Advanced Magnetic Thin-Film Heads Under Read-While-Write Operation

A Read-While-Write (RWW) operation for tape and/or potentially disk applications is needed in the following three cases: 1. High reliability; 2. Data servo systems; 3. Buried servo systems. All these applications mean that the read (servo) head and write head are operative simultaneously. Consequently, RWW operation will require work to suppress the so-called crossfeed field radiation from the write head. Traditionally, write-read crossfeed has been reduced in conventional magnetic recording heads by a variety of screening methods, but the effectness of these methods is very limited. On the other hand, the early theoretical investigations of the crossfeed problem concentrating on the flux line pattern in front of a head structure based on a simplified model, may not be comprehensive. Today a growing number of magnetic recording equipment manufacturers employ thin-film technology to fabricate heads and thereby the size of the modern head is much smaller than in the past. The increasing use of thin-film metallic magnetic materials for heads, along with the appearance of other new technologies, such as the MR reproductive mode and keepered media, has stimulated the need for an increased understanding of the crossfeed problem by advanced analysis methods and a satisfactory practical solution to achieve the RWW operation. The work described in this thesis to suppress the crossfeed field involves both a novel reproductive mode of a Dual Magnetoresistive (DMR) head, which was originally designed to gain a large reproduce sensitivity at high linear recording densities exceeding 100 kFCI, playing the key role in suppressing the crossfeed (the corresponding signal-noise ratio is over 38 dB), and several other compensation schemes, giving further suppression. Advanced analytical and numerical methods of estimating crossfeed in single and multi track thin-film/MR heads under both DC and AC excitations can often help a head designer understand how the crossfeed field spreads and therefore how to suppress the crossfeed field from the standpoint of an overall head configuration. This work also assesses the scale of the crossfeed problem by making measurements on current and improved heads, thereby adapting the main contributors to crossfeed. The relevance of this work to the computer industry is clear for achieving simultaneous operation of the read head and write head, especially in a thin-film head assembly. This is because computer data rates must increase to meet the demands of storing more and more information in less time as computer graphics packages become more sophisticated.Hewlett Packar

Deposit‐Derived Block‐and‐Ash Flows: The Hazard Posed by Perched Temporary Tephra Accumulations on Volcanoes; 2018 Fuego Disaster, Guatemala

The impact of hazardous pyroclastic density currents (PDCs) increases with runout distance, which is strongly influenced by the mass flux. This article shows that the mass flux of a PDC may derive not only from vent discharge during the eruption, but also from partly hot, temporary stores (accumulations) of aerated pyroclastic material perched high on the volcano. The unforeseen PDC at Fuego volcano (Guatemala) on 3 June 2018 happened c.1.5 hr after the eruption climax. It overran the village of San Miguel Los Lotes causing an estimated 400+ fatalities. Analysis of the facies architecture of the deposit combined with video footage shows that a pulsatory block-and-ash flow flowed down the Las Lajas valley and rapidly waxed, the runout briefly increasing to 12.2 km as it filled and then spilled out of river channels, entered a second valley where it devastated the village and became increasingly erosive, prior to waning. Paleomagnetic analysis shows that the PDC contained only 6% very hot (>590°C) clasts, 39% moderately hot (∼200°C–500°C) clasts, and 51% cool (<200°C) clasts. This reveals that the block-and-ash flow mostly derived from collapse of loose and partly hot pyroclastic deposits, stored high on the volcano, gradually accumulated during the last 2–3 years. Progressive collapse of unstable deposits supplied the block-and-ash flow, causing a bulk-up process, waxing flow, channel overspill and unexpected runout. The study demonstrates that deposit-derived pyroclastic currents from perched temporary tephra stores pose a particular hazard that is easy to overlook and requires a new, different approach to hazard assessment and monitoring

Spintronics with individual metal-organic molecules

In this work two ideas of using individual metal organic molecules in applications for data storage are presented. On the one hand, metal-free phthalocyanine is used to form a GMR contact consisting of one single molecule leading to the world smallest magnetic sensor. On the other hand, chromium acetylacetonate was used to study the properties of magnetic molecules adsorbed on surfaces in order to build magnetic bits for date storage

Magnetic record of deglaciation using FORC-PCA, sortable-silt grain size, and magnetic excursion at 26 ka, from the Rockall Trough (NE Atlantic)

Core MD04-2822 from the Rockall Trough has apparent sedimentation rates of ~1 m/kyr during the last deglaciation (Termination I). Component magnetization directions indicate a magnetic excursion at 16.3 m depth in the core, corresponding to an age of 26.5 ka, implying an excursion duration of ~350 years. Across Termination I, the mean grain size of sortable silt implies reduced bottom-current velocity in the Younger Dryas and Heinrich Stadial (HS)-21A, and increased velocities during the Bølling-Allerød warm period. Standard bulk magnetic parameters imply fining of magnetic grain size from the mid-Younger Dryas (~12 ka) until ~8 ka. First-order reversal curves (FORCs) were analyzed using ridge extraction to differentiate single domain (SD) from background (detrital) components. Principal component analysis (FORC-PCA) was then used to discriminate three end members corresponding to SD, pseudo-single domain (PSD), and multidomain (MD) magnetite. The fining of bulk magnetic grain size from 12 to 8 ka is due to reduction in concentration of detrital (PSD 1 MD) magnetite, superimposed on a relatively uniform concentration of SD magnetite pro- duced by magnetotactic bacteria. The decrease in PSD1MD magnetite concentration from 12 to 8 ka is synchronized with increase in benthic d13C, and with major (~70 m) regional sea-level rise, and may therefore be related to detrital sources on the shelf that had reduced influence as sea level rose, and to bottom-water reorganization as Northern Source Water (NSW) replaced Southern Source Water (SSW)

NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications, volume 2

This report contains copies of nearly all of the technical papers and viewgraphs presented at the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Application. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include the following: magnetic disk and tape technologies; optical disk and tape; software storage and file management systems; and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's

Ultrafast demagnetization in metallic ferromagnetic/antiferromagnetic heterostructures

This thesis summarizes experimental work performed on thin-film metallic and magnetic systems by time-resolved soft X-ray reflectivity and magneto-optical Kerr effect measurements. The delay-time-dependent magnetization dynamics in Co, Mn, and Ni after laser excitation are investigated in layered systems. The work aims to study the effects of antiferromagnetic coupling on de- and remagnetization dynamics in an adjacent ferromagnetic film on the ultrafast timescale. The presented work bridges the timescale from the first femtoseconds to macroscopic dynamics after several microseconds. The thesis is divided into a literature review covering the treatment and scientific context of the investigated phenomena and experimental reports where the findings of this work are presented and discussed. The presentation of the experiments is divided into four chapters. First, differences between the ultrafast demagnetization in a Cu/Co/NiMn/Cu(001) system recorded at high and low sample base temperatures are investigated. The report shows that the antiferromagnetic alignment in the NiMn system, present at low temperature, facilitates a faster demagnetization of the adjacent Co layer compared to a magnetically disordered NiMn layer at high temperatures. The second investigation covers the timescale of laser excitation and presents experimental evidence of the optically induced intersite spin transfer in a (Co/Mn)x6/Cu(001) multilayer system. An increase in the magnetic contrast in the antiferromagnetically ordered Mn layer is observed. The magnetic contrast lives for the time of excitation and indicates a realignment of the magnetic moments of the interface layers of Mn in the direction of Co. The third chapter treats simulations of the X-ray reflectivity after laser excitation. The multilayer system investigated in the aforementioned experiment is analyzed with respect to its magneto-optical properties, and the observations recorded with the X-rays are directly correlated with the transient optical response function of the elements. Furthermore, we compare the results of the simulations of the X-ray reflectivity considering structural, electronic, and magnetic effects. The last presented study is concerned with time-dependent magnetization dynamics recorded in Pt/Co multilayers. We investigate the delay-time-dependent Kerr effect and present experimental evidence for different dynamics in a Pt/Co bilayer system compared to a Pt/MnPt/Pt/Co system. Lastly, we investigate the effects of the spatial pump-probe overlap on the magnetization dynamics and link the observation to thermal and lateral transport phenomena

Lithium motion in the anode material LiC6 as seen via time-domain 7Li NMR

Since the commercialization of rechargeable lithium-ion energy storage systems in the early 1990s, graphite intercalation compounds (GICs) have served as the number one negative electrode material in most of today's batteries. During charging the performance of a battery is closely tied with facile Li insertion into the graphite host structure. So far, only occasionally time-domain nuclear magnetic resonance (NMR) measurements have been reported to study Li self-diffusion parameters in GICs. Here, we used several NMR techniques to enlighten Li hopping motions from an atomic-scale point of view. Li self-diffusion in the stage-1 GIC LiC6 has been studied comparatively by temperature-variable spin-spin relaxation NMR as well as (rotating frame) spin-lattice relaxation NMR. The data collected yield information on both the relevant activation energies and jump rates, which can directly be transformed into Li self-diffusion coefficients. At room temperature the Li self-diffusion coefficient turns out to be 10−15m2s−1, thus, slightly lower than that for layer-structured cathode materials such as Lix≈0.7TiS2. © 2013 American Physical Society