Inducing the paramagnetic Meissner effect in Nb disks by surface ion implantation.

Abstract

After implanting Kr ions to a depth of 120 nm below both surfaces of disk-shaped Nb samples, the magnetization in a field-cooling measurement becomes positive at temperatures slightly below the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}9.2 K. In contrast, the field-cooled magnetization on similar disks prior to the ion implanting was diamagnetic. This behavior confirms earlier evidence that the paramagnetic Meissner effect (PME) is extremely sensitive to the surface microstructure. Furthermore the occurrence of the PME in these ion-implanted Nb disks results from the existence of lower ${\mathit{T}}_{\mathit{c}}$ surface defects having a sufficient depth relative to the disk thickness such that the resulting strong flux pinning from these defects gives rise to an inhomogeneous local field distribution. \textcopyright{} 1996 The American Physical Society.