Competitive actions of MnSi in the epitaxial growth of Mn5Si3 thin films on Si(111)

Abstract

Some magnetically ordered phases of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ crystal are proving to be prototypes for the study of the new fundamental spin physics related to the spontaneous breaking of the time-reversal symmetry despite a zero net magnetization. Here, we report on a route to grow epitaxial ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ thin films on Si(111). To this end, we use Mn and Si codeposition in a molecular beam epitaxy system and carefully tune the deposition rates, the growth temperature, and the annealing temperature. We assessed the silicide phase-formation and morphology using reflection high-energy electron diffraction, x-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy. Layers containing only ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ could be stabilized under very restrictive conditions, by tuning the Mn/Si flux ratio to match the compound stoichiometry and adjusting the substrate temperature during growth to 443 K. HRTEM imaging revealed the existence of an interfacial amorphous layer of few nanometers thickness. Annealing the heterostructure up to 573 K led to the formation of MnSi at the vicinity of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$/Si(111) interface, which significantly reduced the nucleation barrier of ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$. High-quality crystalline ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ thin films were then formed with the following epitaxial relationships: ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$(0001)$[01\overline{1}0]//\mathrm{MnSi}(111)[\overline{2}11]//\mathrm{Si}(111)[1\overline{1}0]$. Our experiments showed that the formation of MnSi is enhanced at a growth temperature above 473 K or for a longer annealing step, while the crystalline quality of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ overlayer is correspondingly degraded leading to textured thin films. The growth pathways and structural properties of the manganese silicides can be rationalized in terms of reactions maximizing the free-energy lowering rate. Moreover, we found that the magnetic and the magnetotransport properties can be used as an efficient tool to track both ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ crystallinity and proportion in the deposited layers.