Electron-spin-resonance determination of the internal field within the superconductorYBa2Cu3O7

An electron-spin-resonance method was developed for measuring the strength of the magnetic field at the surface of a superconductor located in an external magnetic field. This method was used to determine the temperature dependence of the susceptibility of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ in a 0.3-T magnetic field.