PhD on topological insulators/magnetic systems for spin-charge conversion
Partners involved: UMPhy (lead), C2N, SOLEIL
Diana SHE has started her PhD in October 2020.
Her main objective will be to study spin to charge current conversion from a BiSb topological insulator. In particular she will optimize growth conditions of BiSb by molecular beam epitaxy(MBE) topped with ferromagnetic half-metals (MnBi, MnSb). The latter are 100% spin polarized at Fermi level and may reduce the current shunting as well. Moreover, she will focus on characterizing topological surface states by ARPES (Angle Resolved PhotoEmision Spectroscopy). And finally she will perform spin transport measurements in order to qualify spin-charge conversion in BiSb.
PhD on ultrafast spintronic
Partners involved: SPEC (lead), UMPhy, SOLEIL
Zixin LI has started his PhD in October 2020. In his PhD work, he will aim at assessing the potential of new spintronic components at the picosecond timescale.
Multiferroïc materials are the focus of an intense research effort due to the significant technological interest of multifunctional materials as well as the rich fundamental physics stemming from the coupling of various order parameters. Among all multiferroïcs, BiFeO3 (BFO) is a material of choice because its two ordering temperatures (ferroelectric FE and AF) are well above room temperature. In addition, a large magneto-electric coupling has been demonstrated in single crystals as well as in thin films. Multiferroïcs are therefore a prototypical playground to understand and master the underlying fundamental mechanisms of different interacting order parameters and in particular antiferromagnetism (AF) whose internal dynamics directly lies the terahertz (THz) and sub-terahertz (sub-THz) ranges. However, due to the lack of net magnetization, controlling AF distributions has been rather challenging. In multiferroïcs, the AF order is coupled to a net polarization and may be controlled by applying an electric field which is consequently very appealing for the manipulation of this interesting yet rather silent order parameter. On the other hand, recent breakthroughs have demonstrated the efficient effect of spin currents in interacting with the AF order parameter. Thus, current-induced AF control also opens new perspectives in Terahertz magnetization dynamics. One downside of multiferroïcs is that these FE/AF textures can be rather challenging to assess. Second harmonic generation, a non-linear optical approach, has proven to be a powerful and elegant way to image complex multiferroïc textures and to untangle the different contributions at play.
The objectives of his work aim at assessing the time evolution of the multiferroïc texture of BiFeO3 thin epitaxial layers when subjected to various types of ultrafast stimuli such as intense femtosecond light pulses, THz pulses and/or ultrafast spin-current bursts.
PhD on static and dynamic properties of skyrmions in ferrimagnetic systems
Partners involved: LPS (lead), UMPhy, SOLEIL
Sujit kumar PANIGRAPHY has started in November 2020.
Thesis Abstract: ” Magnetic skyrmions, nanobubbles with a fixed chirality, are topological magnetic textures in a sense that no continuous path exists to collapse them toward the uniform ferromagnetic state. While many groups are now able to stabilize them and control their motion with electrical current in ferromagnetic layers, experiments are facing some limits (skyrmions size, limited velocities due to pinning, gyrotropic deflection due to topology). These problems could be overcome using antiferromagnetic situations (e.g. synthetic antiferromagnets, antiferromagnetic samples, or ferrimagnetic samples). In those, the zero magnetization should enable much smaller skyrmions, and the exaltation of magnetization dynamics should increase the skyrmion velocity and cancel the gyrotropic deflexion. The purpose of the Ph.D. is, based on our experience on ferromagnetic skyrmions, to implement skyrmions in such materials and probe their dynamics.”
PhD on non-linear spin-wave dynamics in non-reciprocal spin-wave bus
Partners involved: C2N (lead), SPEC, UMPhy
This PhD is planed to study non-linear spin-wave dynamics in Bi substituted Yttrium Iron Garnet (YIG) thin films grown by PLD at UMPhy [SOUM2018] and in Heusler Co2MnX alloys (X = Ge, Si) grown by MBE at Institut Jean Lamour, Nancy, both families of materials having record damping values in the low 10-4.