  A magnetic Skyrmion is a stable two-dimensional nanoparticle describing a
localized winding of the magnetization in certain magnetic materials. Skyrmions
are the subject of intense experimental and theoretical investigation and have
potential technological spintronic applications. Here we show that numerical
computations of frustrated magnets predict that Skyrmions can be tied into
knots to form new stable three-dimensional nanoparticles. These stable
equilibria of twisted loops of Skyrmion strings have an integer-valued
topological charge, known as the Hopf charge, that counts the number of
particles. Rings are formed for low values of this charge, but for higher
values it is energetically favourable to form links and then knots. This
computational study provides a novel impetus for future experimental work on
these nanoknots and an exploration of the potential technological applications
of three-dimensional nanoparticles encoding knotted magnetization.
