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129I TRANSFERRED MAGNETIC HYPERFINE FIELD IN THE β .-IRON TELLURIDE (Fe1+χTe)
T. Birchall, K. Ruebenbauer
To cite this version:
T. Birchall, K. Ruebenbauer. 129I TRANSFERRED MAGNETIC HYPERFINE FIELD IN THE β.- IRON TELLURIDE (Fe1+χTe). Journal de Physique Colloques, 1980, 41 (C1), pp.C1-219-C1-220.
�10.1051/jphyscol:1980170�. �jpa-00219739�
JOURNAL DE PHYSIQUE Colloque Cl, supplbment au n O 1, Tome 41, janvier 1980, page C1-219
129 I TRANSFERRED MAGNETIC HYPERFINE FIEU) IN ME B-IRON TELLURIDE ( ~ e ~ + ~ ~ e )
T. B i r c h a l l and K. Ruebenbauer
Department of C h e h s t r y , McMaster University, 1280 Main S t r e e t , West, HamiZton, Ontarion L8S 4MI;
Canada.
INTRODUCTION
-
There i s considerable i n t e r e s t i n t r a n s i t i o n metal t e l l urides which order magneti cal- l y . In principal such systems can be studied by means of lZ5Te bGssbauer spectroscopy, but t h i s has not proved p a r t i c u l a r l y successful because of t h e large natural linewidth associated with t h e trans- i t i o n /1,2/. An a l t e r n a t i v e approach, i s to make use of the M$ssbauer t r a n s i t i o n which has a much narrower natural linewidth and hence superior resolution. In t e l l uri um compounds t h i s i sachieved by preparing t h e compound of i n t e r e s t with lZ8Te, carrying out a neutron i r r a d i a t i o n t o pro-
i n the coolest p a r t of the evacuated s i l i c a tube so t h a t t h e sample temperature could not exceed 600°C.
The sample was powdered and a small amount of unre- acted iron was removed magnetically. The x-ray d i f f r a c t i o n powder pattern ( ~ u ~ ~ r a d i a t i o n ) of the non-enriched control sample only exhibited 1 ines belonging to the @-iron t e l l u r i d e /4/. 5 7 ~ e !f<ss- bauer spectra were measured f o r the non-enriched sample a t 295 K, 80 K and 6 K versus a 5 7 ~ o ( ~ h ) source.The spectra obtained a r e in substantial agree- ment with the previous data though our room temper- ature spectrum i s much l e s s asymmetric than the, duce l Z 9 ~ e or 1 2 9 m ~ e which populates the lZ91 M ~ S S - e a r l i e r spectrum /5/. The @ Fel+, l Z 8 ~ e gave i dent- bauer excited s t a t e , and using t h i s material as a i c a l spectra, with IS = 0.32 mms-';QS = -0.32 mms-I;
source t o carry out the experiment /3/. We have
r
10.23 mms-I ; and gI1=0.95 representing the degree aused t h i s method to study the hyperfine f i e l d trans- of anisotropy i n the Debye Waller f a c t o r and/or any ferred to t h e iodine atom,on a tellurium s i t e , i n texture in the sample /6/. Figure 1 shows the 295"
B-Iron t e l l uride (Fel+,Te). K spectrum with a 2.2% ~ e ' + impurity (IS=1.19 mms-' ; Experimental
-
High purity iron powder was f i r s t 1.000-reduced under hydrogen i n an alumina boat, then
mixed with tellurium powder ( e i t h e r natural Te or .377-
enriched t o > 99% in l z 8 ~ e obtained from Oak Ridge)
i n an atomic r a t i o Te/Fe = 0.8. The f i n e l y powd- . 9 5 4 -
ered mixture was pressed i n t o a p e l l e t , placed in a closed alumina crucible and sealed in a s i l i c a tube under vacuum ( 1 6 ~ ~ o r r ) . Samples were heated i n a furnace a t a r a t e of 50"hr t o 600°C, annealed a t 600°C f o r 12 hrs, cooled a t a r a t e of 700°/hr t o
I I I I
300°C and annealed f o r 40 hrs. The sample was -3.8 -1.9 0.0 1.9 3.8 f i n a l l y cooled a t 25"/hr t o room temperature. VELOCITY ( MM/S 1
During the thermal processing the sample remained Fig. 1 5 7 ~ e spectrum of 0-Fel+, lZ8Te a t 295 K.
16
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980170
C1-220 JOURNAL DE PHYSIQUE QS=2.49 mms-l) which must a r i s e from reaction with
t h e crucible walls. The 4.2 K spectrum was similar t o t h a t of Hermon e t a1 / 5 / with a d i s t r i b u t i o n of magnetic f i e l d s due to the presence of t h e i n t e r - s t i t i a l iron: i t was not computer f i t t e d .
The sample enriched in l Z 8 ~ e (301119 1 2 8 ~ e ) was then placed in the McMaster reactor f o r 2 hrs. i n a
-2s-1 12g1 thermal neutron flux of % 1013 n.cm.
.
spectra were recorded a t 80 K and 4.2 K with the i r r a d i a t e d B-iron t e l l u r i d e a s a source against a
absorber at the same temperature, and f i t t e d as described in /6/. The spectra a r e shown i n Figure 2. Owing t o the c l o s e geometry, baseline e f f e c t s a r e strong and have been included i n t h e spectral f i t t i n g .
I
parent t h a t there i s a magnetic f i e l d a t t h e iodine.
F i t t i n g t h e spectrum by using the linewidth and quadrupole coupling constant obtained a t 80°K re- s u l t s i n IS=1.03
+ -
0.05 mms-I; a transferred hyper- f i n e f i e l d of 142 KOe with a d i s t r i b u t i o n ( A ~ ) of 60% f 7; and = 64'+ -
5. The f i e l d d i s t r i b u t i o n i s related t o t h e disorder of the iron i n the inter- s t i t i a l s i t e s .The dominant contributions t o the f i e l d a t t h e iodine a r e covalent spin density t r a n s f e r f s and f ~ o from the c l o s e s t iron atoms t o the iodine 5s and 5p o r b i t a l s respectively. The e.f.g. tensor f o r an iodine atom located a t a tellurium s i t e i s a x i a l l y s y m e t r i c and i t s principal component i s p a r a l l e l t o the crystal C axis. Leciejewicz /7/
-12.8 - 6 . 4 0.0 6.4 12.8
V E L O C I T Y ( M M / S 1
Fig. 2 spettrum of B-Feltx 1 2 8 ~ e a t 80 K (up- per) and 4.2 K (lower).
Discussion
-
A t 80 K t h e 1 2 9 ~ parameters a r e 1s =+
-1 2+
0.82
-
0.02 mms ; e q Q127/h = -288-
7 MHz;r -
LO<
1.37
+ -
0.07 mms-' ; q = 0 . ~ h e d i s t o r t i o n i s caused by the tetragonal s t r u c t u r e and i s f u r t h e r augmented by t h e p a r t i a l occupancy of t h e i n t e r s t i t i a l s i t e s by additional iron atoms /5/. A t 4.2 K i t i s ap-has found t h a t t h e iron magnetic moments a r e coup- led ferromagnetical ly within t h e tetragonal planes.
Therefore t h e i s o t r o p i c f i e l d Hs must be perpend- i c u l a r t o the C a x i s , and i t i s l i k e l y t h a t the anisotropic f i e l d HDa i s parallel to the C axis.
Adopting p o = 150 x cme3, < r - 3 ~ l ~ l .5 x 10 24 and H = fpa
x
450 (KOe) /3/, we c a l c u l a t eP O
f s = 1 . l % and fpa = 13.8% f o r s and po covalent t r a n s f e r respectively along the Fe-I bond.
Acknowledgements
-
We would l i k e t o thank Dr. J . E . Greedan and Mr. J . Garrett of t h e Materials Preparation Group, McMaster University, f o r t h e i r help in sample preparation. The Natural Sciences and Engineering Research Council of Canada i s thanked f o r financial support.References-
1 . Kjekshus, A. and Nicholson, D. G . Acta Chem.
Scand.
26
(1972) 3241.2. Nishihara, Y . and Ogawa, S. J . Physique
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(1979) C2-221.
3. Sanchez, J . P . , Friedt, J . M. and Shenoy, G. K.
J . Physique
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(1974) C6-259.4. Gronvold, F . , Haraldsen, H . and Vi hovde, J . Acta Chem. Scand.
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(1954) 1927.5. Hermon, E . , Nolan, R. D . and Shtrikman, S.
Israel J . Chem.
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(1971) 1.6. Ruebenbauer, K. and Birchall, T. Hyperfine I n t . 7 (1979) 125.
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7. Leciejewicz, 3. I n s t i t u t t f o r Atomenergie, Kjeller, Preprint KIR-P129, August (1963), Norway.
