Magnetic hysteresis loops and fast relaxation of vortex lattice in YBaCuO single crystal

The magnetic moment values M at conventional magnetic moment relaxation at constant magnetic field and in magnetic hysteresis loop experiment are directly related and are the same if μ0(dM/dt)CR = χ0/(dBe/dt)MHL. Dependencies of M(dBe/dt) measured by vibrating sample magnetometer on YBa2Cu3O7-δ single crystals at temperatures ranging from 2.5K to 54K are analyzed. Activation energy Ue = -kT[ln(dBe/dt)-C] vs. M is plotted with parameter C being adjusted to form a smooth curve. In this way the critical sweep rate (dBe/dt)c = exp(C) corresponding to the critical state Ue(Mc) = 0 is determined. A detailed analysis shows that ln(dBe/dt)c is determined. A detailed analysis shows that ln(dBe/dt)c increases approximately linearly with temperature. This dependence can be removed by scaling the activation energy by a temperature dependent factor. At temperatures below 5K departure from the thermally activated relaxation occurs, the origin of which can be the quantum tunneling effect