MAGNETIC STUDIES OF Pr1Ba2Cu3O7-δ AND La1Ba2Cu3O7-δ

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MAGNETIC STUDIES OF Pr1Ba2Cu3O7-δ AND

La1Ba2Cu3O7-δ

S. Chittipeddi, Y. Song, J. Gaines, W. Farneth, E. Mccarron, A. Epstein

To cite this version:

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JOURNAL DE PHYSIQUE

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

MAGNETIC STUDIES OF PrlBa2Cu307-g AND LalBa2Cu307-6

S. Chittipeddi (3) *, Y. Song (I), J. R. Gaines (I), W. E. Farneth (2), E. M. McCarron I11 (2) and A. J. Epstein (3)

(I) Department of Physics, University of Hawaii, Manoa, Hawaii, U.S.A.

(2) E.I. du Pont de Nemours and Company, Central Research and Development, Wilmington, DE 11898, U.S.A.

(3) Department of Physics, The Ohio State University, Columbus, OH 43.210, U.S.A.

Abstract. - We report magnetic susceptibility ( X B ~ i n (T))

,

and magnetic scattering (neutron) studies for the superconducting complex LalBazCu307 and the insulating complex Pr1BazCu307-6. The magnetic susceptibility and scattering measurements on the compound Pr1Ba2C~307-~ show no sign of magnetic ordering. For the LalBazCu30.r-6 samples

we observe only a small change in the Pauli susceptibility and a decrease in the Curie-constant as Tc of the samples is increased.

In compounds of the generic form RBa&u3o7-6 of which trivalent R ion is used from among yttrium and the rare earths [I, 21, it has been found that Tc for superconductivity is not substantially altered by the presence of the rare earth. The exceptions to this rule are the Pr, T b and Ce compounds, where the serni- conducting behavior of these compounds [3] has been attributed to the valency of the rare earth ions. The in- corporation of Pr into the Y-Ba-Cu-0 complex leads to drastic decrease in the transition temperature [4] whereas Ce phase segregates into BaCeO3 [5]. This behavior is of particular interest, with respect to the magnetic ordering which occurs in the CuO planes [6, 71; the reason being that if P r (in the compound PrlBazCu307-6) were in a +4 valence, then a simple valence counting argument would show if S = 0, then the most of the cu ions would be in a +2 valence state. The direct observation of (antiferromagnetic) ordering using susceptibility techniques however is difficult due to the magnetic contribution of the Pr ion. The magnetic ordering of the Cu spins in the CuO planes can be studied using elastic neutron scattering techniques. The LalBazCu307-6 system has been the subject of extensive study by our group; Tc of this system of compounds has not been as high as that reported for the corresponding YrBazCusO;.-s case I7]. The role of disorder of La/Ba has already been established to be a major reason for the low Tc's in this system [ti, 91, but until now no correlation has been made, of the interplay between magnetism and disorder.

Lo, Ba2Cu,0,-, O 4

j

0.02 - .- 72 K - 0 04b ₅₀ _IM) ₁₅₀ _2W ₂₅₀ _XI0I T(K)

Fig. 1.

-

Spin Susceptibility XsPin vs. temperature, T for

LalBazCu307-6 at a field of 2.25 kG.

imental error) whereas sample with Tc above 50 K

showed orthorhombicity [9]. The magnetic susceptibility measurements were carried out using a Faraday balance [lo], and an applied field of 2.25 kG. The mea- sured spin susceptibility was fit to a function of the form X ~ p i n = X~ + XPauli + XCurie-Weiss (T)

,

where

x0

refers to the sum of the temperature independent core diamagnetism andathe Van Vleck paramagnetic terms. The core diamagnetism was obtained by adding the core diamagnetism due to the individual components in this system [ll], and the Van Vleck term is assumed to be negligible since ~ a has a closed shell struc- ~ + ture. The Pauli term can hence be obtained by using the infinite temperature intercept in a plot of

xSPln

In this paper we report the results of mag- vs. 1/T. The density of states at the Fermi energy netic susceptibility and elastic neutron diffraction is obtained from the Pauli susceptibility by using the measurements for PrlBazCusO7-6 for samples of relation XPauli =

&D

( E ~ ) (assuming no Coulomb re- LalBazCusO7-6 with zero-resistance temperatures of pulsion). These magnetic measurements together with 44 K (6 = 0.6), 55 K (S = 0.4), and 72 K (6 = 0.25) some of our earlier work [14] establish that as the dis- (see Fig. 1). The LalBa2Cu307-s sample with Tc be- order in the La/Ba case decreases, T, increases and low 50 K was found to be tetragonal (within exper- the degree of localization decreases.

*AT & T Bell Labs, Division 5216, 565 Union Blvd., Allentown, PA 18103, U.S.A.

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C8

-

2142 JOURNAL DE PHYSIQUE

The susceptibility measurements on the Pr1Ba2Cu307-6 sampks were carried out a t a field of 10.54 kG. When

xSP'"

is fit t o an expression of the from XsPin = X0

+

C /

(T

-

0)

,

we obtain axo = 2.19 x

emu/mol, C = 1.37, and a0 = -5 K [12]. This rather large value of X0 is due t o the Van Vleck contri-

bution arising from strong crystal field splittings [12] and can be contrasted with the much smaller Pauli-like susceptibility reported for Y1Ba~CusO7-6 [13].

The elastic neutron diffraction experiments were performed on the triple axis spectrometer at the H4 Satellite beam line a t the High Flux Beam Reac- tor a t the Brookhaven National Labs (HFBR). The LalBazCu307-s system did not show any 3-D magnetic ordering for the superconducting samples, but it is not possible to unambiguously rule out the presence of all 3-D magnetic ordering in the-tegragonal

T, = 44 K sample due to the presence of impurity peaks (nuclear ) of BaCuOz which contaminate our data. In PrlBazCu307-6, the S = 0 case which had an orthorhombic a

-

6 splitting of 0.02 did not show any magnetic ordering even a t temperatures as low as 10 K. The absence of magnetic ordering in this system may arise due t o the changes in the electronic structure caused by Pr which result in destroying the superconductivity. This system did not reveal the presence of either the (1/2, 1/2, 1) or (1/2, 1/2, 1/2) type ordering which occurs in the corresponding oxygen deficient Y ~ B ~ ~ C U ~ O . I - ~ system [6,7]. The samples which were characterized in this study had a large fraction of the non magnetic impurity Ba-Pr-0, whose nuclear peak contaminates the (1/2, 112, 2) peak, but even with that, it is hard t o fully understand the origins of the absence of magnetism in the Cu-0 planes in this compound; though the overlap of the Cu 3d and P r 4f orbitals might be responsible for the absence of superconductivity in this system.

In summary, we have studied the magnetic prop- erties of the LalBa2Cu307-s system, and the Pr1Ba2Cu307-6 system. The susceptibility measurements show that as disorder for the LalBazCu3O.i.-s system decreases, the localization decreases and the Pauli susceptibility changes slightly. No evidence for 3-D magnetic ordering in the Cu-0 planes has been found for the orthorhombic LalBa2Cu307-6 samples. The absence of magnetic ordering in the Cu-0 planes for the oxygen enriched PrlBazCu307-6 samples shows that though the Cu valence can be similar t o that of Y ~ B ~ ~ C U ~ O - / - ~ the presence of the rare earth ion superconductivity is suppressed.

Acknowledgements

This work was supported in part by the Department of Energy Division of Materials Science Grant No. DE- FG02-86ER45271. A000.

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[13] Barbara, B., Rhodes, A., Couack, M., Calemcznt, R. and Bonjour, F., Phys. Lett. 127 (1988) 366; Furneth, W., McLean, R. S., Zuo, F. and Epstein, A. J., submitted.