Laser controlled magnetism in hydrogenated fullerene films

Abstract

Room temperature ferromagnetic-like behavior in fullerene photopolymerized films treated with monatomic hydrogen is reported. The hydrogen treatment controllably varies the paramagnetic spin concentration and laser induced polymerization transforms the paramagnetic phase to a ferromagnetic-like one. Excess laser irradiation destroys magnetic ordering, presumably due to structural changes, which was continuously monitored by Raman spectroscopy. We suggest an interpretation of the data based on first-principles density-functional spin-unrestricted calculations which show that the excess spin from mono-atomic hydrogen is delocalized within the host fullerene and the laser-induced polymerization promotes spin exchange interaction and spin alignment in the polymerized phase.

Response to “Comment on ‘Laser controlled magnetism in hydrogenated fullerene films’” [J. Appl. Phys. 113, 036101 (2013)]

“…Although the appearance of the second order modes at the very low laser intensity is very unlikely in our measurements, we cannot exclude the contribution of C 60 silent modes which become weakly active when attached hydrogens reduce the space symmetry; in a sense, this mechanism is also intrinsic. The peaks in the C-H stretching vibrations region are much stronger than other features in the 1800-4000 cm À1 region, 1 and we believe that the spectrum is the superposition of the mechanisms, intrinsic mechanism being a prevailing one.…”

“…In Ref. 1, we reported that after treatment with monoatomic hydrogen and polymerization, fullerene films show well pronounced magnetic hysteresis and the saturation magnetization corresponds to 0.1-0.2 bohr magneton per fullerene molecule.…”

“…In the paper "Laser controlled magnetism in hydrogenated fullerene films," 1 we reported on room temperature magnetism of fullerenes treated with mono-atomic hydrogen. The study was motivated by the earlier theoretical predictions 2,3 that unpaired spins on fullerene molecules in the polymerized solid phases show long range exchange interaction, which is strong enough to expect ferromagnetism at room temperatures.…”

“…1(a), we show the Raman spectrum of a pristine film. These data were not included in our publication, 1 as the Comment quite rightly states. In the region from 1650 to 4000 cm À1 , the spectrum in Fig.…”

“…1(c), we show the Raman spectrum of pristine and hydrogenated films in the 200-1800 cm À1 range. In this range, ab initio calculations predict the following changes in the Raman spectra due to hydrogenation: (i) lifting the degeneracy of the H g (1), H g (7), and H g (8) modes, (ii) strong enhancement of the latter mode in intensity, and (iii) an appearance of large amount of spectral features around the H g (5) and H g (6) modes. The predicted features, although expectedly weak in intensity, can be identified from the comparison of the spectra of pristine and hydrogen a)…”