Degaussing Research Articles

400 years of exploration

The first book of William Gilbert, De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth), was published more than 400 years ago in 1600. In this work, Gilbert described experiments on an Earth model to explain the observed magnetic field.

Reducing the Writing Temperature of Thermal Assisted Media by Controlling the Composition of FePt

Twenty-nanometer FePt films with 40% Fe content were deposited on MgO substrates at 300degC. A perfect (001) preferred orientation of FePt L10 phase was obtained. After 700degC annealing in vacuum, a room temperature perpendicular anisotropy of as high as 4.5times107 erg/cm3 can be obtained. The Curie temperature of the sample with 40% Fe content is far below the 50% Fe sample, which can effectively reduce the temperature of the thermal writing process. Furthermore, decay of magnetic anisotropy energy (Ku) is much faster than saturated magnetization (Ms ) with rising temperature, which results in a domination of demagnetization (DM) energy at high temperature. Therefore, a further reduction of the switching field can be achieved. Finally, the films show almost the same magnetic properties during 10 times thermal writing processes from 25degC to 300degC, implying this media has high reliability for thermal writing process

The Science of Magnetism Before Gilbert Leonardo Garzoni's Treatise on the Loadstone

Summary This paper presents the main features of the treatise on magnetism written by the Jesuit Leonardo Garzoni (1543–92). The treatise was believed to be lost, but a copy of it has been recently recovered. The treatise is briefly described and analysed. The results of a comparison between Garzoni's treatise, Della Porta's Magia Naturalis (1589), and Gilbert's De Magnete (1600) are also summarized. As claimed in the seventeenth century by Niccolò Cabeo and Niccolò Zucchi, the treatise contains quite a lot of the material to be found subsequently in the Magia Naturalis and in the De Magnete. Most importantly, the treatise presents so many interesting features, well before Gilbert's work, which make it the first example of a modern treatment of magnetic phenomena.

The Man in the Moone and the New Astronomy: Godwin, Gilbert, Kepler

My study discusses the sources of a text which has strong claims to being regarded as the first piece of science fiction in the English language. The Man in the Moone (1638) by Francis Godwin recounts an imaginary journey to the moon by its hero, Domingo Gonsales. It was written in the context of new astronomical theories, among which the most well known are those of Copernicus, Tycho Brahe and Galileo. Although some of his contemporaries (for example John Donne and William Drummond of Hawthornden) expressed disquiet about the unsettling implications of such theories, Godwin uses them as a central element in his story. Like Kepler, in his Somnium …de astronomia lunaris, Godwin utilises fiction in order to confirm aspects of new scientific theory — especially the diurnal rotation of the earth. But, as I show, his imaginary journey chiefly draws on the magnetic philosophy of this English contemporary, William Gilbert, especially the lunar theory proposed by Gilbert in his De magnete and further elaborated in his De mundo sublunaris.

Flux jumps in textured (Nd0.33Eu0.33Gd0.33)Ba2Cu3O7－δ superconductor with high content Gd-211 phase

Flux jumps behavior in textured (Nd0.33Eu0.33Gd0.33)Ba2Cu3O7-δ （with high content of Gd-21 1 phase） have been studied. With the magnetic field parallel to the c axis, partial flux jumps have been obser ved in the temperature range 2—3K, and there were no jumps found above 5K. When ab plane is parallel to the field direction, no flux jumps have been observ ed in the whole temperature range (from 2K to Tc). The anisotropi c flux instability may be due to the anisotropic pinning force and geometrical demagnet ization factor. As the temperature increases,the number of flux jumps is decreas ed, and the third quadrant of M(H) curve is the most flux instability quadra nt. Finally we have studied the magnetic field sweep rate dependence of flux jum p, and discussed the influence of flux creep on flux jump.

Wie funktionierte das Perpetuum mobile des Petrus Peregrinus?

At the conclusion of his Epistula de magnete of 1269, Petrus Peregrinus de Maricourt described the construction of a continually moving toothed wheel that is powered by a magnet. The effectiveness of the device is enhanced by a small rounded weight made of brass or silver that is located between two of the theeth. According to the inventor, this metallic ball “seeks the center of the earth in virtue of its own weight, thereby aiding the motion of the teeth.”

Gilbert, Translated: Silvanus P. Thompson, the Gilbert Club, and the Tercentenary Edition of De Magnete

The Gilbert Club was founded in 1889 by Silvanus Phillips Thompson and his friends to produce an English translation of William Gilbert’s pioneering treatise on magnetism and electricity, De Magnete (1600). In addition, the Club’s promoters wanted to ensure that Gilbert’s place in the history of English science was appreciated and that the tercentenaries of his book (1900) and death (1903) were observed appropriately. The key tool in their project was the publication of a “facsimile” edition of their translation, using antique typefaces and reproducing the exact layout and woodcuts of the Latin text. This allowed their translation to appear as if it had really been published in 1600, and made Gilbert accessible to a late nineteenth-century world in which electricity was suddenly everywhere. Thompson, a physical scientist, engineer, educator, and keen literary enthusiast, hinted cleverly at the tension between these two functions of the translation in the notes he compiled to accompany it. Although Thompson’s project suffered a setback with the appearance of a rival American translation before the Gilbert Club edition was complete, he recovered in time to ensure that Gilbert was given a place in the Elizabethan pantheon in 1903. The celebration of Gilbert provided common ground for the diverse and often controversy-ridden community of British electrical scientists and engineers, and the publication of the facsimile English translation of De Magnete, together with Thompson’s tireless attempts to uncover the authentic details of Gilbert’s life, should be viewed in the context of the late Victorian “invention of tradition,” in which an imagined common past was used as a source of present cohesion. Suitably reconstructed and commemorated, Gilbert himself was translated into modern form as the founder of late nineteenth-century electrical science.

Comment on “Survey tracks current position of South Magnetic Pole” and “Recent acceleration of the north magnetic pole linked to magnetic jerks”

In recent months, two articles have appeared in Eos reporting new positions of the north [Newitt et al., 2002] and south [Barton, 2002] magnetic poles from on‐site measurements of locations for vertical magnetic field dip. Readers should be advised that these reported positions are neither magnetic poles nor geophysically important locations. First let us review some facts about our Earth's field.When a magnetic field can be represented by an axially symmetric dipole pattern similar to the electric field from a pair of equal and opposite electric charges, the axis of this magnetic field is called a pole. For the Earth, Gilbert [1958] first called attention to this dipole feature in his 1600 publication De Magnete. With the magnetic dipole center location corresponding to the Earth's geographic center, and the Earth completely spherical, the exit position of the magnetic dipole corresponded to the location of a fully vertical dip of the field. Global maritime exploration that started around the time of the epic 1492 Columbus voyage greatly depended on the ship compass for navigation and on magnetic declination maps for guidance. It was only natural that considerable interest in special expeditions to locate the mysterious Arctic and Antarctic Earth magnetic poles subsequently arose.

A MILLENNIUM OF GEOMAGNETISM

The history of geomagnetism began around the year 1000 with the discovery in China of the magnetic compass. Methodical studies of the Earth's field started in 1600 with William Gilbert'sDe Magnete[Gilbert, 1600] and continued with the work of (among others) Edmond Halley, Charles Augustin de Coulomb, Carl Friedrich Gauss, and Edward Sabine. The discovery of electromagnetism by Hans Christian Oersted and André‐Marie Ampére led Michael Faraday to the notion of fluid dynamos, and the observation of sunspot magnetism by George Ellery Hale led Sir Joseph Larmor in 1919 to the idea that such dynamos could sustain themselves naturally in convecting conducting fluids. From that came modern dynamo theory, of both the solar and terrestrial magnetic fields. Paleomagnetic studies revealed that the Earth's dipole had undergone reversals in the distant past, and these became the critical evidence in establishing plate tectonics. Finally, the recent availability of scientific spacecraft has demonstrated the intricacy of the Earth's distant magnetic field, as well as the existence of magnetic fields associated with other planets and with satellites in our solar system.

Animism and Empiricism: Copernican Physics and the Origins of William Gilbert's Experimental Method

In the second year of this journal's run, way back in 1941, appeared Edgar Zilsel's classic and still widely cited paper on The Origins of William Gilbert's Experimental Method. 1 Focusing on Gilbert's De magnete of 1600, undoubtedly a seminal text in the history of the experimental method, 2 Zilsel argued that Gilbert borrowed his methodology from elite craftsmen, artisans, and other manual workers involved in mining, smelting, smithing, compass making, navigation, sailing, and other activities which involved working with iron or with magnets. 3 On its appearance the paper contributed to a growing and still continuing debate in the history of science about the relative importance of scholars and craftsmen in the origins of modern science. Although Zilsel's general thesis has been critically evaluated in terms of that wider debate, 4 his very specific claims about the [End Page 99] role of elite craftsmen in providing Gilbert with a ready-made experimental method, have never been properly considered. This paper attempts to reassess Zilsel's claims about the origin of Gilbert's experimental method and, in so doing, to arrive at a richer understanding of what Gilbert was trying to do in De magnete and to suggest an alternative source for his experimentalism.

Virtual Witnessing and the Role of the Reader in a New Natural Philosophy

How did the self-described new natural philosophies of the early modern period displace other philosophic (moral, ethical, legal), and specifically religious, discourses as the locus of truth our culture? Natural philosophy's rejection of disputation and of revelation as means of producing truth favor of the discovery of truth was more accurately an introduction of the invention of truth than of its discovery, and this invention demanded the creation of and participation of a certain kind of reader. Rhetorical examination of the early modern magnetic philosopher William Gilbert's most influential work, De Magnete, * will help us understand the change, to use Thomas Kuhn's oft-misquoted term,2 from a culture that accepted probabilistic truth the natural realm to one that expected moral certainty, from a culture that accepted revelation as a legitimate means of access to truth to one that increasingly recognized only the discovery of truth through sensual experience disciplined through experiment. One way this paradigm change was effected was through the inclusion of the reader as an active participant the new natural philosophies. The reader was included the new natural philosophies by engendering him desires for particular forms of knowledge and particular ways of attaining that knowledge. Peter Dear notes that in the seventeenth century old practices changed and new ones appeared. Those changing practices represent shifts the meaning of experience itself (12-13), and he then asks the question that might well have been on the tongues of many as the old practices gave way to the new: how can a universal knowledge-claim about the natural world be justified on the basis of singular items of individual experience? (13). A crucially important way to justify the universal knowledge-claim on singular items of individual experience

Animism and Empiricism: Copernican Physics and the Origins of William Gilbert's Experimental Method

In the second year of this journal's run, way back in 1941, appeared Edgar Zilsel's classic and still widely cited paper on The Origins of William Gilbert's Experimental Method. 1 Focusing on Gilbert's De magnete of 1600, undoubtedly a seminal text in the history of the experimental method, 2 Zilsel argued that Gilbert borrowed his methodology from elite craftsmen, artisans, and other manual workers involved in mining, smelting, smithing, compass making, navigation, sailing, and other activities which involved working with iron or with magnets. 3 On its appearance the paper contributed to a growing and still continuing debate in the history of science about the relative importance of scholars and craftsmen in the origins of modern science. Although Zilsel's general thesis has been critically evaluated in terms of that wider debate, 4 his very specific claims about the [End Page 99] role of elite craftsmen in providing Gilbert with a ready-made experimental method, have never been properly considered. This paper attempts to reassess Zilsel's claims about the origin of Gilbert's experimental method and, in so doing, to arrive at a richer understanding of what Gilbert was trying to do in De magnete and to suggest an alternative source for his experimentalism.

Gilbert's De Magnete: An early study of magnetism and electricity

Four hundred years might seem an excessively long time to wait for a book review, but there are reasons why a prompt review would have been difficult. Not only is De Magnete written in Latin, but it is also in the form of a scientific textbook. The language problem was overcome by Paul Fleury Mottelay and Silvanus P. Thompson, who translated the book into English in 1893 and 1900, respectively. The latter was published in connection with a beautiful tercentenary limited edition by the Chiswick Press that retains much of the flavor and appearance of the original. But the notion of a scientific textbook was unfamiliar when De Magnete first appeared in 1600. Certainly, scientific subjects and even geomagnetism had been written about (for example, by Petrus Peregrinus in his Epistola De Magnete, 1269), but as reports of equipment and phenomena rather than as in‐depth investigations of a subject with experimental evidence and interpretation.

Foundations of Geomagnetism

The study of the magnetic field of the Earth, or geomagnetism, is one of the oldest lines of scientific enquiry. Indeed, it has often been said that William Gilbert's De Magnete, published in 1600 and predating Isaac Newton's Principia by 87 years, can claim to be the first true scientific textbook; his study was essentially the first of academic rather than practical interest.What then, we may ask, has been accomplished in the nearly 400 intervening years up to the publication of Foundations of Geomagnetism? In short, a wealth of observational evidence, considerable physical understanding, and a great deal of mathematical apparatus have accrued, placing the subject on a much surer footing.The latter two categories are described in considerable detail, and with attendant rigor, in this book. The sphericity of the Earth means that a frequent theme in the book is the solution of the partial differential equations of electrodynamics in a spherical geometry.

Low-field microwave magnetoabsorption in the cuprate superconductors

We review results on the low-field microwave magnetoabsorption (LFMMA) in granular samples of YBCO and BSCCO. First, we show that the virgin response (increase in absorption on first application ofH) obeys a universal form (ΔP/α)=(1+H 0/H)−1. Interpreting this in conjunction with de magnetization isotherms on the same samples, we demonstrate that the data support a model in which the LFMMA arises from field dependent reduction in the critical currents of the weak links in the sample surface. Next, we present examples of the variety of hysteresis loops obtained on subsequent field cycling and interpret them in terms of the universal form provided thatH is replaced by an effective valueH eff. Attempts are made to delineate the various terms appearing inH eff.

Precursors to Peregrinus: The early history of magnetism and the mariner's compass in Europe

Histories of magnetism and the mariner's compass have usually been restricted to a few brief descriptions by Alexander Neckam, Guyot de Provins and Jacques de Vitry, followed by the important Epistola de Magnete of of Peter Peregrinus (1269). But by reviewing the many other early European references to the mariner's compass, we find that there is little in Peregrinus that originating, knowledge of the compass.

IEE Science Education & Technology Division: Chairman's address. Magnetism: it is permanent

Permanent magnet materials have one of the longest histories of any technological phenomenon, stretching from before 4000 BC to now. The early history of lodestones (naturally occurring magnets), their applications and their use to make artificial magnets is described. The early work of the Chinese and European magnet users culminated in the classic text ‘De magnete’ published by William Gilbert in 1600. The developments of the next two centuries were based on Gilbert's work until the development of the electromagnet enabled steels to be magnetised without recourse to a lodestone. The improvements in the magnetic properties of permanent magnets then took place gradually, by the development of steels and by optimising alloy compositions and heat treatments. In the 20th century, three major families of permanent magnet materials (metal, ceramic and rare earth) have been developed. The composition, properties and the method of manufacturing these metal (aluminium-nickel-cobalt-iron), ceramic (barium or strontium ferrite) and the three generations of the rare earth (RCo5, R2Co17 and NdFeB) magnets are described, and the possible applications of permanent magnetic materials are briefly tabulated. Finally using performance indicators that have been defined earlier, it is shown that the performance of permanent magnet materials have increased two-hundred-fold in the 20th century. The past and future of these important commercial engineering materials is permanent.

Magnetic resonance: boundless possibilities … or possible boundaries

Silvanus Thompson was a cultivated and learned man in the sense recognized by the Victorians, but, sadly, largely a thing of the past. He touched many things, improving them all, including translating Gilbert's De Magnete. When he was active, the use of electricity and magnetism in medicine were matters of keen interest, but one can only guess at what a world adapting to Röntgen's wonderful discovery would make of today's evolution of a magnet-based method of observation and measurement into, possibly, the most powerful in vivo diagnostic tool yet discovered. However, it is a reasonable guess that a mind as flexible and receptive as that of Silvanus Thompson would have embraced it with euphoric excitement. Perhaps the single most exciting thing about whole-body magnetic resonance (MR) is its scope. It is possible to design procedures for an almost indefinite repertoire of different studies, each more elaborate than the last and capable of more refined interpretation. The only snag—often mentioned with a sense of resignation—is that the process may take a long time. This reflects the fact that the sensitivity of the technique is limited, and that signal-to-noise ratio (SNR) considerations affect everything that is attempted. Nuclear magnetic resonance (NMR) aficionados are inclined to cloak their activities with a miasma of acronyms and jargon, leading to in vivo spectroscopy, in particular, being viewed as almost impenetrable in its mystique, though imaging can often seem little less opaque.

Magnetic properties of Y 2Fe 14B and Nd 2Fe 14B single crystals

Y 2Fe 14B and Nd 2Fe 14B are ferromagnets in which 3d interactions are dominant. In Y 2Fe 14B, the ▪-axis of the quadraticque est de magnetization. The 3d anisotropy is an order of magnitude weaker than in YCo 5. In agreement with point-charge model, CEF potential in Nd 2Fe 14B favours the ▪-axis at 300 K. At low temperature, the magnetization reorientation observed results from competition between exchange and anisotropy.

Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics

This history of electricity covers the period from Gilbert's De Magnete (published in 1600) and his work on frictional electricity, to Volta's pile (1800), dealing with the work of over 200 physicists on the way. An opening chapter which reviews physical principles to be encountered is followed by one on the institutional backgrounds from which the physicists emerged and the circumstances in which they worked.