Both $\mathrm{Cu}$ and $\mathrm{Fe}$ metals, with face-centered cubic (fcc) crystal structures, are nonmagnetic. However, the substitution of $\mathrm{Cu}$ atoms by Fe in the fcc-$\mathrm{Cu}$ lattice leads to the formation of a random solid solution and the appearance of ferromagnetic order, with a value of the magnetic moment per $\mathrm{Fe}$ atom in a fcc environment even above $2{\mu }_B$. This striking behavior is closely related to magnetovolume effects (Invar), which we have detected by means of lattice thermal expansion and magnetization measurements in $\mathrm{FeCu}$ alloys.

The origin of magnetism in atomically disordered transition-metal–nonmagnetic (i.e., FeAl) alloys has been investigated by dichroism and diffraction measurements at high pressure and by band structure calculations. The results show that, in contrast to earlier studies, besides the effects of the local environment of the magnetic ions, disorder-induced lattice changes play a key role in the magnetic properties of these systems. We demonstrate experimentally and theoretically that about 35–45% of the magnetic moment of ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ alloys arises from lattice expansion effects induced during the disordering process. Such large effects in ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ could actually be related to the moment-volume instability observed in these alloys.