TY  - JOUR
AU  - Nikolić, Violeta N.
AU  - Milić, Mirjana M.
AU  - Zdravković, Jelena D.
AU  - Spasojević, Vojislav
PY  - 2019
UR  - http://TechnoRep.tmf.bg.ac.rs/handle/123456789/5904
AB  - ε-Fe2O3 phase is recognized as an attractive material, in both technological and scientific point of view, since it can achieve very high room-temperature coercivity (10–20 kOe). In this paper, multi-phase samples Fe2O3/SiO2 with slightly different Fe/Si molar ratio were produced by sol–gel synthesis route. The obtained samples were characterized by various experimental techniques including XRD, TA, FTIR, and SQUID (DC and AC magnetic measurements). It was found that both samples consisted of α-Fe2O3 and ε‑Fe2O3 phases embedded in the silica matrix, and showed very similar structural and magnetic properties, except that displayed significantly different room-temperature intrinsic coercivity field values: HciS1 = 14.3 kOe and HciS2 = 7.5 kOe. We have discussed possible origin of thus high intrinsic coercivity field variation. © 2019, Pleiades Publishing, Ltd.
T2  - Russian Journal of Physical Chemistry A
T1  - Origin of the Intrinsic Coercivity Field Variations of ε-Fe2O3
EP  - 383
IS  - 2
SP  - 377
VL  - 93
DO  - 10.1134/S0036024419020316
ER  - 

@article{
author = "Nikolić, Violeta N. and Milić, Mirjana M. and Zdravković, Jelena D. and Spasojević, Vojislav",
year = "2019",
abstract = "ε-Fe2O3 phase is recognized as an attractive material, in both technological and scientific point of view, since it can achieve very high room-temperature coercivity (10–20 kOe). In this paper, multi-phase samples Fe2O3/SiO2 with slightly different Fe/Si molar ratio were produced by sol–gel synthesis route. The obtained samples were characterized by various experimental techniques including XRD, TA, FTIR, and SQUID (DC and AC magnetic measurements). It was found that both samples consisted of α-Fe2O3 and ε‑Fe2O3 phases embedded in the silica matrix, and showed very similar structural and magnetic properties, except that displayed significantly different room-temperature intrinsic coercivity field values: HciS1 = 14.3 kOe and HciS2 = 7.5 kOe. We have discussed possible origin of thus high intrinsic coercivity field variation. © 2019, Pleiades Publishing, Ltd.",
journal = "Russian Journal of Physical Chemistry A",
title = "Origin of the Intrinsic Coercivity Field Variations of ε-Fe2O3",
pages = "383-377",
number = "2",
volume = "93",
doi = "10.1134/S0036024419020316"
}

Nikolić, V. N., Milić, M. M., Zdravković, J. D.,& Spasojević, V.. (2019). Origin of the Intrinsic Coercivity Field Variations of ε-Fe2O3. in Russian Journal of Physical Chemistry A, 93(2), 377-383.
https://doi.org/10.1134/S0036024419020316

Nikolić VN, Milić MM, Zdravković JD, Spasojević V. Origin of the Intrinsic Coercivity Field Variations of ε-Fe2O3. in Russian Journal of Physical Chemistry A. 2019;93(2):377-383.
doi:10.1134/S0036024419020316 .

Nikolić, Violeta N., Milić, Mirjana M., Zdravković, Jelena D., Spasojević, Vojislav, "Origin of the Intrinsic Coercivity Field Variations of ε-Fe2O3" in Russian Journal of Physical Chemistry A, 93, no. 2 (2019):377-383,
https://doi.org/10.1134/S0036024419020316 . .

TY  - JOUR
AU  - Nikolić, Violeta N.
AU  - Milić, Mirjana M.
AU  - Zdravković, Jelena D.
AU  - Spasojević, Vojislav
PY  - 2019
UR  - http://TechnoRep.tmf.bg.ac.rs/handle/123456789/5903
AB  - Origin of the intrinsic coercivity field variations observed by hysteretic measurements established by Nikolic et al. was investigated in detail by ZFC/FC measurements. In this study, magnetic behavior of the samples is further examined by calculation of the ZFC Mn(T) and Mn(H) first derivatives. Performed study showed that the main contribution to the measured coercivity comes from the ε-Fe2O3 particles, characterized by Hci = 24 kOe, although both samples posses SPM ε-Fe2O3 fraction. As a result, Hci values of the samples are differed dependent on the quantity of the SPM ε-Fe2O3 particles in the sample. Mechanism of the intrisic coercivity field variations is discussed. © 2019, Pleiades Publishing, Ltd.
T2  - Russian Journal of Physical Chemistry A
T1  - Origin of the Intrinsic Coercivity Field Variations and Magnetic Study of ε-Fe2O3
EP  - 593
IS  - 3
SP  - 588
VL  - 93
DO  - 10.1134/S0036024419030130
ER  - 

@article{
author = "Nikolić, Violeta N. and Milić, Mirjana M. and Zdravković, Jelena D. and Spasojević, Vojislav",
year = "2019",
abstract = "Origin of the intrinsic coercivity field variations observed by hysteretic measurements established by Nikolic et al. was investigated in detail by ZFC/FC measurements. In this study, magnetic behavior of the samples is further examined by calculation of the ZFC Mn(T) and Mn(H) first derivatives. Performed study showed that the main contribution to the measured coercivity comes from the ε-Fe2O3 particles, characterized by Hci = 24 kOe, although both samples posses SPM ε-Fe2O3 fraction. As a result, Hci values of the samples are differed dependent on the quantity of the SPM ε-Fe2O3 particles in the sample. Mechanism of the intrisic coercivity field variations is discussed. © 2019, Pleiades Publishing, Ltd.",
journal = "Russian Journal of Physical Chemistry A",
title = "Origin of the Intrinsic Coercivity Field Variations and Magnetic Study of ε-Fe2O3",
pages = "593-588",
number = "3",
volume = "93",
doi = "10.1134/S0036024419030130"
}

Nikolić, V. N., Milić, M. M., Zdravković, J. D.,& Spasojević, V.. (2019). Origin of the Intrinsic Coercivity Field Variations and Magnetic Study of ε-Fe2O3. in Russian Journal of Physical Chemistry A, 93(3), 588-593.
https://doi.org/10.1134/S0036024419030130

Nikolić VN, Milić MM, Zdravković JD, Spasojević V. Origin of the Intrinsic Coercivity Field Variations and Magnetic Study of ε-Fe2O3. in Russian Journal of Physical Chemistry A. 2019;93(3):588-593.
doi:10.1134/S0036024419030130 .

Nikolić, Violeta N., Milić, Mirjana M., Zdravković, Jelena D., Spasojević, Vojislav, "Origin of the Intrinsic Coercivity Field Variations and Magnetic Study of ε-Fe2O3" in Russian Journal of Physical Chemistry A, 93, no. 3 (2019):588-593,
https://doi.org/10.1134/S0036024419030130 . .

TY  - JOUR
AU  - Nikolić, Violeta N.
AU  - Spasojević, Vojislav
AU  - Panjan, Matjaž
AU  - Kopanja, Lazar
AU  - Mraković, Ana Đ.
AU  - Tadić, Marin
PY  - 2017
UR  - http://TechnoRep.tmf.bg.ac.rs/handle/123456789/5852
AB  - Several Fe2O3/SiO2 nanostructures were synthesized by the combination of the microemulsion and a sol-gel methods. Based on X-ray powder diffraction (XRD) and magnetic measurements (giant coercivity similar to 2.13 T) we identified epsilon-Fe2O3 (hard magnet) as the dominant crystalline phase. TEM analysis showed a wide size distribution of iron oxide nanoparticles (from 4 to 50 nm) with various morphologies (spherical, ellipsoidal and rod-like). We quantitatively described (computational analysis, MATLAB code) morphological properties of nanoparticles using the ellipticity of the shapes. The as-synthesized hard magnetic material was subjected to a post-annealing treatment at different temperatures (200, 500, 750, 1000 and 1100 degrees C) in order to investigate stability, formation and transformation of the epsilon-Fe2O3 polymorph. We found decreasing coercivity in the thermally treated samples up to the temperature of 750 degrees C (H-c=1245 Oe), followed by an observation of a surprising jump in coercivity H-c similar to 1.5 T after post-annealing at 1000 degrees C. We conclude that the re-formation of the epsilon-Fe2O3 structure during post-annealing at 1000 degrees C is the origin of the observed phenomena. The phase transformation epsilon-Fe2O3 - GT alpha-Fe2O3 and crystallization of amorphous silica in quartz and cristobalite were observed in the sample treated at 1100 degrees C.
T2  - Ceramics International
T1  - Re-formation of metastable epsilon-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis, computational particle shape analysis in micrographs and magnetic properties
EP  - 7507
IS  - 10
SP  - 7497
VL  - 43
DO  - 10.1016/j.ceramint.2017.03.030
ER  - 

@article{
author = "Nikolić, Violeta N. and Spasojević, Vojislav and Panjan, Matjaž and Kopanja, Lazar and Mraković, Ana Đ. and Tadić, Marin",
year = "2017",
abstract = "Several Fe2O3/SiO2 nanostructures were synthesized by the combination of the microemulsion and a sol-gel methods. Based on X-ray powder diffraction (XRD) and magnetic measurements (giant coercivity similar to 2.13 T) we identified epsilon-Fe2O3 (hard magnet) as the dominant crystalline phase. TEM analysis showed a wide size distribution of iron oxide nanoparticles (from 4 to 50 nm) with various morphologies (spherical, ellipsoidal and rod-like). We quantitatively described (computational analysis, MATLAB code) morphological properties of nanoparticles using the ellipticity of the shapes. The as-synthesized hard magnetic material was subjected to a post-annealing treatment at different temperatures (200, 500, 750, 1000 and 1100 degrees C) in order to investigate stability, formation and transformation of the epsilon-Fe2O3 polymorph. We found decreasing coercivity in the thermally treated samples up to the temperature of 750 degrees C (H-c=1245 Oe), followed by an observation of a surprising jump in coercivity H-c similar to 1.5 T after post-annealing at 1000 degrees C. We conclude that the re-formation of the epsilon-Fe2O3 structure during post-annealing at 1000 degrees C is the origin of the observed phenomena. The phase transformation epsilon-Fe2O3 - GT alpha-Fe2O3 and crystallization of amorphous silica in quartz and cristobalite were observed in the sample treated at 1100 degrees C.",
journal = "Ceramics International",
title = "Re-formation of metastable epsilon-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis, computational particle shape analysis in micrographs and magnetic properties",
pages = "7507-7497",
number = "10",
volume = "43",
doi = "10.1016/j.ceramint.2017.03.030"
}

Nikolić, V. N., Spasojević, V., Panjan, M., Kopanja, L., Mraković, A. Đ.,& Tadić, M.. (2017). Re-formation of metastable epsilon-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis, computational particle shape analysis in micrographs and magnetic properties. in Ceramics International, 43(10), 7497-7507.
https://doi.org/10.1016/j.ceramint.2017.03.030

Nikolić VN, Spasojević V, Panjan M, Kopanja L, Mraković AĐ, Tadić M. Re-formation of metastable epsilon-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis, computational particle shape analysis in micrographs and magnetic properties. in Ceramics International. 2017;43(10):7497-7507.
doi:10.1016/j.ceramint.2017.03.030 .

Nikolić, Violeta N., Spasojević, Vojislav, Panjan, Matjaž, Kopanja, Lazar, Mraković, Ana Đ., Tadić, Marin, "Re-formation of metastable epsilon-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis, computational particle shape analysis in micrographs and magnetic properties" in Ceramics International, 43, no. 10 (2017):7497-7507,
https://doi.org/10.1016/j.ceramint.2017.03.030 . .

TY  - JOUR
AU  - Nikolić, Violeta N.
AU  - Tadić, Marin
AU  - Panjan, Matjaž
AU  - Kopanja, Lazar
AU  - Cvjetićanin, Nikola
AU  - Spasojević, Vojislav
PY  - 2017
UR  - http://TechnoRep.tmf.bg.ac.rs/handle/123456789/5822
AB  - Magnetic properties of Fe2O3/SiO2 samples were studied after being produced by sol-gel synthesis and formation of epsilon-Fe2O3 polymorph. Samples were thermally treated, using different annealing temperatures and annealing times. The size and morphological characteristics of the iron oxide nanoparticles were examined using a TEM microscope. We used the ellipticity of shapes, which is a measure of how much the shape of a nanoparticle differs from a perfect ellipse, in order to quantitatively describe morphological properties of nanoparticles. Coercivity measurements were used to identify and monitor the formation of the epsilon-iron oxide phase during the thermal treatments (annealing). Coercivity values were in the range from 1.2 to 15.4 kOe, which is in accordance with previous experience regarding the existence of epsilon-Fe2O3. We have determined the optimal formation conditions for the epsilon-Fe2O3 polymorph (t=1050 degrees C for 7 h, H-c=15.4 kOe), as well as the narrow temperature interval (1050-1060 C) in which the polymorph abruptly vanished (H-c=2300 Oe), on the basis of results of the magnetic properties. The threshold temperature for the epsilon-Fe2O3 phase transformation was measured as 1060 degrees C. We found that different annealing temperatures and annealing times significantly affected magnetic properties of the examined samples.
T2  - Ceramics International
T1  - Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of epsilon-Fe2O3 phase
EP  - 3155
IS  - 3
SP  - 3147
VL  - 43
DO  - 10.1016/j.ceramint.2016.11.132
ER  - 

@article{
author = "Nikolić, Violeta N. and Tadić, Marin and Panjan, Matjaž and Kopanja, Lazar and Cvjetićanin, Nikola and Spasojević, Vojislav",
year = "2017",
abstract = "Magnetic properties of Fe2O3/SiO2 samples were studied after being produced by sol-gel synthesis and formation of epsilon-Fe2O3 polymorph. Samples were thermally treated, using different annealing temperatures and annealing times. The size and morphological characteristics of the iron oxide nanoparticles were examined using a TEM microscope. We used the ellipticity of shapes, which is a measure of how much the shape of a nanoparticle differs from a perfect ellipse, in order to quantitatively describe morphological properties of nanoparticles. Coercivity measurements were used to identify and monitor the formation of the epsilon-iron oxide phase during the thermal treatments (annealing). Coercivity values were in the range from 1.2 to 15.4 kOe, which is in accordance with previous experience regarding the existence of epsilon-Fe2O3. We have determined the optimal formation conditions for the epsilon-Fe2O3 polymorph (t=1050 degrees C for 7 h, H-c=15.4 kOe), as well as the narrow temperature interval (1050-1060 C) in which the polymorph abruptly vanished (H-c=2300 Oe), on the basis of results of the magnetic properties. The threshold temperature for the epsilon-Fe2O3 phase transformation was measured as 1060 degrees C. We found that different annealing temperatures and annealing times significantly affected magnetic properties of the examined samples.",
journal = "Ceramics International",
title = "Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of epsilon-Fe2O3 phase",
pages = "3155-3147",
number = "3",
volume = "43",
doi = "10.1016/j.ceramint.2016.11.132"
}

Nikolić, V. N., Tadić, M., Panjan, M., Kopanja, L., Cvjetićanin, N.,& Spasojević, V.. (2017). Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of epsilon-Fe2O3 phase. in Ceramics International, 43(3), 3147-3155.
https://doi.org/10.1016/j.ceramint.2016.11.132

Nikolić VN, Tadić M, Panjan M, Kopanja L, Cvjetićanin N, Spasojević V. Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of epsilon-Fe2O3 phase. in Ceramics International. 2017;43(3):3147-3155.
doi:10.1016/j.ceramint.2016.11.132 .

Nikolić, Violeta N., Tadić, Marin, Panjan, Matjaž, Kopanja, Lazar, Cvjetićanin, Nikola, Spasojević, Vojislav, "Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of epsilon-Fe2O3 phase" in Ceramics International, 43, no. 3 (2017):3147-3155,
https://doi.org/10.1016/j.ceramint.2016.11.132 . .