A comment upon the use of two criteria in the identification of intrinsic esr in high Tc oxides

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Submitted on 1 Jan 1990

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A comment upon the use of two criteria in the

identification of intrinsic esr in high Tc oxides

A. Deville, B. Gaillard

To cite this version:

2739

LE

JOURNAL DE

_PHYSIQUE

Short Communication

A

comment

_{upon the}

use

of

two

criteria in the identification of

intrinsic ESR

in

_high

_{Tc oxides}

A. Deville and B.

Gaillard

Laboratoire

_{d’Electronique}

des Milieux

_{Condenses(*),}

Université de

_Provence,

Centre

Saint-Jérôme,

13397 Marseille Cedex

13,

France

(Received

5 October

1990,

accepted

9 October

₁₉₉₀₎

Résumé. 2014 Un

_signal

RPE observé dans un

_composé

au bismuth a été récemment attribué à la

_phase

SC,

en

_s’appuyant

sur le _{fait que} deux critères

_(valeur

et

_comportement

_thermique

de

_{l’intensité)}

sont

vérifiés. Nous attirons l’attention sur la faiblesse de cette

_{argumentation,}

et

_rappelons

un

_exemple

canonique.

Abstract. 2014 An

ESR

_signal

detected in a Bi

_compound

has

_recently

been attributed to the SC

_phase,

arguing

that two criteria

_(value

and thermal behaviour of the

_intensity)

were met. We draw

attention .

to the weakness of this

_argument,

_recalling

a canonical

_example.

1

_Phys.

France 51

_{( 1990)}

2739-2741 15 DÉCEMBRE

1990,

1

Classification

Physics

Abstracts 74.70 - 76.30

The

_magnetic

_couplings

could

_{play a}

decisive role in the mechanism of

_{superconductivity}

in the

high

Tc

oxides

_[1,2].

In this context, the interest of ESR is obvious.

_{Unfortunately,}

the resonance

of the

Cu2+

ion of the SC

_phase

has not been detected

_yet.

_{At the moment,} the

_prevalent

_feeling

in the

_high

~’~

community

seems to be that ESR is not able to

_{bring magnetic}

informations in these

materials,

while

_people

_using

ESR still

_try

and

_get

informations in several

_{ways :}

_replacement

of

Cu2+

_by

a

_non-magnetic

_ion,

_replacement

of

Y~

_by

a

_magnetic

ion

_(e.g.

_{Gd3+ )}

_and,

_perhaps

more

_ambitious,

examination of new

_high

_Tc

materials with the

_hope

of

_detecting

intrinsic ESR.

At the recent LT19

_Conference,

it was thus claimed

[3]

_that,

in Bi

_{(Pb)-Sr-Ca-Cu-O,}

a

_strong

ESR

signal

was

_observed,

and that it seemed certain that its

_origin

was not

_impurities.

It was

_argued

that in order not to

_originate

from

_impurities,

the ESR

_signal

had to meet the two

_following

criteria :

1)

the

_signal

should be related to the onset of the

_{superconductivity (i.e.}

_disappear

below

_Tc),

2740

2)

the number of

_{spins responsible}

for ESR should be

_higher

than

10~/g.

It was

_explained

that

these criteria were both verified in that case

_(the

number of

_spins

was of the order of

_10~°/g,

the

_{signal disappeared}

at

_T~),

and concluded that the

_possibility

of

_impurities

had to be

_rejected.

Although

these criteria seem common sense, we wish to stress that

_they

_represent

in fact

_necessary

but not sufficient

conditions.

_Thus,

_contrary

to what seems to be often

_thought,

the

_{disappearance}

of

the

ESR

_signal

below

_Tc

_just

means that the

_magnetic

centres

_(impurities

or

_not)

are

distributed

in the volume of the

_sample,

and that the rf field

is

_expelled

from the

_sample

below

_Te.

In order to be more

_convincing,

we

_briefly

recall our results with

YBa2Cu30~

single crystals

[4,5],

referring

to the

_original

_papers

for more details :

- the

concentration

was 1.3 x

10 20 spins/g,

- the ESR

_{intensity dropped abruptly}

below

_Tc

_(Fig.

_1,

taken from

_[4,5]),

- the

ESR

was moreover

_anisotropic.

Fig.

1. - Thermal variation of the normalized ESR

intensity

I

_(area

under the

_{absorption curve)}

for a

YBa2Cu307

single crystal

(solid

line: Curie

_{law). (from}

_[4]

and

_[5]

_).

In

_[4]

and

_[5]

we

_gave

_experimental

_proofs

that the

_signal

nethertheless came from

_impurities

(the

green

phase

Y2BaCu05) .

As a

_conclusion,

_although

the use of ESR as a tool for

_getting

information

_upon

the

_magnetic

2741

References

[1]

ANDERSON P.

W.,

Science 235

₍₁₉₈₇₎

1196.

[2]

SIGMUND

E.,

STEVENS K. W.

_{H., J.}

_Phys.

C. 20

₍₁₉₈₇₎

6025.

[3]

HAYASHI

Y.,

YOSIDA

_T.,

KONTANI

_N.,

FuKui

_M.,

SAKO

_S.,

FUJITA

_T.,

SASAKURA

_H.,

MINAMIGAWA

_S.,

NAKAHIGASHI

_K.,

_Physica

B 165 & 166

₍₁₉₉₀₎

_1317,

_Proceedings

of the LT19

_Conference,

_16/22

August 1990,

Brighton (G.B.).

[4]

DEVILLE

A.,

GAILLARD

_B.,

NOEL

_H.,

POTEL

_M.,

GOUGEON

_P,

LEVET J.

C.,

Physica

C 153 & 155

₍₁₉₈₈₎

669,

Proceedings

of the HTM2SC Conference 28/2-4/3

1988, Interlaken,

Switzerland.

[5]

DEVILLE

A.,

GAILLARD

B.,

NOEL

H.,

POTEL

_M.,

GOUGEON

P.,

LEVET J.

C., J.

Phys.

France 50

₍₁₉₈₉₎

2357.