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Magnetic imaging of topological antiferromagnets
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Title
Magnetic imaging of topological antiferromagnets
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Sass
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Paul
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1989-
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Paul Sass
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Wu
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Weida
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Weida Wu
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Advisory Committee
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chair
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Vanderbilt
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David
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David Vanderbilt
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internal member
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Chakhalian
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Jak
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Jak Chakhalian
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Advisory Committee
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Lath
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Amit
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Amit Lath
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internal member
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Yang
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Junjie
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Junjie Yang
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Rutgers University
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School of Graduate Studies
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theses
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ETD doctoral
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2020
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2020-10
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2020
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English
Abstract
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Antiferromagnetic order in topological materials has recently become incredibly important in the quest for exotic phenomena such as high temperature quantum anomalous Hall effect, quantized magnetoelectric effect, chiral edge modes, and Weyl and Dirac semimetal states. However, there is a lack of understanding of the antiferromagnetic domains and domain walls in these materials. The control of these domain walls or spin textures is not only important for controlling these states, but also crucial for spintronic applications of antiferromagnets. Despite many efforts, it has been challenging to directly visualize antiferromagnetic domains or domain walls with nanoscale resolution, especially in magnetic field.
In this thesis, we show magnetic imaging of domain walls in several uniaxial antiferromagnets including the topological insulator MnBi$_2$Te$_4$ family and the Dirac semimetal EuMnBi$_2$, using cryogenic magnetic force microscopy (MFM). Our MFM results reveal higher magnetic susceptibility inside the domain walls than in domains. Domain walls in these antiferromagnets form randomly with strong thermal and magnetic field dependence.
Through this application, we also present microscopic evidence of the persistence of uniaxial A-type antiferromagnetic order to the surface layers of MnBi$_2$Te$_4$ single crystals using magnetic force microscopy. Our results reveal termination-dependent magnetic contrast across both surface step edges and domain walls, which can be screened by thin layers of soft magnetism. The robust surface A-type order is further corroborated by the observation of termination-dependent surface spin-flop transitions, which have been theoretically proposed decades ago and not observed in natural antiferromagnets until now.
The direct visualization of these domain walls and domain structures in magnetic field not only provides key ingredients for understanding the electronic properties of the antiferromagnetic topological insulator MnBi$_2$Te$_4$, but also opens both a new way of exploring intrinsic surface metamagnetic transitions in natural antiferromagnets and a new path toward control and manipulation of domain walls or spin textures in functional antiferromagnets.
In this thesis, we show magnetic imaging of domain walls in several uniaxial antiferromagnets including the topological insulator MnBi$_2$Te$_4$ family and the Dirac semimetal EuMnBi$_2$, using cryogenic magnetic force microscopy (MFM). Our MFM results reveal higher magnetic susceptibility inside the domain walls than in domains. Domain walls in these antiferromagnets form randomly with strong thermal and magnetic field dependence.
Through this application, we also present microscopic evidence of the persistence of uniaxial A-type antiferromagnetic order to the surface layers of MnBi$_2$Te$_4$ single crystals using magnetic force microscopy. Our results reveal termination-dependent magnetic contrast across both surface step edges and domain walls, which can be screened by thin layers of soft magnetism. The robust surface A-type order is further corroborated by the observation of termination-dependent surface spin-flop transitions, which have been theoretically proposed decades ago and not observed in natural antiferromagnets until now.
The direct visualization of these domain walls and domain structures in magnetic field not only provides key ingredients for understanding the electronic properties of the antiferromagnetic topological insulator MnBi$_2$Te$_4$, but also opens both a new way of exploring intrinsic surface metamagnetic transitions in natural antiferromagnets and a new path toward control and manipulation of domain walls or spin textures in functional antiferromagnets.
Subject
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Topic
Domain walls
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Physics and Astronomy
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Rutgers University Electronic Theses and Dissertations
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ETD_11129
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1 online resource (xiv, 108 pages) : illustrations
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Ph.D.
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Includes bibliographical references
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School of Graduate Studies Electronic Theses and Dissertations
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rucore10001600001
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Identifier
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doi:10.7282/t3-2q8z-yv02
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Rights
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The author owns the copyright to this work.
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Name
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Sass
GivenName
Paul
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Permission or license
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2020-09-08 16:44:45
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Paul Sass
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Rutgers University. School of Graduate Studies
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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Copyright protected
Availability
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Open
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Permission or license
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