MANGANESE IMPURITIES AND SPIN GLASS LIKE PROPERTIES IN CuZr GLASSY METALS

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MANGANESE IMPURITIES AND SPIN GLASS LIKE PROPERTIES IN CuZr GLASSY METALS

A. Amamou

To cite this version:

A. Amamou. MANGANESE IMPURITIES AND SPIN GLASS LIKE PROPERTIES IN CuZr GLASSY METALS. Journal de Physique Colloques, 1980, 41 (C8), pp.C8-670-C8-673.

�10.1051/jphyscol:19808168�. �jpa-00220269�

JOURNAL DE PHYSIQUE CoZloque C8, supplgment au no$, Tome 41, ao2t 1980, page C8-670

MANGANESE I M F U R I T I E S AND S P I N GLASS L I K E PRQPERTIES I N Cum GLASSY NETALS

A. Amamou

L.A. M.S. E.S. (n0306) Universitg Louis Pasteur, I n s t i t u t Le Be2 4, rue Blaise Pascal 67070 Strasbourg cedex, France.

X6sumQ.- Nous prdsentons une Qtude des propri6tQ.s magnstiques du systsme amorphe (Cu Zr ) Yn 60 40 I-c- c (c 5 10 at X) dans le regime dilu6 et dans le r6gime oii les impuretss magnstiques interag~ssent entre elles. Les caractdristiques des impuretds de manganese dans le r6gime dilu6 sont compar6es 2 celles obtenues dans un alliage cristallin dquivalent ; dans le r6gime plus concentrs la port6e des interactions entre impuretds est discutse.

Abstract.- We present a study on the magnetic ~ r o ~ e r t i e s of the amorphous (Cu Zr ) :4n system 60 40 I-c cThe

(c <_ 10 at %) in the dilute regime and in the interacting regime of magnetic Impurltles.

characteristics of manganese impurities obtained in the dilute regime are compared to those ob- tained in the crystalline counterpart ; in the more concentrated regime the range of the inter- action between magnetic impurities is discussed.

In this paper we study the magnetic properties system. Let us note that manganese atoms in crys- of amorphous ( C ~ ~ ~ Z r ~ ~ ) , - ~ ? l n ~ alloys for c<10 at %; talline Cu and Zr respectively, carry their full the properties of a (Cu5gZr41)gg!h, crystalline moment ; spin glass properties are observed for alloy are also studied. The magnetic state of man- appropriate Yn concentrations /10,11/.

ganese atoms and their long range interactions are Experimental procedure :

considered. Several studies has been recently car- The amorphous alloys has been prepared by the ried out on CuZr glassy metals, in particular con- rapid quenching technique. The X-ray analysis cerning the atomic structure. However, the conclu- showed that the amorphous phase can be obtained sions of the authors are not in agreement with

each other /1,2/. On another hand it has been shown that a single phase exists for crystalline C U ~ 131 ~ ; Zits structure is very close to that ~ ~ ~ of NiloZr7 which presents 4 zirconium sites and 5 nickel sites 141. Photoemission studies /5,6,7/ on CuZr and other Zr based glassy metals show in par- ticular that the electronic structure can be un- derstood in a band model where the Zr d band Lies

for c up to 10 at %. The manganese concentrations have been analyzed by atomic absorption spectrome- try. Specimens of C U ~ and (CuggZr4 ~ Z ~ ~) g+4n1 ~ were prepared as described by Lars Bsenko / 3 / . The magnetization measurements 1121 have been carried out by theFaradaymethod for fields up to 52 kOe and temperatures between 1.7 and 303 K.

Experimental results :

For all the investigated samples, the initial near the Fermi level meanwhile the Cu d band lies susceptibility

x

investigation /9/ concludes to the occurence of a impurities. For glassy C U ~ ~X' Z is ~ of ~ ~ , para-ferromagnetic transition in the Cu Zr Fe

60-c 40 c 0.5 emu/g ; the interpretation of such a va-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808168

lue can be found in ref. 5. With increasing manga- nese concentration, X' first increases linearly then saturates progressively (Table I). This va- riation of X' can be attributed to the host or more likely to the presence of non magnetic impuri-

ties. For the temperature dependent term which is attributed to manganese impurities, all the 0 va- lues are positive (Table I) ; as a function of manganese concentration, they first decrease (0 equals zero for c = 3 at %), then they increase with c. The determined Curie constants (between 35 and 400 emu/g) vary linearly with concentra- tion for c $ ^{2 at} %, then they saturate progressi- vely and seem to decrease for 10 at %. The Curie

constant for the crystalline ( C U ~ ~ Z ~ ~ ~ ) ~ ~ - % ~ is noticeably higher ( 1 10 emu/g) than for the

corresponding amorphous alloy. At low temperatures (T < 20 K) the magnetization shows a continuous approach to-saturation with increasing magnetic field ; this approach becomes slower for high manganese concentrations. Yoreover, at a given

temperature and magnetic field, the magnetization versus c varies linearly for low manganese concen- trations (c

2

(Fig. 1). In other words, :I(H,T)/c is an unique function of H and T for c

2

In the crystalline alloy, the approach to satura- tion is the same as for dilute ambrphous alloys (Fig. 2) _; only some differences can be observed at 1.7 R. However, the value of the magnetizations are noticeably higher than for the amorphous cor- responding alloy.

The previous results show clearly that for the magnetic impurities at least two concentration regimes can be defined ; first the dilute one where

0 0.5

0.5 0.55 3

1 .O 0.60 2

2 .0 0.75 1

3.0 0.9 0

5 .o 1.2 3

7 .O 1.5 7

10.0 1.5 7

1.0 cryst. 0.85 2 Tat

Fig. 1 : Amorphous ( C U ~ ~ Z ~ ~ ~ ) ~ - ~ % ~ variation of the magnetization vs manganese con- ,centration.

-

Fig. 2 : A~proach to the saturation of amorphous and crystalline CuZr alloys with 1 at % of manganese impurities.

the experimental values vary linearly with the manganese concentration and where the magnetic im- purities can be considered as isolated. In the se- cond concentration range the experimental values deviate from linearity ; this can be attributed to the long range interaction between the magnetic moments, therefore this concentration range can be

defined as interacting regime. Let us consider separately the two regimes.

r

JOURNAL DE PHYSIQUE

D i l ~ t e _ - c ~ s ~ t r ~ t i o - ! ! - ~ a n g e ~ s 2 2-af-%

For T 2 4.2 K the magnetization as a func- tion of magnetic field and temperature can be des- cribed by the following equation :

M(H,T) = M~(H/T + t) ) + X'H

where X' is the same as that deduced from the sus- ceptibility analysis. In the low temperature limit (T = 1.7 K) some deviations from the previous law are observed. This suggests that the magnetic impu- rities have characteristic temperatures which are of the same order of magnitude as the considered ones 1131. Let us now evaluate the magnetic moment of the impurities. The analysis of

?I (HIT + 8) shows that it varies approximately as a Brillouin function with g = 2, J = 2.2 (i.e.

p = 4.9 pg). The concentration c of these impuri- ties suggests that only one 1411 atom out of about n is magnetic ; n equals 6.5 for the amorphous al- loys and 4.5 for the crystalline one.

Interacting concentration range and spin glass like

________-- _-_-_-_---

___---

regime : c > ^{2 at} % :

--

---

Since for the spin glass term the definition varies with the authors., let us note that we ad- opt the definition proposed by Tholence and Tournier /14,16/ i.e. alloys where the magneti- zation and the specific heat vary according to a scaling law. In the present case, the magnetization

of the impurities satisfies to such a law for 3 at % 2 c 5 7 at % i.e. (N(H,T)-x'H)/c is an unique function of Hlc and TIC for TIC 5 1.4OK/at%.

This suggests that at low temperature, RKKY type (llr 3 ) interactions occur between magnetic impuri- ties. It is interesting to notice that the spin glass like properties occur in a concentration range where the magnetic impurities are less than 1 at %.

Conclusions :

The magnetic properties of crystalline ( C ~ ~ ~ Z r ~ ~ ) ~ g l r . , can be discussed in terms of local environment/l2, 171 of the manganese atoms. The fact that only one Mn atom out of 4.5 is magnetic suggests that at least two kinds of local environ- ments are present in the compound. The magnetic properties of the amorphous alloys could be under- stood in the same way i.e. the existence of vari- ous local environments in the alloy ; however some disordering effect occurs in the amorphous state since for a same t4n concentration the number of ma- gnetic impurities is less for the amorphous alloy.

The occurence of long range interactions be- tween magnetic impurities gives rise to an impor- tant question about the mean free path of conduc- tion electrons in the amorphous alloys. As a mat- ter of fact, interactions are already detectable for concentrations of magnetic impurities of about 0.4 %. This seems to indicate that the mean free path in an amorphous alloy can equal several interatomic distances.

Acknowlegements :

The author wishes to express his appreciation to Dr Z4.A. Khan for valuable discussions. Thanks are also due to Mrs Ravet for her help concerning the X-rays and chemical analysis.

Fig. 3 : Scaling law in (Cu60Zr40)1-cMnc system in the interacting regime of magnetic impuri- ties.

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