Torque measurements on methylene blue intercalation compounds of 2H-TaS2

The superconducting properties in high magnetic fields of three different methylene blue intercalation compounds of 2H-TaS2 (compounds with 9ه, 12ه and 17ه layer separation) are measured with a torquemeter. The superconducting magnetisation curves can be separated in two parts, a reversible part at high fields and an irreversible part at low fields, defining an irreversibility line as in the organic or high-Tc superconductors. The angular dependence of Hc2 of the 9ه compound can be fitted by the anisotropic Ginzburg-Landau theory giving an anisotropy factor of about 60. The Tc values of these compounds are 3.8 K for the 17ه, 5. l K for the 12ه and 5. l K or 4.6K (depending on the cooling rate) for the 9ه compound, tested by ac-susceptibility. The estimated critical field of dimensional crossover is out of the measured temperature range and cannot be seen in this work.