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Register a new userMagnetic properties, domain wall creep motion and the Dzyaloshinskii-Moriya interaction in Pt/Co/Ir thin films
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We study the magnetic properties of perpendicularly magnetised Pt/Co/Ir thin films and investigate the domain wall creep method of determining the interfacial Dzyaloshinskii-Moriya (DM) interaction in ultra-thin films. Measurements of the Co layer thickness dependence of saturation magnetisation, perpendicular magnetic anisotropy, and symmetric and antisymmetric (i.e. DM) exchange energies in Pt/Co/Ir thin films have been made to determine the relationship between these properties. We discuss the measurement of the DM interaction by the expansion of a reverse domain in the domain wall creep regime. We show how the creep parameters behave as a function of in-plane bias field and discuss the effects of domain wall roughness on the measurement of the DM interaction by domain expansion. Whereas modifications to the creep law with DM field and in-plane bias fields have taken into account changes in the energy barrier scaling parameter $alpha$, we find that both $alpha$ and the velocity scaling parameter $v_{0}$ change as a function of in-plane bias field.
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The interfacial Dzyaloshinskii-Moriya interaction (DMI) is important for chiral domain walls (DWs) and for stabilizing magnetic skyrmions. We study the effects of introducing increasing thicknesses of Ir, from zero to 2 nm, into a Pt/Co/Ta multilayer between the Co and Ta. We observe a marked increase in magnetic moment, due to the suppression of the dead layer at the interface with Ta, but the perpendicular anisotropy is hardly affected. All samples show a universal scaling of the field-driven domain wall velocity across the creep and depinning regimes. Asymmetric bubble expansion shows that DWs in all of the samples have the left-handed N{e}el form. The value of in-plane field at which the creep velocity shows a minimum drops markedly on the introduction of Ir, as does the frequency shift of the Stokes and anti-Stokes peaks in Brillouin light scattering measurements. Despite this qualitative similarity, there are quantitative differences in the DMI strength given by the two measurements, with BLS often returning higher values. Many features in bubble expansion velocity curves do not fit simple models commonly used to date, namely a lack of symmetry about the velocity minimum and no difference in velocities at high in-plane field. These features are explained by the use of a model in which the depinning field is allowed to vary with in-plane field in a way determined from micromagnetic simulations. This theory shows that velocity minimum underestimates the DMI field, consistent with BLS returning higher values. Our results suggest that the DMI at an Ir/Co interface has the same sign as the DMI at a Pt/Co interface.
Antiferromagnetic materials present us with rich and exciting physics, which we can exploit to open new avenues in spintronic device applications. We explore perpendicularly magnetized exchange biased systems of Pt/Co/IrMn and Pt/Co/FeMn, where the crossover from paramagnetic to antiferromagnetic behavior in the IrMn and FeMn layers is accessed by varying the thickness. We demonstrate, through magneto-optical imaging, that the magnetic domain morphology of the ferromagnetic Co layer is influenced by the N${e}$el order of the antiferromagnet (AFM) layers. We relate these variations to the anisotropy energy of the AFM layer and the ferromagnet-antiferromagnet (FM-AFM) inter-layer exchange coupling. We also quantify the interfacial Dzyaloshinskii-Moriya interaction (DMI) in these systems by Brillouin light scattering spectroscopy. The DMI remains unchanged, within experimental uncertainty, for different phases of the AFM layers, which allows us to conclude that the DMI is largely insensitive to both AFM spin order and exchange bias. Understanding such fundamental mechanisms is crucial for the development of future devices employing chiral spin textures, such as N${e}$el domain walls and skyrmions, in FM-AFM heterostructures.
We characterize asymmetric growth of magnetic bubble domains in perpendicularly magnetized Co/Ni multi-layers grown on Pt$_x$Ir$_{1-x}$ seedlayers by application of perpendicular and in-plane magnetic fields. Using a refined model of domain wall creep that incorporates contributions from the anisotropic elastic energy, $varepsilon$, and a chirality-dependent prefactor, $v_0$, we elucidate factors that govern the mobility of Dzyaloshinskii domain walls as a function of seedlayer composition. The interfacial Dzyaloshinskii-Moriya Interaction magnitude is found to decrease monotonically with $x_{Ir}$, which is independently confirmed by Brillouin light scattering (BLS). Moreover, the persistence of significant asymmetry in velocity curves across the full composition range supports previous assertions that a chirality-dependent attempt frequency akin to chiral damping could play a critical role in the observed trends. This work helps resolve fundamental questions about the factors governing Dzyaloshinskii DW creep and demonstrates varying Pt-Ir seedlayer composition as a method to tune DMI.
The Dzyaloshinskii-Moriya interaction (DMI), being one of the origins for chiral magnetism, is currently attracting huge attention in the research community focusing on applied magnetism and spintronics. For future applications an accurate measurement of its strength is indispensable. In this work, we present a review of the state of the art of measuring the coefficient $D$ of the Dzyaloshinskii-Moriya interaction, the DMI constant, focusing on systems where the interaction arises from the interface between two materials. The measurement techniques are divided into three categories: a) domain wall based measurements, b) spin wave based measurements and c) spin orbit torque based measurements. We give an overview of the experimental techniques as well as their theoretical background and models for the quantification of the DMI constant $D$. We analyze the advantages and disadvantages of each method and compare $D$ values in different stacks. The review aims to obtain a better understanding of the applicability of the different techniques to different stacks and of the origin of apparent disagreement of literature values.
We report on magnetic domain wall velocity measurements in ultrathin Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain wall motion, analysis of which yields values for the damping parameter, $alpha$.
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