RESEARCH
SPIN-TORQUE OSCILLATORS
Nano-scale spin-torque oscillators (STOs) are considered as among the most promising spintronic devices for the next generation of ICT (Information and Communication Technologies) devices. Such nano-oscillators are based on two basic spintronic mechanisms: (i) the magnetoresistive effect, which corresponds to the change of resistance of a spin-valve or a magnetic tunnel junction when the relative orientation of the magnetization in the two magnetic layers is changing, and (ii) the effects of spin-transfer torque, which allows manipulating the magnetization state of a ferromagnetic layer through injection of a spin-polarized current and the transfer of spin angular momentum from conduction electrons to local magnetic moments. The spin-transfer torque can trigger self-sustained oscillations of the magnetization, leading to the concept of nano-scale oscillators (see Figure). The frequency of these oscillations is determined by the excited magnetic mode and can go from 100 MHz to 70 GHz depending on the kind of oscillators (magnetic configuration of the free layer and the polarizer).
In our recent works, we studied the synchronization properties of these oscillators and how they interact in networks. STO networks permit to enhance both their emitted power and the spectral coherence as required for the development of bio-inspired and RF spintronic devices.
Key publications:
1. R. Lebrun, S. Tsunegi, P. Bortolotti, H. Kubota, K. Yakushiji, A. S. Jenkins, M. Romera, A. Fukushima, J. Grollier, S. Yuasa and V. Cros, Nature Communications 8, Numéro d’article: 15825 (2017) “Mutual synchronization of spin torque nano-oscillators through a non-local and tunable electrical coupling”
2. A. S. Jenkins, R. Lebrun, E. Grimaldi, S. Tsunegi, P. Bortolotti, H. Kubota, K. Yakushiji, A. Fukushima, G. de Loubens, O. Klein, S. Yuasa, and V. Cros, Nature Nanotechnology 11 (4), 360 (2016) "Spin-torque resonant expulsion of the vortex core for an efficient radiofrequency detection scheme"
3. R. Lebrun, A. Jenkins, A. Dussaux, N. Locatelli, S. Tsunegi, E. Grimaldi, H. Kubota, P. Bortolotti, K. Yakushiji, J. Grollier, A. Fukushima, S. Yuasa, and V. Cros, Phys. Rev. Lett. 115, 017201 (2015) “Understanding of phase noise squeezing under fractional synchronization of a non-linear spin transfer vortex oscillator”
SPIN-ORBITRONIC
Spin-orbitronics is a novel direction of spintronics that exploits the Spin-Orbit Coupling (SOC) to control and detect magnetic textures and spin-currents, or to stabilize topological objects. These effects are intriguing not only for a fundamental perspectives but also for their potential use in memory applications.
Recently, we studied how these new effects permit to access electrically antiferromagnetic materials with compensated magnetic order. In a bilayer consisting of a heavy metal layer with strong spin-orbit coupling and of an antiferromagnetic layer, the resistance state will depend on the relative orientation of spin-accumulation in the heavy metal and of the direction of the antiferromagnetic order as seen on the figure below. By recording the changes of resistance in the heavy metal layer, we can thus extract the magnetic anisotropies and the phase transition of metallic and insulating antiferromagnets.
Key publications:
1. R. Lebrun, A. Ross, O. Gomonay, S. A. Bender, L. Baldrati, F. Kronast, A. Qaiumzadeh, J. Sinova, A. Brataas, R. A. Duine, and M. Kläui, Communications Physics 2 (50) (2019) “Spin-Hall magnetoresistance as a tool to study (T,H) magnetic phase transitions and anisotropies in insulating antiferromagnets”
2. Hajiri, L. Baldrati, R. Lebrun, M. Filianina, A. Ross, N. Tanahashi, M. Kuroda, W. Gan, T. Onur Mentes, F. Genuzio, A. Locatelli, H. Asano, and M. Klaui, Journal of Physics: Condensed Matter (2019) "Spin structure and spin Hall magnetoresistance of epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO3"
MAGNONICS
Magnonics is an emerging research field dealing with spin-waves. Spin-waves correpond to the dynamic eigenmodes of magnetic materials. They represent the magnetic analogues of light waves and can thus be circularly or linearly polarized. Current researchs study how spin-wave can be controlled by spintronic effects, or couple with other wave excitation such as light or sound waves.
We recently demonstrated that spin-orbit effects can be used to drive and detect the propagating spin-waves of antiferromagnets. Below is an image of the nano-devices we developed with two platinum electrodes for spin-wave injection and detection on top of on antiferromagnetic insulator. The propagation length of the spin-waves can reached up to tens of micrometers, allowing their potential implementation in spin-logic nano-devices.
Key publications:
1. R. Lebrun, A. R. Ross, S-A. Bender, A. Quaimzadeh, L. Baldrati, J. Cramer, A. Brataas, R-A. Duine, and M. Klaüi, Nature 561, p. 222–225 (2018) “Electrically tunable long-distance transport through crystalline antiferromagnetic iron oxide”
2. J. Cramer, A. Ross, L. Baldrati, R. Lebrun, and M. Kläui, Phys. Rev. B 89, 104414 (2019) “Spin-dependent and inverse spin Hall effect in Co60Fe20B20”
