Temperature driven magnetic transitions in FePd_3 filled monolayer carbon foam and Fe_3C/α-Fe filled carbon nanotubes

摘要

An unusual observation of magnetic transition and Pd/C rehybridization effects is reported in novel monolayer carbon foam materials filled with doubled FePd3 crystal lattices. We reveal the presence of not previously observed sharp Pd/C interfaces, as confirmed by X-ray photoelectron spectroscopy, which give rise to localized paramagnetic features in the ESR spectra for a g value of 2.05 at 130 K. Also, as revealed by vibrating sample magnetometry and electron spin resonance measurements, an increase in the magnetization values with the decrease of the temperature is found. This result is compatible with a structural rearrangement from a face centered cubic metastable paramagnetic FePd3 phase into a primitive ferromagnetic cubic Fe3Pd phase. Comparative studies performed in Fe3C/alpha-Fe filled thin walled carbon nanotubes also give further confirmations of these unusual types of transitions by revealing a bcc to fcc phase shift with the decrease of the temperature as confirmed by zero field cooled measurements of the magnetization and ESR. In addition, a temperature dependent variation in the intensity and position of the pi-electron's differential absorption feature is observed and implies the possible existence of antiferromagnetic correlations in the carbon-nanotubes structure. Published under license by AIP Publishing.