Anomalous magnetic properties of multi-walled carbon nanotubes embedded with magnetic nanoparticles: Consistent with ultrahigh temperature superconductivity

TL;DR

This study investigates anomalous magnetic behaviors in multi-walled carbon nanotubes embedded with magnetic nanoparticles, suggesting evidence for ultrahigh temperature superconductivity based on magnetization enhancements and thermal cycle effects.

Contribution

It provides experimental evidence of magnetic enhancement and temperature-dependent effects consistent with ultrahigh temperature superconductivity in carbon nanotube composites.

Findings

Magnetic moments are enhanced by about 3 times for embedded nanoparticles.

Enhanced magnetic moments are lost at 1120 K and recovered through thermal cycling.

Magnetic anomalies suggest paramagnetic Meissner effect indicating ultrahigh temperature superconductivity.

Abstract

We report high-temperature (300-1120 K) magnetization data of Fe and Fe3O4 nanoparticles embedded in multi-walled carbon nanotubes. The magnetic impurity concerntations are precisely determined by both high-energy synchrotron x-ray diffractometer and inductively coupled plasma mass spectrometer. We unambiguously show that the magnetic moments of Fe and Fe3O4 nanoparticles are enhanced by a factor of about 3 compared with what they would be expected to have for free (unembedded) magnetic nanoparticles. The magnetization enhancement factor is nearly independent of the applied magnetic field but depends significantly on the cooling rate. What is more intriguing is that the enhanced moments were completely lost when the sample was heated up to 1120 K and the lost moments at 1120 K were completely recovered through several thermal cycles below 1020 K. Furthermore, there is a rapid increase or decrease in the magnetization below about 60 K. The anomalous magnetic properties cannot be explained by existing physics models except for the paramagnetic Meissner effect due to the existence of ultrahigh temperature superconductivity in the multi-walled carbon nanotubes.