but which undergoes a structural transition into a tetragonal state with ferromagnetic order when cooled below its 1=''T''_C = 125 K. In its ferromagnetic state, PuP's easy axis is in the <100> direction.

In NpFe₂ the easy axis is <111>. Above ''T''_C ? 500 K, NpFe₂ is also paramagnetic and cubic. Cooling below the Curie temperature produces a rhombohedral distortion wherein the rhombohedral angle changes from 60° (cubic phase) to 60.53°. An alternate description of this distortion is to consider the length along the unique trigonal axis (after the distortion has begun) and as the distance in the plane perpendicular to . In the cubic phase this reduces to {{Mvar/Mvar|a}} =}} 1.00}}. Below the Curie temperature, the lattice acquires a distortion