IRON MAGNETISM IN RBa2 Cu3 Oz

(1)

HAL Id: jpa-00229284

https://hal.archives-ouvertes.fr/jpa-00229284

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.

IRON MAGNETISM IN RBa2 Cu3 Oz

E. Bauminger, I. Felner, M. Kowitt, I. Nowik

To cite this version:

(2)

JOURNAL DE PHYSIQUE

Colloque C8, Supplement au no 12, Tome 49, d6cembre 1988

IRON MAGNETISM I N RBa2Cu3Oz

E. R. Bauminger, I. Felner, M. Kowitt and I. Nowik Racah Institute of Physics, The Hebrew University, Jerusalem

Abstract. - Magnetic susceptibility and 6 7 ~ e MGssbauer spectroscopy of YBaz ( C U ~ - , F ~ , ) ~ 0,, a: = 0.01 to 0.1, r = 5.9

to 7.1 at temperatures between 4.1 K to 480 K have been performed. Iron in the Cu2 site exhibits magnetic order with

TN = 415 K for z = 6.1.

We report here Mossbauer studies of ~e~~ in RBaz (Cul-,Fez), 0 , , with R = Y or Pr, x = 0.01, and 0.1, and z = 5 . 9 to 7.1 at temperatures between 4.1 K and 480 K. These studies show that the fraction of iron ions which enter the Cu2 site order mag- netically in some of the compounds, with different ordering temperatures. In YBazCusO, the iron spectra reveal magnetic order for z

5

6.5. There is magnetic order in the Cu2 site in tetragonal nonsuperconducting PrBazCu3O6.g, with

TN

= 325 K. There is no magnetic order in superconducting 'YBa~Cu306.9.

The samples were prepared by conventional meth- ods [2]. All samples were analysed by X-ray 'diffraction measurements and their lattice parameters were obtained. These studies showed that all samples were of single phase. We discuss in detail three families of compounds:

a) YBa2 ( C u o . ~ ~ F e ~ . ~ ~ ) , 0, with z = 5.9 to 6.9. In all these compounds the iron replaces Cul ions almost exclusively [3] and no well defined magnetic subspectrum is found in most of these compounds at any temperature above 4.1 K. The spectra obtained at 90 K

and above are all composed of 6 quadrupole doublets, corresponding to 6 inequivalent iron sites, due t o different oxygen neighbour configurations in the Cul site 131.

The relative sizes of the quadrupole splittings in the six sites agree with point charge calculations for ~ e ~ + [3]. At 4.1 K, the spectra for z

5

6.5 show complicated structure. These spectra may be due to spin-glass-like order of the iron in the Cul site 141, but could more reasonably be interpreted as due to slow paramagnetic spin relaxation, since our magnetic measurements [5] performed on YBaz (C~0.gFeo.l)~ 0 6 . 1 show that there is no sign of spin glass ordering at low temperatures. Some of the spectra obtained for 4.1 K with different z values were shown in figure 2 of reference [3].

For z = 6.9 the iron Mossbauer spectrum shows no magnetic hyperfine structure, (Fig. l ) , indicating that in the superconducting state spin relaxation rates are high. They decrease as z decreases and the superconducting transition temperature decreases;

b) YBa2 (Cuo.gFeo.l), 0, with z = 6.1; 6.5 and 7.1. In the samples with z

5

6.5, which are not superconducting, we observe a well defined magnetic sex-

VELOCITY (m/s)

Fig. 1. - MGssbauer spectra of in YBa2 (Cul-,Fez), 0% (with r = 6.9 for x = 0.01 and z = 7.1 for x = 0.1).

tet. We attribute this subspectrum to iron, which now also replaces copper in the Cu2 site and orders anti- ferromagnetically [I]. At 4.1 K the magnetic hyperfine field is 514 kOe and the quadrupole interaction is eqQ/4 = -0.17 mm/s. As the temperature is raised, the magnetic splitting decreases and the NBel temperature in each of the compounds can be obtained. The NBel temperature depends on the oxygen content, increasing as z decreases. No magnetic sextet is observed in superconducting YBaz ( C u o . ~ F e o . ~ ) ~ 07.1, at 90 K (Fig. 1). Figure 2 shows the spectra obtained in YBa2 (Cul-,Fe,), 06.1 a t various temperatures. The well defined magnetic subspectrum is clearly seen and the change of the size of the hyperfine field can easily be followed (Fig. 3). A NQl temperature of 415 K is obtained for YBaz (Cuo.9Fe0.1)~ 06.1. In YBaz (Cuo.gFeo.l), 06.s similar spectra are observed, yet the magnetic ordering temperature in this compound is TN = 280 K, The electric field gradient at the Cu2 site according to point charge calculations is positive and points along the c axis. The mea- sured negative effective quadrupole interaction proves that the magnetic moments lie in the basal plane [I]. The fact that the ordering temperature of Fe in YBaz (Cuo,gFeo.l), Os.l agrees so well with the neu-

(3)

C8 - 2212 JOURNAL DE PHYSIQUE

0.99

-5 0.0 5

VELOCITY (mm/s)

Fig. 2. - Mossbauer spectra of ~e~~ in YBa2 ( C U ~ - , F ~ , ) ~ 06.1.

0 100 200 300 400

Temperature (K'

Fig. 3. - Temperature dependence of the magnetic hyperfine field acting on Fe nuclei in the Cu2 site in RBa2 ( c ~ l - , F e , ) ~ 0,.

tron diffraction results [I] proves that we are indeed measuring through the iron the magnetic ordering of copper in the Cu2 site, and that this ordering is not af- fected by the presence or concentration of the iron im- purity. All spectra at 4.1 K show, besides the well defined sextet, a complicated central subspectrum, similar to those observed in the YBa2 (Cuo.seFeo.o~):, 06.1

samples, which are attributed to iron in the Cul site exhibiting long spin relaxation time phenomena;

c) PrBa2 (Cul-,Fez), 00.9 with

x

= 0.01 and x = 0.1. These tetragonal compounds, with a = b = 3.900 and c = 11.66

A

for

x

= 0.01 and

a = b = 3.927

A,

c = 11.69

A

for x = 0.10, are rich in oxygen yet not superconducting. In these compounds

a well defined magnetic subspectrum is seen even for z = 0.01. It thus seems that in these compounds a

larger fraction of the Fe ions enter the Cu2 site. The Nkel temperature of the iron ions in the Cu2 site is 325 K (Fig. 3) for both x = 0.1 and x = 0.01, proving again that

TN

does not depend on iron concentration. Thus, though this compound is rich in oxygen, like the orthorhombic superconducting compounds, it is nonsuperconducting, and tetragonal, and its magnetic behaviour resembles that of oxygen-poor, tetragonal nonsuperconducting compounds. This shows that the number of oxygen ions alone cannot account for the disappearance of the magnetic interactions in the Cu2 site.

Acknowledgement

This research was supported in part by a grant from the US-Israel Binational Science Foundation (BSF), Jerusalem, Israel.

[I] Tranquada, J. M., Cox, D. E., Kunnmann, W.,

Moudden, H., Shirane, G., Suenaga, M., Zolliker, P., Vaknin, D., Sinha, S. K., Alvarez, M. S., Ja- cobson, A. J. and Johnston, D. C., Phys. Rev. Lett. 60 (1988) 156;

Rossat-Mignod, J., Burlet, P., Jurgens, M. J.

G . M., Henry, J. Y. and Vettier, C., Physica C

152 (1988) 19.

[23 Felner, I., Nowik, I. and Yeshurun, Y., Phys.

Rev.

36 (1987) 3923.

[3] Bauminger, E. R., Kowitt, M., Felner, I. and Nowik, I., Solid State Commun. 65 (1988) 123.

[4] Tanaki, T., Konai, T., Ito, A., Maeno, Y. and Fujita, T., Solid State Commun. 65 (1987) 43. [5] Felner, I., Wolfus, Y., Hilscher, G. and Pillmayr,