3D nanonetworks promise to usher in a new era in modern solid-state physics, with numerous applications in photonics, biomedicine, and spintronics. The realization of three-dimensional magnetic nanostructures could enable ultrafast and low-energy data storage devices. Due to the competing magnetic interactions within these systems, magnetic charges or magnetic monopoles can emerge, which could be used as mobile, binary information carriers.
Researchers at the University of Vienna have now designed the first three-dimensional artificial spin ice lattice to carry unbound magnetic charges. The results, published in the journal *npj Computational Materials*, are the first theoretical demonstration that magnetic monopoles are stable at room temperature and can be guided on demand by an external magnetic field in the new lattice.
Emerging magnetic monopoles have been observed in a class of magnetic materials known as spin ice. However, the atomic scale and the low temperatures required for their stability limit their controllability. This has led to the development of two-dimensional artificial spin ice, in which single-atom moments are replaced by magnetic nanosheets arranged on different lattices. The increased scale allows the emerging magnetic monopoles to be studied on a more readily available platform. Inverting the magnetic orientation of a particular nanoisland allows the monopole to propagate further to a vertex, leaving a trace. This trace, a Dirac string, necessarily stores energy and confines the monopole, limiting its mobility.
Researchers around Sabri Koraltan and Florian Slanovc, led by Dieter Suess at the University of Vienna, have now designed the first three-dimensional artificial spin ice lattice, combining the advantages of atoms and two-dimensional artificial spin ice.
In collaboration with the Nanomagnetism and Magnetism Group at the University of Vienna and the Theoretical Department at Los Alamos National Laboratory in the United States, the advantages of this novel lattice were investigated using micro-electromagnetic simulations. Here, flat two-dimensional nanosheets were replaced by magnetic ellipsoids of rotation, and a highly symmetric three-dimensional lattice was used. "Due to the degeneracy of the ground state, the tension of the Dirac string disappears, releasing the constraint on the magnetic monopole," said Sabri Koraltan, one of the study's first authors. The researchers took this a step further, demonstrating in their simulations that a magnetic monopole propagates within the lattice when an external magnetic field is applied, showcasing its application as an information carrier in three-dimensional magnetic nanonetworks.
Sabri Koraltan added, "We utilize the third dimension and high symmetry in the new lattice to untie the magnetic monopoles and move them in desired directions, almost like real electrons." Another first author, Florian Slanovc, summarized, "The thermal stability of monopoles at room temperature and above could lay the foundation for a breakthrough next generation of three-dimensional storage technology."
