Tuning In-Plane Magnetic Anisotropy and Interfacial Exchange Coupling in Epitaxial La_2/3Sr_1/3CoO₃/La_2/3Sr_1/3MnO₃ Heterostructures

Abstract

Controlling the in-plane magnetocrystalline anisotropy and interfacial exchange coupling between ferromagnetic (FM) layers plays a key role in next-generation spintronic and magnetic memory devices. In this work, we explored the effect of tuning the magnetocrystalline anisotropy of La_2/3Sr_1/3CoO₃ (LSCO) and La_2/3Sr_1/3MnO₃ (LSMO) layers and the corresponding effect on interfacial exchange coupling by adjusting the thickness of the LSCO layer (t_LSCO). The epitaxial LSCO/LSMO bilayers were grown on (110)_o-oriented NdGaO₃ (NGO) substrates with a fixed LSMO (top layer) thickness of 6 nm and LSCO (bottom layer) thicknesses varying from 1 to 10 nm. Despite the small difference (∼0.2%) in lattice mismatch between the two in-plane directions, [001]_o and [11̅0]_o, a pronounced in-plane magnetic anisotropy was observed. Soft X-ray magnetic circular dichroism hysteresis loops revealed that for t_LSCO ≤ 4 nm, the easy axes for both LSCO and LSMO layers were along the [001]_o direction, and the LSCO layer was characterized by magnetically active Co²⁺ ions that strongly coupled to the LSMO layer. No exchange bias effect was observed in the hysteresis loops. In contrast, along the [11̅0]_o direction, the LSCO and LSMO layers displayed a small difference in their coercivity values, and a small exchange bias shift was observed. As t_LSCO increased above 4 nm, the easy axis for the LSCO layer remained along the [100]_o direction, but it gradually rotated to the [11̅0]_o direction for the LSMO layer, resulting in a large negative exchange bias shift. Therefore, we provide a way to control the magnetocrystalline anisotropy and exchange bias by tuning the interfacial exchange coupling between the two FM layers.