Spin nematics in frustrated spin-dimer systems with bilayer structure

Abstract

We study frustrated spin-1/2 dimer systems with bilayer structure in two dimensions, where spins are ferromagnetically coupled in dimers. Our model includes frustrated two-spin exchange interactions as well as four-spin interaction. We pay particular attention to the spin nematic phase, which does not exhibit any magnetic (spin-dipole) order but has a spin-quadrupolar long-range order. Employing a perturbation calculation, a mean-field approximation, and a numerical manyvariable variational Monte Carlo method, we determine ground-state phase diagrams on various two-dimensional lattices. It is found that the model exhibits the spin nematic phase with ferroquadrupolar order in a wide parameter region, in addition to conventional magnetically-ordered phases. In particular, it is shown that even when the four-spin interaction is absent, frustrated two-spin exchange interactions can realize the spin nematic phase as a result of strong interdimer correlations. It is also found that the phase transitions between the spin nematic phase and antiferromagnetic phases can be continuous. Furthermore, we present some exact arguments that various phases including the spin nematic phase and the vector chiral (p-type nematic) phase emerge from an SU(4) symmetric point in the model by the addition of appropriate perturbative interactions. The spin nematic phase generated from the SU(4) point is connected with the spin nematic phase numerically found in the system with only two-spin interactions.arXiv:1907.08373v1 [cond-mat.str-el] 19 Jul 2019 and nontrivial degeneracies in the mean-field solutions are discussed in Appendices A, B, and C, respectively. J 4 J d J J 2. Transition between spin-nematic and A-type AFM phases

Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy–Yb): A Family of Rare-Earth-Based Layered Triangular Lattice Magnets

“…In this respect, very recently, one route for realizing the QSL state based on the dominant Ising-type correlations instead of Heisenberg-type interactions has been experimentally investigated on the triangular-lattice NdTa 7 O 19 , which is instructive to search for novel magnetic states, but limited materials have been identified. From the structural viewpoint, the stacking order of triangular-lattice multilayers as well as the formation of bilayer structures have been proposed to introduce magnetic frustration and generate diverse exotic magnetic states. , Therefore, designing new RE-triangular-lattice materials with different stacking structures and magnetic anisotropy is highly desirable to enrich the exotic magnetic phenomena.…”