Research Projects

Through this project we will establish many metallic centrosymmetric skyrmion (SkX) systems which are fundamentally interesting as well as technologically important. SkXs are vortex-like spin textures which carry non-zero integer characteristic numbers known as SkX number. The asymmetric magnetic exchange known as Dzyaloshinskii–Moriya interaction (DMI) is known to be an important factor for stability of SkX in noncentrosymmetric crystals. Several B20-based chiral compounds such as MnSi have been found to contain SkX lattice. The typical size of an individual SkX when stabilized by DMI can be several tens of nanometers. Due to the large size of the SkX, the SkX density and therefore the total emergent magnetic flux is low. This results in a weak signal of topological Hall effect (THE). Recent theoretical calculations have shown that skyrmions can be stabilized in centrosymmetric magnetic materials where the short-range exchange interactions are frustrated in nature, for example in a triangular lattice. However, the frustrated lattice is not always necessary to stabilize skyrmions since they have also been discovered in square lattices wherein the stabilization mechanism has been attributed to Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions. The most important aspect of SkXs in centrosymmetric compounds is that their size is typically few nanometers, thereby enabling them to be detected by Hall effect in terms of THE contribution because the EMF can be very high. The field of centrosymmetric SkX systems is still at its nascent stage and the exact mechanism involved is still lacking mainly because only a handful of Gd- and Eu-based compounds have been explored. Any example containing transition metal elements with small or no single ion anisotropy is missing in the literature. Our aim through this project is to achieve and establish new metallic centrosymmetric candidates hosting SkXs by focussing our attention to probable structure types (AlB2, ThCr2Si2, BaAl4, and their derivatives to start with), establishing their crystallographic and magnetic structure through various techniques. Other than exploring THE through electrical transport measurements, we will employ resonant elastic x-ray scattering (REXS) and small angle neutron scattering (SANS). Although RKKY interaction and magnetic frustration might be important, the exact mechanism is still not known for SkX in centrosymmetric crystals. We will perform electrical transport under hydrostatic pressure and chemical modifications to understand the mechanism of SkX in centrosymmetric compounds. A significant focus will be on the structure-property relation which will be carried out by fine tuning of structural aspects and the compounds and undertake detailed crystallographic analysis, which is vital for our project which emphasizes the role of centrosymmetry in the crystal structure. Theoretical understanding of these magnetic textures is essential and complementary. The density functional theory (DFT) can also provide insight into the underlying exchange mechanisms by evaluating the conduction electron density and Fermi surface topology. In systems with sufficient carrier concentration, the RKKY interaction dominates, which can be captured by computing magnetic susceptibility from the Lindhard function or from direct spin-spiral total energy calculations. These approaches are particularly important when analyzing metallic frustrated systems, such as AlB₂-type compounds. DFT+U or hybrid functionals can further help in treating the localized 4f electrons of rare-earth elements accurately, while preserving the itinerant behavior of conduction electrons. Hence, with this project we will gain important insight in the field of centrosymmetric SkX through single crystal growth, in-depth crystallography, electrical transport at ambient and high pressure, advanced experimental techniques such as REXS, SANS and state of the art theoretical calculations.