Phase diagram of magnetic polymers

TL;DR

This paper investigates the phase diagram of magnetic polymers, revealing a magnetic field-dependent first-order collapse transition at low temperatures and a second-order transition beyond a multicritical point, supported by mean field analysis and Monte Carlo simulations.

Contribution

It introduces a mean field model for magnetic polymers showing a magnetic field-dependent collapse transition and confirms findings with Monte Carlo simulations.

Findings

First-order collapse transition at low temperature with magnetization jump

Collapse temperature increases with magnetic field, transition becomes second order beyond a multicritical point

Monte Carlo simulations qualitatively agree with mean field results

Abstract

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 the 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.