1981) THE ELECTRONIC AND MAGNETIC PROPERTIES OF Fe-B-Si METALLIC GLASSES CONTAINING TRANSITION METAL ADDITIONS T

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Proc. 4th 1nl. Conf. on Rapidly Quenched Metals (Sendai. 1981)

THE ELECTRONIC AND MAGNETIC PROPERTIES OF Fe-B-Si METALLIC GLASSES CONTAINING TRANSITION METAL ADDITIONS

T. Kemeny*, B. Fogarassy*, I. Vi~czeo*, I.W. Donald+, M.J. Besnus x and H.A. Davies+

* Central Research Institute for Physics, Budapest, Hungary.

o Solid State Physics Laboratory, University of Groningen, The Netherlands.

+ Department of Metallurgy, University of Sheffield, U.K.

x Laboratoire Pierre Weiss, Institute de Physique, Strasbourg, France.

INTRODUCTION

096O~--KJO;;:;;----;200=---=300--I.(X)'-:-:---::500-:---6aJ---T)-r-::C"

FIG.l. Temperature dependence of the electrical resistivity ratio of selected glasses

but cannot be resolved from the transport properties due to the relative proximity of crystallization.

The influence of Tc on thermoelectric power, TEP, of the (Fe 40Ni 60 ) 78BSi alloy is less marked (fig. 2), and is associated wiili an inflection point only. The temperature dependence of the TEP for the paramagnetic Ni-based alloy (NiCrBSi) is, however, app- roximately linear to ~600 K, and is very small in comparison with the ferromagnetic alloys, in agreement with other reports (2).

The influence of Curie point on electrical resistivity, also observed for other

104 1,70

lOB

106

ELECTRONIC TRANSPORT PROPERTIES

The temperature dependence of the electrical resistivity ratio and absolute thermopower of some selected samples are plotted in figures 1 and 2. A well-resolved break in the electrical resistivity of the

(Fe40Ni60)7aB Si alloy is found (fig. 1);

this is a clear indication of a ferromagnetic Curie point, which is also detected by calorimetry and agrees with previous reports (1). The Curie point, T , can also_c be detected by calorimetry for Fe aB7 12Si10'

The electronic structure of non-crystalline metallic materials is a subject of intensive research effort both from theor- etical and experimental points of view.

Despite this great interest however, no reports have been published concerning the de- tailed composition dependence of both bulk and local magnetic properties and electron transport characteristics. In the present paper, we report and discuss the initial results of such a study into the properties of Fe- and Ni-based glasses in which the composition is changed systematically. The glassy alloys, of nominal compositions

(Fel_xTMx)7aB12SilO and (Nil_xTMx)7aB12SilO where TM is a second transition metal, were prepared as ribbons ~20~m thick by melt- -spinning and the amorphous structure veri- fied by X-ray diffraction.

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S·K!iN

FIG.2. Temperature dependence of the absolute thermopower.

2

-8 -9 -10

I , /

V

o

10 20 30 40 50 60 70 80 90 100x -1

-]

-4

So·K/',vV

FIG.4. Thermoelectric power, TEP, and temperature coefficient of resistivity, TCR, of Fe-Ni glasses.

is magnetically diluted by exchanging Fe for Ni, Tc gradually decreases and magnetic dis- order, and consequently electron scattering, increases. Conversely, a significant decrease of the TCR was detected in the paramagnetic state. Similar results were found for (Fel_xCr x ) 78BSi glasses, where the high Tc depression due to Cr (5) makes it poss- ible to determine uA for a range of Fe-rich alloys (figure 5).

The compositional variation of the TCR is interpreted traditionally in the frame- work of a Ziman-type theory, where the dir- ection of the change is taken as an indication of the relative position of the Fenm wavenumber, KF, with respect to the first peak of the structure factor, qp (6). With increasing electron concentration, K

F ^shou~

increase and the TCR should change accord- ing to whether 2K

F approaches or diverges from qp' taking into account the condition for negative TCR, i.e. 2K F qp' This is clearly not the case for all the present alloys, e.g. addition of both Ni and Cr decreases the TCR of the Fe-based glasses despite the fact that Ni increases whilst Cr decreases the average electron concent- Of---f====~

FIG.3. Schematic temperature dependence of the electrical resistivity ratio at Tc '

metallic glasses (3,4), is shown schematic- ally in figure 3. This plot illustrates how the temperature coefficient of resistivity, TCR, for the paramagnetic state, aA' is determined. The composition dependence of TCR, together with the TEP extrapolated to

aOc,

is plotted in figure 4 for the

(Fel_XNi x ) 78BSi glasses. The increase of TCR in the ferromagnetic state, aFM' is interpreted as an increase in the density of states of magnetic excitations with increasing Ni concentration. As glassy FeBSi

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0,5

0 0 5

_)1.-

^1~

I

f<:::::~ ^·x

-0.5

I

/ So ^-1

/ -

-1 I -2

I

I -3

I

Ni78-xCrx

BeSito

I

I<

-4

•

TCR and TEP of Ni-Cr glasses.

FIG.6.

0.5 •

I ^•

t

10 20 30 40 x

FIG.5. TCR of Fe-Cr glasses.

1.5

FIG.7. TCR and TEP of dilute FeBSi glasses.

Ni • Pd x Pt "

V Cr Mn Fe Co Nb Mo

Ta W Re Os Ir

-1 -2 .,]

• TixZr O"Hf ration. As an alternative explanation, the

decreasing TCR should be interpreted with the increasing role of a different electron scattering mechanism which can produce negative TCR, e.g. scatter on localized magnetic moments or local spin fluctuations.

The importance of this kind of magnetic scattering is supported further by our results on Ni-Cr glasses, shown in figure 6.

The co-existence of negative TCR and small positive TEP changing linearly with temperature is usually taken as an indication that 2 KF ⁼ qp' An explanation along this line is however rather difficult as theor- etical calculations indicate (7) that 2 KF

> qp for Fe83B

17, and one would expect even higher 2 KF values for the Ni-based BSi glasses. In addition, negative TCR is not observed in the Ni-rich (FeNi)BSi glasses with the same average electron concentration.

In order to arrive at a clearer under- standing, the transport properties of dilute (Fel_XTMX) 78-B12 Si lO glassy alloys were studied for different TM additions with un- filled 3d, 4d and 5d electron shells. The results, plotted in figure 7, indicate that both TCR and TEP change significantly with TM additions which cause considerable local

spin density perturbations. These results follow the same trend as reported previously

(5) in connection with relative Tc changes.

MAGNETIC PROPERTIES

The average magnetization of

(Fel_XTMX) 78B12Si lO glasses was measured at

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4,2 K for the 3d-impurities (TM = Ti, V, Cr, Mn, Co, Ni and Cu). All these impurities were found to decrease the average magnetic moment per transition metal atom D

TM, the effect being greatest for Ti, V and Cr

(fig. 8); the influence of Mn was intermediate. In general, i t is usual to assume that impurities like Ti~Mn have magnetic

Or

~ ^-2r' I -

^-^~

jl~-6

decreased rapidly. Mn impurities again caused intermediate perturbations. The change in the average iron hyperfine field dHFe/dx and th: change of average iron magnetic moment d~Fe/dx are shown in Fig.9a.

The value of the 3d impurity moments can be calculated from the combination of the average magnetization and iron hyperfine field data using the relation:

~TM = (1 - x) ~Fe + x~i-

The results are shown in Fig.9b. In the case of Ti, the composition range studied

FIG.8. Change of the average transition metal magnetic moment of glassy FeB

12si lO for addition of 3d impurities.

moments which are anti-ferromagnetically coupled to the matrix, thus causing the decrease of average magnetization. Using the well-established proportionality (8) between the iron hyperfine field and iron magnetic moment:-

H

_Fe ⁼ ^aD_Fe^{, with a}

~ 130 kOe/~B' the perturbation of iron magnetic moments due to the impurities can be determined by measuring the iron hyperfine field distribution. 57 Fe Mossbauer spectra were taken at low temperatures (5K and 77K) using standard techniques and the iron hyperfine field distribution p(H) was evaluated by the spectrum-subtraction method (9). The shape of the p(H) of amorphous FeB12Si

lO remained unperturbed for Co, Ni and Cu substitutions, and only a small shift in the average hyperfine field was observed. Very strong perturbation of p(H) was obtained for Ti, V and Cr impurities (the standard deviation of p(H), ~H

lncreased from about the 35k 0e value of Fe78B12SilO to 65k 0e for (FeO,872CrO,128)78 B12SilO)' and the average hyperfine field

- 8

T, v er ~1" r~ Co Ni Cu

,.1

~o

°

.; -2

0 _-~OO m

~ ^::l

l:r~¹⁾ ⁰^>- ^-~

ril

^u ^u^>.

-dOJ ^, , , , , ^, -6

T, '/ Cr '·1n F~ C:> NI Cu

I ^bl

H-

^-.i ^-

: 1 '

-',

" , , ,

T, V er Mn Fe Co NI Cu

FIG.9. a) Change in the average iron hyperfine field and average iron magnetic moment of glassy FeB12Si

lO with addition of 3d impurities.

b) Magnetic moments of 3d impurities in FeB12si

lO glass as calculated from the average magnetization and iron hyperfine field data.

did not allow any definite conclusion; V, Cr and Cu possess no magnetic moments within the error of the evaluation; Mn, Co and Ni have 0,7 ~ 0,3 ~B' 1,2 ~ 0,2 ~B and 0,7 ~ 0,2 ~B ferromagnetically coupled magnetic moments, respectively. V and Cr impurities induce a considerable decrease in the surrounding Fe magnetic moments

(around - 5 ~B)' but within the experimental error we have no indication of the

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presence of antiferromagnetically coupled iron magnetic moments.

The magnetic moment of iron in amorphous Fe78B12silO is 2,11 ~B' very close to that of pure crystalline iron (2,22 ~B).

However, the behaviour of the 3d impurities is quite different from that in crystalline Fe and closely resembles that for crystalline Ni. Impurities like Ti, V and Cr have very small (or zero) magnetic moments but they cause large decreases in the surrounding magnetic moments of the matrix, whilst Co and Ni are like simple dilutants - they have ferromagnetically coupled moments but do not perturb the matrix. This similar behaviour may be casual but the similar effect (5) of 3d impurities on the Curie temperature of this matrix seems to support this analogy. The reason for the compar- able magnetic behaviour of the amorphous matrix and crystalline Ni could be the presence of a full majority spin sub-band in the glass as a result of the strong covalent bonding of the metalloid p- and transition metal d- electrons.

REFERENCES

1. T. Masumoto et aI, Amorphous Magnetism 11, edited by R.A. Levy and R. Hase- gawa, Plenum Press: New York, 1977, p.369.

2. S. Basak, S.R. Nagel and B.C. Giessen, Phys. Rev. B., 21 (1980) 4049.

3. E. Babic et aI, J. Magn. and Magn.

Mat., 15-18 (1980) 249.

4. G. Bohnke and R. Rosenberg, J. Phys- ique ColI., 41 (1980) C8-481.

5. I.W. Donald, T. Kemeny and H.A. Davies, J. Phys. F: Metal ·Phys., 11 (1981) L131.

6. A. Mogro-Campero and J.L. WaIter, Phys. Rev. B., 20 (1979) 5030.

7. B. Fogarassy et aI, Proc. Conf. Met.

Glasses: Sci. and Tech., Budapest 1980, edited by C. Hargitai et aI, CRIP: Budapest, 1981, vol.l, p.407.

8. F. van der Wonde and I. Vincze, J. de Physique,

! l

(1980) Cl-151.

9. I. Vincze, Solid St. Commun. 25 (1978) 689.