Spin reorientation tuned by oxygen content in the double perovskite Sr2YRuO6

Sr2YRuO6 is a double perovskite with a complex magnetic state, including non-collinear arrangement of the ruthenium moments and spin re-orientation. One open issue is the possibility of magnetization reversal leading to an apparent diamagnetic response. In this work we show that when the oxygen content is reduced, the susceptibility curve develops a sharp minimum, in contrast to the broad maximum observed for a well-oxygenated sample. However, the magnetization remains positive regardless of the thermomagnetic history. We explain this effect in terms of the reversal of a net ferromagnetic moment in opposition to the applied field and by a spatial average of the contribution of the grains in the polycrystalline sample. The reversal is observed in deoxygenated samples because the delicate balance between competitive ferromagnetic and antiferromagnetic interactions is altered. The significant reduction of the antiferromagnetic correlations at high temperatures, as evidenced by the magnetic contribution to the specific heat, is consistent with this scenario. The role of the oxygen content is conclusively confirmed by reversibility after re-oxygenation. Our results suggest that Sr2YRuO6−x might host inhomogeneous superconductivity due to local enhancement of spin fluctuations in the neighborhood of the oxygen vacancies.