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Magnetovolume effects in Fe-Pt Invar alloys
Journal of Magnetism and Magnetic Materials 12 (1979) 1-3 © North-Holland Publishing Company
MAGNETOVOLUME EFFECTS IN F e - P t INVAR ALLOYS * K. SUMIYAMA, M. SHIGA and Y. NAKAMURA Department of Metal Science and Technology, Kyoto University, Kyoto, Japan Received 10 January 1979
Thermal expansion and forced volume magnetostriction have been measured for Fe-Pt alloys containing 28-32 at% Pt. Values of the spontaneous volume magnetostriction at 0 K are found to be as large as those in Fe-Ni Invar alloys, while the forced volume magnetostriction at 4.2 K is about one order smaller than observed for Fe-Ni Invar alloys.
1. Introduction
2. Spontaneous volume magnetostriction
The F e - P t Invar alloys show a large thermal expansion anomaly below the Curie temperature in the homogeneous ordered state as well as in the inhomogeneous disordered state [ 1 - 3 ] . The concentration dependence of the magnetic moment follows the Slater-Pauling curve, indicating that Fe atoms have a full moment of about 2.7/aB independent of concentration [4,5]. These results can be explained neither by inhomogeneity models nor by very weak itinerant electron models, even though these models offer reasonable explanations for the Invar behaviours in F e Ni alloys [ 6 - 8 ] . From this point of view, the F e - P t alloy system is very important in order to deepen our understanding of the general origin of the Invar characteristics. This paper reports experimental results for the spontaneous volume magnetostriction and the forced volume magnetostriction of F e - P t Invar alloys containing 2 8 - 3 2 at% Pt, where the fcc structure is stable down to 4.2 K for both ordered and disordered states. The disordered alloys were obtained by rapid water quenching from 900°C, and the ordered alloys by extensive annealing [4], i.e., at 900°C for a day, at 600°C for a week, 550°C for a month and finally at 500-450°C for another month.
The fractional change in length was measured from 4.2 to 800 K by using a dilatometer based on the differential transformer principle and multiplied by three to obtain the volume expansion. The spontaneous volume magnetostriction was then obtained by subtracting the lattice contribution from the observed volume expansion. The spontaneous volume magnetostriction at 0 K, COs(0), is plotted against Pt concentration in fig. 1. It can be seen that 6Os(0) values for the present alloys are the same order of magnitude as those found for Fe-Ni Invar alloys [9], and that Ws(0) for the disordered state is about 10% larger than that for the ordered state. Based on a localized moment model, such a large ~Os(0) can be ascribed to a strong volume dependence of the exchange integral, dJ/dw, and it may be reasonable to assume that dJ/dco of F e - F e atom pairs provides the dominant contribution to ~s(0) [10]. Therefore, the concentration dependence of ~s(0) for both the ordered and disordered states can be written roughly as: ~s(O) = A (Pve- Fe/PTotal), where PFe-F'e is the number of F e - F e nearest atom pairs, /°Total the number of the total atom pairs andA an empirical constant. As a trial, we adjusted the value of A to give the experimental value of Ws(0) for disordered Fe7oPt3o alloy. The calculated value for ordered Fe7oPt3o alloy then shows a good agreement with the observed value. Furthermore, the concentra-
* Paper 3.3 presented at the International Symposium on the Invar Problem, Nagoya, Japan, 4-6 September 1978.
2
K. Sumiyama et al. /Magnetovolume effects in Fe-Pt Invars
10.0
1.5
\x
(a) at 295 K
0 x v
5.0
1.0 S v
~ t ~ . . ~~ 0 × v 0
"'~
0
,~
I
I
I
/
I
28
29
30
31
32
Concentration of Pt (at*/,)
0.0
I
I
I
I
I
I
1.5 (b] at 4.2 K
Fig. 1. Concentration dependence of the spontaneous volume magnetostriction Ws(0) at 0 K for Fe-Pt Invar alloys. o ordered state, • disordered state. The solid lines indicate the calculated results from the equation, Ws(0) = A(PFe--Fe/ PTotal) (see text for details).
1.0
0.5 0.0
--~ 0
tion dependence o f COs(0) calculated by using the same A value (the solid lines in fig. 1) agrees fairly well with the experimental results for b o t h states. According to a theory o f magnetovolume coupling based on the magnetic interaction between pseudolocalized moments [11], the F e - F e atom pair is thought to be the most likely candidate for the origin of the large volume expansion, which is consistent with the present results. The large magnetovolume effects observed in very weak itinerant electron ferromagnets [8] and induced moment ferromagnets [12] have been attributable to the 3d band polarization associated with T c. Although such an itinerant electron picture should also be valid for F e - P t alloys, the estimation is not possible because of the lack of information on the band structure of F e - P t alloys.
I
28
I
29
I
30
Concentration of
I
31
I
32
Pt (at %)
Fig. 2. Concentration dependence of the forced volume magnetostriction dw/dH for Fe-Pt Invar alloys, (a) at 295 K and (b) at 4.2 K. G and o ordered state, = and • disordered state.
Ni Invar alloys [14]. A low value of dco/dH can be expected with the strong ferromagnetism of F e - P t Invar alloys. It is, however, not consistent with the fairly large value of the high field susceptibility observed at 4.2 K [15], because the itinerant electron model predicts that high field susceptibility and forced volume magnetostriction should be proportional to each other. The temperature dependence o f dco/dH was measured by a two strain gauges method between 77 and 550 K. The results obtained follow Kornetzki's relation [16]. Details of these experimental results will be published elsewhere.
3. Forced volume magnetostriction
The concentration dependence of the forced volume magnetostriction, dw/dH, was observed by a three terminal capacitance dilatometer at 4.2 and 295 K in an applied field up to 28 kOe, as shown in fig. 2. Values o f dco/dH at 295 K are comparable with those for F e - N i Invar alloys [13], while at 4.2 K, dco/dH is about one order smaller than those for F e -
References
[1] A. Kussmann, Phys. Z. 38 (1937) 41. [2] M. Hayase, M. Shiga and Y. Nakamura, Phys. Stat. Sol. B46 (1971) Kl17. [3] K. Sumiyama, M. Shiga and Y. Nakarnura, J. Phys. Soc. Japan 40 (1976) 996.
K. Sumiyama et al. / Magnetovolume effects in F e - P t Invars
[4] K. Sumiyama, M. Shiga, Y. Kobayashi, K. Nishi and Y. Nakamura, J. Phys. F8 (1978) 1281. [5 ] Y. Nakamura, K. Sumiyama and M. Shiga, J. Magn. Magn. Mat. 10 (1979) 280. [6] E.I. Kondorskii and V.L. Sedov, J. ApPl. Phys. 31 (1960) 331S. [7] S. Kachi and H. Asano, J. Phys. Soc. Japan 27 (1969) 536. [8] E.P. Wohlfarth, Phys. Lett. 28A (1969) 569. [9] M. Hayase, M. Shiga and Y. Nakamura, J. Phys. Soc. Japan 34 (1973) 925. [10] T. Nakajima, J. Phys. Soc. Japan 19 (1964) 520.
3
[11] J. Kanamori, T. Teraoka and T. Jo, AIP Conf. Proc. 24 (1975) 16. [12] R. Minakata, M. Shiga and Y. Nakamura, J. Phys. Soc. Japan 41 (1976) 1435. [13] M. Matsumoto, T. Kaneko and H. Fujimori, J. Phys. Soc. Japan 26 (1969) 1083. [14] W.F. Schlosser, G.M. Graham and P.P.M. Meincke, J. Phys. Chem. Solids 32 (1971) 927. [15] K. Sumiyama, G.M. Graham and Y. Nakamura, J. Phys. Soc. Japan 35 (1973) 1255. [16] J.S. Kouvel and R.H. Wilson, J. Appl. Phys. 32 (1961) 435.
MAGNETOVOLUME EFFECTS IN F e - P t INVAR ALLOYS * K. SUMIYAMA, M. SHIGA and Y. NAKAMURA Department of Metal Science and Technology, Kyoto University, Kyoto, Japan Received 10 January 1979
Thermal expansion and forced volume magnetostriction have been measured for Fe-Pt alloys containing 28-32 at% Pt. Values of the spontaneous volume magnetostriction at 0 K are found to be as large as those in Fe-Ni Invar alloys, while the forced volume magnetostriction at 4.2 K is about one order smaller than observed for Fe-Ni Invar alloys.
1. Introduction
2. Spontaneous volume magnetostriction
The F e - P t Invar alloys show a large thermal expansion anomaly below the Curie temperature in the homogeneous ordered state as well as in the inhomogeneous disordered state [ 1 - 3 ] . The concentration dependence of the magnetic moment follows the Slater-Pauling curve, indicating that Fe atoms have a full moment of about 2.7/aB independent of concentration [4,5]. These results can be explained neither by inhomogeneity models nor by very weak itinerant electron models, even though these models offer reasonable explanations for the Invar behaviours in F e Ni alloys [ 6 - 8 ] . From this point of view, the F e - P t alloy system is very important in order to deepen our understanding of the general origin of the Invar characteristics. This paper reports experimental results for the spontaneous volume magnetostriction and the forced volume magnetostriction of F e - P t Invar alloys containing 2 8 - 3 2 at% Pt, where the fcc structure is stable down to 4.2 K for both ordered and disordered states. The disordered alloys were obtained by rapid water quenching from 900°C, and the ordered alloys by extensive annealing [4], i.e., at 900°C for a day, at 600°C for a week, 550°C for a month and finally at 500-450°C for another month.
The fractional change in length was measured from 4.2 to 800 K by using a dilatometer based on the differential transformer principle and multiplied by three to obtain the volume expansion. The spontaneous volume magnetostriction was then obtained by subtracting the lattice contribution from the observed volume expansion. The spontaneous volume magnetostriction at 0 K, COs(0), is plotted against Pt concentration in fig. 1. It can be seen that 6Os(0) values for the present alloys are the same order of magnitude as those found for Fe-Ni Invar alloys [9], and that Ws(0) for the disordered state is about 10% larger than that for the ordered state. Based on a localized moment model, such a large ~Os(0) can be ascribed to a strong volume dependence of the exchange integral, dJ/dw, and it may be reasonable to assume that dJ/dco of F e - F e atom pairs provides the dominant contribution to ~s(0) [10]. Therefore, the concentration dependence of ~s(0) for both the ordered and disordered states can be written roughly as: ~s(O) = A (Pve- Fe/PTotal), where PFe-F'e is the number of F e - F e nearest atom pairs, /°Total the number of the total atom pairs andA an empirical constant. As a trial, we adjusted the value of A to give the experimental value of Ws(0) for disordered Fe7oPt3o alloy. The calculated value for ordered Fe7oPt3o alloy then shows a good agreement with the observed value. Furthermore, the concentra-
* Paper 3.3 presented at the International Symposium on the Invar Problem, Nagoya, Japan, 4-6 September 1978.
2
K. Sumiyama et al. /Magnetovolume effects in Fe-Pt Invars
10.0
1.5
\x
(a) at 295 K
0 x v
5.0
1.0 S v
~ t ~ . . ~~ 0 × v 0
"'~
0
,~
I
I
I
/
I
28
29
30
31
32
Concentration of Pt (at*/,)
0.0
I
I
I
I
I
I
1.5 (b] at 4.2 K
Fig. 1. Concentration dependence of the spontaneous volume magnetostriction Ws(0) at 0 K for Fe-Pt Invar alloys. o ordered state, • disordered state. The solid lines indicate the calculated results from the equation, Ws(0) = A(PFe--Fe/ PTotal) (see text for details).
1.0
0.5 0.0
--~ 0
tion dependence o f COs(0) calculated by using the same A value (the solid lines in fig. 1) agrees fairly well with the experimental results for b o t h states. According to a theory o f magnetovolume coupling based on the magnetic interaction between pseudolocalized moments [11], the F e - F e atom pair is thought to be the most likely candidate for the origin of the large volume expansion, which is consistent with the present results. The large magnetovolume effects observed in very weak itinerant electron ferromagnets [8] and induced moment ferromagnets [12] have been attributable to the 3d band polarization associated with T c. Although such an itinerant electron picture should also be valid for F e - P t alloys, the estimation is not possible because of the lack of information on the band structure of F e - P t alloys.
I
28
I
29
I
30
Concentration of
I
31
I
32
Pt (at %)
Fig. 2. Concentration dependence of the forced volume magnetostriction dw/dH for Fe-Pt Invar alloys, (a) at 295 K and (b) at 4.2 K. G and o ordered state, = and • disordered state.
Ni Invar alloys [14]. A low value of dco/dH can be expected with the strong ferromagnetism of F e - P t Invar alloys. It is, however, not consistent with the fairly large value of the high field susceptibility observed at 4.2 K [15], because the itinerant electron model predicts that high field susceptibility and forced volume magnetostriction should be proportional to each other. The temperature dependence o f dco/dH was measured by a two strain gauges method between 77 and 550 K. The results obtained follow Kornetzki's relation [16]. Details of these experimental results will be published elsewhere.
3. Forced volume magnetostriction
The concentration dependence of the forced volume magnetostriction, dw/dH, was observed by a three terminal capacitance dilatometer at 4.2 and 295 K in an applied field up to 28 kOe, as shown in fig. 2. Values o f dco/dH at 295 K are comparable with those for F e - N i Invar alloys [13], while at 4.2 K, dco/dH is about one order smaller than those for F e -
References
[1] A. Kussmann, Phys. Z. 38 (1937) 41. [2] M. Hayase, M. Shiga and Y. Nakamura, Phys. Stat. Sol. B46 (1971) Kl17. [3] K. Sumiyama, M. Shiga and Y. Nakarnura, J. Phys. Soc. Japan 40 (1976) 996.
K. Sumiyama et al. / Magnetovolume effects in F e - P t Invars
[4] K. Sumiyama, M. Shiga, Y. Kobayashi, K. Nishi and Y. Nakamura, J. Phys. F8 (1978) 1281. [5 ] Y. Nakamura, K. Sumiyama and M. Shiga, J. Magn. Magn. Mat. 10 (1979) 280. [6] E.I. Kondorskii and V.L. Sedov, J. ApPl. Phys. 31 (1960) 331S. [7] S. Kachi and H. Asano, J. Phys. Soc. Japan 27 (1969) 536. [8] E.P. Wohlfarth, Phys. Lett. 28A (1969) 569. [9] M. Hayase, M. Shiga and Y. Nakamura, J. Phys. Soc. Japan 34 (1973) 925. [10] T. Nakajima, J. Phys. Soc. Japan 19 (1964) 520.
3
[11] J. Kanamori, T. Teraoka and T. Jo, AIP Conf. Proc. 24 (1975) 16. [12] R. Minakata, M. Shiga and Y. Nakamura, J. Phys. Soc. Japan 41 (1976) 1435. [13] M. Matsumoto, T. Kaneko and H. Fujimori, J. Phys. Soc. Japan 26 (1969) 1083. [14] W.F. Schlosser, G.M. Graham and P.P.M. Meincke, J. Phys. Chem. Solids 32 (1971) 927. [15] K. Sumiyama, G.M. Graham and Y. Nakamura, J. Phys. Soc. Japan 35 (1973) 1255. [16] J.S. Kouvel and R.H. Wilson, J. Appl. Phys. 32 (1961) 435.