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Field dependence of the magnetic susceptibility of some dilute alloys of V in au
Volume 411k, number 2
PHYSICS LETTERS
3 July 1972
FIELD DEPENDENCE OF THE MAGNETIC SUSCEPTIBILITY OF SOME DILUTE ALLOYS OF V IN AU* J.E. Van DAM Kamerlingh Onnes Laboratorium do’ Rijksuniversiteit, Leiden, Holland
and
P.A. BECK Department ofMetallurgy, University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA Received 21 April 1972
Magnetization data at low temperatures for quenched Au-V alloys (I at% and 2 at% V) are presented. From an analysis of these results conclusions are drawn about the concentration dependence of the solute susceptibility.
In a recent paper [1] the solute magnetic susceptibility of Au-V alloys was shown not to be proportional to the solute concentration (above about 0.5 at% V) for quenched specimens. It was noted that the susceptibiity of these quenched specimens shows a field dependence at low temperatures (T< 8K). Some recent magnetization measurements by other investigators [2] also reveal field dependence, while others do not [3] As in the latter case the specimens were slowly cooled, this absence of field dependence is consistent with the results for slowly cooled specimens in ref. [11. The measurements by Creveling and Luo [41 showed a large influence ofheat treatment, but no field dependence. However, a substantial increase in the magnetic-impurity level (Fe) was reported for splattered samples. This gives rise to curvature in the magnetization versus field graphs below 2 K. The low temperature magnetization data for the quenched specimens (fig. 1) were fitted to the following equation:
the best fits were obtained to eq. (1) are shown in table 1. The quality of the fits is quite good, as indicated by the low RMSD values (about 0.5% of M). The table shows that at low temperatures the magnetization consists of a contribution from a very low
800
2
,
20
2.0
15
.
MM~0~_MAU=XOH+cpB[p,H/(T—O)J
Au -v 60
I
~
-
40
10 093
20~
-
H/(T-’~)_(koeIK) (1) I
where x0 is a temperature- and field-independent susceptibiity, B is the Brilouin function with g 2, ji = gS is the average permanent spin moment and c is the concentration of the dipoles. The parameters for which
0.5
I
I
1.0
1.5
2.0
This work was done by one of the authors JEVD as part of
Fig. 1. M2 ( M — x0H) versus H/(T— 6) for two quenched Au-V alloys. The full lines show the values calculated according to the best fits of eq. (1). The data have been obtained at three temperatures. For 0.93 at% V: (a) T1 = 4.13 K, (A) T2 =
the research programme of FO.M., supported by ZWO and TNO.
2.68 K and (ci) T3 = 2.15 K; for 2 at% V: (o)T1 (o)T2 = 3.04 K and (A)T3 2.11 K.
-
*
5
-
.
=
4.07 K,
183
Volume 40A, number 2
PHYSICS LETTERS
concentration of large dipoles and of a contribution from a field- and temperature-independent susceptibility. The Fe impurity level, as reported in ref. [11 is clearly too low to account for the large dipoles. Since Au4V is ferromagnetic at the temperatures of these ,
measurements, it is reasonable to assume that the observed dipole moments are associated with small, atomically ordered regions in the specimens. The small fraction of the V-content of the two alloys that would have to be assumed to participate in these magnetic clusters presumably retain their permanent moments at the temperatures of the measurements by virtue of their very low Kondo temperature. However, the clusters can account for only a very small fraction of the susceptibility measured for the same specimens at high temperatures [1] The apparent absence of field dependence (and, thus, of magnetic clusters) in the slowly cooled specimens may be due to the formation of much larger, and correspondingly fewer, ordered Au4V partides, resulting in virtual saturation at low fields of their contribution to the magnetization. It is significant that the x0 values obtained by least squares fitting (table) are close to the solute susceptibilities one obtains by extrapolation from the low temperature data for alloys in less than I at% V. [ln ref. (1] the low temperature solute susceptibility is designated i~x(O)]As shown in fig. 2, the extrapolation may be based on proportionality with the V-content, at least up to 2 at% V. It was recently suggested [51
(low TK) particles, as in our specimens. These particles might also give rise to the curvature in M versus H, reported in ref. [4]. The present results are consistent with the interpretation of the high temperature solute susceptibility of the alloys with up to 2% V as largely due to dipole moments associated with isolated V atoms. Because of their high Kondo temperature, these dipole moments
0.93 at% V —
—__________
C(ppm)
2.0 at%
—
——•~--~
7.1
32.6
~ (MB) o (K)
9.47 —5
5.57 —0.5
x
37 0.15
93 1174
(106 emu/mol) RMSD (10 emu/mol) _____________
v
Au—V -
-
-
.
1/
1~
‘~
50
1~’
25
c (at Eb
Os
10
0/~
v) 15
20
Fig. 2. Solute susceptibility at T = 0 versus solute concentration for some Au-V alloys (n ref. [II, A this analysis).
disappear at low temperatures and the susceptibility due to the isolated V atoms becomes temperature independent. At higher solute concentrations the expected variation of the Kondo temperature with near neighbor atomic environment of the V atoms may well give rise to a distribution of Kondo temperatures and, thus, to a more complicated temperature dependence of the susceptibility.
References
______________
-
/
100
-
Table I Parameter values of best fits to~.(l)
3 July 1972
.
that the electronic specific heat coefficient is also proportional to the V-content, at least up to 1% V. The concentration effects observed in the resistivity [6] can be ascribed to the presence of strongly magnetic
(11
J.E. Van to Dam, P.C.M. Gubbens and G.J. Van den Berg, Physica, be published. [2] N. Sakamoto, Y. Yamaguchi, S. Waki and S. Ogawa, Proc. 12th Conf. Low Temp. Phys., Kyoto 1970 (ed. Kanda) p. 739. (31 M. Saint-Paul, J. Souletie, D. Thoulouze and B. Tissjer 3. Low Temp. Phys. 7 (1972) 1 29. (4] L. Creveling and H.L. Luo, Phys. Rev. 176 (1968) 614. 151 i.E. Van Dam, Phys. Lett. 38A (1972) 19. (6] W.M. Star, Physica 58 (1972) 623.
PHYSICS LETTERS
3 July 1972
FIELD DEPENDENCE OF THE MAGNETIC SUSCEPTIBILITY OF SOME DILUTE ALLOYS OF V IN AU* J.E. Van DAM Kamerlingh Onnes Laboratorium do’ Rijksuniversiteit, Leiden, Holland
and
P.A. BECK Department ofMetallurgy, University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA Received 21 April 1972
Magnetization data at low temperatures for quenched Au-V alloys (I at% and 2 at% V) are presented. From an analysis of these results conclusions are drawn about the concentration dependence of the solute susceptibility.
In a recent paper [1] the solute magnetic susceptibility of Au-V alloys was shown not to be proportional to the solute concentration (above about 0.5 at% V) for quenched specimens. It was noted that the susceptibiity of these quenched specimens shows a field dependence at low temperatures (T< 8K). Some recent magnetization measurements by other investigators [2] also reveal field dependence, while others do not [3] As in the latter case the specimens were slowly cooled, this absence of field dependence is consistent with the results for slowly cooled specimens in ref. [11. The measurements by Creveling and Luo [41 showed a large influence ofheat treatment, but no field dependence. However, a substantial increase in the magnetic-impurity level (Fe) was reported for splattered samples. This gives rise to curvature in the magnetization versus field graphs below 2 K. The low temperature magnetization data for the quenched specimens (fig. 1) were fitted to the following equation:
the best fits were obtained to eq. (1) are shown in table 1. The quality of the fits is quite good, as indicated by the low RMSD values (about 0.5% of M). The table shows that at low temperatures the magnetization consists of a contribution from a very low
800
2
,
20
2.0
15
.
MM~0~_MAU=XOH+cpB[p,H/(T—O)J
Au -v 60
I
~
-
40
10 093
20~
-
H/(T-’~)_(koeIK) (1) I
where x0 is a temperature- and field-independent susceptibiity, B is the Brilouin function with g 2, ji = gS is the average permanent spin moment and c is the concentration of the dipoles. The parameters for which
0.5
I
I
1.0
1.5
2.0
This work was done by one of the authors JEVD as part of
Fig. 1. M2 ( M — x0H) versus H/(T— 6) for two quenched Au-V alloys. The full lines show the values calculated according to the best fits of eq. (1). The data have been obtained at three temperatures. For 0.93 at% V: (a) T1 = 4.13 K, (A) T2 =
the research programme of FO.M., supported by ZWO and TNO.
2.68 K and (ci) T3 = 2.15 K; for 2 at% V: (o)T1 (o)T2 = 3.04 K and (A)T3 2.11 K.
-
*
5
-
.
=
4.07 K,
183
Volume 40A, number 2
PHYSICS LETTERS
concentration of large dipoles and of a contribution from a field- and temperature-independent susceptibility. The Fe impurity level, as reported in ref. [11 is clearly too low to account for the large dipoles. Since Au4V is ferromagnetic at the temperatures of these ,
measurements, it is reasonable to assume that the observed dipole moments are associated with small, atomically ordered regions in the specimens. The small fraction of the V-content of the two alloys that would have to be assumed to participate in these magnetic clusters presumably retain their permanent moments at the temperatures of the measurements by virtue of their very low Kondo temperature. However, the clusters can account for only a very small fraction of the susceptibility measured for the same specimens at high temperatures [1] The apparent absence of field dependence (and, thus, of magnetic clusters) in the slowly cooled specimens may be due to the formation of much larger, and correspondingly fewer, ordered Au4V partides, resulting in virtual saturation at low fields of their contribution to the magnetization. It is significant that the x0 values obtained by least squares fitting (table) are close to the solute susceptibilities one obtains by extrapolation from the low temperature data for alloys in less than I at% V. [ln ref. (1] the low temperature solute susceptibility is designated i~x(O)]As shown in fig. 2, the extrapolation may be based on proportionality with the V-content, at least up to 2 at% V. It was recently suggested [51
(low TK) particles, as in our specimens. These particles might also give rise to the curvature in M versus H, reported in ref. [4]. The present results are consistent with the interpretation of the high temperature solute susceptibility of the alloys with up to 2% V as largely due to dipole moments associated with isolated V atoms. Because of their high Kondo temperature, these dipole moments
0.93 at% V —
—__________
C(ppm)
2.0 at%
—
——•~--~
7.1
32.6
~ (MB) o (K)
9.47 —5
5.57 —0.5
x
37 0.15
93 1174
(106 emu/mol) RMSD (10 emu/mol) _____________
v
Au—V -
-
-
.
1/
1~
‘~
50
1~’
25
c (at Eb
Os
10
0/~
v) 15
20
Fig. 2. Solute susceptibility at T = 0 versus solute concentration for some Au-V alloys (n ref. [II, A this analysis).
disappear at low temperatures and the susceptibility due to the isolated V atoms becomes temperature independent. At higher solute concentrations the expected variation of the Kondo temperature with near neighbor atomic environment of the V atoms may well give rise to a distribution of Kondo temperatures and, thus, to a more complicated temperature dependence of the susceptibility.
References
______________
-
/
100
-
Table I Parameter values of best fits to~.(l)
3 July 1972
.
that the electronic specific heat coefficient is also proportional to the V-content, at least up to 1% V. The concentration effects observed in the resistivity [6] can be ascribed to the presence of strongly magnetic
(11
J.E. Van to Dam, P.C.M. Gubbens and G.J. Van den Berg, Physica, be published. [2] N. Sakamoto, Y. Yamaguchi, S. Waki and S. Ogawa, Proc. 12th Conf. Low Temp. Phys., Kyoto 1970 (ed. Kanda) p. 739. (31 M. Saint-Paul, J. Souletie, D. Thoulouze and B. Tissjer 3. Low Temp. Phys. 7 (1972) 1 29. (4] L. Creveling and H.L. Luo, Phys. Rev. 176 (1968) 614. 151 i.E. Van Dam, Phys. Lett. 38A (1972) 19. (6] W.M. Star, Physica 58 (1972) 623.