# Why magnetic monopole found in spin ice don't modify the Maxwell's Equations?

Magnetic monopole predicted by Dirac nearly a century ago was found in spin ice as quasi-particle(2). My question is Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? (I know they are not elementary particles but quasi-particles.)

(1) Dirac, P. A. M. Quantised singularities in the electromagnetic field. Proc. R. Soc. A 133, 60–72 (1931)

(2) Castelnovo, C., Moessner, R. & Sondhi, S. Magnetic monopoles in spin ice. Nature 451, 42–45 (2008).

1. They are not elementary particles as anticipated by P.M.Dirac. But the concept comes from the non-zero divergence of magnetization field. In electrostatics when you have $\nabla\cdot \mathbf{P}$ (polarization vector) not equal to zero, you have a concept of bound electric charge since $\rho = -\nabla\cdot\mathbf P$. Similarly when you have non-zero divergence of Magnetization vector , you have concept of magnetic monopole like $\rho=-\nabla\cdot \mathbf M$. In spin ice w.r.t. center of each tetrahedra when you have 3in1out or 3out1in spin configuration, net divergence of magnetization is not zero locally, and you have a monopole or an antimonopole respectively.
2. Even you have a monopole you don't have to modify Maxwell's eqn because here magnetic intensity and magnetization serve as source and sink of magnetic line of force. Thats why even $\nabla \cdot \mathbf B = 0$ you have $\nabla\cdot \mathbf H=-\nabla \cdot\mathbf M$ (because $\mathbf B = \mu_0\cdot(\mathbf H+\mathbf M)$). Furthermore, you don't have a concept of isolated monopole or antimonopole there, with a flip of single spin always generate a monopole-antimonopole there which interacts through long range dipolar interaction or Coloumb's Law.