The peak effect in single-phase B1 MoCy encapsulated in multiwall carbon nanocages

Isothermal magnetization hysteretic loops in nanocrystalline single-phase B1 MoCy encapsulated in multiwall carbon nanocages are studied. The initial magnetization curves show the sharp peak near zero field Hpen and the broad peak at Hp (>Hpen). The peak field Hpen increases exponentially with temperature T; Hpen(T/Tc) = Hpen(0)exp[−T/To] with values of Hpen(0) = 20 kOe and T0 = 1.4 K. On the other hand, the peak field Hp shifts linearly with decreasing T. At low temperatures, the sharp peak and the broad peak merge into a single peak. All of the features of the hysteretic loops have been found in a less anisotropic high-Tc compound of Nd1.85Ce0.15Cu2O8+δ. The value of To is consistent with the model that two-dimensional point vortices are thermally activated near the lateral surface of a layered superconductor.