In addition to the double phase transition (with the Curie temperatures and ), a low-temperature anomaly in the dependence of the magnetization is observed in the bulk magnetic graphite (MG) (with an average granular size of ), which is attributed to the manifestation of the size effects below the quantum temperature and is well fitted by the periodic function with being the bulk magnetization and the thermal de Broglie wavelength. The best fits of the high-temperature data (using the mean-field Curie–Weiss and Bloch expressions) produced reasonable estimates for the model parameters, such as defects mediated effective spin exchange energy (which defines the intragranular Curie temperature ) and proximity mediated interactions between neighboring grains (through potential barriers created by thin layers of nonMG) with energy (which defines the intergranular Curie temperature ) with and being the intergranular distance and characteristic length, respectively.
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1 December 2009
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December 07 2009
Manifestation of finite temperature size effects in nanogranular magnetic graphite
S. Sergeenkov;
S. Sergeenkov
a)
1Department of Physics and Physical Engineering, Materials and Devices Group,
Universidade Federal de São Carlos
, São Carlos, SP 13565-905, Brazil
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N. S. Souza;
N. S. Souza
1Department of Physics and Physical Engineering, Materials and Devices Group,
Universidade Federal de São Carlos
, São Carlos, SP 13565-905, Brazil
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C. Speglich;
C. Speglich
1Department of Physics and Physical Engineering, Materials and Devices Group,
Universidade Federal de São Carlos
, São Carlos, SP 13565-905, Brazil
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V. A. G. Rivera;
V. A. G. Rivera
1Department of Physics and Physical Engineering, Materials and Devices Group,
Universidade Federal de São Carlos
, São Carlos, SP 13565-905, Brazil
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C. A. Cardoso;
C. A. Cardoso
1Department of Physics and Physical Engineering, Materials and Devices Group,
Universidade Federal de São Carlos
, São Carlos, SP 13565-905, Brazil
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H. Pardo;
H. Pardo
2Crystallography, Solid State and Materials Laboratory (Cryssmat-Lab), DEQUIFIM, Facultad de Química,
Universidad de la República
, P.O. Box 1157, CP 11800, Montevideo, Uruguay
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A. W. Mombrú;
A. W. Mombrú
2Crystallography, Solid State and Materials Laboratory (Cryssmat-Lab), DEQUIFIM, Facultad de Química,
Universidad de la República
, P.O. Box 1157, CP 11800, Montevideo, Uruguay
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F. M. Araújo-Moreira
F. M. Araújo-Moreira
b)
1Department of Physics and Physical Engineering, Materials and Devices Group,
Universidade Federal de São Carlos
, São Carlos, SP 13565-905, Brazil
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a)
Electronic mail: sergei@df.ufscar.br.
b)
Electronic mail: faraujo@df.ufscar.br.
J. Appl. Phys. 106, 116101 (2009)
Article history
Received:
September 17 2009
Accepted:
October 23 2009
Citation
S. Sergeenkov, N. S. Souza, C. Speglich, V. A. G. Rivera, C. A. Cardoso, H. Pardo, A. W. Mombrú, F. M. Araújo-Moreira; Manifestation of finite temperature size effects in nanogranular magnetic graphite. J. Appl. Phys. 1 December 2009; 106 (11): 116101. https://doi.org/10.1063/1.3264571
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