A team has observed at the microscopic level how the magnetization response of a single magnetic nanoparticle is shaped by its magnetic anisotropy. The work, published in Nature, makes it possible to follow the behaviour of one nanoscale object rather than measuring statistical ensembles, where differences between particles are averaged out.

Magnetic anisotropy describes how a material's energy depends on the orientation of its magnetization relative to its crystal structure. In individual nanoparticles, this property controls the preferred direction of the magnetic moment and the barrier that must be overcome to reverse it, but measuring it particle by particle has been difficult, and studies have relied on samples containing many objects.

The experiment combines microscopic observation with measurements of the magnetic response of the isolated nanoparticle, allowing the crystal structure and orientation to be directly correlated with magnetic behaviour. The technique opens the door to characterizing nanoparticles one by one, without averaging, which is relevant for the design of magnetic materials and for applications in information storage and biomedicine.

The results show that the magnetization response of the individual particle follows the expected anisotropy, confirming that this property governs behaviour at the nanoscale. The approach could be extended to other nanoparticle systems and to studies of magnetic switching for technological applications.