Online time-differential perturbed angular correlation study with an 19O beam – Residence sites of oxygen atoms in highly oriented pyrolytic graphite

Defect induced magnetism in highly oriented pyrolytic graphite: bulk magnetization and19F hyperfine interaction studies

“…From the fits of the data, the quadrupole interaction frequencies ω Q for the two components were found to be 7.2 and 7.8 Mrad s −1 at 15 K which indicates that the electric field gradients for both the stopping sites are very similar. Using the nuclear quadrupole moment Q = −0.072b [20], the electric field gradients V zz values were estimated to be ≈27 × 10 21 V m −2 , which agree with the results reported in the literature [17,18]. The magnetic interaction frequencies for the two components, however, turn out to be different, the larger fraction showing higher ω L values.…”

“…Besides the density of states and the magnetic moments, we have also calculated the electric field gradient and magnetic hyperfine fields at the F site. As listed in table 1, the principal component of the field gradient V zz for F is found to be ≈28 × 10 21 V m −2 , which agrees well with the experimental value obtained from our experiments as well as those reported in the literature [17,18]. The magnetic hyperfine field B hf for the F impurity at substitutional as well as interstitial sites with no vacancy in its neighborhood turned out to be quite small.…”

“…were constructed. Taking account of the finite quadrupole interaction observed for 19 F in HOPG (ω Q ≈ 8 Mrad s −1 ) [17,18], the measured R(t) spectra were fitted to a perturbation function appropriate for combined electric quadrupole and magnetic dipole interactions [21,22] using the general expression…”

“…Despite the large number of experimental and theoretical results available, there has been skepticism regarding the long range bulk ferromagnetism in graphite because the magnetic signals are generally weak (≤3 × 10 −3 emu g −1 ) and the Curie temperature exceeds 300 K [4]. Furthermore, hyperfine field measurements for 19 F in HOPG under conditions of zero applied magnetic field [18,17] using the perturbed angular correlation (PAC) method did not show the presence of a detectable static magnetic hyperfine field. In view of the above facts, further investigations are desirable, especially using local techniques sensitive to magnetic interactions.…”

Half-life and magnetic moment of the first excited state inI132

“…Regardless of its importance in material science, few probe nuclei for the perturbed angular correlation technique (PAC) are available in the halogen family. Sato et al recently showed 19 F(← 19 O) as to be a usable probe for PAC [9,10]. However, its application to material science is still limited because it requires an online measurement where control of the experimental conditions becomes much more difficult than in an off-line measurement.…”