Magnetic measurements on coevaporated YBa2Cu3O7 thin films

Physica C 162-164 ( 1989 ) 107-108 North-Holland

MAGNETIC MEASUREMENTSON COEVAPORATED YBa2Cu307 THIN FILMS

P.Norling, K.Niskanen, P.Svedlindh, P.Nordblad, L.Lundgren, J.Hudner*, H.Ohls(}n+ and L.Stolt+ Uppsala University, Institute of Technology, Box 534, S-751 21 Uppsala, Sweden *Dept. of Solid State Electronics, Royal Institute of Technology, Box 1298, S-164 28 Kista, Sweden +Swedish Institute of Microelectronics, Box 1084, S-164 28 Kista, Sweden

The field an time dependence of the magnetic susceptibility of coevaporated YBa2Cu307 thin films on SrTiO 3 and sapphire substrates have been investigated. Different relaxation and field dependent behaviour for the two films is reported. .

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The field and time dependence of the magnetic susceptibility of coevaporated YBa2Cu30 7 (YBCO) thin films on SrTiO 3 and sapphire substrates have been investigated in a SQUID-magnetometer in the field range 0.1-100 G and temperature range 30-110K. The films were cut into pieces of size 2 x 2 x 1 0 - 3 mm3 and they were oriented perpendicular to the applied field. The films were fabricated in a mass-spectrometer controlled process described elsewhere 1. Both films were polycrystalline. The film on SrTiO 3 consisted of single crystalline YBCO bars forming rectangular patterns. A similar structure is described by Wang et al. 2 The film on sapphire had a less regular structure. The zero resistance temperature was 91K for the film on SrTiO 3 and 73K for the film on sapphire. In figure la and lb the ZFC, FC (Meissner) and TRM susceptibilities of the two films are plotted. The curves are taken at a heating (ZFC,TRM) or cooling (FC) rate of about 1K/min. The measured low temperature Meissner fraction of only about 1% at an applied field of 1G is a result of a low 0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)

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FIGURE 1 Susceptibility in a field of 1G for the film on a) SrTiO 3 b) sapphire

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P. Norling et aL / Coevaporated YBaeCu307thin films

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FIGURE 2 Relaxation of the ZFC magnetization in a field of 1G for the film on SrTiO3 of the rate is pushed towards lower temperatures. The relaxation of the remanent magnetization shows a similar behaviour. The film on sapphire shows two different magnetization regimes, as described above. The relaxation of the magnetization within the two regimes displays distinctly different behaviours. At temperatures below Tc R=°, the relaxation is similar to that of the film on SrTiO 3, but in the regime between T c R = ° and T c ° n s e t , where the ZFC magnetization is reversible, the relaxation is unmeasurably small. In conclusion the magnetization of the two rims on SrTiO 3 and sapphire displays remarkably different behaviours due to the difference in film structure. REFERENCES 1. H. Ohls6n et al.,this conference 2. Wang et al., Appl.Phys.Lett., 54 (1989) 1573 3. K. Niskanen et al, this conference