38 research outputs found
Magnetic Response Versus Lift Height of Thin Ferromagnetic Films
The interaction between a magnetic force microscope (MFM) tip and ferromagnetic films of Ni, Co90Fe10 and Py with in-plane magnetization has been investigated. The measured interaction, due to the magnetizing of the films by the MFM tip field, was determined by the phase shift of the cantilever response. The tip-film separation or lift height dependent phase shift was found to be independent of the saturation magnetization of the ferromagnetic film. The result is identical for all three films and micromagnetic simulations give similar results. The reason is at a given tip-sample separation the tip induced magnetization of the film creates a demagnetization field which is equal in magnitude to the tip field at that separation
Micromagnetic Domain Structures in Cylindrical Nickel Dots
The magnetic domain structures of cylindrical nickel dots (diameters from 40 nm to 1700 nm) with anisotropy parallel to the cylinder axis is predicted by the ratio of the dot diameter to the stripe period of unpatterned films with the same perpendicular anisotropy. The dominant domain structure for a given ratio increases in complexity as the ratio increases. We present evidence for the full micromagnetic domain structure for the simplest cases
On the Nature of Memory and Rejuvenation in Glassy Systems
The memory effect in a single crystal spin glass
() has been measured using ac susceptibility techniques over a reduced temperature range of
and a model of the memory effect has been developed. A
double-waiting-time protocol is carried out where the spin glass is first
allowed to age at a temperature below , followed by a second aging at a
lower temperature after it has fully rejuvenated. The model is based on
calculating typical coincidences between the growth of correlated regions at
the two temperatures. It accounts for the absolute magnitude of the memory
effect as a function of both waiting times and temperatures. The data can be
explained by the memory loss being a function of the relative change in the
correlated volume at the first waiting temperature because of the growth in the
correlations at the second waiting temperature.Comment: 11 pages, 6 figure
Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites
The effect of an exchange field on electrical transport in thin films of
metallic ferromagnetic manganites has been investigated. The exchange field was
induced both by direct exchange coupling in a ferromagnet/antiferromagnet
multilayer and by indirect exchange interaction in a ferromagnet/paramagnet
superlattice. The electrical resistance of the manganite layers was found to be
determined by the absolute value of the vector sum of the effective exchange
field and the external magnetic field.Comment: 5 pages, 4 figure
Oscillatory Exchange Coupling and Positive Magnetoresistance in Epitaxial Oxide Heterostructures
Oscillations in the exchange coupling between ferromagnetic
layers with paramagnetic spacer layer
thickness has been observed in epitaxial heterostructures of the two oxides.
This behavior is explained within the RKKY model employing an {\it ab initio}
calculated band structure of , taking into account strong electron
scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a
positive current-in-plane magnetoresistance.Comment: 4 pages (RevTeX), 5 figures (EPS
Global maps of soil temperature
Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world\u27s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications
Global maps of soil temperature
Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications