Scientists at the National Institute of Standards and Technology (NIST) have discovered an exotic form of magnetism in a new crystal. This exotic form of magnetism has been linked to an equally exotic type of electron. The unique electronic structure of the crystal creates and protects magnetism.
The material’s unusual structure conducts electricity but causes its electrons to behave like massless particles. Electrons promote the spontaneous formation of a magnetic spiral.
The study reveals a link between the material, the electrons which pass through it in the form of current, and the magnetism of the material.
In their study, the scientists studied a semi-metal made of silicon and the metals aluminum and neodymium. These elements come together to form a crystal, which implies that the atoms that compose it are arranged in a regular repeating pattern.
However, a crystal breaks inversion symmetry, which means that the repeating pattern is different on one side of a crystal’s unit cells – the smallest element in a crystal lattice – than on the other. This arrangement stabilizes the electrons flowing through the crystal, resulting in unusual behavior of its magnetism.
The stability of electrons results in uniformity in the direction of their spins. The semi-metal has a broken symmetry that turns the flowing electrons into Weyl electrons. Weyl electrons have spins oriented either in the direction in which the electron is moving or in the exact opposite direction. This locking of the spins of Weyl electrons in their direction of motion – their momentum – causes the rare magnetic behavior of the semi-metal.
All atoms in the material conduct electricity, giving electrons a springboard as they leap from atom to atom. However, only neodymium (Nd) atoms exhibit magnetism. Due to the susceptibility to the influence of Weyl electrons, the spin of Nd atoms grows curiously.
Collin Broholm, a physicist at Johns Hopkins University who led experimental work at the NIST Center for Neutron Research (NCNR), noted, âA simplified way of imagining it is that the first atom Nd points around 12 o’clock, then the next one around 4 o’clock, then the third one around 8 o’clock. Then the pattern repeats. This beautiful spin “texture” is driven by Weyl electrons when they visit neighboring Nd atoms. “
âEach loop of the spinning spiral is about 150 nanometers long, and the spirals only appear at cold temperatures below 7 K. There are materials with similar physical properties that work at room temperature and they could. be exploited to create efficient magnetic memory devices. “
âMagnetic memory technology like hard drives generally requires you to create a magnetic field for them to work. With this class of materials, you can store information without applying or detecting a magnetic field. Reading and writing information electrically is faster and more robust.
âBasically we might be able to create a variety of materials that have different internal rotational characteristics, and maybe we’ve done that already. As a community, we have created many magnetic structures that we do not immediately understand. After seeing the special character of Weyl-mediated magnetism, we may finally be able to understand and use such exotic magnetic structures. “
- Gaudet, J. et al. Weyl-mediated helical magnetism in NdAlSi. Nat. Mater. (2021). DO I: 10.1038 / s41563-021-01062-8