Chester Alexander

Frequency- and time-resolved measurements of FeTaN films with longitudinal bias fields

The high frequency characteristics of 100 nm FeTaN films have been studied by using both time-resolved inductive techniques and frequency-resolved permeability measurements. Experiments performed as a function of longitudinal bias fields from 120 to 2400 A/m (1.5–30 Oe) showed precessional frequencies from 1.3 to 2.5 GHz, initial permeabilities from 1600 to 500, and damping constants α=0.013 to 0.0045. It is illustrated that the magnetization precessional data obtained from the time-resolved inductive technique can be Fourier transformed to the frequency domain to give the real and imaginary components of a permeability spectrum; this spectrum compares well with data obtained from frequency-resolved permeability measurements. It is also demonstrated that accurate values of the damping constant α can only be determined from permeameters whose bandwidth is two to three times the ferromagnetic resonance frequency of the material to be measured.

ESR Study of the Sugar Radical in Irradiated Deoxyadenosine

Single crystals of deoxyadenosine monohydrate grown from H2O and D2O solutions have been x irradiated and studied by electron spin resonance techniques at room temperature. The results show an isotropic coupling of 7 ± 1.0 G to one β proton and an anisotropic coupling of an α proton with principal values − 22.6 ± 0.5 G, − 16.4 ± 0.5 G, and − 5 ± 0.5 G. The spin density on the carbon atom (C5′), calculated from the above results, is 0.64. The g‐tensor principal values are 2.0029 ± 0.0002, 2.0052 ± 0.0002, and 2.0075 ± 0.0002. These data are consistent with a radical formed in the deoxyribose sugar group as a result of hydrogen abstraction at the C5′ position.

Effect of interface roughness on the exchange bias for NiFe/FeMn

The effect of interface roughness on exchange bias for NiFe/FeMn bilayers is investigated for polycrystalline films and epitaxial films. Three different systems were investigated: polycrystalline Ta (10 nm)/Ni80Fe20 (10nm)/Fe50Mn50 (20 nm) films on oxygen plasma-etched Si(100) or Cu/H–Si(100) and epitaxial Ni80Fe20 (10nm)/Fe60Mn40 (20 nm) films on Cu/H–Si(110). For films grown on plasma-etched substrates, as the etching time is increased, film roughness increases up to 12 nm. For the polycrystalline films grown on ultrathin Cu underlayers, x-ray diffraction shows the fcc (111) texture is greatly reduced as the thickness is increased. The epitaxial Cu/Si(110) buffer layer induces fcc (111) epitaxial growth and modifies the interface morphology. The dependence of exchange bias on roughness for each set of samples is explained in terms of a competition between the interfacial exchange coupling and the af uniaxial anisotropy.

ENDOR and ESR studies of irradiated cytidine

Single crystals of cytidine have been x‐irradiated and studied by electron nuclear double double resonance, electron nuclear double resonance, and electron spin resonance techniques at room temperature. One radical species was studied in detail and the results show anisotropic couplings of an unpaired electron to three hydrogen nuclei with the following principal values: a1, −66.3 MHz, −43.5 MHz, −20.7 MHz; a2, −68.9 MHz, −43.4 MHz, −20.3 MHz; a3, −37.2 MHz, −27.0 MHz, −13.6 MHz. The g tensor principal values are 2.0031, 2.0025, and 2,0021. These data indicate a radical formed in the ribose sugar group with spin density localized on C4′ and C5′.

Theoretical study of magnetostriction in FeTaN thin films

Single layer films of FeTaN have been deposited by dc magnetron sputtering, and the relationships between the magnetostriction and film composition have been studied. A linear increase in magnetostriction with nitrogen content has been explained by the dependence of λ100 on nitrogen concentration. The form of this dependence has been derived based on a theory developed by De Vries for describing the magnetic after effect in iron films with interstitial nitrogen. At room temperature, the best fit for the experimental magnetostriction data was found for an interstitial interaction constant of D=4.18×106 J/m3. The total magnetic anisotropy energy per grain, U110, has also been calculated as a function of the strain for FeN films with a (110) orientation under a tetragonal deformation. This calculation used the results derived for the dependence of the magnetostriction constant, λ100, on nitrogen concentration. The calculated U110 value shows a minimum at a lattice strain value of e11=0.0029, in close agreeme...

Ripple field effect on high-frequency measurements of FeTiN films

Ferromagnetic resonance and permeability linewidths of high-moment FeTiN thin films have been recorded and analyzed using ripple theory in order to separate inhomogeneous broadening from the intrinsic damping of the material. These results are compared to the analysis of the same phenomenon using a simple but common model of amplitude dispersion. The ripple is also used to analyze the behavior of the resonance frequency of a sample when rotated in low fields.

Microstructure and damping in FeTiN and CoFe films

Thermally stable films of FeTiN, have been prepared and characterized by ferromagnetic resonance, x-ray diffraction, x-ray photoelecton spectroscopy, and magnetostriction measurements to determine the relationships between the microstructure and the damping constants. The resonance studies were carried out at multiple frequencies to determine the intrinsic damping constant, α, and the extrinsic damping constant, ΔH0, as well as values of the anisotropy field, Hk, the gyromagnetic ratio, γ, and the saturation magnetization value, 4πMs. Data from similar experiments on CoFe films were compared with the FeTiN data. Our results show no relationship between intrinsic damping and the magnetostriction, but a strong dependence of the extrinsic constant on the grain size.

Thermoluminescence and emission spectra studies of 6‐methylmercaptopurine and 6‐methylmercaptopurine riboside x irradiated at 10 K

In this work we report the first thermoluminescence (TL) and emission spectra studies of the sulphur‐containing DNA base analog 6‐methylmercaptopurine (6MeMP), and its riboside, 6‐methylmercaptopurine riboside (6MeMPR),x irradiated at 10 K. The 6MeMP glow curve exhibits TL peaks at 28, 40, 68, 78, 112, and 140 K with typical emission from each peak consisting of a band possessing maxima at 500 and 530 nm. Only three prominent peaks were found in the 6MeMPR glow curve: 42, 52, and 140 K. Typical emission from each of these TL peaks consisted of a band with maxima at 455 and 485 nm. Thermal activation energies and frequency factors associated with each glow peak were extracted from the experimental data and used in formulating a model to explain the observed emission. Ultraviolet (UV)‐induced glow curves, emission spectra, and photobleaching studies were also conducted in efforts to deduce the mechanisms of charge recombination in 6MeMP and 6MeMPR. The results indicate that metastable states exist in both 6...

High-frequency behavior of electrodeposited Fe-Co-Ni alloys

In this paper, we investigate the high frequency behavior and damping of the FeCoNi films as a function of their composition and microstructure.FeCoNi alloys have been demonstrated to have a low coercivity and high saturation magnetisation.

Role of nitrogen concentration in the thermal stability of the anisotropy in FeTiN thin films

The thermal stability of the anisotropy of FeTiN films has been investigated. The films were prepared by DC reactive sputtering on glass substrates in a N/sub 2//Ar atmosphere, and the N flow rate, chamber pressure, sputtering power and film thickness were varied. Target-substrate distances of 6.7 cm and 4.1 cm were used. For films sputtered at the normal target-substrate distance of 6.7 cm, the anisotropy of FeTiN films rotated about 90 degrees after a 100/spl deg/C, 1 hour annealing in the presence of a 300-400 Oe field perpendicular to the original easy axis. When the 4.1 cm target-substrate distance was used, the anisotropy direction was stable with N concentrations of 6 at.% or less in the films. The anisotropy was unstable for higher N concentrations. X-ray data and stress measurements taken as a function of N concentration showed lattice and stress changes coincident with the stability changes. The dependence of the thermal stability of the film anisotropy on target-substrate distance and N flow rate will be presented and possible mechanisms will be discussed.