Magnetic properties and ordering in C-coated FexCo1−x alloy nanocrystals

Abstract

C-coated FexCo1−x (x=0.50, 0.45, 0.40, 0.35, 0.30, 0.25) nanoparticles were produced using a rf plasma torch. The only C source was acetylene used as a carrier gas. Structural determination by x-ray diffraction indicated a single disordered bcc α-FeCo phase along with graphitic C for all compositions. A Scherrer analysis of the peak widths revealed particles to have an average diameter of 50 nm. A broad log-normal size distribution was found from transmission electron microscopy observations. Magnetic hysteresis loops have been measured to temperatures exceeding 1050 K and revealed relatively high room temperature coercivities (200–400 Oe), with a strong compositional variation similar to that observed in bulk alloys. Larger coercivities are consistent with particles near the monodomain size for these alloys. The temperature dependence of the magnetization revealed the effects of atomic ordering. The variation of the saturation magnetization as a function of temperature showed a discontinuity near the bulk order–disorder (α→α′) transformation temperature, as well as loss of magnetization at the α→γ structural phase transition temperature. Other features of M(T) near 500–550 °C are consistent with prior observations of a “550 °C structural anomaly” which has been observed in bulk alloys with less than perfect order.

Tuning Carbon Content and Morphology of FeCo/Graphitic Carbon Core–Shell Nanoparticles using a Salt‐Matrix‐Assisted CVD Process

“…4, showing a drop in the carbon content of the samples by decreasing the CO fl ow rate. Raman spectra of the FeCo/GC core-shell nanoparticles synthesized at different gas fl ow rates can be seen in Figure 4 b, indicating a sharp graphitic carbon G-band and a disordered D-band.…”

“…[ 1,2 ] Among various magnetic nanoparticles that have been studied for potential biomedical applications, FeCo nanoparticles are promising candidates because of their high saturation magnetization and high Curie temperature. [3][4][5] However, the ease of oxidation, dissolution in acidic environments, and potential toxicity of these materials in their native state restrict their use in biomedical applications. [ 3,6,7 ] A graphitic surface coating not only would address each of these issues, thereby rendering them biocompatible and improving their thermal stability but also would act as a powerful link to covalently attach organic molecules (i.e., drugs) to the magnetic cores.…”

Origin of the magnetic moment enhancement of the ordered Fe50Co50 alloys

“…Based on the well-known Slater-Pauling curve [1], it is expected that Fe-Co alloy with a specific composition exhibits the largest magnetic moment among various iron group alloys. The Fe-Co alloys are popularly used soft magnetic materials [2,3] for ultrahigh-density magnetic recording media because of their relatively low coercive fields. There was also a report on possible nanoscale applications by forming Fe-Co nanowires in self-assembled arrays [4].…”

Structural and magnetic properties of mechanically milled SmCo5:C

“…Other studies have shown that encapsulation of magnetic nanoparticles in carbon can enhance oxidation resistance and increase nanostructure stability. [6][7][8] This article details the effect of carbon on the magnetic properties and oxidation resistance of (SmCo 5 ) x :C 1Ϫx with 0.15рxр1.…”