Abstract
Hexagonal shaped nanoparticles about 60 nm in size were successfully synthesized in tetraethylene glycol solution containing polyvinylpyrrolidone. By the analysis of the electron diffraction pattern, these were identified as a single crystal of Ni carbide with Ni3C − type structure. Their magnetization curve at 5 K was not completely saturated under a magnetic field of 5 T. The thermomagnetization curves after zero-field cooling and after field cooling exhibited the magnetic cooling effect at low temperatures. Furthermore, the 2nd order nonlinear term of AC magnetic susceptibility exhibited a negative divergence at about 17 K. It is concluded that Ni carbide single crystal nanoparticles with the Ni3C − type structure exhibit spin-glass transition at low temperatures.
Highlights
Ni-based nanoparticles precipitated in organic solution have attracted much attention, because a hexagonal phase is obtained while bulk Ni metal has the fcc structure.[1,2,3] The subsequent studies have pointed out that the hexagonal phase is Ni carbide with a Ni3C-type structure.[4,5,6,7] According to the band calculation, Ni3 C without defects is predicted to be nonmagnetic state,[8,9] and the introduction of Ni-rich regions due to carbon site defects is expected to cause a ferromagnetic state.[8]
It is concluded that Ni carbide single crystal nanoparticles with the Ni3C-type structure exhibit spin-glass transition at low temperatures
The magnetization under the magnetic field of 0.5 T after field cooling (FC) decreases with increasing temperature
Summary
Ni-based nanoparticles precipitated in organic solution have attracted much attention, because a hexagonal phase is obtained while bulk Ni metal has the fcc structure.[1,2,3] The subsequent studies have pointed out that the hexagonal phase is Ni carbide with a Ni3C-type structure.[4,5,6,7] According to the band calculation, Ni3 C without defects is predicted to be nonmagnetic state,[8,9] and the introduction of Ni-rich regions due to carbon site defects is expected to cause a ferromagnetic state.[8]. Diffraction peaks of the fcc and hexagonal structures were observed for nanoparticles synthesized without PVP. No peaks assigned to the fcc structure were observed for nanoparticles synthesized with PVP. Nanoparticles synthesized with PVP were identified as a single phase of Ni carbide with the Ni3C-type structure. It was revealed by transmission electron microscope (TEM) observation that nanoparticles synthesized with PVP were a single crystal of Ni carbide with the Ni3C-type. Magnetic properties of such a high quality specimen of Ni3C-type Ni carbide were investigated by both DC and AC magnetic measurements
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
