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How would silicon affect magnetic and transport properties of (Fe-V)80(BSi)20 glasses?
Journal of Magnetism and Magnetic Materials 125 (1993) 315-318 North-Holland
How would silicon affect magnetic and transport properties of (Fe-V) 80(BSi) 2o glasses ? S.U. J e n a, y . y . C h e n a, J.S.C. J a n g b a n d C.H. T s a u b a Institute of Physics, Academia $inica, Taipei, Taiwan, ROC b Materials Research Laboratory, ITRI, Chutung, Hsinchu, Taiwan, ROC
Received 24 November 1992
Two series of amorphous (Fe10o_xVx)8oB20 and (Fel0o_yVy)aoB14Si 6 alloys have been made by the rapid quenching method. The measured physical properties include the saturation moment (trs), electrical resistivity (Po), specific heat'(C), and anisotropic magnetoresistance (Ap/po) at 4 K. The X and Y dependences of those physical properties are studied, respectively. When comparing o's,or go, or Ap/po data of (Feloo_xVx)aoB20and (Feloo_yVr)soB14Si6 glasses, we can see the differences caused by replacing boron with silicon in limited ranges of X or Y. The Debye temperature 0o of (Feloo_xVx)aoB20 glasses is briefly examined.
1. Introduction
2. Experiments
In the past, a few studies have been made on the magnetic and transport properties of ( F e V)8o(BSi)20 glasses [1-3], but a systematic investigation on how different metalloids would affect these physical properties is lacking. In this paper, we have made two series of (Fel00_xVx)80B2o and (Fe10o_yVy)80B14Si6 glasses. The total concentration of the metalloids is fixed at 20 at%, but one element of the metalloids, namely silicon, is changed from 0 to 6 at%. Our purpose is twofold: (i) to study the X and Y dependences of the measured properties such as saturation magnetization O-s, electrical resistivity Po, specific heat C, and anisotropic magnetoresistance A o / p o respectively, and (ii) to compare data of the two glasses in the case of X = Y.
The samples were splat-cooled from the melt by a melt-spinner. The rotating velocity of the copper wheel was in the range 25-35 m / s . The X-series samples were about 3 mm wide, and the Y-series samples about 1 mm wide. Each ribbon was checked by X-ray spectroscopy to ensure that no crystalline phase was present. The thickness t of each sample was determined by observing its cross-section in SEM. Because some of the glasses showed non-uniform thickness along its width, we had to estimate average values, tare. In general, tare --- 25 Ixm for (Fel0o_xVx)a0B20 and tar e = 15 I~m for (Fel00_ r Vy)80BlaSi 6. The error in tav~, which is about 2 - 5 % , may cause the same error in the resistivity value. Magnetization measurements were made at 5 K in a constant field of 1 T by a S Q U I D magnetometer. For electrical resistivity or anisotropic magnetoresistance measurement, a standard four-probe technique was used. The sample was mounted on the cooling head of a liquid helium
Correspondence to: Dr S.U. Jen, Institute of Physics,Academia
Sinica, Taipei, Taiwan, ROC. Tel: 886-2-789 9621; fax: 886-2783 4187.
0304-8853/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
S.U. Jen et aL / Magnetic and transport studies o f (Fe-V)so(BSi)2o glasses
316 10.00 9.75 £"9.50 9.25 "-~.~9.00
?
~8.75
~8.5o C/T =O.0347013T~+B.74
8.25 8.00
0 . 0 ' ' ' d.'o' ' To'.6 ' T5'.6 'zb'.6 ' 'z'5.0 T2 ( K2 )
Fig. 1. Linear fit of specific heat C data below 5 K plotted as C~ T versus T 2 of (Fe98V2)soB20 glass.
cryostat. In zero magnetic field, we measured P0 at 4 K. When varying the field, we obtained A p / p o = (p~ - p ~ ) ( 2 / 3 p ~ + l/3p~), where p~ and p ~ are the resistivities in the saturating parallel and perpendicular fields respectively [4]. Usually a field of 1 kG is large enough to saturate the sample in any direction. The specific heat measurements were carried out using the relaxation time method, which is most suitable for small samples. However, if the sample weight is less than 1 mg, there may be problems in measuring C accurately [5], so several pieces cut from one ribbon had to be stacked together with N-grease to increase their weight. Because the X-series samples were larger in size, their specific heat data are more reliable, and are presented here. Our calorimeter was calibrated by measuring the specific heat of pure aluminium in the temperature range 2-5 K. A typical C / T versus T 2 plot of (Fe98Vz)80B20 is shown in fig. 1.
where y= is the electronic coefficient, y~_~. is the spin-glass coefficient [7], NA = 6.02 × 10fi~/mole, k B is Boltzmann's constant, 0 D is the Debye temperature, and B is the coefficient due to the magnon excitations. From ref. [6], it can be calculated that the magnon contribution to total specific heat is negligible in the temperature range 2-5 K. Therefore, we use only the first and second terms in eq. (1) to approximate C. In fig. 1, the linear fit is pretty good. Also, no downward deviation is found in each C / T versus T 2 plot. From the fit, we find 3' and 0 D, which are shown as functions of X in fig. 2. From previous studies [7,8], it is known that the approximated percolation limit of the spinglass state in (Fe-V)77Bt3Si10 is X c = 8-12 at%. From fig. 2 of this study, we find that X c for (Fe-V)80B20 is in the range 5-10 at%. The criterion for defining Xc here is by analysing the inset of fig. 2 that there exists a rise and a transition region near X = 5-10 at%. Hence, it seems that the change of total amount of B - S i metalloids or silicon replacement have little effect on the magnetic phase diagram (between ferromagnetic and spin-glass phases). However, the shifting of X~ observed here is not as large as that caused by changing B - S i metalloids to P - B - A I metalloids in the F e - V metallic glasses [7]. For X < X c, it is believed that (Fe-V)80B20 glasses are in a ferromagnetic state. Then, their
( Fe,oo_Y LoBo 390.00 ~ 20.00 17,00 ~
370.00 350.00
3. Results and discussion
In ferromagnetic alloys, the specific heat at low temperatures is written as [6]:
C = T T + A T 3 + B T 3/2
270.00 0.00
+ B T 3/2 ,
(1)
a°°o.oo 5.00 . . x ( t~)
o
290.00
250.00
(T)3 = (~'~+~%in)r+234NAkB
v 11.00
330.00 310.00
0
~ 14.00
5.00
I0.00
X
15.00
( at. ~ )
20.00
25.00
Fig. 2. Debye temperature 0 D and specific heat coefficient y as a function of vanadium concentration X in (Feloo_ x Vx)8oB2o glasses.
S.U. Jen et al. / Magnetic and transport studies of 200.00 ..--..180.00 ~
© -(Feloo_xVx)aoBzo . ~
(Fe-V)so(nSi)2o glasses
317
160.00
• -- ( F e l°°-vVv)a°B14S16
150.00 100oo
140.00 120.00
¢~ 140.00 (~o 130:00
120.00
100.00 80.00 ................... ~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.00 5,00 10.00 15.00 20.00 25.00
X,Y(at.%) Fig. 3. Saturation magnetization a s plotted versus X or Y in (Feloo_xVx)80B20 or (Feloo_yVy)soB14Si 6 glasses.
Ye is roughly a constant and equals 8.3 m J / m o l • K 2"
As to the Debye temperature 0O, fig. 2 shows that there is a minimum 0 o at X - - 5 at%. The decrease in 0 D may be associated with the increase in the density of low-energy phonon modes [6]. Here, it is considered that this effect becomes greatest when the vanadium concentration equals 5 at%. It should be noted that same phenomenon, i.e. a minimum 0D, also occurs in crystalline F e - V alloys [9]. I n addition, 0 o of the crystalline F e - V alloy is higher than that of the amorphous F e - V counterparts. This is because that the metalloid sensitivity of 0 O is the same in our case as that in ref. 6. Figure 3 shows the magnetization data of both series of glasses at T = 5 K. The downward deviation of o-s of (Fe-V)soB2o at X = 5-10 at% may be connected with the incipient spin-glass phase in the sample. In (Fe-V)8oBt4Si 6 glasses, we also observe similar but less prominent drop in o-s at Y = 5 - 1 2 at%. For X < X c = 5 - 1 2 at%, both glasses are in a ferromagnetic state, and trs[(FeV)8oB2o] > o-~[(Fe-V)80B14Si6]. This agrees with the room-temperature findings in ref. [10] that if boron is replaced by silicon in Fes0B2o_zSiz, tr~ gradually decreases with increasing Z. Note, because the testing temperatures used in the magnetic measurements are higher than that used in the calorimetric measurement, X c determined magnetically is less reliable.
O - (Fe~o0_xVx)aoBz0 • - ( F e lo0_vVv)aoB taSi0
110.00 ................................................ 0.00 5.00 10.00 15.00
20.00
25.00
X , Y ( at.% ) Fig. 4. Residual resistivities Po of (Feloo_xVx)soB2o and (Feloo_yVy)8oB14Si6 glasses. The residual resistivity Po of the two series of glasses is shown in fig. 4. Obviously, Po is an increasing function of X and Y, respectively. It seems that as the vanadium concentration continues to increase, Po of (Fe-V)8oB20 approaches 145 i~Ilcm, and that of (Fe-V)8oBI4Si 6 approaches 165 ~Elcm. By substituting silicon for boron, Po increases at least 1.09-1.14 times. Another interesting thing is that if Po > 140 pA-lcm, the temperature coefficient of resistivity (TCR) below room temperature would become negative [11], in agreement with the Mooij correlation [12]. Finally, we discuss the anisotropic magnetoresistance hp/po of the two glasses at T = 4 K. As 1.00
o.9o ~-" 0.80 0.70
T=4K ~
©-(Fetoo-xVx)aoBzo 14Sio
0.60 0
Q 0.50 0.40 <~
0.30 0.20 0.10 0.00
.........
0.00
, .......................................
5.00
10.00
15.00
20.00
25.00
X , Y ( at.% ) Fig. 5. Anisotropic magnetoresistance as a function of X and Y in (Femo_xVx)aoB20and (Fe10o_yVy)aoB14Si 6 glasses.
318
s.u. Jen et aL / Magneticand transportstudiesof (Fe-V)so(BSi)2oglasses
shown in fig. 5, the o p e n circle data, representing Ap/po o f (Fe-V)80B20, almost coincide with the solid circle data, representing that of ( F e V)80B14Si6, expect for X, Y < 5 at%. T h e overlapping of the two A p / p o curves indicates that once the material is in a spin-glass state, silicon will have no effect on Ap/po. However, w h e n X, Y < 5 at%, the glass is in a f e r r o m a g n e t i c state, and silicon will r e d u c e Ap/po. This can be understood f r o m the fact that A p / p o is closely related to o-~ and P0. Generally, if ~rs is higher and Po is lower at the same time, Ap/po will surely bec o m e larger, and vice versa. H e n c e , as we comp a r e figs. 3, 4 and 5, it is easy to show that the above statement is correct.
4. Conclusions W e have studied the m a g n e t i c and transport properties of two series of glasses, namely (Fel00_xVx)80B20 and (Fe100_yVy)80B14Si6 . T h e X and Y d e p e n d e n c e s of or, P0, and Ap/po are discussed separately. T o summarize o u r findings in this work: (1) T h e r e p l a c e m e n t of b o r o n by silicon in the metalloids has no effect on trs and h p / p o , if the glass is in a spin-glass state. (2) B o t h o's and Ap/po of (Feloo_xVx)80B20 are larger than that of (Fe100_yVy)soB14Si 6, respectively (with X = Y), w h e n the glass is in the f e r r o m a g n e t i c state. (3) I n the case of Po, we find
that silicon will only increase its value f r o m the X to the c o r r e s p o n d i n g Y sample.
Acknowledgement This project was s u p p o r t e d by the National Science Council of R O C u n d e r G r a n t s No. N S C 80-0208-M001-85 and N S C 78-0208-M001-65.
References [1] F.E. Luborsky, J.L. Walter and E.P. Wohlfarth, J. Phys. F: Metal Phys. (1980) 959. [2] E.M.T. Velu, P. Rougier, and R. Krishnan, J. Magn. Magn. Mater. 54-57 (1985) 265. [3] L.T. Tong, J. Ren and S.S. Yan, IEEE MAG-23 (1987) 2314. [4] J.P. Jan, in Solid State Physics, eds. F. Seitz and D. Turnbull (Academic Press, New York, 1957) vol. 5. [5] C.N. King, R.B. Zubeck, and R.L. Greene, Low Temperature Physics-LT13, eds. K.D. Timmerhaus, W.J. O'Sullivan and E.F. Hammel (Plenum Press, New York, 1974) vol. 4. [6] D.G. Onn, J. Appl. Phys. 52 (1981) 1788. [7] U. Mizutani and M. Hasegawa, Physica B149 (1988) 267 (cf. fig. 11). [8] T. Miyazaki, I. Okamoto, Y. Ando and M. Takahashi, J. Phys. F: Metal Phys. 18 (1988) 1601 (cf. fig. 2). [9] S.U. Jen and Y.Y. Chen, unpublished data. [10] R. Hasegawa and R.C. O'Handley, J. Appl. Phys. 50 (1979) 1551. [11] S.U. Jen and J.Y. Yuh, J. Magn. Magn. Magter. 79 (1989) 143. [12] J.H. Mooij, Phys. Stat. Solidi (a) 17 (1973) 521.
How would silicon affect magnetic and transport properties of (Fe-V) 80(BSi) 2o glasses ? S.U. J e n a, y . y . C h e n a, J.S.C. J a n g b a n d C.H. T s a u b a Institute of Physics, Academia $inica, Taipei, Taiwan, ROC b Materials Research Laboratory, ITRI, Chutung, Hsinchu, Taiwan, ROC
Received 24 November 1992
Two series of amorphous (Fe10o_xVx)8oB20 and (Fel0o_yVy)aoB14Si 6 alloys have been made by the rapid quenching method. The measured physical properties include the saturation moment (trs), electrical resistivity (Po), specific heat'(C), and anisotropic magnetoresistance (Ap/po) at 4 K. The X and Y dependences of those physical properties are studied, respectively. When comparing o's,or go, or Ap/po data of (Feloo_xVx)aoB20and (Feloo_yVr)soB14Si6 glasses, we can see the differences caused by replacing boron with silicon in limited ranges of X or Y. The Debye temperature 0o of (Feloo_xVx)aoB20 glasses is briefly examined.
1. Introduction
2. Experiments
In the past, a few studies have been made on the magnetic and transport properties of ( F e V)8o(BSi)20 glasses [1-3], but a systematic investigation on how different metalloids would affect these physical properties is lacking. In this paper, we have made two series of (Fel00_xVx)80B2o and (Fe10o_yVy)80B14Si6 glasses. The total concentration of the metalloids is fixed at 20 at%, but one element of the metalloids, namely silicon, is changed from 0 to 6 at%. Our purpose is twofold: (i) to study the X and Y dependences of the measured properties such as saturation magnetization O-s, electrical resistivity Po, specific heat C, and anisotropic magnetoresistance A o / p o respectively, and (ii) to compare data of the two glasses in the case of X = Y.
The samples were splat-cooled from the melt by a melt-spinner. The rotating velocity of the copper wheel was in the range 25-35 m / s . The X-series samples were about 3 mm wide, and the Y-series samples about 1 mm wide. Each ribbon was checked by X-ray spectroscopy to ensure that no crystalline phase was present. The thickness t of each sample was determined by observing its cross-section in SEM. Because some of the glasses showed non-uniform thickness along its width, we had to estimate average values, tare. In general, tare --- 25 Ixm for (Fel0o_xVx)a0B20 and tar e = 15 I~m for (Fel00_ r Vy)80BlaSi 6. The error in tav~, which is about 2 - 5 % , may cause the same error in the resistivity value. Magnetization measurements were made at 5 K in a constant field of 1 T by a S Q U I D magnetometer. For electrical resistivity or anisotropic magnetoresistance measurement, a standard four-probe technique was used. The sample was mounted on the cooling head of a liquid helium
Correspondence to: Dr S.U. Jen, Institute of Physics,Academia
Sinica, Taipei, Taiwan, ROC. Tel: 886-2-789 9621; fax: 886-2783 4187.
0304-8853/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
S.U. Jen et aL / Magnetic and transport studies o f (Fe-V)so(BSi)2o glasses
316 10.00 9.75 £"9.50 9.25 "-~.~9.00
?
~8.75
~8.5o C/T =O.0347013T~+B.74
8.25 8.00
0 . 0 ' ' ' d.'o' ' To'.6 ' T5'.6 'zb'.6 ' 'z'5.0 T2 ( K2 )
Fig. 1. Linear fit of specific heat C data below 5 K plotted as C~ T versus T 2 of (Fe98V2)soB20 glass.
cryostat. In zero magnetic field, we measured P0 at 4 K. When varying the field, we obtained A p / p o = (p~ - p ~ ) ( 2 / 3 p ~ + l/3p~), where p~ and p ~ are the resistivities in the saturating parallel and perpendicular fields respectively [4]. Usually a field of 1 kG is large enough to saturate the sample in any direction. The specific heat measurements were carried out using the relaxation time method, which is most suitable for small samples. However, if the sample weight is less than 1 mg, there may be problems in measuring C accurately [5], so several pieces cut from one ribbon had to be stacked together with N-grease to increase their weight. Because the X-series samples were larger in size, their specific heat data are more reliable, and are presented here. Our calorimeter was calibrated by measuring the specific heat of pure aluminium in the temperature range 2-5 K. A typical C / T versus T 2 plot of (Fe98Vz)80B20 is shown in fig. 1.
where y= is the electronic coefficient, y~_~. is the spin-glass coefficient [7], NA = 6.02 × 10fi~/mole, k B is Boltzmann's constant, 0 D is the Debye temperature, and B is the coefficient due to the magnon excitations. From ref. [6], it can be calculated that the magnon contribution to total specific heat is negligible in the temperature range 2-5 K. Therefore, we use only the first and second terms in eq. (1) to approximate C. In fig. 1, the linear fit is pretty good. Also, no downward deviation is found in each C / T versus T 2 plot. From the fit, we find 3' and 0 D, which are shown as functions of X in fig. 2. From previous studies [7,8], it is known that the approximated percolation limit of the spinglass state in (Fe-V)77Bt3Si10 is X c = 8-12 at%. From fig. 2 of this study, we find that X c for (Fe-V)80B20 is in the range 5-10 at%. The criterion for defining Xc here is by analysing the inset of fig. 2 that there exists a rise and a transition region near X = 5-10 at%. Hence, it seems that the change of total amount of B - S i metalloids or silicon replacement have little effect on the magnetic phase diagram (between ferromagnetic and spin-glass phases). However, the shifting of X~ observed here is not as large as that caused by changing B - S i metalloids to P - B - A I metalloids in the F e - V metallic glasses [7]. For X < X c, it is believed that (Fe-V)80B20 glasses are in a ferromagnetic state. Then, their
( Fe,oo_Y LoBo 390.00 ~ 20.00 17,00 ~
370.00 350.00
3. Results and discussion
In ferromagnetic alloys, the specific heat at low temperatures is written as [6]:
C = T T + A T 3 + B T 3/2
270.00 0.00
+ B T 3/2 ,
(1)
a°°o.oo 5.00 . . x ( t~)
o
290.00
250.00
(T)3 = (~'~+~%in)r+234NAkB
v 11.00
330.00 310.00
0
~ 14.00
5.00
I0.00
X
15.00
( at. ~ )
20.00
25.00
Fig. 2. Debye temperature 0 D and specific heat coefficient y as a function of vanadium concentration X in (Feloo_ x Vx)8oB2o glasses.
S.U. Jen et al. / Magnetic and transport studies of 200.00 ..--..180.00 ~
© -(Feloo_xVx)aoBzo . ~
(Fe-V)so(nSi)2o glasses
317
160.00
• -- ( F e l°°-vVv)a°B14S16
150.00 100oo
140.00 120.00
¢~ 140.00 (~o 130:00
120.00
100.00 80.00 ................... ~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.00 5,00 10.00 15.00 20.00 25.00
X,Y(at.%) Fig. 3. Saturation magnetization a s plotted versus X or Y in (Feloo_xVx)80B20 or (Feloo_yVy)soB14Si 6 glasses.
Ye is roughly a constant and equals 8.3 m J / m o l • K 2"
As to the Debye temperature 0O, fig. 2 shows that there is a minimum 0 o at X - - 5 at%. The decrease in 0 D may be associated with the increase in the density of low-energy phonon modes [6]. Here, it is considered that this effect becomes greatest when the vanadium concentration equals 5 at%. It should be noted that same phenomenon, i.e. a minimum 0D, also occurs in crystalline F e - V alloys [9]. I n addition, 0 o of the crystalline F e - V alloy is higher than that of the amorphous F e - V counterparts. This is because that the metalloid sensitivity of 0 O is the same in our case as that in ref. 6. Figure 3 shows the magnetization data of both series of glasses at T = 5 K. The downward deviation of o-s of (Fe-V)soB2o at X = 5-10 at% may be connected with the incipient spin-glass phase in the sample. In (Fe-V)8oBt4Si 6 glasses, we also observe similar but less prominent drop in o-s at Y = 5 - 1 2 at%. For X < X c = 5 - 1 2 at%, both glasses are in a ferromagnetic state, and trs[(FeV)8oB2o] > o-~[(Fe-V)80B14Si6]. This agrees with the room-temperature findings in ref. [10] that if boron is replaced by silicon in Fes0B2o_zSiz, tr~ gradually decreases with increasing Z. Note, because the testing temperatures used in the magnetic measurements are higher than that used in the calorimetric measurement, X c determined magnetically is less reliable.
O - (Fe~o0_xVx)aoBz0 • - ( F e lo0_vVv)aoB taSi0
110.00 ................................................ 0.00 5.00 10.00 15.00
20.00
25.00
X , Y ( at.% ) Fig. 4. Residual resistivities Po of (Feloo_xVx)soB2o and (Feloo_yVy)8oB14Si6 glasses. The residual resistivity Po of the two series of glasses is shown in fig. 4. Obviously, Po is an increasing function of X and Y, respectively. It seems that as the vanadium concentration continues to increase, Po of (Fe-V)8oB20 approaches 145 i~Ilcm, and that of (Fe-V)8oBI4Si 6 approaches 165 ~Elcm. By substituting silicon for boron, Po increases at least 1.09-1.14 times. Another interesting thing is that if Po > 140 pA-lcm, the temperature coefficient of resistivity (TCR) below room temperature would become negative [11], in agreement with the Mooij correlation [12]. Finally, we discuss the anisotropic magnetoresistance hp/po of the two glasses at T = 4 K. As 1.00
o.9o ~-" 0.80 0.70
T=4K ~
©-(Fetoo-xVx)aoBzo 14Sio
0.60 0
Q 0.50 0.40 <~
0.30 0.20 0.10 0.00
.........
0.00
, .......................................
5.00
10.00
15.00
20.00
25.00
X , Y ( at.% ) Fig. 5. Anisotropic magnetoresistance as a function of X and Y in (Femo_xVx)aoB20and (Fe10o_yVy)aoB14Si 6 glasses.
318
s.u. Jen et aL / Magneticand transportstudiesof (Fe-V)so(BSi)2oglasses
shown in fig. 5, the o p e n circle data, representing Ap/po o f (Fe-V)80B20, almost coincide with the solid circle data, representing that of ( F e V)80B14Si6, expect for X, Y < 5 at%. T h e overlapping of the two A p / p o curves indicates that once the material is in a spin-glass state, silicon will have no effect on Ap/po. However, w h e n X, Y < 5 at%, the glass is in a f e r r o m a g n e t i c state, and silicon will r e d u c e Ap/po. This can be understood f r o m the fact that A p / p o is closely related to o-~ and P0. Generally, if ~rs is higher and Po is lower at the same time, Ap/po will surely bec o m e larger, and vice versa. H e n c e , as we comp a r e figs. 3, 4 and 5, it is easy to show that the above statement is correct.
4. Conclusions W e have studied the m a g n e t i c and transport properties of two series of glasses, namely (Fel00_xVx)80B20 and (Fe100_yVy)80B14Si6 . T h e X and Y d e p e n d e n c e s of or, P0, and Ap/po are discussed separately. T o summarize o u r findings in this work: (1) T h e r e p l a c e m e n t of b o r o n by silicon in the metalloids has no effect on trs and h p / p o , if the glass is in a spin-glass state. (2) B o t h o's and Ap/po of (Feloo_xVx)80B20 are larger than that of (Fe100_yVy)soB14Si 6, respectively (with X = Y), w h e n the glass is in the f e r r o m a g n e t i c state. (3) I n the case of Po, we find
that silicon will only increase its value f r o m the X to the c o r r e s p o n d i n g Y sample.
Acknowledgement This project was s u p p o r t e d by the National Science Council of R O C u n d e r G r a n t s No. N S C 80-0208-M001-85 and N S C 78-0208-M001-65.
References [1] F.E. Luborsky, J.L. Walter and E.P. Wohlfarth, J. Phys. F: Metal Phys. (1980) 959. [2] E.M.T. Velu, P. Rougier, and R. Krishnan, J. Magn. Magn. Mater. 54-57 (1985) 265. [3] L.T. Tong, J. Ren and S.S. Yan, IEEE MAG-23 (1987) 2314. [4] J.P. Jan, in Solid State Physics, eds. F. Seitz and D. Turnbull (Academic Press, New York, 1957) vol. 5. [5] C.N. King, R.B. Zubeck, and R.L. Greene, Low Temperature Physics-LT13, eds. K.D. Timmerhaus, W.J. O'Sullivan and E.F. Hammel (Plenum Press, New York, 1974) vol. 4. [6] D.G. Onn, J. Appl. Phys. 52 (1981) 1788. [7] U. Mizutani and M. Hasegawa, Physica B149 (1988) 267 (cf. fig. 11). [8] T. Miyazaki, I. Okamoto, Y. Ando and M. Takahashi, J. Phys. F: Metal Phys. 18 (1988) 1601 (cf. fig. 2). [9] S.U. Jen and Y.Y. Chen, unpublished data. [10] R. Hasegawa and R.C. O'Handley, J. Appl. Phys. 50 (1979) 1551. [11] S.U. Jen and J.Y. Yuh, J. Magn. Magn. Magter. 79 (1989) 143. [12] J.H. Mooij, Phys. Stat. Solidi (a) 17 (1973) 521.