EPR study of paramagnetic Fe3+ centers in iron-implanted TiO2 rutile

Full text: An interest to the studies in the field of ferromagnetic semiconductors is driven by their potential applications in the spintronic devices. In this context, the observation of room temperature ferromagnetism in TiO2 rutile doped by various magnetic ions [1,2] has attracted considerable attention. The local environment of doped magnetic ions has a drastic effect on the magnetic properties of these materials. In this study, the local structure of Fe ions in the single crystalline rutile-TiO2 host doped by ion-beam implantation has been studied by Electron Paramagnetic Resonance (EPR) technique. Single crystalline (100) and (001) TiO2 rutile substrates have been implanted with 40 keV Fe+ ions to a fluence of 1.50 1017 ions/cm2 at ion current densities of 8 □A/cm2. Then the implanted samples have been annealed at T=950C in air during 1 hour. It has been found that annealing procedure results in diffusing the most of iron impurity out of the rutile matrix. Moreover, as a result of post-implanting thermal treatment the samples became transparent and the color of samples changed from dark-grey to light-yellow. EPR spectra of the annealed samples have been recorded in X-band (9.8 GHz) at room temperature. The spectra have been interpreted to correspond to the transitions among the spin multiplet (S=5/2, L=0) of the paramagnetic Fe3+ ion. Analysis of EPR spectra shows that iron in the TiO2 rutile host substitutes for Ti4+ ions. Two equivalent Fe3+ centers have been observed in the EPR spectra in correspondence with two equivalent octahedral positions of Ti ions in the rutile structure. The spin Hamiltonian of the Fe3+ centers includes two terms which are the nearly isotropic Zeeman term and the crystal field interaction of orthorhombic symmetry: H=gβHS+D(Sz2-35/12)+E(Sx2-Sy2)+(a/6)(Sx4+Sy4+Sz4-707/16)+(7/36)xF[Sz4- (95/14)Sz2+81/16] where S(Sx,Sy,Sz) is the spin operator; g, D, E, a, and F are the experimentally determined spin-Hamiltonian parameters. It has been found that the EPR spectra of the Fe3+ centers can be described by a set of experimental parameters of the spin-Hamiltonian which is slightly different from that of reported in the literature for a bulk rutile crystal [3]. The obtained EPR results are discussed with respect to the structural properties of the Fe-implanted TiO2 rutile samples. References: [1] Y. Matsumoto, M. Murakami, T. Shono et al., Science 291 (2001) 854. [2] Z. Wang, J.Tang, Le Duc Tung, W. Zhou, L. Spinu, J. Appl. Phys . 93 (2003) 7870. [3] P. O. Andersson, E. L. Kollberg, A. Jelenski, Phys. Rev. B. 8 (1973) 4956.