In-situ Annealing Study of Pt/Co Interface and its Effect on Perpendicular Magnetic Anisotropy of Pt/Co/MgO

Heavy metal (HM)/ferromagnetic metal (FM)/oxide structures, such as Ta/CoFeB/MgO and Pt/Co/MgO, have been the focus of numerous studies owing to the enhanced perpendicular magnetic anisotropy (PMA) and large spin orbit torque (SOT). Post-annealing treatment is often necessary in fabricating devices involving these multilayer structures because it does not only enhance both the PMA of the magnetic layer and transport properties of the devices but also ensures thermal stability [1]–[4]. Previous studies often annealed the entire structure together and therefore it was difficult to evaluate the respective role of the top and bottom interfaces separately. To address this issue, in this study we investigated the annealing effect of Pt/Co/MgO using an in-situ deposition and measurement setup which allows to study the annealing effect of the two interfaces separately. Specifically, we deposited Pt/Co, Pt/Co/MgO and Pt/Co/Mg step by step and in between we annealed the samples between 100°C - 300°C and measured the anomalous Hall effect (AHE) in-situ. Deposition and measurement were both conducted in an ultra-high vacuum (UHV) system without exposing the sample to ambient. The samples were deposited on $2 \times 2$ mm ² square wafers to fit the magnetic holder which provides a perpendicular magnetic field. Layers of Ta(1.5)/Pt(3) (the number inside the parentheses indicates the thickness in nm) were first deposited ex-situ using dc magnetron sputtering and then quickly loaded into the UHV system, followed by the deposition of Co or Mg using Knudsen cell cells in a preparation chamber. After deposition, the samples were transferred in-situ to the nanoprobe chamber for oxygen exposure and AHE measurements. The oxygen exposure is precisely controlled by a low-dosage oxygen source. The AHE measurements were conducted by probing the four corners of the samples using the nanoprobes.