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119Sn Mössbauer study of CexLa1−xNiSn
ELSEVIER
Physica B 206 & 207 (1995) 832-833
1195n M6ssbauer study of CexLal_xNiSn a
•
bc
M. Polikarpov ~, V.M. Cherepanov , M.A. Chuev a'*, S.S. Yakimov a, F.G. Ahev ' , R.V. Scolozdra a "Russian Scientific Centre 'Kurchatov Institute', 123182, Moscow, Russian Federation ~Facultad de Ciencias, Universidad Autonoma de Madrid, 28049, Madrid, Spain ~Physics Department, Moscow State University, 117234, Moscow, Russian Federation dL'vov State University, 290022, L'vov, Ukraine
Abstract
I]9Sn Mossbauer spectra of the CexLa~ xNiSn compounds with x = 0, 0.85 and 1 have been measured at 300K and 5 K. Spectral analysis within hyperfine energy distribution and sharpening methods reveals relaxation broadening at 5 K for all the compounds, which indicates the presence of magnetic fluctuations at low temperatures. Relaxation broadening is the most pronounced in the spectrum of Ce0.85La0.~sNiSn.
I. Introduction
In recent years, the Kondo semiconductor CeLaNiSn has been actively studied in order to clarify the mechanism of the quasi-gap formation below 6 K, which is attributed to coherence effects in the Kondo lattice. The gap properties are supposed to be related to strong magnetic correlations [1]. LaNiSn and Ce0.85La0 15NiSn are the normal and Kondo metals. As was suggested in Ref. [2], the substitution of non-magnetic La atoms for Ce dilutes heavy-hole gas resulting in the transformation of the non-magnetic CeNiSn ground state into a magnetic one. The idea has been verified using 1195n Mossbauer spectroscopy [3], however, no signs of magnetic order were observed in Ceo.gLao lNiSn down to 1.5 K. In this paper, 119Sn Mossbauer spectra of CexLa~_xNiSn with x = 0 , 0.85 and 1 have been measured at 300K and 5 K to separate features
* Corresponding author.
inherent to the compounds with various electronic ground states.
2. Results and discussion
The samples under investigation were prepared by the conventional argon arc method, t19Sn Mossbauer measurements were performed at 300 K and 5 K using an ordinary constant acceleration spectrometer with CaSnO 3 as a source. Mossbauer spectra of the CexLa l_xNiSn compounds are shown in Fig. 1. Each spectrum looks like a non-resolved doublet of broad lines, the 5 K spectra being broader than those at 300 K. In order to identify a more detailed structure of the spectra two 'modelless' methods were applied including the search for the hyperfine energy distribution [4] in its improved version [5] and the sharpening method for Mossbauer spectra [6]. In the first method, a spectrum is regarded as the superposition of elementary components (single Lorentzian lines in our case), weighted factors of which are easily found using the linear mean square fitting
0921-4526/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0921-4526(94)00599-0
M. Polikarpov et al. / Physica B 206 & 207 (1995) 832-833
LaNiSn
Ce.asLa.,sNiSn
CeNiSn
T:300 K ~
"z' ; ' 2 ' ~ ' ;-'z'
Velocity, mm/s
; ' ~ ' ; ' ;'2'
Velocity, mm/s
; ' ~ ' ~ '
Velocity, mra/s
Fig. 1. 1195n Mossbauer spectra (squares) and corresponding hyperfine distributions (diagrams) of CexLaI ~NiSn.
procedure with adjustable restrictions on the smoothness of the distribution obtained. The hyperfine energy distributions are shown in Fig. 1 above the
Ce.esLa.lsNiSn
SHARP3
•
AFt=0.4
,.
SHARP3
~
corresponding experimental spectra. Clearly, the distributions allow qualitative conclusions about the evolution of the spectra with temperature and composition to be made. So, at least for Ce0 ssLa0 15NiSn, we can definitely conclude that the short-range magnetic correlations present at 5 K, which contrasts with the results of Kobayashi et al. [3]. Moreover, the distributions reveal not only the total broadening but also the presence of long Lorentzian wings in the spectra taken at 5 K for all the compounds. The latter is strong evidence for the existence of a relaxation process in the compounds at 5 K, which may be attributed to appearance of magnetic fluctuations at low temperatures. The second (sharpening) method used for the new representation of experimental spectra results in the effective narrowing of Mossbauer lines in the source and absorber, transforming the Lorentzian lineshape to the Lorentizian power one. In addition, the method allows an estimate of the extra Lorentzian absorber linewidth AFL to be made (see Fig. 2) which may be due to the presence of a dynamical process in the system studied in Ref. [6]. From the analysis of the 5 K spectra using the sharpening procedure, the average values of the effective magnetic fluctuations frequencies are evaluated to be 30 MHz, 50 MHz and 33 MHz for the Ce/La l_xNiSn compounds with x = 0, 0.85 and 1, respectively. In conclusion, the analysis of 1199n Mossbauer spectra of CexLal_xNiSn using the hyperfine energy distribution and sharpening methods give evidence for the presence of magnetic fluctuations at 5 K in all of the compounds. Short-range magnetic correlations are supposed to be present around 5 K in Ce018sLao 15NiSn.
• • AFt~ 0
•
•
,~¢
EXP
833
.
References
•
f
Velocity, m m / s Fig. 2. Experimental (EXP) and sharpened (SHARP3) spectra of CeHsLao.15NiSn.
[1] T. Takabatake, M. Nagasawa, H. Fujii et al., Phys. Rev. (B) 45 (1992) 5740. [2] S. Doniach and P. Fazekas, Philos. Mag. (B) 65 (1992) 1171. [3] H. Kobayashi, F.E. Wagner, G.M. Kalvius and T. Takabatake, Hyperline Interactions (1994) (in press). [4] J. Hesse and A. Rubartsch, J. Phys. (E) 7 (1974) 526. [5] A.M. Afanas'ev and M.A. Chuev, unpublished. [6] A.M. Afanas'ev and E.Yu. Tsymbal, Hyperfine Interactions 62 (1990) 325.
Physica B 206 & 207 (1995) 832-833
1195n M6ssbauer study of CexLal_xNiSn a
•
bc
M. Polikarpov ~, V.M. Cherepanov , M.A. Chuev a'*, S.S. Yakimov a, F.G. Ahev ' , R.V. Scolozdra a "Russian Scientific Centre 'Kurchatov Institute', 123182, Moscow, Russian Federation ~Facultad de Ciencias, Universidad Autonoma de Madrid, 28049, Madrid, Spain ~Physics Department, Moscow State University, 117234, Moscow, Russian Federation dL'vov State University, 290022, L'vov, Ukraine
Abstract
I]9Sn Mossbauer spectra of the CexLa~ xNiSn compounds with x = 0, 0.85 and 1 have been measured at 300K and 5 K. Spectral analysis within hyperfine energy distribution and sharpening methods reveals relaxation broadening at 5 K for all the compounds, which indicates the presence of magnetic fluctuations at low temperatures. Relaxation broadening is the most pronounced in the spectrum of Ce0.85La0.~sNiSn.
I. Introduction
In recent years, the Kondo semiconductor CeLaNiSn has been actively studied in order to clarify the mechanism of the quasi-gap formation below 6 K, which is attributed to coherence effects in the Kondo lattice. The gap properties are supposed to be related to strong magnetic correlations [1]. LaNiSn and Ce0.85La0 15NiSn are the normal and Kondo metals. As was suggested in Ref. [2], the substitution of non-magnetic La atoms for Ce dilutes heavy-hole gas resulting in the transformation of the non-magnetic CeNiSn ground state into a magnetic one. The idea has been verified using 1195n Mossbauer spectroscopy [3], however, no signs of magnetic order were observed in Ceo.gLao lNiSn down to 1.5 K. In this paper, 119Sn Mossbauer spectra of CexLa~_xNiSn with x = 0 , 0.85 and 1 have been measured at 300K and 5 K to separate features
* Corresponding author.
inherent to the compounds with various electronic ground states.
2. Results and discussion
The samples under investigation were prepared by the conventional argon arc method, t19Sn Mossbauer measurements were performed at 300 K and 5 K using an ordinary constant acceleration spectrometer with CaSnO 3 as a source. Mossbauer spectra of the CexLa l_xNiSn compounds are shown in Fig. 1. Each spectrum looks like a non-resolved doublet of broad lines, the 5 K spectra being broader than those at 300 K. In order to identify a more detailed structure of the spectra two 'modelless' methods were applied including the search for the hyperfine energy distribution [4] in its improved version [5] and the sharpening method for Mossbauer spectra [6]. In the first method, a spectrum is regarded as the superposition of elementary components (single Lorentzian lines in our case), weighted factors of which are easily found using the linear mean square fitting
0921-4526/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0921-4526(94)00599-0
M. Polikarpov et al. / Physica B 206 & 207 (1995) 832-833
LaNiSn
Ce.asLa.,sNiSn
CeNiSn
T:300 K ~
"z' ; ' 2 ' ~ ' ;-'z'
Velocity, mm/s
; ' ~ ' ; ' ;'2'
Velocity, mm/s
; ' ~ ' ~ '
Velocity, mra/s
Fig. 1. 1195n Mossbauer spectra (squares) and corresponding hyperfine distributions (diagrams) of CexLaI ~NiSn.
procedure with adjustable restrictions on the smoothness of the distribution obtained. The hyperfine energy distributions are shown in Fig. 1 above the
Ce.esLa.lsNiSn
SHARP3
•
AFt=0.4
,.
SHARP3
~
corresponding experimental spectra. Clearly, the distributions allow qualitative conclusions about the evolution of the spectra with temperature and composition to be made. So, at least for Ce0 ssLa0 15NiSn, we can definitely conclude that the short-range magnetic correlations present at 5 K, which contrasts with the results of Kobayashi et al. [3]. Moreover, the distributions reveal not only the total broadening but also the presence of long Lorentzian wings in the spectra taken at 5 K for all the compounds. The latter is strong evidence for the existence of a relaxation process in the compounds at 5 K, which may be attributed to appearance of magnetic fluctuations at low temperatures. The second (sharpening) method used for the new representation of experimental spectra results in the effective narrowing of Mossbauer lines in the source and absorber, transforming the Lorentzian lineshape to the Lorentizian power one. In addition, the method allows an estimate of the extra Lorentzian absorber linewidth AFL to be made (see Fig. 2) which may be due to the presence of a dynamical process in the system studied in Ref. [6]. From the analysis of the 5 K spectra using the sharpening procedure, the average values of the effective magnetic fluctuations frequencies are evaluated to be 30 MHz, 50 MHz and 33 MHz for the Ce/La l_xNiSn compounds with x = 0, 0.85 and 1, respectively. In conclusion, the analysis of 1199n Mossbauer spectra of CexLal_xNiSn using the hyperfine energy distribution and sharpening methods give evidence for the presence of magnetic fluctuations at 5 K in all of the compounds. Short-range magnetic correlations are supposed to be present around 5 K in Ce018sLao 15NiSn.
• • AFt~ 0
•
•
,~¢
EXP
833
.
References
•
f
Velocity, m m / s Fig. 2. Experimental (EXP) and sharpened (SHARP3) spectra of CeHsLao.15NiSn.
[1] T. Takabatake, M. Nagasawa, H. Fujii et al., Phys. Rev. (B) 45 (1992) 5740. [2] S. Doniach and P. Fazekas, Philos. Mag. (B) 65 (1992) 1171. [3] H. Kobayashi, F.E. Wagner, G.M. Kalvius and T. Takabatake, Hyperline Interactions (1994) (in press). [4] J. Hesse and A. Rubartsch, J. Phys. (E) 7 (1974) 526. [5] A.M. Afanas'ev and M.A. Chuev, unpublished. [6] A.M. Afanas'ev and E.Yu. Tsymbal, Hyperfine Interactions 62 (1990) 325.