The family of magnetic materials has been traditionally divided into the ferromagnetic branch known for several millennia and the antiferromagnetic branch known for nearly a century. Researchers from the Institute of Physics of the Czech Academy of Sciences have recently made a discovery of a new branch of the magnetic family, termed altermagnetic.
The discovery was published earlier this year in Nature. Now they publish a second Nature article in which they reveal the first direct microscopic images of an altermagnet. The work was performed in collaboration with scientists from the University of Nottingham, synchrotron facilities in the UK, Sweden and Switzerland, and Max Planck institute and Johannes Gutenberg University in Germany.
The magnetization in ferromagnets offers a range of physical phenomena used, among others, for making embedded memory bits in advanced-node integrated circuits. This so-called spintronic technology is the first in the history of IT to complement semiconductor bits on processor chips. However, the magnetization in ferromagnets also imposes principal limitations on the spatial, temporal and energy scalability of these spintronics IT devices.
Since 2020, the team from the Institute of Physics in Prague with collaborators has published a series of articles theoretically identifying the new branch of altermagnetic materials, featuring a unique combination of alternating direction of north and south poles on neighboring magnetic atoms
with an alternating orientation of anisotropic local crystal environment of these atoms. Such a magnetic phase removes the scalability limits imposed by the magnetization of ferromagnets, while still allowing for the physical phenomena facilitating the functionality of the spintronic IT. Apart from spintronics, the prediction of altermagnetism caught attention in many fields of condensed matter physics, with more than five hundred studies reported by scientists from all over the world over the past two years.
In the first Nature paper published earlier this year, the Prague team with collaborators reported measurements of quantum energy levels in a prototypical altermagnetic material MnTe, providing the first spectroscopic evidence of altermagnetism. In the present paper, the team reports direct real-space microscopic images of the ordering of the alternating north and south magnetic poles in MnTe.
The employed high-resolution microscopy is only available at the most advanced measurement facilities at synchrotrons and, besides the experimental skills, requires the preparation of extra high-quality samples and a well-informed quantitative theoretical guidance. The invested effort, however, paid off because, quoting Tomas Jungwirth - a senior coordinator of the work: ”Seeing is believing”. The reported microscopic images represent a milestone which is expected to initiate extensive experimental research of altermagnets, as well as the development of altermagnetic spintronic devices towards future highly scalable IT.
Amin, O.J., Dal Din, A., Golias, E. et al. Nanoscale imaging and control of altermagnetism in MnTe. Nature 636, 348–353 (2024). doi.org/10.1038/s41586-024-08234-x
