Effect of Gd3+ ion on the structural and magnetic properties of (Nb and Al) co-doped rutile TiO2 single crystal

Abstract

In this study we investigated the influence of Gd3+ ions on the structural and magnetic properties of (Nb + Al) codoped TiO2 single crystals with nominal composition Ti0.995(Nb0.667Al0.333)0.005O2 (TNA) and Ti0.995(Nb0.667(Al0.1665Gd0.1665))0.005O2 (TNAGd) grown in an optical traveling floating zone (TFZ) furnace. The crystal structure and phase purity investigated by X-ray diffraction (XRD) and High resolution transmission electron microscopy (HRTEM) images of selected area electron diffraction (SAED) patterns confirmed the rutile crystal nature for both TNA and TNAGd samples. The magnetic properties were studied from 3 to 400 K in magnetic fields up to 60 kOe. ZFC/FC curves revealed paramagnetic behavior for TNA sample, while the presence of Gd3+ ions in the crystal structure drastically affected the magnetic properties turning to ferromagnetic behavior. The isothermal magnetization, M(H) curves for TNAGd samples were analyzed by the bound magnetic polaron (BMP) model. At the lowest temperature the values of the total moment of BMP’s (M0), spontaneous moment of a single BMP (ms), and the concentration of BMP’s (N) were found to be 1.58 emu/cm3, 840 μB, and 3.2 × 1019BMP/cm3, respectively. The number of Gd3+ ions per BMP was ̃113 and 75% of Gd3+ ions were inside the BMP’s and the remaining 25% were outside but diluted in the matrix or interacting antiferromagnetically.