Rafal E. Dunin-Borkowski

Abstract Hopfions are three-dimensional topological solitons formed by closed loops of vortex strings, often taking the shape of rings. In magnetic crystals, hopfions have so far been observed only in unusual configurations in which hopfion rings are linked to skyrmion strings. Although theory predicts the existence of stable, isolated hopfions, their experimental realization has remained challenging.

Abstract Elucidating the valence change mechanism in oxides memristors remains challenging due to subtle oxygen vacancy migration. Here, we quantify individual oxygen vacancies and observe their dynamic evolution during resistive switching using in-situ transmission electron microscopy. In SrNbO3.4, when fewer than 3 oxygen vacancies per unit formula form, they distribute uniformly. This solid-solution structure ensures reversible oxygen vacancy creation and annihilation.