Ferromagnetism in chemically synthesized<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Ce</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>nanoparticles by Ni doping

This work reports the discovery of room-temperature ferromagnetism in $5--9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ sized ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{O}}_{2}$ nanoparticles $(0.01\ensuremath{\leqslant}x\ensuremath{\leqslant}0.20)$ prepared using a sol-gel based chemical method at room temperature and under ambient conditions. Particle induced x-ray emission studies were used to determine the dopant concentrations. Magnetic measurements of the chemically synthesized ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{O}}_{2}$ samples at room temperature showed coercivity in the $40--120\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$ range, and the saturation magnetization showed a maximum of $1.21\phantom{\rule{0.3em}{0ex}}\mathrm{memu}∕\mathrm{g}$ ($8.59\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}∕\mathrm{Ni}$ ion) for $x=0.04$. Average crystallite sizes and lattice parameters estimated from x-ray diffraction and transmission electron microscopy studies showed a gradual decrease with $x$ in the entire doping range, while the lattice strain showed a minimum for $x=0.04$. Optical studies revealed direct band gap energies ranging from $3.23\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}3.99\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ with a minimum for $x=0.04$. A high Curie temperature of ${T}_{C}=665\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ was obtained for $x=0.03$.