Unusual exchange bias in Sr₂FeIrO₆/La_0.67Sr_0.33MnO₃ multilayer

Here, we study interface induced magnetic properties in a 3d-5d based multilayer made of La_0.67Sr_0.33MnO₃ and double perovskite Sr₂FeIrO₆, respectively. Bulk La_0.67Sr_0.33MnO₃ is metallic and shows ferromagnetic (FM) ordering above room temperature. In contrast, bulk Sr₂FeIrO₆, is an antiferromagnet (AFM) with a Néel temperature around 45 K ([Formula: see text]) and exhibits an insulating behavior. Two set of multilayers have been grown on SrTiO₃ (1 0 0) crystal with varying thickness of FM layer. A multilayer with equal thickness of La_0.67Sr_0.33MnO₃ and Sr₂FeIrO₆ (∼10 nm) shows exchange bias (EB) effect both in conventionally field cooled (FC) as well as in zero field cooled (ZFC) magnetic hysteresis measurements which is rather unusual. The ZFC EB effect is weakened both with increasing maximum field during initial magnetization process at low temperature and with increasing temperature. Interestingly, a multilayer with reduced thickness of La_0.67Sr_0.33MnO₃ (∼5 nm) does not exhibit ZFC EB phenomenon, however, the FC EB effect is strengthened showing much higher value. We believe that an AFM type exchange coupling at the interface and its evolution during initial application of magnetic field causes this unusual EB in present multilayers.