Quantifying the critical thickness of electron hybridization in spintronics materials

In the rapidly growing field of spintronics, simultaneous control of electronic and magneticfi properties is essential, and the perspective of ‘building’ novel phases is directly linked to the ability of controlling the tuning parameters, e.g., thickness and doping, in both homo- and heterostructures. Looking at the relevant parameters in interface-driven spintronics, the reduced symmetry at a surface and/or interface corresponds to a severe modification of the overlap of electron orbitals on different sites, i.e., a change of electron hybridization that substantially influences the band structure, even turning a metal into an insulator or suppressing/enhancing a ferromagnetic state. Here we report a chemically and magnetically sensitive depth-dependent analysis of two paradigmatic spintronics systems, namely La1-xSrxMnO3 and (Ga,Mn)As. Supported by cluster calculations obtained in the Anderson impurity model, we find a crossover between surface and bulk in electron hybridization/correlation and we identify a spectroscopic fingerprint of bulk metallic character and ferromagnetism vs. depth. The critical thickness and the gradient of electron hybridization are directly measured, setting an intrinsic limit of 3 and 10 unit cells from the surface, respectively for (Ga,Mn)As and La1-xSrxMnO3, for fully restoring bulk electronic properties. Our results give new insights into the design and engineering of interface-basedspintronics devices.