  In a quest of enriching the area of d0 magnetism in oxide materials, we have
undertaken to study Mg-doped TiO2 compounds. The Ti1-xMgxO2 (x=0, 0.02, 0.04
and 0.06) nanoparticles were prepared by solid-state reaction route. The X-ray
diffractions (XRD) patterns of these samples indicate single phase of
tetragonal rutile-structure of TiO2. The refinement of the XRD patterns reveals
no change in the crystallographic lattice parameters in comparison to pure TiO2
upon Mg doping and it indicates that Mg2+ ions do not enter core grains and
form core/shell structure. SEM observations reveal the uniform morphology with
nanometric grains in the range of 150-200 nm. The measurement of magnetic
properties of these compounds indicates that pure TiO2 and Ti0.98Mg0.02
compounds exhibit paramagnetic behavior and Ti0.96Mg0.04 compound exhibits
ferromagnetic (FM) phase superimposed with the dominating paramagnetic phase.
However, Ti0.94Mg0.06 compound exhibits ferromagnetic to paramagnetic
transition with FM transition temperature of 180.2 K. The measurements of zero
field and field cooled magnetization data indicate low temperature magnetic
irreversibility for x=0.06 sample and it was attributed to the competing AFM
(core) and the FM (shell) interactions. The measurement of hysteresis curves at
various temperatures indicates domain wall pinning and an exchange-bias
behavior.
