MAGNETIC SUSCEPTIBILITY OF (La1-xCax)2 CuO4-y (0 ≤ x ≤ 0.05)

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MAGNETIC SUSCEPTIBILITY OF (La1-xCax)2

CuO4-y (0

≤ x ≤ 0.05)

K. Kojima, K. Ohbayashi, M. Udagawa, T. Hihara

To cite this version:

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JOURNAL DE PHYSIQUE

Colloque C8, Suppl6ment au no 12, Tome 49, dkcembre 1988

MAGNETIC SUSCEPTIBILITY OF (Lal-xCaz)2 C U O ~ - ~ (0 5 x 5 0.05)

K. Kojima, K. Ohbayashi, M. Udagawa and T . Hihara

Faculty of Integrated Arts and Sciences, Hiroshima University, Hiroshima 730, Japan

Abstract. - Magnetic susceptibilities ~ f ( L a ~ - , C a , ) ~ Cu04-, with X

<

0.05 X were measured as a function of temperature. The oxides are antiferromagnetic for a:

<

0.01 and superconductive for X

2

0.035. For 0.01

5

X

5

0.025 X is decomposed of a Curie-Weiss and a linear temperature dependent components. The latter is of the same nature as in the normal state of superconductive oxides.

The mechanism of the magnetic properties in the high temperature superconductors containing Cu ion is considered to be closely related t o that of the su- perconductivity. In (Lal-,Bax)2 CUO~-, for example, the sample of X = 0 is an antiferromagnet with the NBel temperature of T ~ = 2 2 0 K [l]. With increasing

X, TN decreases rapidly, and for X

2

0.05 this system becomes superconductive [2]. For 0.008

<

X

5

0.025

a glass-like magnetic state was suggested by the 1 3 ' ~ a NQR measurement [3].

In this work the magnetic susceptibilities of (Lal-,Ca,), CuOl-, with 0

<

X

5

0.05. were mea-

sured in order to investigate the X dependence of TN

and magnetic properties of the normal state of superconductive samples and the glass-like magnetic state at lower X values. The procedure of the sample prepara-

tion was described elsewhere [4]. The magnetic susceptibility measurements were made from 4.7 K t o room temperature by using a Faraday balance.

The temperature dependences of the susceptibility X (T) are shown in figure 1. -The behaviours of X (T) are classified into three concentration ranges: (a) 0

<

X

5

0.009, (b) 0.01

<

X 5 0.025 and (c) 0.035

5

X

5

0.05.

In the range (a) the X (T) curves for X = 0 and 0.009 show a broad peak at 268 and 8 K, respectively, which is attributed to the antiferromagnetic(AF) transition. The X (T) curves for X = 0.007 and 0.008 show no

clear peak, but an inflection (indicated by the arrows in figure la) a t about 150 K, which probably corresponds to TN. TN decreases rapidly from about 270 K for X = 0

to 8 K for 0.009 with increasing X, and it was reported that TN is below 5 K for X = 0.01 [2]. Below about

40 K X (T) for X = 0, 0.007 and 0.008 show a small

decrease, which is attributed to the superconducting transition as in pure LazCuO4 [5].

In the range (b) (Fig. lb) the susceptibilities increase monotonically with lowering the temperature, showing no A F and superconducting transition.

In the range (c) (Fig. lc) the samples are superconductive below about 30 K. The susceptibilities a t a low field of 120 Oe, which are shown in the insert of figure lc, suggest that the samples are bulk supercon-

Fig. 1.

-

Temperature dependence of magnetic susceptibility of (Lal-,Ca,)2 CuOr-, with 0

5

X

5

0.05 at 4.7 kOe. The arrows indicates the antiferromagnetic transition temperature. In the insert the susceptibilities at 120 Oe are shown, and the arrows indicate the superconducting transition temperatures.

ductors. The transition temperatures are 19 and 21 K for z = 0.035 and 0.05, respectively. In the normal state above about 30 K, the X (T) curves show almost linear increases with increasing the temperature.

The rapid increase of X (T) at low temperatures in the range (b) suggests a Curie-Weiss contribution of C/ ( T

-

B), where C is the Curie constant and 0 the

paramagnetic Curie temperature. The Curie-Weiss fitting to the experimental data on X (T) , however, is un- successful. In the analysis of X (T) we assume a form of X = C / (T

-

B)

+

X O

+

AT, where C, 0, X0 and A

are the fitting parameters. The experimental results of X (T) for X = 0.015 and 0.025 are well described by

this equation, although the fitting to the experimental data for X = 0.01 is U ~ S U C C ~ S S ~ U ~ . The fitted curves are

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C8

-

2200 JOURNAL DE PHYSIQUE

compared with the measured values in figure 2, where the susceptibility values after substracting the Curie- Weiss components are also plotted. The obtained parameters are listed in table I, where the effective Cu moments pee, in stead of C, are given. The value of

pee for X = 0.015 is larger than that for X = 0.025. This is consistent with the NQR result that the inter- nal magnetic field at 13'~a decreases with increasing

X for 0.008

5

X

5

0.025 [3]. It is to be noted that both the calculated curves for X = 0.015 and 0.025 exhibit systematic upward-deviations from the experimental data below about 10 and 7 K, respectively. This seems to suggest some kind of ordering below these temperatures, and we suppose that the deviations are associated with a glass-like magnetic state previously referred [3, 61, although the temperature range of measurements is limited to establish the def- inite conclusion:

Fig. 2. - Temperature dependence of magnetic susceptibility of (Lal-,Ca,)2 Cu04-, with X = 0.015 and 0.025. The open circles indicate the measured values, and the curves represent the fitting ones of X = C/ (T

-

8 ) + X 0 + A T with the parameters listed in table I. The closed circles indicate the components of susceptibility after subtracting the Curie-Weiss components.

Table I.

-

Magnetic susceptibility data for

(Lal-,C&), C U O ~ - ~

The susceptibilities in the range (b) exhibit a linear temperature dependent contribution, which probably come from the same origin as those of X (T) in the normal state of the superconducting samples of the range (c). The linear temperature dependence of X

(Tj

was observed in (Lal-,Sr,), CUO~-, and is attributed to delocalized electron contributions [7]. This suggests the presence of delocalized electrons in the samples of the range (b), which are semiconductive at low temperatures [4]. It is supposed that the delocalized electrons in the range (b) have a rather low mobility, and, with increasing X, the delocalized electron states over- lap with each other, resulting in the superconducting state in the range (c).

In conclusion, (Lal-,Ca,), CuO4-, are antiferromagnetic for X

<

0.01 and superconductive for X

1

0.035. In the intermediate range of X the susceptibility can be decomposed of a Curie-Weiss component and a linear temperature dependent one (including a constant). The latter is of the same nature as the susceptibility in the normal state of superconductive oxides. The magnetic property of this system varies continuously with increasing X.

[l] Vaknin, D., Shinha, S. K., Moncton, D. E., John- ston, D. C., Newsam, J. M., Safinya, C. R. and King, H. E., Jr., Phys. Rev. Lett. 58 (1987) 2802.

[2] Fujita, T., Aoki, Y., Maeno, Y., Sakurai, J., Fukuba, H. and Fujii, H., Jpn J. Appl. Phys. 26 (1987) L368.

[3] Kitaoka, Y., Ishida, K., Hiramatsu, S. and Asayarna, K., J. Phys. Soc. Jpn 57 (1988) 734.

[4] Kojima, K., Ohbayashi, K., Udagawa, M. and Hi- hara, T., Jpn J. Appl. Phys. 27 (1988) L852. [5] Grant, P. M., Parkin, S. S. P., Lee, V. Y., Engler,

E. M., Ramirez, M. L., Vazquez, J. E., Lim, G., Jacowitz, R. D. and Greene, R. L., Phys.

Rev.

Lett. 58 (1987) 2482.

[6] Budnick, J. I., Chamberland, B., Yang, D. P., Nie- dermayer, Ch., Golnik, A., Recknagel, E., Ross- rnanith, M. and Weidinger, A., Ewophys. Lett. 5

(1988) 651.