First-Principles Study of Ferromagnetism in Epitaxial Si-Mn Thin Films on Si(001)

Abstract

Density-functional theory calculations are employed to investigate both the epitaxial growth and the magnetic properties of thin Mn and MnSi films on Si(001). For single Mn adatoms, we find a preference for the second-layer interstitial site. While a monolayer Mn film is energetically unfavorable, a cappingSi layer significantly enhances the thermodynamic stability and induces a change from antiferromagnetic to ferromagnetic order. For higher Mn coverage, a sandwiched Si-Mn thin film (with CsCl-like crystal structure) is found to be the most stable epitaxial structure. We attribute the strong ferromagnetic intralayer coupling in these films to Mn 3d-Si 3s3p exchange. DOI: 10.1103/PhysRevLett.92.237202 PACS numbers: 75.70.-i, 75.50.Pp A possible route to spintronics devices involves the injection of spin-polarized current from a ferromagnetic (FM) metal into a semiconductor [1,2]. In this context, FM-metal-semiconductor heterojunctions have attracted considerable attention [3][4][5][6][7]. From the viewpoint of applications, it would be highly desirable to grow welldefined FM films on the most common semiconductor, silicon, in particular on the technologically relevant Si(001) surface. However, common FM metals (Fe, Co) react strongly with Si, and the resultant silicide films are weakly magnetic or even nonmagnetic (NM), and, thus, unsuitable for spintronics devices. We note that Mn atoms, in suitable chemical environments, possess sizable magnetic moments. Moreover, both fcc-Mn and some Mn-Si compounds are closely lattice matched with the Si(001) surface. We therefore investigated the suitability of thin films of manganese or its intermetallic Mn-Si compounds for growing FM films on Si(001). Thus far, there are only a few experimental studies on Mn=Si111 [8-10], and even fewer on Mn=Si001 [11]. Theoretical investigations are lacking.In this Letter, we present first-principles calculations for pseudomorphic Mn and Mn-Si films on Si(001), focusing on their atomic structure, stability, and magnetic properties. On the basis of our calculations, we propose that metastable FM MnSi films on Si(001) can be grown that lend themselves to applications in spintronics: First, we find Mn atoms to prefer a second-layer interstitial site to sites at the surface or in the third layer. This opens the possibility to grow Si-Mn layered structures with a welldefined, atomically sharp interface on Si(001) required to obtain high spin injection efficiency [6]. Second, we predict a two-layer Si-Mn sandwich structure to display the desired FM metallic behavior.The calculations are performed using densityfunctional theory, employing the all-electron fullpotential augmented plane-wave plus local-orbital method (APW LO) [12]. The generalized gradient approximation (GGA) [13] is adopted for the exchangecorrelation potential, since it was demonstrated [14] and confirmed by our test calculations that GGA gives a much better description for bulk Mn than the local-spin-density approximation. Our GGA calculations for the fcc-Mn give the corr...

Ab initiostudy of the magnetic ordering in Si/Mn digital alloys

“…20 In this study, Mn was found to be incorporated into Si as an interstitial dopant in good agreement with recent first-principles calculations. [23][24][25] The interstitial Mn was also observed in thin films irradiated by ultraviolet light releasing metal species into the semiconductor substrate. 26 Meanwhile, molecular beam epitaxy produces samples with mostly substitutional Mn in the Si matrix.…”

The growth of manganese layers on Si(100) at room temperature: A photoelectron spectroscopy study

“…In order to circumvent these problems we are investigating the feasibility of a surface-driven approach for the incorporation of Mn into a Si matrix. This approach has been suggested in several theoretical studies, which indicate that selected Mn-Si surface structures, and delta-doped layers of Mn embedded in Si might indeed be ferromagnetic [11,[16][17][18][19][20][21][22][23]. A set of recent STM studies has been geared towards the investigation of the formation of Mn surface structures on the Si(1 0 0) surface [18][19][20]24].…”

Half-metallic ferrimagnetism in the and alloys adopting the zincblende and wurtzite structures from first-principles

“…The case where the sp atom comes from the IVth column of the periodical table has attracted much less attention in literature and to the best of our knowledge only the cases of MnC [8,9,10], MnSn [9] and MnSi [11,12,13] in the zincblende lattice have been studied. In this manuscript we study using the full-potential nonorthogonal local-orbital minimum-basis band structure scheme (FPLO) [14] within the local density approximation (LDA) [15] the case of [Sc 1−x V x ]C and [Sc 1−x V x ]Si alloys for x taking the values 0, 0.1, 0.2, ...,0.9, 1.…”