Magnetic hysteresis of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ single crystals in very high magnetic fields above 100 T

Magnetic hysteresis of single crystals of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ was measured in pulsed high magnetic fields above 100 T. The data were analyzed taking into account the temperature increase due to the application of pulsed fields. It is argued that values of magnetic fields at which the magnetic hysteresis disappears can be reasonably interpreted as ${\mathrm{B}}_{\mathrm{c}2}$ at low temperatures. The estimated upper critical fields at absolute zero were ${\mathit{B}}_{\mathit{c}}$ $2^{\mathrm{\parallel }}$(0)=40±5 T and ${\mathrm{B}}_{\mathrm{c}2}^{\mathrm{\perp }}$(0)=110±10 T, which leads to the anisotropy ratio of about 3.