We report far-infrared optical properties of a thin NbN superconductor in magnetic field, B, up to 10 T. Transmission, Tr (T,B), of monochromatic linearly polarized laser beam with frequency below and above an optical gap is measured both below and above T-c. Tr(T,B=0) is well described by the BCS-based model that approximates the sample as a mixture of superconductors with different T-c. T-r(T,B not equal 0) appears qualitatively different for Voigt and Faraday geometry. To calculate optical properties, we use Bruggeman's approach and present a phenomenological model accounting for both field orientations. The model captures all observed features of the Tr(T,B) data.

Transmission of terahertz waves through a thin layer of the NbN superconductor deposited on a sapphire substrate was studied as a function of temperature in zero field as well as in magnetic field perpendicular to the sample. For photon energies lower than optical gap, detailed temperature measurements in zero field provide BCS-like curves with a pronounced peak below the critical temperature. In accordance with the BCS model, the temperature peak disappears as the energy of incident radiation is increased above the gap. In non-zero field, the temperature behavior of transmission is modified because the gap is suppressed and vanishes at upper critical field. In addition, the presence of quantized vortices in the superconducting film substantially changes shape of the temperature curves.

Magnetic properties of the manganese ferrites Mn(x)Fe(3-x)O(4) are markedly influenced by the valence states of Mn and Fe ions and by their distribution between the octahedral and tetrahedral sublattices. Hyper. ne methods are capable of providing useful information on these characteristics, which is difficult to obtain otherwise. In the present contribution the Mn(x)Fe(3-x)O(4) (0.52<x<1.80) cubic single crystals are studied by means of (57)Fe nuclear magnetic resonance (NMR) at the liquid helium temperature. High quality samples and sensitive NMR equipment allowed to detect several well resolved (57)Fe NMR spectral lines in the frequency range of 67-74 MHz in zero external magnetic field. In order to find out the location of iron nuclei from which the lines originate we applied external magnetic fields up to 1T. This approach allows assignment of two spectral lines to iron nuclei in octahedral sublattice and one spectral line to irons in tetrahedral sublattice. (c) 2008 Elsevier B.V. All rights reserved.

Temperature dependence of far-infrared transmission of NbN thin films deposited on MgO and Si substrates was measured at several frequencies from 0.4 to 4.3 THz. Activated exponential increase of relative penetration depth at low temperatures and a peak in transmission near Tc were observed for frequencies below the optical gap. On the other hand, the transmission measured at frequencies above the gap exhibits only flat, almost linear temperature dependence. This behaviour is consistent with the BCS theory of superconductivity. Similar measurements were performed also on YBa2Cu3O7−δ thin films deposited on MgO and sapphire substrates. Low-temperature variation of transmission indicates the d-wave symmetry. The peak below Tc predicted by the BCS theory is not observed. Flat temperature dependence of transmission at higher frequencies shows that the photon energy was sufficient for excitation over the optical gap. The s-wave BCS theory is adequate for NbN films but not for the YBa2Cu3O7−δ materials. Using the theoretical BCS model we show that the transmission peak is not correlated to the coherence peak in real conductivity at given frequency and other parameters relevant to experiment.

Spectral dependencies of the Faraday rotation of the series of thin manganese ferrite films prepared by RF magnetron sputtering were measured. Faraday rotation spectra show deep minima near a photon energy of 2.5eV, characteristic for the presence of the Fe3+ ions in the tetrahedral and octahedral positions of the spinel lattice. Fitting procedure resolves the basic parameters of the transitions.

Recent measurements of the Faraday rotation in the visible and near infrared spectral region on the copper ferrite films prepared by the sputtering method showed the anomalous behavior of rotation at 1.8 mum wavelength. Supposing the presence of Cu2+ ion on the A site under the cubic crystal field V(T-d), the spin-orbit coupling zeta (l . s), the low symmetry crystalline field V(S-4), and the molecular field AS(z)[S-z(Fe)] from the iron spin [S-z(Fe)], we can calculate the line shape of the observed anomaly.

The nanocrystalline MnxFe3−xO4 (x=0, 1.18, 1.56, and 1.9) spinel ferrite thin films were investigated by means of the x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Mn and Fe L2,3 edges. The cationic distributions of thin spinel ferrite films for x=1.18 and 1.56 were determined using a crystal field atomic multiplets scheme for arbitrary symmetry. The results are compared with the distribution of cations obtained from the differential thermogravimetry analysis of fine powders of corresponding compositions.

Pulse laser ablation deposition is used to produce thin films of SrFe12−xAlxO19 hexaferrites, with x in the interval 0≤x≤4. The structural, magnetic, optical and magneto-optical properties of the films are investigated using XRD, AFM, MFM, VSM, transmission photometry and spectroscopic Faraday polarimetry. The films exhibit smooth optical surface and strong perpendicular anisotropy due to the almost complete texture with the c-axis normal to the film plane. The values of the film lattice constant, c, anisotropy field, HA, and magnetic anisotropy, K, are found to be very close to those of the corresponding bulk material. Absorption, Faraday rotation and ellipticity spectra of SrFe12−xAlxO19 hexaferrite films are determined over the spectral range 300–2000 nm and analysed in terms of the microscopic dielectric tensor theory. Six paramagnetic lines and two diamagnetic lines are identified and assigned to specific electron transitions. Furthermore, the fractional magnitudes of prominent extrema of the Faraday rotation spectra are examined as functions of Al3+ concentration to obtain an insight into the mechanism by which Fe3+ cations contribute to the MO spectra of M-type hexaferrites.

Measurements of the far-infrared magnetotransmission of YBa2(ZnxCu1−x)3O7−δ thin film (x∼0.025) deposited on a wedged MgO substrate are reported. The application of magnetic field perpendicular to the ab plane produces at low temperature a linear increase of transmission for frequencies below ∼30cm−1. We present a model of high-frequency vortex dynamics which qualitatively explains these results.

Saturation magnetization and magnetic anisotropy data of BaFe12 − xTixO19 single crystals are presented in relation to the crystal chemistry of these compounds. For x = 0.2 an enhancement of the anisotropy is observed, whereas for higher Ti-concentrations the temperature coefficient of the magnetization decreases substantially.

Acoustical losses, Young's modulus and electrical conductivity of the M-type hexaferrite BaTiFe11O19 are reported. The acoustical relaxations at 100 and 400 K are related to electron transitions between the Fe ions.

Optical absorption and Faraday rotation of vacancy-defective spinel Mn-ferrite thin films Mn1.18Fe1.82O4+δ were studied in the visible and near-infrared regions. To introduce cation vacancies the films were oxidised between 150 C and 475°C. The resulting decrease of the absorption brought about the figure of merit of oxidised samples below 480 nm superior to that of the original Mn-ferrite films.

The Faraday rotation and optical absorption of the Co- and Ti-substituted barium hexaferrite thin films measured in the 500–2000 nm wavelength range at room temperature are presented together with the results of the Faraday rotation measurements carried out on selected samples at 80 K. The spectral dependences of the Faraday coefficient are described and interpreted using a set of optical electron transitions belonging to either cobalt or iron cations occupying the tetrahedral and/or octahedral positions in the spinel blocks of hexagonal ferrite crystal lattice.

Optical absorption and the Faraday rotation spectra of iron(III) in ferrimagnetic oxides may be interpreted using 3d crystal field and the pair excitation processes. Band assignments and ligand–field parameters are in agreement with the results of SCF-Xα-SW molecular orbital calculations of (FeO4)5− and (FeO6)9− clusters. The pair excitation processes are strongly influenced by the nature and strength of the superexchange interactions. The presence of the ferrimagnetism in ferrites and garnets induces greater covalency effects of the Fe3+–O2− bonds. The nephelauxetic ratios β35 of iron(III) in hematite, ferrites, and garnets show that the greater covalency of the Fe3+–O2− chemical bonds in these oxides is related to the magnetic structure.

Optical and magneto-optical properties of several single and layered Co-, Ti- and Al-substituted hexaferrite thin films prepared by the sol-gel method were investigated. The Faraday coefficient exhibits pronounced extrema in the infrared and visible part of the spectra. Broad maxima of the figure of merit at 700 to 900 and 1400 to 1800 nm regions show that some of the materials could be considered as the candidates for magneto-optical recording materials at interesting laser wavelngths of 800 and 1500 nm.

Cubic spinel ferrite films containing cobalt, copper and manganese were prepared by the rf sputtering from targets formed by intimate mixtures of ferrite powders. Additional heat-treatments at temperatures of about 450°C introduce cation vacancies which have positive influence on the magneto-optical properties of films. Figure of merit shows maxima at 600, 850 and 1500 nm which classifies these films to promissing materials for magneto-optical recording.

Acoustic losses in single crystals of Mn-ferrite were studied in the temperature range of 180–650 K. Loss peaks were observed at 232 and 537 K with activation energies of 0.3 and 0.8 eV, respectively. The 232 K peak arises from the relaxation of electrons between cations on octahedral sites. The 537 K peak is ascribed to the exchange of cations and their vacancies on octahedral sites. A small peak was observed at around 290 K after a heat treatment in reducing atmosphere. Heat treatments at 300 and 600° C affect the oxygen stoichiometry and the distribution of cations between octahedral and tetrahedral sites.

A novel, perminvar-like behaviour of the magnetization curves in the hard direction of titanium containing bulk and thin film barium hexagonal ferrites was observed at low temperatures. The DC moments and AC susceptibilities in the 1-1000 Hz frequency range were measured by VSM and SQUID magnetometers in the easy and hard magnetic directions at temperatures from 5 to 300 K. The perminvar-like effects were explained on the basis of the reorientation of Fe2+-Ti4+ pairs in octahedral 12k sites of the hexagonal lattice.

Pure and Co, Ti-substituted hexagonal barium ferrite (BaFe12O19, BaM) films were prepared by the dip-coating method from alkoxides. After repeated dipping, drying and calcining at 500°C for about 15 minutes in an oxygen atmosphere, polycrystalline films with a thickness of 1–1.8 μm on SiO2 substrates were obtained. Spectral dependencies of the Faraday rotation and the optical transmission of BaCoxTixFe12-2xO19 (0 ≤ x ≤ 0.8) films were measured in the range from 500 to 2500 nm at room temperature. The absorption coefficient did not display much structure, but specific Faraday rotation spectra of Co, Ti-ferrite films showed local maxima at 720, 1475 and 1750 nm. At those wavelengths, the magneto-optical figure of merit attains its maximum values. For comparison of the crystallization and magnetic properties, Ba(CoTi)xFe12-2xO19 (x = 0.9) powder has also been prepared by the sol-gel method.

The temperature dependence of the Faraday rotation in the near-infrared wavelength region is calculated in comparison with that observed in Co2+-containing hexaferrites by using the molecular field approximation. The calculation results show that the Faraday rotation decreases in the whole wavelength region and shifts to a lower energy with an increase in temperature, which is in agreement with the experimental results.