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On the influence of point defects on the kondo-effect in Zn-Mn
Solid State Communications,Vol. 9, pp. 1171—1173, 1971 .Pergamon Press.
Printed in Great Britain
ON THE INFLUENCE OF POINT DEFECTS ON THE KONDO-EFFECT IN Zn—Mn E.F. Wassermann, H. Falke and H.P. Jablonski II. Physikalisches Institut der RWTH, 51 Aachen, Germany (Received 30 April 1971 by G.E. Leibfried)
After isochronal annealing (150—400°C)remarkable changes in the T~-depression, the Kondo-slope, and residual resistivity ratio are observed in cold-rolled Zn- 20p.p.m. Mn samples. The 24 hr 400°-sample -sample shows no change in the Kondo—log T behaviour after 3 MeV electron irradiation at 6°K.The results indicate that point defects do not change the temperature dependent spin flip scattering amplitude. 10
IN A RECENT paper’ we reported about the occurence of superconductivity and Kondo-effect in very dilute Zn—Mn alloys. For an alloy containing nominally 15p.p.m. Mn it was shown that both the transition temperature and the resistance anomaly (expressed in 3p/c3 lnT) strongly depend on the metallurgical pretreatment of the samples. We started with a specimen which had been quenched from melt (72hr, 700°C)in water and then coldrolled (98%). This alloy showed a strong depression of the superconducting transition temperature A T = —0.35°K,the value being consistent with the high dT~/dc 300°K/at.% as found by Boato et a!. for the Zn—Mn system. Isochronal annealing of the sample in a 150 torr Argon atmosphere at tempera-
(o’b~~niIs]
8 6
3InT ~ Kondo-slope
2 0 0.6 N
~ ~TC 0.2
____________________________
-‘-j
tures between 150 and 400°Clead to a reduction Df the T,, -depression. The Kondo-slope ap/a lnT, being highest for the cold-rolled sample, was also reduced during the annealing procedure and finally nearly vanished after annealing for 24 hr at 400°C. In this paper we report about a more detailed analysis of these phenomena for a new sample series with 20p.p.m. Mn. The Mn-concentration has been by two methods, atomicdetermined absorption-, and independent mass-spectrometry.3 Parallel to the alloys a series of reference Znspecimen is given the same treatment as the 20 p.p.m. samples so that after measurement of the resistivity in the same temperature range 1171
~ ~ r~2
___~~d:~t~tY rU0T Ratio ~.2
3 c~Id-,III.d24h150
2~h2OO 2th 260’ 241,300’ 341, 400
j,rodj~t,d
FIG. 1. Change of Kondo-slope (c3p/alnT), superconducting transition temperature (— A T,, = T~0 T~)11~Y and =residual (r4.2 = R4~2/R393 T2ulOy —resistivity r ~°~) afterratio progressive isochronal 4.2 Ar ~42 annealing of a cold-rolled Zn + 2Op.p.m. Mn alloy. After annealing at 400°Cthe sample labelled ‘irradiated’ has been bombarded at 6°Kwith 3MeV electrons for 24 hr, warmed up to room-temperature, and then remeasured at low temperatures. —
1172
POINT DEFECTS ON THE KONDO-EFFECT IN Zn—Mn
Vol. 9, No. 13
(0.3—80°K)proper deduction of the matrix effects is possible.
To see if point defects are also responsible for the remarkable change in Kondo-slope in our
Figure 1 shows the changes in residual resis3 mT during isotivity ratio at 4.2K, ATE, and dp/ chronal annealing of the 20 p.p.m. alloy. The be-
alloys we introduce interstitials and vacancies into the 24 hr 400°C-sampleby electron irradiation. The irradiation is carried out for 24 hr in a liquid helium flow cryostat at about 6°Kwith 3MeV elec-
haviour is similar to that of the 15p.p.m. sample reported earlier. 1 There is a drop in the residual resistivity ratio after the first annealing step at
trons. The average damage rate is about 15n~cm/hr. This corresponds to an increase in the residual resistivity at 4.2K from 29 n[~cm to about 400 nIl cm.
150°C.This reduction is equally observed for the pure Zn-matrix (re), the alloy (r~0Y )~ and also the difference A T~0y TølOy r42 We believe 4.2 4.2
After warming up to room temperature and transfer
that annealing of lattice defects produced by the rolling process as well as recrystallization lead to this recovery. The decrease in r 4~~ and T~oY between 300 and 400°C can be ascribed to the
value is left.
=
—
~‘.
into the He3 -cryostat an increase in residual re-
sistivity ratio of about 6% compared to the starting
30
1—~i•~L-j
vanishing and furtherofannealing the strongofrecrystallization lattice defects. For texture Zn— Mn alloys the rolling texture is equal to the recrystall~atinn fe~~ure, both do notofchange up beto 4 The constancy A r~°Y 300°Cannealing. tween 150 and 400°C indicates that the Mn stays in solution during the total annealing procedure. On the other hand, the T~-depression shows a linear reduction with rising annealing temperature. This behaviour could be explained by progressive precipitation of the Mn. However, looking at the combined effects, residual resistivity ratio, Kondoslope, and susceptibility,5 it is likely that more complicated processes like changes in the Mndistribution or formation of superconducting shorts should also be considered. The Kondo-slope shows equivalent behaviour up to 300°Cannealing, although the relative reduction is much less than in the case of ATE. A pronounced drop is observed after annealing at 400°C. Since r~ and T~0y show an equal drop in the same region while A r~0y stays constant, we suspect that the drop in the Kondo-slope is attributed to a property of the matrix rather than being due to precipitation of the Mn-impurities, The idea that point detects, sitting close to magnetic impurities lead to an enhancement of the resistance anomaly, was recently pointed out in a paper by ~orn6 to explain his measurements of the Kondo-effect on heavily disordered thin films.
I
r.tQcml 25
I
I
I
I
Zn+2oppmMn
a S.
-
20
.f~
cOld-rOIl.d
•..f....
C .
-
......
-
..
10 ~
....~
5
-
-
‘n”°~ ~
0
I
0.3 0.5
400•C I
1
2
5
I
K
20
II
40 60
ioo°p~
Temperature FIG. 2. Difference in electrical resistivity Ap = Paiioy PZn per unit concentration versus temperature for a Zn + 2Op.p.m. Mn alloy in three different metallurgical states. The large error bars in the temperature range, where deviations from the Matthiessen-rule occur, indicate the estimated uncertainty after subtracting the Zn-matrixvalues.
Figure 2 shows the A,o/c values as a function of temperature for the same 2Op.p.m. Mn-sample in the cold-rolled, annealed 24 hr 400°C,and electron irradiated state. Within experimental accuracy there is no change in Kondo-slope before and after electron irradiation. There is only a small increase in T (see also Fig. 1). From this we conclude that the healing out of point defects is obviously not responsible for the sharp drop in 3p/~ lnT between 300 and 400°C annealing. Recently Kraut and
Vol. 9, No. 13
POINT DEFECTS ON THE KONDO-EFFECT IN Zn—Mn
Wollenberger7 showed that the Kondo-resistivity anomaly in a Cu—100 p.p.m. Mn alloy is negligibly changed by intec~t.itiaJsclosely attached to the Mn-atoms. Taking also these results7 into consideration we further conclude that no enhancement of the temperature dependent spin flip scattering amplitude is achieved if pairs of impurity atoms and point defects are formed. Theoretical calculations by Everts and Keller* also indicate that nonmagnetic impurities do not change the mT-behaviour considerably.
1.
1173
We therefore suspect that the drop in Kondoslope has other origins, probably the annealing of dislocations anchored at the magnetic impurities combined with the vanishing of the rolling-texture. Acknowledgements The authors thank Prof. Dr. W. Schilling, KFA Julich, for making the irradiatior experiment possible. We are indebted to Dr. Rau and the staff of the irradiation group for the technical performance of the irradiation experiment. Many thanks also to Dr. H. Wollenberger for submittance of unpuhlished data on Cu—Mn. —
REFERENCES WASSERMANN E.F., FALKE H. and JABLONSKI H.P., Proc. 12th mt. Conf. on Low Temp. Phys., Kyoto, 1970, (in press).
2. 3.
5.
BOATO G., GALLINARO G. and RIZZUTO C., Phys. Rev. 148, 353 (1966). Mass spectrometry by Fulmer Research Institute, Stoke Poges, Buckinghamshire, England. Reinvestigation of the 15 p.p.m. sample discussed in reference 1 revealed a true content of 10 p.p.m. Mn. WASSERMANN G. and GREWEN J., Texturen metallischer Werkstoffe, Springer, Berlin, 1962, p. 258. SCHLABITZ W., WASSERMANN E.F. and FALKE H., Z. Physik, to be published.
6.
KORN D., Z. Physik 238, 275 (1970).
7.
KRAUT A. and WOLLENBERGER H., Solid Stale Commun. 9, 1169 (1971).
8.
EVERTS H.U: and KELLER
4.
J.,
Z. Phys. 240, 281 (1970).
Nach isochronem Anlassen (150—400°C)kaltgewalzter Zn-20 p.p.m. Mn Proben treten beträchtliche Anderungen in det T~-Absenkung,. im Kondo-Anstieg und im Restwiderstandsverhältnis auf. Die 24 hr bei 400° angelassene Probe zeigt nach Bestrahlung bei 6°Kmit 3MeV Elektronen keine Anderung im Kondo- lnT- Verhalten. Die Ergenbnisse deuten darauf hin, daB Punktdefekte keinen wesentlichen EinfluB auf die temperaturabhängige Spinflip-Streuamplitude haben.
Printed in Great Britain
ON THE INFLUENCE OF POINT DEFECTS ON THE KONDO-EFFECT IN Zn—Mn E.F. Wassermann, H. Falke and H.P. Jablonski II. Physikalisches Institut der RWTH, 51 Aachen, Germany (Received 30 April 1971 by G.E. Leibfried)
After isochronal annealing (150—400°C)remarkable changes in the T~-depression, the Kondo-slope, and residual resistivity ratio are observed in cold-rolled Zn- 20p.p.m. Mn samples. The 24 hr 400°-sample -sample shows no change in the Kondo—log T behaviour after 3 MeV electron irradiation at 6°K.The results indicate that point defects do not change the temperature dependent spin flip scattering amplitude. 10
IN A RECENT paper’ we reported about the occurence of superconductivity and Kondo-effect in very dilute Zn—Mn alloys. For an alloy containing nominally 15p.p.m. Mn it was shown that both the transition temperature and the resistance anomaly (expressed in 3p/c3 lnT) strongly depend on the metallurgical pretreatment of the samples. We started with a specimen which had been quenched from melt (72hr, 700°C)in water and then coldrolled (98%). This alloy showed a strong depression of the superconducting transition temperature A T = —0.35°K,the value being consistent with the high dT~/dc 300°K/at.% as found by Boato et a!. for the Zn—Mn system. Isochronal annealing of the sample in a 150 torr Argon atmosphere at tempera-
(o’b~~niIs]
8 6
3InT ~ Kondo-slope
2 0 0.6 N
~ ~TC 0.2
____________________________
-‘-j
tures between 150 and 400°Clead to a reduction Df the T,, -depression. The Kondo-slope ap/a lnT, being highest for the cold-rolled sample, was also reduced during the annealing procedure and finally nearly vanished after annealing for 24 hr at 400°C. In this paper we report about a more detailed analysis of these phenomena for a new sample series with 20p.p.m. Mn. The Mn-concentration has been by two methods, atomicdetermined absorption-, and independent mass-spectrometry.3 Parallel to the alloys a series of reference Znspecimen is given the same treatment as the 20 p.p.m. samples so that after measurement of the resistivity in the same temperature range 1171
~ ~ r~2
___~~d:~t~tY rU0T Ratio ~.2
3 c~Id-,III.d24h150
2~h2OO 2th 260’ 241,300’ 341, 400
j,rodj~t,d
FIG. 1. Change of Kondo-slope (c3p/alnT), superconducting transition temperature (— A T,, = T~0 T~)11~Y and =residual (r4.2 = R4~2/R393 T2ulOy —resistivity r ~°~) afterratio progressive isochronal 4.2 Ar ~42 annealing of a cold-rolled Zn + 2Op.p.m. Mn alloy. After annealing at 400°Cthe sample labelled ‘irradiated’ has been bombarded at 6°Kwith 3MeV electrons for 24 hr, warmed up to room-temperature, and then remeasured at low temperatures. —
1172
POINT DEFECTS ON THE KONDO-EFFECT IN Zn—Mn
Vol. 9, No. 13
(0.3—80°K)proper deduction of the matrix effects is possible.
To see if point defects are also responsible for the remarkable change in Kondo-slope in our
Figure 1 shows the changes in residual resis3 mT during isotivity ratio at 4.2K, ATE, and dp/ chronal annealing of the 20 p.p.m. alloy. The be-
alloys we introduce interstitials and vacancies into the 24 hr 400°C-sampleby electron irradiation. The irradiation is carried out for 24 hr in a liquid helium flow cryostat at about 6°Kwith 3MeV elec-
haviour is similar to that of the 15p.p.m. sample reported earlier. 1 There is a drop in the residual resistivity ratio after the first annealing step at
trons. The average damage rate is about 15n~cm/hr. This corresponds to an increase in the residual resistivity at 4.2K from 29 n[~cm to about 400 nIl cm.
150°C.This reduction is equally observed for the pure Zn-matrix (re), the alloy (r~0Y )~ and also the difference A T~0y TølOy r42 We believe 4.2 4.2
After warming up to room temperature and transfer
that annealing of lattice defects produced by the rolling process as well as recrystallization lead to this recovery. The decrease in r 4~~ and T~oY between 300 and 400°C can be ascribed to the
value is left.
=
—
~‘.
into the He3 -cryostat an increase in residual re-
sistivity ratio of about 6% compared to the starting
30
1—~i•~L-j
vanishing and furtherofannealing the strongofrecrystallization lattice defects. For texture Zn— Mn alloys the rolling texture is equal to the recrystall~atinn fe~~ure, both do notofchange up beto 4 The constancy A r~°Y 300°Cannealing. tween 150 and 400°C indicates that the Mn stays in solution during the total annealing procedure. On the other hand, the T~-depression shows a linear reduction with rising annealing temperature. This behaviour could be explained by progressive precipitation of the Mn. However, looking at the combined effects, residual resistivity ratio, Kondoslope, and susceptibility,5 it is likely that more complicated processes like changes in the Mndistribution or formation of superconducting shorts should also be considered. The Kondo-slope shows equivalent behaviour up to 300°Cannealing, although the relative reduction is much less than in the case of ATE. A pronounced drop is observed after annealing at 400°C. Since r~ and T~0y show an equal drop in the same region while A r~0y stays constant, we suspect that the drop in the Kondo-slope is attributed to a property of the matrix rather than being due to precipitation of the Mn-impurities, The idea that point detects, sitting close to magnetic impurities lead to an enhancement of the resistance anomaly, was recently pointed out in a paper by ~orn6 to explain his measurements of the Kondo-effect on heavily disordered thin films.
I
r.tQcml 25
I
I
I
I
Zn+2oppmMn
a S.
-
20
.f~
cOld-rOIl.d
•..f....
C .
-
......
-
..
10 ~
....~
5
-
-
‘n”°~ ~
0
I
0.3 0.5
400•C I
1
2
5
I
K
20
II
40 60
ioo°p~
Temperature FIG. 2. Difference in electrical resistivity Ap = Paiioy PZn per unit concentration versus temperature for a Zn + 2Op.p.m. Mn alloy in three different metallurgical states. The large error bars in the temperature range, where deviations from the Matthiessen-rule occur, indicate the estimated uncertainty after subtracting the Zn-matrixvalues.
Figure 2 shows the A,o/c values as a function of temperature for the same 2Op.p.m. Mn-sample in the cold-rolled, annealed 24 hr 400°C,and electron irradiated state. Within experimental accuracy there is no change in Kondo-slope before and after electron irradiation. There is only a small increase in T (see also Fig. 1). From this we conclude that the healing out of point defects is obviously not responsible for the sharp drop in 3p/~ lnT between 300 and 400°C annealing. Recently Kraut and
Vol. 9, No. 13
POINT DEFECTS ON THE KONDO-EFFECT IN Zn—Mn
Wollenberger7 showed that the Kondo-resistivity anomaly in a Cu—100 p.p.m. Mn alloy is negligibly changed by intec~t.itiaJsclosely attached to the Mn-atoms. Taking also these results7 into consideration we further conclude that no enhancement of the temperature dependent spin flip scattering amplitude is achieved if pairs of impurity atoms and point defects are formed. Theoretical calculations by Everts and Keller* also indicate that nonmagnetic impurities do not change the mT-behaviour considerably.
1.
1173
We therefore suspect that the drop in Kondoslope has other origins, probably the annealing of dislocations anchored at the magnetic impurities combined with the vanishing of the rolling-texture. Acknowledgements The authors thank Prof. Dr. W. Schilling, KFA Julich, for making the irradiatior experiment possible. We are indebted to Dr. Rau and the staff of the irradiation group for the technical performance of the irradiation experiment. Many thanks also to Dr. H. Wollenberger for submittance of unpuhlished data on Cu—Mn. —
REFERENCES WASSERMANN E.F., FALKE H. and JABLONSKI H.P., Proc. 12th mt. Conf. on Low Temp. Phys., Kyoto, 1970, (in press).
2. 3.
5.
BOATO G., GALLINARO G. and RIZZUTO C., Phys. Rev. 148, 353 (1966). Mass spectrometry by Fulmer Research Institute, Stoke Poges, Buckinghamshire, England. Reinvestigation of the 15 p.p.m. sample discussed in reference 1 revealed a true content of 10 p.p.m. Mn. WASSERMANN G. and GREWEN J., Texturen metallischer Werkstoffe, Springer, Berlin, 1962, p. 258. SCHLABITZ W., WASSERMANN E.F. and FALKE H., Z. Physik, to be published.
6.
KORN D., Z. Physik 238, 275 (1970).
7.
KRAUT A. and WOLLENBERGER H., Solid Stale Commun. 9, 1169 (1971).
8.
EVERTS H.U: and KELLER
4.
J.,
Z. Phys. 240, 281 (1970).
Nach isochronem Anlassen (150—400°C)kaltgewalzter Zn-20 p.p.m. Mn Proben treten beträchtliche Anderungen in det T~-Absenkung,. im Kondo-Anstieg und im Restwiderstandsverhältnis auf. Die 24 hr bei 400° angelassene Probe zeigt nach Bestrahlung bei 6°Kmit 3MeV Elektronen keine Anderung im Kondo- lnT- Verhalten. Die Ergenbnisse deuten darauf hin, daB Punktdefekte keinen wesentlichen EinfluB auf die temperaturabhängige Spinflip-Streuamplitude haben.