Interplay between the lattice and spin degrees of freedom in (Sr _1-xCa_x)₃Ru₂O₇

The (Sr_1-xCa_x)₃Ru₂O₇ solid solution series exhibits complex magnetic ground states, ranging from an itinerant metamagnetic state, to a quasi-two-dimensional (2D) heavy-mass nearly ferromagnetic (FM) state, and finally to a long-range antiferromagnetically ordered state. In this paper, we investigate the evolution of structural distortion and magnetic anisotropy with Ca content in this material system. Our results show that both the magnetic phase transitions and magnetic anistropy of this system couple with the evolution of structure distortion. The transformation from the itinerant metamagnetic to the nearly ferromagnetic state is accompanied by an increase in the rotation of the RuO6 octahedra while the transition from 2D nearly FM state to the antiferromagnetic state coincides with the onset of tilting of the RuO6 octahedra. Octahedral tilting also causes magnetic anistropy. These results demonstrate that the lattice and spin degrees of freedom are coupled in (Sr_1-xCa_x)₃Ru ₂O₇.