Optical characteristics of an epitaxial Fe3Si/Si(111) iron silicide film

Abstract

1.Currently, ferromagnetic iron silicide Fe 3 Si turns out to be a promising material for such applications as spin transistors, magnetoresistive memory, and mag neto optical devices [1][2][3][4] owing to its high Curie temperature (about 840 K), relatively high magnetic permeability, low magnetic and crystallographic anisotropy, high electrical resistivity, and high spin polarization (as high as 43%). During the last decade, thin films of this material have been widely studied. A lot of papers deal with the interplay of their structural and magnetic characteristics [5,6], as well as with the transport properties and developments of prototypes of spintronic devices [7,8]. However, the electronic structure and optical properties of Fe 3 Si are still rather poorly studied. In particular, the energy dependence of its relative permittivity is treated only in one theo retical paper [9], the results of which have not been verified by experiment. The main aims of our work are to study the optical characteristics of an epitaxial Fe 3 Si/Si(111) iron silicide film and to determine the dispersion of the relative permittivity ε using the spec troscopic ellipsometry technique. 2.The Fe 3 Si film was obtained by the thermal evap oration technique in ultrahigh vacuum at the recon structed Si(111)7 × 7 surface. The formation of the film structure was controlled by an LEF 751M high speed laser ellipsometer [10]. The technique used for the preparation of the atomically clean Si(111)7 × 7 surface, the process of growth of Fe 3 Si/Si(111)7 × 7 film, and the data on the structure of this film and its magnetic properties were described in [11].The data obtained by single wavelength ellipsome try for the synthesized Fe 3 Si/Si(111) film (Fig. 1) were analyzed by the method described in [12]. This analy sis was based on the optical model involving a homo geneous isotropic film at a semi infinite isotropic sub strate. The value obtained for the thickness of the formed film agrees well with the data provided by transmission electron microscopy. It equals 27 nm.In Fig. 1, we can see that the behavior of the thick ness at the initial stages of the film growth is not phys ical. The calculated refractive index n and the coeffi cient of absorption k vary drastically beginning from values close to the optical parameters of silicon (n = 3.93 and k = 0.54) to those characteristic of conduct ing materials (n = 3.43 and k = 3.54). We attribute such behavior at the initial stage of the film formation to the epitaxial island growth mechanism, rather than to layer by layer growth. After 45 min of film growth, the thickness begins growing monotonically and n and k achieve values remaining unchanged in the course of further growth. Thus, when the effective thickness achieves 5 nm, the Fe 3 Si film forms as a continuous layer. The values of the real and imaginary parts of the relative permittivity determined by the laser ellipsom etry (λ = 632.8 nm) at a temperature of 150° are ε' = -0.97 and ε'' = 24.07, respectively.3. In the present work, the energy ...

Analysis of optical and magnetooptical spectra of Fe5Si3 and Fe3Si magnetic silicides using spectral magnetoellipsometry

“…The magnetization angle β is defined as (5) To calculate the values of n and k for the ferromagnet from the Snell law of refraction, the authors of [16] pro pose that only coefficients B 5 and B 6 be used: (6) However, the algorithm proposed in [16] encoun ters difficulties associated with simultaneous exact calculation by the least square method of all six inter mediate coefficients B 1-6 appearing in the expression for δI/I. The values of δI/I determined by formula (3) appear in the expression (7) where g i = g i (t 1 , t 2 ) are functions depending on the angles of rotation of the polarized (t 1 ) and analyzer (t 2 ).…”

“…To calculate coefficients B 1-6 exactly and to sub stantially reduce the time of magnetooptical measure ments, we independently calculated coefficients B 5 and B 6 using expression (6), where n and k were deter mined using multiangle ellipsometry. Using the result ing values of B 5 and B 6 and the system of equations based on expression (7), we calculated coefficients B 1⎯4 .…”

“…Silicide Fe 3 Si is characterized by a large electron spin polarization factor [4,5] and can be grown epi taxially on a Si(111) single crystal [6,7]. In turn, the Fe 5 Si 3 silicide implanted in silicon demonstrates the giant magnetoresistance effect (2400%) [1], but is thermodynamically unstable in the bulk state at room temperature [8].…”

“…The electronic structure and the spectral optical properties of Fe 3 Si have been studied in detail in only two publications [6,9]. However, the spectral magnetooptical properties of Fe 5 Si 3 and Fe 3 Si have not been analyzed in the literature except for measurement of Faraday rotation in a Fe 5 Si 3 polycrystalline film [10].…”

“…According to the spectral ellipsometry data, the total thickness of the Fe 3 Si layer was 27 nm. The results of determining the spectral dependence of the complex refractive index N for Fe 3 Si from multiangle spectral ellipsometry data are also given in [6].…”