clearly identified in the local structure between 15 – 300 K. This finding is in contrast to the average structure which shows only one type of bond length in this temperature range but two types of bond lengths are suggested at considerably higher temperatures. This suggests that whereas the LS and HS CoO6-octahedra coexist, they are randomly distributed in the crystal lattice at lower temperatures and become ordered at higher temperatures. The introduction of charge carriers in the structure does not eliminate the coexistence of both the LS and HS states, indicating that with the transition to the ferromagnetic metallic state, the spin configuration is not entirely of the HS character and structural inhomogeneities are present.

scholarly journals Open-Bundle Structure as the Unfolding Intermediate of Cytochrome c′ Revealed by Small Angle Neutron Scattering

Biomolecules ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 95
Author(s):  
Takahide Yamaguchi ◽  
Kouhei Akao ◽  
Alexandros Koutsioubas ◽  
Henrich Frielinghaus ◽  
Takamitsu Kohzuma
Keyword(s):  
Neutron Scattering ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Function Analysis ◽  
Dynamic Structure ◽  
Random Coil ◽  
Radius Of Gyration ◽  
Intermediate Structure ◽  
Cyt C ◽  
Bundle Structure

The dynamic structure changes, including the unfolding, dimerization, and transition from the compact to the open-bundle unfolding intermediate structure of Cyt c′, were detected by a small-angle neutron scattering experiment (SANS). The structure of Cyt c′ was changed into an unstructured random coil at pD = 1.7 (Rg = 25 Å for the Cyt c′ monomer). The four-α-helix bundle structure of Cyt c′ at neutral pH was transitioned to an open-bundle structure (at pD ~13), which is given by a numerical partial scattering function analysis as a joint-clubs model consisting of four clubs (α-helices) connected by short loops. The compactly folded structure of Cyt c′ (radius of gyration, Rg = 18 Å for the Cyt c′ dimer) at neutral or mildly alkaline pD transited to a remarkably larger open-bundle structure at pD ~13 (Rg = 25 Å for the Cyt c′ monomer). The open-bundle structure was also supported by ab initio modeling.

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