Uses of classical Monte Carlo Technique in Complex Magnetism Jung Hoon Han(Sungkyunkwan Univ.) Several examples of using classical Monte Carlo simulations to study complex phases of magnetism will be discussed. The first is the derivation of the phase diagram of the J1-J2 planar spin model where J2 is the strength of biquadratic spin exchange. A novel magnetism-free chiral-nematic phase is shown to exist on a triangular lattice. The second example is the multiferroic BiMn2O5 compound, for which a complex spin-lattice model was used to demonstrate the existence of a critical end point. Final example is the Heisenberg-Dzyaloshinkii-Moriya model of ferromagnet, appropriate for chiral magnets such as MnSi, where the Monte Carlo simulation was employed to show the existence of field-induced multiple spiral phase, also known as the Skyrme crystal phase. For the last two examples I will also discuss the relevant experiments, which helps highlight the utility and importance of this old technique in modern magnetism research.