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heavy metals (Pt, Ta, etc.) at the interface with ferromagnetic layers (FM) in systems exploiting spin-to-charge conversion effects. [1-4] However, there are several aspects to investigate. First, the role played by the specific chemical bonds and/or the presence of magnetically dead layers in affecting the spin-to-charge conversion efficiency is not completely understood. So, an investigation and optimization of the chemical, structural and magnetic properties of the FM/TI interfaces [2,5] is mandatory. Moreover, from the technological point of view, the growth of FM is usually conducted ex situ, after the synthesis of TI. The surface of the TI is often protected by a capping layer during the transfer, [6] but the efficient removal of such protective layer is not always easy, and the trade-off between benefits and criticalities in using an interlayer, is still under debate. We propose an alternative method to prepare the TI surface, consisting of a mild rapid thermal annealing (RTA) process prior to the FM deposition. In particular, our focus is the interface between Fe and the 3D-TI Sb 2 Te 3 produced by metal-organic chemical vapor deposition (MOCVD). [7] A previous study of as-deposited Fe/Sb 2 Te 3 heterostructures [8] revealed that only 50% of the Fe atoms at the interface (out of the 1 nm Fe in contact with Sb 2 Te 3) were coordinated in a pure ferromagnetic phase. The remaining part of the Fe atoms at the interface were found in paramagnetic configurations, detrimental in view of charge-to-spin interconversion. As compared to results available for similar systems, [9-12] a general bonding mechanism was suggested, involving the Fe atoms and the chalcogenide element in chalcogenidebased TI. Here, we demonstrate that the proposed RTA methodology improves the TI structural quality and promotes the Fe/Sb 2 Te 3 interface reconstruction, yielding the maximization of the ferromagnetic component in contact with the TI. To this aim, we combined interface-sensitive 57 Fe conversion electron Mössbauer spectroscopy (CEMS), grazing incidence X-ray diffraction and reflectivity (GIXRD/XRR), time-of-flight secondary ions mass spectrometry (ToF-SIMS) and vibrating sample magnetometry (VSM). The proposed method can be easily extended When coupled with ferromagnetic layers (FM), topological insulators (TI) are expected to boost the charge-to-spin conversion efficiency across the FM/TI interface. In this context, a thorough control and optimization of the FM/TI interface quality are requested. Here, the evolution of the chemical, structural, and magnetic properties of the Fe/Sb 2 Te 3 heterostructure is presented as a function of a rapid mild thermal annealing conducted on the Sb 2 Te 3-TI (up to 200 °C). While the bilayer is not subjected to any thermal treatment upon Fe deposition, the annealing of Sb 2 Te 3 markedly improves its crystalline quality, leading to an increase in the fraction of ferromagnetic Fe atoms at the buried Fe/Sb 2 Te 3 interface and a slight lowering of the magnetic coercivity of the Fe layer. The met...

Composite bilayer multiferroics combining ferroelectric (FE) and ferromagnetic (FM) thin‐film materials in a heterostructure and exhibiting magnetoelectric (ME) coupling effect are of great scientific and technological interest. In particular, electronically driven ME coupling implies that the FE polarization orientation affects the magnetic properties of FM at the interface with FE. Unlike metals, where the electric field penetrates over distances of 1–2 unit cells only, magnetic semiconductors, particularly doped EuS, with a ≈10 nm screening length appear a viable alternative. In addition, EuS exhibits a metal–insulator transition, thus offering new functionalities in nanoelectronics. Meanwhile, ultrathin polycrystalline films of doped HfO2, such as Hf0.5Zr0.5O2 (HZO), stabilized in the noncentrosymmetric orthorhombic phase, are identified as a novel class of robust FE materials. In this work, FM EuS integrated with FE HZO in a bilayered structure is promoted as a prospective composite multiferroic. The functionality of both ultrathin FM‐EuS and FE‐HZO layers as well as their compatibility in a capacitor configuration is demonstrated. The comprehensive information on the structural, chemical, and electronic properties of EuS/HZO interface endorses it as a promising medium for magnetoelectric coupling phenomena, particularly, the effect of polarization reversal in FE‐HZO on the magnetic and transport properties in EuS.