Chiral Spin Textures in Magnetic Nanostructures

Georgetown University, Washington DC

Investigators

Abstract

Nontechnical Abstract: Magnetic moments in magnets can form various configurations known as spin textures, such as domain walls where the moments form a winding configuration connecting adjacent domains with different magnetization directions. Usually, the rotational sense of the moments in spin textures is expected to be achiral, where the left- and right-handed rotations are equally possible. In certain magnetic thin films, the broken inversion symmetry of atomic structure at the interface between magnetic and heavy metal layers leads to an interfacial effect which lifts the chiral degeneracy and stabilizes chiral spin structures such as spin spirals, chiral domain walls or magnetic skyrmions. These chiral spin textures exhibit a preferred handedness and fascinating topological characteristics. Their extraordinary properties provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. This project aims at significantly advancing the field by unlocking a number of degrees of freedom for a better understanding and control of such spin textures. Several novel spin textures are investigated, including exotic types of skyrmions and chiral domain walls in 2-dimensional thin films and topological spin textures such as Mobius bands in 3-dimensional magnetic structures. They have the potential to fundamentally transform the energy landscape for future information storage. This project provides valuable training opportunities for students in university as well as national laboratory and other facilities. The principal investigator actively engages in a variety of efforts to broaden participation from underrepresented groups through course offering, public lectures, exchange visits, and professional conference organization. Technical Abstract: Chiral spin textures are investigated to demonstrate a number of new degrees of freedom to better control them, including antiskyrmion Hall angle, topological number, chemisorbed species, and 3-dimensional topological configuration. Anisotropic Dzyaloshinskii-Moriya interaction is utilized to stabilize antiskyrmions in magnetic thin films. The antiskyrmion Hall angle is explored for controlling skyrmion trajectory or topological sorting, which can be potentially used for designing complex skyrmionics devices. High winding number skyrmions are demonstrated, which unlocks the topological number as a new degree of freedom that may support novel topological functionalities in logic devices. Effects of chemisorbed species under vacuum onto ferromagnet films are studied to induce chiral domain walls and enable direct writing of skyrmions without magnetic or electric fields. Chemisorptions of low atomic number atoms and organic molecules are studied to induce reversible switching of magnetic chirality and tuning of perpendicular magnetic anisotropy. Novel types of 3-dimensional topological spin textures such as Mobius bands are fabricated and their topological characters are investigated. These novel spin textures offer new mechanisms for robust and low dissipation information storage, which is well aligned with grand challenges for future nanoelectronics. This project includes a wide variety of efforts to broaden participation from underrepresented groups. Students involved receive excellent exposure to research experience in academia, government laboratory and other research facilities. This DMR grant supports research on chiral spin structure in magnetic nanoparticles with funding from the Condensed Matter Physics (CMP) and the Electronic and Photonic Materials (EPM) Programs in the Division of Materials Research of the Mathematical and Physical Sciences Directorate. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.