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Magnetic properties of amorphous Co-HR (HR = Gd, Dy, Er) alloys
39
Journal of Magnetism and Magnetic Materials 73 (1988) 39-45 North-Holland, Amsterdam
MAGNETIC
PROPERTIES
OF AMORPHOUS
Co-HR
(HR = Gd, Dy, Er) ALLOYS
YANG Xingbo and T. MIYAZAKI Department
of Applied Physics, Tohoku Uniuersity, Sendai 980, Japan
Received 4 December 1987; in revised form 25 January 1988
Investigation of magnetic properties was carried out in the temperature range from 4.2 to 500 K on amorphous Co,,_,HR, (HR = Gd, Dy, Er; 50 6 x Q 70) alloys prepared by a liquid-quenching technique through measuring magnetixation and susceptibility. The magnetic moment inherent in the Co ion disappears around x = 60. That the experimental values of the average magnetic moment per atom for x < 60 are smaller than the contributing values from the mere HR3’ ion may be associated with chemical’and magnetical short-range ordering present in the amorphous Co-HR alloys. No field-cooling effect was observed in the investigated amorphous samples.
1. Introduction
2. Experimenta’
Rare earth-transition metal alloys are perhaps the most rewarding materials in amorphous magnetism because of the opportunity that they present for systematic study of the effects of anisotropy, exchange and electron localization etc. [l]. In a previous investigation we analyzed the magnetic properties of amorphous Co,,_,LR, (LR = Pr, Nd, Sm; 50 6 x Q 70) alloys based on a localized moment model, and concluded that the magnitude of the effective magnetic moment of Co decreases with an increase of x and vanishes around x = 60 [2]. The reduction in 3d moment in such alloys may be due to one or more of the following mechanisms: (i) charge transfer between the composing metals, (ii) hybridization and mixing effects of orbitals between composite metals and (iii) environmental effects depending on compositional short-range ordering [3]. On the other hand, for the heavy rare earth-rich cobalt alloys the magnetic data reported in the literature are not many [4-71. In the present study, we have extended our interest to the Co,,_,HR, (HR = Gd, Dy, Er; 50 d x < 70) amorphous alloys prepared by a liquid-quenching method. In the following, we discuss their magnetic properties in comparison with those of amorphous Co,,_.LR, alloys.
Co,,_,HR, (HR = Gd, ;Dy, Er; 40 Q x d 70) alloy ribbons ‘were prepared .by liquid-quenching in an atmosphere of purified argon gas using alloy buttons of the appropriate composition which had been made by arc melting from 99.9 wt% pure rare earth and 99.95 wt% pure cobalt. The ribbons fabricated in this way w:ere about 15 to 18 urn thick and 0.6 mm wide. X;ray< structural analysis was performed with the Debye-Sherrer method using a filtered Fe-Ka radiation. The X-ray diffraction photographs for the, alloys, in the cd% position range 50 d x Q 70 exhibited a halo, indicating that an amorphous State was achieved in these alloys. The amorphous ribbons showed an excellent pliability. The temperature dependence of magnetization and susceptibility were measured by increasing temperature from-42 to 500:K and using a Faraday-type magnetic balance in applied fields up to 14 kOe.
3. Experimental results Figs. la and b show the isothermal magnetization curves of the CoNGdm and Co,Er,, amorphous alloys, which are typical of the Co-Gd
0304-8853/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
40
Yang Xingbo, T. Miyazaki
/ Magnetic properties of amorphous Co-HR
160 4 2 K9 13
@ 90
b
80
17
2 .% 60
b 30 0
21 26
I
36 106 294
1
au’0
3
6 H
I
I
9
12
I
I5
0
I
bmO
17
3
6
9 H
(kOe)
Fig. 1. The isothermal magnetization curves for the CoaGdw
and Co-Er systems, respectively. The isothermal magnetization curves for both alloys exhibit a ferromagnet-like behaviour. The magnetization presents a tendency to saturation in the field of 14 kOe at 4.2 K for Co,Gd,,, but does not for Co,Er,, which exhibits a strong high-field susceptibility at low temperatures. The Arrott-plots corresponding to figs. la and b are shown in figs. 2a and b, respectively. A linear relationship between a* and H/a is observed in a wide temperature range. The magnetization behaviour for the Co-Dy alloys resembled that of the Co-Er alloys.
(a) and Co,Er,
12
The 14 kOe magnetization obtained at 4.2 K is plotted in fig. 3 against x for the Co,,_,HR, alloys, increasing with a rise in HR content. Figs. 4a, b and c show the temperature dependence of the 14 kOe magnetization of liquidquenched CO~~._~HR, (HR = Gd, Dy, Er; 40 < x & 70) alloys. The open and solid circles represent the data taken on heating the samples from 4.2 K after cooling them to 4.2 K from room temperature in zero and 14 kOe fields, respectively. A field-cooling effect is observed in the crystalline Co-Er and Co-Dy alloys (x = 40), but not in the
HAT
(gOe/emu)
Fig. 2. The isothermal Arrott-plots O* vs. H/o
15
(b) amorphous alloys.
32
H/C
_
(kOe)
96
“b
_
54
for the Co,Gd,O
(a) and Co,Er,,
(gOe/emu)
(b) amorphous alloys.
Yang Xingbo, T. Miyazaki
240
220
co 200
7
180
2 ”
b
P
160
COIOO-XDYX L
f
j-
140
120
100 I
80 40
50
I
1
60
70
80
X
Fig.
3. The
14 kOe magnetization amorphous Co,,_,HR,
as a function alloys.
41
amorphous alloys (x 2 50). All amorphous Co-HR alloys show a long tail on the magnetization vs. temperature curves after a rapid decrease in magnetization with increasing temperature. This is slightly different from the light rare earth-cobalt alloys (see ref. [2]). Generally speaking, the present alloys can be classified as ferromagnetic. The Curie temperature signalling the ferromagnetism-paramagnetism transition was determined by plotting the intersection crz of the a* vs. H/a straight lines with the a2 axis against T, as illustrated in the inset of figs. 2a and b. In the paramagnetic regime, the variation of the inverse susceptibility with temperature for all amorphous alloys obeys the Curie-Weiss law. In the case of the Co-Gd alloys, the x-l vs. T curves on heating and cooling coincide with each other, this indicates no occurrence of crystallization below 500 K. This agrees with the result of Buschow et al.: that no crystallization takes place below 580 K (310” C) [8]. We obtained the Weiss temperature t$ and average effective moment j&r per atom from the intersections of the x-l vs. T lines with the T axis and their slopes. Fig. 5 gives the com-
I
I
I
/ Magnetic properties of amorphous Co-HR
of x for
6 80
0 80 ?
40
2 ”
0 80
b 40
0 80
0
100
200
300 T
400
500
(K)
Fig. 4. The temperature dependence of the 14 kOe magnetization and inverse susceptibility for the Co,oo_xGdx (a), CO~~.~D~~ and CO~,,,_~E~, (c) amorphous alloys. Open circles: zero-field-cooled, solid circles: field-cooled.
0))
42
Yang Xingbo, T. Miyazaki
/ Magnetic properties
of amorphous Co-HR
plings between the lanthanide and transition metal moments. In the case of their amorphous alloys in which the orbital moment is not zero, the resultant effect of the exchange interaction and local random anisotropy gives rise to a canted ferrimagnetic order with a fan-like arrangement of the rare earth spins (sperimagnetic structure). That the magnetization of the Co-Er and Co-Dy alloys is far from being saturated in a 14 kOe field at 4.2 K is characteristic of the noncollinear structure of the HR spins dominated by the strong local random anisotropy. On the other hand, the effects of local random anisotropy are believed to be quite little on the magnetism of the Co-Gd alloys since
position dependence of T,and 8, for the CO~~_~ HR, alloys. T, is roughly identical to 8,. T, (or or,) steeply decreases with an increase in HR content and gradually above x = 60. This tendency is very similar to that of the LR-Co alloys. The average effective moment p,,, is shown in fig. 6 as a function of HR content. The p,, increases with HR content, exhibiting a composition dependence different from that of the LR-Co system [2]. 4. Discussion All heavy lanthanide-transition metal alloys which are magnetic show antiferromagnetic cou-
120
3
80
2
40
I
0
0
120
3
80
2
80
T
(K)
Fig. 4 (continued).
Yang Xingbo, T. Miyazaki
/ Magnetic properties of amorphous Co-HR
the orbital angular moment of the Gd ion equals zero. Consequently, the ferrimagnetic ordering can be realized in the amorphous Co-Gd alloys. Assuming that the Co-Gd alloys are nearly saturated in 14 kOe at 4.2 K, we derived the average saturation moment using the magnetization data presented in fig. 3 and plotted it in fig. 7. CL,quickly rises with R content, showing a similar composition dependence with p,,,. According to a localized moment model the moment per average atom, F,, may be expressed by jI, = [xp(Gd)
f (100 - x)/.~(Co)]/100,
where p(Gd) and I
43
and Co atom, respectively. Assuming p(Gd) = 7~,, we calculated the I using the data shown in fig. 7, and found that the Co moment rapidly decreases with the Gd content from about 0.6~~ in Co,,GdSO to about zero in Co,Gd,,. For x > 60 the Co ion has roughly no contribution to ji, of the alloys. The broken line given in fig. 7 represents the contribution of the mere Gd to the j& of the alloys, which is in good agreement with the experimental data points above 60 at% Gd in the error limit. The behaviour that the change of the inverse susceptibility with temperature obeys the CurieWeiss law in the paramagnetic regime suggests
(1)
are the moment per Gd I60
5
1 80 2
3
1 80
b
2
; B
0
: ID “0 _
120 4 80 2
40
0
4 80 2
100
200
T
(K)
Fig. 4 (continued).
T x
Yang Xingbo, T. Miyazaki
44
150t
r
120
,
,
,
/ Magnetic properties of amorphous Co-HR
1
61 r
I 40 I
0' 40
50
I
60
1
I
70
80
X Fig. 5. The Curie temperature (0) and Weiss temperature (0) as a function of x for the amorphous Co,,_,HR, alloys. The A mark in the case of Co-Gd alloys and the 0 mark in the case of Co-Dy alloys are T, data of ref. [4] and ref. [5], respectively.
that the localized moment model is proper for the present three CO~~_.~HR, systems. The average effective moment per atom can be presented by F,‘fr = [ XP~(HR)
+
(100 - ~p~(c~)]/ioo,
,
I
50
I
,
60
,
I
70
I
I 80
X Fig. 6. The average effective moment Fe,,, as a function of x for the amorphous Cot,_,HR, alloys.
tion of the p,, data points from the broken line for x < 60 is probably associated with the existence of moments inherent in Co ions, indicating that P(Co) # 0 in the x < 60 alloys. However, why the experimental p,,, values are smaller than those
(2)
where P(HR) and P(Co) are the effective moment per HR atom and Co atom at X, respectively. Assuming that the rare earth ions retain their normal HR3’ character and that Co has no contribution to pefr, we obtained the broken lines shown in fig. 6 using eq. (2). It can be seen that the p,,, data points for the composition of x > 60 almost agree with the values presented by the broken line in the error limit. This suggests that the conclusion of P(Co) = 0 near x = 60 is also appropriate for the Co-HR as for the Co-LR alloys. The devia-
2’ 40
I
I
I
I
50
60
70
80
X Fig. 7. The average saturation moment p, as a function of x for the Co,,_,Gd, amorphous alloys at 4.2 K.
Yang Xingbo, T. Miyazaki / Magnetic properties of amorphous Co-HR
given by the broken lines below 60 at’% HR is still a unclear problem. It may be associated with the chemical and magnetical short-range ordering in the present amorphous Co-HR alloys, seeming able to be explained by the effect of local spin fluctuations (fluctuations in the direction and the amplitude of the local spin density) [9,10]. From the above analysis, we can draw the conclusion that Co no longer sustains a moment above 60 at% rare earth for all lanthanide rare earth-cobalt amorphous binary alloys.
45
age magnetic moment per atom for x < 60 are smaller than the contributing values of the mere HR3’ ion can be considered to be due to the chemical and magnetical short-range ordering present in the investigated amorphous Co-HR alloys.
Acknowledgement
Authors would like to thank Dr. S. Ishio for many stimulating discussions.
5. summaly
The magnetic properties of amorphous Co,,_,HR, (HR = Gd, Dy, Er; 40 < x d 70) alloys prepared by a liquid-quenching technique have been investigated by measuring magnetization and susceptibility in the temperature range from 4.2 to 500 K. The results can be summarized as follows: (1) The amorphous state is achieved over the composition interval 50 < x < 70. (2) The susceptibility shows a Curie-Weiss-type temperature dependence in paramagnetic state. 6, is roughly identical to T, determined by the Arrott-plot method. (3) The magnetic moment inherent in the Co ion vanishes around 60 at% HR. (4) The reasons why the experimental values of the aver-
References [l] K. Moojani and J.M.D. Coey, Magnetic Glasses (NorthHolland, Amsterdam, 1984) chap. VI. [2] X.-b. Yang, T. Izumi, T. Miyazaki, C. Horie and M. Takahashi, J. Magn. Magn. Mat. 67 (1987) 365. [3] K.H.J. Buschow, J. Appl. Phys. 53 (1983) 2578. [4] K.H.J. Buschow, J. Appl. Phys. 51 (1980) 2795. [5] P.C.M. Gubbens, A.M. van der Kraan and K.H.J. Buschow, Phys. Stat. Sol. (a) 64 (1981) 657. [6] K. Fukarnichi, M. Kikuchi, T. Masumoto and M. Matsuura, Phys. Lett. A 73 (1979) 436. [7] A.S. JaswaI, D.J. Sellmyer, M. Engelhardt, 2. Zhao, A.J. Arko and K. Xie, Phys. Rev. B35 (1987) 996. [8] K.H.J. Buschow and A.G. Dirks, J. Phys. D13 (1980) 251. [9] T. Moriya and Y. Takahashi, J. Phys. Sot. Japan 45 (1978) 397. [lo] H. Hasegawa, Solid State Phys. 14 (1979) 369 (in Japanese).
Journal of Magnetism and Magnetic Materials 73 (1988) 39-45 North-Holland, Amsterdam
MAGNETIC
PROPERTIES
OF AMORPHOUS
Co-HR
(HR = Gd, Dy, Er) ALLOYS
YANG Xingbo and T. MIYAZAKI Department
of Applied Physics, Tohoku Uniuersity, Sendai 980, Japan
Received 4 December 1987; in revised form 25 January 1988
Investigation of magnetic properties was carried out in the temperature range from 4.2 to 500 K on amorphous Co,,_,HR, (HR = Gd, Dy, Er; 50 6 x Q 70) alloys prepared by a liquid-quenching technique through measuring magnetixation and susceptibility. The magnetic moment inherent in the Co ion disappears around x = 60. That the experimental values of the average magnetic moment per atom for x < 60 are smaller than the contributing values from the mere HR3’ ion may be associated with chemical’and magnetical short-range ordering present in the amorphous Co-HR alloys. No field-cooling effect was observed in the investigated amorphous samples.
1. Introduction
2. Experimenta’
Rare earth-transition metal alloys are perhaps the most rewarding materials in amorphous magnetism because of the opportunity that they present for systematic study of the effects of anisotropy, exchange and electron localization etc. [l]. In a previous investigation we analyzed the magnetic properties of amorphous Co,,_,LR, (LR = Pr, Nd, Sm; 50 6 x Q 70) alloys based on a localized moment model, and concluded that the magnitude of the effective magnetic moment of Co decreases with an increase of x and vanishes around x = 60 [2]. The reduction in 3d moment in such alloys may be due to one or more of the following mechanisms: (i) charge transfer between the composing metals, (ii) hybridization and mixing effects of orbitals between composite metals and (iii) environmental effects depending on compositional short-range ordering [3]. On the other hand, for the heavy rare earth-rich cobalt alloys the magnetic data reported in the literature are not many [4-71. In the present study, we have extended our interest to the Co,,_,HR, (HR = Gd, Dy, Er; 50 d x < 70) amorphous alloys prepared by a liquid-quenching method. In the following, we discuss their magnetic properties in comparison with those of amorphous Co,,_.LR, alloys.
Co,,_,HR, (HR = Gd, ;Dy, Er; 40 Q x d 70) alloy ribbons ‘were prepared .by liquid-quenching in an atmosphere of purified argon gas using alloy buttons of the appropriate composition which had been made by arc melting from 99.9 wt% pure rare earth and 99.95 wt% pure cobalt. The ribbons fabricated in this way w:ere about 15 to 18 urn thick and 0.6 mm wide. X;ray< structural analysis was performed with the Debye-Sherrer method using a filtered Fe-Ka radiation. The X-ray diffraction photographs for the, alloys, in the cd% position range 50 d x Q 70 exhibited a halo, indicating that an amorphous State was achieved in these alloys. The amorphous ribbons showed an excellent pliability. The temperature dependence of magnetization and susceptibility were measured by increasing temperature from-42 to 500:K and using a Faraday-type magnetic balance in applied fields up to 14 kOe.
3. Experimental results Figs. la and b show the isothermal magnetization curves of the CoNGdm and Co,Er,, amorphous alloys, which are typical of the Co-Gd
0304-8853/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
40
Yang Xingbo, T. Miyazaki
/ Magnetic properties of amorphous Co-HR
160 4 2 K9 13
@ 90
b
80
17
2 .% 60
b 30 0
21 26
I
36 106 294
1
au’0
3
6 H
I
I
9
12
I
I5
0
I
bmO
17
3
6
9 H
(kOe)
Fig. 1. The isothermal magnetization curves for the CoaGdw
and Co-Er systems, respectively. The isothermal magnetization curves for both alloys exhibit a ferromagnet-like behaviour. The magnetization presents a tendency to saturation in the field of 14 kOe at 4.2 K for Co,Gd,,, but does not for Co,Er,, which exhibits a strong high-field susceptibility at low temperatures. The Arrott-plots corresponding to figs. la and b are shown in figs. 2a and b, respectively. A linear relationship between a* and H/a is observed in a wide temperature range. The magnetization behaviour for the Co-Dy alloys resembled that of the Co-Er alloys.
(a) and Co,Er,
12
The 14 kOe magnetization obtained at 4.2 K is plotted in fig. 3 against x for the Co,,_,HR, alloys, increasing with a rise in HR content. Figs. 4a, b and c show the temperature dependence of the 14 kOe magnetization of liquidquenched CO~~._~HR, (HR = Gd, Dy, Er; 40 < x & 70) alloys. The open and solid circles represent the data taken on heating the samples from 4.2 K after cooling them to 4.2 K from room temperature in zero and 14 kOe fields, respectively. A field-cooling effect is observed in the crystalline Co-Er and Co-Dy alloys (x = 40), but not in the
HAT
(gOe/emu)
Fig. 2. The isothermal Arrott-plots O* vs. H/o
15
(b) amorphous alloys.
32
H/C
_
(kOe)
96
“b
_
54
for the Co,Gd,O
(a) and Co,Er,,
(gOe/emu)
(b) amorphous alloys.
Yang Xingbo, T. Miyazaki
240
220
co 200
7
180
2 ”
b
P
160
COIOO-XDYX L
f
j-
140
120
100 I
80 40
50
I
1
60
70
80
X
Fig.
3. The
14 kOe magnetization amorphous Co,,_,HR,
as a function alloys.
41
amorphous alloys (x 2 50). All amorphous Co-HR alloys show a long tail on the magnetization vs. temperature curves after a rapid decrease in magnetization with increasing temperature. This is slightly different from the light rare earth-cobalt alloys (see ref. [2]). Generally speaking, the present alloys can be classified as ferromagnetic. The Curie temperature signalling the ferromagnetism-paramagnetism transition was determined by plotting the intersection crz of the a* vs. H/a straight lines with the a2 axis against T, as illustrated in the inset of figs. 2a and b. In the paramagnetic regime, the variation of the inverse susceptibility with temperature for all amorphous alloys obeys the Curie-Weiss law. In the case of the Co-Gd alloys, the x-l vs. T curves on heating and cooling coincide with each other, this indicates no occurrence of crystallization below 500 K. This agrees with the result of Buschow et al.: that no crystallization takes place below 580 K (310” C) [8]. We obtained the Weiss temperature t$ and average effective moment j&r per atom from the intersections of the x-l vs. T lines with the T axis and their slopes. Fig. 5 gives the com-
I
I
I
/ Magnetic properties of amorphous Co-HR
of x for
6 80
0 80 ?
40
2 ”
0 80
b 40
0 80
0
100
200
300 T
400
500
(K)
Fig. 4. The temperature dependence of the 14 kOe magnetization and inverse susceptibility for the Co,oo_xGdx (a), CO~~.~D~~ and CO~,,,_~E~, (c) amorphous alloys. Open circles: zero-field-cooled, solid circles: field-cooled.
0))
42
Yang Xingbo, T. Miyazaki
/ Magnetic properties
of amorphous Co-HR
plings between the lanthanide and transition metal moments. In the case of their amorphous alloys in which the orbital moment is not zero, the resultant effect of the exchange interaction and local random anisotropy gives rise to a canted ferrimagnetic order with a fan-like arrangement of the rare earth spins (sperimagnetic structure). That the magnetization of the Co-Er and Co-Dy alloys is far from being saturated in a 14 kOe field at 4.2 K is characteristic of the noncollinear structure of the HR spins dominated by the strong local random anisotropy. On the other hand, the effects of local random anisotropy are believed to be quite little on the magnetism of the Co-Gd alloys since
position dependence of T,and 8, for the CO~~_~ HR, alloys. T, is roughly identical to 8,. T, (or or,) steeply decreases with an increase in HR content and gradually above x = 60. This tendency is very similar to that of the LR-Co alloys. The average effective moment p,,, is shown in fig. 6 as a function of HR content. The p,, increases with HR content, exhibiting a composition dependence different from that of the LR-Co system [2]. 4. Discussion All heavy lanthanide-transition metal alloys which are magnetic show antiferromagnetic cou-
120
3
80
2
40
I
0
0
120
3
80
2
80
T
(K)
Fig. 4 (continued).
Yang Xingbo, T. Miyazaki
/ Magnetic properties of amorphous Co-HR
the orbital angular moment of the Gd ion equals zero. Consequently, the ferrimagnetic ordering can be realized in the amorphous Co-Gd alloys. Assuming that the Co-Gd alloys are nearly saturated in 14 kOe at 4.2 K, we derived the average saturation moment using the magnetization data presented in fig. 3 and plotted it in fig. 7. CL,quickly rises with R content, showing a similar composition dependence with p,,,. According to a localized moment model the moment per average atom, F,, may be expressed by jI, = [xp(Gd)
f (100 - x)/.~(Co)]/100,
where p(Gd) and I
43
and Co atom, respectively. Assuming p(Gd) = 7~,, we calculated the I using the data shown in fig. 7, and found that the Co moment rapidly decreases with the Gd content from about 0.6~~ in Co,,GdSO to about zero in Co,Gd,,. For x > 60 the Co ion has roughly no contribution to ji, of the alloys. The broken line given in fig. 7 represents the contribution of the mere Gd to the j& of the alloys, which is in good agreement with the experimental data points above 60 at% Gd in the error limit. The behaviour that the change of the inverse susceptibility with temperature obeys the CurieWeiss law in the paramagnetic regime suggests
(1)
are the moment per Gd I60
5
1 80 2
3
1 80
b
2
; B
0
: ID “0 _
120 4 80 2
40
0
4 80 2
100
200
T
(K)
Fig. 4 (continued).
T x
Yang Xingbo, T. Miyazaki
44
150t
r
120
,
,
,
/ Magnetic properties of amorphous Co-HR
1
61 r
I 40 I
0' 40
50
I
60
1
I
70
80
X Fig. 5. The Curie temperature (0) and Weiss temperature (0) as a function of x for the amorphous Co,,_,HR, alloys. The A mark in the case of Co-Gd alloys and the 0 mark in the case of Co-Dy alloys are T, data of ref. [4] and ref. [5], respectively.
that the localized moment model is proper for the present three CO~~_.~HR, systems. The average effective moment per atom can be presented by F,‘fr = [ XP~(HR)
+
(100 - ~p~(c~)]/ioo,
,
I
50
I
,
60
,
I
70
I
I 80
X Fig. 6. The average effective moment Fe,,, as a function of x for the amorphous Cot,_,HR, alloys.
tion of the p,, data points from the broken line for x < 60 is probably associated with the existence of moments inherent in Co ions, indicating that P(Co) # 0 in the x < 60 alloys. However, why the experimental p,,, values are smaller than those
(2)
where P(HR) and P(Co) are the effective moment per HR atom and Co atom at X, respectively. Assuming that the rare earth ions retain their normal HR3’ character and that Co has no contribution to pefr, we obtained the broken lines shown in fig. 6 using eq. (2). It can be seen that the p,,, data points for the composition of x > 60 almost agree with the values presented by the broken line in the error limit. This suggests that the conclusion of P(Co) = 0 near x = 60 is also appropriate for the Co-HR as for the Co-LR alloys. The devia-
2’ 40
I
I
I
I
50
60
70
80
X Fig. 7. The average saturation moment p, as a function of x for the Co,,_,Gd, amorphous alloys at 4.2 K.
Yang Xingbo, T. Miyazaki / Magnetic properties of amorphous Co-HR
given by the broken lines below 60 at’% HR is still a unclear problem. It may be associated with the chemical and magnetical short-range ordering in the present amorphous Co-HR alloys, seeming able to be explained by the effect of local spin fluctuations (fluctuations in the direction and the amplitude of the local spin density) [9,10]. From the above analysis, we can draw the conclusion that Co no longer sustains a moment above 60 at% rare earth for all lanthanide rare earth-cobalt amorphous binary alloys.
45
age magnetic moment per atom for x < 60 are smaller than the contributing values of the mere HR3’ ion can be considered to be due to the chemical and magnetical short-range ordering present in the investigated amorphous Co-HR alloys.
Acknowledgement
Authors would like to thank Dr. S. Ishio for many stimulating discussions.
5. summaly
The magnetic properties of amorphous Co,,_,HR, (HR = Gd, Dy, Er; 40 < x d 70) alloys prepared by a liquid-quenching technique have been investigated by measuring magnetization and susceptibility in the temperature range from 4.2 to 500 K. The results can be summarized as follows: (1) The amorphous state is achieved over the composition interval 50 < x < 70. (2) The susceptibility shows a Curie-Weiss-type temperature dependence in paramagnetic state. 6, is roughly identical to T, determined by the Arrott-plot method. (3) The magnetic moment inherent in the Co ion vanishes around 60 at% HR. (4) The reasons why the experimental values of the aver-
References [l] K. Moojani and J.M.D. Coey, Magnetic Glasses (NorthHolland, Amsterdam, 1984) chap. VI. [2] X.-b. Yang, T. Izumi, T. Miyazaki, C. Horie and M. Takahashi, J. Magn. Magn. Mat. 67 (1987) 365. [3] K.H.J. Buschow, J. Appl. Phys. 53 (1983) 2578. [4] K.H.J. Buschow, J. Appl. Phys. 51 (1980) 2795. [5] P.C.M. Gubbens, A.M. van der Kraan and K.H.J. Buschow, Phys. Stat. Sol. (a) 64 (1981) 657. [6] K. Fukarnichi, M. Kikuchi, T. Masumoto and M. Matsuura, Phys. Lett. A 73 (1979) 436. [7] A.S. JaswaI, D.J. Sellmyer, M. Engelhardt, 2. Zhao, A.J. Arko and K. Xie, Phys. Rev. B35 (1987) 996. [8] K.H.J. Buschow and A.G. Dirks, J. Phys. D13 (1980) 251. [9] T. Moriya and Y. Takahashi, J. Phys. Sot. Japan 45 (1978) 397. [lo] H. Hasegawa, Solid State Phys. 14 (1979) 369 (in Japanese).