Large-scale Domain Engineering in Two-Dimensional Ferroelectric CuInP2S6 via Giant Flexoelectric Effect

Room-temperature ferroelectricity in two-dimensional materials offer a potential route for developing atomic-scale functional devices beyond Moore’s law. However, as a key for the technology implementations of ferroelectrics in electronics, the controllable generation of uniform domains remains challenging in two-dimensional ferroelectrics at current stage because domain engineering through an external electric field at 2D limit inevitably leads to large leakage current and material break-down. Here, we demonstrate a voltage-free method, the flexoelectric effect, to artificially generate large-scale stripe domains in two-dimensional ferroelectric CuInP2S6 with single domain lateral size at the scale of several hundred microns. With giant strain gradients (~106 m−1) at nanoscale, we mechanically switch the out-of-plane polarization in ultrathin CuInP2S6. The flexoelectric control of ferroelectric polarization is understood with a distorted Landau-Ginzburg-Devonshire double well model as evidenced by the shifted ferroelectric hysteresis loops and the first-principle calculations. Through substrate mechanical strain engineering, the stripe domain density is controllable. Our results not only highlight the potential of developing van der Waals ferroelectrics-based memories but also offer the opportunity to study ferroelectric domain physics in two-dimensional materials.

Enhancement of Magnetoelectric Effect in Compositionally Graded Ferroelectric/Ferromagnetic Pb(1−x)SrxTiO3/CoFe2O4 Nanocomposites

In this study, phase-field model is developed for ferroelectric/ferromagnetic nanocomposites, in which ferroelectric composition is spatially varied along the thickness of ferroelectric layers. The developed phase field model is applied to investigate the effect of composition gradient on magnetoelectric response of the multilayer nanocomposite. Stripe domain structures are observed in both ferroelectric and ferromagnetic layers, however the sizes of magnetic domains are larger than that of polarization ones. Particularly, the size of polarization domains and geometry of domain walls are altered according to the gradient of ferroelectric composition. The obtained results suggest that the larger the composition gradient is, the higher the magnetoelectric effect becomes. The enhancement of magnetoelectric effect is attributed to the concentration of energy in ferroelectric layer, which originates from the spatial variation of ferroelectric composition.

Magnetic Domain Structure in Ferromagnetic Kagome Metal DyMn6Sn6

Two types of magnetic domains, that is, type-I domain belt domain and type-II new stripe domain, are observed in a kagome metal DyMn6Sn6 by microscopic magneto-optic Kerr imaging technique. From 255 to 235 K, the spin reorientation is observed directly in DyMn6Sn6. We analyze the structure of two types of domains through brightness distribution of the images. The type-II domain exists from 235 to 160 K by zero-field cooling (ZFC). At the same time, type-I domain and type-II domain coexist and transform into each other with variation of temperature. Type-II domains can easily transform into type-I domains when the temperature and magnetic field changes, and this process is irreversible. These results demonstrate that the type-I domain is more stable than the type-II domain. The phase diagram of magnetic domains in DyMn6Sn6 is obtained.

A Ti/Pt/Co Multilayer Stack for Transfer Function Based Magnetic Force Microscopy Calibrations

Magnetic force microscopy (MFM) is a widespread technique for imaging magnetic structures with a resolution of some 10 nanometers. MFM can be calibrated to obtain quantitative (qMFM) spatially resolved magnetization data in units of A/m by determining the calibrated point spread function of the instrument, its instrument calibration function (ICF), from a measurement of a well-known reference sample. Beyond quantifying the MFM data, a deconvolution of the MFM image data with the ICF also corrects the smearing caused by the finite width of the MFM tip stray field distribution. However, the quality of the calibration depends critically on the calculability of the magnetization distribution of the reference sample. Here, we discuss a Ti/Pt/Co multilayer stack that shows a stripe domain pattern as a suitable reference material. A precise control of the fabrication process, combined with a characterization of the sample micromagnetic parameters, allows reliable calculation of the sample’s magnetic stray field, proven by a very good agreement between micromagnetic simulations and qMFM measurements. A calibrated qMFM measurement using the Ti/Pt/Co stack as a reference sample is shown and validated, and the application area for quantitative MFM measurements calibrated with the Ti/Pt/Co stack is discussed.

A Ti/Pt/Co Multilayer Stack for Transfer Function Based Magnetic Force Microscopy Calibrations

Magnetic force microscopy (MFM) is a widespread technique for imaging magnetic structures with a resolution of some 10 nanometers. MFM can be calibrated to obtain quantitative (qMFM) spatially resolved magnetization data in units of A/m by determining the calibrated point spread function of the instrument, its instrument calibration function (ICF), from a measurement of a well-known reference sample. Beyond quantifying the MFM data, a deconvolution of the MFM image data with the ICF also corrects the smearing caused by the finite width of the MFM tip stray field distribution. However, the quality of the calibration depends critically on the calculability of the magnetization distribution of the reference sample. Here, we discuss a Ti/Pt/Co multilayer stack which shows a stripe domain pattern as a suitable reference material. A precise control of the fabrication process combined with a characterization of the sample micromagnetic parameters allows to reliably calculate the sample’s magnetic stray field, proven by a very good agreement between micromagnetic simulations and qMFM measurements. A calibrated qMFM measurement using the Ti/Pt/Co stack as a reference sample is shown and validated and the application area for quantitative MFM measurements calibrated with the Ti/Pt/Co stack is discussed.