RESISTIVITY AND MAGNETORESISTANCE OF Fe-Ni-P-B AMORPHOUS ALLOYS

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RESISTIVITY AND MAGNETORESISTANCE OF Fe-Ni-P-B AMORPHOUS ALLOYS

G. Böhnke, M. Rosenberg

To cite this version:

G. Böhnke, M. Rosenberg. RESISTIVITY AND MAGNETORESISTANCE OF Fe-Ni-P-B AMORPHOUS ALLOYS. Journal de Physique Colloques, 1980, 41 (C8), pp.C8-481-C8-484.

�10.1051/jphyscol:19808120�. �jpa-00220217�

JOURNAL DE PHYSIQUE

CoZZoque C8, suppZ6ment au n08, Tome 41, aoiit 1980, page

,RESISTIVITY AND MAGNETORESISTANCE OF Fe-Ni-P-B AMORPHOUS ALLOYS

G. Bshnke and M. Rosenberg

I n s t i t u t fiir ExperimentaZphysik V I , R u b - U n i v e r s i t a t , 0-4630 Bochm, R.F.A.

Introduction

The interest in the electrical transport properties of amorphous 3d-transition metal alloys with metal- loid glassformers has strongly increased in the last years for several reasons 1 .

The conduction electrons strongly scattered on structural disorder have a rather short mean free path of 3-5 8 and the value of the resistivity P is unusually high for a metallic state (2 loo pncm).

There is a minimum in the low temperature behaviour of

at Tmin with a logarithmic term prevailing in the temperature dependence below T . . The explana-

mln

tions for this behaviour, i.e. scattering on a two level system depending on structure proposed by Cochrane et a1.2 or a Kondo type scattering with a purely magnetic origin are still controversial.

In the case of ferromagnetic amorphous alloys some more aspects have to be taken into account, as the temperature dependent magnetic contribution to the resistivity and its anisotropy. In order to get more information about the influence of magnetic order on the electron scattering in amorphous alloys, a study of the resistivity and magnetore- sistivity dependence on temperature of Fe Ni P

x 80-x 14 B and Fe Ni B Si (B20 for x220) has been un-

6 x 80-x 19 1 dertaken.

Experimental and results

The samples mentioned above were produced by the rotating drum technique and the electrical resi- stance was measured with a four-point dc-method in the temperature range 4.2 - 500 K. The contacts to the samples were prepared by ultrasonic bonded thin A1 wires.

The magnetoresistance was measured below room tem- perature down to 4.2 K in magnetic fields up to

1.6 koe parallel and up to

kOe perpendicular to the current direction, i.e. the ribbon axis. In all measurements a current of loo mA was used and as thermometers a Pt-resistor above 50 K and a Ge-re- sistor below 50 K. The electrical resistivity nor-

malized to its value at 273.2

for both investigat- ed series are shown in Fig. 1 a und b. The typical variation with magnetic field and temperature of the parallel and transverse magneKoresistivity is given for Fe Ni P B in Fig. 2. Above the Curie

20 60 14 6

temperature Tc, in this case 232 K, the magneto- resistance is isotropic. From the parallel and transverse resistivities one can determine the an- isotropic magnetoresistance

IT) 1273)

Fe, Ni,-, B19 Si,'

"320

x.10

-

xn13

--

,

I

^K

Fig. 1 a und b

Electrical resistivities vs. temperature for a ~ e ~ N i ~ ~ - ~ P l q B 6 and b FexNigo-x B1gSil(B2~)

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808120

PHYSIQUE

were p and p are the zero field extrapolated

II I

saturation values. Fig. 2 shows the positive longi- tudinal and the negative transverse effects below Tc, which are typical for all measured ferromag- netic samples. The square root of the anisotropic magnetoresistance normalized to its value extra- polated to o K is plotted in Fig. 3 a and b for both investigated systems against (T/T~) 3/2 .

Fig. 2

Parallel and transverse magnetoresistance of Fe Ni P B at several temperatures. The first

20 60 14

one is positive and the second one negative below

Discussion

As can be seen in Fig. 1 a and b the electrical resistivities of the investigated compositions ex- hibit minima in the low temperature range, as the effect of a negative logarithmic term. We tried to fit the experimental data to the expression

2 2 p(T)

. a + aiT

a T~ + ^blln(T + b2)

2

with the values of the coefficients given in Table 1. Both, the residual resistivities and the coefficients of the linear terms are monotonically changing with the iron content, but in opposite directions. The values of bl and b do not vary in

2

a sensitive and regular manner with the composition, thus giving some support to the view that the loga- rithmic term has mainly a structural origin as pro- posed by Cochrane et a ~ . ~ . A fit of the experimen-

tal data to a T3l2 dependence, as mentioned in ref.3 did not lead to any improvement.

The value of T . and the resistivity behaviour in mln

the vicinity of T can be better obtained from the

C'

temperature derivative of the normalized resisti-

Fe,Ni,,B, Si, lBzo)

Fig. 3 a and b

Square root of the normalized anisotropy of the magnetoresistance vs. normalized temperature

(T/T~I for a

x Ni So-x

14 B 6

b FexNi80-xB19Sil (B20) .

vity, which is given in Fig. 4 for

FexNi80-xB19Sil(B20). In all. cases a change in the slope of the resitivity was observed (Table 2), but starting just

- 30 K above the magnetically de- termined Tc. In both ranges below and above Tc the resistivities change practically linearly with tem- perature. Assuming, that the linear term below Tc is the sum of the magnetic p and the thermal non-

m

magnetic contributions pth and above T it repre- sents the second one only, one can determine the constant contribution to the resistivity above T of the electron scattering on the paramagnetically disordered spins. The values of

(T

and pth(Tc)

m c

are given in Table 2. he former one is ir? good

agreement with those determined in the case of cry-

stalline alloys

We conclude therefore, that the

magnetic contribution to the resistivity has pro-

F%~bxB19Si, (Bzo)

T I K

Fig. 4

9 - / p

(273K) vs. temperature for

dT

Fe Ni B Si (B x 80-x 19 1 20

bably the same origin in both crystalline and amor- phous alloys of 3d-metals and that it represents an important part of the temperature range above T

C

in which the temperature derivative of the resisti- vity still changes before reaching the step in the paramagnetic range. A similar behaviour, supported by evidence from specific heat measurements, was already mentioned recently by other authors 5. It seems reasonable to assume that in the investigated amorphous alloys magnetic short range order occurs above T over a temperature range which increases with decreasing Fe-content, reaching for instance about 130 K in the case of FeloNi70B19Sil:

From the dependence of the anisotropic magneto- resistivity on temperature it can be seen, that the values extrapolated to o K increase with the amount of Fe (Table 1) and that above

the magnetoresi- stivity becomes isotropic (Fig. 2). The plot of the square root of the anisotropy A~(T) normalized to its value bp(0 K) versus ( T / T ~ ) ~ / ~ has a linear behaviour over a large temperature range (Fig. 3 a and

suggesting a proportionallity between AP(T) and Ms(T). The slopes of the curves have to give 2 the coefficients B in the Bloch law,

3/2

Ms

Mso (l-B3/2 (T/Tc) 3/2) . In the cases of Fe B and Fe40Ni40P14B6, for which B was ob-

80 20 3/2

tained from magnetic, Mossbauer and neutron dif- fraction measurements, our experimental values are about 20% higher.

Conclu'sions

For both systems, FexNi80-xP14B6 and

Fe Ni B Si (B

the temperature dependence of x 80-x 19 1 20

the electrical resistivity is governed by the lo- garithmic and the linear terms, the last one becom-

ing dominant above about loo K. As in the case of ferromagnetic crystalline 3d-metals and alloys, the magnetic contribution is the most important term in the temperature dependence of resistivity below T

c' as a result of electron scattering on the spin-dis- order. In the compositions with high Ni concen;tra- tion magnetic short range order seems to occur in a relative large temperature range above T . ^{The an-}

isotropic magnetoresistivity increases rather strongly with the Fe concentration and its tempera- ture dependence seems to scale with M 2 .

Table 1

Atomic AP

a

--(OK)

percentage a

bl b2 ' a v

0----

Fe Ni P B Si 10-4K-1

20 60 14 6 - 0.958 2.26 2.09 4.5 0.91 30 50 14 6 - 0.957 1.04 0.97 5.1 1.08 40 40 14 6

4.84 15.6 1.29 60 20 14 6 - 0.980 0.49 0.77 3.9 2.54 70 lo 14 6

0.71 8.0 2.48 lo 70 -- 19 1 0.854 6.55 3.17 5.6 0.72 13 67 -- 19 1 0.872 5.70 3.50 5.9 1.13 16 64 -- 19 1 0.889 5.24 4.06 6.8 1.19 20 60 -- ²⁰

3.95 7.6 1.33 40 40 -- ²⁰

0.10 5.0 1.87 80*----2o*-0.975 0.98 1.05 2.5 6.27

* ~ e t ~ l a s 2605 received from Allied Chemical Corp.

Table 2 Atomic

-4 -1

percentage al/lo

pm(Tc) Pth(Tc)

- -

Fe Ni B Si T<Tc T>T pRcm pacm

Acknowledgements

We wish to thank Dr. F. Luborsky for giving us samples for the present investigation and U.Janssen, W. Kettler,

Theile and R. Wernhardt for their kind assistance in the computational fitting of the experimental data. The project was financially supported by the Deutsche Forschungsgemeinschaft.

References

:1. C.C. Tsuei, Amorphous Magnetism

Plenum

Press, N.Y., 181 (1977)

JOURNAL DE PHYSIQUE

2.

Cochrane, R. Harris, J.O. Strom-Olson, M.J. Zuckermann, Phys.Rev.Letters,s,

(1975)

3.

E. BabiE, Z. Marohnie, M. Ocko, A. HamziE, K. Saub, P. Pivac, Magnetism and Magnetic Materials,

Proc.

Munich, to be published

4. R.J. Weiss, A.S. Marotta, J. Phys.Chem.Solids,

302

-

5. E. BabiE, B. Fogarassy,

Kemeny, Z. MarohniE,

K. Saub, Magnetism and Magnetic Materials,

ICM Proc.

Munich, to be published