Determination of easy axis in a Chemical Ferromagnet, 4-(p-Chlorobenzylideneamino)-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidin-1-oxyl)

J. Jeong1, T. M. Briere3, N. Sahoo1,2, T.P. Das1, S. Ohira4, K. Nishiyama3, K. Nagamine3,4

Department of Physics, State University of New York at Albany, Albany, New York, 12222, USA
2  Department of Radiation Oncology, Albany Medical College, Albany, New York, 12208, USA
3  Meson Science Laboratory, High Energy Accelerator Research Organization (KEK), Tsukuba-Shi, Ibaraki, 305, Japan
Muon Science Laboratory, Institute for Physical and Chemical Research (RIKEN), Wako Shi, Saitama, 351-01, Japan

Using the Hartree-Fock Cluster procedure [1], we have studied the trapping of muon (m+) and muonium (Mu) in the chemical ferromagnet p-Chlorobenzene-TEMPO and the muon hyperfine tensors at the trapping sites to evaluate the hyperfine fields expected there. A singlet Mu is trapped near the oxygen site and a triplet Mu is trapped at the bridge nitrogen site. The sites where trapping is found to occur for m+ are adjacent to the chlorine, bridge nitrogen and oxygen sites. However, the calculated hyperfine tensors are too large or too small at all other sites, except the m+ site at the chlorine and the singlet Mu site at oxygen, to explain the two observed mSR frequencies [2]. The direction of the easy axis for the magnetization in the ferromagnetic state is obtained as (010) [3] by fitting the observed frequencies [2] using our calculated hyperfine tensors for the m+ trapping site adjacent to chlorine and the singlet Mu trapping site adjacent to oxygen. Comparison will be made with the prediction of the easy axis from dipole-dipole interactions between the magnetic moments on the various molecules in the solid, these magnetic moments being primarily localized for each molecule on the NO group.

[1]  “Electronic Properties of Solids using Cluster Methods” Ed. T. A. Kaplan and S. D. Mahanti; Plenum Press, New York (1995)
[2]  S. Ohira, Master’s Thesis, University of Tokyo, Japan (1997).
[3]  J. Jeong, et al, Bull. Am. Phy. Soc. 45, No. 1, 1039 (2000)

(back to Abstracts page)