Phase Selection in Mn–Si Alloys by Fast Solid‐State Reaction with Enhanced Skyrmion Stability

Abstract

B20‐type transition‐metal silicides or germanides are noncentrosymmetric materials hosting magnetic skyrmions, which are promising information carriers in spintronic devices. The prerequisite is to prepare thin films on technology‐relevant substrates with magnetic skyrmions stabilized at a broad temperature and magnetic‐field working window. A canonical example is the B20‐MnSi film grown on Si substrates. However, the as‐yet unavoidable contamination with MnSi1.7 occurs due to the lower nucleation temperature of this phase. In this work, a simple and efficient method to overcome this problem and prepare single‐phase MnSi films on Si substrates is reported. It is based on the millisecond reaction between metallic Mn and Si using flash‐lamp annealing (FLA). By controlling the FLA energy density, single‐phase MnSi or MnSi1.7 or their mixture can be grown at will. Compared with bulk MnSi, the prepared MnSi films show an increased Curie temperature of up to 41 K. In particular, the magnetic skyrmions are stable over a much wider temperature and magnetic‐field range than reported previously. The results constitute a novel phase selection approach for alloys and can help to enhance specific functional properties, such as the stability of magnetic skyrmions.

The origin for the increased Curie temperature of B20-MnSi films

“…However, they have not detected skyrmions in their lms. In our thick lms, both magnetic skyrmions and an enhanced Curie temperature are detected [22]. Therefore, the understanding of the magnetic properties of MnSi lms is far from satisfactory.…”

“…substrates. Here, the lm thickness is xed at around 40 and 60 nm and the amount of MnSi 1.7 is varied since we changed the FLA energy slightly [22]. Therefore, T C of MnSi lms is not determined by its crystalline orientation, texture or the mixture with MnSi 1.7 .…”

On Curie temperature of B20-MnSi films

“…3 c and d, the T C always remains around 43 K with increasing amount of the MnSi 1.7 phase on Si(100) or (111) substrates. Here, the film thickness is fixed at around 40 and 60 nm and the amount of MnSi 1.7 is varied since we changed the FLA energy slightly 22 . Therefore, T C of MnSi films is not determined by its crystalline orientation, texture or the mixture with MnSi 1.7 .…”

“…The details about the preparation have been reported in Ref. 22 . All samples used in this manuscript are summarized in Table 1 .…”

Re-Examination of the Microstructural Evolution in Undercooled Co-18.5at.%B Eutectic Alloy

“…Most solidification behaviors take place outside of the equilibrium state because of the rapid cooling rate or the large undercooling (∆T), which result in various microstructures and properties [2,3]. So far, the microstructural evolution and phase selection behaviors of undercooled melts have been investigated in many systems, such as the Mn-Si [4] and Cu-Sn [5] systems, using cyclic overheating combined with glass fluxing [6], directional solidification [5], and laser melting [7], with in situ observations [8] or numerical simulations [9], to manipulate and control the microstructures and properties. For instance, the uniform nature and refinement of the grains can be obtained as the ∆T increases, which can effectively improve the yield strength [10] and the physical properties [11].…”