Multi-Critical Behavior of Irreversibility Lines for Rb3C60 Fullerenes

Ming-Fong Tai；Chien-Min Sung

Chinese Journal of Physics

36卷2S期（1998 / 04 / 01）

457 - 462

英文

The irreversibility lines of polycrystalline and single-crystal Rb3C60 fullerenes determined by M(T) curves and M(H) l oops are well characterized by a simple 3- dimensional power law function : Hirr(T) = H0( 1 - T/T,)”, with various n values obtained in different field regions and for different specimens. For polycrystalline Rb3C60 powders, the irreversibility field in the low field region (Hirr ＜ 1 T) obeys the power function with R = 2, which suggests that a vortex-lattice melting transition may have occurred. However, in the high field region (Hirr ＞ 1 T), n = 3/2. This reduced exponent may be explained by the model of thermally activated vortex motion with collective pinning. For Rb3C60 crystals, the irreversibility line can be perfectly fitted to a linear relation, i.e., n = 1 : Hirr(T) = a(1 - T/T,), where a = 4.8 T and T0 = 60.0 K for H ＜ 3.2 T; and a = 7.92 T and T0 = 30.3 K for H ＞ 3.2 T. This is the first reported linear temperature-dependence of the irreversibility field.