Critical and geometric properties of magnetic polymers across the globule-coil transition

We study a lattice model of a single magnetic polymer chain, where Ising spins are located on the sites of a lattice self-avoiding walk in d=2. We consider the regime where both conformations and magnetic degrees of freedom are dynamic, thus the Ising model is defined on a dynamic lattice, and conformations generate an annealed disorder. Using Monte Carlo simulations, we characterize the globule-coil and ferromagnet-to-paramagnet transitions, which occur simultaneously at a critical value of the spin-spin coupling. We argue that the transition is continuous---in contrast to d=3 where it is first-order.

Our results suggest that at the transition the metric exponent takes the theta-polymer value ν=4/7 but the crossover exponent φ≈0.7, which differs from the expected value for a θ-polymer.