NMS-LAB
Research Interests
Skyrmions/Antiskyrmions
Magnetic skyrmions/antiskyrmions, which are topologically protected vortex-like objects with a twisted spin configuration, are predicted to provide a basis for the novel high density solid-state memory devices - Racetrack Memories. Magnetic materials with broken inversion symmetry, where the asymmetric Dzyaloshinskii–Moriya interaction modifies the uniform magnetic state to a swirling state, are suitable candidates to achieve skyrmions/antiskyrmions. The intriguing non-trivial topology of the skyrmions grants them a number of advantages, like low threshold current for their motion and ability to avoid defects. In addition, it is very interesting to study their dynamical properties related to different kind of topological spin states.
In this regard, the inverse tetragonal Heusler materials with D2d crystal symmetry were found to be consisting of all requirements to host antiskyrmions. Our work aims on finding novel materials in the Heusler family that can display small-scale antiskyrmions preferable for their use in devices. The materials will be prepared both in bulk and thin film forms and the characterization will be performed using DC magnetizations and AC susceptibility, topological Hall effect measurements and Lorentz Transmission Electron Microscopy (LTEM) imaging.
Compensated/ Anti-ferromagnetic spintronics
The utilization of Skx/ASkx as an information carrier or as a data storage element has several advantages over the domain wall based racetrack memory. Nevertheless, a major drawback that hinders their implication in spintronic devices is the presence of Magnus force that pushes the Skx/ASkx towards edge of the device. Such discrepancy can be avoided in case of antiferromagnetic (AFM) Skx/ASkx consisting of two oppositely aligned magnetic sublattices. However, no experimental findings of AFM Skx are reported so far. The realization of the AFM-Skx can be achieved either by finding suitable AFM materials or designing a completely compensated ferrimagnetic (FiM) materials that can host skyrmions by tuning the chemical composition simultaneously preserving the desired underlying symmetry. Our plan is to design Skx/Askx hosting magnetically compensated materials and characterizing them using existing direct techniques, such as, small angle neutron scattering (SANS), Lorentz transmission electron microscopy (LTEM), spin-resolved scanning tunnelling microscopy and indirect ways, such as, topological Hall effect and magnetic entropy measurements.
Anomalous and Topological Hall Effect
In condensed matter physics the Hall effect is one of the most interesting transport phenomenon widely studied across all kinds of materials, where the interplay between the topology and symmetry gives rise to several types of Hall effects, such as, anomalous Hall effect (AHE) Quantum Hall effect, Spin Hall effect, topological Hall effect (THE), etc. The AHE, which in general scales with the magnetization of a ferro-/ferrimagnet, can also be found in non-collinear triangular antiferromagnet with zero net magnetic moment, Weyl semimetal and different topological materials owing to the non-vanishing Berry curvature in momentum space. In contrast, the electron transport in some of the non-trivial spin structures with finite topological number can result in topological Hall effect, arising from the real space Berry curvature. The measurement of THE helps in the characterization of non-trivial spin structures like skyrmions and antiskyrmions. We extensively focus on the measurement of AHE and THE in various exotic materials.
Exchange bias
Exchange bias (EB) is associated with the unidirectional anisotropy developed at the interface shared between two differently ordered magnetic structures (magnetically soft/hard). As a result, the soft magnetic layer behaves as if it experiences some internal magnetic field. Our motivation is to use this internal field as a source for the stabilization of skyrmions/antiskyrmions at zero external field, indispensable for realization of skyrmion based memory devices. We plan to make use of this interfacial coupling to stabilize spontaneous skyrmions/antiskyrmions with help of competition between the interfacial and bulk DMI.
