Low field magnetization measurements on single crystals of superconducting YBa2Cu3O7-δ

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Low field magnetization measurements on single crystals of superconducting YBa2Cu3O7-δ

J. Hammann, M. Ocio, A. Bertinotti, D. Luzet, E. Vincent, A. Revcolevschi, J. Jegoudez

To cite this version:

J. Hammann, M. Ocio, A. Bertinotti, D. Luzet, E. Vincent, et al.. Low field magnetization mea- surements on single crystals of superconducting YBa2Cu3O7-δ. Journal de Physique, 1987, 48 (10), pp.1593-1597. �10.1051/jphys:0198700480100159300�. �jpa-00210593�

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Low field magnetization measurements on single crystals ^of superconducting YBa2Cu3O7-03B4 J. Hammann, ^M. Ocio, ^A. Bertinotti, ^D. Luzet, ^E. Vincent, ^A. Revcolevschi+ and J. Jegoudez+

Service de Physique ^{du Solide et} de Résonance Magnétique, CEN-Saclay, ⁹¹¹⁹¹ Gif-sur-Yvette Cedex,

France

+Laboratoire de Chimie des Solides, Université Paris-Sud, Orsay, ^France

(Reçu ^le 9 juillet 1987, accepti ^le Q0 juillet 1987)

Résumé.-Des mesures d’aimantation _par magnétométrie SQUID à champ ^{faible ont} été effectuées sur des monocris- taux d’YBa2Cu3O7-03B4 supraconducteurs ^en dessous de Tc ⁼ 95K. Elles révèlent un comportement anisotrope ^de

l’aimantation. L’effet Meissner (toujours inférieur à 10% ) ^{est 2 à 3 fois} plus important suivant la direction c que dans le plan (a,b). Une transition unique à ^{95K est observée} lorsque ^le champ ^est parallèle à ^c. Perpendiculairement à c,

une singularité probablement ^{liée au} passage d’une seconde ligne de transition apparait ^sur la courbe d’aimantation à 84K _pour 3 G. Dans les trois cristaux étudiés, ^{on a détecté une} trés faible polarisation ferromagnétique dirigée approximativement ^{suivant c.}

Abstract.-Low field (H ~ 3G) magnetization measurements have been performed ^{on small} single crystals ^of super-

conducting YBa2Cu3O7-03B4 (Tc ~ 95K) using ^a SQUID magnetometer. They ^revealed anisotropic properties ^{in the} temperature dependence ^{of the} magnetization. The Meissner effect (always smaller than 10 % ) ^{is 2 to 3 times} larger along ^{the c} direction than along ^{one of the} perpendicular directions. A sharp unique transition at 95K is observed with the field parallel ^{to c. In the} perpendicular ^{direction a} second transition line seems to be crossed at T ⁼ 84K with

an applied field of 3G. In all three crystals studied, ^a very small ferromagnetic polarization, pointing approximately along ^{the c} direction, is observed.

J. Physique ⁴⁸ (1987) ^1593-1597 OCTOBRE 1987,

Classification ^.

Physics ^Abstracts

74.70 - 74.30C

LE JOURNAL DE PHYSIQUE

Very ^few experiments ^{have been} published ^to

date on single crystals ^{of the} extensively ^studied high Tc superconductors. ^{In order to check the mecha-}

nisms leading ^{to the} high temperature transitions,

such experiments ^{are indeed} very important, ^{but due}

to the small sizes of the available crystals, ^{the mea-}

surements are quite ^difficult.

Large anisotropies ^have already ^been pointed ^out respectively ^{in the coherence} lengths ^for TmBa2Cu3 07-6 [1] ^{and in the} higher ^{critical field} Hc2 ^for YBa2 Cu30x [2]. ^{These systems are} characterized by ^{a cris-} tallographic arrangement favouring ^{a two} dimensional behaviour. They display ^an orthorhombic structure

with nearly equal ^{values of} the lattice parameters ^a and b, ^{and a much} larger ^{value for c} [3 - 5]. ^The

observed anisotropies ^{appear between} directions _par- allel and perpendicular ^{to the} cristallographic ^{c direc-}

tion. The published ^{results stem from} measurements in large applied magnetic ^{fields. We} present ^{in this}

paper ^a study ^{of the low field} magnetic properties ^of single crystals ^of YBa2Cu307-6 using SQUID mag-

netometry.

The measurements were done in fields always

smaller than 3G, applied ^either parallel ^or perpendic-

ular to the c direction. Two experimental procedures

were used. First the sample ^{was cooled} down into its

superconducting ^{state in zero} field, ^{the field was then}

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198700480100159300

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applied ^{and the} magnetization ^{recorded as a function}

of increasing temperatures (ZFC curves). ^{Second, the}

field was applied ^{at a} temperature larger ^{than the}

transition temperature Tc ^and again ^the magnetiza-

tionwas measured at constant field as a function of temperature (FC curves). ^These procedures yield ^re- spectively ^the shielding ^{and the Meissner effects.}

Three different single crystals ^have been inves-

tigated. They ^were extracted from sintered single phase preparations ^of YBa2Cu307-6 characterized

by a Tc ^{value of 95K.} Two of the crystals (# ^{1 and}

# 3) ^{came from the same} preparation. ^{All of them}

were checked by X-ray diffraction. They present ^the orthorhombic structure expected ^{for the} supercon-

ducting phase [3] ^{with lattice} parameters ^{of a =} 3.833 A, ^{b =} 3.88Q A,c =11.67oA. The diffraction pat-

terns show that they ^{consist of several} crystals ^twin-

ned along ^the (a, b) ^{plane with a} well defined common c axis. Crystals # ¹ and # ^{3 are} platelets ^{with char-}

acteristic sizes of respectively, ^{0.2 x 0.2 x 0.1 mm and}

0.3 x 0.35 x 0.13 mm. Crystal # ^{2 has the} shape ^of

a truncated pyramid ^{of size 0.18 x 0.18 x 0.16. This} nearly ^cubic shaped ^{crystal is in fact not strictly sin-}

gle, ^a principal twinned crystal being associated with

some microcrystals showing ^a distribution of c direc- tions within an angle of 6°. This presents ^{no draw-} back for the present experiments ^{since the} crystals

have only ^been visually oriented with an accuracy of that order.

Figure ^{1 and} Figure ^{2 show the} temperature ^de- pendences of the ZFC and FC magnetizations ⁱⁿ the

case of the largest crystal (# 3) ^{with an} applied ^field

of 2.85G respectively parallel ^and perpendicular ^to

the c axis. The reported ^{values are} corrected for the contribution of the sample holder which has been measured in a separate ^{run. The} magnetic ^moment

of the sample ^is determined at each temperature by extracting ^the sample ^{from the} pick-up ^{coils and mea-} suring ^the flux variation. The change ^of position ^is

small enough ^so that the field applied ^{to the sam-} ple ^{does not} change by ^{more than 0.3 % . The scale}

in the figures corresponds ^to arbitrary units. The

experiment ^has only,been roughly calibrated by ^mea- suring ^the shielding ^{effect of a lead} droplet (diameter

~ 0.12 mm) ^{below its} superconducting transition and

assuming ^{that it} corresponds ^to the maximum shield-

ing x = - 4 ^(emu).

Along ^{the c direction} (Fig.1), ^a unique sharp

transition is seen to occur at 95K. The shielding ^ef-

fect is much larger than the Meissner effect. Taking

into account the demagnetizing factor, ^the shielding

amounts to about 44 % whereas the Meissner effect is only ^3.3 % . ^In crystal #1 ^the shielding ^{rate is the}

same but the Meissner effect is more than twice as

large, being equal ^{to 7.6% . This} last value is about

Fig.l.- Zero field cooled (open circles) and field cooled (crosses) magnetization ^versus temperature ^for crystal #3 ^{in an} applied

field of 2.85 G parallel ^{to c.}

Fig.2.- Zero field cooled (open circles) ^and field cooled (crosses) magnetization ^versus temperature ^for crystal #3 ^{in an} applied

field of 2.85 G perpendicular ^{to c.}

the _average value measured on the sintered material from the same preparations [6].

Perpendicular ^{to the c direction} (Fig.2), ^the

sharp ^decrease appearing ^{at 95K is followed at 84K} by ^another singularity. ^{The occurence and the lo-}

cation of the singularity ^{has been checked in a sec-}

ond run and the behaviour was quite reproducible. ^It

seems that for the applied ^{field of 2.85 G two transi-}

tion lines are crossed as the temperature varies. The overall shielding rate amounts in this case to 37%,

the demagnetizing ^factor being taken into account.

This value is approximately ^{the same as} along ^{c. The}

Meissner effect is here only ^{1.7 % which is almost half}

the value measured in the parallel ^case.

The results corresponding ^to the different sam-

ples ^{studied are} gathered ⁱⁿ table I. The anisotropy ^of

the Meissner effect could only be checked in crystals

Table IJ Main results observed on the difi’erent crystals, parallel ^and perpendicular ^{to the} cristallographic ^c direction,

in an applied field of ^{!.85 G.} (crystals # ^{1 and # 3 are from the same} preparation).

#1 ^and #3. ^In crystal #2 the Meissner effect was too small to be measured. The existence of a singular point ^{at 84 K in the direction} perpendicular ^{to c is} apparent in all three crystals.

Figure ³ shows the detailed FC magnetization

curves for crystals ^{3 with the field of 2.85 G} applied parallel ^and perpendicular ^{to c. The} singularity ^at

84 K for the ^case of the field perpendicular ^{to c is}

also well marked on the Meissner effect.

Fig.3.- Meissner effect of crystal#3 ^{in an} applied ^{field of 2.85}

G applied parallel ^{to c} (open circles) ^and perpendicular ^{to c} (crosses).

In figure 3, ^it appears very clearly that the dia-

magnetic susceptibility showing up in the _supercon-

ducting ^{state is} superimposed ^{on a} positive magneti-

zation which is temperature independent ^{above 95 K}

at least _{up to} 120 K. A _very similar behaviour has been reported ⁱⁿ Lal.8Bao.2CU04 [7] ^and assigned ^to

a paramagnetic susceptibility ^of copper ions in a non

superconducting phase. ^{In our case} however, ^{a com-} plementary experiment ^{has been} performed, ^{in which}

the field of 2.85 G ^was reversed. In this procedure,

the variation of magnetization ^{below 95 K was re-}

versed, but the base line remained positive though ^it

was smaller than in the direct experiment. ^{The result}

means that the positive magnetization corresponds ^to

a ferromagnetic polarization ^which slightly ^decreases

as the field is reversed but cannot be reversed by ^the

small fields applied ⁱⁿ this ^work.

In crystal #3, ^{the value of the} positive magneti-

zation is almost twice as large with the field parallel

to c than with the field perpendicular ^{to c. A mea-}

surement in zero’field showed that the ferromagnetic polarization ^{was oriented} along ^a direction about 30°

from the c axis. The same type ^of measurement made

on crystal # ^{1 led to an} equivalent result. But in the

case of crystal # ^{2 the} polarization ^{was found to be} along ^c. These differences _may be due to the different values of the demagnetizing factors. In crystals ¹ and # ^{3 the} demagnetizing ^factor along ^c (perpen-

dicular to the platelets) ^{is large and the c} direction is thus not a favourable direction for the polarization.

In crystal # ^{2 the} demagnetizing factor is about the

same along ^all cristallographic directions. The results in zero field on crystal # ^{2 are} plotted ⁱⁿ figure ^{4. It}

appears that the measured value along ^{c remains con-}

stant up to ^room temperature.

The absolute value of the detected polarization

is _very small. The total magnetic ^{moment of each} sample ^is given in table I. For crystal # ^{1 which} yields

the largest value, ^the polarization ^{does not exceed} 0-00114B per copper ion. It is worthy ^{to note that the}

resultant magnetic ^{moment decreases as the volume}

of the sample ^increases.

One possible explanation ^for the observed be- haviour is that ^a spontaneous magnetic ^{moment de-} velops ^at high temperatures (T > 300K). ^{But due to}

the demagnetizing ^{field the} compact sintered material is divided in domains with alternate magnetization, canceling the overall moment. The small crystals ^ex-

tracted from the bulk might be formed of a finite number of such quenched domains. This would lead to an uncompensation ^{of the} magnetic ^{moment which}

would be the largest in the smaller sample ^{and could}

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Fig.4.- Temperature dependence (up ^{to room} temperature) ^of

the ferromagnetic polarization ^of crystal #2, ^{in zero} field, ^mea-

sured along ^c (open circles) ^and perpendicular ^{to c} (crosses).

explain ^the very low value of the measured polariza-

tion. The suggested interpretation ^can (and should)

of course be easily ^{checked in a classical} magnetiza-

tion experiment.

The origin ^{of the} spontaneous ^{moment remains} unclear. No magnetic ordering ^has been found in the superconducting phase. ^{Indeed results of NMR}

measurements did not show _any such ordering [8]

in agreement ^with preliminary ^{Mossbauer measure-}

ments on iron doped (0.8%) samples ^{which did not} give any evidence for a magnetic polarization ^{of the}

Mossbauer probe [9]. ^{It is difficult to} assign ^the spon- taneous moment observed in our experiment ^{to a} par- asitic phase ^{outside the} crystals ^{since the moment is} strongly pinned ^{to the} cristallographic directions of the single crystals ^{and no extra} phase could be de-

tected by X-ray diffraction. It is however not impos-

sible that structural defects in the crystals yield ^lo-

calised moments on the _copper which might ^induce

the observed effect. Further experiments ^{are cur-} rently performed ^{in order to clear} up the situation.

To conclude on the anisotropy ^{of the} supercon-

ducting properties, ^{the main result from the} compar- ative measurements along ^and perpendicular ^{to the c}

axis concerns the difference in the amounts of Meiss-

ner effect detected and the existence, perpendicular

to c, of a second well defined singular temperature.

Whereas parallel ^{to c the field} rejection ^is very sharp

at the transition temperature, perpendicular ^{to c the}

field rejection ^{occurs in two distinct} steps. ^{The be-} haviour is best seen on the shielding ^effect perpendic-

ular to c. As the temperature ^{increases a first sudden} field penetration ^{occurs around 84 K} (H=2.85 G).

The penetration ^is then about 50% of the total effect.

A final sharp penetration ^occurs slightly ^{below 95 K.}

A behaviour of that kind has already ^{been observed in}

sintered material where all cristallographic ^directions

are represented (see for instance refs. [10, 11).It ^was

usually assigned ^to imperfections ^{of the} compound.

It _appears however from our experiments that it is

an intrinsic behaviour which must be related to the two dimensional character of the material. The extra

singularity ^is possibly ^{much more sensitive to stoi-}

chiometric imperfections ^{and to the} applied ^{field than}

the first transition temperature. Measurements with different values of the field are of course needed in order to determine the shape ^{of the} transition lines crossed.

We wish to thank G. Sarma and J.P. Carton for many fruitful discussions and R. G6rard-Deneuville for his technical skill.

References

[1] NOEL, H., GOUGEON, P., PADIOU, J., LEVET, J.C., POTEL, P., LABORDE, O., MONCEAU, P., Preprint (Mai 1987).

[2] ^YASUHIRO Iye, ^TSUYOSHI Tamegai, ^HIROYUKI Takeya, ^HUMIHIKO Takei, ^{Subm. to} Jpn. Appl.

Phys. ^Lett. (1987).

[3] CAVA, R.J., BATTLOG, B., ^VAN DOVER, R.B., MURPHY, D.W., SUNSHINE, S., SIEGRIST, T., REMECKA, J.P., RIETMAN, E.A., ZAHURAK, S., ESPINOSA, G.P., Phys.Rev.Lett. ^{58 1676} (1987).

[4] DAVID, W.I.F., HARRISON, W.T.A., GUNN, J.M.F., MOZE, O., SOPER, A.K., DAY, P., ^JOR-

GENSEN, J.D., HINKS, D.G., BENO, M.A., ^SO- DERHOLM, L., CAPONE, D.W., SCHULLER, I.K., SEGRE, C.U., ZHANG, K., GRACE, J.D., Nature, 327,310, ^{Mai 1987.}

[5] CAPPONI, J.J., CHAILLOUT, C., HEWAT, A.W., LEJAY, P., MAREZIO, M., NGUYEN, N., ^RA- VEAU, B., SOUBEYROUX, J.L., THOLENCE, J.L., TOURNIER, R., Europhys.Lett. ^{3 1301} (1987).

[6] MONOD, P., RIBAULT, M., D’YVOIRE, F., ^JE- GOUDEZ, J., COLLIN, G., REVCOLEVSCHI, A.,

J. Phys. ^{to be} published (August 1987).

[7] MOODENBAUGH, A.R., SUENAGA, M., ASANO, T., SHELTON, R.N., KU, H.C., MCCALLUM, R.W., KLAVINS, P., Phys. ^{Rev. Lett. 58 1885} (1987).

[8] LUTGEMEIER, H., PIEPER, M.W., ^{Submitted to}

Solid State Comm.

[9] HODGES, J., JEHANNO, G., IMBERT, P., ^Private

Communication.

[10] GALLAGHER, W.J., SANDSTROM, R.L., DINGER,

T.R., SHAW, T.M., CHANCE, D.A., ^{Submitted to}

Solid State Commun. (1987).

[11] GRANT, P.M., BEYERS, R.B., ENGLER, E.M.,

LIM, G., PARKIN, S.S.P., RAMIREZ, M.L., LEE, V.Y., NAZZAL, A., VAZQUEZ, J.E., SAVOY, R.J., Preprint (March 1987).