Transverse Kerr Effect Spectra Research Articles

Effect of Phase Transformations of a Metal Component on the Magneto-Optical Properties of Thin-Films Nanocomposites (CoFeZr)x (MgF2)100-x.

The results of complex studies of structural-phase transformations and magneto-optical properties of nanocomposites (CoFeZr)x (MgF2)100−x depending on the metal alloy content in the dielectric matrix are presented. Nanocomposites were deposited by ion-beam sputtering onto glass and glass-ceramic substrate. By studying the spectral and field dependences of the transversal Kerr effect (TKE), it was found that the transition of nanocomposites from superparamagnetic to the ferromagnetic state occurs in the region of xfm~30 at%, that corresponds to the onset the formation of ferromagnetic nanocrystals CoFeZr with hexagonal syngony in amorphous dielectric matrix of MgF2. With an increase of concentrations of the metal alloy for x > xfm, the features associated with structural transitions in magnetic granules are revealed in the TKE spectra. Comparison of the spectral and concentration dependences of TKE for nanocomposites on the glass and glass-ceramics substrates showed that the strongest differences occur in the region of the phase structural transition of CoFeZr nanocrystals from a hexagonal to a body-centered cubic structure at x = 38 at.% on the glass substrates and at x = 46 at.% on glass-ceramics substrates, due to different diffusion rates and different size of metal nanocrystals on amorphous glass substrates and more rough polycrystalline glass-ceramics substrates.

Magnetic Inhomogeneity Manifestations in the Magneto-Optical Spectra of (In-Mn)As Layers

Spectral, temperature, and magnetic field dependences of the magneto-optical transversal Kerr effect (TKE) as well as optical properties of (In,Mn)As samples prepared by ion implantation followed by pulsed laser melting were studied, and a strong TKE response was detected at low temperatures. The presence of a characteristic structure in the TKE spectra in the transition region around the Λ point of the InAs band structure confirms the intrinsic nature of observed ferromagnetism. The TKE temperature dependences recorded in different spectral regions exhibit nonmonotonous behavior, indicating magnetic inhomogeneity of the samples studied. The character of the TKE magnetic field dependences also confirms the presence of magnetic inhomogeneity in the samples.

The Transverse Kerr Effect, Modeled in (CoFeZr)x(Al2O3)(1 −х) Nanocomposites

Spectral dependences of the transverse Kerr effect (TKE) are studied in (CoFeZr)x(Al2O3)(1 − х) magnetic nanocomposites. TKE spectra are modeled for an unannealed composite using the Maxwell–Garnett approximation (MGA) in an effective medium. TKE calculations are made by considering the particle sizes of the nanocomposite (the quasi-classical size effect). The experimental data are found to be consistent with the theoretical TKE spectra.

Magneto-optical spectroscopy of diluted magnetic semiconductors GaMnAs prepared by ion implantation and further impulse laser annealing

Ga1−xMnxAs layers prepared by ion implantation and subsequent pulsed laser annealing with the planned Mn concentrations of x = 0.01–0.08 have been studied using the magneto-optical transversal Kerr effect (TKE) and spectral ellipsometry. The spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) have been calculated for the layers. The obtained spectra of the diagonal PT components show that the layers under study maintain the zinc-blende crystal structure of the parent GaAs semiconductor. All studied samples reveal a strong TKE response at low temperatures with a dependence of an effective Curie temperature (at which TKE appears) on the Mn concentration. A number of extrema in the low-temperature TKE and MCD spectra are close to the energies of transitions in the Γ and L critical points of the parent semiconductor band structure that confirms the intrinsic ferromagnetism of the Ga1−xMnxAs layers. The MCD spectra shape and its change with Mn concentration increasing are discussed on a base of the valence-band model of ferromagnetism in DMS.

Probing the electronic structure of Ni–Mn–In–Si based Heusler alloys thin films using magneto-optical spectra in martensitic and austenitic phases

Thin films of Ni52Mn35−xIn11+xSi2 were fabricated by magnetron sputtering on MgO (001) single crystal substrates. Magnetization as function of temperature for Ni52Mn35In11Si2 exhibits features consistent with a magnetostructural transition (MST) from an austenitic phase to a martensitic phase, similar to the bulk material. We observed that the martensitic transformation is externally sensitive to small changes in chemical composition and stoichiometry. It has been found that thin films of Ni52Mn34−xIn11+xSi2 with x=0 and 1 undergo a temperature-induced MST or remain in a stable austenitic phase, respectively. Comparison of magneto-optical transverse Kerr effect spectra obtained at 0.5–4.0eV in the 35–300K temperature interval reveal insignificant differences between the martensitic and austenite phases. We found that the field and temperature dependencies of the transverse Kerr effect are quite different from the magnetization behavior, which is attributed to magnetic inhomogeneity across the films. To elucidate the effects of magnetostructural phase transitions on the electronic properties, we performed density functional calculations of the magneto-optical Kerr effect.

Transversal Kerr effect of In1−xMnxAs layers prepared by ion implantation followed by pulsed laser annealing

In1−xMnxAs (x = 6.9%) layers prepared by ion implantation and subsequent pulsed laser annealing have been studied using the magnetooptical transversal Kerr effect (TKE) and spectral ellipsometry. Ellipsometry data reveal the good crystal quality of the layers. The samples show ferromagnetic behaviour below 77 K. Near the absorption edge of the parent InAs semiconductor, large TKE values are observed. In the energy regions of the transitions in the Γ and L critical points of the InAs Brillouin zone, there are several clearly defined structures in the low-temperature TKE spectra. We have calculated the spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) for our samples. A number of extrema in the obtained MCD and PT spectra are close to the energies of transitions in the critical points of the parent semiconductor band structure, which confirms the intrinsic ferromagnetism of the Mn-doped InAs layers.

Magneto-Optical Properties of Multilayer Nanostructures with Composite Magnetic Layers near Percolation Threshold

Spectra and field dependencies of Transversal Kerr Effect (TKE) for [(Co45Fe45Zr10)46(Al2O3)54(X)/Si (Y)]nmultilayers (ML) with thin layers (X < 2,5 nm; Y < 3,5 nm) have been studied in the energy range 0,5 – 4,0 eV. It was found that TKE field dependencies in the nearest infrared (IR) and visible energy ranges exhibit anomalous behavior. TKE spectra measured in weak (~30 Oe) and strong (~2 kOe) magnetic fields were essentially different. It was shown that magneto-optical response of multilayered structure composite-silicone is the sum of magnetic composite layers and composites formed on interface contributions. And these contributions may have an opposite sign of TKE. Interface magnetic states depend on composite and semiconductor layers’ thicknesses and FM phase concentration in composite layers.

Magnetic and Magneto-Optical Research of Ni<sub>43.7</sub>Mn<sub>43.6</sub>In<sub>12.7</sub> Ribbons

We report the magnetic and magneto-optical (MO) properties of the Heusler Ni43.7Mn43.6In12.7 alloy ribbon in martensitic and austenitic states. The samples were produced by rapid solidification using the melt-spinning technique. The difference between the transformation temperatures obtained from magnetization and transverse Kerr effect (TKE) measurements shows that the chemical composition and/or microstructure are not identical in the bulk and at the ribbon surface. The TKE spectra profile in the spectral energy range of 0.5-3.5 eV does not change significantly at the martensitic transformation that indicates on a very similar electronic structure in martensitic and austenitic states.

Above Room Temperature Ferromagnetism in Si:Mn and TiO2−δ:Co

We present recent experimental results on the structural, electrical, magnetic, and magneto-optical properties of Mn-implanted Si and Co-doped TiO(2-delta) magnetic oxides. Si wafers, both n- and p-type, with high and low resistivity, were used as the starting materials for implantation with Mn ions at the fluencies up to 5 x 10(16) cm(-2). The saturation magnetization was found to show the lack of any regular dependence on the Si conductivity type, type of impurity and the short post-implantation annealing. According to XMCD Mn impurity in Si does not bear any appreciable magnetic moment at room temperature. The obtained results indicate that above room temperature ferromagnetism in Mn-implanted Si originates not from Mn impurity but rather from structural defects in Si. The TiO(2-delta):Co thin films were deposited on LaAlO3 (001) substrates by magnetron sputtering in the argon-oxygen atmosphere at oxygen partial pressure of 2 x 10(-6)-2 x 10(-4) Torr. The obtained transverse Kerr effect spectra at the visible and XMCD spectra indicate on intrinsic room temperature ferromagnetism in TiO(2-delta):Co thin films at low (< 1%) volume fraction of Co.

Peculiarities in Optical and Magneto-Optical Spectra of GaMnSb Layers Grown by Laser Ablation

Optical and magneto-optical properties of GaMnSb layers fabricated on GaAs (001) substrates by laser ablation technique were studied using spectral ellipsometry (E =1.24-3.25 eV) and the transversal Kerr effect (TKE) (E = 0.5 4.2 eV) as well as atomic and magnetic force microscopy. Spectra of the constituents of the diagonal components of the permittivity tensor as well as TKE depended substantially on the layer fabrication conditions. At room temperature a strong resonant band was observed in the TKE spectra for the GaMnSb layers with low Mn content in the energy range E 0.5-1.5 eV. This resonant TKE band was explained by excitation of surface plasmons in MnSb nanoclusters, which arose during the growth of the layers. In the energy region E &gt;1.5 eV the TKE spectra were related to interband transitions in MnSb inclusions.

Features of Magneto-Optical Response on Multilayer Nanostructures {(Co&lt;sub&gt;45&lt;/sub&gt;Fe&lt;sub&gt;45&lt;/sub&gt;Zr&lt;sub&gt;10&lt;/sub&gt;)&lt;sub&gt;Z&lt;/sub&gt;(Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;100-Z&lt;/sub&gt;/α-Si:H}&lt;sub&gt;n&lt;/sub&gt;

Spectral and field dependencies of Transversal Kerr Effect (TKE) for [(Co45Fe45Zr10)Z(Al2O3)100-Z(X)/α-Si:H(Y)] n multilayers have been studied in the energy range 0.5 - 4.0 eV. It was found that TKE field dependencies in the nearest IR energy range exhibit anomalous behavior for structures only with thin Si layers and this behavior vanishes with increasing of the Si layer thickness. TKE spectra measured in small and large magnetic fields were essentially different. It was shown that magneto-optical response of multilayered structure composite-silicon is the sum of contributions from two composites: (Co45Fe45Zr10) - Al2O3 + Si + silicides and (Co45Fe45Zr10) - Si + silicides, which have a different sign of TKE in the nearest IR spectrum and their magnetic states depend both on composite and semiconducting layer thicknesses.

Magneto-Optical Spectroscopy of Heusler Alloys: Bulk Samples, Thin Films and Microwires

We report magneto-optical spectra of the Heusler bulk alloys Ni-Mn-In, thin films Ni-Mn-Ga, microwires Ni-Mn-In and Ni-Mn-Ga in martensitic and austenitic states. Transversal Kerr effect (TKE) was studied at an angle of light incidence of 68° with respect to the sample plane, in the energy range 0.5 eV &lt; E &lt; 4.0 eV, at 50 350 K temperatures, and in magnetic fields up to 3.5 kOe. The TKE spectra profile does not change too much at martensitic transformation in Ni2MnGa thin films, only magnitudes of characteristic maxima decrease. The magneto-optical response of Ni2MnGa microwires is very similar to that for Ni2MnGa thin films. For most of studied bulk samples, the TKE signal is very weak (about 10-5), about two orders of magnitude smaller than for thin films, and in many cases could not be detected at all. It indicates the strong dependence of the magneto-optical response of Heusler alloys on the quality of optically or electrochemically polished surfaces and their microstructure.

The Influence of Quantum Size Effects on Magnetic Properties of Thin-Film Systems

Results on the investigation of magnetic and magneto-optical properties of Fe/NML/Fe (NML: Mo, Ta) thin-film systems are presented. The examined samples were prepared by DC magnetron sputtering technique. The hysteresis loops and spectral dependencies of the transverse Kerr effect (TKE) were measured employing the magneto-optical magnetometer and the magneto-optical spectrometer, respectively. The saturation field of the examined trilayers was revealed to oscillate as a function of the NML layer thickness, and the period of these oscillations to depend on the Fe layer thickness. The TKE spectra of the studied systems were found to be identical but the TKE values depend on the thickness of both Fe and Mo, Ta layers.

On Nature of Resonant Transversal Kerr Effect in InMnAs and GaMnAs Layers

Optical and magneto-optical properties of In(Ga)MnAs layers fabricated by laser ablation on GaAs(100) substrates were studied. Spectra of the optical constants and the transversal Kerr effect (TKE) depended substantially on the conditions of layer fabrication and testified to the presence of MnAs inclusions in all the samples. The cross-sectional transmission electron microscopy revealed the presence in the layers of inclusions 10-40 nm in size. At room temperature, a strong resonant band was observed in the TKE spectra of some In(Ga)MnAs layers in the energy range 0.5-2.7 eV. The resonant character of the TKE spectra was explained by excitation of surface plasmons in the MnAs nanoclusters embedded in the semiconductor host.

Resonant enhancement of the transversal Kerr effect in the InMnAs layers

Spectral dependences of the transversal Kerr effect (TKE) as well as of the realand imaginary parts of the permittivity of InMnAs layers were studied. Pulsedlaser ablation of Mn and InAs targets was used to form the layers on GaAs(100)substrates. Spectra of the optical constants and TKE depended substantially on layerfabrication conditions and testified to the presence of MnAs inclusions in the samples.The cross-sectional transmission electron microscopy revealed the presence ofinclusions of size 10–40 nm in the layers. At room temperature a strong resonant bandwas observed in the TKE spectra of the InMnAs layers in the energy range of0.5–2.2 eV. In this band the TKE was comparable in magnitude but opposite in signto that in the strong ferromagnetic MnAs. The resonant character of the TKEspectra was explained by excitation of surface plasmons in the MnAs nanoclustersembedded in the InMnAs semiconductor host. Modelling the TKE spectra for(InAs)1 − X:(MnAs)X nanocomposites in the effective-medium approximation (Maxwell–Garnett approximation)confirmed the assumption on the plasmon mechanism of the resonant enhancement of thetransversal Kerr effect in the InMnAs layers.

Optical and magneto-optical properties of nanostructured yttrium iron garnet

Bulk dense samples of nanostructured yttrium iron garnet Y3Fe5O12 with crystallite sizes of 20–40 nm are prepared by high-pressure torsion from a garnet powder with micron grains. The absorption and Faraday rotation spectra in the IR range and the transverse Kerr effect spectra in the visible spectral range for these samples are measured. The absorption and magneto-optical effect spectra are in agreement with the corresponding spectra of single crystals. The appearance of additional absorption bands at 2 and 3 μm is associated with the violation of the stoichiometry of the nanogarnet and the possible contamination of the initial material. The specific Faraday rotation in the transparency window is approximately 1.5 times smaller than the corresponding quantity for single crystals. The extrema in the Kerr effect spectra coincide with those for single crystals, are smaller in magnitude, and are smeared. On the whole, the prepared bulk samples are transparent in the IR spectral range and exhibit optical and magneto-optical characteristics comparable to the corresponding parameters for single crystals. The high density of point defects of the nanogarnet is primarily due to the violation of the stoichiometry and the valence state of iron ions.

Magneto-optical spectroscopy of diluted magnetic oxides TiO 2−δ: Co

We report an experimental study on transversal Kerr effect (TKE) in magnetic oxide semiconductors TiO 2−δ:Co. The TiO 2−δ: Co thin films were deposited on LaAlO 3 (0 0 1) substrates by magnetron sputtering in the argon–oxygen atmosphere at oxygen partial pressure of 2×10 −6–2×10 −4 Torr. It was obtained that TKE spectra in ferromagnetic samples are extremely sensitive to the Co-volume fraction, the crystalline structure, and technology parameters. The observed well-pronounced peaks in TKE spectra for anatase Co-doped TiO 2−δ films at low Co (<1%) volume fraction are not representative for bulk Co or Co clusters in TiO 2−δ matrix that indicates on intrinsic ferromagnetism in these samples. With increase of Co-volume fraction up to 5–8% the fine structure of TKE spectra disappears and magneto-optical response in reflection mode becomes larger than that for thick Co films

Optical and Magneto‐optical Spectroscopy of Manganites

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Optical and magneto-optical spectroscopy of manganites

The present review is concerned with optical and magneto-optical (MO) properties of manganites studied by optical absorption, ellipsometry and the transverse Kerr effect (TKE). The possibilities of these methods for getting information on the electronic structure of manganites, its relationship with the magnetic ordering and phase separation are demonstrated. Different approaches for description spectra (the band approach, cluster methods and effective medium theory) are used. Evolution of manganites’ optical and MO spectra under doping, temperature and magnetic field is discussed. The features of TKE spectra are connected with charge-transfer transitions in MnO 6 complexes with different valence.

Transverse Kerr effect in one-dimensional magnetophotonic crystals: Experiment and theory

Magneto-optical transverse Kerr and Faraday effects are studied experimentally and theoretically in one-dimensional magnetophotonic crystals fabricated from a stack of four repetitions of layers of Bi-substituted yttrium iron garnet and SiO 2 layers. The results of theoretical calculations in the framework of modified matrices approach are consistent with the obtained experimental data with the exception of the one cusp at 480 nm in the transverse Kerr effect spectra. Possible mechanisms of this disagreement are discussed.