Controlling magnetism in molecular thin films
File(s)
Author(s)
Soukeras, Demetris Liam
Type
Thesis
Abstract
Spintronics have led to a dramatic increase in computer performance from the mid 1990’s, by replacing transistor-based information technologies with logic elements controlled by magnetic properties. The capabilities of computers are inherently limited by the size and performance of spin valves.
To significantly improve the performance of spintronic devices new materials must be discovered. Organic electronics has shown that some organic semiconductors such as metallo-phthalocyanines (MPcs) have many desirable properties including long spin relaxation times. The key requirement for phthalocyanines to be incorporated into spintronic devices is coercivity sufficient to maintain the direction of magnetisation at room temperature while maintaining good spin transport, long spin coherence and chemical stability.
Recent developments in the field have produced thin films of cobalt phthalocyanine with antiferromagnetic coupling up to 100 K. The first strategy proposed to improve these magnetic properties in this thesis is through the synthesis of Rh(II)Pc. DFT simulations predict that Rh(II)Pc could have a strongly antiferromagnetic ground state with a Néel transition above room temperature depending on sufficient overlap of dz2 orbitals.
The second strategy explored in this thesis is utilising mixed phthalocyanine thin films and control of growth conditions to develop an alternating phthalocyanine superstructure. Given the antiparallel arrangement of the spins, CoPc (S=1/2) has no resultant magnetic moment, applications requiring a net magnetisation are thus infeasible. It is here where mixed films have potential. Manganese phthalocyanine (MnPc) and fluorinated cobalt phthalocyanine (F16CoPc) are grown via organic molecular beam deposition (OMBD) to develop thin film superstructures. In-depth GIXD and simulation confirm generation of an alternating MnPc:F16CoPc film. The p-n phthalocyanine superstructure was self-assembled by pushing the growth conditions to the thermodynamic regime, The spectroscopic and magnetic properties of the mixed film are characterised against the single films, and the impact of increased substrate temperature is explored.
To significantly improve the performance of spintronic devices new materials must be discovered. Organic electronics has shown that some organic semiconductors such as metallo-phthalocyanines (MPcs) have many desirable properties including long spin relaxation times. The key requirement for phthalocyanines to be incorporated into spintronic devices is coercivity sufficient to maintain the direction of magnetisation at room temperature while maintaining good spin transport, long spin coherence and chemical stability.
Recent developments in the field have produced thin films of cobalt phthalocyanine with antiferromagnetic coupling up to 100 K. The first strategy proposed to improve these magnetic properties in this thesis is through the synthesis of Rh(II)Pc. DFT simulations predict that Rh(II)Pc could have a strongly antiferromagnetic ground state with a Néel transition above room temperature depending on sufficient overlap of dz2 orbitals.
The second strategy explored in this thesis is utilising mixed phthalocyanine thin films and control of growth conditions to develop an alternating phthalocyanine superstructure. Given the antiparallel arrangement of the spins, CoPc (S=1/2) has no resultant magnetic moment, applications requiring a net magnetisation are thus infeasible. It is here where mixed films have potential. Manganese phthalocyanine (MnPc) and fluorinated cobalt phthalocyanine (F16CoPc) are grown via organic molecular beam deposition (OMBD) to develop thin film superstructures. In-depth GIXD and simulation confirm generation of an alternating MnPc:F16CoPc film. The p-n phthalocyanine superstructure was self-assembled by pushing the growth conditions to the thermodynamic regime, The spectroscopic and magnetic properties of the mixed film are characterised against the single films, and the impact of increased substrate temperature is explored.
Version
Open Access
Date Issued
2023-03-17
Date Awarded
2024-02-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Heutz, Sandrine
Heeney, Martin
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)