TY  - JOUR
AU  - Milivojević, Dušan
AU  - Babić-Stojić, Branka S.
AU  - Jokanović, Vukoman R.
AU  - Jagličić, Zvonko
AU  - Brankovic, D.
AU  - Jović, Nataša G.
AU  - Čolović, Božana M.
AU  - Čupić, Svetlana D.
AU  - Kojić, Dušan
PY  - 2013
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/5471
AB  - The magnetic properties of mesoscopic materials are modified by size and surface effects. We present a sol-gel method used to tailor these effects, and illustrate it on Co1+yAl2-yO4 spinel. Nanocomposites made of spinel oxide Co1+yAl2-yO4 particles dispersed in an amorphous SiO2 matrix were synthesized. Samples with various mass fractions -x of Co1+yAl2-yO4 in composite, ranging from predominantly SiO2 (x = 10 wt%) to predominantly spinel (x = 95 wt%), and with various Co concentrations in spinel y were studied. The spinel grain sizes were below 100 nm with a large size distribution, for samples with predominant spinel phase. Those samples showed Curie-Weiss paramagnetic behavior with antiferromagnetically interacting Co ions (theta approximate to -100 K). The grain sizes of spinel stays confined in 100 nm range even in the spinel samples diluted with as low as 5 wt% concentration of amorphous SiO2. For the samples with predominant SiO2 the crystalline nanoparticles are well separated and of size of around 100 nm, but with presence of much smaller spinel nanoparticles of about 10 nm. The magnetic properties of the samples with predominant silica phase showed complex behavior, spin-glass magnetic freezing at the lowest temperatures and lower absolute value of theta and consequently lower exchange constant.
T2  - Science of Sintering
T1  - Sol-gel as a Method to Tailor the Magnetic Properties of Co1+yAl2-yO4
VL  - 45
IS  - 1
SP  - 69
EP  - 78
DO  - 10.2298/SOS1301069M
ER  - 

@article{
author = "Milivojević, Dušan and Babić-Stojić, Branka S. and Jokanović, Vukoman R. and Jagličić, Zvonko and Brankovic, D. and Jović, Nataša G. and Čolović, Božana M. and Čupić, Svetlana D. and Kojić, Dušan",
year = "2013",
abstract = "The magnetic properties of mesoscopic materials are modified by size and surface effects. We present a sol-gel method used to tailor these effects, and illustrate it on Co1+yAl2-yO4 spinel. Nanocomposites made of spinel oxide Co1+yAl2-yO4 particles dispersed in an amorphous SiO2 matrix were synthesized. Samples with various mass fractions -x of Co1+yAl2-yO4 in composite, ranging from predominantly SiO2 (x = 10 wt%) to predominantly spinel (x = 95 wt%), and with various Co concentrations in spinel y were studied. The spinel grain sizes were below 100 nm with a large size distribution, for samples with predominant spinel phase. Those samples showed Curie-Weiss paramagnetic behavior with antiferromagnetically interacting Co ions (theta approximate to -100 K). The grain sizes of spinel stays confined in 100 nm range even in the spinel samples diluted with as low as 5 wt% concentration of amorphous SiO2. For the samples with predominant SiO2 the crystalline nanoparticles are well separated and of size of around 100 nm, but with presence of much smaller spinel nanoparticles of about 10 nm. The magnetic properties of the samples with predominant silica phase showed complex behavior, spin-glass magnetic freezing at the lowest temperatures and lower absolute value of theta and consequently lower exchange constant.",
journal = "Science of Sintering",
title = "Sol-gel as a Method to Tailor the Magnetic Properties of Co1+yAl2-yO4",
volume = "45",
number = "1",
pages = "69-78",
doi = "10.2298/SOS1301069M"
}

Milivojević, D., Babić-Stojić, B. S., Jokanović, V. R., Jagličić, Z., Brankovic, D., Jović, N. G., Čolović, B. M., Čupić, S. D.,& Kojić, D.. (2013). Sol-gel as a Method to Tailor the Magnetic Properties of Co1+yAl2-yO4. in Science of Sintering, 45(1), 69-78.
https://doi.org/10.2298/SOS1301069M

Milivojević D, Babić-Stojić BS, Jokanović VR, Jagličić Z, Brankovic D, Jović NG, Čolović BM, Čupić SD, Kojić D. Sol-gel as a Method to Tailor the Magnetic Properties of Co1+yAl2-yO4. in Science of Sintering. 2013;45(1):69-78.
doi:10.2298/SOS1301069M .

Milivojević, Dušan, Babić-Stojić, Branka S., Jokanović, Vukoman R., Jagličić, Zvonko, Brankovic, D., Jović, Nataša G., Čolović, Božana M., Čupić, Svetlana D., Kojić, Dušan, "Sol-gel as a Method to Tailor the Magnetic Properties of Co1+yAl2-yO4" in Science of Sintering, 45, no. 1 (2013):69-78,
https://doi.org/10.2298/SOS1301069M . .

TY  - JOUR
AU  - Brankovic, D.
AU  - Jokanović, Vukoman R.
AU  - Babić-Stojić, Branka S.
AU  - Jagličić, Zvonko
AU  - Lisjak, Darja
AU  - Kojić, Dušan
PY  - 2009
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/3635
AB  - An inhomogeneous system of aggregates of Co3O4 nanocrystallites dispersed in an amorphous SiO2 matrix has been studied. X-ray diffraction and atomic force microscopy reveal a bimodal distribution of crystallite sizes, smaller nanocrystallites with dimension below 10 nm and larger nanocrystallites of about 20 nm. The Co3O4 nanocrystallites enter the composition of nanograins with dimension 20-60 nm. The nanograins build aggregates with dimension 200-500 nm. A large value of the effective magnetic moment per Co2+ ion obtained from the high-temperature susceptibility measurements indicates possible disturbance of the normal spinel structure in which a fraction of Co3+ ions also possesses magnetic moment. An analysis based on the temperature dependence of the coercive field has shown that the smaller nanocrystallites behave as superparamagnetic particles with a blocking temperature of about 10 K. Simultaneous existence of two relaxation processes is observed in the frequency dependence of the imaginary part of the ac magnetic susceptibility in the vicinity of T = 15.8 K. The temperature dependence of the width of the distribution function of relaxation times obtained from the Cole-Cole diagrams exhibits behaviour characteristic for spin glass dynamics in a temperature range above 17.6 K and is temperature independent below 15.8 K, which is a property of superparamagnetic particles. The variation of the width of the distribution function between 17.6 and 15.8 K indicates that interference of the superparamagnetic and spin glass dynamics occurs. It has been found that average relaxation time increases with decreasing temperature from tau(c) LT 10(-4) s at 17.6 K to 1.5 x 10(-1) s at 15 K. The increase of the average relaxation time with decreasing temperature, the observed blocking temperature of the superparamagnetic moments at about 10 K and interference appearing between the two spin dynamics suggest that the magnetic moments in the smaller as well as in the larger nanocrystallites are subject to a thermally activated blocking process at low temperatures.
T2  - Journal of Physics: Condensed Matter
T1  - Interference effect between superparamagnetic and spin glass correlated moments in a system of dispersed Co3O4 nanocrystallites
VL  - 21
IS  - 9
DO  - 10.1088/0953-8984/21/9/095303
ER  - 

@article{
author = "Brankovic, D. and Jokanović, Vukoman R. and Babić-Stojić, Branka S. and Jagličić, Zvonko and Lisjak, Darja and Kojić, Dušan",
year = "2009",
abstract = "An inhomogeneous system of aggregates of Co3O4 nanocrystallites dispersed in an amorphous SiO2 matrix has been studied. X-ray diffraction and atomic force microscopy reveal a bimodal distribution of crystallite sizes, smaller nanocrystallites with dimension below 10 nm and larger nanocrystallites of about 20 nm. The Co3O4 nanocrystallites enter the composition of nanograins with dimension 20-60 nm. The nanograins build aggregates with dimension 200-500 nm. A large value of the effective magnetic moment per Co2+ ion obtained from the high-temperature susceptibility measurements indicates possible disturbance of the normal spinel structure in which a fraction of Co3+ ions also possesses magnetic moment. An analysis based on the temperature dependence of the coercive field has shown that the smaller nanocrystallites behave as superparamagnetic particles with a blocking temperature of about 10 K. Simultaneous existence of two relaxation processes is observed in the frequency dependence of the imaginary part of the ac magnetic susceptibility in the vicinity of T = 15.8 K. The temperature dependence of the width of the distribution function of relaxation times obtained from the Cole-Cole diagrams exhibits behaviour characteristic for spin glass dynamics in a temperature range above 17.6 K and is temperature independent below 15.8 K, which is a property of superparamagnetic particles. The variation of the width of the distribution function between 17.6 and 15.8 K indicates that interference of the superparamagnetic and spin glass dynamics occurs. It has been found that average relaxation time increases with decreasing temperature from tau(c) LT 10(-4) s at 17.6 K to 1.5 x 10(-1) s at 15 K. The increase of the average relaxation time with decreasing temperature, the observed blocking temperature of the superparamagnetic moments at about 10 K and interference appearing between the two spin dynamics suggest that the magnetic moments in the smaller as well as in the larger nanocrystallites are subject to a thermally activated blocking process at low temperatures.",
journal = "Journal of Physics: Condensed Matter",
title = "Interference effect between superparamagnetic and spin glass correlated moments in a system of dispersed Co3O4 nanocrystallites",
volume = "21",
number = "9",
doi = "10.1088/0953-8984/21/9/095303"
}

Brankovic, D., Jokanović, V. R., Babić-Stojić, B. S., Jagličić, Z., Lisjak, D.,& Kojić, D.. (2009). Interference effect between superparamagnetic and spin glass correlated moments in a system of dispersed Co3O4 nanocrystallites. in Journal of Physics: Condensed Matter, 21(9).
https://doi.org/10.1088/0953-8984/21/9/095303

Brankovic D, Jokanović VR, Babić-Stojić BS, Jagličić Z, Lisjak D, Kojić D. Interference effect between superparamagnetic and spin glass correlated moments in a system of dispersed Co3O4 nanocrystallites. in Journal of Physics: Condensed Matter. 2009;21(9).
doi:10.1088/0953-8984/21/9/095303 .

Brankovic, D., Jokanović, Vukoman R., Babić-Stojić, Branka S., Jagličić, Zvonko, Lisjak, Darja, Kojić, Dušan, "Interference effect between superparamagnetic and spin glass correlated moments in a system of dispersed Co3O4 nanocrystallites" in Journal of Physics: Condensed Matter, 21, no. 9 (2009),
https://doi.org/10.1088/0953-8984/21/9/095303 . .