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Electrical resistivity and Curie temperature of amorphous (FeNi)PC alloys
Volume 42A, number 6
PHYSICS LETTERS
15 January 1973
ELECTRICAL RESISTIVITY AND CURIE TEMPERATURE OF AMORPHOUS (Fe-Ni)-P-C ALLOYS* R. HASEGAWA and J.A. DERMON W.M. Keck Laboratory of EngineeringMaterials, California Institute of Technology, Pasadena, California 91109, USA Received 28 October 1972 Low temperature electrical resistivity and Curie temperature of amorphous (Fe 100_x Nix)75 P15C10 alloys (0 ~ x ~ 50) were studied. An application of the data to a result of a coherent potential approximation method leads to an explanation of the low temperature resistivity anomaly in terms of an electron-magnon interaction.
Among the amorphous alloys obtained by rapidquenching from the liquid state, the amorphous Fe75P15C10 alloys are unique in the sense that they contain two different glass formers. Due to this fact, the structure of these alloys seems to be complicated. In a study, these alloys have been described by a randomized b.c.c. iron at least up to the first nearest neighbours [1]. A more recent study shows that the approximate composition of the equilibrium alloy is 56 at.% Fe3P, 37 at.% Fe3C and
7 at.% Fe [21. This may indicate that the local structures in the amorphous state are based on these atomic configurations and these phases are mixed randomly. This picture was used in describing the magnetic properties of an amorphous Mn75P15C10 alloy [3] which was obtained by analogy to the Fe-P-C amorphous alloy. While the problem whether or not the amorphous Fe-P-C alloy has a single or several amorphous phases has to be clarified yet, its macroscopic magnetic properties are less controversial [4] They are briefly characterized by a ferromagnetic Curie temperature of about 590°K,the .
*
Work supported by the U.S. Atomic Energy Commission. 1.000
0.9 90
-
0.976~ 0.975
5
0 IS 20
(°K) E 0.980
0.990
•
-
-
•S • •.
0.970
•s
—
E 0.980
-
097~~ 50 100 0.960
150
200 I
(°K) 0
I
50
100
I
50
200
250
300
TEMPERATURE (°K) 2 dependence Fig. of the 1. resistivity. Resistivity versus temperature for an amorphous (Fe80Ni20)75P15C10 alloy. The insets show the In T and the T 407
Volume 42A, number 6
PHYSICS LETTERS
15 January 1973
Table 1 Results of resistivity measurements on amorphous (Fejoo..x NiX)I 5PISC1O alloys. The value Tm is the resistivity minimum temperature 4) c(107)d(104) Tm(°K) T x prm(I.L~.cm) aa b(10 0(°K) 0 10 20 30 40
194.32 134.80 168.10 181.70 180.56
0.968 0.970 0.977 0.959 0.968
0.961 0.957 0.961 0.945 0.945
—6.20 —6.82 —7.10 —6.48 —9.11
coercive force of 3 Oe [5] and the saturation magnetic moment of 2.1 ~B [6] The electjical resistivity of this amorphous alloy showed a minimum in the resistivity versus temperature curve [7]. Although the occurrence of the resistivity minimum was attributed to the amorphous nature of the alloy, it has not been clearly explained. An attempt is made in this study to explain the resistivity anomaly. The alloys studied have the composition (Feioo~Ni~)75Pi5Cio where x is changed from 0 to 50 and were prepared by a procedure similar to that described elsewhere [5]. An X-ray analysis shows that the alloys are amorphous for x ~ 40 and contain a small amount of crystalline phases for ~ > 40. The resistivity of the present alloys was measured by a conventional four-probe method between 4.2 and 300°K.A typical example of the results is shown in fig. 1. The resistivity can be fitted to the following formulas 2, T<
a’+dT
6.10 6.80 3.32 8.50 5.50
.1101
11
—1
7
—1’~
I
0
0.8
0
EXPERIMENTAL CPA
0.7 (Feio0~Ni~)75 P~C~
.1
‘‘~Fe-Ni i.LanU
0, where IA-B stands for the exchange integral between A and B atom. This is shown by the dotted line in fig. 2. The fitting of the T data to the CPA c result with ~N~Ni = 0 implies that a Ni-P-C alloy would be paramagnetic if it is obtained in an amorphous 408
110 150 210 180 240
T>T0
meLIlou ~°J WiUIJF~Fe
~N~Ni
20 20 30 17 30
state. The fitting with the above mentioned values of the different exchange integrals to the Curie temperature data which has a broad maximum at x 20 suggests that the density of the spin wave states at a given low spin wave energy has a shallow minimum at this composition and increases as x is increased. It is noticed in table 1 that a similar trend was obtained in the value of bi versus x, although a broad minimum in I bI versus x is not clear due to the scattering in the data. While the correlation between T~and b is rather poor due mainly to the relatively small change of T~with x, a more definite support for a similar correlation has been recently found in amorphous Fe-Ni-Pd-P alloys [91. In this case I bI increased from about 250 to 50°K.These observations may indicate that the logarithmic temperature dependence of the resistivity originates from an electron-magnon interaction discussed elsewhere [10]
where Prm (resistivity at room temperature), a, a’, b, d and T0 are listed in table 1. The Curie temperature T~of the amorphous alloys was determined by using an inductance bridge and is plotted in fig. 2 in a unit normalized to the value T~= 585°Kof a Fe75P15C10 alloy. These data were fitted to the results obtained by a coherent potential approximation 1
1.30 1.44 1.30 1.88 1.68
0.(:o
=
.
10 .
20
30
40
50
Fig. 2. Curie temperature ratio versus x for the amorphous (Fe~o~~ Ni~)7sP15C10 alloys. The value of Tc for x 0 is taken as 585°K.
Volume 42A, number 6
PHYSICS LETTERS
The implication of this interpretation is that the magnon system could have some degree of internal freedom because of the amorphous nature of the present alloys. Consequently the resistivity anomaly tends to be suppressed in an imperfectly quenched ferromagnetic alloys as observed previously [7].
References [11 S.C.H. 469.
Lin and Pol Duwez, Phys. Stat. sol. 34 (1969)
15 January 1973
[2] P.K. Rastogi and Pol Duwez, J. Non-Cryst. Sol. 5 (1970) 1. [3] R. Hasegawa, Phys. Rev. B3 (1971) 1631. 141 There are some uncertainties as to the magnetic properties of the Mn-P-C alloys. See A.K. Sinha, J. Appl. Phys. 42 (1971) 338. [5] Pol Duwez and S.C.H. Lin, J. Appi. Phys. 38 (1967) 4096. [61 C.C. Tsuei, G. Longworth and S.C.H. Lin, Phys. Rev. 170 (1968) 603. [7] S.C.H. Lin, J. Appi. Phys. 40(1969) 2173. [8] E-N. Foo and D-H. Wu, Phys. Rev. B5 (1972) 98. [9] R. Hasegawa, to be published. [10] R. Hasegawa, Phys. Lett. 36A (1971) 207.
409
PHYSICS LETTERS
15 January 1973
ELECTRICAL RESISTIVITY AND CURIE TEMPERATURE OF AMORPHOUS (Fe-Ni)-P-C ALLOYS* R. HASEGAWA and J.A. DERMON W.M. Keck Laboratory of EngineeringMaterials, California Institute of Technology, Pasadena, California 91109, USA Received 28 October 1972 Low temperature electrical resistivity and Curie temperature of amorphous (Fe 100_x Nix)75 P15C10 alloys (0 ~ x ~ 50) were studied. An application of the data to a result of a coherent potential approximation method leads to an explanation of the low temperature resistivity anomaly in terms of an electron-magnon interaction.
Among the amorphous alloys obtained by rapidquenching from the liquid state, the amorphous Fe75P15C10 alloys are unique in the sense that they contain two different glass formers. Due to this fact, the structure of these alloys seems to be complicated. In a study, these alloys have been described by a randomized b.c.c. iron at least up to the first nearest neighbours [1]. A more recent study shows that the approximate composition of the equilibrium alloy is 56 at.% Fe3P, 37 at.% Fe3C and
7 at.% Fe [21. This may indicate that the local structures in the amorphous state are based on these atomic configurations and these phases are mixed randomly. This picture was used in describing the magnetic properties of an amorphous Mn75P15C10 alloy [3] which was obtained by analogy to the Fe-P-C amorphous alloy. While the problem whether or not the amorphous Fe-P-C alloy has a single or several amorphous phases has to be clarified yet, its macroscopic magnetic properties are less controversial [4] They are briefly characterized by a ferromagnetic Curie temperature of about 590°K,the .
*
Work supported by the U.S. Atomic Energy Commission. 1.000
0.9 90
-
0.976~ 0.975
5
0 IS 20
(°K) E 0.980
0.990
•
-
-
•S • •.
0.970
•s
—
E 0.980
-
097~~ 50 100 0.960
150
200 I
(°K) 0
I
50
100
I
50
200
250
300
TEMPERATURE (°K) 2 dependence Fig. of the 1. resistivity. Resistivity versus temperature for an amorphous (Fe80Ni20)75P15C10 alloy. The insets show the In T and the T 407
Volume 42A, number 6
PHYSICS LETTERS
15 January 1973
Table 1 Results of resistivity measurements on amorphous (Fejoo..x NiX)I 5PISC1O alloys. The value Tm is the resistivity minimum temperature 4) c(107)d(104) Tm(°K) T x prm(I.L~.cm) aa b(10 0(°K) 0 10 20 30 40
194.32 134.80 168.10 181.70 180.56
0.968 0.970 0.977 0.959 0.968
0.961 0.957 0.961 0.945 0.945
—6.20 —6.82 —7.10 —6.48 —9.11
coercive force of 3 Oe [5] and the saturation magnetic moment of 2.1 ~B [6] The electjical resistivity of this amorphous alloy showed a minimum in the resistivity versus temperature curve [7]. Although the occurrence of the resistivity minimum was attributed to the amorphous nature of the alloy, it has not been clearly explained. An attempt is made in this study to explain the resistivity anomaly. The alloys studied have the composition (Feioo~Ni~)75Pi5Cio where x is changed from 0 to 50 and were prepared by a procedure similar to that described elsewhere [5]. An X-ray analysis shows that the alloys are amorphous for x ~ 40 and contain a small amount of crystalline phases for ~ > 40. The resistivity of the present alloys was measured by a conventional four-probe method between 4.2 and 300°K.A typical example of the results is shown in fig. 1. The resistivity can be fitted to the following formulas 2, T<
a’+dT
6.10 6.80 3.32 8.50 5.50
.1101
11
—1
7
—1’~
I
0
0.8
0
EXPERIMENTAL CPA
0.7 (Feio0~Ni~)75 P~C~
.1
‘‘~Fe-Ni i.LanU
0, where IA-B stands for the exchange integral between A and B atom. This is shown by the dotted line in fig. 2. The fitting of the T data to the CPA c result with ~N~Ni = 0 implies that a Ni-P-C alloy would be paramagnetic if it is obtained in an amorphous 408
110 150 210 180 240
T>T0
meLIlou ~°J WiUIJF~Fe
~N~Ni
20 20 30 17 30
state. The fitting with the above mentioned values of the different exchange integrals to the Curie temperature data which has a broad maximum at x 20 suggests that the density of the spin wave states at a given low spin wave energy has a shallow minimum at this composition and increases as x is increased. It is noticed in table 1 that a similar trend was obtained in the value of bi versus x, although a broad minimum in I bI versus x is not clear due to the scattering in the data. While the correlation between T~and b is rather poor due mainly to the relatively small change of T~with x, a more definite support for a similar correlation has been recently found in amorphous Fe-Ni-Pd-P alloys [91. In this case I bI increased from about 250 to 50°K.These observations may indicate that the logarithmic temperature dependence of the resistivity originates from an electron-magnon interaction discussed elsewhere [10]
where Prm (resistivity at room temperature), a, a’, b, d and T0 are listed in table 1. The Curie temperature T~of the amorphous alloys was determined by using an inductance bridge and is plotted in fig. 2 in a unit normalized to the value T~= 585°Kof a Fe75P15C10 alloy. These data were fitted to the results obtained by a coherent potential approximation 1
1.30 1.44 1.30 1.88 1.68
0.(:o
=
.
10 .
20
30
40
50
Fig. 2. Curie temperature ratio versus x for the amorphous (Fe~o~~ Ni~)7sP15C10 alloys. The value of Tc for x 0 is taken as 585°K.
Volume 42A, number 6
PHYSICS LETTERS
The implication of this interpretation is that the magnon system could have some degree of internal freedom because of the amorphous nature of the present alloys. Consequently the resistivity anomaly tends to be suppressed in an imperfectly quenched ferromagnetic alloys as observed previously [7].
References [11 S.C.H. 469.
Lin and Pol Duwez, Phys. Stat. sol. 34 (1969)
15 January 1973
[2] P.K. Rastogi and Pol Duwez, J. Non-Cryst. Sol. 5 (1970) 1. [3] R. Hasegawa, Phys. Rev. B3 (1971) 1631. 141 There are some uncertainties as to the magnetic properties of the Mn-P-C alloys. See A.K. Sinha, J. Appl. Phys. 42 (1971) 338. [5] Pol Duwez and S.C.H. Lin, J. Appi. Phys. 38 (1967) 4096. [61 C.C. Tsuei, G. Longworth and S.C.H. Lin, Phys. Rev. 170 (1968) 603. [7] S.C.H. Lin, J. Appi. Phys. 40(1969) 2173. [8] E-N. Foo and D-H. Wu, Phys. Rev. B5 (1972) 98. [9] R. Hasegawa, to be published. [10] R. Hasegawa, Phys. Lett. 36A (1971) 207.
409