HAL Id: jpa-00229261
https://hal.archives-ouvertes.fr/jpa-00229261
Submitted on 1 Jan 1988
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.
EVIDENCE FOR THREE DIMENSIONAL
MAGNETIC ORDERING IN ErBa2Cu3O7
T. Chattopadhyay, P. Brown, D. Bonnenberg, S. Ewert, H. Malletta
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Suppl6ment au no 12, Tome 49, d6cembre 1988
EVIDENCE FOR THREE DIMENSIONAL MAGNETIC ORDERING IN ErBa2Cu307
T. Chattopadhyay (I' '), P. J. Brown (3), D. Bonnenberg (4), S. Ewert (4) and H. Malletta (2)
(I) Centre d'Etudes Nucle'aires, DRF/SPh-MDN, 85X, 38041 Grenoble Cedez, France
(2) Institut fiir Festkiirpqrforschun der KFA Jiilich, 51 70 Jiilich, F. R. G.
(3) Institut Laue-Langevin, 156X, 38042 Grenoble Cedez, France
(4) Institut fiir Werkstoffe der Elektrotechnik and 2. Physikalisches Institut, RWTH Aachen, F.R.G.
Abstract. - Neutron diffraction experiments on polycrystalline samples of ErBa2Cus07 show that Er moments are ordered three-dimensionally a t T = 140 mK. Two independent propagation vectors kl = (112 0 0) and k2 = (112 0 112) are required t o index the magnetic reflections. Er moments are inclined at an angle of 32 deg t o the c-axis and the ordered magnetic moment a t 140 mK is 4.9 (2) p ~ .
The discovery of superconductivity in (Lal-,Sr,)2Cu04 [l] (T, = 40 K ) and in YBa2Cu307-6 [2] (T, = 90 K) has been followed by in- tensive theoretical and experimental study of this class of compounds. It has been observed that the Y ions in YBazCuaO7-a can be fully substituted by several rare earth ions without changing the T, value significantly [3]. The magnetic properties of these compounds show
that the rare earth moments order at low tempera- tures [4]. Neutron diffraction experiments have estab- lished that Gd- and Dy-based compounds order three dimensionally with the propagation vector (1/2 1/2 1/2) a t TN = 2.2 and 0.8 K, respectively 15, 61. Lynn
et al. [7] has observed two-dimensional ordering of Er moments in ErBazCu307 a t about 0.5 K. This two- dimensional ordering persists down t o 0.3 K. In the present paper we report the observation of the three- dimensional ordering of Er moments of ErBazCu307 a t about 140 mK by neutron diffraction from polycrys- talline samples.
Polycrystalline samples of ErBazCu3O.r were syn- thesised by conventional ceramic powder technique starting from Er203, CUO and BaCO3. The supercon- ducting transition temperature was determined to be
T, = 91 f 1 K from electrical resistivity measurements (Fig. 1). Neutron diffraction experiments were per- formed a t the high flux reactor of the Institut Laue- Langevin with the diffractometer D20 using a neutron wavelength of 2.406
-4
with the sample in a 5 ~ e - 4 ~ e dilution cryostat.50 100 150 200 250 300 Temperature IK)
Fig. 1. -Electrical resistivity of ErBa2CusO.r as a function of the temperature showing the sharp drop a t 91 K.
Figure 2 shows the diffraction diagrams a t 4.2 K and 140 mK together with a difference diagram. The difference diagram shows extra peaks which can be as- sumed t o be of magnetic origin. These peaks can be indexed assuming two independent propagation vec- tors k l = (1/2 0 0) and kz = (112 0 1/2). Our experi- mental resolution does not permit us t o distinguish be- tween [loo] and [010] directions and we will assume in the following that the components of the propagation vectors in the a-b plane are parallel t o a* rather than to b*. The orientation of the magnetic moments has been determined from the intensities of the diffraction peaks a n d is shown in figure 3. Both propagation vec-
-20 1
I 0 20 30 40 SO I 2 8 (deg.)
Fig. 2. - Neutron diffraction diagram of ErBa2Cu307 (a) a t 4.2 K, (b) at 140 mK; ( c ) difference between data a t
140 mK and a t 4.2 K. 300 zoo A 100
d
.-
C a 300e
B-
200 *, +.-
V),=
roo a ErBa2Cu307h
= 2-406a - 1 4.2 K - b-
140 mK -C8 - 2170 JOURNAL DE PHYSIQUE tors give rise to antiferromagnetic coupling of moments
in the chains parallel to a and ferromagnetic coupling of chains parallel to b. The result implies the existence of two domains, one corresponding to each propaga- tion vector. In the domain with propagation vector
kl = (1/2 0 0)' successive Er ions along the c-axis are parallel, whereas for ka = (1/2 0 1/2) they are an- tiparallel. It is somewhat surprising that the domains appear to be equally populated. This model of mag- netic structure is consistent with the two-dimensional ordering observed by Lynn et al. [7]. The magnetic moments are oriented by an angle of 32 deg to the c- axis in the b-c plane. The magnetic moment per Er atom, taking into account the division into two do-
mains, is 4.9 (3) pg a t T = 140 mK. .4lthough the free ion moment of ~ r is 9 ' ~pg crystal field effects must be considered a t this low temperature. Our experimental value of the magnetic moment agrees closely to the estimated value of the magnetic moment of 4.5 p~ ob- tained from the heat capacity data [8].
Fig. 3. - Schematic representation of the magnetic struc- ture of ErBa2Cu307 showing the orientation of the mo- ments in two unit cells in each direction. (a) A section perpendicular to [OOl] at z = 0, (b) a section perpendicular to [loo] at x = 0 for the kl domain, (c) a section perpen- dicular to [loo] at x = 0 for the k2 domain. The moments in adjacent sections of both types are reveresed.
An alternative interpretation of the diffraction in- tensities would be that the two different propagation vectors coexist in the crystal. This would result in a structure in which alternate layers of Er atoms perpen- dicular to the c-axis have no ordered magnetic moment and the remaining layers couple ferromagnetically giv- ing a sequence along the c-axis (+0
+
0).
Such a model would explain the equivalence of the moments corre- sponding to the two propagation vectors, but seems physically unlikely. It should be emphasised that thediffraction data cannot distinguish between these two types of models.
The present neutron diffraction evidence for three- dimensional magnetic ordering in ErBazCu~O7 raises once again the question of the mechanism of the mag- netic interaction between the rare earth (RE) atoms in REBa2Cu307 along c-axis along which the RE atoms are separated by about 12
A.
Since the substitution of Y by the magnetic RE ions has little or no effect on the superconductivity, the interaction between the mo- ment of the RE ion and the conduction electrons must be very weak resulting in a weak Ruderman-Kittel- Kasuya-Yosida (RKKY) interaction. Several authors [7, 91 have pointed out the importance of the dipolar interaction in these compounds. However, the dipolar interaction cannot by itself explain the coupling be- tween RE atoms separated by about 12A
along the c-axis. Superexchange via 0 and/or Cu atoms should also be considered t o understand the'magnetic order- ing in these compounds. Crystal field effects result- ing in anisotropy are also important in determining the magnetic moment directions in ErBazCu307. The magnetic structure determined in the present experi- ment shows that the sign of the exchange coupling be-tween RE moments along the c-axis must arise from a delicate balance of competing interactions.
[I] Bednorz, J. G. and Miiller, K. A., 2. Phys. Con- densed Matter 64 (1986) 189.
[2] Wu, M. K., Ashburn, J. R., Torng, C. J., Hor, P. M., Meng, R. L., Gao, L., Haung, Z. J., Wang, Y.
Q. and Chu, C. W., Phys. Rev. Lett. 58 (1987) 908.
[3] Hor, P. H., Meng, R. L., Wang, Y. Q., Gao, L., Haung, Z. J., Bechtold, J . , Forster, K. and Chu, C. W., Phys. Rev. Lett. 58 (1987) 1891.
141 Brown, S. E., Thompson, J . D., Willis, J. O., Atkin, R. M., Zirngiebl, E., Smith, J. L., Fisk, Z. and Schwarz, R. B., Phys. Rev. B 36 (1987) 2298.
[5] McK. Paul, D., Mook, H. A., Havat, A. W., Sales, B. C., Boatner, L. A., Thompson, J. R. and Mostoller, M., Phys. Rev. B 37 (1988) 2341. [6] Goldman, A. I., Yang, B. X., Tranquada, J., Crow, J. E. and Jee, C. S., Phys. Rev. B 36
(1987) 7234.
[7] Lynn, J . W., Li, W. H., Ku, H. C., Yang, H. D. and Shelton, R. N., Phys. Rev. B 36 (1987) 2374. [8] Dunlap, B. D., Slaki, M., Hinks, D. G., Soder- holm, L., Beno, M., Zhang, K., Segre, C., Crab- tree, G. W., Kwok, W. K., Malik, S. K., Schuller, I. K., Jorgensen, J. D. and Sungaila, Z., J. Magn.
Magn. Muter. 68 (1987) L139.
