Annealing behavior of magnetic anisotropy in CoNbZr films

The effect of magnetic and nonmagnetic annealing on the magnetic anisotropy in CoNbZr films, formed by a DC opposing-targets sputtering method, was investigated. It was revealed that the origin of the magnetic anisotropy is the directional ordering of the magnetic atoms. The anisotropy fields and the direction of the easy axis obtained when the films are annealed in zero magnetic field are almost the same as those for the magnetic field parallel to the easy axis of the as-deposited films. When the films are annealed in a magnetic field perpendicular to the easy axis, the anisotropy field induced in parallel with the magnetic field, H_k(t), is well represented by the following formula: ln {1-H_k(t )/H_k(∞)∝-√Tt, where H_k(∞) is the thermal equilibrium value of the anisotropy field and D is the diffusion constant. The activation energy of the as-deposited film is 0.86 eV. Annealing the film increases the activation energy which is 2.1 eV when the film is annealed at a temperature of 450°C for 2 h     

Properties of the W-type hexaferritePbZn2Fe16O27

W-type Pb-hexaferrites were prepared by standard ceramic methods. The lattice constants found by refinement were a=0.59140±0.00006 nm and c=3.29209±0.00041 nm. The X-ray density of a typical composition PbZn_1.9Fe_15.3O_25.8 was ρ=5.32 g/cm³ and the Vickers microhardness value h _v=6 kN/mm². A plot of the saturation magnetization versus temperature is given. The extrapolated value of the saturation magnetization (H→∞, T→0) was σ_s=108 emu×g^-1, and the Curie temperature was T_c=600±20 K     

Analysis of the noise sources in an optically pumped cesium beamresonator

The main noise sources that affect the clock signal detection in an optically pumped cesium beam resonator are determined and their influence on the clock S/N ratio is evaluated. The following noise sources are taken into account: atomic shot noise, fluorescence photon noise, laser frequency noise, and clock signal detection noise. A theoretical model that predicts the variations of the S/N ratio as a function of different parameters characterizing the atom-laser interaction is developed. The main conclusion concerns the saturation of S/N value for high atomic flux due to laser frequency fluctuations. All the theoretical predictions were experimentally verified     

High performances boron doped γ-Fe2O3particles prepared from oxalic precursors

γ-Fe₂O₃ particles (L≈0.15 to 0.2 μm, L/D≈2 to 5) with coercivity up to 400 Oe have been prepared from oxalic precursors. To preserve the particle form, the oxalates were doped with boron. The effects due to this element was studied during the different thermal treatments which effect the pseudomorphous transformation of oxalate particles into spinel ferrite. ESCA spectroscopy, and X-ray measurements could point out the presence of a Fe₃BO₅ phase at the surface of γ-Fe₂O₃ particles. In spite of the important mass losses (H₂O, CO, CO₂) and the important crystallographic structure modifications occurring during the transformation of oxalate into magnetic oxide, γ-Fe₂O ₃ particles obtained by this method have very good textural characteristics. Boron-doped γ-Fe₂O₃ particles were used to make 3.5-in diskettes with standard formulation. In these conditions, media properties were comparable to trading diskettes properties     

Lateral magnetic inhomogeneities in Co-Cr layers detected by FMR

Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T_s) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T_s results in an increase of both the bulk saturation magnetization M_s and the perpendicular coercivity H_c^⊥. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T_s. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M _s, or in geometric structure, resulting in different values of the demagnetizing factor N_d, are the most probable causes of the observed effects     

Hybrid method for computing demagnetizing fields

A hybrid finite-element-boundary integral method is proposed for computing demagnetizing field. For a three-dimensional (3-D) mesh with N nodes in the magnetic region, the method requires storage O( N^4/3), and no nodes outside the magnetic region need to be considered. The method is suitable for nonlinear calculations, can be adapted to handle curved boundaries, and is especially convenient when the magnetic region consists of several parts whose relative positions are variable     

Development of high-quality ceramic powders for Sr0.9Ca0.1Zn2-W type hexagonal ferrite for permanentmagnet devices

Fine ceramic powders of Sr_0.9Ca_0.1Zn₂ Fe₁₆O₂₇ (Sr_0.9Ca_0.1Zn ₂-W) ferrite, of almost single domain grain size ~1 μm, have been synthesized successfully by sintering for a few hours a mixture of SrCO₃, CaCO₃, ZnO, and α-Fe₂ O₃ in stoichiometric amounts at an effectively low temperature (T_s) of ~1100°C. Carbon dioxide evolves in the reaction Sr(Ca)CO₃+2ZnO+8 α-Fe₂D₃ &lrarr2;Sr(Ca)Zn₂Fe₁₆O₂+C₂ , making fine pores in the sample, which prevent large grain growth of the material and result in a very loose powder. The small ⩽10% substitution of Sr by Ca activates the reaction, but preserves the crystallization of the small-sized grains. This yields magnetic properties useful for most permanent magnet applications, with a promisingly high coercivity H_c~3650 Oe and saturation magnetization M_s~65 emu/g. A considerably better saturation magnetization M_s~85 emu/g can be obtained by sintering the samples at higher T_s~1300°C, but that results in a rather very low coercivity H_c~105 Oe     

Ta additive effect on RF magnetron sputtered CoCr films

Magnetic properties for sputtered CoCrTa films (18 at.% Cr and 2.0-3.0 at.% Ta), which were deposited under various background pressures P_i, and argon sputtering pressures, P _Ar, have been examined. The perpendicular anisotropy field H_k for CoCrTa films maintains high values of 5-6 kOe in a wide range of P_i and P_Ar , as compared with that for CoCr films. In order to optimize Ta composition, magnetic properties and crystalline microstructures for Ta additive content (0-4.0 at.%) have been investigated. H_k and perpendicular coercivity H_c⊥ increase with increasing Ta concentration above 2.0 at.% Ta. C-axis orientation is improved by adding Ta to CoCr films. However, above 3.0 at.% Ta, H_c⊥ steeply decreases and domain wall motion is observed, owing to the increase in crystalline grain size. The appropriate Ta composition is 2.0-3.0 at.%     

A measurement of the NBS electrical watt in SI units

The National Bureau of Standards (NBS) electric watt in SI units to be: W_NBS/W=K_W =1-(16.69±1.33) p.p.m. The uncertainty of 1.33 p.p.m. has the significance of a standard deviation and includes the best estimate of random and known or suspected systematic uncertainties. The mean time of the measurement is May 15, 1988. Combined with the measurement of the NBS ohm in SI units: Ω_NBS/Ω=K_Ω =1-(1.593±0.022) p.p.m., this leads to a Josephson frequency/voltage quotient of E_J=E₀[1+(7.94±0.67) p.p.m.] where E₀=483, 594 GHz/V     

Measuring harmonic distortion and noise floor of an A/D converterusing spectral averaging

The author proposes to use spectral averaging techniques to measure the harmonic distortion and noise floor of an analog/digital (A/D) digitizing subsystem. The noise floor of an ideal B-bit A/D converter is derived in closed form. It is shown that this noise floor is a function of the A/D resolution B, the record length N, and the equivalent noise bandwidth E_B of the window function used in the discrete-Fourier-transform (DFT) computation. For an example, the noise floor is given for the case in which the magnitude square of the spectrum is averaged. Both experimental and simulation results are presented and it is shown that they are in good agreement with the theoretical results     

Effect of stress on the law of approach to saturation magnetizationin carbon steels

In high fields where the magnetization is approaching saturation, the resolved magnetic polarization I can be expressed by a power series of the inverse of external field H as: I=I_s-b/H ²-c/H³ . . ., or alternatively in terms of the reversible permeability μ_rev=1+(2b/H³+3c/H⁴+ . . .)/μ₀ where I_s is the spontaneous magnetic polarization and b, c, are constants. These equations express the law of approach to saturation magnetization. The coefficient b for a cubic crystal has been deduced as b=0.0762/I_s[K+1.5(λ₁₀₀-λ ₁₁₁)σ]², where σ is the applied stress and others are magnetic constants. The values of reversible permeability μ_rev under biasing field H were measured for carbon steels with applied stresses. The results showed that the square root of 2b changed linearly with the applied stress, The values of magnetic constant K andλ₁₀₀ -λ₁₁₁ were calculated, They agreed with the standard values, but were affected by chemical composition and heat treatment of materials, especially in λ₁₀₀-λ₁₁₁     

Global iterative solution of dielectric spectroscopy equations

A global method is presented for solving the permittivity equations for open- and short-circuited coaxial lines of general length for broadband measurements by iterating the recurrence schemes z_n+1=c cot z_z and z _n+1=c tan z_n, respectively, and their inverses. The global iteration theory of Fatou and Julia (see J. L. Howland and R. Vaillancourt, Num. Math., vol.46, 323-337, 1985), coupled with linear extrapolation and interpolation and Steffensen's acceleration procedure, supplies starting values and guarantees convergence even near double roots. When R_Z⩾0 for open, and R_Z⩽0 for short circuit terminations Newton's method, with appropriate starting values, converges to the desired roots. A combination of the three iterative schemes results in an almost global method of solution. Numerical results are quoted     

A flash Josephson A/D converter constructed with one-junctionSQUIDs

A novel approach to the construction of a flash-type Josephson A/D (analog/digital) converter is presented. Simulations show that one-junction SQUID (superconducting quantum interference device) comparators can have a greater than fivefold advantage in bandwidth over the two- or three-junction SQUIDs in an A/D circuit. Assuming a Nb junction technology, the simulations show that a 6-bit A/D converter using one-junction SQUID comparators could have a sampling rate of ~20 GHz with ~5 bits of resolution for a 5-GHz input signal. Detailed analysis and simulations of an A/D converter constructed with one-junction SQUIDs are presented. Further improvement can be made by using a coding algorithm which requires 2N-1 comparators, instead of N, for an N-bit A/D converter     

Determination of overwrite specification in thin-film head/disksystems

A self-consistent write analysis using the Preisach model is presented and used to calculate overwrite in thin-film head/disk systems. Two overwrite characterization procedures are discussed, and for each of the procedures the calculated values are compared with measurements. Through a correlation of overwrite, nonlinear peak shifts, and readback output voltage the authors determine the overwrite requirement. They show that whereas -30 dB of overwrite will ensure a satisfactory overall performance of the recording system, a much lower overwrite, say -20 dB, can work in certain situations. An analytical implementation of the self-consistent model is presented and verified with measurements. The analytical approach can be used to determine the overwrite at any applied field for any head/disk combination. The authors introduce a normalized effective field h_n, which depends on M_rδ, H_c, and other head/disk parameters. It is shown that a value of h _n greater than 0.8 is needed for overwrite values of better than 25 dB. The importance of various head/disk parameters in optimizing the overwrite is also discussed     

An accurate wide-band phase shifter for sinusoidal signals using anarrow pulse duty cycle network

A technique for producing a constant phase shift of sinusoidal signals independent of frequency by using a narrow pulse switching network is proposed. A phase-locked loop circuit multiplies the frequency of the input signal by an integer factor N and, with a monostable vibrator, provides narrow pulses which excite the MOSFET switches of the network. The working frequency range of the circuit extends to more than five decades and gives a maximum error that cannot exceed 360/N°     

Sintered Sm2(Co, Fe,Cu,Zr)17 magnets withlight rare earth substitutions

The effects of partial substitution of light rare earths for Sm in (Sm_1-xR_x)₂ (Co,Fe,Cu,Zr)₁₇ have been investigated where R=Ce, Pr, Nd, Pr_0.5Nd _0.5, Ce_0.2Pr_0.4Nd_0.4 and x=0-0.5. Experiments show that both remanence and maximum energy product are improved for x=0.1-0.2, depending upon compositions and heat treatments. For a composition Sm_0.8R_0.2(Co_0.633Fe_0.286 Cu_0.061Zr_0.020)_7.59 with R =Ce_0.2Pr_0.4Nd_0.4, the authors obtained B_r=11.57 kG, _MH_c =15.5 kOe, _BH_c=10.33 kOe, H_k=10.03 kOe, and (BH)_max=30 MGOe     

Using model-based parameter estimation to increase the efficiencyof computing electromagnetic transfer functions

Two main ideas are introduced: (1) the use of model-based parameter estimation based on rational function approximations, which reduces the number of frequencies at which solutions or samples are required; (2) a sampling approach that uses frequency derivatives of the response and a novel analytical technique based on differentiating the moment method impedance equation, which provides derivative information in a time proportional to N² in contrast with the N³ dependence in solving the original problem. Antenna input admittances are modeled using frequency samples and derivatives. The rational function model is shown to offer a large advantage over polynomial interpolation of a frequency response. Application of the frequency-derivative approach is demonstrated for problems having well-defined resonances such as a dipole antenna, and for more challenging problems having narrow resonances     

An integration-type high-speed analog-to-digital converter

An analog-to-digital (A/D) converter consisting of a switched-capacitor integrator, comparator, and control circuit is presented. The conversion process consists of voltage-to-frequency (V/F) conversion to determine the upper M bits of an N-bit representation of an analog input voltage and the subsequent voltage-to-time (V/T) conversion to determine the remaining lower N -M bits. The total clock cycle required for N-bit resolution is 2^M+2^N-M at most. The circuits for the V/F and V/T conversion share most of the components and thus the converter can be implemented with the minimum component count. Error analysis shows that a conversion accuracy higher than 12 bits can be expected from its CMOS monolithic realization. Prototype converters built using discrete components have confirmed the principles of operation     

A low field determination of the proton gyromagnetic ratio in water

The proton gyromagnetic ratio in H₂O is measured by the low-field method. γ'_p(low)=2.67513376×10⁸ s^-1 T^-1 (0.11 p.p.m.), leads to a value of the fine structure constant of α^-1=137.0359840 (0.037 ppm) and a value for the quantized Hall resistance in SI units of R_H=25812.80460 Ω (0.037 p.p.m.). To achieve this result, the dimensions of a 2.1-m solenoid were measured with an accuracy of 0.04 μm, and the NMR (nuclear magnetic resonance) frequency of a water sample was measured in the field of the solenoid