THE NON-METALLIC SPIN GLASS SYSTEM (Eusr) S H

THE NON-METALLIC SPIN GLASS SYSTEM (EuSr) S H. Maletta, W. Felsch

To cite this version:

H. Maletta, W. Felsch. THE NON-METALLIC SPIN GLASS SYSTEM (EuSr) S. Journal de Physique Colloques, 1978, 39 (C6), pp.C6-931-C6-933. 10.1051/jphyscol:19786413. jpa-00217884

HAL Id: jpa-00217884 https://hal.archives-ouvertes.fr/jpa-00217884 Submitted on 1 Jan 1978

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE Colloque C6, supplément au n° 8, Tome 39, août 1978, page C6-93I

THE NON-METALLIC SPIN GLASS SYSTEM (EuSr)S

H. Maletta1" and W. Felscht+

+ Institut flir FestkSvpevforsohung, KFA Jillioh, 5170 JUliah, West-Germany tt J. Physik. Institut der UniversitSt, 3400 GSttigen, West-Germany

Résumé.- L'aimantation à bas champs, la susceptibilité ac, la diffraction de neutrons et l'effet Mossbauer en (Eu Sr )S manifestent un comportement de type verre de spins pour x _< 0,5, en dépit d'échantillons qui ne sont pas métalliques. La température critique est observée en fonction de la fréquence et du champ magnétique appliqué.

Abstract.- Low-field magnetization, ac susceptibility, neutron diffraction and Mossbauer measure ments in (Eu Sr )S reveal a spin glass like behaviour at x< 0.5 in spite of the samples not being metallic. The critical temperature is observed to depend on the measuring frequency and the magnetic field applied.

1. INTRODUCTION.- The classical spin glasses one has focussed on in recent years are produced by diluting magnetic ions in a non-magnetic metallic matrix at low concentration (e.g. 1 at % Fe in Au) /l/. There fore sometimes it is believed that the RKKY inter action via the conduction electrons is necessary for spin glass behaviour. Here we report on the insulating system (Eu Sr )S where we have experi mental evidence that all of the magnetic properties commonly used to characterize metallic spin glasses are also found in this non-metallic system below x = 0.5.

2. THE TYPE OF MAGNETIC ORDER.- The series (Eu Sr )S x 1-x' is based on the ferromagnetic insulator EuS diluted with diamagnetic SrS, the two compounds being iso- structural (NaCl) with nearly the same lattice Fig. 1 : Concentration dependence of the ordering constant. Figure 1 shows the concentration depen temperatures (Curie temperature T , spin dence of the magnetic ordering temperature glass temperature T,) in (Eu Sr )S

(Tc(x) : x > 0.5, Tf(x) : x _< 0.5). The Curie tem perature T decreases strongly around x £ 0.5 results of recent neutron diffraction measurements indicating a change into a different type of magnetic /3/ on Eu S S shown in figure 2 demonstrates order below this concentration. We are able to that there is no long-range coherent magnetic order identify this as a spin glass type of ordering with below T_. Instead one can realize in the figure a the help of the following properties : The tempe strong peaking of the scattered intensity at low rature dependence of the initial susceptibility angles, together with a broad bump around the first measured by an ac technique (117 Hz, 10-5 shows a Bragg angles, indicating short-range ferromagnetic ordering. This coupling sets-in at a much higher maximum at a temperature defined as Tf and plotted in figure 1 for x <_ 0.5. At high temperature T » T, temperature than Tf. Studying the static magnetiza the susceptibility follows a Curie-Weiss law with a tion below T, one observes Ihl no spontaneous magne positive temperature 6 over the whole concentration tization, a remanent magnetization and an increased region 0 < x <_ 1 /2/, hence the maximum in X(T) magnetization at sufficiently low applied fields observed cannot be interpreted as a transition into after field cooling, and long-time relaxation phe- an antiferromagnetically ordered state. One of the

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19786413 nomena. In the very low Eu concentration regime in one obtains a relative increase of Tf proportional (EuSr) S, spin glass properties have already been to log v and I/x. Performing the same technique with obtained by magnetization measurements in 151. a superposed low static magnetic field B results in a reduction of Tf linear with field and concentration at low fields. The field effect on the maximum value of x is much stronger than e.g. in AuFe / 1 / . Mijssbauer effect measurements at the Eu nuclei /7/ reveal an anomalous temperature and concentration dependence at lower Eu concentration showing the complex dynamics around Tf, too.

4. CONCLUSION.- The experimental results on the insulating (EuSr)S complied above demonstrate the similarity of the spin glass behaviour generally studied in dilute alloys. In EuS the two kinds of exchange interactions with opposite sign are well studied 181. Presumable these two competing exchange interactions, together with the dipole-dipole coupling, are responsible in (EU~S~~-~)Sbelow x = 0.5 for the spin glass type of ordering. The frequency Fig. 2 : Difference between two neutron diffraction spectra at 1.3 K (T < Tf) and 10 K (T > T ) versus dependence of Tf illustrates the complex character the scattering angle 20 in Euo.,, SrOe6S. ~iepositions of the transition into the spin glass order in of the Bragg angles are indicated (EuSr)S where a broad spectrum of frequences down to very low values influences the dynamics. Similar 3. THE TRANSITION AT Tf.- The temperature Tf defined effects on Tf (v) are expected to be found in very by the ac-x measurement is found in (EuSr)S to be dilute alloys, an indication is already seen from systematically at a higher temperature than the figure 2 of reference 191. maximum of x derived from the static magnetization in low field. A similar behaviour is known for CuMn Acknowledgements.- One of the authors (H.M.) is (8 %) for which a difference of Tf is reported 161 indebted to the CNRS of Grenoble for the possibility dependent on the measureing time. These results are to perform the static magnetization measurement at consistent with the frequency (v) dependence of T f low temperatures during a stay there. The neutron measured by the ac-x technique, one of the results diffraction experiments have been performed on the is shown in figure 3. Within the range available DIB multicounter instrument of the ILL reactor in Grenoble. We also acknowledge the permanent interest of Pr. W. Zinn in this work, and thank Dr. H. Pink, Siemens AG, Munich, for the preparation of the samples.

Fig. 3 : Frequency dependence of the spin glass temperature in Eu Sr S determined by the maximum in th$"Jc-~~'~~ References

/I/ Cannella, V. and Mydosch, J.A. Phys. Rev. 6 (1972) 4220 /2/ ~Gbler,U. and Maletta, H., to be published ; Westerholt, K., Ghosh, B., Siratori, K, Methfessel, S. and Petzel, T., Physica 86-88B (1977) 740 131 Maletta, H. and Convert, P., to be published 141 Maletta, H., Felsch, W. and Tholence, J.L., J. Magn. Magn. Mat., in print /5/ Holtzberg, F., Tholence, J.L. and Tournier, R., Second Int. Symp. on Amorphous Magnetism, Troy 1976 /6/ Murani, A.P. and Tholence, J.L., Solid State Comm. 2, (1977) 25 171 Maletta, H. and Crecelius, G., J. Physique Colloq.,x ( 1976) C6-645 181 Crecelius, G., Maletta, H., Pink, H. and Zinn, W.., J. Magn. Magn. Mat. 5 (1977) 150 /9/ Tholence, J.L. and Tournier, R., J. Physique Colloq., -35 (1974) C4-229