${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$'s unsurpassed, hard magnetic properties for a wide range of temperatures result from a combination of a large volume magnetization from Fe and a strong single-ion anisotropy from Nd. Here, using finite temperature first-principles calculations, we focus on the other crucial roles played by the Fe atoms in maintaining the magnetic order on the Nd sublattices, and hence the large magnetic anisotropy, and directly generating significant uniaxial anisotropy at high temperatures. We identify effective spins for atomistic modeling from the material's interacting electrons and quantify pairwise and higher order, nonpairwise magnetic interactions among them. We find the Nd spins couple most strongly to spins on sites belonging to two specific Fe sublattices: $8j_1$ and $8j_2$. Moreover, the Fe $8j_1$ sublattice also provides the electronic origin of the unusual, nonmonotonic temperature dependence of the anisotropy of ${\mathrm{Y}}_2{\mathrm{Fe}}_{14}\mathrm{B}$. Our work provides atomic-level resolution of the properties of this fascinating magnetic material.

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• Electronic structure
• Magnetic anisotropy
• Magnetic interactions
• Magnetic order