Probing and tuning the atomistic antisymmetric exchange interaction at interfaces
Final Report Abstract
Within this project we designed, fabricated and investigated several atomically engineered magnetic multilayers and superlattices, grown on substrates with a large spin-orbit coupling. We quantified both the symmetric and antisymmetric magnetic exchange interactions in such layered structures, with the particular attention on the antisymmetric Dzyaloshinskii–Moriya interaction. In the following we outline the main results of our studies. (i) By investigating ultrathin Co films on Ir(001) we discovered a chirality-inversion of the atomistic Dzyaloshinskii–Moriya vectors in layered magnets. The effect is in analogy to the change in the character of the Heisenberg exchange interaction from ferromagnetic to antiferromagnetic. Such an effect is expected to be observed in many other layered magnetic structures grown on substrates with a large spin-orbit coupling. (ii) A careful investigation of the exchange and spin-orbit scattering during the magnon excitation process revealed that, under some circumstances, spin-orbit scattering can overcome the exchange scattering mechanism and lead to a nonreciprocal magnon excitation. Since in the ferromagnetic films the time-reversal symmetry is broken, the magnon amplitude becomes dependent on the direction of the static magnetization. The effect is general and can be employed to excite nonreciprocal magnons in ultrathin magnetic films and nanostructures grown on heavy-element substrates or even in more complex heterostructures with a large spin-orbit coupling. Moreover, such an effect is not restricted to the scattering experiments and must also be present in the transport based tunneling experiments, in which a spinpolarized current is used to excite magnons. (iii) We discovered that the magnon-magnon decay via multi-magnon scattering process is active in the systems with Dzyaloshinskii–Moriya interaction. However, the contribution of multi-magnon scattering is orders of magnitude smaller than the Landau damping, which describes the decay of magnons to single-particle Stoner excitations, non-trivial correlation effects (dominated by electron-magnon scattering) and disorder. (iv) Performing experiments on specifically designed multilayer structures made of Co and Ni atomic layers we could probe, for the first time, the full dispersion relation of the acoustic magnon mode, which is partially localized in the Ni monolayer. Thereby, we could quantify the Heisenberg exchange parameters within the Ni atomic layer. We identified a rather weak exchange coupling within the Ni monolayer, even though the magnon exchange stiffness was observed to be rather large. The large magnon stiffness constant was attributed to the low spin density of Ni atoms, in agreement with our first-principles calculations. (v) We examined the impact of the number of electrons in the d-states of the interface atomic layer, as well as the number and the sequence of the atomic layers on the Dzyaloshinskii–Moriya interaction. Performing comprehensive experiments on several different magnetic multilayers made of Fe, Co and Ni grown on Ir(001) we demonstrated that the number of electrons in the 3d states does not only influence the magnitude of the Dzyaloshinskii–Moriya vectors, but also its chirality. Moreover, we showed that changing the number and the sequence of the magnetic layers are also very crucial and may be used as a tool to tune this antisymmetric interaction. (vi) By investigating atomically architectured nanomagnets formed as periodic magnetic stripes on the reconstructed Ir(001) surface, we could show, for the first time, that such atomically designed nanostripes provide a suitable platform for the excitation and propagation of laterally confined ultrafast terahertz magnons.
Publications
-
Generation of spin-polarized hot electrons at topological insulators surfaces by scattering from collective charge excitations. Communications Physics, 4(1).
Zakeri, Khalil; Wettstein, Janek & Sürgers, Christoph
-
Theory of spin-polarized high-resolution electron energy loss spectroscopy from nonmagnetic surfaces with a large spin-orbit coupling. Physical Review B, 106(23).
Zakeri, Khalil & Berthod, Christophe
-
Chirality-inverted Dzyaloshinskii-Moriya interaction. Physical Review B, 108(10).
Zakeri, Khalil; Marmodoro, Alberto; von Faber, Albrecht; Mankovsky, Sergiy & Ebert, Hubert
-
Direct Probing of a Large Spin–Orbit Coupling in the FeSe Superconducting Monolayer on STO. ACS Nano, 17(10), 9575-9585.
Zakeri, Khalil; Rau, Dominik; Jandke, Jasmin; Yang, Fang; Wulfhekel, Wulf & Berthod, Christophe
-
Correlations, disorder, and multimagnon processes in terahertz spin dynamics of magnetic nanostructures: A first-principles investigation. Physical Review B, 109(22).
Paischer, Sebastian; Eilmsteiner, David; Maznichenko, Igor; Buczek, Nadine; Zakeri, Khalil; Ernst, Arthur & Buczek, Paweł A.
-
Giant Spin-Orbit Induced Magnon Nonreciprocity in Ultrathin Ferromagnets. Physical Review Letters, 132(12).
Zakeri, Khalil & von, Faber Albrecht
-
Magnons and fundamental magnetic interactions in a ferromagnetic monolayer: The case of the Ni monolayer. Physical Review B, 109(18).
Zakeri, Khalil; von Faber, Albrecht & Ernst, Arthur
-
Unraveling the Complexity of the Dzyaloshinskii–Moriya Interaction in Layered Magnets: The Full Magnitude and Chirality Control. Advanced Materials, 37(35).
Zakeri, Khalil; von Faber, Albrecht; Mankovsky, Sergiy & Ebert, Hubert
