Nanoscopic processes of Current Induced Switching in thin tunnel junctions

In magnetic nanostructures one usually uses a magnetic field to commute between two resistance (R) states. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current, preferably of low intensity. Such Current Induced Switching (CIS) was recently observed in thin magnetic tunnel junctions, and attributed to electromigration of atoms into/out of the insulator. Here we study the Current Induced Switching, electrical resistance, and magnetoresistance of thin MnIr/CoFe/AlO$_x$/CoFe tunnel junctions. The CIS effect at room temperature amounts to 6.9% R-change between the high and low states and is attributed to nanostructural rearrangements of metallic ions in the electrode/barrier interfaces. After switching to the low R-state some electro-migrated ions return to their initial sites through two different energy channels. A low (high) energy barrier of $\sim$0.13 eV ($\sim$0.85 eV) was estimated. Ionic electromigration then occurs through two microscopic processes associated with different types of ions sites/defects. Measurements under an external magnetic field showed an additional intermediate R-state due to the simultaneous conjugation of the MR (magnetic) and CIS (structural) effects.Comment: 6 pages, 4 figure

Early Aspects at ICSE 2007: Workshop on Aspect-Oriented Requirements Engineering and Architecture Design

The “Early Aspects @ ICSE’07” is the 11th workshop in the series of Early Aspects workshops [1] which focuses on aspect identification during the requirements engineering and architecture derivation activities. The specific aim of the present workshop is twofold: (a) to initiate creation of an Early Aspects application demonstration and comparisons benchmark; and (b) to solicit submission of new research

Critical issues in ionospheric data quality and implications for scientific studies

Ionospheric data are valuable records of the behavior of the ionosphere, solar activity, and the entire Sun-Earth system. The data are critical for both societally important services and scientific investigations of upper atmospheric variability. This work investigates some of the difficulties and pitfalls in maintaining long-term records of geophysical measurements. This investigation focuses on the ionospheric parameters contained in the historical data sets within the National Oceanic and Atmospheric Administration National Geophysical Data Center and Space Physics Interactive Data Resource databases. These archives include data from approximately 100 ionosonde stations worldwide, beginning in the early 1940s. Our study focuses on the quality and consistency of ionosonde data accessible via the primary Space Physics Interactive Data Resource node located within the National Oceanic and Atmospheric Administration National Geophysical Data Center and the World Data Center for Solar-Terrestrial Physics located in Boulder, Colorado. We find that, although the Space Physics Interactive Data Resource archives contained an impressive amount of high-quality data, specific problems existed involving missing and noncontiguous data sets, long-term variations or changes in methodologies and analysis procedures used, and incomplete documentation. The important lessons learned from this investigation are that the data incorporated into an archive must have clear traceability back to the primary source, including scientific validation by the contributors, and that the historical records must have associated metadata that describe relevant nuances in the observations. Although this report only focuses on historical ionosonde data in National Oceanic and Atmospheric Administration databases, we feel that these findings have general applicability to environmental scientists interested in using long-term geophysical data sets for climate and global change research.Peer ReviewedPostprint (published version

Formation and structural characterization of Ni nanoparticles embedded in SiO₂

Face-centered cubic Ni nanoparticles were formed in SiO₂ by ion implantation and thermal annealing. Small-angle x-ray scattering in conjunction with transmission electron microscopy was used to determine the nanoparticle size as a function of annealing temperature, whereas the local atomic structure was measured with x-ray absorption spectroscopy. The influence of finite-size effects on the nanoparticle structural properties was readily apparent and included a decrease in coordination number and bond length and an increase in structural disorder for decreasing nanoparticle size. Such results are consistent with the non-negligible surface-to-volume ratio characteristic of nanoparticles. In addition, temperature-dependent x-ray absorption spectroscopy measurements showed the mean vibrational frequency (as obtained from the Einstein temperature) decreased with decreasing nanoparticle size. This reduction was attributed to the greater influence of the loosely bound, under-coordinated surface atoms prevailing over the effects of capillary pressure, the former enhancing the low frequency modes of the vibrational density of statesThis work was financially supported by the Australian Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication Facility

Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves. The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure

Wasted positive intentions: the role of affection and abundance on household food waste.

This qualitative study, grounded theory oriented, identifies familial affection and preference for abundance as major drivers of wasted food in lower-middle income American families. These positive intentions provide an improved understanding of household food waste, a problem with high environmental impact and moral implications. Based on empirical data collected with twenty caregivers via in-depth interviews, observations, and analysis of photos, this study provides novel explanations, such as on how stockpiling comfort foods in abundance ? a form of both boosting positive self-emotions and showing affection for kids ? can promote more wasted food. Other antecedents identified include multiplicity of choices, convenience, procrastination and unplanned routines. In sum, this research identifies a negative outcome of affection and food abundance in the family context, while providing a theoretically relevant general framework to help understand the food waste phenomenon. Authors suggest increasing the awareness of nutritional gatekeepers through behavioral economics principles

Food waste paradox: antecedents of food disposal in low income households.

This article aims to identify antecedents of food waste among lower-middle class families ? a paradox, given the financial constraints this population faces. The importance of this research is evident in escalating environmental pressures for better use of our planet?s scarce resources. Given that most of the world is low-income, any behavioral change in this population is likely to have a considerable impact. Empirical data were collected from 14 lower-middle income Brazilian households, based on observations, in-depth interviews, photographs and a focus group (n56). Five major categories of food waste antecedents were identified: (1) excessive purchasing, (2) overpreparation, (3) caring for a pet, (4) avoidance of leftovers and (5) inappropriate food conservation. Several subcategories were also found, including impulse buying, lack of planning and preference for large packages. Surprisingly, findings show that strategies used to save money ? such as buying groceries in bulk, monthly shopping trips, preference for supermarkets and cooking from scratch ? actually end up generating more food waste. This mitigates the savings made during the purchasing phase

Group Theory analysis of phonons in two-dimensional Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDCs) have emerged as a new two dimensional materials field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers $N$ ($N$ even or odd) drives changes in space group symmetry that are reflected in the optical properties. The understanding of the space group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e. $2Ha$, $2Hc$ and $1T$, as a function of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical selection rules and Raman tensors are discussed.Comment: 32 pages, 4 figure