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TIME DEPENDENCE OF EC-AFTEREFFECTS IN COBALT SULPHATE MEASURED BY TIME DIFFERENTIAL MÖSSBAEUR COINCIDENCE
TECHNIQUE
H. Berlin, J. Schmand
To cite this version:
H. Berlin, J. Schmand. TIME DEPENDENCE OF EC-AFTEREFFECTS IN COBALT SULPHATE
MEASURED BY TIME DIFFERENTIAL MÖSSBAEUR COINCIDENCE TECHNIQUE. Journal
de Physique Colloques, 1980, 41 (C1), pp.C1-135-C1-136. �10.1051/jphyscol:1980132�. �jpa-00219700�
JOURNAL DE PHYSIQUE Colloque C1, suppldment au n O 1, Tome 41, janvier 1980, page C1-135
TIME
DEPENDENCE OF EC-AFTEREFFECTS IN COBALT SULPHATE MEASURED BY TIE DIFFERENTIAL M~~SSBAER COINCIDENCE TECHNIQUEH. Berlin and J. Schmand
I n s t i t u t F. Kernphysik der UniuersiMt MUnster, CorrensstraBe, 0-44 MUnster.
1. Theory 9 ns. The measured TDMC-spectra were cor-
Line intensities measured by time diffe- rential Moessbauer coincidence (TDMC) tech- nique can be calculated exactly by thetime
filtering theory (TFT) [ 1
I . Differences between our experimental and theoretical
spectra gave us reason to suppose that we had got experimental evidence for dynami- cal EC-aftereffects, such as local lattice vibrations. Therefore we modified the ra- diation amplitude of Lynch et al. [I] by
rected by subtracting the random coinci- dence spectra. Because numerical fits were too time wasting determination of the expe- rimental parameters a and y was done by nu- merical calculation of TDMC-spectra with varying parameters y and a, comparing them with the measured spectra.
3. Results
3.1 "cA-doted CoS04 -7 H20-source.
Parameters of time integral measured spec- a time dependent Debye-Waller factor (DWF), tra are listed in the following table.
given in this form by Dash and Nussbaum [2].
So we started intensity calculations with the numerically determined Fourier trans- formation of
a (t)
=.l<fq,
exp(-a e x p ( - ~ t ) + i w ~ t - ~ t )r
(1) where <fq> = temperature dependent DWF, a = measure for the initial nuclearlattice dislocation, y = relaxation constant, wo=S. I n t . L i n e Quadr. I s o m .
Temp. Width s p l i t t shift [K] [%I [mm/s] [mm/s] [mm/sl FeI1- 293 4.24 0.67 2.744 -1.480 comp. 115 4.77 0.54 2.772 -1.415 20 4.59 0.71 2.776 -1.433
~e'"- 293 6.65 0.66 1.027 -0.625 comp. 115 7.59 0.61 1.148 -0.429 20 8.08 0.62 1.123 -0.462 10magn. Hf-splitting, HS518 KG.
resonance frequency, and
r
= decay con- TDMC-spectra of sources at 293 K (fig. la) stant of the Moessbauer level. Time depen- showed neither the agreements between expe- dence of the isomeric shift (IS) we could rimental and TFT-calculated spectra as pub- calculate numerically, starting with lished by Triftshguser a. Craig [3] nor thea (t) = exp[i(%+D-expl- ytl- :)t] (2) time dependence of ~e'II-line intensities where D is a relaxing energy shift caused as measured by Hoy a. Wintersteiner [4].
by atomic EC-aftereffects. Optimal description of our experimental 2. Experimental TDMC-spectra we gained with (1) and parame:
Our 10 ~Ci~polyester capsuled CoS04'7 H20 ters Y and sgiven in fig. Ib. The complex sources (pink colour) were prepared by CoS04'7 H20-structure may cause the long crystalization. Heating some of them weon- relaxation time of 36 ns. On the other hand ly got crystal water poor sources (light- at 20K the spectra did not show any influ- violet). Apparative resolution time was ence of dynamical aftereffects (fig. 21,
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980132
C1-136 JOURNAL DE PHYSIQUE
Fig. la Fig. Ib
Fig. 2
Fig. 1
-
3: Fig.3 * Crn1.lTDMC-spectra sor different time windows, measured with a K4Fe(CN)6'3H20-absorber of effective thickness 0=13. ~ r k w n spectra are calculated.
Fig. I: CoSO4'7H2O-source at 293
k ,
cal-culation a) by TFT and <fq> = 0.35, b) with (1) and <fq> = 0.48, y = 4l and a = 0.5.
Fig. 2: CoS04'7H20source at 20K, calcula- tion as in fig. la but <fq> = 0.48.
been shortened by the higher heat conducti- vity at lower temperatures. In TDMC spectra at 20X a magnetic hf-splitting was not seen. Nevertheless, a magnetic phase tran- sition could be the reason for thestriking
~e*' -1jne intensity decrease in the last time window. Local heating after EC momen- tanously may exceed the exchange interac- tion of the ~e'*-atomspins. After about 150 ns the local disturbance has dissipa- ted but because of low intensity a magne- tic hf-sextett is not visible.
3.2 Crystal water poor CoS04-sources.
No phase transition was found down to 10K.
Experimental TDMC-spectra show in the first three time windows a weak time dependence of IS and quadrupol splitting (fig. 3).
Such time dependence of IS is given by our calculations with amplitude (2) and also by a similar formalism of Kankeleit '151.
The larger covalent bounding character of crystal-water poor sources may be a reason that changes of interatomic distances af- ter EC may be more effective than inCoS04' 7. H20 sources.
References:
[I1 Lynch, F.J., Holland, R.E., and HamA mermesh, M., Phys.Rev.
120
(1960) 513 I21 Dash, J.G. a. Nussbaum, R.H., Phys.Rev. Lett. 16 (1966) 567
131 Triftshauser, W. a. Craig, P.P., Phys.
Rev..' 162 (1967) 274
t41 Hoy, G.R. a. Wintersteiner, P.P., Phys.
Rev. Lett. 28 (19721 877
151 Kankeleit, E., 2. Phys. 275 (1975) 119 Fig. 3: crystal water poor CoS04-source
at 293 K, calculation as in fig. la.
what could mean that relaxation time has
