Journal of Magnetism and Magnetic Materials 25 (1982) 307-309 307 North-Holland Publishing Company

THE SPIN GLASS-LIKE BEHAVIOUR OF TH E GLASSY (Sb2S3)x(Sbl3)yFe:

A. ZENTKO

hlstitute of Experimental Physics, Slovak Academy of Sciences, 041 54 Kogice, Czechoslovakia

T. SVEC

Department of Experimental Physics, Faculty, of Sciences, P.J. Saf&rik Universi(v, Kogice, Czechoslovakia

I.D. TURYANITSA and V.P. PINZENIK

State University, Uzhgorod, USSR

Received 26 November 1980; in revised form 4 November 1981

Low field magnetic susceptibility of a glassy semiconductor (Sb2S3)x(SbI 3 )yFe: reveals a spin glass-like behaviour in spite of the sample not being metallic. The critical temperature is observed to depend on the concentration of the iron atoms (T M =0.179z°'76).

1. Introduction

Traditionally, the spin glasses are coupled with magnetically diluted metallic alloys such as Cu, Ag, Au as a solvent with very small amounts ( < 1 at%) of transition metals as a solute. Therefore sometimes it is believed that the RKKY interac- tion via conduction electrons is necessary for the spin glass behaviour. On the other hand, the spin glass-like behaviour was observed in the such in- sulating dilute compounds as EuxSrl_xS [1] or MnO. A1203 • SiO 2 [2]. In this paper we report an investigation of the magnetic properties of the semiconducting glass Sb2S 3 • SbI 3. Fe.

of the glasses examined exhibited any crystalline features. In table 1 the glass transition temperature Tg, crystallization temperature Tcr, melting temper- ature T m, and density of investigated samples are summarized.

The ac susceptibility has been measured using a mutual inductance bridge operating at 12 kHz. The amplitude of the ac field was kept below 160 A / m . Measurements were done in the temperature range 3.1-15 K. Temperature measurements were made with a carbon sensor for T > 4 .2K and using the vapour pressure of 4He below 4.2 K.

3. Results and discussion

2. Experiment

The glasses of the present study were prepared by heating mixtures of the elements in evacuated sealed silica ampoules for six days at a temper- ature of 900°C, followed by quenching to room temperature. Finally, the samples were examined for crystallinity. The glasses were examined using X-rays, DTA and microstructural analyses. None

The variation of low field susceptibility with temperature for all investigated samples is shown in fig. 1. From this figure it is clear that the susceptibility exhibits a cusp at a temperature T M. The concentration dependence of T M has the form T M : A g 0"76, where A is 0.179 K/a t% Fe and z is the concentration of iron atoms. An additional small static field of a few thousand A / m produces a rounding of the peaks as for classical spin glasses

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308 A. Zentko et al. / Properties of the glass Sb_,S.¢. ShI ¢. Fe

Table I Data for glassy semiconductors Sb2S 3- Sbl3Fe

Sample Tg T.~ T,,, T M &el 0p v ~ 10 ~ X(TM)>~ 10' (K) (K) (K) (K) (/.%~) (K) (kgm 3) (m ~ kg i)

(Sb2 $3 )0.v4,~( SbI 3 )o.25 Feo.~l 427 479 637 4.51 7.44 0.2 4.44 56 (Sb2 $3 )o.75(SbI 3 )o.245 Feox~ 5 427 479 638 4.6 6.99 0.04 4.44 245 (Sb2 Sa )o.73(Sbl 3 )o.25 Feo.o2 430 498 653 4.85 4.91 0.0 4.46 462

[3]. The inverse of the susceptibility, l /x, was plotted for all samples (fig. 2). These plots are linear in T down to temperatures close to T M. From the intercept and slope of the plots of 1/X vs. T we have found the paramagnetic Curie tem- perature, 0p, and the effective number of Bohr magnetons per iron atom, Pelf, using classical molecular field analysis. Table 1 shows the values of T M (determined by the maximum in x(T)) , 0p and perf. The large values found for Pcff in these

glassy semiconductors indicate considerable super- paramagnetic clustering just as for some diluted metallic systems [4]. The values of Pelf for our glasses decrease as the concentration rises. The paramagnetic Curie temperatures, Op, are equal to zero or positive.

The principal result of the present work is the presence of the sharp peak in the temperature dependence of the low field magnetic susceptibility of S b - S - I F e glasses. The existence of such a max-

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Fig. 1. The ac susceptibility versus temperature. (a) (Sb2S3)o.v30(SbI3)o.250Feo.02, (b) (Sb2S3)o.vs(Sb13)o.245Feo.o05 and (c) (Sb2S3)o.74~(SbIOo.25F%xxn).

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o o

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7 7

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, / , / f • • , 1 I , , L , I , , , ,

5 10 TEK3 Fig. 2. The inverse susceptibi|ity versus temperature (the deno- tation o f c u r v e s as in fig. I).

A. Zentko et al. / Properties of the glass Sb,S~. SbI.,. Fe 309

imum is typical for spin glasses and we suggest that T M marks the onset of the spin glass state in the investigated samples, T M being the freezing temperature. Further evidence for a such conclu- sion is the fact that the peaks in x(T) are reduced and rounded in a relatively small static field. The value of the exponent in the concentration depen- dence of T M (T M ~ z °76) is close to the measure- ments reported by Mydosh [5] for the metallic spin glasses (T M ~ z°55-z °'75) and is in good agreement with the value derived from the theory of Freu- denhammer [6] (T M ~ z°3-z°62). The decrease of Peff and 0p with increasing z is due, probably, to

the increasing antiferromagnetic interaction be- tween Fe -Fe near neighbors.

References

[1] H. Maletta and W. Felsch, J. de Phys. 39 (1978) C6-931. [2] J.P. Renard, J. Pommier, J. Ferre and K. Knorr, J. de Phys.

39 (1978) C6-936. [3] V. Cannella and J.A. Mydosh, Phys. Rev. B6 (1972) 4220. [4] V. Cannella, in: Amorphous Magnetism, eds. H.O. Hooper

and A.M. de Graaf (Plenum Press, New York, 1973) p. 195. [5] J.A. Mydosh, AIP Conf. Proc. 24 (1974) 131. [6] A. Freudenhammer, J. Magn. Magn. Mat. 6 (1977) 97.