Competition between Spin Nematic and Spin Density Wave Orders in Spatially Anisotropic Frustrated Magnets in Magnetic Fields

Magnetic multipolar order including spin nematic order is one of the current topics in frustrated magnetism. Recently, frustrated spin chains with ferromagnetic nearest-neighbor coupling J1 and antiferromagnetic next-nearest-neighbor one J2 have been theoretically shown to exhibit multipolar quasi long-range orders in the wide region of J1/J2 as an external magnetic field is applied. In addition, it is known that several kinds of quasi one-dimensional cuprates can be described by this J1-J2 spin chain. Particularly, a recent experiment shows that LiCuVO4, one of the cuprates, possesses a new phase near saturation and it is expected to be a spin nematic ordered phase. Motivated by these results, we have completed the field-temperature phase diagram for spatially anisotropic magnets consisting of weakly coupled J1-J2 spin chains, by making use of accurate results of the single J1-J2 spin chain. The phase diagram contains spin nematic and spin-density-wave ordered phases, and these two orders compete with each other. We will discuss some universal features of the phase diagram and the relevance of our result to LiCuVO4.