Manifestation of finite temperature size effects in nanogranular magnetic graphite

Details Manifestation of finite temperature size effects in nanogranular magnetic graphite Manifestation of finite temperature size effects in nanogranular magnetic graphite

2009-12-29

arxiv.org/abs/0912.5347v1

Journal of Applied Physics 106, 116101 (2009)

Physics

Condensed Matter

Materials Science

Scientific paper

10.1063/1.3264571

In addition to the double phase transition (with the Curie temperatures T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the magnetization is observed in the bulk magnetic graphite (with an average granular size of L=10nm), which is attributed to manifestation of the size effects below the quantum temperature. 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 J=12meV (which defines the intragranular Curie temperature T_C) and proximity mediated interactions between neighboring grains (through potential barriers created by thin layers of non-magnetic graphite) with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and characteristic length, respectively.

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