Amorphous metals have unusual magnetic properties that arise due to the disordered atomic arrangement. We show that Cox(Al70Zr30)100−x (65 < x < 92 at. %) amorphous alloys have a distribution in the local magnetic coupling and ordering temperature, which can be explained by nanoscale composition variations. We use competing anisotropies induced by the substrate and an applied field during growth to probe the Co concentration distribution. Only regions with high enough Co concentration develop a magnetic anisotropy along the magnetic field during growth, whereas regions of low Co concentration have an anisotropy dictated by the substrate. A Gaussian distribution in the Co concentration of width 5.1 at. % is obtained from the variation in anisotropy. The results demonstrate the importance of composition variations for emergent magnetic properties and have far reaching implications for the properties of disordered materials in general.
