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Neutron scattering studies on magnetic excitations in complex ordered manganites

Abstract

This thesis deals with magnetic excitations in three different Manganese oxides, single-layered LaSrMnO{sub 4}, charge- and orbital-ordered La{sub 1/2}Sr{sub 3/2}MnO{sub 4}, and multiferroic TbMnO{sub 3}, which are studied by means of inelastic neutron scattering. The properties of the first system, LaSrMnO{sub 4}, are governed by the complex interplay of orbital, spin, and lattice degrees of freedom typical for the physics of manganites. The magnetic low-temperature behavior is quite unusual, and the comprehensive analysis of the spin-wave spectrum of LaSrMnO{sub 4} suggests a heterogenous ground state with ferromagnetic orbital polarons embedded in an antiferromagnetic background. The doped system La{sub 1/2}Sr{sub 3/2}MnO{sub 4} exhibits a stable charge- and orbital-ordered state, which today is discussed very controversially, as it is of great relevance for the colossal increase of electric conductivity at the metal-insulator transition in perovskite manganites. Analyzing the spin-wave dispersion of the ordered state, we find an excellent agreement with classical predictions by Goodenough and reject a recent alternative proposal. The different strength of the ferromagnetic and antiferromagnetic exchange in the CE-type ordering leads to the conclusion that the magnetic state has to be considered as a weak AFM coupling of stable FM elements. This thesis is further supported by the thermal  More>>
Authors:
Publication Date:
Sep 15, 2007
Product Type:
Thesis/Dissertation
Report Number:
INIS-DE-0453
Resource Relation:
Other Information: TH: Diss.
Subject:
36 MATERIALS SCIENCE; MANGANESE OXIDES; LAYERS; SPIN WAVES; COUPLING; CORRELATIONS; MAGNONS; COLLECTIVE EXCITATIONS; PHONONS; MAGNETIC FIELDS; INELASTIC SCATTERING; TEMPERATURE DEPENDENCE; MAGNETIC PROPERTIES; NEUTRON DIFFRACTION; M1-TRANSITIONS; LANTHANUM OXIDES; STRONTIUM OXIDES; TERBIUM OXIDES; VIBRATIONAL STATES; ANTIFERROMAGNETISM; FERROMAGNETISM; ANISOTROPY; ORTHORHOMBIC LATTICES; DISPERSION RELATIONS
OSTI ID:
21084245
Research Organizations:
Koeln Univ. (Germany). Mathematisch-Naturwissenschaftliche Fakultaet
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
TRN: DE08FA343
Availability:
Commercial reproduction prohibited; INIS; OSTI as DE21084245
Submitting Site:
DEN
Size:
219 pages
Announcement Date:
Oct 09, 2008

Citation Formats

Senff, D. Neutron scattering studies on magnetic excitations in complex ordered manganites. Germany: N. p., 2007. Web.
Senff, D. Neutron scattering studies on magnetic excitations in complex ordered manganites. Germany.
Senff, D. 2007. "Neutron scattering studies on magnetic excitations in complex ordered manganites." Germany.
@misc{etde_21084245,
title = {Neutron scattering studies on magnetic excitations in complex ordered manganites}
author = {Senff, D}
abstractNote = {This thesis deals with magnetic excitations in three different Manganese oxides, single-layered LaSrMnO{sub 4}, charge- and orbital-ordered La{sub 1/2}Sr{sub 3/2}MnO{sub 4}, and multiferroic TbMnO{sub 3}, which are studied by means of inelastic neutron scattering. The properties of the first system, LaSrMnO{sub 4}, are governed by the complex interplay of orbital, spin, and lattice degrees of freedom typical for the physics of manganites. The magnetic low-temperature behavior is quite unusual, and the comprehensive analysis of the spin-wave spectrum of LaSrMnO{sub 4} suggests a heterogenous ground state with ferromagnetic orbital polarons embedded in an antiferromagnetic background. The doped system La{sub 1/2}Sr{sub 3/2}MnO{sub 4} exhibits a stable charge- and orbital-ordered state, which today is discussed very controversially, as it is of great relevance for the colossal increase of electric conductivity at the metal-insulator transition in perovskite manganites. Analyzing the spin-wave dispersion of the ordered state, we find an excellent agreement with classical predictions by Goodenough and reject a recent alternative proposal. The different strength of the ferromagnetic and antiferromagnetic exchange in the CE-type ordering leads to the conclusion that the magnetic state has to be considered as a weak AFM coupling of stable FM elements. This thesis is further supported by the thermal evolution of the ordered state, revealing anisotropic correlations and the close competition of FM and AFM correlations above the Neel transition, as well as by the doping dependence of the charge- and orbital-ordered state, which is interpreted on the basis of a different response of the magnetic system with respect to additional electrons or holes. In the orthorhombic perovskite TbMnO{sub 3} the electric polarization is closely coupled to the magnetic degrees of freedom via a complex, non-collinear magnetic ordering. Precisely characterizing the different magnon excitations allows to identify all relevant modes of the ferroelectric phase, which for systems with strong electromagnetic coupling were predicted to contain a new type of collective excitations - strongly hybridized phonon-magnon vibrations - which have not been observed experimentally before. The temperature and momentum dependence, as well as the response of the different modes to an external magnetic field, is reported in detail, and the results strengthen recent theoretical concepts explaining the strong magnetoelectric coupling in the fascinating class of multiferroic oxides. (orig.)}
place = {Germany}
year = {2007}
month = {Sep}
}