Energy barrier versus switching field for patterned Co₈₀Pt₂₀ alloy and Co/Pt multilayer films

Two Co/Pt multilayer samples have been fabricated with a difference in the number of bilayers, leading to a total magnetic layer thickness of 3nm and 20nm. From these films, large arrays of magnetic islands have been patterned using laser interference lithography and ion beam etching. We have investigated the switching field distribution (SFD) of approximately 80 islands and thermal switching field distribution SFDTof individual islands of both samples using the anomalous Hall effect. We compare the results of these measurements with the (SFDT) of a previously investigated alloy with a magnetic layer thickness of 20nm by comparing the results of over 1000 hysteresis loops of a single weak island and a single strong island. We found that that the energy barrier for the multilayer islands increases with increasing switching field, whereas it was previously found that the energy barrier for the alloy stays constant with varying switching fields. When comparing the two multilayer samples, we observe that the grain size, anisotropy, and switching field distribution are more or less independent on thickness, whereas the switching field at both 0K and 300K decreases with film thickness

Distance matters! Cumulative proximity expansions for ranking documents

In the information retrieval process, functions that rank documents according to their estimated relevance to a query typically regard query terms as being independent. However, it is often the joint presence of query terms that is of interest to the user, which is overlooked when matching independent terms. One feature that can be used to express the relatedness of co-occurring terms is their proximity in text. In past research, models that are trained on the proximity information in a collection have performed better than models that are not estimated on data. We analyzed how co-occurring query terms can be used to estimate the relevance of documents based on their distance in text, which is used to extend a unigram ranking function with a proximity model that accumulates the scores of all occurring term combinations. This proximity model is more practical than existing models, since it does not require any co-occurrence statistics, it obviates the need to tune additional parameters, and has a retrieval speed close to competing models. We show that this approach is more robust than existing models, on both Web and newswire corpora, and on average performs equal or better than existing proximity models across collections

Tungsten-siliconnitride medium for mega- to gigayear data storage

Throughout the ages humanity has stored data in order to preserve important information for generations to come. As the years have progressed the amount of data that can be stored efficiently has increased tremendously, the lifespan of this type of data storage however is severely limited. Within this paper we investigate the possibility to store data by encapsulating W in a SiN matrix.We show that using accelerated thermal aging the possible lifespan of this medium can be investigated and expected to reach well into the millions of years, preserving data for thousands of future generations. The first steps into fabrication of such a medium are discussed

Simulation of position sensitivity of the anomalous Hall effect on a single magnetic dot

To overcome the superparamagnetic effect caused by scaling bit and grain sizes in magnetic storage media different approaches are investigated. One alternative is bit patterned magnetic media (BPM) where each bit is represented by a single domain magnetic dot. A key problem with BPM is the large difference in magnetic field necessary to switch the magnetization direction of the various dot which is characterized by the switching field distribution

Determination of bit patterned media noise based on island perimeter fluctuations

We measured the fluctuation in shape of magnetic islands in bit patterned media fabricated by laser interference lithography. This fluctuation can be accurately described by a model based on a Fourier series expansion of the perimeter of the islands. The model can be easily linked to amplitude and jitter noise. We show that the amplitude and jitter noise are in principle correlated, and the jitter noise increases with increasing island area. The correlation is small for media prepared by laser interference lithography, but expected to gain importance for high density bit patterned media