Antiferromagnetic interlayer coupling of (111)-oriented La_0.67Sr_0.33MnO₃/SrRuO₃ superlattices

We report a strong antiferromagnetic (AFM) interlayer coupling in ferromagnetic La_0.67Sr_0.33MnO₃/SrRuO₃ (LSMO/SRO) superlattices grown on (111)-oriented SrTiO₃ substrate. Unlike the (001) superlattices for which the spin alignment between LSMO and SRO is antiparallel in the in-plane direction and parallel in the out-of-plane direction, the antiparallel alignment is observed along both the in-plane and out-of-plane directions in the present sample. The low temperature hysteresis loop demonstrates two-step magnetic processes, indicating the coexistence of magnetically soft and hard components. Moreover, an inverted hysteresis loop was observed. Exchange bias tuned by the temperature and cooling field was also investigated, and positive as well as negative exchange bias was observed at the same temperature with the variation of the cooling field. A very large exchange field (H_EB) was observed and both magnitude and sign of the H_EB depend on the cooling field, which can be attributed to an interplay of Zeeman energy and AFM coupling energy at the interfaces. The present work shows the great potential of tuning a spin texture through interfacial engineering for the complex oxides whose spin state is jointly determined by strongly competing mechanisms.