D-AI49 99i INYESTIGATION OF ELECTRIC AND MAONETIC PROPERTIES OF 1/1INTERCALTED ORAPHITE(U) BOSTON UNIV MA DEPT OF PHYSICS6 0 ZIMMERMAN 15 NOV 84 20-219-6340-5 AFOSR-TR-84-1229

UNCLSSIF IED RFOSR-82-0286F/22/3 NL

EEEEEEEEEEEEI

ILL

14-

IIIJIL25I1.

MICROCOPY RESOLUTION TEST CHARTNATIONAL BRfU AOf LITANEIA4DS fI 9t A

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4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED

INVESTIGATION OF ELECTRIC AND MAGNETIC PROPERTIES a@@& fl'wtm4 (OF INTERCALATED GRAPHITE 12 MOS. STARTING SEP. 30 '83

6. PERFORMING ORG. REPORT NUMBER

20-219-6340-57. AUTHOR(a) S. CONTRACT OR GRANT NUMBER(e)

GEORGE 0. ZIMMERMAN AFOSR 82-0286

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASKPHYSICS DEPARTMENT AREA & WORK UNIT NUMBERS 0

BOSTON UNIVERSITY 2306/C3BOSTON, MA 02215 ' '

I I. CONTRQLLING OFFICE NAME AND ADDRESS 12. REPORT DATEAFvRINE NOVEMBER 15, 1984BUILDING 410 13. NUMBER OF PAGESBOLLING AFB, DC 20332 Ii 0

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•SUPPLEMENTARY NOTES

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INTERCALATED GRAPHITE SMAGNETISMELECTRICAL CONDUCTIVITYIRON CHLORIDE

20. ABSTRACT (Continue on reverse side If necesery and Identify by block number)

THIS YEAR, BECAUSE OF THE MOVE OF THE PHYSICS DEPARTMENT OF BOSTON UNIVERSITY S@,. TO NEW QUARTERS, THE RESEARCH FACILITIES AND THE L.ABORATORY HAVE BEEN SIGNIFI-

CANTLY UPGRADED. THE UPGRADING INCLUDED NEW PUMPING SYSTEMS AS WELL AS CON-TROL AND DATA ACQUISITION DEVICES, SO THAT NOW THE DATA CAN BE SAMPLED, COL-LECTED AND ANALYZED BY COMPUTER.

ALTHOUGH THE UPGRADING TAKES SOME TIME, THE IMPROVED FACILITIES ALLOWED CER-

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TAIN MEASUREMENTS, SUCH AS THE CONDUCTIVITY MEASUREMENT WHiICHWOULD HAVE BEEN IMPOSSIBLE BEFORE. THE MOST SIGNIFICANT DISCOVERIES DURINGTHE PAST YEAR WERE THE DISCOVERY OF A CONDUCTIVITY MAXIMUM IN FeCI 3-INTER-CALATED GRAPHITE ALONG THE C-AXIS. THE MAXIMUM COULD BE SUPPRESSED BY AMAGNETIC FIELD AS SMALL AS 0.4MT. AN ACCOMPANYING SUSCEPTIBILITY MAXIMUMOBEYS THE SCALING LAW WITH AN EXPONENT OF APPROXIMATELY TWO.

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0

Scientific

Abo Report on

Investigation of Electric and Magnetic Properties of Intercalated Graphite

Grant No. AFOSR 82-0280

Grant Period 12 Months Starting 83 Sept. 30

Project, Task 2300/C3-

November 15, 1084j

By George 0. Zimmiermani__________Accension For

Principtil Investigator -

Physics Department DT I T;.B

Boston University U'rejusjtification

Boston, MA 02215 -

Di.ntribiftion/.

Ava±1rnbility CodesAvail aind/or

T117.t Special

Made to

Dr. M. Swerdlow

Dr. H. Weinstock

Building 410

Bolling AFB. DC 20332

Abstract

This year, because of the move of the Physics Department of Boston Universityto new quarters, the research facilities and the laboratory have been significantlyupgraded. The upgrading included new pumping systems as well as control and dataacquisition devices, so that now the data can be sampled. collected and analyzedby computer.

Although the upgrading takes some time, the improved facilities allowed certainmeasurements, such as the conductivity measurement in appendix 2 which worldhave been impossible before. The most significant discoveries during the past yearwere the discovery of a conductivity maximum in FeC/ 3-intercalated graphite alongthe c-axis. The maximum could be suppressed by a magnetic field as small as0.4mT. An accompanying susceptibility maximum obeys the scaling law with anexponent of approximately two.

Progress Report

During the investigation of FeCIlincalated graphite at this laboratory. severalimportant discoveries were made about the electric and magnetic properties of thesesubstances. It was found that in well characterized FeC1I samples there was a mag-netic susceptibility maximum indicating a nrgnetic transition at 6.5 K in stage oneand at 1.72 K in stage two. At higher temperatures the magnetic susceptibilityof these samples obeyed the Curie-Weiss law with the theta indicating an antifer-romagnetic interaction within the layers and a ferromagnetic one between layersin stage one and antiferromagnetic interactions both within and between layers instage two. Figure 1 shows the susceptibilities as a function of temperature whileFigure 2 shows the inverse susceptibility and the Curie-Weiss law. Table 1 lists thevarious parameters for the transitions

IL . .. .

... ... . . . . .... ,° ' ~ - -* . oP.. o~~-..°. .. "*-* O.j * A ." . . .o . . .. .. . . . . .. °

440- me 0 14

*e" fr it~ e I Tonew"W 191Soq

scale. ~ ~ !o :e tgeI e 2 ca"-s ? 31CceI. 7h soidlies,..tanThe U&S~eZI f-&Ld as fxed.3*ch par less.- 2:-urn..-c . = d J .

*la -&&cs n epniua*C12s :0tebslPas ac

30- *M1 &M2COfStg IgM-c.sl La :b Ir Urc*r=

'M~hCA b Jcezd n hesctCl~r"*IG

7ASLZ .1 taae Uss th za~zscc prv, ,-asOf :o cc~von00

a~. a-&a 1.7d -7ped.5.a

occurs i n al ineralte g±rapht t . . htmai u ocrsi)ah tg

atth same te peatre bust its size ec roers ifcatly caretw wthsag.sigrsho s hismaimu i sage1..4 nd6. hesie o ths m xi um ep nd

4 ".'Aasure-

'e-St for =agnetCic

• I

X.'Ts grahL*-ZqeCtu

states 1,1 ,and

r....|x

LZ 1.6 1.0 e -Temoefature (K)1

sensitively on the applied magnetic field. Figure 4 shows this maximum as a functionof temperature, which is in zero (higher peak) magnetic field for a stage 6 sample.

S"

I.°

I..

° " I

4

7

450-400-

:35;j300-

250

E -00-

150-100-

5030--

1.5 1.3 1.7 1.8T(K)

FICURE 4

Figure 4

The magnetic susceptibility of stage 6 FeCl 3 intercalated graphite as a-unction of temperature. he peak occurs at T - 1.749 K.

¢'~.. . .. . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . ..

Figure 5 shows the maximum in different zagnatic fields applied alonig thec-axis while Figure 6 shows the field dependence along the a-axis.

3

2 5

FIGSRE S4

Figure 5

The nagnecic susceptibility of stage 6 FeCl 3 intercalated graphite in thetemperature region of the susceptibility mnaximum as a function of the acoiiedexternal magnetic field. The field is applied along the c-axis w'hile themeasuring field is icg the a-axis.

6

350

300

250

200t150 S1

I I

1.5 1 .70 1 5 1 SO1.T(K)

FIGURE 6

-ioure 6Th anetic susceptibility of stage 6 FeC13 intercalated graphite in e

Meprauergoofhesseibiy maxim~a -ucto If th le

external magnetic field. -he field is applied along the b-axis while the

measurinig field is along the a-axis.

- ' - -- - - -

7

The notations near the various traces indicate the magnetic field in gauss. Onenotes that a field applied along the a-a-xis is much more effective in suppressingthe maximum than a field along the c-axis. The measuring field was always alongthe a-axis. In order to explore the critical properties of the system one needs to

6 apply the shape correction. since the susceptibility at the maximum in zero appliedmagnetic field is very large. When such a correction is applied the peak becomesvery large and sharp. Fig. 7 shows the natural logarithm of the corrected maximumas a fuinction of the reduced temperature t= (T- T,);2T,. The units are arbitrarybut one notes the sharpness of the maximum. Fig. 8 shows that the susceptibilityobeys a power law near the critical point.

E-I5~4E

33

I C-1 21 C

C)FTGUREU

DI a ca o fcorete fr hesao o -hesacl.-,e ogri of::,

re'7isplttd gairs, : e:,duedtapeac

; /

8

ti TE, I PLCT

I ./7i7I- .- / -I

* L*I,1 .-L...

"- - M ,-Jre

• . . . . /

I I'

26_ zz2;"t

_ y

- A-

5I 1I

.1 - .. .. ... I.. .... ...... . .. ...

*_ 6. .. 1t . ._6 P6.. ._6 . 6 *I . 6 r.t " . ._ ._6 ,'. .6i ._6 6_, C,

FIGURES -_ kl," T .T...-.- I

*Figure 3""-

*.rie naturailcgoarith.m off the susceptibility pl.otted against the logari.thm or the "-

reduced ternoerature, showing "_hat the transition obeys a power law

"( ±- - w.Z~ith v/ = l.i75.

- T"c

9

F igS. 9a and b show the logarithm of the maximu-rn susceptibility as a func-tion of the appl ied field in gauss along the c and a axes respectively,

,A while Figures 10a and b show the temperature of the susceptibility maximaas a function- of the applied field along the c and a axes respectively.

'9-.

40L

B(GAUSS)

T GURE_ 9 a

:z.re9a

The _oza_4:' or the iofe s sucoi~~'nxiasc ng 5 as a::.o orhe apolied magnetoic field along --he :-ax~s.

1 . ~ . .. .. .. .*. . . . . . . . .

* i0

/10

/ 4

-- I

4 0

0 2 4 E, 8 10 12 ±4 i±3(GAUSS)

FTGUR E 9b

Figure 9b

-.. e logarithm of the size of the suscepribilit; maxima shown in Fig. 6 as a.'-ction of :he applied magnetic field along te;e *-axis.

.- .

176

M EEl1 27 4

B(GAUSS)FIGUJRE 10a

The temoera:tjre of the susceptibi.it' neak shown in Fi.Sas a unc-ion ofthacv'~iec magnepic field along the c-axis.

12

i71t7

175:

~L4

1t74,/ 174L4~

174174'

1 174

F I G ~ p ~ l o bB ( G A U S S )

3 D p j ~ nag ec ' ie ld alon g ' , :be F igaxisa

~ ~

- -. -*~ *-xIC:ion

%*

13

One notes that there is a distinct change in the behavior of the maxima from the lowto a high field. This change takes place at 17 gauss if the field is applied along thec-axis while the crossover point is 7.5 gauss if the field is applied along the a-axis.The lines denote the least squares fit to the low and high temperature behavior re-spectively. Similar phenomena were found in NViC 2 and CoC 2 intercalated graphite.By measuring the in-phase and out-of-phase components of the susceptibility, onecan infer that there is a resistivity maximum at the maximum in susceptibility. Thein and out of phase (quad) susceptibilities of stage 6 are shown in Figure 11 whileFigure 12 shows the conductivity as deduced from the phase shift.

L= 2..ase and ouc af .ase, susc.Pc±bI_-7 as a !ur;c:40Q I C of :e=VeraC:'.r LM zero Ma3=6:4C

S--- '- ,fie-ld. Quad .democins :he ou:*~~~o 2h. _ *pse C~zc~en:

1 "

. ... . . . . .

T

T - a i: ,.- t4 C_ ,11 t'.. . . . 7 ,

.-.. ,_...:5 "- - -, -- .:onduc: . .v±T ' '

r 2"- .1 - / -- e:12: r _ \ &c zznduct-*7! in:at

.. ................... ... .. .. ......

14

It was also shown that the size of the susceptibility maximum can be correlated.within a stage 2 sample, with the number of vacancies in that sample as measuredby the M6ssbauer effect. This was shown for samples which have 7'o of iron sitesneighbors to vacancies. 9V% and 11T. The susceptibilities as well as the N'6ssbauerspectra are shown in Figures 13 and 14. This. along with

°r.1

. .I

rIG. 13 .S-ncaiairy -=w tempenmrs for .tdL'!cr~t napzt gpcr-FC.)~peunda. -he raepabiry %s piorted in aebitry =-sb a san.jc% --vr ±s

(or di. ?a~ve aount difact it MrnUUahA. saMoin : saotgie Urc. oie 3.'0I e'000% W

a , I, :

-I 3 11 3 1

AfM Sao" U 5pz 2. Te pan oa of tle -wo peaki vucs corM :.ic .- n lata neuar~mebaur tou a~cncsam mu dl~ed tp the suiwI net ZAp, ~C~rv is rneasigdrelave tbei.centre of nny of an Iranfi ,~o ~et

'* t? *- - - p -. .t -. -- -..

15

the power dependence of the susceptibility peak. corrected for the shape factor.at temperatures above the maximum, argues strongly that the maximum is anindication of a spin glass transition.

We have recently investigated stage 3 FeCI3 graphite and find that its charac-teristics are similar to those of stage 2. Also, in an attempt to see a temperaturehysteretic behavior of the 1.7 K transition we cooled the sample in a magnetic field.A different susceptibility should have been observed for a spin-glass but none wasfound.

Working on this grant during the grant period were:

G. 0. Zimmerman - P.I.

Dr. C. Nicolini - Research Associate

Dr. A. Ibrahim - Research Associate

K. Galuszeewski - Graduate Student

A. Kaplan - Undergraduate Student

A. Papaconstantino - Graduate Student

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Appendix I

Publication in Extended Abstracts

'84 M.R.S. Meeting, Boston Nov. 26-30

CRITICAL WON3IIT yOF ME X4MNETIC ANMALY OF STAME-6 FoCi 2 DMCAL AT

GRAKITE+

G.O. Zimmerman. C.NicoLini. D. Solenberger. D. Gata. B. golmesPhysics DepartmentBoston. MA 02215

We have discovered a susceptibility maximai in all stages of FeCi, inter-calated graphite which occurs at about 1.70(K.1,2 The size of the maxiam variesby a factor of 30, being smallest in stage 1 and greatest in stage 6. This phe-nomenon appears to be two dimensional in origin. The temperature of the staximudoes not vary from stage to stage. In stage 2. we have correlated the size ofthe maxim with the amber of iron vacancies3. The measurements shown here arefor stage-6 FeCi, intercalated graphite where the maximu is most pronounced.

400Hc 356-

;256 .92

L 266

Ha toois

Figure 1 P6 .9 17 .6 13

Inltercalated Graphite PT1 K)91.3 130 18Hm is the measuring field TKHa and Hc are externally applied fields Figure 2

Susceptibility as a function of temperature in ani apPliedmagnetic field (numbers denote field in Gauss)

1 0 Fig. 1 shows the geometry of our arrangement. The susceptibility was meas-ured by a standard A.C. 4 technique at 40Hz with the measuring field Han parallel

*to the graphite planes. The measuring field was always malier than 0.1 G.

* Fig. 2 shows the magnetic susceptibility as a function of temperature. Thehighest peak is zero magnetic field, while the consecutively lower peaks are infields of 0.96, 1.92, 2.88, 3.84. 5.75. 7.67, 11.50 and 15.34 G respectively

* along the a-direction (Fig. 1). One observes that in addition to attenuating* the maxim=, an applied field shifts the temperature of the maxim to a higher* temperature.

*Because of the high susceptibility at the maximus the external measuringfield which each individual magnetic spin sees is shielded by the neighboringspins and that shielding depends on the shape of the sample. Te measure text andwould like to measure V~int. where Xdenotes the magnetic susceptibil ity. )- mnt isthe response of the magnetic spin to the field it exeine whl 5et i hresponse to an external field. The relation betweenrit andt'zet is5

.. . . . . . . . .A- *. . . . .

If one &esumes that at the maximum. Xint is infinite, thenI 0

When this correction is applied to the susceptibility at zero applied magnetic

field one obtains the points in Fig. 3.12 ^12

>-,. 11

-J

- 4

-- a.C.)

4 4

3-

-. 5 .5 27 -6 -5 -4 -3 -21*( T-Tc )/Tc LH( ( T-Tc )/Tc)

Figure 3 Figure 4

Natural logarithm of the susceptibility at 0 field as a function of Logarithm of the susceptibility at 0 field as a function of thethe reduced tmnperature reduced temperatum showing the universal power law behavior

+ is shiape-corrected susceofrtlity .-- Tk is uncorrected susceptibility xxT To and y " 1.85 ± .1 for T < To. The slopes of thedrawn lines denote the values of y. Although similar functional behavior of the 0susceptibility has been observed in many other systems and is a consequence ofthe universality of the characteristics of second order phase transitions, thevalue of y is between 1 and 1.25 in three dimensional transitions, while it ispredicted to be 1.75 for a two dimensional Ising model. Our values appear to behigher than that. We are thus dealing with a now phenomenon.

-2 ... 2 • .I -

PAGE 3

1.5.5

- ~ 4.5

X ~31 2 2 3 2

H/Ho N/Ho

Figure 5 Figure 6

Temperature dependence Of the maximujm as a function of Logarithm of the maximum susceptibility as a function ofthe applied magnetic fil the applied magnetic field

+:Hc 4- a Hx=Ha xs~

Fig. 5 shows the magnetic field dependence of the taiiperature at the sus-ceptibility maximii + denotes the points for the field applied along a directionnormal to the planes while x denotes the field applied parallel to the planes.The temperature is the reduced temperature multiplied by 100 where To is the temperature of the maxim= at zero field. The field is the field in units of nowhere Ho is 17 G for the Ho direction and 7.5 G for the Ha direction, and denotesthe transition from low field to high field behavior. A field applied along Hais more than a factor of 2 moret effective than that applied along Be. The slope

of (T - Tc)/Tc at low field is a factor of 3 greater than that at high field.

Fig. 6 shows the size of maxim, plotted on a logarithms scale as a func-tion of the scaled field H/Ho with + along He and x along Ha as shown in Fig. 1.with the sane values of Ho as in Fig. 5 again and observes a low and a highfield behavior/

with~low -1.3 .$high -0.6 for Ha and~low 1 l4high -0.4 for Ho. Similar beha-vior was observed in other magnetic intercalation compO-A.711,s. 2

1) G.O. Zimmerman. B.W. Holmes and G. Dresselhaus, Extended Abstracts ofthe 15th Biennial Conference on Carbon. University of Pennsylvania p. 42.

2) M. Elahy, C. ?icolini, G. Dresselhaus and G.O. Zimmerman, Solid State* Communications 41, 289 (1982).

3) S.E. Millman and G.0. Zimmerman, Sournal of Physics .-=., 189 (1983).4) E. Maxwell, Review of Sci. Inst. aL 553 (1965).

*5) D. De Ilerk, JAnR jAk 2U Phzz..k. YMZ p. 7, Springer Verlag (1956).

Appendix II

Publication in Extended Abstracts

'84 M.R.S. Meeting

Boston Nov. 26-30

Electrical Conductivity of F*C1 3 Intercalated Graphite.

A. Ibrahim. G.O. Zinema. cad K. Galuszeaki

Physics Departmeut. Boston University

Boston, X& 02215

Introduct ion

The electrical conductivity of stago-6 FsC23 intercalated Hallits

was measured is the vaciaity of the 1.75K susceptibility sanmayL , bymeasuring the out of phase a.*. susceptibility. The measurements weremade at frequencies betwean 40 ad 1000 Hz and as a function of the mag-matie field. The electrieal conductivity is one of the properties mostdrastically chaged byttocalation both in acceptor and donor graphiteJtercalation composds CmJ ( an) cad spocial atteutioa has beem paid to

their ia-pla. coadetvityveo4 which can be a factor of 10' greater thu

that along the c-azia (perpendicular to the plaes). Oz measurements were

stimulated by the fact that we observed a axim in the ot-of-phase mag-netic susceptibility. ( . accmpanying ca is-p soe susceptibility, .maxzi whom the measuring field was parallel to the plIeas. No such mzi-

m was observed with the field log the c-asa which would have measured

the ia-plas conductivity. X is proportional to the conductivity, cndwith the measuring magatic field parallel to the plane we are maily sam-pling the changes in the conductivity aloug the c-asia. The mazim is t*caes at a tmperature typically doew by 2 a 10--l lowsr thum that of 'as shown is Pig. (1).

1.'r 0-"

i i

t.7 1 .

In-one and out-q(-ih&%* coagonents of the Suscep-tibility s a 5 (vction or teaosrbture in zero f1id

%

* .. * * .O . ." . . . . ~ . .

... .. . .. . .. . .. . .. . .. . .. . .. .

Expe rimental

The samples were prepared by a standard technique and analyzed forstagia# fidelity by x-ray analysis. Mossbaser analysis verified the FeCl,content and amber of vacancies. Preparation of the sampl* and moredetails about the experimental technique can be found in ref [41. Theconductivity measurements were made by a standard a bridge method operat-Lag at frequency ia the range of 40-1000 Zz. By using a phase sensitivedetector we were able to observe both the in-phase (related to the suscep-tibility) and the out-of-phase (proportional to the conductivity) sigaa.The orientation of the magnetic field at the sample was perpendicular tothe a-axis. therefore the magnetic maments in the basal-plane and the con-ductivitios c ia the s-c plans were measured with the variation comingfrom the conductivity along the c-axis.

Results and Discussion

The most striking result in this work is the temperature dependenceof the s-axis conductivity which exhibits an anomaly in the form of asharp peak at temperatures near 1.73K in zero magnetic field. This conm-ductivity behavior is indeed correlated with the same anomaly which wehave sqep in the ins-plane magnetic susceptibility ( 4 and reported in thisvolume 2ZJ* As shown in Vig.(2) the peek is very sensitive to any externalapplied magnetic field. it disappears in a field I = 56 and at frequency f

-39.7 IN. The field dependence of the conductivity may relate this ann-to the mechansisms which causes the peek in X. IAn eahanoment in a isexpected when the system has a magnetic anomasly.

A.s shown in Plg.M3. the conductivity at the peek monotonicallydecrease* as the applied magnetic field increases. This reflects the factthat there is a microscopic process which depends on the magnetic phase ofthe system and causes the peak in a. Fig. (4) shows the shift in tem-perature of the peak. for different values of the applied field. Thisshift indicates that the magnetic contribution is the dominant mechanismto the peak in a. F(14x,

0 550 ties

"a, 1 Z 9.4..0

0.1..

-T a

FIGURE 2 FIGURSE 3

The an-plane conduct'ivty as a function of temoor- The conductivity at the peaks as a function, -$hest n~ am n applied .Sqnetlc '1q10 appliedlmagnetic (aild and the treouency

d .. . .

riThere are other effects which might interfere with these measure-

ments. for example, skin effect or size effect. For materials of amatallic-Like conductivity, the skin effects can be eliminated if the fre-queasy is in the range of f 1 2 a 106P' (f in Zz. p in uLc.). Within thelimits of the resistivity of out sampvle, a typical value of f should beless than 20z: which is much higher then the maximis frequency which hasbeam used (f 1. 1 Us) . Thp size effect would be a major factor only ifthe manl free path is comparable with the sample size. Therefore, we donot expect any contribution to our data from those effects.

Te also have measured a at different frequencies and Fig.(S) showsthe frequency dependence of a at the peak. As shown by Fig.(4) andFig.(S). the anomaly in a persists at all frequencies but we have observeda variation in the magnitude of the peaks, also they are shifted to dif-forest temperatures. This frequency behavior was compared with reporteddata between the out-of-phase component and 1/fe for a similar bridge (61;they were very consistent as far as the peak size is concerned althoughthe temperture variation is real. Therefore, no frequency effects inter-fete with the data ad the observed peak size variation is just afrequency dependence in the bridge itself.

2.51 300I O f.39.7 Hz

aa I .. .x le "I'40 86 0. *f.397.8

IL 9D

e~eI ~. 0 s.0V1.73 1.74 1.75 1.76 16 17 1.8 1.9 2.0

1( K) TK)FIGURE 4 FIGURE 3

The te.perature of the peas as a function of thehoole-1 agntic ieldandthe requncyThe nm-plant conductivity as a function ot t.oora-5001.1 a~nticFied ed te f~qunc4 turt in a ero field and at iatforent freave*'cait

In conclusion, low temperature phase* transition of c-axis conductivi-ty has been seen in stage-6 GIC and is related to the same phenomena whichcauses the peak in the magnetic susceptibility. The above anomaly is rem-iniscent of spngas behavior where at a certain temperature themagnetic spins are frozen.

*Supported by the Air Force Office Of Scientific ftsea~rchk AFOSR Grant92-0286.

1. N. Ilahy, C. Micolini. G. Dresselhass and G.O. Zimmeroan. SolidState Cam. 41. 2S9 (1982).

2. G.O. Zimmrman. C. 4icolini. D. Solenborger. D. Gets. B. Rai"ea(presented in this Volume).

3. A.R. tbbelohole. Proc. Roy. So. Ah.7. 289 (1972.N4. C. Zelier. L.A. Pendrys. and F.L. Vogel. 3. of Nat. Sct. 14. 2241

(1979).S. S.C. Siaghkal. Physics ')95. 336 (1.960) .6. N.D. Daybll. Rev. Sc. Inst. 38. 1412 (1%7)T.

FILMED

2-85

DTlC