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Volume 106, Issue 11, 01 December 2009
106(2009); http://dx.doi.org/10.1063/1.3264571View Description Hide Description
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.