Dynamics of magnetism in Fe-Cr alloys with Cr clustering

The dynamics of magnetic moments in iron-chromium alloys with different levels of Cr clustering show unusual features resulting from the fact that even in a perfect body-centered-cubic structure, magnetic moments exhibit geometric magnetic frustration resembling that of a spin glass. Due to the long range exchange coupling and configuration randomness, magnetic moments of Cr solutes remain noncollinear at all temperatures. To characterize magnetic properties of Fe-Cr alloys, we explore the temperature dependence of magnetization, susceptibility, Curie temperature, and spin-spin correlations with spatial resolution. The static and dynamic magnetic properties are correlated with the microstructure of Fe-Cr, where magnetization and susceptibility are determined by the size of Cr precipitates at nominal Cr concentrations. The Curie temperature is always maximized when the solute concentration of Cr in the alpha phase is close to 5 to 6 at. %, and the susceptibility of Fe atoms is always enhanced at the boundary between a precipitate and solid solution. Interaction between Cr and Fe stimulates magnetic disorder, lowering the effective Curie temperature. Dynamic simulation of evolution of magnetic correlations shows that the spin-spin relaxation time in Fe-Cr alloys is in the 20 to 40 ps range.