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Magnetic ordering versus spincompensation of iron in copper-gold alloys
Volume
26A,
number
10
PHYSICS
LETTERS
for the x = 0.05 sample. The values of the magnetic moment per Fe atom in table 1 have been obtained from the ~(0, 0) values. Extrapolation to zero Fe content seems to indicate an upper limit for the effective Fe moment at about 40 PH. Extension of the experiments to lower Fe concentrations to other Ni concentrations and to other impurities (e.g. Co) is in progress.
8 April
1968
We gratefully acknowledge the helpful assistance of S. Proost and H. Schinkel in some of the experiments.
haviour
References 1. F. R.De Boer. Phys. Letters
C. J. Schinkel and J. Biesterbos, 25A (1967) 606.
*****
MAGNETIC
ORDERING VERSUS SPINCOMPENSATION IN COPPER-GOLD ALLOYS
OF
IRON
W. M.STAR Kamerlingh
Onnes
Laboratoyi,
Received
Leiden,
4 March
The Netherlands
1968
The Kondo temperature of Fe in Cu-Au alloys decreases when the Au-concentration of the host increases. Magnetic ordering makes a resistance maximum when the Kondo temperature becomes lower than the ordering temperature of the uncompensated spin.
Present theory suggests [l] that when a localized magnetic moment is formed the Kondo temperature TK X (EF /k) exp (- l/p IJ 1) shifts from a very high value of order EF/~ to below 1°K. This is mainly due to a decrease in the s-d exchange constant IJ / . Iron in copper is on the edge of having a magnetic moment and this is reflected in the relatively high TK of about 16’K [2]. Iron in gold probably has a TK below 1°K. The density of states per atom p obtained from electronic specific heat is in gold slightly higher than in copper. The lower value of TK for iron in gold must be caused by a smaller o / J 1, and thus a smaller /JI, this in turn coming from a narrowing and shifting of the virtual bound state with respect to the Fermi level when the Fermi energy decreases [3]. We have measured the electrical resistivity of iron in Cu-Au solvent alloys in order to observe in more detail the shift of TK and the effect of magnetic ordering in a temperature region where effects of spincompensation are also important. In this letter we present results of 0.15 at. % Fe in Cu (I), Cu i Au $ (II), Cu $ Au i (III), Cu $ Au : (IV), Cu + Au ; (V), Cu + Au ; (VI) and Au (VII) (see fig. 1; alloy I has been left out), thus covering with equal spacings the whole copper-gold system. 502
Applying the procedure of ref. 4, which gives TK = lOoK for Cu-Fe, we estimate TK N 4’K for alloy II and TK = 1°K for alloy III. In the other alloys interactions between Fe spins become too important to make possible any reasonable guess. Further discussion will be given in a future paper when results on the same Cu-Au alloys with lower Fe-concentration are available. Anyway, the qualitative aspects of the TK shift are clear. Going towards copper from the gold rich end we see the temperature of the resistivity maximum decreasing and omax - omin increasing. Two effects are responsible here. First the large electron scattering by the host alloy which reduces the interactions between the magnetic moments [5]. Second the TK shift. In general one can say that magnetic ordering becomes important (resistivity maximum) when the concentration of magnetic atoms is so high that the ordering temperature is above the Kondo temperature, or when the concentration is so high that not enough conduction electrons are available to compensate all impurity spins [S] and this incomplete compensation gives the inter impurity interactions its chance. The above argument could explain the resis-
Volume 26A, number 10
8.60
PHYSICS LETTERS
t e m p e r a t u r e tail of the r e s i s t a n c e a n o m a l y s u g g e s t s a T K of o r d e r l ° K and this m i g h t explain the r e l u c t a n c e of Zn-Mn to show a r e s i s t a n c e m a x i m u m . P r o b a b l y Cu ~ Au ~ - F e is a c o m a r a b l e type of alloy. E x t r a p o l a t i o n of our c o n c l u s i o n s toward p h ase C u - Z n a l l o y s with F e i m p u r i t y [10] s u g g e s t s a T K w e l l , a b o v e 30°K and probably much h i g h e r on the zinc r i c h end of the phase. If F e w e r e b e t t e r so l u b l e in C u - Z n one might expect A u - V - l i k e b e h a v i o u r . This conclusion d i f f e r s from Caplin's. E x t r a p o l a t i o n t o w ar d s A u P d - F e s u g g e s t s a f u r t h e r l o w e r i n g of TK r e l a t i v e to A u F e. T h i s point is being i n v e s t i g a t e d , a s is the effect of the T K shift on s p e c i f i c heat and m a g n e t i c s u s ceptibility. F i n al l y we want to point out a r a t h e r s t r i k i n g r e s e m b l a n c e between our r e s u l t s and those of S a r a c h i k e.a. [11] on F e in NbMo and MoRe alloys. The s i m i l a r r e s u l t s s u g g e s t a s i m i l a r explanation.
ZE
12.34 0.0t00
~P. cm
p.Qcm
"lTr
3.30
7 . 4 . 1 l-
8April 1968
9P--- ~EE
This work is p a r t of the r esear ,ch p r o g r a m of the "Stichting F . O . M . ", and has been spons o r e d by "Z. W. O." and "T. N. O.". 1.35 0
T
P
'tO
15
OK
20
Fig. 1. Resistivity of Cu-Au alloys with 0.15 at. % Fe. The numbers are explained in the text. The scale is the same for all alloys. Lattice resistivity has not been subtracted. tivity m a x i m u m o b s e r v e d by S v e n s s o n [7] in cold w o r k e d C u F e a l l o y s with about 1% F e and m o r e , although the low s o l i d solubility of F e in Cu c o m p l i c a t e s the situation and one would h a v e to suppo s e that cold work b r i n g s p r e c i p i t a t e d F e again into solution. T h e r e s i s t i v i t y m a x i m u m in Cu-15 at. % Au - 0 . 5 at. % F e as o b s e r v e d by Cole s [8] is u n d e r s t o o d in a s i m i l a r way. We think that Zn-Mn is a n o t h e r good e x a m p l e of an alloy w h e r e spin c o m p e n s a t i o n c o m p l i c a t e s the m a g n e t i c o r d e r i n g p r o c e s s [9]. The high
References 1. J.R. Sehrieffer, d. Appl. Phys. 38 (1967) 1143. 2. M.D. Daybell and W. A. Steyert, Phys. Rev. Letters 18 (1967) 398. 3. J. Friedel, Nuovo Cimento Suppl. 7 (1958) 287. 4. M. D. Daybell and W. A. Steyert, Rev. Mod. Phys., to be published. 5. A.J.Heeger, A . P . K l e i n a n d P . T u , Phys. Rev. Letters 17 (1966} 803. 6. Y. Nagaoka, J. Phys. Chem. Solids 27 (1966) 1139. 7. K.Svensson, Proc. 10th Int. Conf. on Low Temp. Physics, Moscow 1966. 8. B. R. Coles, private communication. 9. F.T.Hedgcock and C. Rizzuto, Phys. Rev. 163 (1967) 517. 10. A.D. Caplin, Proc. Phys. Soc. 92 (1967) 739. 11. M.P. Sarachik, E. Corenzwit and L. D. Longinotti, Phys. Rev. 135 (1964) A1041.
503
26A,
number
10
PHYSICS
LETTERS
for the x = 0.05 sample. The values of the magnetic moment per Fe atom in table 1 have been obtained from the ~(0, 0) values. Extrapolation to zero Fe content seems to indicate an upper limit for the effective Fe moment at about 40 PH. Extension of the experiments to lower Fe concentrations to other Ni concentrations and to other impurities (e.g. Co) is in progress.
8 April
1968
We gratefully acknowledge the helpful assistance of S. Proost and H. Schinkel in some of the experiments.
haviour
References 1. F. R.De Boer. Phys. Letters
C. J. Schinkel and J. Biesterbos, 25A (1967) 606.
*****
MAGNETIC
ORDERING VERSUS SPINCOMPENSATION IN COPPER-GOLD ALLOYS
OF
IRON
W. M.STAR Kamerlingh
Onnes
Laboratoyi,
Received
Leiden,
4 March
The Netherlands
1968
The Kondo temperature of Fe in Cu-Au alloys decreases when the Au-concentration of the host increases. Magnetic ordering makes a resistance maximum when the Kondo temperature becomes lower than the ordering temperature of the uncompensated spin.
Present theory suggests [l] that when a localized magnetic moment is formed the Kondo temperature TK X (EF /k) exp (- l/p IJ 1) shifts from a very high value of order EF/~ to below 1°K. This is mainly due to a decrease in the s-d exchange constant IJ / . Iron in copper is on the edge of having a magnetic moment and this is reflected in the relatively high TK of about 16’K [2]. Iron in gold probably has a TK below 1°K. The density of states per atom p obtained from electronic specific heat is in gold slightly higher than in copper. The lower value of TK for iron in gold must be caused by a smaller o / J 1, and thus a smaller /JI, this in turn coming from a narrowing and shifting of the virtual bound state with respect to the Fermi level when the Fermi energy decreases [3]. We have measured the electrical resistivity of iron in Cu-Au solvent alloys in order to observe in more detail the shift of TK and the effect of magnetic ordering in a temperature region where effects of spincompensation are also important. In this letter we present results of 0.15 at. % Fe in Cu (I), Cu i Au $ (II), Cu $ Au i (III), Cu $ Au : (IV), Cu + Au ; (V), Cu + Au ; (VI) and Au (VII) (see fig. 1; alloy I has been left out), thus covering with equal spacings the whole copper-gold system. 502
Applying the procedure of ref. 4, which gives TK = lOoK for Cu-Fe, we estimate TK N 4’K for alloy II and TK = 1°K for alloy III. In the other alloys interactions between Fe spins become too important to make possible any reasonable guess. Further discussion will be given in a future paper when results on the same Cu-Au alloys with lower Fe-concentration are available. Anyway, the qualitative aspects of the TK shift are clear. Going towards copper from the gold rich end we see the temperature of the resistivity maximum decreasing and omax - omin increasing. Two effects are responsible here. First the large electron scattering by the host alloy which reduces the interactions between the magnetic moments [5]. Second the TK shift. In general one can say that magnetic ordering becomes important (resistivity maximum) when the concentration of magnetic atoms is so high that the ordering temperature is above the Kondo temperature, or when the concentration is so high that not enough conduction electrons are available to compensate all impurity spins [S] and this incomplete compensation gives the inter impurity interactions its chance. The above argument could explain the resis-
Volume 26A, number 10
8.60
PHYSICS LETTERS
t e m p e r a t u r e tail of the r e s i s t a n c e a n o m a l y s u g g e s t s a T K of o r d e r l ° K and this m i g h t explain the r e l u c t a n c e of Zn-Mn to show a r e s i s t a n c e m a x i m u m . P r o b a b l y Cu ~ Au ~ - F e is a c o m a r a b l e type of alloy. E x t r a p o l a t i o n of our c o n c l u s i o n s toward p h ase C u - Z n a l l o y s with F e i m p u r i t y [10] s u g g e s t s a T K w e l l , a b o v e 30°K and probably much h i g h e r on the zinc r i c h end of the phase. If F e w e r e b e t t e r so l u b l e in C u - Z n one might expect A u - V - l i k e b e h a v i o u r . This conclusion d i f f e r s from Caplin's. E x t r a p o l a t i o n t o w ar d s A u P d - F e s u g g e s t s a f u r t h e r l o w e r i n g of TK r e l a t i v e to A u F e. T h i s point is being i n v e s t i g a t e d , a s is the effect of the T K shift on s p e c i f i c heat and m a g n e t i c s u s ceptibility. F i n al l y we want to point out a r a t h e r s t r i k i n g r e s e m b l a n c e between our r e s u l t s and those of S a r a c h i k e.a. [11] on F e in NbMo and MoRe alloys. The s i m i l a r r e s u l t s s u g g e s t a s i m i l a r explanation.
ZE
12.34 0.0t00
~P. cm
p.Qcm
"lTr
3.30
7 . 4 . 1 l-
8April 1968
9P--- ~EE
This work is p a r t of the r esear ,ch p r o g r a m of the "Stichting F . O . M . ", and has been spons o r e d by "Z. W. O." and "T. N. O.". 1.35 0
T
P
'tO
15
OK
20
Fig. 1. Resistivity of Cu-Au alloys with 0.15 at. % Fe. The numbers are explained in the text. The scale is the same for all alloys. Lattice resistivity has not been subtracted. tivity m a x i m u m o b s e r v e d by S v e n s s o n [7] in cold w o r k e d C u F e a l l o y s with about 1% F e and m o r e , although the low s o l i d solubility of F e in Cu c o m p l i c a t e s the situation and one would h a v e to suppo s e that cold work b r i n g s p r e c i p i t a t e d F e again into solution. T h e r e s i s t i v i t y m a x i m u m in Cu-15 at. % Au - 0 . 5 at. % F e as o b s e r v e d by Cole s [8] is u n d e r s t o o d in a s i m i l a r way. We think that Zn-Mn is a n o t h e r good e x a m p l e of an alloy w h e r e spin c o m p e n s a t i o n c o m p l i c a t e s the m a g n e t i c o r d e r i n g p r o c e s s [9]. The high
References 1. J.R. Sehrieffer, d. Appl. Phys. 38 (1967) 1143. 2. M.D. Daybell and W. A. Steyert, Phys. Rev. Letters 18 (1967) 398. 3. J. Friedel, Nuovo Cimento Suppl. 7 (1958) 287. 4. M. D. Daybell and W. A. Steyert, Rev. Mod. Phys., to be published. 5. A.J.Heeger, A . P . K l e i n a n d P . T u , Phys. Rev. Letters 17 (1966} 803. 6. Y. Nagaoka, J. Phys. Chem. Solids 27 (1966) 1139. 7. K.Svensson, Proc. 10th Int. Conf. on Low Temp. Physics, Moscow 1966. 8. B. R. Coles, private communication. 9. F.T.Hedgcock and C. Rizzuto, Phys. Rev. 163 (1967) 517. 10. A.D. Caplin, Proc. Phys. Soc. 92 (1967) 739. 11. M.P. Sarachik, E. Corenzwit and L. D. Longinotti, Phys. Rev. 135 (1964) A1041.
503