Interfacial Dzyaloshinskii-Moriya interaction (IDMI) is important for its roles in stabilizing the skyrmionic lattice as well as soliton-like domain wall motion leading towards new generation spintronic devices. However, achievement and detection of IDMI is often hindered by various spurious effects. Here, we demonstrate the occurrence of IDMI originating primarily from W/CoFeB interface in technologically important W/CoFeB/SiO2 heterostructures using Brillouin light scattering technique. Due to the presence of IDMI, we observe asymmetry in the peak frequency and linewidth of the spin-wave spectra in the Damon-Eshbach (DE) geometry at finite k wave-vectors. The DMI constant is found to scale as the inverse of CoFeB thickness, over the whole studied thickness range, confirming the presence of IDMI in our system without any extrinsic effects. Importantly, the W/CoFeB interface shows no degradation down to sub-nanometer CoFeB thickness, which would be useful for devices that aim to use pronounced interface effects.

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Direct Observation of Interfacial Dzyaloshinskii-Moriya Interaction from Asymmetric Spin-wave Propagation in W/CoFeB/SiO 2 Heterostructures Down to Sub-nanometer CoFeB Thickness

In the growing field of $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}s$, spin waves (magnons) are manipulated as information carriers, particularly for data processing. Thus controlling the propagation of spin waves is of paramount interest here. This investigation considers a ferromagnetic bilayer with dipolar coupling as a potential nonreciprocal magnonic device, in which frequency dispersion is reciprocal for parallel yet nonreciprocal for antiparallel orientation of layer magnetizations. This is progress in the technological implementation of magnonic devices with asymmetric transmission properties, since reconfigurability can be easily achieved just by switching, without any rotation of the applied magnetic field.

Reconfigurable Spin-Wave Nonreciprocity Induced by Dipolar Interaction in a Coupled Ferromagnetic Bilayer

Layered magnetic structures: antiferromagnetic type interlayer coupling and magnetoresistance due to antiparallel alignment

Layered Fe/Cr structures are known to display antiferromagnetic‐type interlayer coupling and a new magnetoresistance (MR) effect due to antiparallel magnetization alignment. The strength of the coupling is found to be similar in multilayered structures and in double layers. The oscillatory behavior of the coupling, previously found by Parkin, More, and Roche [Phys. Rev. Lett. 64, 2304 (1990)] on sputtered polycrystalline samples, is here confirmed for epitaxial samples, obtained by thermal evaporation. The new MR effect is interpreted as due to a spin‐dependent scattering of the electrons at the Fe‐Cr interfaces. The investigations have been extended to Fe/V, Fe/Mn, Fe/Cu, Co/Au, Co/Cr, and Co/Cu structures where the antiparallel alignment of the ferromagnetic layers is obtained via hysteresis effects. A MR effect due to antiparallel alignment, which is strong for Co/Au and Co/Cu but weak in the other cases, has been found.

Layered magnetic structures: Antiferromagnetic-type interlayer coupling and magnetoresistance due to antiparallel alignment

Molecular beam epitaxy (MBE) and sputtering systems have been used in recent years to create a variety of epitaxial ultrathin films. It is of the utmost importance to employ experimental techniques which can determine their basic magnetic properties straightforwardly and quantitatively. In the following four sections of this chapter ferromagnetic resonance (FMR), Brillouin light scattering (BLS) and nuclear magnetic resonance (NMR) will be described. It will be shown that these techniques are uniquely suited for the study of ultrathin films. They provide us with all the essential parameters describing the magnetic properties of ultrathin films. FMR and BLS are very sensitive techniques enabling films one monolayer (ML) thick to be readily investigated.

J. Barnaś

Papers

Spin waves in exchange-coupled epitaxial double-layers