X-ray electron density analysis of chemical bonding in permanent magnet Nd2Fe14B

Author: mycolabadmin
9/29/2025
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Summary

Scientists used advanced X-ray technology to peek into the atomic structure of a super-strong magnet called Nd2Fe14B, which is used in everything from wind turbines to electric cars. Despite the material being extremely difficult to analyze because it contains many heavy atoms, researchers successfully mapped out how electrons are distributed and how atoms bond together. They discovered that iron atoms form a complex 3D network that is crucial for creating the magnet’s exceptional strength, with one particular iron atom (Fe2) being essential for connecting the different layers.

Background

Nd2Fe14B is a super-strong metallic magnet with vital applications in modern technology, yet its complex chemical bonding and local atomic structure remain poorly understood. The compound’s complexity, featuring six independent Fe sites, two independent Nd sites, and one B site, combined with its heavy atom composition, makes it an exceptionally challenging material for X-ray charge density analysis. Understanding the chemical bonding is crucial for comprehending the material’s extraordinary magnetic properties.

Objective

This study aimed to quantify and analyze the complex chemical interactions in Nd2Fe14B using high-resolution synchrotron single-crystal X-ray diffraction data at 25 K to model its electron density. The research sought to overcome the material’s extremely low suitability factor of 0.02 for X-ray electron density analysis and provide fundamental insight into the electronic structure underlying its exceptional magnetic properties.

Results

The X-ray electron density analysis revealed that Nd atoms are positive (∼+1), B is negative (−1.7), Fe4 is negative (−0.44), and remaining Fe atoms are near neutral (±0.1). The d orbitals of all Fe atoms are close to evenly populated with asphericity values of 0.46–1.50. The molecular graph shows a comprehensive Fe–Fe interaction framework with Fe2 identified as crucial for establishing the 3D structure. Debye temperatures were estimated at 345–383 K from anisotropic displacement parameters.

Conclusion

Despite the exceptional challenges posed by Nd2Fe14B’s complexity and heavy atom composition, successful multipole modelling of its electron density was achieved. The results confirm local anisotropy in Fe bonding environments and establish a ‘metal-like’ multidirectional bonding framework where Fe2 plays a critical role in the 3D magnetic structure. These findings provide fundamental chemical insights into the bonding responsible for the compound’s outstanding magnetic properties.

Published in:IUCrJ,
Study Type:Experimental Research,
Source: 10.1107/S2052252525007602