KONDO EFFECT AND LOCALIZED SPIN FLUCTUATIONS IN THE Zn-TRANSITION METAL SYSTEM

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KONDO EFFECT AND LOCALIZED SPIN

FLUCTUATIONS IN THE Zn-TRANSITION METAL SYSTEM

P. Ford, C. Rizzuto, E. Salamoni, P. Zani

To cite this version:

P. Ford, C. Rizzuto, E. Salamoni, P. Zani. KONDO EFFECT AND LOCALIZED SPIN FLUCTUA- TIONS IN THE Zn-TRANSITION METAL SYSTEM. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-221-C1-223. �10.1051/jphyscol:1971170�. �jpa-00214497�

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JOURNAL DE PHYSIQUE Colloque C I, supplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1

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221

KONDO EFFECT AND LOCALIZED SPIN FLUCTUATIONS IN THE Zn-TRANSITION METAL SYSTEM

P. J. FORD, C. RIZZUTO, E. SALAMONI, P. ZANI Gruppo Nazionale di Struttura della Materia del C . N. R., Istituto di Scienze Fisiche dell'Universita, 16132 Genova, Italy

R&um6. - La rCsistivit6 a basse temperature de Z V , ZsCr, Z*Mn et e F e a CtC mesuree. Des variations du type effet Kondo ont 6tC trouvhs dans tous ces alliages. La valeur approchee de TK CvaluCe pour ces systemes en utilisant soit une fonction de Hamann ou une simple loi en T2 est T ~ ( c r )

-

²OK, TK(M~)

-

¹OK, Tx(Fe)

-

⁸⁰OK, Tx(V)

-

^TK(Fe).

Abstract. - The low temperature resistivity of ZnV, ZnCr, ZnMn, Z g e has been measured and it has been found to be consistent with a Kondo type of behaviour for all alloys : the approximate values for Tx evaluated for these systems, by comparing them to a Hamann function or to a simple T2 law are TK(C~)

-

²^OK^;^TK(Mn)

-

¹^OK^;^Tx(Fe)

-

⁸⁰^O^K^;

TK(V)

-

^Tx(Fe).

We report here some data obtained in an accurate systematic study of the Zn-transition metal alloy system, which lies between the well studied Kondo systems based on Cu and Au, and the non magnetic Al based system.

The presence of a magnetic moment in ZnMn and ZnCr has been shown in previous publicat~ns [I, 21,

-

and in both alloys a resistance minimum has been observed, but extensively studied only in ZnMn [3,4,5].

In ZnFe, on the other hand, a slight resistance minimum'was observed [6], its order of magnitude being about lo3 times smaller than in 3 M n or ZnCr with the same concentration, and nearer to the size of the minimum which was later found in &Mn and AlCr [7],!and which was related to the presence of localized spin fluctuations (LSF).

We present here resistivity measurements on ZnV, ZnCr, ZnMn, and ZnFe. Measurements on ~ n ~ i a n d Z C O , now in are not yet conclusive.

-

The temperature interval was between 0.4 and 20 OK, and the accuracy of the measurements enabled us to follow in detail the resistivity behaviour of extremely dilute magnetic alloys. The starting base metals and the preparation technique of the alloys was such to avoid spurious contributions to the temperature dependent part of the resistivity.

In figures 1 and 2 the behaviour of the resistivity for one representative sample of each alloy system is shown : this behaviour is found to be concentration independent up to -- 40 ppm both in ZnCr and in ZnMn, above which concentration we oKerve a sud-

-

den increase of the log T slope by a factor -- 3 for ZnCr ; the mechanism of this increase is not yet

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clearly understood but its effect resembles an increase in the value of the localized spin. Both in ZnCr and in 3 M n the situation above about 40 ppm% further complicated by the appearance of long range interac- tions : for this reason we will confine our discussion to samples of lower concentration. The data for ZnV seem to be concentration independent up t o t h e maximum solid solubility (- 100 ppm at) while some

4 6 &Mn 2 p.p.m.

FIG. 1.

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The resistivity of Z C r and e M n as a function of

log T and Tz. The T z plot relates to a smaller temperature interval and the line shown has been used to extrapolate 6.

concentration dependence observed in the Fe alloys above 200 ppm cannot be unequivocably considered as due to metallurgy, but again we will *consider data only below this concentration.

Results in. Figs. 1 and 2 are plotted both on a log T and (for the lowest temperatures) on a T2 scale. The

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971170

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C 1 - 222 P. J. FORD, C . RIZZUTO, E. SALAMONI, P. ZANI

FIG. 2. - The resistivity of e F e and ZnV : the log T scale is the same as in Fig. 1 while the T2 scale goes over a larger

temperature interval than in Fig. 1.

data for ZnMn and ZnCr can be reproduced to better than 1 part in by fitting to the expression derived by Hamman 181 :

the values to be given to the parameters are : pa. cm ZnCr : A = 14.5

+

¹^---

- a t % '

pa. cm ZnMn : A = 12

+

²^----

- a t % '

This fit, however, has a well defined meaning only for ZnCr, while it is relatively insensitive to the values of ~ T a n d S for ZnMn whose resistivity has a smaller second derivative:

We notice that the spin values in both cases are lower than previously postulated [I, 91 : this might be due to the comparison being made below T', as

pointed out by Heeger [lo]. We notice also that, for ZnMn,

- TK and S are different from those found from susceptibility measurements [Ill ; however, if S = 2 and TK = 0.2 OK [11] are used, the accuracy of the fit decreases by an order of magnitude. On the other hand the value of TK obtained by us agrees with earlier values inferred from resistivity measurements [3Y 4, 121.

Considering the T2 plots we observe that, in going from Mn to Cry Fe and V, respectively, a linear T 2 plot fits increasingly larger temperature intervals : if we compare it with the approximate formula

valid in the L. S. F. case, or for TITK Q 1, we obtain OM,,

-

^2.5^OK,^OC,

-

^{4.5 OK,}ÔF, ^{80 OK,}ÔV ÔF,

the fact that the characteristic temperatures thus obtained agree fairly well with TK for Mn and Cr enables us to infer that ZnFe and ZnV have a high Kondo temperature and z r e f o r e resemble AuV and AuCo [13].

In figure 3 we report the values of the specific resistivity at 4.2 OK, for all the alloys considered, as a function of the atomic number of the impurity, as determined in this and in previous works 114, 151.

FIG. 3. - The resistivity of the Zn alloys at 4.2 OK : present data ; A Boato et al. (Ref. 14) ;

+

Hedgcock et a[. (Ref. 15).

The present data are derived from analysis at lower concen- trations than Refs. 14 and 15. A line through the Zn data, and that reproducing the A1 alloys (Ref. 14) are drawn for compa-

rison.

The well defined peak observed in this figure sug- gests that in all these alloys the resistivity at 4.2OK has reached or nearly reached its zero temperature value : this shape is not changed by adding the values of B obtained above to the resistivities for ZnMn

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KONDO EFFECT AND LOCALIZED SPIN FLUCTUATIONS IN THE Zn-TRANSITION C 1

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223 and ZnCr (assuming T,

-

4.2 OK for both). By also if we try to evaluate the high temperature limit, this curve to the data for the ~1 alloys i. e. subtracting B : this would imply that ,the ;virtual [14] we see that the two resistivities have a similar bound State in all cases is not completely split and behaviour with a constant scaling parameter of the hence that the localized spin fluctuations lifetime is order of 2.5 : the shape of the Zn curve is not altered short compared to systems like CuMn - or - CuCr.

References COLLINGS (E. W . ) , HEDGCOCK (F. T.) and MUTO ( Y . ) ,

Phys. Rev., 1964. 134, 1521.

MUTO (Y.), J. Phys. Soc. Japan, 1960, 15, 2119.

HEDGCOCK (F. T.) and RIZZUTO (C.), Phys. Rev., 1967, 163, 517.

MARTIN (D. L.), Phys. Rev., 1968, 167, 640.

WASSERMANN (E. F.), Z. Physik, 1970, 234, 347.

CAPLIN ( A . D.), Phys. Letters, 1967, 26 A, 46.

CAPLIN ( A . D.) and R r z z u ~ o (C.), Phys. Rev. Letters, 1968, 21, 746.

HAMMANN @. R.), Phys. Rev., 1967, 158, 570.

BOATO (G.), GALLINARO (G.) and RIZZUTO (C.), Phys. Rev., 1966, 148, 353.

HEEGER ( A . J.), Solid State Physics, Vol. 23, 283 ed.

by F. Seitz, D . Turnbull and H . Ehrenreich, Academic Press, New York, 1969.

NEWROCK (R. S.), SERIN (B.) and BOATO (G.), Bull.

Am. Phys. Soc., 1969,14,371, and to be published.

BOATO (G.) and RIZZUTO (C.), Proceedings of the 11th lnternational Conference on Low Tempe- rature Physics, vol. 2, 1062, St. Andrews, 1968.

LORAM (J. W . ) , FORD ( P . J . ) and WHALL (T. E.), J. Phys. Chem. Solids, 1970, 31, 763.

BOATO (G.), BUGO ( M . ) and RIZZUTO (C.), Nuovo Cimento, 1966, 45, 226.

HEDGCOCK (I?. T.) and MUIR ( W . B.), Phys. Rev., 1963, 129, 2045.