26.08.2021 - 14:15
On 26 August at 14:15 Helina Seemen will defend her doctoral thesis “Atomic layer deposition and microscopic analysis of magnetically and electrically polarizable thin solid films” for obtaining the degree of Doctor of Philosophy (in Materials Science).
Associate Professor Aile Tamm, University of Tartu
Professor Kaupo Kukli, University of Tartu
Professor Emeritus Jyrki Räisänen, University of Helsinki (Finland)
Senior Research Fellow Olga Volobujeva, Tallinn University of Technology
The constant development of technology has been possible thanks to the development of new materials and technological methods. However, there remains a continual demand for new novel materials or material combinations with new or improved functionalities for electronics and information technology development to continue. One such attractive type of material is thin solid film material with multiferroic properties. Such materials have both ferroelectric and ferromagnetic properties, i.e. they are polarized by external electric and magnetic fields and can maintain polarization even if they are not continuously subjected to an external electric or magnetic field. Multiferroic materials are also attractive because they could be used in new generation memory devices since electric and magnetic fields could be used to store and read data.
Therefore, novel material combinations that were expected to show magnetic and electric polarization under the influence of external field at room temperature were created and characterized in the Thesis. For this, potentially ferromagnetic and ferroelectric materials (mainly metal oxides) were combined into multilayer structures and mixed films using the atomic layer deposition method. The atomic layer deposition method was used to fabricate thin solid films because it is already widely used in the field of microelectronics and allows to deposit films with high quality and controlled thickness.
The results showed that, in addition to the material combinations, the properties of the materials expectedly depended on the phase composition and deposition recipe. The metastable phases of several metal oxides were successfully stabilized, which affected the magnetic and electrical properties of the deposited films. Most of the created materials showed ferromagnetic-like behaviour by demonstrating non-linear magnetization and hysteresis under the influence of an external magnetic field. Few materials behaved similarly to the ferroelectric material under the influence of an external electric field.
W. Ostwaldi 1, aud B103