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arXiv · 2212.01137

Depth-resolved measurement of the Meissner screening profile in a niobium thin film from spin-lattice relaxation of the implanted $\beta$-emitter $^{8}$Li

Ryan M. L. McFadden·Md Asaduzzaman·Terry J. Buck·David L. Cortie·Martin H. Dehn·Sarah R. Dunsiger·Robert F. Kiefl·Robert E. Laxdal·C. D. Philip Levy·W. Andrew MacFarlane·Gerald D. Morris·Matthew R. Pearson·Edward Thoeng·Tobias Junginger
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Abstract

We report measurements of the Meissner screening profile in a Nb(300 nm)/Al$_{2}$O$_{3}$ thin film using $^{8}$Li $\beta$-detected nuclear magnetic resonance ($\beta$-NMR). The NMR probe $^{8}$Li was ion-implanted into the Nb film at energies $\leq$ 20 keV, corresponding to mean stopping depths comparable to Nb's magnetic penetration depth $\lambda$. $^{8}$Li's strong dipole-dipole coupling with the host $^{93}$Nb nuclei provided a "cross-relaxation" channel that dominated in low magnetic fields, which conferred indirect sensitivity to the local magnetic field via the spin-lattice relaxation (SLR) rate $1/T_{1}$. From a fit of the $1/T_{1}$ data to a model accounting for its dependence on temperature, magnetic field, and $^{8}$Li$^{+}$ implantation energy, we obtained a magnetic penetration depth $\lambda_{0}$ = 51.5(22) nm, consistent with a relatively short carrier mean-free-path $\ell$ = 18.7(29) nm typical of similarly prepared Nb films. The results presented here constitute an important step towards using $^{8}$Li $\beta$-NMR to characterize bulk Nb samples with engineered surfaces, which are often used in the fabrication of particle accelerators.

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Ryan M. L. McFadden, Md Asaduzzaman, Terry J. Buck, David L. Cortie, Martin H. Dehn, Sarah R. Dunsiger, Robert F. Kiefl, Robert E. Laxdal, C. D. Philip Levy, W. Andrew MacFarlane, Gerald D. Morris, Matthew R. Pearson, Edward Thoeng, Tobias Junginger. 2022-12-02. Depth-resolved measurement of the Meissner screening profile in a niobium thin film from spin-lattice relaxation of the implanted $\beta$-emitter $^{8}$Li. https://doi.org/10.1063/5.0175532

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