Canted antiferromagnetic ground state in Sr3Ir2O7

We have characterized the ground state of Sr3Ir2O7 by performing measurements of electrical resistivity, magnetic susceptibility, magnetization, specific heat and electron diffraction ( ED). Polycrystalline samples of Sr3Ir2O7 have been synthesized by using a high- pressure technique. Sr3Ir2O7 exhibits weak ferromagnetism with a small ferromagnetic component ( 2 x 10(-3) mu(B)/Ir) below T-C similar to 280 K. The temperature dependence of the electrical resistivity. shows semiconducting- like behaviour; d rho/dT < 0 with an anomaly near T-C. From the result for specific heat, a lambda-type anomaly appears at TC, indicating a second- order phase transition. The ED patterns below and above TC imply that there is no evidence of structural phase transition at TC with substantial symmetry change. These experimental results exclude the possibility of ferromagnetic ordering with extremely small magnetic moments below TC. Taking into account that certain pairs of Ir4+ ions lose the centre of inversion, this leads to the conclusion that the weak ferromagnetism is derived from canted antiferromagnetism.