Iron group impurities in Β-FeSi2sstudied by EPR

Abstract

Using EPR we have investigated bulk single crystals of ␤-FeSi 2 grown by chemical vapor transport. By an interpretation of the hyperfine structure combined with intentional doping during crystal growth, we prove that most of the paramagnetic centers observed arise from isolated iron group impurities. The 3d transition metals Cr, Mn, and Co, and with less certainty Ni and Cu, have been identified. The angular variations of the corresponding spectra show orthorhombic symmetry and can be explained with an electronic spin Sϭ 1 2 . The substructure of the EPR lines due to the ligand hyperfine interaction indicates an eightfold Si coordination. The simple center model of an impurity atom substituting for iron is consistent with the observed spin, symmetry, and coordination. Whereas Cr and Mn can occupy either of both crystallographically inequivalent Fe sites Co, Ni, and Cu prefer one site. For Cu, however, an interstitial incorporation also seems possible.

Comment on “Electron spin resonance studies in β-FeSi2 crystals” [J. Appl. Phys. 80, 1678 (1996)]

“…4 A more comprehensive paper on this subject is forthcoming. 5 ͑II͒ We believe that AK obtained by their CVT technique ␤-FeSi 2 crystals of the same real structure as ours which is supported by their report of crystals ''in the form of thin needles.'' Nevertheless, the crystalline perfection of the samples is high and one should perform a rigorous measurement of the angular variation of the EPR line positions.…”

“…All the centers, which we reported on, possess orthorhombic symmetry with their principal axes system of the g tensor coinciding with the orthorhombic crystal system. 4,5 The three principal g values of each center could be determined from the turning points in the pattern of the EPR line positions obtained by the rotation of the needle-like crystals about their longitudinal axis which was kept perpendicular to the static magnetic field. In Fig.…”

Solution growth of n-type - single crystals using Sn solvent

“…Table 2 shows the list of facet angles measured from the crystal grown towards the h0 1 1i and h0 1 0i directions. The crystals grown towards the h0 1 1i direction had ten growth facets belonging to symmetry equivalent faces of f1 0 0g; f1 1 1g and f3 1 1g; whereas those grown towards the h0 1 0i direction had eight growth facets belonging to those of f1 0 0g; f0 0 1g and f1 0 1g: These Miller indexes of the growth facets are reported in both solution and CVT-grown b-FeSi 2 single crystals [9,11,15]. Table 2 List of growth facets observed in the needle-like crystals grown toward the h0 Fig.…”

“…By analyzing the diffraction patterns and the intensity ratio of the diffraction spots, we identified that the facets (I) and (II) were (1 0 0) and (0 0 1) face, respectively, and the needle axis was parallel to the h0 1 0i direction. Irmscher et al reported that the needle-like b-FeSi 2 crystals grown by the CVT method had rotational twins parallel to f1 0 0g faces and their needle axis is parallel to the ½0 1 0 and ½0 0 1 direction due to the rotation of the b-c plane [15]. In our observations, however, no rotational twin was found in the crystals grown toward the h0 1 0i direction, and no crystals grown toward the h0 0 1i direction were found.…”

MAGNETIC PROPERTIES OF Fe0.95Co0.05Si2 SEMICONDUCTING FILM

“…13,15 Electron paramagnetic resonance (EPR) studies further revealed that there are a variety of paramagnetic centers in β-FeSi 2 due to the isolated iron group impurities. 16 Recently, Hamdeh et al suggested that the chemical-disorder can induce the magnetism in nanoparticles of β-FeSi 2 using the Mössbauer spectroscopic analysis. 17 Hattori et al also observed the formation of the ferromagnetic interface (Fe 3 Si) between the β-FeSi 2 film and Si substrate owing to the chemical-disorder at the interface.…”