HAL Id: jpa-00219696
https://hal.archives-ouvertes.fr/jpa-00219696
Submitted on 1 Jan 1980
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.
HIGH-PRESSURE MÖSSBAUER STUDIES ON 151Eu IN SELECTED Eu INTERMETALLIC COMPOUNDS
M. Abd-Elmeguid, H. Micklitz, K. Buschow
To cite this version:
M. Abd-Elmeguid, H. Micklitz, K. Buschow. HIGH-PRESSURE MÖSSBAUER STUDIES ON 151Eu
IN SELECTED Eu INTERMETALLIC COMPOUNDS. Journal de Physique Colloques, 1980, 41
(C1), pp.C1-127-C1-128. �10.1051/jphyscol:1980128�. �jpa-00219696�
JOURNAL DE PHYSIQUE Colloque C1, mpplkment au
n
O 1, Tome 41, janvier 1980, page C1-127HIGH-PRESSWE
M&SBAUER
STUDIES ON 151~uIN
SELECTEDELI INTER$€TALLIC
CCh'WOWX M.M. Abd-Elmeguid, H. Micklitz and K.J.H. Buschow+
Ruhr-Universit8t Bochwn, ~xperimentaZphysik 1V, 4630 Bochwn, W. -Germmy.
+
Philips Research Laboratories, Ehdhoven, fie Netherlands.High-pressure Wssbauer studies on15'Eu in EuA12, EuA14, EuSn3, EuCu5 and EuZn2 gave information about the pressure dependence of the different con- tributions to the effective hyperfine field Beff at the Eu2+-site in these systems /I/. The analysis of the Massbauer data was based on the assumption of a pressure independent core-polarization, Beore* N M R experiments on Eu intermetallic compounds by Kropp
7. 8
et al. /2/ show a well localized 4f ( S712) state for EU" in EuCu5 but indicate at the same time an unstable ~ u ~ + - v a l e n c ~ in EuPt2 and EuPd2. Their NMR results on Eux(Ca,Ba) Pt and E~~(,ca,Ba),-~Pd~
I-x 2
have been interpreted by assuming a "chemical press- ure" dependent Eu-valency. tZigh-pressure WLssbauer experiments on I5'3u in EuPt2 offer the possibility to prove the validity of such an assumption.
We have examined the I5'3u Miissbauer spectrum of EuPt2 at 0, 30 and 65 kbar and at 4.2 K using the high pressure cell described by Abd-Elineguid et al.
/I/. The I5'Eu Mijssbauer spectrum of Euo 95Ba0 Oft2 at 0 kbar and 4.2 K was also measured. The compress ibility of EuPt has been determined to be
2
K=O. 53 (2)xl ~-~kbar-' using a hydrostatic pressure cell and 1JaCl as a calibrating material. The ob- tained hyperfine parameters as the results of the least square fits to the measured spectra are pre- sented in table 1 and figs. 2 and 3 respectively.
The spectrum of EuPt at 0 kbar gives a measured 2
effective hyperf ine field of B~~ = - 4 b ~ taking
2 1
Vzz=O. 1 x 1 0 ~ ~ V/cm corresponding to AEg=z. eQVzz
"2.5 MHz or =0.15 mm/s and a line width of r/2 = 1.5 mm/s as it usually measured in Eu intermetallic compounds. While this field is smaller than that given by Wickman et al. /3/ it is larger than that of Kropp et al. /2/ (Beff=-2.86 TI. An unusual line width of r/2=2.48 mm/s is needed in order to fit
the 0 kbar spectrum with Beff=-2.86 T. The isomer shift S is -8.6(1) mm/s relative to the 15'
sd3 116ssbauer source. The pressure induced change of the isomer shift is as/ap=0.6 (3)x10-~ (mm/s.kbar) corresponding to aS/alnV=-1 l(2) mm/s in agreement
I I , I
-15 -10 -5 0 5 10 15
V (rnm/sl
Fig.1: 15'~u Massbauer spectra o f EuPt2 at 0 and 65 kbar.
T h e MBssbauer spectrum Of BU0.95Ba0.05Pt2 at 0 k b a r i s also shown; in a11 cases t h e source and absorber were kept at 4.2 K. T h e dashed line repreeents the value of the isomer shift f o r EuPt2 at 0 kbar.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980128
C1-128 JOURNAL DE PHYSIQUE
with the previous measurements by Moser et al. 141.
This value is even smaller than in the other Eu-in- termetallic compounds /I/ and is typical for the compression of the outer electron shells. The iso-
mer shift-of E u ~ ~ is identical to that ~ ~ B ~ ~ ~ ~ ~ P ~ ~ of EuPt2 (s. table 1). This shows clearly that the
~u'+-valency is not effected by the Ba substitution and that the assumption of an E U ~ + valence instabi- lity /2/ is not correct.
The magnitude of Beff decreases linearly with pressure independent on the line width used ( s.
table 1 and fig. 3). For r/2=1.5 mm/s one obtains aBeff /ap=-1 .2(4).
~.kbar-l .
This is the same order of magnitude as the values obtained for otherr/2= 1,5mfWs
EuPt A 1-12 = 248mmls
1
I a
I
0 10 20 30 1 0 5 0 6 0 70
P f k b o r )
Fig.2: M a g n e t i c h y p e r f i n e f i e l d a s a f u n c t i o n o f a p p l i e d p r e s s u r e f o r E u P t 2 a s s u m i n g t w o d i f f e r e n t l i n e widths.
F o r c o m p a r i s o n t h e v a l u e o f B e f f g i v e n b y K r o p p et al.
I 2 1 i s a l s o included.
EuPtZ
Eu intermetallic compounds /I/. In order to discuss
-
d -&,o - A zu these results the effective hyperfine field of the Es - 6 . 2 -
~ u ~ + - i o n should be divided into three contributions: v)
Beff=Bcore+Bce+Bthf, where B is the contribution ce
-8.6
from conduction electron polatization by the magne-
tic ion itself and Bthf represents all other con- I 1 I
, 1
0 10 2 0 3 0 1 0 5 0 6 0 7 0
tributions from neighbouring magnetic ions. Our P f kborl
results can be easily interpreted assuming that Fig.3: P r e s s u r e d e p e n d e n c e o f t h e i s o m e r s h i f t f o r E u P t 2 at 4.2 K.
Bcore is pressure independent and that the contri-
bution Bthf is mainly responsible for the observed to +20(5) T. This means that the observed decrease pressure dependence of Beff in the intermetallic of the magnitude of Beff in EuPt is caused by in-
2
systems /I/. The value of Bthf in EuPt was deter- 2 creasing Bthf under pressure. The lower measured
mined by Kropp at al. /2/ to be ~ositive and equals value of B eff in E u ~ . ~ ~ B ~ ~ . ~ ~ P ~ ~ relative to EuPt2
Table I : Byparfine paraasters of luPt2 and E u ~ , ~ ~ B ~ ~ . ~ ~ P ~ ~
at 0 kbar (s. table 1) could be attributed to a
a s the result of tbe least aquare fits to the I6ssbauer opcctra
taking vZz.o.~~~o1' v/cmZ and two different line width. r . change of the density of states at the fermi sur- face of the non-s electrons in this compound.
References:
111 M.M.Abd-Elmeguid and G. Kaindl. Ilyperfine Interactions 4 (1978) 420 and M.M. AM-Ellseguid aud C. k i n d l to be published.
121 H. Kropp. W. Zipf. E. Dotmann and K.U.J. Buschow to be published.
131 H.H. W i c h n n . J.H. Wernick. R.C. S h e w o d and C.F. Wagner, J. Phya.
Chem. Solids 2 (1968) 181.
141 J. Moser, U.F. Klein, C. Wortmann and G.M. Kalvius, Physica (a) This Iioa width was the result of tb. learnt aquare fit to tbe (1977) 243.
maa#urad data Lakina Bsff at 0 kbar as aivan by Kropp et a1.121.
(b) 00 fit V.8 possible with PI2-2.48 a d s .
