A Practical Algorithm for Fitting Magnetic Moment Data for Superconducting Thin Films and Multilayers in Parallel Magnetic Fields*

Superconducting thin films and multilayers in DC magnetic fields applied nearly parallel to the film plane can yield spurious magnetization data dominated by extreme shape anisotropy and strong diamagnetism of a confined supercurrent. This situation may lead to highly reproducible discontinuities or apparently random ``instabilities'' when measured with SQUID magnetometers such as the ubiquitous Quantum Design MPMS, which requires samples to behave as an ideal point-dipole. We have devised an accurate multipole fitting routine for the raw SQUID voltmeter output that eliminates spurious contributions to the axial dipole moment from transverse (off-axis dipole) or non-point-dipole axial magnetizations. We demonstrate this method as applied to Nb/Ni multilayers and Nb thin films and foils of various thicknesses that probe the influence of supercurrent confinement on the non-dipole response.