High Hc Values Research Articles

Measurement of total nonmethane organic carbon (Cy): Development and application at Chebogue Point, Nova Scotia, during the 1993 North Atlantic Regional Experiment campaign

A technique was developed for the measurement of total nonmethane organic carbon (Cy) in the gas phase based on cryogenic collection, preseparation of CO, CH4 and CO2, conversion of all carbon to CH4, and measurement by flame ionization detector. Collection and recovery efficiencies were found to be essentially quantitative for C2‐C7 hydrocarbons and better than 95 and 93% for methanol and formaldehyde, respectively. CO2 prevented the measurement of the C2 hydrocarbons in atmospheric samples, and system response to ambient water vapor limited the precision of the measurement at very low Cy. The measurement system had an estimated uncertainty of 10% at ambient mixing ratios of 100 ppb C, and a detection limit of between 5 and 7 ppb C. Cy was measured in Boulder, Colorado, during June of 1993 and at Chebogue Point, Nova Scotia, during the North Atlantic Regional Experiment intensive campaign, August to September 1993. Cy values ranged from several hundred ppb C to 11 ppb C in Boulder, and from 177 to below 5 ppb C at Chebogue Point, with medians of 55 and 11 ppb C, respectively. Cy was found to correlate with both CO and O3 at higher levels of those two pollutants. The sum of Cy and the C2 hydrocarbons was virtually always equal to or greater than the sum of the hydrocarbons. Several exceptions to this occurred when high HC values were observed in cannister samples but not Cy measurements. These instances were attributed to short‐term perturbations from local sources. There was a net difference between total nonmethane organic carbon and the sum of hydrocarbons and carbonyls of 3.5±7.8 ppb C overall. This difference appears to be broadly correlated with anthropogenic pollution. There does not appear to be a significantly large reservoir of reactive carbon unaccounted for by hydrocarbon or carbonyl measurements.

Influence of sputter gas and sputter pressure on the structure and magnetic properties of Co–Pt–Cr thin films (abstract)

The magnetic properties of high density recording media have been shown to be very sensitive to the film microstructure. We have investigated the influences of different sputter gases (Ar, Xe, Kr) and different sputter pressures (3 to 24 mTorr) on the microstructures and magnetic properties of CoPtCr/Cr thin films. The magnetic properties of the films (coercive field, Hc, coercive squareness, S*, and remanant moment, Mr) were determined using a vibrating sample magnetometer. The microstructures were examined by transmission electron microscopy and x-ray diffraction. For all three gases studied the microstructures and properties of the CoPtCr films were found to change with sputter pressure in similar manners. Films deposited at the lowest pressure consisted of well connected, equiaxed grains. With only a slight increase in pressure, the grains formed chains separated by small gaps. As the gas pressure increased further, the chains became better defined and the gaps between them widened. The coercive squareness and coercive field correlate with the film microstructures. S* decreased with increasing sputter gas pressure, and Hc first increased and then decreased. For all three sputter gases, Hc reached a maximum around 12 mTorr. Likewise, S* decreased quite slowly with increasing pressure up to 12 mTorr and then exhibited a sharp drop between 12 and 18 mTorr. From these results it appears that the sputter pressure, rather than the mass of the sputter gas, is most important for the microstructural development of the film. Likewise, the values of S* were found to be independent of the sputter gas. However, in spite of the similar microstructures, films deposited with Ar had higher values of Hc than films deposited with Xe or Kr, for all sputter pressures examined. The role of the sputter gas mass will be discussed.

Microstructural features of a Fe-20Mo-5Ni-0.12C magnetic alloy

The Fe-20Mo-5Ni-0.12C alloy after hot rolling presented coarse precipitates with the following approximated composition: 56.30%Mo, 35.96%Fe, 1.68%C, 2.01%Ni and traces of W (0.54%). One may deduce that, in agreement with the chemical analysis, that the coarse precipitates are carbides of type M{sub 6}C where M is Fe or Mo. Ni and W are present as solid solution elements, and are preferentially dissolved in the {alpha} matrix. The precipitates are stable at temperatures as high as 1,250 C. They are ferromagnetic carbides and are responsible for the high Hc values of the alloy.

Convective heat transfer measured directly with a heat flux sensor

A heat flux disk has been developed that directly measures the convective heat transfer in W/m2. When the sensor is calibrated on an aluminum cylinder, the calibration constant obtained is greatest in still air. As air movement increases, the calibration constant is reduced with increasing convective heat transfer coefficient, 0.5%.W-1.m2.K. The influence of wind on the calibration value is greatly reduced when the sensor is attached to a surface with lower thermal conductivity. The local convective heat transfer coefficient (hc) of the human body was measured. The leg acts in a manner similar to that of a cylinder, with the highest hc value at the front facing the wind and the lowest approximately 90 degrees from the wind, and in the wake a value is obtained that is close to the average hc value of the leg. When hc is measured at several angles and positions all over the body, the results indicate that the body acts approximately as a cylinder with a hc value related to the wind speed as hc = 8.6.v0.6 W.m-2.K-1, where v is velocity.

X-ray, electrical conductivity, magnetic and infrared studies of the system Co2−x Ge1−x Fe2x O4

X-ray, electrical conductivity, magnetic hysteresis and IR studies for the system Co2−x Ge1−x Fe2x O4 were carried out. All the compounds, 0⩽x⩽1, showed cubic symmetry. X-ray intensity calculations, magnetic hysteresis measurements and IR studies indicated the presence of Ge4+ at tetrahedral, Co2+ at octahedral and Fe3+ at both the sites. The activation energy and threshold frequency decreased with increasing value ofx. The compounds withx⩽0.5 arep-type and those withx⩾0.75 aren-type semiconductors. Magnetic hysteresis indicated that all the compounds are ferrimagnetic except forx=0 which is antiferromagnetic. The shapes of χ/χ i vsT plots, highH c values andJ R/Js ratios showed that all the compounds exceptx=0 exhibit single-domain behaviour. Curie temperature,T c increased with increasing Fe3+ ions. The probable ionic configuration for the system is suggested as Ge 1− 4+ Fe 3+ [co 2− 2+ Fe 3+ ]O 4 2− .

Rotatable Anisotropy and Property Control of CoZr Sputtered Films

To clarify the origin of rotatable anisotropy observed in CoZr sputtered films, the effects of Ar pressure and other conditions during RF sputtering of samples on glass were studied. Increases in Ar pressure give rise to sharp jumps in film coercivity Hc and anisotropic field Hk; films with a rotatable anisotropy, as determined from magnetization curves and domain observations, had extremely high Hc and Hk values. If the film magnetostriction is positive-valued, tensile stresses in the film due to high Ar pressures will give rise to an anisotropy with the easy axis within the plane of the film.

EuO Films Doped with Fe and Gd

EuO films doped with Fe and Gd+++ raise the Curie temperature to ≳200 °K (from 70°K for EuO). The magnetic moment is slightly reduced to 200 emu/g (vs 232 emu/g for EuO). The characteristic optical absorption band, which is due to an electronic transition from 4f to 5d levels of Eu++ ions, remains unchanged with the peak absorption of 2.4×105/cm at 5800 Å. The longitudinal Faraday rotation at 6328 Å with an incident angle of 65° is 1.9×105 and 1.4×105 deg/cm at 7.0 and 77°K, respectively. Films deposited on several types of glasses possess square hysteresis loops with higher values of Hc (86 ∼ 100 Oe at T<10°K and less than 53 Oe at T=77°K), both of which are essential for device applications.