Antiferromagnetic thin films attract significant interest for future low-power spintronic devices [1]. Multiferroics, such as bismuth ferrite BiFeO3, in which antiferromagnetism and ferroelectricity coexist at room temperature, appears as a unique platform for spintronic [2] and magnonic devices [3]. The nanoscale structure of its ferroelectric domains has been widely investigated with piezoresponse force microscopy (PFM), revealing unique domain structures and domain wall functionalities [4]. However, the nanoscale magnetic textures present in BiFeO3 and their potential for spin-based technology remain concealed. In this report, we present two different antiferromagnetic spin textures in multiferroic BiFeO3 thin films with different epitaxial strains, using a commercial non-invasive scanning Nitrogen-Vacancy (NV) magnetometer based on a single NV defect in diamond, with a calibrated NV flying height of 60 nm and a proven DC field sensitivity of 1 T/Hz. Two BiFeO3 samples were grown on DyScO3 (110) and SmScO3 (110) substrates (later mentioned as BFO/DSO and BFO/SSO, respectively) using pulsed laser deposition. The striped ferroelectric domains in both samples are first observed by the in-plane PFM. The scanning NV magnetometry (SNVM) confirms the existence of the spin cycloid texture, with zig-zag wiggling angles of 90 and 127, and propagation wavelength of DSO=64 nm andSSO=103 nm, respectively. At the local scale, the combination of PFM and SNVM allows to identify the relative orientation of the ferroelectric polarization and cycloid propagation directions on both sides of a domain wall. For the BFO/DSO sample, the 90-degree in-plane rotation of the ferroelectric polarization imprints the 90-degree in-plane rotation of the cycloidal propagation direction along k1=[-1 1 0], corresponding to the type-I cycloid. On the contrary, in the BFO/SSO sample, the propagation vectors are found to be along k1'=[-2 1 1] and k2'= [1 -2 1] directions in the neighboring domains separated by the 71 domain wall. It is worth to mentioned that in the previous report [5], BFO/SSO, prepared in another growth chamber, showed G-type antiferromagnetic textures, compared to the observed type-II cycloid here. Our results here shed the light on future potential for reconfigurable nanoscale spin textures on multiferroic systems by strain engineering.
In this work , we describe the design, realisation and characterization of the magnetic version of the Galton Board, an archetypal statistical device originally designed to exemplify normal distributions. Although simple in its macroscopic form, achieving an equivalent nanoscale system poses many challenges related to the generation of sufficiently similar nanometric particles and the strong influence that nanoscale defects can have in the stochasticity of random processes. We demonstrate how the quasi-particle nature and the chaotic dynamics of magnetic domain-walls can be harnessed to create nanoscale stochastic devices [1]. Furthermore, we show how the direction of an externally applied magnetic field can be employed to controllably tune the probability distribution at the output of the devices, and how the removal of elements inside the array can be used to modify such distribution.
Magnetic skyrmions are magnetic textures, topologically different from the uniform ferromagnetic state, holding a lot of promise for applications as well as of fundamental interest. They have been observed in magnetic multilayers at room temperature only a couple of years ago [1]. In magnetic multilayers, a key to stabilize magnetic skyrmions is the Dzyaloshinskii-Moriya interaction, obtained at the interfaces between ferromagnetic layers and heavy-metal/oxides spacers, which promotes a unique chirality of the skyrmionic spin textures. Combined with spin-orbit torques generated in heavy-metal layers, this unique chirality allows very efficient current-induced motion at speeds reaching 100m/s [2].
In this presentation, we report about our predictions and observations of hybrid chirality in skyrmionic systems, arising from a competition between the Dzyaloshinskii-Moriya interaction and the other magnetic interactions. After having demonstrated a direct evidence of such hybrid chirality [3] by probing the surface spin ordering of multilayers with circular dichroism in X-ray resonant magnetic scattering [4], we will discuss the impact of hybrid chirality in technologically relevant multilayers depending on different parameters such as the number of stacked layers, interfacial anisotropy or interlayer exchange coupling. In the perspective of technological applications of skyrmions, controlling their chirality to match the spin-orbit torques injection geometry of the multilayers is required to achieve efficient current-induced motion.
[1] C. Moreau-Luchaire et al, Nat. Nano. 11, 444 (2016).
[2] A. Hrabec et al, Nat. Comm. 8, 15765 (2017).
[3] W. Legrand et al, arXiv:1712.05978v2 (2017).
[4] J.-Y. Chaleau et al, Phys. Rev. Lett. 120, 037202 (2018).
Sub-100-nm skyrmions are stabilized in magnetic metallic multilayers and observed using transmission electron microscopy, magnetic force microscopy, scanning transmission X-ray microscopy and X-ray resonant magnetic scattering. All these advanced imaging techniques demonstrate the presence of 'pure' Neel skyrmion textures with a determined chirality. Combining these observations with electrical measurements allows us to demonstrate reproducible skyrmion nucleation using current pulses, and measure their contribution to the transverse resistivity to detect them electrically. Once nucleated, skyrmions can be moved using charge currents. We find predominantly a creep-like regime, characterized by disordered skyrmion motion, as observed by atomic force microscopy and scanning transmission X-ray microscopy. These observations are explained qualitatively and to some extent quantitatively by the presence of crystalline grains of about 20nm lateral size with a distribution of magnetic properties.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.