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 × 10⁻³ μ_B/Ir) below T_C∼280 K. The temperature dependence of the electrical resistivity ρ shows semiconducting-like behaviour; dρ/dT<0 with an anomaly near T_C. From the result for specific heat, a λ-type anomaly appears at T_C, indicating a second-order phase transition. The ED patterns below and above T_C imply that there is no evidence of structural phase transition at T_C with substantial symmetry change. These experimental results exclude the possibility of ferromagnetic ordering with extremely small magnetic moments below T_C. 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.