Magnetic phase diagram of the triangular lattice antiferromagnet CuFe1-xAlxO2

We have performed magnetic susceptibility, neutron diffraction and specific heat measurements on the triangular lattice antiferromagnet CuFe1-xAlxO2 for x <= 0.050. A magnetic phase diagram for temperature vs x was determined. The various magnetically ordered phases compete with each other on the x-T magnetic phase diagram, strongly suggesting that the quasi-Ising orderings are stabilized in CuFeO2 with delicate balance of competing interactions. In the ground state for 0.014 < x < 0.030 [low-temperature (LT) phase], the magnetic structure consists of two magnetic modulations with slightly different wave numbers. Moreover, we observed the change in magnetic diffraction patterns in the LT phase, which corresponds to a crystallographic distortion from "hexagonal" to "orthorhombic", suggesting that the Ising anisotropy in CuFeO2 is closely related to the crystallographic distortion.