- Email: [email protected]
Mössbauer-effect study of the influence of vanadium on spin- and charge-density waves of chromium
Journal of Magnetism mad Magnetic Materials 157/158 (1996) 653-654
~4
journalof magnetism and magnetic materials
ELSEVIER
MiSssbauer-effect study of the influence of vanadium on spin- and charge-density waves of chromium S.M. Dubiel a,*, j. Cie~lak a, F.E. Wagner b a Faculty of Physics and Nuclear Techniques, The University of Mining and Metallurgy (AGH), PL-30-059 Krakdw, Poland b Physik-Department E-15, Technical University of Munich, D-85747 Garching, Germany Abstract The influence of vanadium on spin- and charge-density waves (SDW and CDW, respectively) in single-crystal chromium is investigated by 1195nMBssbaner spectroscopy. DOping with vanadium quenches SDWs: both the maximum hyperfine (hf) field, //max, and the average h f field, H a, decrease linearly with vanadium content, x, the former at a rate of 26.2 k O e / a t % and the latter at 18.7 k O e / a t % . The decrease of the normalized Hmax and that of H a is the same within the error limit, and equal to 0.3 per at%. Keywords: Antiferromagnetism; Charge- and spin-density waves; MSssbauer spectroscopy
Imperfect nesting of the Fermi surface (FS) in chromium results in the formation of spin-density waves (SDWs) that can be described by a series of odd-harmonics, H2i i [1]: SDW = ~ H 2 i _ 1 s i n [ ( 2 i -
1)Qr + 6s],
(1)
where Q is the wave and r the position vector, and 6 s is the phase shift between the SDW and the lattice. SDWs through the s p i n - p h o n o n interaction create charge-density waves (CDWs), which, in turn, can be expressed in terms of even-harmonics, S2i [2]: C D W = ~S2i sin(2iQr + ~ ),
netic moment, /x~, at 0.12/xB/at% and Q* at 0 . 0 1 7 / a t % (Q* = -2roE~a, where e is the incommensurability parameter and a the lattice constant). The addition of ~ 4 at% V quenches the SDW totally. In this paper results obtained on single-crystal samples of Crl00_xVx alloys with 0 _ < x _ < 5 by means of ll9Sn
(2)
where 6 is the phase shift between the SDW and the CDW. The degree of nesting of the FS can be altered by changes of the electron concentration which occur as atoms of different valence are introduced into the chromium matrix by alloying. Consequently, various physical properties of the S D W such as its amplitude, periodicity, the N~el (T N) and the spin-flip (TsF) temperatures depend on the alloying element and its concentration. Among such elements V and M n play a special role as neighbouring elements in the periodic table. The first decreases the electron density at the FS and quenches the SDW, while the second acts as an electron donor, and supports the SDW [3]. In particular, in C r - V alloy, TN decreases at a rate of 82 K / a t % , TsF at 100 K / a t % , the average mag-
43
~
0
v [mm/s]
4
8
119Sn M~Sssbauer spectra of single-crystal samples of Crl00_xVx alloys with (a) x = 0, (b) x = 0.5, (c) x = 2.5 and (d)
Fig. 1. * Corresponding author. Fax: dubiel @novell.ftj.agh.edu.pl.
+48-12-340010;
email:
x = 5.3 measured at 295 K. Solid lines represent the best-fit spectra.
0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. SSDI 0 3 0 4 - 8 8 5 3 ( 9 5 ) 0 1 0 5 6 - 4
654
S.M. Dubiel et al. / Journal of Magnetism and Magnetic Materials 157/158 (1996) 653-654
Table 2 Normalized rate of decrease, R, of the average magnetic moment, /xa, the N~el temperature, TN, the incommensurability wave vector, Q *, and the maximum (Hm~x) and average (H a) hf field for single-crystal Crl00_xVx alloys R
/Xa
TN
Q*
Hmax
Ha
-0.30 ~
-0.27 a
--0.26 ~
--0.29
--0.31
Calculated according to data from Ref. [3].
(¢) ' ~
(d) -12
"~
-6
0 V [mm/s]
6
12
Fig. 2. The same as for Fig. 1 but measured at 4.2 K. Mtissbauer spectroscopy are presented and discussed. This method is well-suited to investigate SDWs and coexisting CDWs as it supplies information on both simultaneously. Single-crystal samples for the present study were prepared by cutting ~ 500 /zm thick platelets from bulk pieces. The platelets were first mechanically and then electrolytically polished down to ~ 100 /xm thickness. Probe ll9Sn nuclei were then introduced into the C r - V matrix by diffusion at 1600 K. Their final concentration in the solution, which was determined by microprobe analysis, was 0.16(1) at% in all samples studied ( x = 0, 0.5, 2.5 and 5.0). lI9Sn M/Sssbauer spectra were recorded at 295 and 4.2 K in transmission geometry using a standard spectrometer and a drive operating in sinusoidal mode. T-Rays of 23.8 Table 1 Best-fit spectral parameters obtained for single-crystal samples of Crl00_xVx alloys by means of the method described in Ref. [4]. H-values are in kOe and S-values in m m / s x H1 H3 n5 H7 Hn~x H~
s2 S4 86 S8 SO
T = 4.2 K
T = 4.2 K
T = 4.2 K
T = 295 K
0 93.6(5) 2.4(5) - 0.6(4) - 0.2(4) 91.1 60.0
0.5 75.5(9) 0(1) 1.0(5) - 1.3(3) 79.1 48.1
2.5 21.3(5) - 2.2(3) 1.1(5) - 0.9(7) 25.5 13.2
0 57.1(5) 0.8(4) 0.6(3) - 0.5(4) 57.4 36.6
keV energy were supplied by a CallVmSnO3 source maintained at 295 K. The spectra registered at 295 K are displayed in Fig. 1. It can be seen that they all consist of a single line only for x v~ 0, in accordance with the phase diagram of the system [3]. Their spectral parameters have the same values within error limits, i.e. FWHF, F = 0.96 m m / s ; isomer shift, S = 1.54 m m / s . The spectra measured at 4.2 K, shown in Fig. 2, exhibit more structure, hence they yield more information on the underlying SDWs and CDWs. In order to analyze them we applied the method of harmonic analysis recently developed by the present authors [4]. The best-fit spectral parameters obtained in this way, i.e. the higher-order harlnonics, H2i_ 1 and S2i , the maximum hf field, Hmax, the average h f field, H a, and the average isomer shift, S 0, are displayed in Table 1. It is clear that addition of vanadium to the chromium matrix drastically quenches SDWs. Hmax, and hence the amplitude of the SDW, decreases linearly with x at the rate of 26.2 k O e / a t % , as does H a, but at the rate of 18.7 k O e / a t % . It is known that other physical properties of the SDW such as Ts , Tsr, /xa and Q * also exhibit a linear decrease with x. Hence, it is interesting to compare their rate of decrease quantitatively. In order to do so properly, one has to compare their normalized rate of decrease, R = ( d N / N ) / d x ( N = T N, TSF, /xa, Q *, Hmax and Ha). The R-values obtained in this way are presented in Table 2, from which it follows that R -- constant. This is, in our opinion, an important result, as it means that all these quantities have the same relative change per at% V added. As some of them, for example TN and Q *, are directly related to the Fermi surface, the results of Table 2 suggest that other quantities, in particular//max and Ha, also have the same origin. As far as CDWs are concerned, the appropriate spectral parameters shown in Table 1 have vanishingly small values. This result may indicate that vanadium doping also suppresses the C D W of chromium, which seems to be quite a reasonable conclusion.
0.00(3) 0.00(2) 0.00(2) 0.00(2)
References
0.01(3) 0.00(2) 0.00(3) 1.48
[1] [2] [3] [4]
0.01(3) 0.00(3) 0.00(3) 1.54
0.00(3) 0.00(4) 0.00(7) 1.50
0.03(2) 0.02(2) 0.001(2) 1.56
W.M. Lomer, Proc. Phys. Soc. (London) 80 (1962) 489. K. Machida and M. Fujita, Phys. Rev. B 30 (1984) 5284. E. Fawcett et al., Rev. Mod. Phys. 66 (1994) 25. J. Cieglak and S.M. Dubiel, Nucl. Instr. and Meth. B 95 (1995) 131.
~4
journalof magnetism and magnetic materials
ELSEVIER
MiSssbauer-effect study of the influence of vanadium on spin- and charge-density waves of chromium S.M. Dubiel a,*, j. Cie~lak a, F.E. Wagner b a Faculty of Physics and Nuclear Techniques, The University of Mining and Metallurgy (AGH), PL-30-059 Krakdw, Poland b Physik-Department E-15, Technical University of Munich, D-85747 Garching, Germany Abstract The influence of vanadium on spin- and charge-density waves (SDW and CDW, respectively) in single-crystal chromium is investigated by 1195nMBssbaner spectroscopy. DOping with vanadium quenches SDWs: both the maximum hyperfine (hf) field, //max, and the average h f field, H a, decrease linearly with vanadium content, x, the former at a rate of 26.2 k O e / a t % and the latter at 18.7 k O e / a t % . The decrease of the normalized Hmax and that of H a is the same within the error limit, and equal to 0.3 per at%. Keywords: Antiferromagnetism; Charge- and spin-density waves; MSssbauer spectroscopy
Imperfect nesting of the Fermi surface (FS) in chromium results in the formation of spin-density waves (SDWs) that can be described by a series of odd-harmonics, H2i i [1]: SDW = ~ H 2 i _ 1 s i n [ ( 2 i -
1)Qr + 6s],
(1)
where Q is the wave and r the position vector, and 6 s is the phase shift between the SDW and the lattice. SDWs through the s p i n - p h o n o n interaction create charge-density waves (CDWs), which, in turn, can be expressed in terms of even-harmonics, S2i [2]: C D W = ~S2i sin(2iQr + ~ ),
netic moment, /x~, at 0.12/xB/at% and Q* at 0 . 0 1 7 / a t % (Q* = -2roE~a, where e is the incommensurability parameter and a the lattice constant). The addition of ~ 4 at% V quenches the SDW totally. In this paper results obtained on single-crystal samples of Crl00_xVx alloys with 0 _ < x _ < 5 by means of ll9Sn
(2)
where 6 is the phase shift between the SDW and the CDW. The degree of nesting of the FS can be altered by changes of the electron concentration which occur as atoms of different valence are introduced into the chromium matrix by alloying. Consequently, various physical properties of the S D W such as its amplitude, periodicity, the N~el (T N) and the spin-flip (TsF) temperatures depend on the alloying element and its concentration. Among such elements V and M n play a special role as neighbouring elements in the periodic table. The first decreases the electron density at the FS and quenches the SDW, while the second acts as an electron donor, and supports the SDW [3]. In particular, in C r - V alloy, TN decreases at a rate of 82 K / a t % , TsF at 100 K / a t % , the average mag-
43
~
0
v [mm/s]
4
8
119Sn M~Sssbauer spectra of single-crystal samples of Crl00_xVx alloys with (a) x = 0, (b) x = 0.5, (c) x = 2.5 and (d)
Fig. 1. * Corresponding author. Fax: dubiel @novell.ftj.agh.edu.pl.
+48-12-340010;
email:
x = 5.3 measured at 295 K. Solid lines represent the best-fit spectra.
0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. SSDI 0 3 0 4 - 8 8 5 3 ( 9 5 ) 0 1 0 5 6 - 4
654
S.M. Dubiel et al. / Journal of Magnetism and Magnetic Materials 157/158 (1996) 653-654
Table 2 Normalized rate of decrease, R, of the average magnetic moment, /xa, the N~el temperature, TN, the incommensurability wave vector, Q *, and the maximum (Hm~x) and average (H a) hf field for single-crystal Crl00_xVx alloys R
/Xa
TN
Q*
Hmax
Ha
-0.30 ~
-0.27 a
--0.26 ~
--0.29
--0.31
Calculated according to data from Ref. [3].
(¢) ' ~
(d) -12
"~
-6
0 V [mm/s]
6
12
Fig. 2. The same as for Fig. 1 but measured at 4.2 K. Mtissbauer spectroscopy are presented and discussed. This method is well-suited to investigate SDWs and coexisting CDWs as it supplies information on both simultaneously. Single-crystal samples for the present study were prepared by cutting ~ 500 /zm thick platelets from bulk pieces. The platelets were first mechanically and then electrolytically polished down to ~ 100 /xm thickness. Probe ll9Sn nuclei were then introduced into the C r - V matrix by diffusion at 1600 K. Their final concentration in the solution, which was determined by microprobe analysis, was 0.16(1) at% in all samples studied ( x = 0, 0.5, 2.5 and 5.0). lI9Sn M/Sssbauer spectra were recorded at 295 and 4.2 K in transmission geometry using a standard spectrometer and a drive operating in sinusoidal mode. T-Rays of 23.8 Table 1 Best-fit spectral parameters obtained for single-crystal samples of Crl00_xVx alloys by means of the method described in Ref. [4]. H-values are in kOe and S-values in m m / s x H1 H3 n5 H7 Hn~x H~
s2 S4 86 S8 SO
T = 4.2 K
T = 4.2 K
T = 4.2 K
T = 295 K
0 93.6(5) 2.4(5) - 0.6(4) - 0.2(4) 91.1 60.0
0.5 75.5(9) 0(1) 1.0(5) - 1.3(3) 79.1 48.1
2.5 21.3(5) - 2.2(3) 1.1(5) - 0.9(7) 25.5 13.2
0 57.1(5) 0.8(4) 0.6(3) - 0.5(4) 57.4 36.6
keV energy were supplied by a CallVmSnO3 source maintained at 295 K. The spectra registered at 295 K are displayed in Fig. 1. It can be seen that they all consist of a single line only for x v~ 0, in accordance with the phase diagram of the system [3]. Their spectral parameters have the same values within error limits, i.e. FWHF, F = 0.96 m m / s ; isomer shift, S = 1.54 m m / s . The spectra measured at 4.2 K, shown in Fig. 2, exhibit more structure, hence they yield more information on the underlying SDWs and CDWs. In order to analyze them we applied the method of harmonic analysis recently developed by the present authors [4]. The best-fit spectral parameters obtained in this way, i.e. the higher-order harlnonics, H2i_ 1 and S2i , the maximum hf field, Hmax, the average h f field, H a, and the average isomer shift, S 0, are displayed in Table 1. It is clear that addition of vanadium to the chromium matrix drastically quenches SDWs. Hmax, and hence the amplitude of the SDW, decreases linearly with x at the rate of 26.2 k O e / a t % , as does H a, but at the rate of 18.7 k O e / a t % . It is known that other physical properties of the SDW such as Ts , Tsr, /xa and Q * also exhibit a linear decrease with x. Hence, it is interesting to compare their rate of decrease quantitatively. In order to do so properly, one has to compare their normalized rate of decrease, R = ( d N / N ) / d x ( N = T N, TSF, /xa, Q *, Hmax and Ha). The R-values obtained in this way are presented in Table 2, from which it follows that R -- constant. This is, in our opinion, an important result, as it means that all these quantities have the same relative change per at% V added. As some of them, for example TN and Q *, are directly related to the Fermi surface, the results of Table 2 suggest that other quantities, in particular//max and Ha, also have the same origin. As far as CDWs are concerned, the appropriate spectral parameters shown in Table 1 have vanishingly small values. This result may indicate that vanadium doping also suppresses the C D W of chromium, which seems to be quite a reasonable conclusion.
0.00(3) 0.00(2) 0.00(2) 0.00(2)
References
0.01(3) 0.00(2) 0.00(3) 1.48
[1] [2] [3] [4]
0.01(3) 0.00(3) 0.00(3) 1.54
0.00(3) 0.00(4) 0.00(7) 1.50
0.03(2) 0.02(2) 0.001(2) 1.56
W.M. Lomer, Proc. Phys. Soc. (London) 80 (1962) 489. K. Machida and M. Fujita, Phys. Rev. B 30 (1984) 5284. E. Fawcett et al., Rev. Mod. Phys. 66 (1994) 25. J. Cieglak and S.M. Dubiel, Nucl. Instr. and Meth. B 95 (1995) 131.