In this work, graphene-based systems that are described by mixed spin-3/2 and spin-5/2 are studied using the . A diagram of the structure is shown bellow:

enter image description here

The Hamiltonian used is:

\begin{equation} \tag{1} {H_I} = - J\sum\limits_{\left\langle {i,j} \right\rangle } {{S_i}{\sigma _j}} - {J_\sigma }\sum\limits_{\left\langle {i,j} \right\rangle } {{\sigma _i}{\sigma _j}} - {J_S}\sum\limits_{\left\langle {i,j} \right\rangle } {{S_i}{S_j}} - {K_v}\left( {\sum\limits_i {S_i^2} + \sum\limits_j {\sigma _j^2} } \right). \end{equation}

Here $\left\langle {i,j} \right\rangle$ refers to the sum over the nearest neighbors pairs, $\left[ i,j \right]$ means sum over the next-nearest neighbors pairs, $J$, $J_\sigma$ and $J_S$ are the exchange interaction constants between sites $\sigma−S$, $\sigma−\sigma$ and $S−S$, respectively (see diagram above), and $K_v$ is the crystal field anisotropy constant. The spins moments can take values $\sigma = ±3/2,±1/2$ and $S=±5/2,±3/2,±1/2$.

How are $J$, $J_\sigma$, $J_S$, $\sigma$ and $S$ chosen?

  • $\begingroup$ It depends what behavior you are interested in. Are you comparing to an experimental system? Another numerical model? $\endgroup$ – taciteloquence Mar 23 at 17:55
  • $\begingroup$ You would consider S to be the number of unpaired electron on your magnetic atom, typically. For eg, if you have an Fe atom with a moment of 3 bohr magneton, S would just be 3*(1/2). If you can't eyeball 'S', you can simply infer it from your DFT calculation. All other parameters in your question can be estimated through first-principles, through DFT. I just answered a question regarding the calculation of Js, hopefully that points you in the right direction: mattermodeling.stackexchange.com/questions/1548/… $\endgroup$ – Xivi76 Mar 23 at 20:23
  • $\begingroup$ @Xivi76 As this is one of our longest standing unanswered questions, do you think you'd be able to turn this into an answer at some point (if you have time)? $\endgroup$ – Nike Dattani Apr 18 at 2:59

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