Magnetic domain formation in La1-xSrxMnO3 nanowires studied with resonant soft x-ray scattering

Chen, Xiaoqian

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https://hdl.handle.net/2142/72899 Copy

Description

Title

Magnetic domain formation in La1-xSrxMnO3 nanowires studied with resonant soft x-ray scattering

Author(s)

Chen, Xiaoqian

Issue Date

2015-01-21

Director of Research (if dissertation) or Advisor (if thesis)

Abbamonte, Peter M.

Doctoral Committee Chair(s)

Eckstein, James N.

Committee Member(s)

• Abbamonte, Peter M.
• Peng, Jen-Chieh
• Ryu, Shinsei

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• phase separation
• nanowires
• colossal magnetoresistive (CMR) manganite
• resonant soft x-ray scattering

Abstract

Phase separation and nanoscale fluctuation in strongly correlated systems are known to exist around their phase transitions. They are directly connected to the ordering mechanisms that cause magnetic orders, density waves, or superconductivity. These orders likely have their origins rooted in the differences in the correlation lengths of the underlying competing orders. Therefore studying materials in size that is comparable to these fluctuations can disentangle the complexity of the mechanism. To serve this purpose, we studied magnetic domain formation in La(1-x)Sr(x)MnO3 (LSMO) nanowires. In theory, a 1D ferromagnetic wire is not capable of forming a single domain without an applied field. Therefore, it is meaningful to study how the spatial confinement contributes towards magnetic domain formation. In particular, how its phase transition differs from that of the bulk, how magnetization density distributes inside the nanowires, and what the domain sizes are inside the nanowires. For this purpose, we fabricated arrays of nanowires 30nm tall, 80nm wide from LSMO thin films using e-beam lithography. Magnetization measurements performed on these wires showed an anomalous increase in the magnetization at temperatures far below the Curie point of the bulk material. Around this temperature, coexisting phase separated domains were observed with transport measurements. To understand these observations, resonant soft x-ray scattering studies were performed on Mn L-absorption-edge with an applied field and varying polarization at different temperatures. Our results suggest nontrivial magnetic domain formation inside the nanowires that may be phase separated at low temperature. In the end, we suggest a phase retrieval model to reconstruct the real space evolution of the magnetization density in nanowires to better understand the magnetic systems measured with resonant soft x-ray scattering.

Graduation Semester

2014-12

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http://hdl.handle.net/2142/72899

Copyright and License Information

Copyright 2014 Xiaoqian Chen

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