Size-dependent dielectric behaviour of magnetic Gd₂O₃nanocrystals dispersed in a silica matrix

Abstract

Magnetic nanocrystalline Gd2O3 particles have been successfully synthesized in a silica glass matrix by the sol–gel method at calcination temperatures of 700 °C and above. The optical spectra, corresponding to the transition from ground 8S7/2 to the excited 6P, 6I and 6D multiplets, show a large blue shift which increases with decreasing particle size. Calculated free ion parameters represent different electrostatic and spin–orbit interactions of nanocrystalline Gd2O3 compared with the bulk Gd2O3. The thermal behaviour of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of Gd2O3 nanocrystals in the 5–300 K temperature interval have demonstrated that the Gd2O3 nanocrystals present in these glasses display superparamagnetic–ferromagnetic transition at low temperatures. The present Gd2O3 nanoparticles embedded in the silica glass matrix show a high (∼103) dielectric constant with considerable low loss and good temperature-independent character associated with an important technological implication which promises wide applications in memory devices.

Ultra small Gd2O3 nanoparticles: Absorption and emission properties

“…4, an absorption peak of low intensity appears at 312 nm. This peak at 312 nm is attributed to 8 S 7/2 to 6 P 7/2 transition in Gd 2 O 3 NPs and it corresponds to a red shift of approximately 2 nm compared to the bulk Gd 2 O 3 [32]. Similar shift in peak position was also noticed in Ref.…”

“…Among these multiplets, the lowest lying multiplet above the ground state is 6 P 7/2 . In the bulk Gd 2 O 3 absorption through 8 S 7/2 to 6 P 7/2 transition corresponds to approximately 310 nm [32]. As shown in the inset of Fig.…”

“…Transition of an electron from 4f to 5d involves high energy and absorption peaks appear below 220 nm [15] which we do not consider here. The seven electrons in Gd 4f orbitals have a total of 3432 multiplets [15] and the ground state is 8 S 7/2 [15,17,32]. Among these multiplets, the lowest lying multiplet above the ground state is 6 P 7/2 .…”

Luminomagnetic K2 Gd1− x Zr(PO4 )3 :Tb x 3+ phosphor with intense green fluorescence and paramagnetism

“…6). As the magnetization curve shows zero coercive field and no saturation and the magnetization decreases with decrease in concentration of Gd 3þ ions in the lattice with substitution of Tb 3þ ions, for the K 2 GdZr(PO 4 ) 3 :Tb 3þ particles, the spin contribution from Gd 3þ is the reason for the observed magnetic behavior [10,11].…”

“…This interaction results into a long range ordered exchange force inducing paramagnetic behavior. The maximum number of unpaired 4f electrons is 7 in Gd 3þ and KGP particles have shown magnetic behavior [10]. Moreover, spin magnetic moment of Tb 3þ is 6/7 of the magnetic moment of Gd 3þ .…”