Measurement of the energy barrier distribution in the antiferromagnetic layer of exchange-biased materials

The value of exchange field of two FeMn–NiFeCobased spin valves with varying thickness of the pinned ferromagnetic layer has been determined as a function of temperature. The complexities caused by thermal activation of the antiferromagnet during measurement have been overcome by the development of a measurement protocol. The values of the exchange field obtained provide a measure of the degree of order in the antiferromagnet. Thus it is possible to determine the distribution of energy barriers to reversal for the system. We find that for a 110-A -thick pinned NiFeCo layer a broad distribution exists, whereas for an 80-A layer, the distribution is bimodal and has a component subject to thermal activation at temperatures down to 260 K

Determination of activation volumes of reversal in perpendicular media

We discuss a method for the determination of activation volumes of reversal in perpendicular media. This method does not require correction for the self-demagnetizing field normally associated with these media. This is achieved by performing time dependence measurements at a constant level of magnetization. From the difference in time taken for the magnetization to decay to a fixed value at two fields-separated by a small increment DeltaH, the activation volume can be determined. We report data for both CoCrPt alloy films and a multilayer film, typical of those materials under consideration for use as perpendicular media. We find activation volumes that are consistent with the hysteresis curves of the materials. The activation volume scales qualitatively with the exchange coupling. The alloy films have significantly lower activation volumes, implying that they would be capable of supporting a higher data density

Time dependence in perpendicular media with a soft underlayer

In this paper we describe measurements of magnetic viscosity or time dependence in magnetic thin films suitable for use as perpendicular recording media. Generally, such effects cannot be measured using conventional magnetometry techniques due to the presence of a thin (0.1 mum) soft underlayer (SUL) in the media necessary to focus the head field. To achieve our results we have developed an ultrastable MOKE magnetometer, the construction of which is described. This has enabled us to measure nominally identical films with and without the presence of the SUL. We find that the presence of the SUL narrows the energy barrier distribution in the perpendicular film increasing the nucleation field (H-n), reducing the coercivity (H-c) and results in an increase in the squareness of the loop. This in turn results in an increase in the magnitude of the viscosity in the region of the H-c but that the range of fields over which the viscosity occurs is reduced

Monolithic centrifugal microfluidic platform for bacteria capture and concentration, lysis, nucleic-acid amplification, and real-time detection

We report the design, fabrication, and characterization of a polymer centrifugal microfluidic system for the specific detection of bacterial pathogens. This single-cartridge platform integrates bacteria capture and concentration, supernatant solution removal, lysis, and nucleic-acid sequence-based amplification (NASBA) in a single unit. The unit is fabricated using multilayer lamination and consists of five different polymer layers. Bacteria capture and concentration are accomplished by sedimentation in five minutes. Centrifugation forces also drive the subsequent steps. A wax valve is integrated in the cartridge to enable high-speed centrifugation. Oil is used to prevent evaporation during reactions requiring thermal cycling. Device functionality was demonstrated by real-time detection of E. coli from a 200-muL sample

Magnetic characterization of perpendicular recording media

In this paper, we describe techniques for the magnetic characterization of perpendicular recording media. Such measurements made using traditional techniques, such as the vibrating sample magnetometry (VSM) and alternating gradient force magnetometer (AGFM), have to be corrected for the sample shape demagnetizing factor, which is often found not to be equal to -4p. For measurements other than the simple hysteresis loop, such as remanence curves, this correction must be carried out in real time and we describe the method by which this can be achieved and the process for achieving the correct demagnetization of perpendicular films prior to measurements of the isothermal remanent magnetization curve. A further complication is that real perpendicular media have a soft underlayer beneath the recording layer, which swamps and confuses signals from instruments such as VSM or AGFM. Hence, we describe the construction and use of a magnetooptical Kerr effect magnetometer, which does not penetrate significantly into the soft layer and enables the perpendicular layer to be measured independently. We describe the properties of a traditional alloy perpendicular medium and a Co-Pd multilayer system, which in the latter case exhibits multiple switching behavior. We also address the issue of the effect of the soft underlayer on the coupling in similar longitudinal films and find that the presence of the underlayer induces significant additional coupling effects that may well give rise to an increase in noise in recorded signal

Rotation of the pinning direction in the exchange bias training effect in polycrystalline NiFe/FeMn bilayers

For polycrystalline NiFe/FeMn bilayers, we have observed and quantified the rotation of the pinning direction in the exchange bias training and recovery effects. During consecutive hysteresis loops, the rotation of the pinning direction strongly depends on the magnetization reversal mechanism of the ferromagnet layer. The interfacial uncompensated magnetic moment of antiferromagnetic grains may be irreversibly switched and rotated when the magnetization reversal process of the ferromagnet layer is accompanied by domain wall motion and domain rotation, respectively

The effect of lameness before and during the breeding season on fertility in 10 pasture-based Irish dairy herd

Background: The effects of lameness on fertility have been documented frequently but few data are available from seasonally breeding, pasture-based herds (such as those used in Ireland) where cows are housed during the winter months but managed at pasture for the remainder of the year. This study determined the prevalence of lameness in a group of 786 cows in 10 pasture-based Irish dairy herds before, during and after the breeding season and assessed the relationship between lameness and the reproductive performance in these herds through serial locomotion scoring during the grazing period. Results: Lameness prevalences of 11.6 % before, 14.6 % during and 11.6 % after the breeding season were found and these compared favourably to results from housed cattle and are similar to other studies carried out in grazing herds. A Cox proportional hazards model with locomotion score as time varying covariate was used. After controlling for the effect of farm, month of calving, body condition score at calving, body condition score loss after calving and economic breeding index, cows identified as lame during the study were less likely to become pregnant. Cows lame before the earliest serve date but no longer lame during the breeding season, cows becoming lame after the earliest serve date and cows identified lame both before and after this date were respectively 12 %, 35 % and 38 % less likely to become pregnant compared to cows never observed lame during the study. However, these findings were only significant for cows becoming lame after the earliest serve date and cows lame both before and after the start of breeding. Conclusions: This study found that the reproductive efficiency was significantly (p 0.05) lower in these animals compared to cows never diagnosed as lame. In addition to lameness status, nutritional status and genetics were found to influence the reproductive performance in pasture-based Irish dairy herds

The geometry of antisymplectic involutions, I

We study fixed loci of antisymplectic involutions on projective hyperkahler manifolds of K3([n])-type. When the involution is induced by an ample class of square 2 in the Beauville-Bogomolov-Fujiki lattice, we show that the number of connected components of the fixed locus is equal to the divisibility of the class, which is either 1 or 2

Impacts of elevated CO<inf>2</inf>, climate change and their interactions on water budgets in four different catchments in Australia

© 2014 Elsevier B.V. Future water availability is affected directly by climate change mainly through changes in precipitation and indirectly by the biological effects of climate change and elevated atmospheric CO2 concentration (eCO2) through changes in vegetation water use. Previous studies of climate change impact on hydrology have focused on the direct impact and little has been reported in the literature on catchment-scale the indirect impact. In this study, we calibrated an ecohydrological model (WAVES) and used this model to estimate the direct and indirect effects and the interactive effect between climate change and eCO2 on water availability in four different catchments in Australia with contrasting climate regime and vegetation cover. These catchments were: a water-limited forest catchment and an energy-limited forest catchment, a water-limited grass catchment and an energy-limited grass catchment. The future meteorological forcing was projected from 12 GCMs representing a period centred on 2050s and future CO2 concentration was set as 550ppm. Modelling experiments show that impacts of eCO2 and projected climate change on vegetation growth, evapotranspiration (ET) and runoff were in the same magnitude but opposite directions in all four catchments, except for the effects on runoff in the energy-limited grass catchment. Predicted responses of runoff to eCO2 indicate that eCO2 increased runoff in the energy-limited forest catchment by ~2% but decreased runoff in other three catchments from 1% to 18%. This study indicates that rising CO2 increases ecosystem water use efficiency but it does not necessarily result in increased runoff because elevated CO2 also stimulates vegetation growth and increases ET. Elevated CO2 was proved to have greater impacts on runoff than climate change in the forest catchments. Modelling experiments also suggest that interactive effects between climate and CO2 are important, especially for predicting leaf area index (LAI) and ET in grassland catchments or runoff in water-limited catchments, where interactive effects were 1-6%. It implies that the assumption that linear combination of individual effects in most of previous studies is not appropriate. This study highlights the importance of considering elevated CO2 in assessing climate change impacts on catchment-scale water balance and failure to account for direct eCO2 effect or its interactive effects can lead to large bias in the predictions of future water budgets, especially for the water-limited catchments in Australia