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THE RESISTIVITY OF AMORPHOUS METALLIC
ALLOYS DOWN TO 60 mK
R. Cochrane, F. Hedgcock, B. Kästner, W. Muir
To cite this version:
JOURNAL DE PHYSÏQUE Colloque C6, supplément au n" 8, Tome 39, août 1978, page C6-939
THE RESISTIVITY OF AMORPHOUS METALLIC ALLOYS DOWN TO 60 mK
R.W. Cochrane, F.T. Hedgcock, B.J. Kastner and W.B. Muir
E. Rutherford Laboratory, UoGill University, Montreal H3A 2T8 Canada.
Résumé.- On a mesuré la résistivité de quelques alliages amorphes métal-métaloides entre 60 mK et 300 K. La résistivité à basse température est plus ou moins semblable pour tous les échantillons. Elle décroît avec l'augmentation de la température jusqu'à un minimum au voisignage de 10 K. Aux températures plus élevées on trouve, entre les divers échan-tillons, des différences profondes qu'on attribue à l'influence particulière du Mo sur la diffusion électronique.
Abstract.- We have measured the resistivity of a number of metal-metalloid amorphous alloys from 60 mK to room temperature. The low temperature behaviour is qualitatively similar for all the alloys : a decreasing resistivity with increasing temperature to a resisitivity minimum in the vicinity of 10 K. Marked differences in the temperature dependences at higher
temperatures are attributed to the scattering from particular components such as Mo.
Considerable interest has focused on the temperature dependence of the resistivity in amor-phous metallic alloys where one commonly observes a resistance minimum and a temperature variation of the form, - In T, at lower temperatures /l/. Seve-ral models have been proposed to explain this be-haviour such as scattering from localized spin excitations in amorphous ferromagnets / 2 / , the temperature dependence of the Debye-Waller factor
13/, and scattering from tunneling states in the
non crystalline structure /4/. The latter model predicts a resistivity term, p °= - ln(T2 + A2) , implying that p should saturate below A < 1 K, a temperature characteristic of the energy splitting of the tunneling states. Though saturation of the resistivity has been reported for several alloy systems /5,6/ very little is known in detail about the general resistivity behaviour of amorphous alloys at very low temperatures.
In this paper, we report resistance mea-surements from 60 mK to 40 K on four amorphous ferromagnets, Feit0Niitop14B6 (metglas 2826), Fe^g
Ni<toB20> Fe80B20(2 6 0 5) a n d F e78M o2B20 (2605 A) •
For the last sample we have extended the data to 296 K because of the exceptional behaviour of the resistivity of this alloy at higher temperatures.
The measurements below 40 K were made in a dilution refrigerator using an A.C. - four
termi-nal method with resolution of a few parts in 106
111. The samples (typical size 6 x 0.2 x 0.005 cm3)
were attached to the mixing chamber with GE 7031 varnish using mylar foil for electrical insulation.
At temperatures below 0.1 K thermal contact of the samples was maintained with a heat flow of less
than 3 nW per cm2 of contact area.The temperature
above 0.4 K was measured by a calibrated Ge resis-tor and below 0.4 K by a Speer carbon resisresis-tor ca-librated against CMN. Theerror in the temperature determination was + 3 % above 0.4 K and + 5 % below 0.4 K.
The figure shows the normalized resistivity data on a log T scale for all samples. The most striking feature of the data is that the tempera-ture dependent resistivity of three of the samples is qualitatively identical, the exception being the Fe73Mo2B20sample which has a maximum at 28 K
follo-wed by a second minimum at 165 K 18/.
At low temperatures all the samples show a minimum below which p increases as log T (straight
lines in figure.). At still lower temperatures the resistivity deviates from log T towards saturation at the point indicated by the vertical arrow; the approach to saturation is so gradual that the re-sistivity is still increasing at 60 mK as reported earlier for Feit0Nit*oplltB6 1^1 • A fit of the
func-tion, ln(T2 + A2) , to the resistivity data is
generally poor below 0.3 K.If the tunneling model is correct this behaviour implies that a distri-bution of A values is required to fit the data over the entire temperature range.
A closer look at the figure allows the following points to be made :
1) the resistivities Fe^gNi^gPmBg and Fe^oN;i-M.oB20
below 10 K differ only by a scaling factor. This
17 - T.2
f a c t o r must be due t o t h e d i f f e r i n g m e t a l l o i d components.
2) The r e s i s t i v i t i e s of Fe40Ni40B20 and F e g O B p ~ below 4 K have t h e same t o t a l change b u t a s l i g h t l y d i f f e r e n t temperature dependence. This change i n behaviour i s due t o t h e d i f f e r e n t t r a n s i t i o n e l e - ments.
3) Below 4 K t h e r e s i s t i v i t i e s of Fe80B20 and Fe78 Mo2B20 a r e i d e n t i c a l .
F i g . 1 : Normalized r e s i s t i v i t y a s a f u n c t i o n of l o g T. The lower t h r e e curves have been z e r o s h i f t e d a s i n d i c a t e d by t h e h o r i z o n t a l arrows. The f u l l curve
i s a f i t t o l n ( ~ ~
+
A ~ ) w i t h d = 0.45 K. T h i s l a s t p o i n t , i n c o n t r a s t w i t h t h e v e r y d i f f e r e n t behaviour of t h e s e a l l o y s a t h i g h e r tempe- r a t u r e s , i n d i c a t e s t h a t t h e Mo p l a y s a unique r o l e i n t h e e l e c t r o n i c s c a t t e r i n g . We s u g g e s t , t h e r e f o r e , t h a t a 4d- t r a n s i - t i o n m e t a l l i k e Mo i n low c o n c e n t r a t i o n does not change t h e average s t r u c t u r e o r t h e e l e c t r o n i c den- s i t y of s t a t e s b u t r a t h e r i n t r o d u c e s a l o c a l i z e d and p o s s i b l y r e s o n a n t s c a t t e r i n g c e n t e r i n t h e s e amorphous a l l o y s . Table : Experimental d a t a Sample Fe40~i40P14B20 1432 7
0.9605 20 8.1 2 0.1 (metglas 2826*) Fe40Ni40B20 1 2 7 2 6 0.9279 19 5.42
0.1 F e 8 ~ B 2 ~ 1 2 5 2 6 0.9694 15 4.52
0.1 (metglas 2605*) Fe78M02B20 1 2 5 2 6 0.9991 8(165) 4.0+0.1** (metglas 2605A*)* supplied by Allied Chemical Corporation
N.J.**
taken at 2 K.References
/ I / See f o r example : Hasegawa, R. and T s u e i , C . C . , Phys. Rev. (1971) 214.
/ 2 / Madhukar, A. and Hasegawa, R., S o l i d S t a t e Commun.
3
(1974) 61.131 Markowitz, D . , Phys. Rev.
B
(1977) 3617. /41 Cochrane, R.W., H a r r i s , R., Strom-Olsen, J . O . ,and Zuckermann, M.J. Phys. Rev. L e t t .
35
(1975) 676./ 5 / Rapp, O . , Bhagat, S.M., and Johannesson, Ch., S o l i d S t a t e Commun.
2
(1977) 83.161 Rapp. O . , Grindberg, J.E., and Rao, K.V.,Proc. 23rd Conf. Magnetism and Mag. M a t e r i a l s , Minneapolis U.S.A. (1977).
/ 7 / Cochrane, R.W., K z s t n e r , B.J. and Muir, W.B. t o be p u b l i s h e d .
I 8 1 Rayne, J . A . and Levy, R.A., i n Amorphous Magne-
t i s m 11, p. 319, e d i t e d by Levy,.R.A. and Hasegawa, R., Plenum P r e s s , New York and London
