Angular-dependent torque magnetometry on single-crystal HgBa₂CuO_4+y near the critical temperature

Angular-dependent torque magnetization measurements on a HgBa2CuO4+y microcrystal performed close to the critical temperature Tc are analyzed within the framework of three-dimensional (3D) XY critical behavior. In a finite magnetic field the magnetic torque is given by the derivative of a universal scaling function dG(z)/dz, where the scaling argument z depends on temperature, field, and the angle between the field and the c axis of the sample. We are able to determine dG/dz quantitatively by scaling the angular-dependent torque data. Universal constants and critical amplitudes for HgBa2CuO4+y are calculated. © 1999 American Physical Society.