Interface Dzyaloshinskii-Moriya interaction in the interlayer antiferromagnetic-exchange coupled Pt/CoFeB/Ru/CoFeB systems

Abstract

Abstract-Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchangecoupled (IEC) Pt/Co 20 Fe 60 B 20 (1.12 nm)/Ru/Co 20 Fe 60 B 20 (1.12 nm) systems have been studied theoretically and experimentally. Vibrating sample magnetometer has been used to measure their magnetization at saturation and their interlayer exchange coupling constants. These latter are found to be of an antiferromagnetic nature for the investigated Ru range thickness (0.5-1 nm). Their dynamic magnetic properties were studied using Brillouin light scattering (BLS) technique. The BLS measurements reveal pronounced non-reciprocal spin waves propagation.In contrast to the calculations for symmetrical IEC CoFeB layers, this experimental nonreciprocity is Ru thickness and thus coupling strength dependent. Therefore, to explain the experimental behaviour, a theoretical model based on the perpendicular interface anisotropy difference between the bottom and top CoFeB layers has been developed. We show that the Ru thickness dependence of the spin wave non-reciprocity is well reproduced by considering a constant iDMI and different perpendicular interfacial anisotropy fields between the top and bottom CoFeB layers. This anisotropy difference has been confirmed by the investigation of the CoFeB thickness dependence of effective magnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linear behaviour has been observed. * belmeguenai.mohamed@univ-paris13.fr, 2 I-IntroductionThe exchange interaction plays an important role in magnetism and therefore is responsible of several phenomena in magnetic materials. This interaction can be direct (involving an overlap of electron wave functions from the neighboring atoms and Coulomb electrostatic interaction) or indirect (little or no direct overlap between neighboring electrons and mediated through an intermediary atoms). The direct exchange interaction between electrons arises from the Coulomb interaction and is responsible for the microscopic magnetic having the same wavelength and propagating along two opposite directions [9]. It is manifested by a difference between the frequencies of these two SWs. The DMI constant determination is thus reduced to this simple frequency difference measurement. Several experimental methods [10][11][12], largely based on how this interaction alters the properties of domain walls, were employed recently but Brillouin light scattering (BLS) spectroscopy remains the most direct method for DMI characterization. This scheme is simple, efficient, reliable and straightforward since few parameters are required for the experimental data fit [13,14]. It also allows the investigation of both in-plane and perpendicular spontaneously magnetized films in contrast to domain wall techniques. DMI can be induced by a lack of inversion symmetry of the compound and a strong spin-orbit coupling. This can be achieved by using heavy metal/ferromagnet (HM/FM) heterostructures, giving rise to interfacial DMI. 3Indirect exchange interactions such as coupling between two ...

Temperature dependence of the Dzyaloshinskii-Moriya interaction in ultrathin films

“…1(a). The main sources of the perpendicular anisotropy and DMI are the Pt/CoFeB interfaces, with the CoFeB/Ru interfaces mainly acting to break the symmetry of the structure [17].…”

Room-temperature stabilization of antiferromagnetic skyrmions in synthetic antiferromagnets

“…The choice of a trilayer, breaking the inversion symmetry along the stacking direction, enables interfacial DMI, while Pt/Co interfaces provide the largest DMI found so far in sputtered systems [32], as well as significant PMA. The addition of a second interface with Ru does not degrade the DMI [33]. In Co/Ru/Co multilayers, the Ru layer provides an RKKY coupling between the Co layers, whose sign obeys to an oscillatory behavior depending on its thickness t Ru [34], with an antiferromagnetic peak at around 0.8 nm.…”

Modification of Dzyaloshinskii-Moriya-Interaction-Stabilized Domain Wall Chirality by Driving Currents

“…3(b) the wallwidth depends on D yx and an electric field in z direction is expected to induce a spin current J y x via the spin Hall effect. This mechanism for the current-induced DMI could be particularly relevant in the multi-layer geometry, in which the magnetic layers are coupled by an antisymmetric RKKY-type of DMI [38].…”