The g-factor for free electron is 2,002319. what mechanisms give the shift in g-factor. We have for Diamond the g-factor is 2,0027 for broken bond of C-C. For material from graphite (with different content of graphite) like coal,anthracite, g-factor can be from 1,9999 to 2,0040. How can explain these situations?
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The shift in g-factor (ESR) or resonance frequency (NMR) can be explained by the local ordering/local magnetic field around an atom. Keyword: Spin-orbit interaction. Therefore minor changes to the amount of defects/strain/crystallinity can be responsible for a g-factor shift. Especially in graphite the anisotropy of the g-factor needs to be considered.
Article Effect of lattice compression on -factor in graphite
g factor ~2 is for free electron creates by Bohr magneton. Increase of g-factor depends on crystal field. Asymmetry of the field makes difference between parallel and perpendicular g-factor. Crystal field degeneration will change total spin of electron and degenerated energy state of electron of d-orbital will deduce the spin transition +_1/2,+_3/2 etc.
The free electron g-factor or the Lande’ g-factor is a dimensionless quantity and is equal to 2.0023. The g-factor can be modified by spin-orbit interaction. For systems with large spin-orbit interaction, it could be very high. For example, for narrow gap semiconductors like PbTe and its alloy, Pb_1-xSn_xTe, its magnitude is 10 to 50 times larger[1]than the free electron value. In these systems the spin-orbit interaction has pronounced effects. In diluted magnetic semiconductors, in addition to spin-orbit interaction, the interaction between free electrons/holes with localized moments can also modify the g-factor. It is called s-d or sp-f hybridization.[2,3]. The g-factor can be determined from NMR and EPR experiments. The dependence of the EPR shift on the g-factor is described by us [4,5] for diluted magnetic semiconductors, Pb_1-xMn_xTe and Sn_1-xMn_xTe. The g-factors can also be anisotropic. Graphite being a layered material, the g-factor could be anisotropic.
1. R. L. Hota and G. S. Tripathi, . Theory of effective g-factors in ternary semiconductors: application to Pb1-xSnxTe, J. Phys. Condens. Matter 3 (1991) 6299.
2. R. L. Hota, G. S. Tripathi and J. N. Mohanty, Theory of effective g-factors and effective masses in diluted Magnetic Semiconductors, Phys. Rev. B47 (1993) 9319.
3. R. C. Patnaik, and G. S. Tripathi, Spin-orbit and sp-f hybridization induced anisotropy of g-factors and effective masses in Pb_1-xEu_xTe, Solid State Commun. 112(1999) 669.
4. R. K. Das, G. S. Tripathi and P. K. Misra, Theory of spin-EPR shift: Application to Pb_1-xMn_xTe, Phys. Rev.B72(2005) 035216.
5. K. Dash and G. S. Tripathi, Theory of spin- EPR shift of Mn2+ in p-Sn_1-xMn_xTe Semicond. Sci. Technol. 24(2009) 11504.
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