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Submitted on 1 Jan 1979
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EFFECT OF THERMAL TREATMENT ON
MÖSSBAUER SPECTRA IN Fe-Ni INVAR ALLOYS
T. Takeda, S. Komura
To cite this version:
T. Takeda, S. Komura. EFFECT OF THERMAL TREATMENT ON MÖSSBAUER SPECTRA IN Fe-Ni INVAR ALLOYS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-165-C2-166.
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EFFECT OF THERMAL TREATMENT ON MOSSBAUER SPECTRA IN F
e"Ni INVAR ALLOYS
T. Takeda and S. Komura
Faculty of Integrated Arts and Sciences, Hiroshima University, Hiroshima, Japan
Many Mossbauer studies of Fe-Ni alloys have been reported /],2/. In the present work, the Moss- bauer effect of 57Fe was measured in Fej Ni alloys in order to study whether atomic ordering exists or not. The Mossbauer effect of 57Fe is one of the most powerful tools in order to study how the atomic mo- ment is affected by the local environment, since we can get information on the atomic moment of each iron atom by using an empirical relation between the atomic moment and the internal magnetic field. The spontaneous magnetization in the invar region of Fe- Ni alloys decreases rapidly with increasing iron concentration and the atomic moment is considered to be sensitive to the local environment. Though long- range ordering of atoms is absent in iron rich Fe-Ni alloys /3/, the Mossbauer spectrum is considered to depend strongly on the existence of short-range or- der.
Fe-Ni alloys were prepared by melting 99.9%
pure iron and nickel together in an arc furnace un- der argon atmosphere. The range of atomic concentra- tions in produced alloys are 31% < Ni < 50%. The ingots were filed into powders and heat-treated in four different ways for Mossbauer effect measure-*
ments; AL series of samples were annealed at 400°C fcfr 24 hours and finally quenched into water, AH se- ries annealed at 800°C for two hours and finally quenched, BL series annealed at 600°C for two weeks and then at 400°C for a week and finally quenched and BH series were obtained by annealing BL series at 800°C for an hour and by quenching subsequently.
No contamination of bcc phase in the specimens was found at room temperature by X-ray diffraction. The Mossbauer spectrometer used for the present study was of a constant acceleration drive type and
14.4 keV y- r ay source was 3 mCi S7Co diffused in Cu.
The line broadening of the Mossbauer spectra observed in these alloys is mainly due to a wide distribution of internal magnetic field. In order to obtain the distribution function P(H) of internal magnetic field H, the method developed by Window /4/
was employed, in which the function P(S)was decompo- sed into a series-expansion of trigonometric func- tions as
The unknown coefficients a are determined by least- n
squares fitting.
Mossbauer spectra observed in Fe6e.iNi3i.9 of AL and AH series at room temperature are shown in figure 1, in which the solid lines are the calculated spectra using the distribution function P(.H) shown in figure 2.
Fig. 1 : Mossbauer spectra measured at room tempera- ture in 31.9% Ni alloys annealed at 400°C(AL series) and at 800°C(AH series). The solid lines are the calculated spectra by using the distribution function P(H) shown in figure 2.
JOURNAL DE PHYSIQUE
Colloque C2, supplément au n° 3, Tome 40, mars 1979, page C2-165
Résumé.- Nous avons mesuré l'effet Mossbauer du s7Fe dans des alliages Fej_j.Nij.du type de l'invar.
La fonction de répartition des champs hyperfins magnétiques P(#) pour les échantillons recuits à 400° C se déplace vers les grandes valeurs de H par rapport à ceux des échantillons recuits à 800°C.
Ceci suggère l'existence d'un ordre à courte distance dans les échantillons recuits à 400°C.
Abstract.- The Mossbauer effect of S7Fe was measured in Fej__Ni alloys in invar region. The distri- bution functions P(H) of internal magnetic field for the samples annealed at 400°C are shifted to higher values of H than those annealed at 800°C. This fact gives an evidence for a short-range or- der in the samples annealed at 400°C.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979258
JOURNAL DE PHYSIQUE
Fig. 2 : Distribution function P(H) of the internal magnetic field obtained by least-squares fitting from the Mi;ssbauer spectra. The solid lines show the distribution for AL series of samples annealed at 400'~ and the dotted lines for AH series annealed at 800'~.
The lines of Miissbauer spectra observed in AL and BL series of samples which were annealed at 40O0C were obviously narrower and more separate from each
If a short-range order of A13Ti or CuoAu type developes in the samples annealed at 40O0c, the num- ber of the nearest-neighbor nickel atoms around an iron atom increases. The increase of the number of the nearest-neighbor nickel atoms enhances the ato- mic moment of the iron atom in invar region /1,2/
and consequently the distribution of internal magne- tic field is shifted to higher magnetic field. The dependence of P(H) on the thermal treatment is thus considered to indicate that there is a short-range order in the alloys annealed at 400'~.
The authors wish to thank Mr. N. Itano for his assistance in measurements and preparations of the samples.
References
/ 1 / Tomiyoshi, S., Yamamoto, H. and Watanabe, H., J. Phys. Soc. J a p a n s (1971) 1605.
/ 2 / Shiga, M., Maeda, Y. and Nakamura, Y., J. Phys.
Soc. Japan
2
(1974) 363./3/ Veeraraghavan, V.G., Eagen, C.F., Harrison, H.R.
and Winchell, P.G., J. Appl. Phys.
47
(1976)4768.
other thanthose AH and BH series which were annealed /4/ Window, B., J. Phys. E : Sci. Instrum.
5
(1971)401.
at 800'~ as shown in figure 1 . The functions P(H) obtained by least-squares fitting from the spectra are shown in figure 2 and figure 3. The solid lines for the samples annealed at 400°C are shifted to higher magnetic field than the dotted lines for those annealed at 800°C.
Fig. 3, : Distribution function P(H) of the internal magnetic field obtained by least-squares fitting from the M%sbauer spectra. The solid lines show the distribution for BL series of samples annealed at 400'~ and the dotted Lines for BH series annealed at 800°C.
