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Transport properties and magnetic interactions in acceptor-type magnetic graphite intercalation compounds

1989; American Physical Society; Volume: 40; Issue: 1 Linguagem: Inglês

10.1103/physrevb.40.622

1095-3795

N.-C. Yeh, K. Sugihara, M. S. Dresselhaus, G. Dresselhaus,

Advanced Battery Materials and Technologies

Results on the resistivity of stage-1 and stage-2 ${\mathrm{CoCl}}_{2}$ graphite intercalation compounds (GIC's) as a function of temperature (T) and magnetic field (H) are reported. The anomalies observed in the resistivity measurements at the magnetic phase transitions are explained by an interaction based on \ensuremath{\pi}-d electron coupling. The contrasts in the T and H dependences of the resistivity between the stage-1 and stage-2 compounds for T${T}_{\mathrm{cl}}$ and H${H}_{c2}$ are attributed to the different correlation lengths in the c-axis antiferromagnetic ordering. The magnitude of the interplanar antiferromagnetic coupling constant (J') in stage-1 ${\mathrm{CoCl}}_{2}$ GIC's and the \ensuremath{\pi}-d exchange coupling constant (${J}_{\ensuremath{\pi}\mathit{\ensuremath{-}}d}$) are estimated from the transport measurements. Magnetic exchange mechanisms are proposed by considering the relative contributions of the superexchange, dipole-dipole, and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. We conclude that the superexchange interaction is the dominant magnetic interplanar coupling mechanism in pristine ${\mathrm{CoCl}}_{2}$ and stage-1 ${\mathrm{CoCl}}_{2}$ GIC's, and is of comparable importance to the dipole-dipole interaction in stage-2 compounds. The dipole-dipole interaction is the dominant mechanism in higher stage GIC's (n\ensuremath{\ge}3). The RKKY interaction is always found to be negligibly small, due to the quasi-two-dimensional electronic properties of these acceptor GIC's.