Scanning SQUID Susceptometry of a paramagnetic superconductor

J. R. Kirtley; B. Kalisky; J. A. Bert; C. Bell; Y. Hikita; H. Y. Hwang; J. H. Ngai; Y. Segal; F. J. Walker; C. H. Ahn; K. A. Moler

doi:10.1103/physrevb.85.224518

arXiv · 1204.3355

Scanning SQUID Susceptometry of a paramagnetic superconductor

J. R. Kirtley·B. Kalisky·J. A. Bert·C. Bell·Y. Hikita·H. Y. Hwang·J. H. Ngai·Y. Segal·F. J. Walker·C. H. Ahn·K. A. Moler

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Abstract

Scanning SQUID susceptometry images the local magnetization and susceptibility of a sample. By accurately modeling the SQUID signal we can determine the physical properties such as the penetration depth and permeability of superconducting samples. We calculate the scanning SQUID susceptometry signal for a superconducting slab of arbitrary thickness with isotropic London penetration depth, on a non-superconducting substrate, where both slab and substrate can have a paramagnetic response that is linear in the applied field. We derive analytical approximations to our general expression in a number of limits. Using our results, we fit experimental susceptibility data as a function of the sample-sensor spacing for three samples: 1) delta-doped SrTiO3, which has a predominantly diamagnetic response, 2) a thin film of LaNiO3, which has a predominantly paramagnetic response, and 3) a two-dimensional electron layer (2-DEL) at a SrTiO3/AlAlO3 interface, which exhibits both types of response. These formulas will allow the determination of the concentrations of paramagnetic spins and superconducting carriers from fits to scanning SQUID susceptibility measurements.

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J. R. Kirtley, B. Kalisky, J. A. Bert, C. Bell, Y. Hikita, H. Y. Hwang, J. H. Ngai, Y. Segal, F. J. Walker, C. H. Ahn, K. A. Moler. 2012-04-16. Scanning SQUID Susceptometry of a paramagnetic superconductor. https://doi.org/10.1103/physrevb.85.224518

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