Neutron scattering investigations of spinel ferrimagnets: symmetry and magnetoelastic domain wall patterning

The interplay and coupling of distinct order parameters, such as between magnetic order and superconductivity in cuprates or between spin and lattice distortions in type-II multiferroics present some of the most complex problems in condensed matter physics and materials science. Even in situations where the local physics behind such couplings is well described, unexpected behaviors can arise on the mesoscale where local symmetries are broken by defects such as domain-walls, which are ubiquitous features of ordered phases. My thesis work involves an extended series of neutron and X-ray diffraction and thermodynamic measurements on ferrimagnetic spinel materials (Mn3O4 , MnV2O4 , FeV2O4). These materials are known for strong couplings between spin and lattice degrees of freedom which give rise to giant magnetoelastic and magnetodielectric couplings. Chapter 3 reports on a strain-induced nanoscale patterning of magnetoelastic domain walls in the bulk of single crystals of Mn3O4 and MnV2O4 . The domain-walls are observable using small-angle neutron scattering, which allows us to track their organizational behavior as a function of temperature and applied magnetic field. As I demonstrate with parallel single-crystal neutron diffraction and macroscopic measurements, the response of these domain wall patterns to environmental stress and applied magnetic fields greatly influences the large-scale magnetostrictive and magnetodielectric behaviors. Chapter 4 reports on the discovery of a coherent superstructure modulation in MnV2O4 which develops at the same magnetic transitions as the stripe domains. I will also present my work on the spinel multiferroic FeV2O4 , which has a cascade of low-temperature magnetic and structural transitions. Diffraction results in Chapter 5 imply that the high-temperature space-group of this material may need to be reinterpreted. As Chapter 6 shows, small-angle neutron scattering and neutron diffraction uncover increasingly complex mesoscopic behaviors in this material as symmetries are progressively reduced for each low-temperature phase.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Kish, Lazar L.

Contributors dc:contributor

• MacDougall, Gregory J
• Cooper, Stephen L
• Shoemaker, Daniel P
• Stone, Michael

• domain walls
• domains
• neutron scattering
• SANS
• small-angle neutron scattering
• neutron diffraction
• magnetic response
• spinels
• ferrimagnetism
• Mn3O4
• MnV2O4
• FeV2O4

Statement dc:rights

• Copyright 2022 Lazar Kish

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/117619

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F117619