Magnetic-field dependence of the ac susceptibility in granular ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$: Data and models

For a sintered rod of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ at 78.3 K, detailed data are reported for the complicated dependence of the ac susceptibility χ̃=χ’-iχ’ ’ on applied ac and dc fields, ascribed to the inter- and intragranular components of the material. The intergranular data are understood in detail by a modified critical-state model, assuming a critical current density ${\mathit{J}}_{\mathit{c}}$(H)∼${\mathit{H}}^{\mathrm{-}2}$. $chi tilde (H sub roman dc )— also displays hysteresis which is not readily explicable by this model.