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List of Symbols, Abbreviations, and Acronyms
2- D two-dimensional
3- D three-dimensional
AFM atomic force microscopy
CMR colossal magnetoresistance
CNT carbon nanotube
Co cobalt
CoFe2O4 cobalt ferrite
CVD chemical vapor deposition
EDS energy dispersive spectroscopy
Fe iron
In indium
KrF krypton fluoride
MFM magnetic force microscopy
MW multi-walled
MWCNT multi-wall carbon nanotube
Ni nickel
NiCo nickel cobalt
PLD pulsed laser deposition
Pt platinum
PVD physical vapor deposition
RF radio frequency
SEM scanning electron microscopy
Si silicon
SiO2 silicon dioxide
VSM vibrating sample magnetometer
Abstract
The high demand for nanoelectronics devices, high density magnetic memories, sensors, and energy storage for the future force and warfighters have led us to develop unique methods to fill vertically aligned nanofibers with magnetic nanoparticles such as cobalt ferrite (CoFe2O4), iron (Fe), and nickel cobalt (NiCo). In this work, pulsed laser deposition (PLD) is used to fill CoFe2O4 and DC magnetron sputtering is used to fill Fe and NiCo in carbon nanotubes (CNTs). The filled CNTs are characterized by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), atomic force microscopy (AFM), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM). Magnetization measurements in-plane and out-of-plane with respect to the sample's surface of CNTs filled with CoFe2O4 indicates a reasonable coercivity of 0.4 T. The magnetic anisotropy is, however, found out to be randomly oriented indicating a polycrystalline structure. The unique difference between the in-plane and out-of-plane magnetizations is the sharing produced by the demagnetizing field in the perpendicular direction.
1. Introduction and Background
Since the first comprehensive and detailed characterization of carbon nanotubes (CNTs) by Iijima in 1991 [1], the saga to fill the low-dimensional space inside CNTs with different types of applications-related materials has continued. Pristine CNTs possess incredible mechanical and electrical properties [2, 3] besides the hallowed enclosed volume of space. This low-dimensional space provides an excellent opportunity to enhance the property of CNTs by filling it with applications-related materials [4], A few examples include improved photovoltaic performance demonstrated in platinum (Pt)-filled CNTs [5] and the possibility of lightweight wide-band microwave absorbers using ferromagnetic-filled CNTs [6], CNTs filled with magnetic nanoparticles are attractive candidates for active elements in changeable diffraction gratings, filters, and polarizer [7],
Filling CNTs with both ferromagnetic and ferroelectric materials could be another way of coupling...