Finite-size effects in the nuclear magnetic resonance of epitaxial palladium thin films

Abstract

We have measured the NMR of 8 Li + implanted in a set of thin epitaxial films of Pd. We find a large, negative, strongly temperature-dependent Knight shift K consistent with previous measurements on polycrystalline films. The temperature dependence of the shift exhibits a characteristic deviation from the susceptibility χ (T). In particular, at low temperature, K(T) continues to follow a simple Curie-Weiss dependence. This result provides important insight into the origin of the low-temperature behavior of χ (T) in strongly paramagnetic metals. In addition, we find the room temperature shift depends on film thickness, with changes on the order of 20% between films 100 nm and 30 nm thick. We also observe a surface-related resonance in both Au-capped and uncapped films with a small positive shift. These features bear a striking similarity to the Pt NMR line shapes in much smaller Pt particles. However, they seem to originate, not from adsorbed species, but rather in confinement effects on the highly exhange-enhanced Pd d band.

Investigation of ionic and anomalous magnetic behavior in CrSe2 using 8Li β-NMR

“…The coincidence of a site change with the structural transitions also seems fortuitous. Rather, we speculate that the unshifted line may correspond to 8 Li stopping in a magnetically distinct near-surface layer, an effect that has also been previously observed in metallic palladium [39]. However, it remains to be understood how 8 Li in such a layer would be proximally sensitive only to the lower transition.…”

Scanning gradiometry with a single spin quantum magnetometer

“…This is slightly smaller than the value of pure Pd (χ Pd = 7.66•10 −4 [59]). The decreased susceptibility may be attributed to either a finitesize effect [60] or hydrogen adsorption [61]. Repeating the same experiment with Bi, a diamagnetic sample, produces an experimental value of χ Bi = −(1.7 ± 0.1) • 10 −4 , which matches the accepted room temperature value of χ Bi = −1.67 • 10 −4 [59].…”

Impact of opal nanoconfinement on electronic properties of sodium particles: NMR studies

“…The results at room temperature obtained mostly for clusters of platinum, silver, copper, and rhodium and for surface of a palladium film showed drastically broadened lines ( [6,7,20] and references therein). The Knight shift dominated by d-like hyperfine fields and the lineshape for Pt-clusters and Pd-surface were treated on the basis of the layer-model deconvolution.…”