Highly accurate soft-XMCD data recorded on a ${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$ single crystal, through the spin reorientation transition show that the average Fe orbital moment (a) is proportional to the macroscopic Fe anisotropy constant, and (b) diverges 15 K below the reorientation transition temperature. This divergence is indicative of a critical behavior and it is related to a tetragonal distortion. These results give experimental evidence of the mutual dependence between orbital moment, macroscopic magnetic anisotropy, and tetragonal distortion. Furthermore, it is argued that the critical behavior of the orbital moment is at the origin of similar divergences previously observed in Mössbauer and Hall-effect data.

• Received 4 February 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.429