Fan, Meng (2017-05). Microstructure and Functionalities in Epitaxial Manganites Based Vertically Aligned Nanocomposite Thin Films. Doctoral Dissertation. Thesis uri icon

abstract

  • Vertically aligned nanocomposite (VAN) presents as a novel material platform for creating high-quality self-assembled, nano-pillars of one phase in matrix of another structures. In the past decade, extensive efforts have been devoted and demonstrated the great potential of VAN thin films in enabling novel and enhanced functionalities. Mixed valence La1-xSrxMnO3 (LSMO) exhibits unique magnetic and transport properties, promising for spintronic device applications. In this dissertation, novel and enhanced magnetic and electrical functionalities including low-field magnetoresistance (LFMR), magnetic exchange bias (EB), etc., are explored using VAN design, with a focus on the LSMO based materials. By selecting CeO2 and CuO as the secondary phases and optimizing the growth conditions, large and tunable LFMR in a wide temperature region has been achieved in LSMO: CeO2 and LSMO: CuO VAN films. Detailed analysis indicate that the phase boundaries, the secondary phase domain size, and the strain states in the films contribute to the enhanced LFMR in different temperature regions. Perpendicular exchange bias (PEB) is desired in next-generation memories to offer perpendicular unidirectional magnetic anisotropy. By confining ferromagnetic (FM) and antiferromagnetic (AFM) hetero-interfaces coupling in the vertical direction, strong PEB effect are demonstrated in the LSMO: LaFeO3 VAN films. The microstructures, PEB behavior correlated with the composition variation, strain tuning and cooling field effect are analyzed. A spin-glass (SG) state at the vertical interfaces is ascribed to be responsible for the remarkable PEB here. Conventional VAN films tend to present random distributed pillars in matrix structure. Achieving spatial ordering is timely demanded. Here, a novel approach are introduced for one-step self-organization growth of VAN films with long range ordering by substrate nano-templating. The SrTiO3 (001) substrates with surface nanopatterns of alternating chemical terminations developed by thermal treatment are demonstrated to be effective for selective growth of well-ordered VAN structures, using LSMO: CeO2 as a prototype. Remarkable enhanced magnetic and transport properties is achieved for the templated films. The studies in this dissertation exploited the capability of the unique VAN structures in enhancing the magnetic and transport performance of LSMO based nanocomposite materials. Great enhanced LFMR, PEB as well as well-ordered nanostructures have been achieved. The VAN design provide a powerful way in enabling novel and enhanced functionalities, promising for spintronic devices applications.
  • Vertically aligned nanocomposite (VAN) presents as a novel material platform for creating high-quality self-assembled, nano-pillars of one phase in matrix of another structures. In the past decade, extensive efforts have been devoted and demonstrated the great potential of VAN thin films in enabling novel and enhanced functionalities. Mixed valence La1-xSrxMnO3 (LSMO) exhibits unique magnetic and transport properties, promising for spintronic device applications. In this dissertation, novel and enhanced magnetic and electrical functionalities including low-field magnetoresistance (LFMR), magnetic exchange bias (EB), etc., are explored using VAN design, with a focus on the LSMO based materials.

    By selecting CeO2 and CuO as the secondary phases and optimizing the growth conditions, large and tunable LFMR in a wide temperature region has been achieved in LSMO: CeO2 and LSMO: CuO VAN films. Detailed analysis indicate that the phase boundaries, the secondary phase domain size, and the strain states in the films contribute to the enhanced LFMR in different temperature regions.

    Perpendicular exchange bias (PEB) is desired in next-generation memories to offer perpendicular unidirectional magnetic anisotropy. By confining ferromagnetic (FM) and antiferromagnetic (AFM) hetero-interfaces coupling in the vertical direction, strong PEB effect are demonstrated in the LSMO: LaFeO3 VAN films. The microstructures, PEB behavior correlated with the composition variation, strain tuning and cooling field effect are analyzed. A spin-glass (SG) state at the vertical interfaces is ascribed to be responsible for the remarkable PEB here.

    Conventional VAN films tend to present random distributed pillars in matrix structure. Achieving spatial ordering is timely demanded. Here, a novel approach are introduced for one-step self-organization growth of VAN films with long range ordering by substrate nano-templating. The SrTiO3 (001) substrates with surface nanopatterns of alternating chemical terminations developed by thermal treatment are demonstrated to be effective for selective growth of well-ordered VAN structures, using LSMO: CeO2 as a prototype. Remarkable enhanced magnetic and transport properties is achieved for the templated films.

    The studies in this dissertation exploited the capability of the unique VAN structures in enhancing the magnetic and transport performance of LSMO based nanocomposite materials. Great enhanced LFMR, PEB as well as well-ordered nanostructures have been achieved. The VAN design provide a powerful way in enabling novel and enhanced functionalities, promising for spintronic devices applications.

publication date

  • May 2017