Interplay of structure and magnetic properties in MnSi, a concentrated spin-glass

We have performed an extended x-ray-absorption fine-structure (EXAFS) measurement of the Mn environment in amorphous $(a-)\mathrm{MnSi}$. Whereas the Mn magnetic moments in crystalline MnSi order as a helical antiferromagnet below 29 K, $a-\mathrm{MnSi}$ is a concentrated spin-glass with a transition temperature of 22 K. The nearest neighbors of Mn in $a-\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{i}$ are shown to consist of five to six Si atoms at a mean distance of 2.43 ± 0.02 Å. There is no evidence for either a single close Si neighbor or a well-defined shell of Mn neighbors, such as are found in the crystal. We propose a framework within which the different magnetic behaviors of the crystalline and amorphous forms can be understood in terms of atomic order and competing magnetic interactions. We also discuss the implications of observing spin-glass behavior in concentrated as well as dilute moment systems.