MÖSSBAUER EFFECT IN Dy2O2S

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MÖSSBAUER EFFECT IN Dy2O2S

M. Belakhovsky

To cite this version:

M. Belakhovsky. MÖSSBAUER EFFECT IN Dy2O2S. Journal de Physique Colloques, 1971, 32 (C1),

pp.C1-915-C1-916. �10.1051/jphyscol:19711325�. �jpa-00214358�

JOURNAL DE PHYSIQUE

Colloque C 1, supplbment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 -

MOSSBAUER EFFECT IN D g 2 0 2 S

M. BELAKHOVSKY

Centre d 7 ~ t u d e s Nucltaires, 38, Grenoble, France

R6sum6.

On a 6tudik les proprietes magnktiques du compose Dy202S par effet Mossbauer sur le noyau de 161Dy.

Les parametres nucleaires determines valent

gl/go

1,243

0,010, Ql/Qo

+ 1,007

0,010. Sur monocristal, la disparition des raies

0 dans l'etat ordonnk a montre que l'axe d'antiferromagnetisme est parallkle

l'axe c

qui est un axe d'ordre

pour le site de Dy3+ (symetrie C3v)

contrairement

des resultats trouvks preddemment par diffrac- tion neutronique

la valeur obtenue pour le moment magnetique

saturation est (8,O

0,3)

montrant une influence sensible du champ cristallin.

Abstract.

The Mossbauer effect at the 161Dy nucleus has been used to investigate the magnetic properties of Dy202S. The nuclear parameters have been found to be

gl/go

1.243

0.010, Ql/Qo

+

0.010. In a single crystal experiment, the disappearance of the

0 lines demonstrates that the antiferromagnetic axis is parallel to the c-axis (three fold axis for the Dy3+ site of

symmetry), contrary to previous neutron diffraction results

the value found for the magnetic moment at saturation is (8.0

0.3)

showing a net influence of the crystalline field.

I. Introduction.

In this work the recoilless lies in the problem of the linearity of the drive absorption spectra of the 26 keV

rays from 1 6 1 m ~ y system [5].

situated in Dy,O,S have been recorded at various

temperatures. This compound belongs to the family

In

of rare earth oxisulfides T,O?S, which is of increasing

figure 1 we represent the crystallographic and magnetic interest [I].

The crystal structure can be described in the space group ~3 m (D: d) with 2 T in f

3, u) (u

0.3), 2 0 in

+, v)

0.6) and 1 S in (0, 0, 0)

the point group of Dy3+ is C,,. The susceptibility measu- rement shows that 1 / ~ versus T varies linearly with a Curie constant equal to that of the free ion, so that the overall splitting of the ground multiplet is of the order of a few tenth of Kelvins

the first excited multi- plet lies far above it. The magnetic cell of Dy202S has been found by neutron diffraction [2] to corres- pond to the propagation vector k

[O,

$1.

The motivation of this study lies in the discrepancy between the values of the magnetic moment, as determined by neutron diffraction a t 1.5 OK (4.41 p,) and magnetization measurements (8.6 pB at 1.13 OK)

[31.

11. Experimental results and discussion. 11.1 -

- AS it is well known, the hyperfine interactions measured by Mossbauer effect or other techniques, involve the product of two quan- tities, one of nuclear origin and the other of electronic origin. Therefore as far as solid state physics is concer- ned, one must know accurately the nuclear moments.

From a conlputer fit of our experimental results on Dy,02S (Fig. 3 4 we derive the ratio for the magne- tic moments

" "

- 1.243 f 0.010 Pg

and the ratio for the electric quadrupole moments :

These values are in complete agreement with those of Bowden et al. [4] with a somewhat better precision.

The discrepancy with the other authors probably

FIG. 1.

-Magnetic structure of DyzOzS as determined

neutron diffraction measurements (see ref.

structures of Dy202S, determined by neutron diffrac- tion [2]

the magnetic ordering consists of an anti- ferromangetic collinear arrangement, but some uncer- tainty exists because of the measured very low magnetic moment.

From the comparison of the Mossbauer spectra taken a t 1.5 OK for the single crystal and powder sample respectively (Fig. 2 and Fig. 3a), we see that there are less lines in figure 2 where only 10 lines are present. The Am

0 lines have vanished. From this observation we immediately conclude that the hyper- fine magnetic field is directed along the c-axis, thus demonstrating that (within +

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711325

(21-916 M. B ELAKHOVSKY

FIG. 2. -

Mossbauer spectrum of

single crystal, exhi- biting the disappearance of the

lines.

FIG. 3a, b, c, d.

- Mossbauer spectra of

powder sample at different temperatures

figure

a computer

1. the magnetic moments are indeed collinear

2. their direction is not perpendicular but parallel to the c-axis, contrary to the neutron diffraction results.

Of course, because of its local nature, a hyperfine measurement cannot distinguish the relative orien- tation of next neighbour magnetic moments ; neutron diffraction measurements are under way in our labo- ratory, to elucidate this point.

The experimental parameters are given in the follow- ing table

The quadrupole interaction is fairly large, and

is supposed to be zero since the c-axis is a three fold axis.

The hyperfine interaction seems to remain constant with an increase of the temperature, so that we get for the magnetic moment of the 4 f shell the saturation value

we have

(8.0 + ^0.3)

showing that crystalline field effects are important in this compound.

The spectra of the Dy202S polycrystalline sample show that relaxation takes place

even at 1.5 OK the central peak is greater than expected from the compu- ted spectrum, and its intensity grows with the tempe- rature together with a broadening of the lines, and eventually only the central peak is observed at about 6 OK.

The broadening of the lines takes place between 50K and 6 OK i. e. at temperatures corresponding to the N6el temperature found by neutron diffraction (T

5.8 OK).

111. Conclusion.

- This study is a clear example of the usefulness of the Mijssbauer effect technique for the study of magnetic structure, especially when single crystals are available. The determination of the absolute value of the magnetic moment can be reached within a few percent, as well as its direction.

These results are interesting especially for neutrons highly absorbing substances when the neutron diffgac- tion results are difficult t o interpret, and always less accurate

more typically, experiments with single crystal of Gd compounds using the 1 6 1 ~ y (26 keV)

rays could give direct information on the magnetic moment direction of the Gd ion.

Acknowledgements. - We thank C . Jeandey for making a computer program available for us, R. Bal- lestracci for preparing the Dy202S single crystal, and R. Rossat-Mignod and J. Chappert for helpful discussions.

References

[I] For a review of recent results, see

Proceedings of

(J.), Colloque International des Terres the 8th Rare Earth Research Conference, Reno Rares, Grenoble 1969.

(am1 1970) Edited by Thomas

Henrie and [4] BOWDEN (G. J.), BUNBURY

St.

and WILLIAMS R.

Lindstrom (1970). (J. M.),

1967,

612.

[2] BALLESTRACCI (R.). BERTAUT (E.

QUEZEL

L51 Independently

1968,

1001. recently found

pe/pr

1.237 f 0.005, Qe/Qg

= 1.0004 &

0.0003, in agreement with .our [3] QUEZEL (G.), BALLESTRACCI

and ROSSAT MI- results. We thank him for communicating this

result prior to