Magnetic transitions in helimagnets

The nature of the phase transition in body-centered-tetragonal helimagnets is studied for the first time by extensive Monte Carlo simulations with both XY and Heisenberg spins. In the XY case, evidence of a first-order transition associated with the loss of chiral ordering is found in addition to a second-order transition due to the breaking of basal plane ordering at a higher temperature. The temperature range of the intermediate phase depends on the turn angle Q so that for some range of Q these two transitions coincide. In the Heisenberg case, only one second-order transition is found. Critical exponents {α} and {ν} associated with the second-order transition are calculated using finite-size scaling. Discussion and comparison with theories and experiments are given.