HYPERFINE INTERACTIONS IN DyFe2

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HYPERFINE INTERACTIONS IN DyFe2

St. Japa, K. Krop, M. Przybylski

To cite this version:

St. Japa, K. Krop, M. Przybylski. HYPERFINE INTERACTIONS IN DyFe2. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-199-C1-200. �10.1051/jphyscol:1980161�. �jpa-00219730�

JOURNAL DE PHYSIQUE Coiioque Cl

,

suppi&ment au n o 1, Tome 41, janvier 1980, page C1-199

HYPERFINE INTERACTIONS I N DyFe2

St. Japa, K. Krop and M . ~rzybylsii

Zaklad Piizyki Ciala Stalego, Akaderrria G6miczo-Hutnieza, Al.Micki&cza 30, K r a k h , Poland.

Intermetallic R% compounds were investi- gated by many authors. The obtained re- sults suggest, that in a particular series e.g. RFe2,the magnetic properties depend weakly on the kind of R atom. A crystalli- ne anisotropy of rare earth element is re- sponsible however for the easy axis direc- tion. In a case when the easy axis and a local direction of the EFG main axis do not coincide and at the same time quadru- pole interaction is not much smaller tnan the magnetic one, sny approximations used for the description of nuclear energg le- vels may be unsatisfactory. From our inves tigation arises, that Q F e Z is an example of such a case.

In Q P e 2 structure / space group Fd3m/ all Be atoms are crystallographically equiva- lent. If we asswne that the EFG tensor for particular atom has the same type of sym- metry as the point symmetry of the atom site then the EPG tensor in Q P e 2 should posses axial symmetry. Because the easy direction is [loo], there is the sa- me angle 8 between the easy direction and the local EFG main axis for each Fe atom.

One can expect an identical value of hy- perfine interaction for all atoms and the

MBssbauer spectrum should contain only one sextet.

The solution for energy eigenvalues in ca- se of axially symmetric EPG tensor in the

first approximation is given by the for- mula

The expression e2gQ

(3~020-4)

,I, be

4 ²

referred to as QS and spectrum fits accor- ding to formula /I/ we call "diagonal se- xtetsW.If q =O or co& =I@

,

^{the spec-}

trum should not exhibit afly quadrupole splitting because QS is eqial to zero.

In DyFe2 the angle 8 fulfils the condi- tion that co& = l / e

.

The numerical fits indicate however significant contribution of the quadrupole splitting to the measu- red spectra. The obtained QS value does not depend on temperature and equals 0.03 mmJs.Moreover, all our spectra show 0.04 mm/s shift of the observed positions of 2 and

5

lines with. re'spect to those expected from formula /'I/. These results prove that expression /I/ is not suffi-

cient for correct nuclear energy levels

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980161

c1-200 JOURNAL DE PHYSIQUE

d e s c r i p t i o n of 5 7 ~ e i n DgFe2 s t r u c t u r e . According t o [I] the f u l l Hauiltonian of hyperfine i n t e r a c t i o n s may be w r i t t e n i n t h e form:

where P2& a r e teal c o e f f i c i e n t s describing t h e ^{3 G} tensor. The t h i r d component of formula /2/ one can t r e a t a s diagonal Ra- miltonian perturbation. I n t h e DyFe2 case i t i s convenient t o chose t h e XFG t e n s o r p r i n c i p a l axes system because t h e only nonvanishing ^I-= a r e bere Pz0 and r i 2 j d i a - gonal element and assymetry paramei;er/.

After transformation t o magnetic coordina- t e s system t h e I4F.G t e n s o r i s defined bg f i v e new P2acoefficients / or t h r e e , i f the EPG tensor has the a x i a l s y m e t r y / .

*he ld8ssbauer s p e c t r a were f i x t e d accor- ding t o t h e progrtut, i n which t h e energy eigenvalues were given by t h e s o l u t i o n s of iianiltonian / 2 / . Our r e s u l t s a r e as follows :

/ I / t h e f i t s with l?i2=0 / a x i a l syimetry of L E G tensor/ a r e not s a t i s f a c t o r y ,

j2,. tile ;ribs wii;i~ l r e e 2:2 parameter a r e f a r b e t t e r a s diagonal s e x t e t fits.

x'

vaiues a r e i n i-ilis case same a s f o r six independent l i n e s f i t s . The .?20 ana rZ2 C iru 1,u-L iepeilii O n tempera- t u r e /Fig.?/. P20 parameter f u l f i l s t h e r e i a t i o n

accordance with the tendency t h a t hyperfi- ne i n t e r a c t i o n p a r m e t e r s depend only wea- kly on ^d aton.

Pig.1. P20 and l?Z2 c o e f f i c i e n t s vs. temperature / f o r DyYe2/.

In conclusion, t h e a p p l i c a t i o n of appro- ximation /I/' i n t h e case of JyFe2 leads t o t h e i n c o r r e c t values of hyperfine in- t e r a c i o n parameters. The c o r r e c t values a r e obtained by taBing i n t o account off- -diagonai elenents of i3FG tensor. Jxe de- rived r e s u l t s i n d i c a t e moreover vnaG the

& C i t e n s o r i n uyae2 has not a x i a l symme-

t r y *

rieserences ^:

[I] A r i f ,S.i(. ,Bunbury ,D.St .r. bowd den,^. J., Day, ^H. K.

,

^J. Phy s

.

^F: :Zeta1 I-ny s.

,

Z/1973/

1037.

[2]Gubbens,k-.C.~.,v'au xpeldoorn,J.H.F., Van der Kraar1,A. Id.

,

Buschow, K. H. J.

,

^J.

i2hys.F: Ketal Phys.,4 /19'/4/ 921.

For DyFe2 we g e t then

Se4 -

^-0.306 m / s . This value is c l o s e t o

we-0 -

=-0.38 m/s obtained by Gubbens e t , a l . C21 l o r Yir'e2 , i n