Phase diagram of magnetic polymers

We consider polymers made of magnetic monomers (Ising or Heisenberg-like) in a good solvent. These polymers are modeled as self-avoiding walks on a cubic lattice, and the ferromagnetic interaction between the spins carried by the monomers is short-ranged in space. At low temperature, these polymers undergo a magnetic induced first order collapse transition, that we study at the mean field level. Contrasting with an ordinary Theta point, there is a strong jump in the polymer density, as well as in its magnetization. In thr presence of a magnetic field, the collapse temperature increases: while the discontinuities decrease. Beyond a multicritical point, the transition becomes second order and Theta-like. Monte Carlo simulations for the Ising case are in qualitative agreement with these results