An important discovery has been made in studying van der Waals (vdW) magnetic materials. A team of physicists from the University of Hong Kong (HKU), Texas Tech University (TTH), and the University of Michigan (UMich) has experimentally observed a transition in nickel-phosphorus trisulfide (NiPS3).
NiPS3, a van der Waals material type, is widely studied because of its potential applications in electronic devices and energy storage. The layers in this material can be easily stacked or separated, allowing scientists to determine their properties with varying thicknesses.
Now, for the first time, physicists have discovered that this material changes its magnetic properties as it becomes thinner.
This is a significant discovery as it allows scientists to understand how to control the magnetic properties of materials at very small scales. It could lead to technological advancements, such as more efficient electronics, high-density data storage, and innovative computing devices that consume less energy.
In condensed matter physics, studying materials requires understanding their transition between different phases or states as their properties change. These transitions often involve changes in the material’s symmetry, which is known as symmetry breaking.
In NiPS3, researchers observed intermediate symmetry breaking, resulting in a vestigial order. This term, akin to evolutionary vestigial traits, describes retaining a simpler order form during symmetry breaking. Specifically, as NiPS3 is thinned, its original magnetic order transitions into a 2D vestigial state known as Z3 Potts-nematicity. Unlike complete symmetry breaking, vestigial order only involves breaking some symmetries.
Despite several examples from a theoretical standpoint, experimental realizations of vestigial order have remained challenging.
However, this study sheds the first light on this issue, demonstrating that such a phenomenon can be observed through dimension crossover.
Scientists studied NiPS3 using nitrogen-vacancy (NV) spin relaxometry and optical Raman quasi-elastic scattering. NV spin relaxometry helped them characterize the melting process in the primary order. The optical Raman quasi-elastic scattering method allowed them to observe the emergence of the vestigial order as the thickness changed.
The team also performed large-scale Monte Carlo simulations to visualize the magnetic phase for bilayer NiPS3.
This study is the first to carefully track two distinct symmetries as dimensions change, revealing the transition from primary to vestigial order. Large-scale Monte Carlo simulations identified the vestigial phase transition during this crossover.
The study offers a detailed understanding of the differences between 2D and 3D physics.
Scientists noted, “With this advancement, we are inching closer to realizing Feynman’s vision of layered materials and devices with precisely engineered layers.”
Journal Reference:
- Zeliang Sun et al, Dimensionality crossover to a two-dimensional vestigial nematic state from a three-dimensional antiferromagnet in a honeycomb van der Waals magnet, Nature Physics (2024). DOI: 10.1038/s41567-024-02618-6
