Spin injection, transmission and detection in antiferromagnets

Orateur : Soutenance de Thèse de Lamprini FRANGOU

Antiferromagnetic spintronics is an emerging research field in the area of information technology that exploits the unique combination of properties of antiferromagnets. It is their high excitation frequency, robustness against external fields, zero net magnetization and possibilit y of generating large magneto-transport effects that makes them so interesting. Spin transfer, spin-orbit coupling and spin caloritronics constitute the phenomena that have shaped much of the recent research and development towards pure antiferromagnetic spintronics. Here we investigate spin transfer torque and spin pumping in both metallic and insulating antiferromagnets by means of ferromagnetic resonance technique, in ferromagnetic spin injector – NiFe, CoFeB / (spin conductor – Cu) / antiferromagnetic spin sink – IrMn, NiFeOx, NiO trilayers. Temperature dependence measurements of the ferromagnetic relaxation revealed a novel spin pumping effect associated to the linear fluctuations at the magnetic phase transition of the antiferromagnet, regardless its electronic state and the nature of the spin transport. This opens new ways towards more efficient spin pumping, while providing at the same time a versatile method to probe the critical temperature of ultrathin films with ze ro net magnetization. Next, in an effort to probe linear as well as non-linear fluctuations in the antiferromagnet we conducted electrical measurements in spin Hall geometry. A novel non-monotonous temperature dependence of transverse dc voltage was sometimes observed, mostly associated to the properties of a specific ferromagnet : Permalloy, unrelated to spin rectification effects. These findings add to a growing body of literature on spin current absorption, highlighting the ability of ferromagnets to act as spin current detectors, in phenomena involving magnetization dynamics. Finally, we used exchange bias to investigate and subsequently engineer the magnetic and electric properties of various antiferromagnets intended for diverse spintronic applications including reading via tunneling anisotropic magnetoresistance.

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