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Frustrated Spin Systems

The spin systems in which the local magnetic interactions cannot be optimized in such a way to achieve a unique global energy minimization are known the magnetic frustrated systems. Magnetic frustration could be arisen as the result of the geometry of the lattice on which the spins are located, or the competition between different exchange interactions. Geometric frustration usually exists in the anti-ferromagnets, composed of triangular units such as triangular, kagome and pyrochlore lattices. The competition between the first and second anti-ferromagnetic exchange interactions can also lead to frustration in the systems which may not be geometrically frustrated, like square and honeycomb lattices.

The main interests of our group is the study of novel states emerging at classical and quantum level in these systems, such as classical and quantum liquid states, valence bond orderings, Coulomb phase and possible phase transitions arising due to the introduction of perturbations such as anisotropies. We employ abinitio methods, based on Density Functional Theory (DFT), to find effective spin Hamiltonian for the real frustrated magnetic materials. Then, the ground state and excited states of the obtained Hamiltonian is investigated by various methods, namely, Monte Carlo simulation, Spin wave analysis, exact diagonalization etc, and the results is compared with the experiments.

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