Easily Activated Flux Creep and Anisotropic Fluctuation in Ndcecuo Thin Films
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EASILY ACTIVATED FLUX CREEP AND ANISOTROPIC FLUCTUATION IN NdCeCuO THIN FILMS S. Hatta, S. Hayashi, H. Adachi and K. Wasa Central Research Laboratories of Matsushita Electric Industrial Co., Ltd., Moriguchi, Osaka 570, Japan ABSTRACT The diamagnetic properties of NdCeCuO films with electron The 6 critiqal current density ( Jc ) was carriers were studied. the calculated to be 0.73 x 10' A/cm'. These films indicated very strong magnetic relaxation with small activation energy, the significant resistive broadening in the critical region and the largely fluctuated diamagnetization. These results suggested the very weak pinning forces to cause the easily activated flux motion in these specimens. INTRODUCTION Since the electron carrier type superconductor, LnCeCuO many (Ln=Nd, Pr, Sm ) was discovered by Tokura et al[l], investigations were carried out. The physical properties of this system were mainly characterized by using bulk specimens such as sintered ceramics and single crystals. However, in order to study the magnetic relaxation or flux pinning, we need more homogeneous specimens with higher supercurrent density ( Jc ). For the purpose of our investigation, NdCeCuO thin film was initially prepared by Hayashi et al[2J . This film was recognized to have excellent properties such as much lower resistivity in the normal state and higher Jc than those of the previously reported bulk specimens. Therefore, it is beneficial to measure the physical properties, using this film. In this paper, we report the magnetic properties of this film, particularly, with respect to the motion and pinning of fluxoids. EXPERIMENTAL NdCeCuO thin films were prepared by an rf magnetron sputtering under the similar conditions as noted in the previous work [2. The chemical composition of the film was about Nd(1.85)Ce(0.15)Cu(1)O(x). The film thickness was approximately 8000 A. The crystalline structure was highly oriented with c axis perpendicular to the film plane. The resistivity in the normal state at room tempe~ature 2 was about 1.2 x 10- 02 cm, and Jc at 4.2 K was 0.73 x 10 A/cm . The onset temperature was about 24 K and the zero resistance temperature was 22 K. The magnetization was measured by an rf SQUID susceptometer in the temperature range up to 30 K. The external field ( Hex ) was applied with a definite angle ( ) between the field direction and the film plane. The magnetic relaxation was measured at constant temperature, as soon as Hex was applied. Its demagnetization was carried out by zero field cooling from room temperature. The resistivity of the film was measured by a standard four probe method under DC magnetic field up to 1 T.
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Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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RESULTS AND DISCUSSION is By an x ray diffraction pattern, the c axis length determinel to 3 be 12.06 A. Hall coeffiiients are obtained to be These cm /C at 77 K. cm /C at 290 K and -6 x 10-3 x 10 values are very small, compared with the reported values This means that t determined by using single crystals[3]. elestron ca
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