P h y s i c a C 2 3 5 - 2 4 0 ( 1 9 9 4 ) 3 1 1 9 - 3 1 2 0 P H Y S I C A (~ N o r t h - H o l l a n d

Hall effect s tudies of the mixed and normal states of Y l -xPrxBa2Cu307-8 (0 ___ x _< 1 ) and YBa2Cu3Oy (6.35 < y _ 7) single crystals

C. C. Almasan a, S. H. Han a, K. Yoshiara a,1 , M. Buchgeister a, D. A. Gajewski a, J. Herrmann a, A. P. Paulikas b, Chun Gu b, B. W. Veal b, and M. B. Maple a

aDepartment of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA 92093, USA

bArgonne National Laboratory, Argonne, IL 60439, USA

Hall effect measurements on single crystal specimens of Yl-xPrxBa2Cu307-8 (0 _< x <_ 1) and YBa2Cu3Oy (6.35 <_ y_< 7) revealed a "negative Hall anomaly" below Tc, in the mixed state. For both systems, the depth A of the negative Hall signal scales with T/T c, while the maximum value of A decreases monotonically with decreasing Tc and vanishes at Tc = 68 K. These results show that the sign anomaly is not consistent with models that invoke pinning to explain this effect, and suggest that the negative anomaly could have an intrinsic origin. Hall effect measurements in the normal state of both systems show that the cotangent of the Hall angle can be described by cotOH = AT 2 + B, where A increases linearly with decreasing Tc for both systems, while B increases linearly with decreasing Tc for Y1 -xPrxBa2Cu307-5 and is constant within experimental error for YBa2Cu3Oy.

Measurements of the longitudinal resistivity Pxx and Hall resistivity Pxy as a function of temperature T (10 K _< T _< 270 K) and magnetic field H up to 8 T were carried out on eight Yl-xPrxBa2Cu307-5 (0 <_ x < 1) and four YBa2Cu3Oy (6.35 <_ y_< 7) single crystals. A five-probe contact arrangement was used. The Hall voltage Vxy was obtained from the antisymmetric part of the transverse voltage (measured while sweeping the magnetic field at constant temperature) under magnetic field H reversal. In our measurements, HIIc and the same critical current density J of 100 Ncm 2 was applied to all the samples, with H_LJ [1,2].

For the crystals with x <0.15 ory >6.73, Vxy is positive for T > Tc and displays a "negative Hall anomaly" a few degrees below Tc which shifts to higher fields at lower temperatures. A similar behavior was reported by Jia et al. [3] and Xiong and Xiao [4]. The negative Hall region occurs where Vxx increases rapidly with increasing field [1,2]. For x > 0.24 or y < 6.73, only a positive Hall signal is observed.

Figure 1 contains a plot of the magnitude of the minimum Hall signal A, obtained from

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3 i i 2[ / . . ~ • x=o.13 I < , 7 .- . • y=8.,s l / ~ ,, ,,~ . y=s.73

>~2 r o , . . . . -/- . • ox.o .x 50 60 70 80 90 10C == °

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1 Y1 .xPrxB a2 C U 307-6 We • a, •

0 o , , , , - , , - - ~ " - - - - - •

. . . . • . . . . • . . . . • - - - i

0.7 0.8 0.9 1 1.1 T/T

c

Fig. 1. Magnitude of the minimum value t~ of Vxy(H) for single crystals of YBa2Cu3Oy and Yl-xPrxBa2Cu307-5 taken at different temper- atures vs reduced temperature T/T c. The data exhibit a maximum Area x which is plotted in the inset vs Tc.

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SSDI 0 9 2 1 - 4 5 3 4 ( 9 4 ) 0 2 1 2 5 - 2

3120 C.C. Almasan et al./Plo,sica C 235 240 (1994) 3119 3120

Vxy vs H curves, vs the reduced temperature T/T c, for both systems. The result for x = 0 is similar to the one reported by Luo et al. for epitaxial YBa2Cu307 films [5]. The interesting features of all these curves is that, for both systems, A is nonzero over the same reduced temperature range (0.88 <T/Tc -< 1) and, Amax scales and decreases monotonically with Tc, as shown in the inset. The close similarity of the profiles and the monotonic evolution of Arnax with Tc for both systems suggest that the negative anomaly has an intrinsic origin and is not determined by extrinsic factors. Moreover, the suppression of Amax with decreasing Tc suggests that the negative Hall anomaly is not due to flux pinning since flux pinning increases with increasing x, for low x values. This result is in agreement with the recent findings by Budhani et al. [6], who reported a decrease in the magnitude of the sign anomaly of TI2Ba2Ca2Cu3Olo thin films with increasing defect concentration through heavy-ion-irradiation.

With regard to the normal state behavior of the Hall voltage, Anderson recently proposed [7] for the cotangent of the Hall angle co teH -= Pxx/RHH the following temperature dependence: coteH = AT 2 + B, where A is related to the bandwidth of the carriers and B is due to magnetic impurity scattering. The simultaneous measurements of Pxx and 1/RH enabled us to calculate coteH(T) for different x and y values. For both systems, we fitted the coteH vs T 2 data taken in a field of 6 T with the above equation. Figure 2 contains a plot of the values obtained from these fits for the slope A and the intercept B vs Tc for different x and y values. The slope A increases linearly with decreasing Tc for both systems, while B increases linearly with decreasing Tc for Yl-xPrxBa2Cu307-5 and is constant within the experimental error for YBa2Cu3Oy. These results agree with a previous report for epitaxial films by Xiong et al. [4] and disagree with measurements by Jiang et al. [8] on Yl-xPrxBa2Cu307-a single crystals in which B was found to increase while A was constant within their experimental resolution.

120 (33

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80

~-~ 60

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-20

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B for YBa2C U3Oy [] [D []

--E- - A for YBa2Cu3Oy 113 []

I - , , , . , . , $ i i i

0 2o 40 6o 80 To(K)

oo

Fig. 2. Slope A and intercept B vs T c for Yl-xPrxBa2Cu307-a and YBa2Cu3Oy single crystals. The value of H was 6T.

This research was supported by the U. S. Department of Energy under Grant No. DE- FG03-86ER-45230. MB acknowledges partial support from the Alexander-von Humboldt Foundation; JH acknowledges support from the German Academic Exchange Service.

1permanent address: Material and Electronic Devices Laboratory, Mitsubishi Electric Corp., Sagamihara, Kanagawa, Japan

R E F E R E N C E S

[1] M. B. Maple et al., Journal of Superconductivity 7, 97 (1994).

[2] C.C. Almasan et al., Physica B (in press). [3] Y.X. Jia, J. Z. Liu, M. D. Lan, and R. N.

Shelton, Phys. Rev. B 47, 6043 (1993). [4] P. Xiong, G. Xiao, and X. D. Wu, Phys.

Rev. B 47, 5516 (1993). [5] J. Luo et al., Phys. Rev. Lett. 68, 690

(1992). [6] R.C. Budhani, S. H. Liou, and Z. X. Cai,

Phys. Rev. Lett. 71, 621 (1993). [7] P. W. Anderson, Phys. Rev. Lett. 67,

2992 (1991). [8] W. Jiang, J. L. Peng, S. J. Hagen, and R.

L. Greene, Phys. Rev. B 46, 8694 (1992).