FMR and TEM Studies of Co and Ni Nanoparticles Implanted in the SiO<Subscript>2</Subscript> Matrix

Fused silica plates have been implanted with 40 keV Co⁺ or Ni⁺ ions to high doses in the range of (0.25–1.0) × 10¹⁷ ions/cm², and magnetic properties of the implanted samples have been studied with ferromagnetic resonance (FMR) technique supplemented by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The high-dose implantation with 3d-ions results in the formation of cobalt and nickel metal nanoparticles in the irradiated subsurface layer of the SiO₂ matrix. Co and Ni nanocrystals with hexagonal close packing and face-centered cubic structures have a spherical shape and the sizes of 4–5 nm (for cobalt) and 6–14 nm (for nickel) in diameter. Room-temperature FMR signals from ensembles of Co and Ni nanoparticles implanted in the SiO₂ matrix exhibit an out-of-plane uniaxial magnetic anisotropy that is typical for thin magnetic films. The dose and temperature dependences of FMR spectra have been analyzed using the Kittel formalism, and the effective magnetization and g-factor values have been obtained for Co- and Ni-implanted samples. Nonsymmetric FMR line shapes have been fitted by a sum of two symmetrical curves. The dependences of the magnetic parameters of each curve on the implantation dose and temperature are presented.     

Magnetic resonance of intrinsic defects in the spin-Peierls magnet CuGeO3

Magnetic resonance in pure single-crystal CuGeO₃ at frequencies 9–75 GHz in the temperature range 1.2–25 K is investigated. Splitting of the magnetic-resonance line into several spectral components is observed at temperatures below 5 K, where spin-Peierls dimerization suppresses the magnetic susceptibility and the ESR signal intensity. Analysis of the magnetic resonance spectra over a wide frequency range with different directions of the magnetic field at different temperatures makes it possible to identify among these components the ESR signals due to defects, having effective spin S=1/2 and spin S=1, in the spin-Peierls phase. The g factor corresponding to these ESR signals is the same and close to the value characteristic for the ion Cu²⁺. Another magnetic-resonance line is characterized by a strongly anisotropic g factor and an increase (at a threshold in the excitation power) in the susceptibility both at resonance and in the line wings. These signals are tentatively attributed to two possible types of planar defects arising on the walls of domains of the spin-Peierls state with different values of the dimerization phase. Zh. éksp. Teor. Fiz. 114, 1876–1896 (November 1998)     

Nonlinear optical absorption and refraction of epitaxial Ba0.6Sr0.4TiO3 thin films on (001) MgO substrates

Highly epitaxial Ba_0.6Sr_0.4TiO₃ (BST) ferroelectric thin films were fabricated on (001) MgOsubstrates by pulsed laser deposition. The nonlinear optical absorption coefficients (β) and refraction indices (γ) of the BST thin films on (001) MgO substrates were investigated using the single beam Z-scan technique with femtosecond laser pulses at the wavelengths of 790 nm and 395 nm, respectively, at room temperature. The nonlinear absorption coefficients of BST thin films were measured to be ∼0.087 cm/GW and ∼0.77 cm/GW at 790 nm and 395 nm, respectively. The nonlinear refraction indices of BST thin films exhibit a strong dispersion from a positive value of 6.1×10^-5 cm²/GW at 790 nm to a negative value of -4.0×10^-5 cm²/GW at 395 nm near band gap. The dispersion of γ is roughly consistent with Sheik-Bahae’s theory for the bound electronic nonlinear refraction resulting from the two-photon resonance. These results show that the BST film is a promising material as a candidate for nonlinear optical applications. PACS 42.70.Mp; 78.20.-e; 81.05.-t     

Mössbauer Studies of Dilute 119Sn and 57Fe in SrRuO3 and Sr2FeRuO6

Nuclear magnetic resonance on oriented ¹⁷⁵Hf in iron host has been measured. Samples of ¹⁷⁵HfFe were made by recoil implantation of the precursor ¹⁷⁵Ta isotope. The resonance frequency and the resonance line width have been determined to be 139.0 (1) MHz and FWHM = 2.7 (2) MHz, respectively, in an external magnetic field of 0.1 T. The resonance width was very narrow compared with the previously reported value of 11.0 (1.1) MHz. With the known value of the magnetic moment of μ(¹⁷⁵Hf) = −0.62 (3) μ_N, the hyperfine field has been deduced as B _HF = −73.6 (3.5) T.     

Preparation and optical properties of sol–gel neodymium-doped germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid thin films

Germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid spin-coating thin films doped with neodymium ions are prepared by a sol–gel technique and a spin-coating process. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with germanium isopropoxide are used as matrix precursors. Thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy are used to study the structural and optical properties of the hybrid thin films. The results indicate that films that are crack-free and have a high transparency in the visible and near-infrared range can be obtained; a strong UV absorption region at short wavelength ∼200 nm, accompanied with a shoulder peaked at ∼240 nm, due to the neutral oxygen monovacancy defects, is also identified. Upconversion emission properties of the transparent dried gel and the thin films heated at different heat treatment temperatures and doped with different neodymium ion concentrations are studied; a relatively strong room-temperature yellow to violet upconversion emission at 397 nm (⁴ D _3/2→⁴ I _13/2) is observed under a xenon lamp excitation with yellow light at the wavelength of 580 nm (⁴ I _9/2→⁴ G _5/2). The effect of Nd³⁺ doping concentration and heat treatment temperature on upconversion emission of the thin films is also studied. The mechanism of the upconversion is proposed. PACS 81.05.Kf; 81.20.Fw; 78.55.Hx     

Magnetic resonance absorption in isolated metal/insulator/metal nanodot arrays with transmission geometry

In this study, we have systematically investigated a magnetic resonance absorption and tunability of absorption wavelength in isolated metal-insulator-metal (MIM) nanodot arrays with transmission geometry. The elemental electromagnetic resonances and their hybridizations are studied using 3-dimensional finite-difference time-domain (FDTD) calculation and resonance properties including the resonance peak tunability, magnetic permeability and quality (Q) factor are characterized with respect to the coupling strength. We have found the existence of electric and magnetic resonance mode in the MIM (Au/MgF₂/Au) structure and the magnetic resonance has larger wavelength tunability than the electric resonance. The absorption cross section calculation revealed that absorption is the dominant extinction process at the magnetic resonance only. Magnetic permeability (μ) calculations for the various MIM parameters showed the maximum value of the imaginary part of μ is 16.1 with Q factor of 9.2 when the size of nanodot is 200 nm and the inter-dot distance is 300 nm. The presented calculations can be used to tune the response of the magnetic resonance absorption with a variable resonance wavelength and Q factor by using the simple MIM structures with transmission geometry.     

Ion-beam induced changes in magnetic and microstructural properties of thin iron films

Changes in magnetic and structural properties of 60–82 nm iron films induced by heavy-ion implantation were studied using the magneto-optical Kerr effect, M?ssbauer spectroscopy, Rutherford backscattering spectroscopy, X-ray diffraction, and X-ray absorption fine structure. The influence of ion-beam parameters (ion mass, fluence) and of sample parameters (external magnetic field and stress during implantation) were investigated. The Fe films, some of them containing a thin ⁵⁷Fe marker layer for M?ssbauer spectroscopy, were deposited on Si(100) substrates, by electron-beam and effusion-cell evaporation. The films were irradiated with ²⁰Ne, ⁵⁶Fe, ⁸⁶Kr and ¹³²Xe ions at energies chosen so that the implantation profiles peaked near the middle of the Fe films. The as-deposited films were magnetically isotropic and had a high coercivity. After ion implantation, the coercivity decreased and magnetic anisotropy developed. Both changes correlated with a decrease in the internal film stress. External mechanical stress applied during the irradiation had hardly any influence on the magnetic texture, opposite to an external magnetic field applied during or before ion implantation. The results are compared with those obtained for ion-irradiated polycrystalline Ni films and epitaxial Fe films and discussed with respect to the role of radiation-induced extended defects as pinning centers.     

Cross section and resonance strength measurements of 19F(p, αγ)16O at Ep= 200–800 keV

An excitation function of the ¹⁹F(p, αγ)¹⁶O reaction has been measured over the proton beam energy range E_p= 200–800 keV using a 4 π NaI summing spectrometer. A new resonance was found at E_R= 237 keV and its properties Γ_R, σ_R and ωγ have been extracted. The strengths of all resonances at E_p= 200–800 keV have been also extracted. The importance of the 1⁺ resonance at E_R= 11 keV is discussed and its width has been estimated taking into account interference effects with the strong 1⁺ resonance at E_R= 340 keV. The reaction rates have been calculated over a wide range of temperatures and compared with the rates of the (p, α₀) and (p, α_π) branches of the ¹⁹F(p, α)¹⁶O reaction. Received: 21 June 1999 / Revised version: 30 September 1999     

Ion beam synthesis and investigation of nanocomposite multiferroics based on barium titanate with 3d metal nanoparticles

Samples of nanocomposite multiferroics have been synthesized by implantation of Co⁺, Fe⁺, and Ni⁺ ions with an energy of 40 keV into ferroelectric barium titanate plates to doses in the range (0.5–1.5) × 10¹⁷ ions/cm². It has been found that nanoparticles of metallic iron, cobalt, or nickel are formed in the barium titanate layer subjected to ion bombardment. With an increase in the implantation dose, the implanted samples sequentially exhibit superparamagnetic, soft magnetic, and, finally, strong ferromagnetic properties at room temperature. The average sizes of ion-synthesized 3d-metal nanoparticles vary in the range from 5 to 10 nm depending on the implantation dose. Investigation of the orientation dependence of the magnetic hysteresis loops has demonstrated that the samples show a uniaxial (“easy plane”) magnetic anisotropy typical of thin granular magnetic films. Ferromagnetic BaTiO₃: 3d metal samples are characterized by a significant shift of the ferromagnetic resonance signal in an external electric field, as well as by a large (in magnitude) magnetodielectric effect at room temperature. These results indicate that there is a strong magnetoelectric coupling between the ferroelectric barium titanate matrix and ion-synthesized nanoparticles of magnetic metals.     

Magnetic resonances spectroscopy of nanosize particles La0.7Sr0.3MnO3

Using a co-precipitation method, perovskite-type manganese oxide La_0.7Sr_0.3MnO₃ nanoparticles (NPs) with particle size 12 nm were prepared. Detailed studies of both ⁵⁵Mn nuclear magnetic resonance and superparamagnetic resonance spectrum, completed by magnetic measurements, have been performed to obtain microscopic information on the local magnetic structure of the NP. Our results on nuclear dynamics provide direct evidence of formation of a magnetically dead layer, of the thickness ≈2 nm, at the particle surface. Temperature dependences of the magnetic resonance spectra have been measured to obtain information about complex magnetic properties of La_0.7Sr_0.3MnO₃ fine-particle ensembles. In particular, electron paramagnetic resonance spectrum at 300 K shows a relatively narrow sharp line, but as the temperature decreases to 5 K, the apparent resonance field decreases and the line width considerably increases. The low-temperature blocking of the NPs magnetic moments has been clearly observed in the electron paramagnetic resonances. The blocking temperature depends on the measuring frequency and for the ensemble of 12 nm NPs at 9.244 GHz has been evaluated as 110 K.     

Proton NMR study of molecular motion in bulk and in highly drawn fiber polyamide-6

The proton motion in bulk and highly drawn fiber polyamide-6 has been studied by field cycling relaxometry and proton line shape measurements. The dips in theT ₁ dispersion allowed for the determination of the¹⁴N quadrupole coupling tensor. The fact that only one set of¹⁴N nuclear quadrupole resonance lines, has been found shows that all N-H groups in nylon-6 are H-bonded. A striking difference in the main line width transition and the low-frequency molecular dynamics has been observed between a slowly cooled “bulk” polyamide-6 sample and a rapidly cooled and highly drawn “fiber” sample by wide line proton nuclear magnetic resonance line shape and spin-lattice relaxation time measurements. This result is consistent with the picture that shearing melt processing procedures, such as spinning, plant stable and long-lived crystallization nuclei into the amorphous phase which impose additional motional constraints on the surroundings and inhibit the self-diffusion process.     

Special features of wide-band EPR spectroscopy of singlet states in weak magnetic fields

A resonance change in microwave absorption in zero magnetic field, which is not due to magnetic-field dependence of the energy levels of the spin systems, is observed for a number of non-Kramers paramagnetic ions (Cr²⁺, Ni²⁺, Fe²⁺) in synthetic forsterite. It is shown that these signals could be due to narrowing of the homogeneous spin packet of an inhomogeneously broadened EPR line in zero magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 370–375 (10 September 1998)     

Investigation of third-order nonlinear optical properties of NNDC-doped PMMA thin films by Z-scan technique

A novel chalcone derivative, (2E)-1-(2,4-di- chloro-5-fluorophenyl)-3-[4-dimethylamino)phenyl]prop-2-en-1-one, abbreviated as NNDC, was prepared and characterized by elemental analyses, infrared (IR) and proton nuclear magnetic resonance (¹H NMR) spectrum, and thermal analyses. The NNDC-doped poly(methyl methacrylate) (PMMA) thin films with five different doping concentrations by weight were prepared by using a spin-coating method. Their linear optical properties were investigated by using a prism coupling measuring system. The third-order nonlinear optical properties of NNDC in 1,2-dichloroethane (NNDC/1,2-dichloroethane) solution and NNDC-doped PMMA (NNDC/PMMA) films were investigated by using the laser Z-scan technique with 20 ps pulses at 532 nm. A self-focusing effect was observed from the Z-scan curves for solution and thin films and the nonlinear refractive index of the film increases with the increase of the doping concentration. In addition, nonlinear absorption was negligible for all samples. The magnitude of third-order nonlinear refraction index n ₂ and the third-order nonlinear susceptibility χ ⁽³⁾ for thin films were 10⁻¹⁵ m²/W and 10⁻⁹ esu, respectively, which are about three orders larger than that of NNDC/1,2-dichloroethane solution. Some necessary analyses were presented. The results show that this material is a promising candidate for application in the nonlinear optical devices at 532 nm.     

Spectroscopic characterization of indian standard sand

The characterization of Indian standard sand (IS650:1991 as per B.I.S. approval) was performed by X-ray diffraction, IR and Raman spectroscopy, and nuclear magnetic resonance techniques. The principal reflections occurring at the d-spacings of 4.2408, 3.3440, and 1.8292 ? confirm the presence of α-quartz crystalline structure in the sample. The calculated unit cell parameters are: a = 4.9294 ?, c = 5.4093 ?, and V = 113.832 ?³. Mid-IR spectrum shows the characteristic doublet for α-quartz at 797 and 778 cm^–1. The Al/Al+Si ratio has been calculated from the position of the absorption band at 1100 cm^–1. Raman spectrum of the sample has two strong peaks at 203 cm^–1 and at 462 cm^–1 for A1 vibrational mode characteristic of α-quartz. Two bands at 1410 and 1930 nm in near-IR spectrum indicate the presence of both molecular water and an OH group. A broad double band centered near 1210 nm and a weak band at 1050 nm attest the presence of Fe²⁺ and Fe³⁺ respectively in the sample. The signal near g ∼ 4 is characteristic of isolated Fe³⁺ ions in the distorted octahedral or tetrahedral crystalline field. ²⁹Si NMR spectrum shows a strong signal at –107 ppm corresponding to quartz.     

Magnetic Properties of Thin Metal-Polymer Films Prepared by High-Dose Ion-Beam Implantation of Iron and Cobalt Ions into Polyethylene Terephthalate

Thin metal-polymer composite films have been prepared by high-dose ion-beam implantation of Fe⁺ and Co⁺ ions into polyethylene terephthalate. The implantation of 40 keV ions at room temperature with doses from 2 · 10¹⁶ to 4 · 10¹⁷ cm⁻² have been performed, with the ion current density of 4 μA/cm². The effects of implantation dose on the film morphology and crystal structure have been investigated via atomic force and magnetic force microscopy and X-ray diffraction. The magnetic properties of synthesized structures have been studied by ferromagnetic resonance and with a vibrating-sample magnetometer. It was established that the properties of ion-implanted samples strongly depend on both the implantation dose and the type of implanted ions. The implantation dose at which the magnetic phase is formed for iron-implanted samples is significantly lower than that for cobalt-implanted ones. At high implantation doses due to polymer sputtering metal-containing layers are formed close to the sample surface for both ions. In this dose range the magnetic properties of implanted samples changed dramatically due to particle oxidation. The coercivity of synthesized layers reaches 180 and 300 Oe for iron- and cobalt-implanted samples, respectively. Authors' address: Vladimir Yu. Petukhov, Kazan Physical-Technical Institute, Sibirskii trakt 10/7, 420029 Kazan, Russian Federation     

Spectral components that form UV absorption spectrum of Ce3+ and Ce(IV) valence states in matrix of photothermorefractive glasses

We have measured the UV absorption spectra of photothermorefractive glasses of the system Na₂O-ZnO-Al₂O₃-NaF-SiO₂ doped by cerium oxide in the range of (2.8–5.0) × 10⁴ cm⁻¹ (360–200 nm). The spectra have been processed by the method of dispersion analysis based on the analytical convolution model for the complex dielectric function of glasses. We show that the absorption band centered at 3.3 × 10⁴ cm⁻¹ (∼303 nm) that is attributed to the transition 2F _5/2 → 5d in the Ce³⁺ ion, is an envelope of three spectral components. The broad absorption range (3.5–4.7) × 10⁴ cm⁻¹ (200–270 nm) that is commonly interpreted as a charge transfer band of the Ce(IV) valence state, is an envelope of at least three spectral components.     

Structure and magnetic properties of Zn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O nanorods synthesized by a simple sol–gel method using metal acetylacetonate and poly(vinyl alcohol)

Room-temperature ferromagnetism was observed in Zn_0.9Co_0.1O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl alcohol) gel. The XRD, FT-IR and SAED analyses indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. The specific magnetization of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar to that of Zn_0.9Co_0.1O nanoparticles prepared by polymerizable precursor method. We suggest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exciton/donor binding energy of ZnO.     

Optical transmittance spectroscopy of concentric-shell fullerenes layers produced by carbon ion implantation

Concentric-shell fullerenes, also called carbon onions, produced by carbon ion implantation into silver thin films, and subsequently deposited on a silica substrate, were studied by optical transmission spectroscopy in the wavelength range 0.2 - 1.2 μm. In this interval, the strongest absorption is due to the π-plasmon of sp²-like carbon. The position of the plasmon absorption band clearly evolved from 265 nm at low fluence to 230 nm at high implantation fluences. A simulation of the optical spectra based on dielectric models of the concentric-shell fullerenes layer allowed us to identify the first peak as due to disordered graphite and the latter to the carbon onions. The concentration of residual graphite and the filling fraction of the carbon onions produced at high fluences could be estimated by fitting the optical spectra with computed transmittance curves. Received 13 July 2000     

The magnetic hyperfine field of bromine in iron by NMR/ON

Nuclear magnetic resonance of⁸²Br oriented at low temperature in iron has been observed with a sample prepared by ion implantation atT<0.2 K. The asymmetric resonance signal can be decomposed in a broad background signal and a narrow line of FWHM=1.8 (4) MHz which can be attributed to⁸²Br in undisturbed substitutional sites of Fe. From the center frequency of this narrow line (B _ext=0)=201.86(13) MHz we derive the magnetic hyperfine field asB _hf(BrFe)=81.38(6) T. This value is considerably larger than the result of theoretical calculations.     

Application of a continuous-wave tunable erbium-doped fiber laser to molecular spectroscopy in the near infrared

Development of a continuous-wave tunable fiber laser-based spectrometer for applied spectroscopy is reported. Wide wavelength tunability of an erbium-doped fiber laser (EDFL) was investigated in the near-infrared region of 1543–1601 nm. Continuous mode-hop free fine frequency tuning has been accomplished by temperature tuning in conjunction with mechanical tuning. The overall spectroscopic performance of the EDFL was evaluated in terms of frequency tunability along with its suitability for molecular spectroscopy. High-resolution absorption spectra of acetylene (C₂H₂) were recorded near 1544 nm with a minimum measurable absorption coefficient of about 3.5×10^-7 cm^-1/Hz^1/2 for direct absorption spectroscopy associated with a 100-m long multipass cell. Detections of C₂H₂ at different concentration levels were performed as well with high dynamic detection range varying from 100% purity to sub ppmv using cavity ring down spectroscopy. A 3σ-detection-limited minimum detectable concentration (MDC) of 400 ppbv has been obtained by using the transition line P_e(22) of the ν₁+ν₃+ν₅ ¹(Π_g)-ν₅ ¹(Π_u) hot band near 1543.92 nm with a detection bandwidth of 2.3 Hz. This corresponds to a minimum detectable absorption coefficient of 6.6×10^-11 cm^-1/Hz^1/2. The sensitivity limit could be further improved by almost one order of magnitude (down to ∼60 ppbv) by use of the P_e(27) line of the ν₁+ν₃(Σ_u ⁺)-0(Σ_g ⁺)combination band near 1543.68 nm. PACS 42.55.Wd; 42.62.Fi; 07.57.Ty; 07.88.+y