Nanoparticles of NbC produced by laser ablation in liquid: a study of structural, magnetic and superconductivity properties

TL;DR

This study synthesizes NbC nanoparticles via laser ablation, revealing their structural, magnetic, and superconducting properties, and highlights the coexistence of superconductivity and magnetism at the nanoscale.

Contribution

It demonstrates a controlled synthesis method for NbC nanoparticles and provides detailed analysis of their magnetic and superconducting behaviors.

Findings

NbC nanoparticles have an $T_C$ of approximately 10 K.

Magnetic loops indicate coexistence of superconductivity and magnetism.

Surface defects likely contribute to ESR signals.

Abstract

Niobium carbide (NbC) is a high-field Type II superconductor with a critical temperature ($T_C$) of 11.1 K, just above that of pure Nb ($T_C = 9$ K). Downsizing NbC to the nanoparticle scale introduces significant alterations in its critical field and/or the superconducting temperature. Here we report on superconducting NbC nanoparticles with $T_C \approx$ 10 K synthesized by laser ablation in acetone, using the lens-target distance (laser fluence) and centrifugation as control parameters of the particle size. X-ray diffraction analyses certified the cubic NbC phase and electron microscopy images revealed spherical particles with average size near 8 nm, with no apparent size dependence on fluence. Besides, magnetization curves exhibited magnetic loops featuring a saturation magnetization around $10^{-3} \mu_B$/molecule along with a small and typical superconducting loop for all investigated samples. We also observed a suppression of the diamagnetic behavior below $T_C$ upon decreasing laser fluence. Moreover, all samples exhibited a weak electron spin resonance (ESR) Curie-like signal at $g\approx2.0$ probably associated with localized defects in the particle's surface. The intriguing coexistence of superconductivity and magnetism in nanoparticles has recently garnered significant research attention. This complex scenario and unique properties are due to the substantial increase of surface-to-volume ratio in these superconducting NbC nanoparticles and further investigation would be crucial to unveil novel material properties and shed new light on our understanding of the superconducting phenomenon in this new morphology.