Room‐temperature ferromagnetism in Mn‐implanted TiO ₂

Abstract

TiO 2 single crystals were doped with Mn using the ion implantation technique at high doses leading to Mn concentrations of up to 7 at.% Mn. The Mn-doped TiO 2 orders ferromagnetically above room temperature. The magnetic moment of the as-implanted samples (0.3 µ B per Mn) is reduced after thermal annealing at 400• C under oxygen atmosphere due to a reduction of the oxygen deficiency. The moment recovers after annealing at higher temperatures reaching 0.4 µ B per Mn which indicates the incorporation of Mn atoms on substitutional sites. Electron spin resonance measurements show two types of signals which are independent of the orientation of the magnetic field corresponding to Mn 2+ and Mn 2+ -O-Mn 2+ . In addition, four lines are strongly dependend on the orientation of the magnetic field and can be attributed to Mn 4+ .

EPR study of Mn-implanted single crystal plates of TiO2 rutile

“…Our theoretical modelling provides a set of the spin-Hamiltonian parameters, which are close to those of reported in the literature for Mn 4 + ions in a bulk rutile crystal [18,19,25]. It should mentioned that both our work and the literature data [18,19] indicate that in the recent works of Menzel et al [23] and Iacomi et al [24] a wrong assignment of the single (without hyperfine structure) EPR lines as the resonance signal of Mn 4 + ions has been made. These lines should be attributed to other paramagnetic species (probably to Fe 3 + ions).…”

“…Besides, an assignment of the hyperfine lines at the central part of the spectra, given in Refs. [23,24], as due to the Mn 2 + ions is also unconvinced. [100]…”

“…On the other hand, Electron Paramagnetic Resonance (EPR) is well-known technique to probe the local magnetic and structural properties of crystals. In particular, it is a very efficient method for the investigations of the local environment around a substitutional magnetic ion in various crystal hosts [18][19][20][21][22][23][24][25][26][27][28][29].…”

Synthesis of TiO2nanocrystals controlled by means of the size of magnetic elements and the level of doping with them

“…More recently, TiO 2 doped with dilute magnetic elements, so called diluted magnetic semiconductor, has attracted new attention for the realization of spintronics applications, since room temperature ferromagnetism (RTFM) was reported in anatase TiO 2 thin film doped with Co [5]. In addition, many experiments have been reporting ferromagnetism above room temperature in TiO 2 doped with 3d transition metals [6][7][8][9]. However, the mechanism of RTFM in TiO 2 doped with magnetic elements is not clarified, because experimental results have also been reported indicating that ferromagnetism derives from nanometre-sized Co clusters [10][11][12][13][14][15], and that defects such as O vacancies may induce the ferromagnetism [16].…”