HAL Id: jpa-00217884
https://hal.archives-ouvertes.fr/jpa-00217884
Submitted on 1 Jan 1978
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
THE NON-METALLIC SPIN GLASS SYSTEM (EuSr)
S
H. Maletta, W. Felsch
To cite this version:
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 constant. Figure 1 shows the concentration depen-dence of the magnetic ordering temperature
(Tc(x) : x > 0.5, Tf(x) : x _< 0.5). The Curie tem-perature T decreases strongly around x £ 0.5 indicating a change into a different type of magnetic order below this concentration. We are able to identify this as a spin glass type of ordering with the help of the following properties : The tempe-rature dependence of the initial susceptibility measured by an ac technique (117 Hz, 10- 5 shows a
maximum at a temperature defined as Tf and plotted
in figure 1 for x <_ 0.5. At high temperature T » T, the susceptibility follows a Curie-Weiss law with a positive temperature 6 over the whole concentration region 0 < x <_ 1 /2/, hence the maximum in X(T) observed cannot be interpreted as a transition into an antiferromagnetically ordered state. One of the
Fig. 1 : Concentration dependence of the ordering temperatures (Curie temperature T , spin glass temperature T,) in (Eu Sr )S
results of recent neutron diffraction measurements /3/ on Eu S S shown in figure 2 demonstrates that there is no long-range coherent magnetic order below T_. Instead one can realize in the figure a strong peaking of the scattered intensity at low angles, together with a broad bump around the first Bragg angles, indicating short-range ferromagnetic ordering. This coupling sets-in at a much higher temperature than Tf. Studying the static
magnetiza-tion below T , one observes Ihl no spontaneous magne-tization, a remanent magnetization and an increased magnetization at sufficiently low applied fields after field cooling, and long-time relaxation
nomena. I n t h e v e r y low Eu c o n c e n t r a t i o n regime i n (EuSr) S, s p i n g l a s s p r o p e r t i e s have a l r e a d y been o b t a i n e d by m a g n e t i z a t i o n measurements i n
151.
Fig. 2 : D i f f e r e n c e between two neutron d i f f r a c t i o n s p e c t r a a t 1.3 K (T < T f ) and 10 K (T > T ) v e r s u s t h e s c a t t e r i n g a n g l e 2 0 i n Euo.,, SrOe6 S. ~ i e positions of t h e Bragg a n g l e s a r e i n d i c a t e d
3 . THE TRANSITION AT Tf.- The temperature Tf d e f i n e d by t h e ac-x measurement i s found i n (EuSr)S t o be s y s t e m a t i c a l l y a t a h i g h e r temperature t h a n t h e maximum of
x
d e r i v e d from t h e s t a t i c m a g n e t i z a t i o ni n low f i e l d . A s i m i l a r behaviour i s known f o r CuMn (8 %) f o r which a d i f f e r e n c e of Tf i s r e p o r t e d
161
dependent on t h e measureing time. These r e s u l t s a r e c o n s i s t e n t w i t h t h e frequency (v) dependence of T f measured by t h e ac-x technique, one of t h e r e s u l t si s shown i n f i g u r e 3. Within t h e range a v a i l a b l e
one o b t a i n s a r e l a t i v e i n c r e a s e of Tf p r o p o r t i o n a l t o log v and I/x. Performing t h e same t e c h n i q u e with a superposed low s t a t i c magnetic f i e l d B r e s u l t s
i n a r e d u c t i o n of Tf l i n e a r w i t h f i e l d and concen- t r a t i o n a t low f i e l d s . The f i e l d e f f e c t on t h e maxi- mum v a l u e of
x
i s much s t r o n g e r than e.g. i n AuFe/
1/
.
Mijssbauer e f f e c t measurements a t t h e Eu n u c l e i / 7 / r e v e a l an anomalous temperature and con- c e n t r a t i o n dependence a t lower Eu c o n c e n t r a t i o n showing t h e complex dynamics around Tf, too.4. CONCLUSION.- The experimental r e s u l t s on t h e i n s u l a t i n g (EuSr)S complied above demonstrate t h e s i m i l a r i t y of t h e s p i n g l a s s behaviour g e n e r a l l y s t u d i e d i n d i l u t e a l l o y s . I n EuS t h e two k i n d s of exchange i n t e r a c t i o n s w i t h o p p o s i t e s i g n a r e w e l l s t u d i e d 181. Presumable t h e s e two competing exchange i n t e r a c t i o n s , t o g e t h e r w i t h t h e d i p o l e - d i p o l e cou- p l i n g , a r e r e s p o n s i b l e i n ( E U ~ S ~ ~ - ~ ) S below x = 0.5
f o r t h e s p i n g l a s s type of o r d e r i n g . The frequency dependence of Tf i l l u s t r a t e s t h e complex c h a r a c t e r of t h e t r a n s i t i o n i n t o t h e s p i n g l a s s o r d e r i n
(EuSr)S where a broad spectrum of frequences down t o very low v a l u e s i n f l u e n c e s t h e dynamics. S i m i l a r e f f e c t s on Tf (v) a r e expected t o be found i n v e r y d i l u t e a l l o y s , an i n d i c a t i o n i s a l r e a d y seen from f i g u r e 2 of r e f e r e n c e 191. Acknowledgements.- One of t h e a u t h o r s (H.M.)
i s
indebted t o t h e CNRS of Grenoble f o r t h e p o s s i b i l i t y t o perform t h e s t a t i c m a g n e t i z a t i o n measurement a t low t e m p e r a t u r e s d u r i n g a s t a y t h e r e . The neutron d i f f r a c t i o n experiments have been performed on t h e DIB m u l t i c o u n t e r i n s t r u m e n t of t h e ILL r e a c t o r i n Grenoble. We a l s o acknowledge t h e permanent i n t e r e s t of P r . W. Zinn i n t h i s work, and thank D r . H. Pink, Siemens AG, Munich, f o r t h e p r e p a r a t i o n of t h e samples.Fig. 3 : Frequency dependence of t h e s p i n g l a s s
temperature i n Eu S r S determined by
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
(
