Geometric frustration in Mott insulators permits perturbative electron fluctuations controlled by local spin configurations [1]. The simplest example is an equilateral triangle, “trimer”, of spins with S = 1/2, where low-energy degrees of freedom consist of built-in magnetic and electric dipoles arising from the frustrated exchange interaction. Such trimers, when weakly coupled, can be used to build multiferroics by design [2]. An organic molecular magnet known as TNN [3], with three S = 1/2 nitronyl nitroxide (NN) radicals in a perfect C3 symmetric arrangement, is an ideal building block, as was demonstrated by recent experiments on a single crystal comprising TNN and CH3CN. The fascinating thermodynamic phase diagram of this molecular crystal, TNN·CH3CN, is in excellent agreement with our theory, which predicts multiferroic behavior and strong magnetoelectric effects arising from an interplay between magnetic and orbital degrees of freedom [4]. Our study thus opens up new avenues for designing multiferroic materials using frustrated molecular magnets.

References:
[1] L. N. Bulaevskii, C. D. Batista, M. V. Mostovoy, and D. I. Khomskii, Phys. Rev. B 78, 024402 (2008).
[2] Y. Kamiya and C. D. Batista, Phys. Rev. Lett. 108, 097202 (2012).
[3] Y. Nakano et al., Polyhedron 24, 2147 (2005).
[4] Y. Kamiya et al., in preparation.