A dilution refrigerator for nmr measurements of magnetic compounds

JF 17

Physica 107B (1981) 617-618 North.Holland PublishingCompany

A D I L U T I O N R E F R I G E R A T O R FOR NMR M E A S U R E M E N T S

OF MAGNETIC COMPOUNDS

Muneaki Fujii and Akira Hirai D e p a r t m e n t of Physics,

Faculty of Science,

Kyoto University,

Kyoto 606, Japan

We have built a simple dilution measurements

of magnetic

r e f r i g e r a t o r which is suitable for nmr

compounds.

59Co spin echo signals in Co(HCO0) 2

2H20 were observed below 200 mK. I) D e s c r i p t i o n

of the apparatus

The e x p e r i m e n t a l

apparatus

cally drawn in fig.1. ber(B)

is schemati-

The mixing cham-

and two sample cells(C,D)

made of STYOAST

are all

1266 to prevent an eddy

current heating and a reduction factor of the r.f.

coil(K).

in the Q

The thermo-

meters and a sample are immersed

in the

superfluid phase of the 3He-4He mixture. The d e m o u n t a b l e

seals(E)

with soap and

glycerine[l] . are used to connect the sample

cells to the mixing

chamber.

8

With this seal it is easy to exchange the samples.

Variable

capacitor(J)

can

be a d j u s t e d from the top flange with a Cu-Ni

G E

connecting rod(I).

(A) is a continuous type heat e x c h a n g e r that consists

of spiral brass inner tube

and Im long Cu-Ni outer tube. [2] The carbon resistors

(MATSUSHITA

), used as thermometers,

against the s u s c e p t i b i l i t y our primary temperature

[4 •

For we

thermometric

supplied from N.B.S.

Our e x p e r i m e n t a l

as follows;

of CMN.

standard,

used the s u p e r c o n d u c t i v e fixed point device

I/4watt

were calibrated

conditions were

The temperature

range of

the sample was from 1.6 K down to 40 mK. The nmr f r e q u e n c y range was from 10 MHz up to 300 MHz.

The applied m a g n e t i c

field range was from 0 T to 0.1 T.

A; heat exchanger. B: mixing chamber. C,D; sample cells. E; d e m o u n t a b l e seal. F.G.H; thermometers. I; c o n n e c t i n g rod. J; v a r i a b l e capacitor. K; r.f. coil. L: paper mesh. M; sample. Fig.

I.

Schematic

0378-4363/81/0000-0000/$02.50

© Noah-Holland PublishingCompany

drawing of the apparatus.

617

618

2) Pulsed nmr measurement

of 59Co in

Co(HCOO) 2 2H20. As an example, we report a 59Co nmr experiment

in Co(HCO0) 2 2H20.

Co(HCO0) 2 2H20 has two independent

sites

, A and B, in the unit cell [4] and shows a sandwich

structure

from the magnetic

point of view [5.6]. site reveal

Magnetic

. below TN(=

ed a n t i f e r r o m a g n e t i c two dimensional allel

this sample ated with

where

B-site

A-site

The heat

maximum that

OOoo 0

,

,

,

I

. . . .

ions show a of

associ-

Fig.

J

,

,

,*;

230

I

240

Frequency(NHz)

even at 2.

Spin echo spectrum

of 59Co in Co(HCO0) 2

2H20 at 40 mE in zero applied

field.

at T N and

at 0,5 K.

59Co nmr signal

can 0

be observed

,

220

ions

capacity

the phase transition

It is expected

%

in a plane par-

while

[7] shows an anomaly

a Schottky-type

OO0°

ions at A-

(so called)"paramagnetic"

the temperature

0e

•

5.1 K), a cant-

character

long range order.

•

O000 o

order of a quasi

to the bc-plane,

remain

I

.;% qlo

far below 0.5 K. where

6 0

B-site

0

ions are also expected range order.

Indeed,

to be in a long we have succesfully

observed

the 59Co spin echo signals

powdered

sample

applied

of this

magnetic

compound

up to date,

served only one signal range between

0 0

C

0

in zero

0

O

0

I

,-,,i

in this

we have ob-

in the frequency

10 MHz and 300 MHz.

Fig.

Temperature signal

We

dependence

intensity

[1] Mota,A.C., [~

in fig.

spin echo spectrum

2.

From this

spectrum

we can determine

R.S.I.

Frossati,G..

reasing

dependence

the spin echo signal ly.

of this nmr signal

in fig.

the temperature,

3.

below

short.

C6

(1978)

[6] Abe,H..

150 mK.

82

rapid-

1.2~sec

150 mK it was very

[4

and Watanabe. T.,

19 (1964) 41

(1976)

J.Phys.Soc. Jpn.

Matsuura~M.,

717

and Matsuura,M..

J.Phys.Soc.Jpn.

By dec-

became larger

Spin echo decay time was

at 40 mK, and above

J.de Phys.

Nakai.Y.

J.Phys.Soc,Jpn.

= 2.2 ~ 0.3 MHz

is shown

1541

C6 (1978)

1166

[5] Yamakawa,H. intensity

42 (1971)

J.de Phys.

[3] Soulen,R.J.Jr., [4] Osaki,K.,

Temperature

of the nmr

at 229.5 MHz.

1 578

H N = 22.8 A 0.12 T 3e2q~ 2I(21-T)h

I

500 T( mK)

References

site.

is shown

•

3.

regard this signal as one from the AThe observed

o

are expect-

ed (from A-site and from B-site but,

in a

field below 200 mK.

Two kinds of 59Co nmr signals compound),

@

43 (1977)

Blote,H.W.J.

Huiskamp. W.J.,

Physica

798

and

50 (1970)

444