NMR MEASUREMENTS ON LIQUID 3He CONFINED IN ALUMINA AND PLATINUM POWDERS AND GRAFOIL

HAL Id: jpa-00217533

https://hal.archives-ouvertes.fr/jpa-00217533

Submitted on 1 Jan 1978

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

NMR MEASUREMENTS ON LIQUID 3He

CONFINED IN ALUMINA AND PLATINUM

POWDERS AND GRAFOIL

H. Godfrin, G. Frossati, D. Thoulouze, M. Chapellier, W. Clark

To cite this version:

JOURNAL DE PHYSIQUE Colloque C6, supplement au n° 8, Tome 39, aout 1978, page C6-287

NMR MEASUREMENTS ON L I Q U I D 3H e CONFINED IN ALUMINA AND PLATINUM POWDERS AND GRAFOIL

XX ++

H. Godfnn, G. Frossati, D. Thoulouze, M. Chapellier and W.G. Clark

C.N.R.S., BP 166X 38042 Grenoble - France

**DPG/SRM Orme dee Mevisiers, 91190 Saolay - Fvanee

++

Physios Dept., UCLA California 90024, U.S.A.

Résumé.- Nous présentons des mesures de la susceptibilité et du temps de relaxation Ti de l'3He liquide confiné dans du grafoil, dans de la poudre d'alumine de 400 A et dans de

la poudre de platine de 8u. Nous observons une susceptibilité de Curie-Weiss correspon-dant à une monocouche d'^He adsorbé qui serait responsable du fort taux de relaxation. Ces effets sont supprimés par quelques couches d,l*He.

Abstract.- We report susceptibility and Ti measurements of liquid 3He confined in grafoil, 400 A alumina powder, and 8u platinum powder. We observe a Curie-Weiss susceptibility corresponding to a monolayer of adsorbed 3He that would be responsible for the high

re-laxation rate. These effects are suppressed by a few ^He layers.

Ahonen et al. /I/ showed recently that the susceptibility of liquid ^He confined between mylar foils or in carbon powders, at temperatures in the mK range, can be described by the expression X = TjCa + B> where B is the Fermi liquid (tempe-reature independent) susceptibility of the "bulk"

A

3He, and -=—5- the Curie-Weiss susceptibility of

the adsorbed 3He layers. The parameter 0 was found

to be positive on mylar (vO.5 IDRI and on carbon particles (MD.8 m K ) .

We report here CW NMR susceptibility mea-surements on 3He confined in grafoil, 400 A

alumi-na powder and 8u platinum powder, and pulsed NMR measurements of Tj performed on the same samples. The 3 NMR coils were placed in an araldite cell, located in the mixing chamber of a dilution refri-gerator HI. Thermal contact was achieved by means of copper plates, through the 3He cell, with sin-tered silver powder on both sides.

The surface of the grafoil sample was 1.1 m % and the surface of alumina 4.1 m measured by the B.E.T. technique. The sintered silver in the cell and filling line had a surface of 2.7 m2.

The CW NMR measurements were performed at 757 and 923.2 kHz (233 and 285 Gauss) using a low level Q-meter. The susceptibility is obtai-ned by integration of the absorption signal, and given in arbitrary units. We use a commercial IT bridge for the Tj measurements, at 250 kHz (77 Gauss).

The temperature T was given by the Curie susceptibility of the platinum powder measured either by CW or pulsed NMR. The Curie constant of

the platinum thermometer was determined by cali-bration against the CMN susceptibility, measured with the mutual inductance technique above 10 mK.

The cell was flushed with 3He, and filled at IK with "pure" 3He (<100 ppm 4H e ) . All the

measurements were performed at zero pressure. In the last part of the experiment we added ^0.3 % of ^He. This amount is equivalent to 2.7 layers, with M O1 9 atoms/m2 x layer /3/.

SUSCEPTIBILITY MEASUREMENTS : In grafoil and A

alumina, the Curie-Weiss term =—r becomes larger than the bulk susceptibility B for temperatures below 10 mK (Figure 1, curve 1). In the platinum powder, even at 2.6 mK, the Curie-Weiss contribu-tion was not relevant.

The addition of 4He reduces drastically the Curie-Weiss term (Figure 1, curves 3 and 4 ) ; it vanishes practically in grafoil (98 % reduction of A ) , but less in alumina (80 % reduction).

In the last case, this figure was only 70 % in the few hours after the ^He was added, and the "stable" value of 80 % was reached after one day. A similar effect was observed in grafoil.

Within the accuracy of the measurements (M % below 20 mK and ^3 % at higher temperatures) in the temperature range 2.6 mK - 100 mK, we

A

observe no deviation from the fit x = ifZK + B for

pure 3He and x = f- + B <f~« B) f°r 3He + ^He.

In grafoil ~ = 3.0 mK, 0 = (0.58 ± 0.14)mK A

-and in alumina ^ = 9.2 mK, 0 = (0.030 ± 0.10)mK, o

for both frequencies.

20

If we calculate the number of adsorbed

3 ~ e

layers, following the procedure of reference

/l/, we find 0.9 layers on grafoil and

on alumi-

na.

Fig.

The susceptibiligy of liquid 3 ~ e

at zero

pressure confined in

400

A

alumina powder, vs.

temperature T, at 923.2 kHz.

A

Curve

fitted by X

G

Curve 2 : 3 ~ e

+

4 ~ e

results, after a few hours

Curve 3 : 3 ~ e

+

4 ~ e

results, after one day, fitted

T 1

MEASUREMENTS : The results are summarized in

Figure 2. In all the samples, T1 increases with T

in all the temperature range (3

to

in

pure 3 ~ e .

When 4 ~ e

is added, T1 increases by one

to two orders of magnitude at low temperatures and

shows a maximum at 20

The same bahaviour of

T1 in pure 3 ~ e

has been observed in a cell filled

with copper wires /4/ and in platinum powders

The relaxation of the magnetization, after a 90"

pulse, was not exponential; the T1 values given

here are the short time constants measured just

after the pulse; we supposed that the slowly rela-

xing part of the magnetization wias due to 3 ~ e

far

from the powder

.

Comparing the thermal behaviour of T1

in platinum with the one in grafoil and alumina,

one can deduce that the confined liquid and the

adeorbed layers in each substrate relax with a

single T1, in agreement with known values of the

spin diffusion coefficient. The relaxation takes

place at the level of the adsorbed 3 ~ e

layers,

probably on magnetic impurities at the surface of

the substrates.

Fig. 2 : The spin lattice relaxation time T1 vs.

temperature, for pure 3 ~ e

in :

platinum;

2) alumina;

3) grafoil and 3 ~ e

4 ~ e

in

4)

plati-

num;

alumina;

grafoil.

Dotted line minimum measurable T1.

CONCLUSION.- We measure on different substrates a

magnetic susceptibility corresponding to a mono-

layer of adsorbed 3 ~ e

with ferro-magnetic interac-

tions, responsible for the high relaxation rates.

Adding 4 ~ e ,

the Curie-Weiss term vanishes and Tl

increases; this is coherent with the picture

of a replacement of the 3 ~ e

adsorbed layers by 4He.

However, it is difficult to understand that

2 or 3 layers of 4 ~ e

are necessary to eliminate

the Curie-Weiss contribution. There ltesults also

provide an experimental support to theoretical

predictions /6/ that relate the magnetic suscepti-

lity of 3 ~ e

and substrates to the relaxation time

T1 and the "magnetic" Kapitza resistance, allowing

R e f e r e n c e s

/ l / Ahonen, A.I., Kodama, T., K r u s i u s , M., Paalanen, M.A., Richardson, R.C., Schoepe, W., Takano, Y . , J . Phys. C

2

(1976) 1665.Ahonen, A.I., Kokko, J . , Lounasmaa, O.V.,

Paalanen, M.A., Richardson, R.C., Schoepe, W., Takano, Y . , i n "Quantum F l u i d s and S o l i d s " E d i t e d by S.B. T r i c k e y , E.D. Adams and J . W . D u f t y , (Plenum P r e s s , New-York) 1977.

/ 2 / F r o s s a t i , G., G o d f r i n , H., H Q b r a l , B., Schumacher, G . , Thou- l o u z e , D., Proc. of t h e HakonL I n t e r n a t i o n a l Symposium o n ULT P h y s i c s

-

131 Daunt, J . G . e t a l . , "Monolayer and Submonolayer helium f i l m s " . E d i t e d by J.C. Daunt and E. L e r n e r , (Plenum P r e s s , New York)

1973.

/ 4 / R a m , H., P e d r o n i , P . , Thomson, J.R., Meyer, H., J . Low Temp. Phys.

2

/ 5 / Varoquaux, E . , P r i v a t e c o r m n i c a t i o n .

/ 6 / BQal-Monod, M.T., M i l l s , D.L., J . Low Temp. Phys.

30

/ 7 / BLal-Monod, M.T., M i l l s , D.L., t h i s c o n f e r e n c e . / 8 / HGbral, B., t h e s i s , Grenoble (1978).

191 Hbbral, B., F r o s s a t i , G., Godfrin, H., Schumacher, G., Thoulouze

D . , t h i s c o n f e r e n c e .

/10/ BLal

-

2