A review of the superconducting magnetic properties of doped fullerenes is presented. Experimental results on the main superconducting properties, such as the critical fields and the characteristic lengths, are critically discussed. Different methods to evaluate the lower critical field are discussed. Finally, experimental data on properties connected to flux pinning, such as the critical current density, the irreversibility line and the pinning force, are summarized and discussed.
Magnetic susceptibility, magnetization curves and flux creep of superconducting Rb3C60 with Tc = 27.5 K have been studied. The critical current for Rb3C60 was evaluated to be 4 · 106 A/cm2 at 7 K and 10 kOe, which is considerably higher than for K3C60. The flux creep measurements give the activation energy of U(7 K) ≈ 3.3 · 10-2 eV.
The lower critical magnetic field Hc1 of superconducting Rb 3 C 60 (Tc=28.5 K ) is estimated by different methods. The zero temperature value is found to be given by Hc1=16.2±1.0 mT, and the penetration depth is λL=215±10 nm . The Bean model analysis leads to threshold fields of 5.3 mT for T=5 K , and 4.0 mT for T=17 K . The big influence of intergranular connections on Hc1 is demonstrated. Good agreement between the low- and the high-field analysis is found.
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