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- Title
- THE STRUCTURAL AND MAGNETIC STABILITY OF SELECT FERROUS HEUSLER SYSTEMS
- Creator
- Hasier, John J.
- Date
- 2017, 2017-05
- Description
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Heusler based functional or smart materials are a deep well of solutions to future energy, heat transport and mechanization problems. The half...
Show moreHeusler based functional or smart materials are a deep well of solutions to future energy, heat transport and mechanization problems. The half-metallic ferromagnetic nature of these crystalline intermetallic compounds is the source of their extraordinary properties. The loss of this magnetic ordering places limits on the range of application temperatures making knowledge of the Curie point of these novel materials essential for understanding of their limitations. High throughput continuous wavelet transform spectrum analysis of magnetic balance data generated on a custom modified Setaram Setsys Evolution 16/18 Differential Scanning Calorimeter- Differential Thermal Analyzer with simultaneous Thermogravimetric Analyzer was performed on select Fe, Co and Mn based Heusler compounds. The phase stability of Co-Fe-Si compounds is explored in relation to the high-Curie Temperature Co2FeSi and Fe2CoSi compounds via generation of equilibrium ternary isothermal phase diagrams at 1160 C and 800 C to enable greater control of the microstructure for future thermomechanically processed bulk smart device fabrication.
Ph.D. in Materials Science and Engineering
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- Title
- SPIN TRANSPORT AND SPIN-ORBIT TORQUES IN ANTIFERROMAGNETS
- Creator
- Saglam, Hilal
- Date
- 2019
- Description
-
The electron has two fundamental degrees of freedom, i.e., charge and spin. Existing semiconductor electronics utilizes the charge degree of...
Show moreThe electron has two fundamental degrees of freedom, i.e., charge and spin. Existing semiconductor electronics utilizes the charge degree of freedom in its functionalities. Spintronics seeks, in addition, to exploit the spin degree of freedom, which can suggest promising pathways for low-power and faster operations. In conventional spintronics devices, ferromagnetic materials (FMs) have been employed as active components. However, it has recently been recognized that antiferromagnetic materials (AFMs) can also play an active role in spintronic devices. Antiferromagnets have several advantages over ferromagnets; for instance, they have net zero magnetization so that they are invisible to external magnetic fields. Also, they show resonances in the terahertz frequency range. Towards this end, this thesis focuses on spin transport and spin-orbit torques in various antiferromagnetic materials. With respect to the former, I demonstrated that spin currents can be transmitted efficiently through a metallic antiferromagnet FeMn. I detect two distinctly different spin transport regimes, which can be associated with electronic and magnonic spin currents. With respect to the latter, I investigated a possible correlation between two important spintronics concepts, i.e., spin-orbit torques and exchange bias since the ferromagnetic/antiferromagnetic interface is crucial for both phenomena. The measured spin Hall angles suggest that these two effects are independent of each other, although it is worthy to mention that there are still strong spin-orbit torques even when the antiferromagnet is directly exchange coupled to the ferromagnet. Furthermore, I discuss anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in another metallic antiferromagnet, FeRh, which undergoes a temperature driven antiferromagnetic-to-ferromagnetic phase transition. The temperature dependent results show a drastic suppression of both AHE and ANE signals in the antiferromagnetic phase. Interestingly, these non-vanishing signals are opposite in sign compared to their ferromagnetic counterparts, which can suggest changes of inherent symmetries in the electronic structure of FeRh across its magnetic phase transition.
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