Optical and magneto-optical properties of Co/Pt multilayered films

Both experimental and computer-simulated magneto-optical (MO) and optical spectroscopies of Co/Pt multilayered films (MLF) with a nearly constant Pt sublayer thickness and variable Co sublayer thickness, as well as pure Co and Pt, and Co_0.51Pt_0.49 alloy films, have been performed in the energy range 1.1–4.7 eV. The simulations were achieved by solving the multireflection task for various models of the MLF. The comparison between experimental and computer-simulated optical properties of the Co/Pt MLF allowed us to evaluate the thickness of the interfacial regions with the alloyed components. The diagonal and off-diagonal components of the optical conductivity tensor were calculated not only for the pure Co and Co_0.51Pt_0.49 alloy films, and the whole Co/Pt MLF, but also for the spin-polarized Pt layers in the Co/Pt MLF.     

Structure and magnetic properties of Fe/Cu multilayered films

Mutually insoluble Fe/Cu multilayered films prepared by a dc-magnetron sputtering system with a rotating substrate-holder have been studied. The periodicity of the multilayers was confirmed by X-ray diffraction. The results of magnetization measurements and Mössbauer spectroscopy at 300 and 77 K show that the samples with the Fe layer thinner than 9 Å exhibit superparamagnetism. The temperature dependence of the spontaneous magnetization follows Bloch's law for all samples, with the spin-wave temperature coefficient B inversely proportional to the thickness of the Fe layer. The results of torque measurements show that the magnetization is normal to the film plane for the samples with the Fe layer thinner than 6 Å.     

Effect of bcc-fcc phase transition on the compton profiles of iron

The effect of the- or bcc-fcc phase transition on the electron momentum distribution and Compton profiles of iron has been theoretically examined by a band structure calculation in the two phases. The calculated band Compton profile for the bcc phase shows a good agreement with the experimental results by Phillips and Weiss. The calculated directional Compton profiles show significant changes while going from the bcc to the fcc phase.     

Magnetic properties and structures of Fe/MgF2 multilayered films

Multilayers composed of Fe and MgF₂ with layer thicknesses between 9 Å and 100 Å and of 30 Å, respectively, were prepared with an ultrahigh-vacuum deposition technique. Medium-angle X-ray data show that the Fe layers in the BCC phase have considerable (1 1 0) texture. Periodicity due to multilayered structures was confirmed by a small-angle X-ray diffraction study and cross-section transmission electron microscope for films with Fe layer thicknesses >45 Å. In an Fe/MgF₂(9 Å/30 Å) sample, an island structure for the Fe layers was suggested by the existence of superparamagnetism in a film. At 4.2 K, enhancements of both magnetization and hyperfine field were observed in films having Fe layers thinner than 40 Å. The maxima in the magnetization (233 emu/g of Fe) and in the average hyperfine field (390 kOe) at 4.2 K were found in an Fe/MgF₂(9 Å/30 Å) film and were approximately 105% and 115% that of the bulk α-Fe, respectively. The thickness dependence suggests a 12% enhancement in the magnetic moment of interface Fe atoms. No exchange bias was found in the films, implying that antiferromagnetic fluorides are not formed at the interface, which is different from the case of Fe/LiF and Fe/CaF₂ multilayers.     

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.     

Magnetic and electronic properties of Fe/Cu multilayered nanowires: A first-principles investigation

By using the first-principles calculations, we have systematically investigated the equilibrium structure, magnetic and electronic properties of one-dimensional Fe/Cu multilayered nanowires. We find that the stability of the Fe/Cu multilayered nanowires decreases with increasing concentration of nonmagnetic Cu layers, suggesting that rich Fe nanowires are more stable. Analysis of the average magnetic moment (μ_av) per Fe atom in the Fe/Cu multilayered nanowire suggests that there is a slight increase in μ_av with the increase in the number of nonmagnetic Cu layers, which was attributed to the increased Fe–Cu distance with increase in the Cu layers at interfacial layers. Furthermore, analysis of the band structures of these nanowires suggests strong dependence of conductance on the nonmagnetic Cu spacer layer thickness and a half-metallic character is observed for moderate Cu atoms substitutions, opening up the possibility for their application in magnetoelectronics or spintronics.     

Photoluminescence and magneto-optical properties of multilayered type-II ZnTe/ZnSe quantum dots

Multilayered Zn–Se–Te structures grown by migration enhanced epitaxy are studied by temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL. The PL consists of two bands: a blue band, overlaid with band edge sharp lines, dominant at low temperatures and high excitation, and a green band, which appears at elevated temperature and low excitation. Upon varying excitation intensity by four orders of magnitude, the green band peak energy shifts by ∼60 meV, indicating recombination of excitons in type-II quantum dots (QDs); no significant shift is observed for the blue band. Therefore, the green emission is attributed to ZnTe/ZnSe type-II QDs, which co-exist with isoelectronic centers, responsible for the blue and band edge emissions. The existence of type-II ZnTe/ZnSe QDs is further confirmed by magneto-PL, for which the observed oscillations in the PL intensity as a function of magnetic field is explained in terms of the optical Aharonov–Bohm effect.     

Direct magneto-optical observation of a structural phase transition in thin films of manganites

The spontaneous formation of twins in La(2/3)Ca(1/3)MnO3 films below T(S) approximately 105 K is observed by a magneto-optical technique. The twins are revealed as stripes along the {110} directions where magnetization tilts out of the film plane due to the stresses in twins. Their appearance is associated with a martensitic phase transition in the film triggered by the cubic-to-tetragonal transition in the SrTiO3 substrate. It is found that magnetization of the films proceeds by inhomogeneous rotation of magnetic moments. This is due to the presence of microscopic structural inhomogeneities. Their dominating role in the low-temperature transport can explain small effects of the transition at T(S) on the resistivity.     

Optical and magneto-optical resonances in nanocorrugated ferromagnetic films

We report here on optical and magneto-optical spectra investigations of nanostructured Co and Ni films deposited on top of polymethyl methacrylate (PMMA) colloidal crystal. Resonant peculiarities have been observed in both spectra; their positions are scaled with the PMMA sphere diameter and depend on incident angle. Asymmetry of the resonance lineshapes as well as change of the direction of magneto-optical rotation has been observed. Both the surface plasmon resonance and the interference between reflections from the colloidal crystal and from the nanostructured film should be considered to explain the obtained results.     

Magnetic phase transition in Co/Cu/Ni/Cu(100) and Co/Fe/Ni/Cu(100)

Magnetic phase transitions in coupled magnetic sandwiches of Cu/Co/Cu/Ni/Cu(100) and Cu/Co/Fe/Ni/Cu(100) are investigated by photoemission electron microscopy. Element-specific magnetic domains are taken at room temperature to reveal the critical thickness at which the magnetic phase transition occurs. The results show that a coupled magnetic sandwich undergoes three types of magnetic phase transitions depending on the two ferromagnetic films' thickness. A phase diagram is constructed and explained in the process of constructing Monte Carlo simulations, which corroborate the experimental results.     

Superconducting properties and phase locking transition in NbN films

We report superconducting measurements on NbN film ($\text{d =}\text{820}\text{A}\text{?}$) obtained by sputtering characterized by a columnar structure (grain size ? 120 Å). At the largest temperatures, the paraconductivity is tri-dimensional and of the Azlamasov-Larkin form. Near T_c it becomes bi-dimensional when 2ξ(T) is larger than the width of the sample. Below T_c, the behavior of the resistance is described in terms of phase-locking transition. The values of the corresponding critical exponents are discussed.     

Fe含量和粒径对Fe/Cu颗粒膜结构和磁性的影响

采用共蒸发法制备不同组分的Fe/Cu颗粒膜,将样品分两组进行退火和不退火处理. 根据测量及分析,确定了不同成分的Fe/Cu颗粒膜的相组成和晶体结构;找出了 Fe/Cu颗粒膜矫顽力与粒径的关系,利用此关系由自发形核理论可知,提高功率,快速蒸镀薄膜,可得到细密颗粒的Fe/Cu颗粒膜,从而降低矫顽力,减少磁滞损耗.