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Page 1: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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Page 2: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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The group (13 participants) discussed how MAG-NET could optimise pollution studiesover the coming months and agreed on two activities.

City surveys

To survey as many European cities within the MAG-NET programme as possible formagnetic properties of leaves (similar to survey of Birmingham) during one week in May2001. Each group would apply a consistent sampling protocol outlined at the meeting.

Magnetism and Pollution review paper.

Aims: -To produce a multi-authored review paper for a non-magnetic audience topromote the techniques and results in areas of urban planning, environmental health andpollution monitoring.

- To concentrate on urban environments and contemporary processes rather thanhistorical records from sediments

- To emphasize good examples already published or obtained, rather thantechniques and problems..

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Particular naturally occurring rocks have beenknown to have the ability to attract the element ironsince 600 B.C.. This rock was referred to as the"Magnesian stone" by the ancient people of Greece andRome because this special rock was found near theformer city of Magnesia in present-day western Turkey.The knowledge of the iron-attracting stone grew slowlybut steadily. Approximately A.D. 100, the Chinesediscovered that the stone could magnetize a piece ofiron, and less than 900 years later, they learned to usethat magnetized iron as a compass, or direction - findingdevice. Jumping to the 17th century we find ...

Kircher, Athanasius (c.1602-1680). Jesuit priestand a scientist from Geissen in Germany. In 1635 he wasmade professor of mathematics at the CollegiumRomanum in Rome by Pope Urban VI. He was theearliest to attempt to view microscopic organisms in1658 , us ing a p r imi t ive microscope which heconstructed. Some forty-four books and more than 2,000extant letters and manuscripts attest to the extraordinaryvariety of Kircher's interests and to his intellectualendowments. His studies covered practically all fieldsboth in the humanities and the sciences. Among manyother things, he described a device for measuringmagentic force using a balance, promulgated the use ofmagnetic inclinations to find longitude ...

His first book was "Ars Magnesia" (The art ofmagnetism) (1631). Another book on magnetism is"Magnes sive de arte magnetica" (Rome, 1640). In "Arsmagna lucis et umbrae"(The great art of light andshadow) (Rome, 1644), Kircher applied "magna" to"magnes" of his first work. He argued that light -the"attracting magnes of all things" and connected with the

heavens by an unknownchain- behaves exactlyl i k e t h e m a g n e s . Hediscussed the projectingo f s u n l i g h t o rcandlel ight on planemirrors , which werepainted with coloredpictures, or through anillustrated glass sphere.O n l y T h o m a sRasmussen Walgenstensucceeded in uniting thisprinciple of projectingtranslucent pictures byrays having a pointlikesource with G. Porta'sproject ion through a

hole, to the true magic lantern. Exploring the myth ofArchimedes' burning mirrors, Kircher stated that themore times light is reflected between several planemirrors, the more burning power the rays will obtain.He thus supported the story of Archimedes' purporteddevice.

Sources:Catholic Enciclopedia: www.newadvent.org/cathen/Clandening Library: clendening.kumc.edu/Galileo Project: es.rice.edu/ES/humsoc/Galileo/Further links at: www.bahnhof.se/~rendel/kirlinx.html

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Page 3: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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The magnet ic s ignature in loess-paleosolsequences has been used to determine paleoclimate,especially precipitation and temperature. Modern soilsserve as a basis for calibration. Studying recent soils istherefore useful to enhance our understanding of therelation between climate and magnetic properties ofsoils. Soil formation processes lead to the differentiationof soil types which are defined in soil classificationsystems. These soil formation processes also have aninfluence on the pedogenic formation of magnetite, thekey process for paleoclimate reconstruction. Hence, weaim to build up a database of typical susceptibilityvalues for the different soil types and to understand thelink between magnetic properties and soil type, parentmaterial, and climate.

The soil samples of the Austrian soil survey were usedto determine the different influences on the magneticsignature of recent soils. Information on bedrock, soiltype, land use and heavy metals are available for thesesamples. Susceptibility was determined at up to 5depths.

0.8 1.2 1.6 2 2.4susceptibility (normalized to the layer 40-50 cm)

50

40

30

20

10

0

depth

(cm)

medianquartiles

ChernozemCambisolAnthrosol

0 20 40 60 80 100

susceptibility (10-8 m3/kg)

50

40

30

20

10

0

depth

(cm)

medianquartiles

ChernozemCambisolAnthrosol

Figure 1: Typical susceptibility profiles for soils on loess

As a pilot study for the database, loess sites inLower Austria and Burgenland were analysed. Cleardifferences between the soil types were found in theabsolute susceptibility values as well as in the relativeenrichment of topsoil susceptibility compared to thelayer between 40 and 50 cm depth (Figure 1).

The factors related to susceptibil i ty wereestablished by interpretation of correlation coefficientsand by principal component analysis. Magnetic particlesseem to be preferentially bound to organic matter inchernozem and to clay particles in cambisol.

Additionally, the influence of gleyzation wasanalyzed. Gleysols show no enrichment of the topsoilrelative to the layer between 40 and 50 cm andsusceptibility tends to rise with depth. The maininfluence on susceptibility in the subsoil of gleysols isthe geological component. In the topsoils, there is also aconsiderable influence of a pedological component(Figure 2).

PC 1

PC 2 susc

humus

clay

Co

Mo

CuZn

Cd

topsoil

PC 1

PC 2

susc

humus

clay

Co

MoCu

Zn

Cd

subsoil

Figure 2: Result of principal component analysis for gleysols.

Page 4: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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Magnetic hysteresis parameters were measured forthree sample sets of respirable atmospheric particulatecollected in Munich, Germany, and were compared withpollution data and meteorological data using principalcomponent analysis. The samples sets were collected attwo urban locations by the filter method during August1998 to July 1999. At one location, aerosol particulatewith grain sizes < 70 µm (PM70) and < 10 µm (PM10)were collected, whereas at the other only PM70 wascollected. The samples were measured in weeklybatches, with the longest data set being 40 weeks.

Initial magnetic analysis found that the primarymagnetic mineral was magnetite (or maghemite), in thegrain size range 0.1-5 µm, which is small enough to beparticularly dangerous to humans as these particles canbe inhaled deeply into the lung. On comparison with theother data, it was found that the magnetic hysteresisparameters generally had a stronger correlation with themeteorological data than with the pollution data.Correlations with the pollution data were found to behighly site dependent, that is, at one location there was astrong relationship between the magnetic parameters andvehicular derived combustion pollutants, but not at theother. The mineralogical and domain state dependentmagnetic, hysteresis parameters were found to bestrongly correlated to the meteorological data. Inparticular the coercive force and the relative humiditywere found to be strongly anti-correlated for all threedata sets, which was unexpected as iron oxides are

known to be none hygroscopic, that is, they do notinteract with water in the air. As the coercive force isinversely proportional to grain diameter, this means thatincreases in the relative humidity preferentially removesmaller grains. To explain this a simple model isproposed, based on the fact that magnetite is known tochemisorb sulphur dioxide in the presence of photons(sun light). Now sulhur dioxide is known to be highlyhygroscopic, that is, it aborbs water, therefore in thismodel it is proposed that these sulphur dioxide rimsabsorb water, increasing the particle size which directlyeffects its residency time (see figure). As smallerparticles have a greater surface to volume ratio, they aremore strongly effected by differences in the relativehumidity.

In summary two results were found; firstlyparticulate mass and total magnetic content are notalways correlated, and secondly the meteorological dataeffects the grain size distribution of airborne particulate.Both of these results suggest that measuring themagnetic susceptibility as a rapid method of assessingthe bulk magnetic content of atmospheric particulate canbe misleading.

We have submitted a paper dealing with this studyto Atmospheric Environment, and it is currently underreview. If people would like a copy of this paper, if it isaccepted then do not hesitate to contanct us.

Page 5: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

example, the exchange interaction between a magnetitegrains and an oxidised outer rim of either hematite ormaghemite can be identified at high fields usingrotational hysteresis, but is not so readily observed inconventional hysteresis, due to the swamping of themagnetic signal by reversible processes at high fields. InFigure 2, the results of Day, O'Reilly and Banerjee(1970) nicely demonstrate this, where it is seen that theeffect of oxidation significantly increases Wrh at hightemperatures. Deviations in stoichiometry normallyincrease the irreversibly of hysteresis, an example ofwhich is shown in Figure 3. Stress also effects suchcurves.

Clearly the ability to detect either domain state orsmall irreversible processes due to oxidation, non-s to ich iomet ry o r s t r ess have app l ica t ions fo renvironmental magnetists. Figure 4 depicts rotationhysteresis curves for four dust samples collected inautumn of last year in Munich. The two samplescollected later in the year have higher peak valuesindicating a smaller grain size, however the generalshape appears to be the same suggesting that the sourcematerial is identical.

Unfortunately sample preparation is not as straightforward as for conventional hysteresis. This is becauseit is essential for the magnetic grains to be fixed withinthe sample. If a grain is not fixed then in a high field theentire particle will rotate, instead of the magnetic vector.To prevent this, Keller (1997) has developed a simplepreparation method. The samples are first lightlypressed into small holders (approximately 20-30 mgmaterial). Note if the samples are pressed with toomuch vigor this induces an art if icial unwantedanisotropy. The samples are then held by pouring in afixing agent. It is necessary for the fixing agent to be asviscous as possible, so that it can permeate the material

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Rotational hysteresis is a little-used rock magnetictechnique which has many potential uses in the field ofenvironmental magnetism. It is not my intention here todiscuss the physics of rotational hysteresis, as this can befound in several standard physics books, for example,Bozorth (1951), Chikazumi (1964) and Cullity (1972). Iwill simply summarise what the technique measures,applications and sample requirements.

A rotational hysteresis measurement is made byusing a torque magnetometer, and measuring the torqueas a function of field angle for a series of constant fieldsbetween 0 to 1.4 T (or greater). For each field, it isnecessary to calculate the net torque energy or rotationalhysteresis loss (Wrh) per rotation. For reversibleprocesses Wrh is equal to zero, for irreversible it is non-zero. Clearly for a large field the magnetic moment of asample follows the magnetic field and Wrh = 0 J, and fora zero field, there is zero torque (Wrh = 0 J). In betweenthese values there are range of fields where the torque isnon-zero and hence Wrh due to irreversible processes isnon-zero. Plotting Wrh as a function of field, gives riseto series of characteristic curves (Figure 1). The theoryfor single domain (SD) grain curves is well understood,whilst for multidomain grains the interpretation is stillsemi-qualitative.

Rotational hysteresis differs from more standard"conventional" hysteresis curves (that is, a sample fixedwhilst the magnetic field is cycled from a large positiveto negative field), in that it measures only irreversibleprocesses in the magnetic sample, unlike conventionalhysteresis which measures the combined effect of boththe reversible and irreversible components. Smallirreversible processes which are swamped by thereversible component during conventional hysteresis canbe clearly seen during rotational hysteresis. For

0 400 800 1200

0

0.04

0.08

0.12

30-50 µm50-75 µm

Figure 1. Rotational hysteresis curves for synthetic multidomainmagnetite samples produced by hydrothermal recrystallisation.

Figure 2. Evolution of Wrh-H curves for magnetite during heattreatment in air. The successive heat treatments were: curve; 1, 3.5hours at 500 °C, 2, 17 hours at 500 °C, 3, 13.5 hours at 700 °C (plus17 hours at 500 °C). Taken from Day et al. (1970).

Wrh

(J/

kg)

H (kA/m)

Page 6: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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leaving no small air pockets. For room temperaturemeasurements it is best to use cetyl alcohol whichf reezes a t 40 °C, and i s very v i scous a t roomtemperature, for higher temperature measurements it isnecessary to use a high-temperature glue which isdiluted with acetone to make it more viscous. Themachine in Munich is sensitive enough to measure aminimum peak value of approximately Wrh = 10-7 J, orroughly 1-2 mg of pseudo-single domain (PSD)magnetite material. To measure one high resolutionWrh versus field curve takes about 12 hrs, but the systemin Munich is completely automated, making themeasurement relatively non-time consuming.

As a final comment, rotational hysteresis ispowerful tool. There are two within the network(Munich and Zurich), however, as with other magnetictools it should be realised that it must be used inconjunction with other magnetic techniques to elucidatethe full picture.

12008004000

0

0.004

0.008

0.012

19/9-5/10 (Hc = 8.9 mT)24/9-8/10 (Hc = 8.9 mT)8/10-21/10 (Hc = 11.8 mT)21/10-16/11 (Hc = 10.2 mT)

References

Bottoni, G., Rotational hysteresis and magnetic anisotropy of particlesfor magnetic recording, J. Magn. Magn. Mater., 140-144,2207-2208.

Bozorth, R. M. Ferromagnetism, Van Nostrand, 1951.Chikazumi, S., Physics of Magnetism, Wiley, 1964.Cullity, B. D., Introduction to Magnetic Materials, Addison-Wesley,

1972.Day, R., W. O'Reilly, and S. K. Banerjee, Rotational hysteresis study

of oxidized basalts, J. Geophys. Res., 75, 375-386.Keller, R., Magnetische Eigenschaften und Rotationshysterese von

Titanomagnetitpartikeln Fe3-xTixO4 der Zusammensetzungx = 0 . 6 u n d x = 0 . 7 i n d e r G rö ß e v o n E i n b e r e i c h s ,Pseudeinbereichs- und Vielbereichsteilchen, PhD thesis,University of Munich, 1997.

Figure 4. Rotational hysteresis of four dust samples collected inthe autumn of 1999 in Munich. The later two samples werecollected during a period of high pressure. The conventionalhysteresis parameter, the coercive force (Hc), is shown forreference. The samples with larger Hc also have higher peak Wrhvalues, both of which is indicative of smaller SD/PSD-like grains.

Figure 3. Rotational hysteresis of pure and Ir-doped chromiumdioxide. The effect of impurities is to increase both the positionand height of the peak Wrh. Taken from Bottoni (1995).

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Page 7: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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M e d i t e r r a n e a n p i s t o n c o r e L C 0 7(latitude/longitude 38°08.72N/10°04.73E, water depth488 m) was collected by the R.V. Marion Dufresne in1995 (MAST II PALAEOFLUX Programme) from alocation north of the Skerki channel at the western sideof the Sicily strait (see figure in the front cover). The23.66 m of core LC07 have been continuously sampledwith ca. 1m long u-channel samples at the BOSCORrepository in the Southampton Oceanography Center,UK (photo in the cover). The upper 0.5 m wereunsuitable for u-channel sampling due to sedimentdisturbances. Magnetic measurements on the u-channelswere obtained on a 2G Enterprises high-resolution pass-through cryogenic magnetometer at the Isti tutoNazionale di Geofisica e Vulcanologia in Rome, Italy.Measurements on the u-channels were done at 1 cmspacing although smoothing occurs due to the width ofthe response function of the magnetometer pick-up coils[Weeks, 1993]. Low field magnetic susceptibility (k),laboratory imparted remanences (anhysteretic remanentmagne t i z a t i on , ARM; i so the rma l r emanen tmagnetization, IRM) and their respective alternatingfield demagnetizations, together with some interparametric ratios, all at 1-cm spacing, constitute the rockmagnetic data gained in these cores. In addition,hysteresis loops were generated from small driedsediment samples collected at 5-cm spacing. Hysteresis

measurements were done on an alternating gradientforce magnetometer (AGFM, Micromag, PrincetonMeasurements Corporation) at the University of Utrecht,Netherlands. Values of saturation magnetization (Ms),saturation remanence (Mrs) and coercive force (Hc) weredetermined from hysteresis loops. The coercivity ofremanence (Hc r) was obta ined f rom backf ie lddemagnetization of Mrs in the AGFM.

The downcore ChRM inclination values indicatethat core LC07 expands the entire Brunhes (C1n) and theupper part of the Matuyama Chronozones (C1r.1r andpart of C1r.1n or Jaramillo subchron). The unambiguouslocation of the Matuyama/Brunhes (M/B) and upperJaramillo (UJ) reversals at 17.83 mbsf and 22.48 mbsfrespectively indicate that mean sediment accumulationrate (SAR) is 2.29 cm/ky for the Brunhes and 2.19cm/ky for chron C1r.1r. The astronomically calibratedages of 0.778 Ma (M/B) and 0.990 Ma (UJ) are used[Tauxe, 1996, Shackleton, 1990].

Several studies have shown the usefulness ofsome rock magnetic parameters as climatic proxies inmarine sediments and have used them to establish timemodels by correlating them to a target climatic template(i.e. reference isotopic curve or astronomical solution)for cores where any other independent dating was not

F ig . 1 . Some rock magne t i cparameters for the lower part ofLC07 and the proposed correlationto the oxygen isotope record fromODP site 677. Normal polaritiescorreponding to the Brunhes chornand Jaramillo subcron are indicatedas grey color. Core breaks areindicated by vertical dashed lines.T h e L a s k a r i n s o l a t i o n a n deccentricity solutions for the sameinterval are plotted.

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Page 8: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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available, i. e. [Robinson, 1986, Guyodo, 1999]. Adetailed and reliable time model is necessary for theanalysis and comparison of paleointensity data fromdifferent cores. Here we examine the lower part of therecord where the presence of magnetostratigraphicboundaries (i.e the M/B and UJ reversals) provides thenecessary tie points to further develop the time model.

Low field susceptibility K, IRM, ARM and NRMgenerally reflect variations in the concentration offerromagnetic minerals. However, K and IRM are biasedtoward coarse grained magnetite and ARM and NRMtoward fine grained magnetite. The NRM also partlyreflects the intensity of the geomagnetic field at the timeof sediment locking-in. For magnetic assemblagesdominated by magnetite, the ratio ARM/K is indicativeof magnetite grain size within the fraction from stablesingle-domain though multidomain behaviour [King,1982]. For core LC07, dominance of magnetitecontribution to the NRM is compatible with the AFdemagnetization characteristics. However, a relativelysmall antiferromagnetic (goethite/hematite) contributionto the IRM is likely.

Downcore variations of ARM/K from core LC07(Fig. 1) shows various highs and lows which areindicative of grain size variations with maximum valuesindicating relative smaller grain sizes. The mediandestructive field of ARM (MDFARM) varies from 33 mT

to 40 mT and essentially follows the ARM/K trend.Downcore variation of K anticorrelate to ARM/K andMDFARM . Although K is normally taken as a measureof ferromagnetic mineral concentration, it is also knownto show a grain size dependence for magnetite [Maher,1988], increasing through the SD-PSD-MD range whichis consistent with the observation from core LC07.

The M/B reversal is firmly establish to occur at778 kyr within interglacial marine isotopic stage (MIS)19 [Tauxe, 1996]. The position of the M/B boundary at17.83 mbsf in core LC07 occurs within a prominent highof the ARM/K parameter (Fig. 1) which can be inferredto correlate with MIS19. Indeed, the downcore variationsof ARM/K (and also MDFARM) (Fig. 1) can easily becorrelated to an oxygen isotopic template (the benthicrecord from ODP Site 677 [Shackleton, 1990] is taken asthe target curve and the AnalySeries software [Paillard,1996] is used for correlation and tuning purposes).Different highs and lows in the ARM/K are correlated torespective high/lows corresponding almost to allinterglacial and glacial stages from MIS 19 to MIS 29(Fig. 1) implying only minor adjustments to a constantsedimentation accumulation rate (SAR) model dictatedby the M/B and UJ reversal boundaries.

Some considerations regarding the connectionbetween the rock magnetic parameters and the climaticsystem at the Mediterranean location of core LC07 canbe made. Assuming the validity of the time model putforward above and that magnetite dominates theferromagnetic fraction, it is seen that warm interglacialperiods are characterized by relatively small grain sizes(i.e, associated to low K values and high KARM/Kratios) (Fig. 1). Cold glacial events are dominated byrelative coarser ferromagnetic fraction (i.e highest Kvalues and lowest ARM/K values). This is furthercorroborated by the hysteresis ratios, which depict atrend within the pseudo-single domain (PSD) field (Fig.2) from relative "fine-grained" values for the interglacialperiods to relative "coarse-grained" values for the glacialperiods. Therefore, the interplay of a detrital/eolian fluxand a biogenic flux, could potentially be evaluated in thelight of integrated studies. Moreover, estimates ofrelative paleointensity along core LC07 can now beadequately transferred to the time domain and amanuscript concerning the relative geomagneticpaleointensity across the Matuyama/Brunhes boundarydown to the Jaramillo subchron is on the way.

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Page 9: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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Introduction

A number of instruments are used in MAG-NETlaboratories to measure magnetic susceptibility. Theywork in variable field, frequency, temperature, and havedifferent internal calibration, or calibration samplesprovided by different manufacturers.

It is therefore desirable to obtain a reliable cross-calibration, internal to a laboratory (e.g. in betweenKappabridge KLY-2 or KLY-3, Bartington probes,Micromag…) or inter-laboratory, so that easiercompilation of consistent databases is achievable.

In CEREGE Aix-en-Provence and INGV Roma,we have chosen to use a paramagnetic oxide, Gd2O3, forthis purpose. The features of rare earths salts have beenhighlighted in the last issue of the IRM Quarterlynews l e t t e r (Vo l . 10 , No . 3 ) . The i r magne t i csusceptibility is totally independent of frequency andfield (up to 10 T above a temperature of 50 K) and theirtemperature variation is predicable with high accuracy.On top of these features (shared by all paramagnets notonly RE) is the fact that RE oxides, especiallyGadolinium, provides larger signal than the lightertransition elements (Fe, Mn…), are very stable with timein mass and susceptibility (they do not oxide or hydrate,like FeSO4 for example). Finally rare earths products arevery pure and the impurities are mostly other rare earthwith similar magnetic properties. Gd2O3 has a tabulatedspecific magnetic susceptibility χ = 1845 m3/kg at 20°C.Its temperature dependence above 50 K is described by aCurie-Weiss law, χ=C / (T-θ) (with paramagnetic Curieθ = -18 K).

Therefore room temperature (t in Celsius)measurements can be corrected to a referencetemperature of 20°C by the formula: χc= χ (291+t)/311.

Experimental protocol

A 100 g batch of Gd2O3 99.9% (ref. 27,851-3)was obtained from Aldrich, and a set of 10 standardplastic cubes with about 7 g of powder were prepared,for future distribution among the members of thenetwork. Mass was obtained with a precision of 0.1 mg(Table 1). Unfortunately due to the high cost of theproduct it was not possible to fill totally the boxes,which have about two thirds of the volume filled by theGd2O3 powder. The magnetic susceptibility of theplastic cube makes only 0.4% of the total signal.However it was subtracted by measuring empty boxesprior to other measurements. Each box was measured forthe first set of measurements in CEREGE but later onlya reference box was measured. The few percentvariability of the signal of different boxes is totallynegligible.

The first set of measurements of the ten boxes wasmade in CEREGE on a KLY-2 with standard coil,bought in 1985. A second set of measurements, made inINGV, involve three different instruments, in sixdifferent configurations: a KLY-3 (bought in 2000,internal calibration), a KLY-2 (bought in 1990),equipped with a standard or large volume coil (bothprovided with specific external calibration samples), aBartington with small sample probe (MS2B at high andlow frequencies), or with a 45 mm loop (MS2C). At thisoccasion it was discovered that the paramagnetic

All susceptibility values are in (10-9 m3/Kg) and corrected to 20°C. Yellow columns refer to measurementsdone in CEREGE, orange columns to measurements done at INGV.

Table 1. List of susceptibility measurements for standard cubes of Gd2O3

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Page 10: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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calibration sample (MnCO3) provided by Bartington wasuseless as its mass was unknown and the manufacturerprovided only the specific susceptibility value.

F ina l l y i t was r ea l i z ed t ha t due t o t heinhomogeneity of the Bartington small probe, the non-complete filling of the boxes induced a large error.Therefore the samples were remeasured after optimizingthe position of the sample.

Interpretation of results

Table 1 yields an extremely well defined meanvalue for the KLY-2 CEREGE measurements, with astandard deviation (s.d.) of ca. 0.5‰. This clearlydemonstrates that this material is suitable for cross-calibration using different samples from the same batch,instead of the tedious procedure of circulating the samesamples among various laboratories. The results beingmainly interesting in terms of cross-calibration, Fig.1represents the average χ with its standard deviation,normalized to the mean CEREGE value.

The various Kappabridge means are consistentwithin 1%, indicating that the AGICO Company hasprovided consistent calibration samples since 16 years.The large coil data is more scattered as expected for thelower range used (2 instead of 5) for the measurement.Interestingly KLY-3 do not appears to be more precisethan KLY-2 with standard coil (INGV data, obtained thesame day in the same room), in contradiction with theclaimed “higher sensitivity”. Why INGV data is a bitmore dispersed (1‰ is still not bad) may be linked to aslightly less stable electromagnetic environment, orbetter operation.

Bartington discrete sample probe yield a largerscatter (s.d. of 4-5‰, reduced to 3‰ after centering),and overall a large difference (9% lower) withKappabridge. Hopefully the two frequencies yield equalmean values. This difference appeared to be almost fullyremedied after optimizing the centering of the cubewithin the sensor. Thus, although after proper centeringthe cross-calibration with Kappabridge is good at 1%, itis unrealistic to assume that every measurement madewith this instrument will be performed at optimal

position. Moreover it is likely that a full cube of Gd2O3

will not yield the same χ, due to the bell shape of theresponse function. Centered thin samples should showlarger χ than thicker samples. Therefore it is likely thatBartington values may have a 10% difference withKappabridge values.

Finally the data obtained with the Bartington loop,inserted in line with the 2G-cryogenic magnetometer andused to obtain automatic measurements on u-channel orset of discrete samples, has to be multiplied by aconstant to account for the discreteness and the volumeof the samples. Using a factor 4 produced a reasonablevalue, but the dispersion is much larger than with thediscrete sample probe.

Absolute calibration and future work

With respect to the value tabulated by Landolt andBornstein (Vol. III/4a), our CEREGE KLY-2 value is5% lower. Before asking every laboratory to shift their χvalue by this amount there is a need for a critical reviewof the various tabulated measurements (e.g. Landolt andBornstein have several values). Other interest of Gd2O3powder is that it can be used to cross-calibrated highfield susceptibility measured with Micromag, or otherhysteresis loop system, as well as calibrating thetemperatures in χ–T experiments, in particular usingCSL2 or 3. Further work will address this aspect later.

As a preliminary example Fig.2 provides a CSL2curve obtained in CEREGE on an old batch of Gd2O3.The inverse susceptibility is almost perfectly linear andthe intercept with T axis is at –15.3 K, quite close fromexpected value of -18 K.

By using one Gd2O3 cube in each laboratory it isexpected that we will be able to cross calibrate all MAG-NET susceptibility measurements within an error betterthan one percent. The main difficulty is to preciselymeasure temperature and make the appropriatecorrection. It is advisable to use this cube once tocalibrate the internal or external calibration samples ofthe instruments if these are insensitive to temperatureand then use their recalculated values for dailymeasurements.

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Page 11: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

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Page 12: magnet/MAGazine/Magazine_03.pdf · In "Ars magna lucis et umbrae"(The great art of light and shadow) (Rome, 1644), Kircher applied "magna" to "magnes" of his first work. He argued

European Union of Geosciences(EUG) XI, April 8-12, 2001,Strasbourg, FRANCE, Fax: +33-3-88-60-38-87; [email protected]; ; Abstract Deadline:November 30, 2000Web Site: eost.u-strasbg.fr/EUG

Conference on The Study ofEnvironmental Change UsingIsotope Techniques, Vienna,AUSTRIA, April 23-27, 2001,Fax:+43-1-26007;[email protected];Web Site:www.iaea.org/worldatom/Meetings/Planned/2001/; Abstract Deadline:November 10, 2000

May 29 - June 2, 2001, AGU 2001Spring Meeting, Boston, Mass.,U.S.A., Fax: +1-202-328-0566; E-mail: [email protected]; WebSite: www.agu.org/meetings/;Abstract Deadline: March 1, 2001

AMERICAN ASSOCIATION OFPETROLEUM GEOLOGISTS(Annual Meeting), Denver,Colorado, 3-6 June 2001. Fax: +1918 560 2684 or 800/281-2283;[email protected]

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June 13-18, 2001, Millennial-scaleEvents in the North AtlanticRegion During Termination 1,Coleraine, Northern Ireland, UK,www.ulst.ac.uk/termination1.html;Abstract Deadline: January 1, 2001

WATER-ROCKINTERACTION, Sardinia, Italy,10-15 June 2001. Rosa Cidu,Dipartimento di Scienze dellaTerra, via Trentino 51, I-09127Cagliari, Italy; [email protected]

July 16-20, 2001, DetectingEnvironmental Change: Scienceand Society, London, UK, Fax:+44-20-7387-7565; E-mail:[email protected]; Web Site:www.nmw.ac.uk/change2001;Abstract Deadline: May 1, 2000

August 19-23, 2001 InternationalSymposium on Ice Cores andClimate, Kangerlussuaq,GREENLAND, Fax: +44-1223-336543; E-mail:[email protected]; Web Site:www.spri.cam.ac.uk/igs/home.htm

August 19-30, 2001, First JointScientific Assembly of theInternational Association ofGeomagnetism and Aeronomy

(IAGA) and the InternationalAssociation of Seismology andPhysics of the Earth's Interior(IASPEI) Hanoi, VIETNAM Fax:+84-48-364-696; E-mail: [email protected]; Web Site:www.IAGAandIASPEI.org.vn;Abstract Deadline: February 1,2001

International Conference onGEOMORPHOLOGY (5th),Tokyo, Japan, 23-28 August 2001.Prof. Kenji Kashiwaya, Dept. ofEarth Sciences, KanazawaUniversity, Kakuma,wwwsoc.nacsis.ac.jp/jgu/

International Association ofMATHEMATICAL GEOLOGY(6th Int'l Conference), Cancún,Mexico, 6-16 September 2001.Gina Ross, Kansas GeologicalSurvey; [email protected];www.kgs.ukans.edu/Conferences/IAMG/index.html

GEOLOGICAL SOCIETY OFAMERICA (Annual Meeting),Boston, Massachusetts, USA, 5-8November 2001. fax: +1 303 4471133; [email protected];www.geosociety.org/meetings/index.htm

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