Characterization of the interfacial structure and perpendicular magnetic anisotropy in CoFeB‐MgO structures with different buffer layers

Abstract

In this study, we describe the deposition of Hf and Mo metal layers individually on Ta to compose new buffer layers, ie, Ta/Hf and Ta/Mo, where CoFeB/MgO stacks are deposited using magnetron sputtering. The synthesised Ta/Hf buffer has higher surface roughness, while the Ta/Mo buffer has lower surface roughness as compared with the Ta buffer. The surface roughness of the buffer appears to influence the interface of the subsequently deposited layers, resulting in rougher or smoother CoFeB/MgO interfaces. Additionally, we present a report on the magnetic properties of Ta, Ta/Hf, and Ta/Mo buffer samples. As the annealing temperature is below 200°C, the saturation magnetisation (Ms) values for all buffer layers increase at similar rates, whereas the effective magnetic anisotropy energy (K eff ) values increase at varying rates. After annealing at 350°C, K eff reaches its maximum value for Ta/Hf and Ta/Mo buffer layers, whereas the CoFeB/MgO interface width decreases to a minimum value. The width increases as the annealing temperature is increased over 350°C, and K eff gradually decreases with increase in the annealing temperature. The CoFeB/MgO interface width is primarily dependent on the buffer/CoFeB interface width, which is a critical parameter to obtain high perpendicular magnetic anisotropy (PMA) and high-quality films. This work provides perspectives for understanding and controlling PMA from the viewpoint of interfacial structure. Subsequent studies found that the observed PMA in Ta/CoFeB/MgO sandwiches originates primarily from the CoFeB/MgO interface. 1,[4][5][6][7] More recently, the CoFeB/nonmagnetic metal counter interface has been reported to also affect the perpendicular anisotropy originating from CoFeB/MgO. [7][8][9][10][11][12] Typically, the thickness of CoFeB must be less than 1.5 nm in order to obtain a perpendicular easy axis. 1,8,12 Owing to the limitations on the required thickness, any influence of the counter interfaces of CoFeB with the buffer layer and MgO on the structural, morphological, and PMA properties of CoFeB layers warrants careful investigation.In the X-ray reflectivity (XRR) measurement conducted herein, we use Cu as the anode material and an X-ray wavelength of 0.154 nm to investigate the interface till submonolayer resolution in terms of roughness and/or intermixing. 13 XRR and atomic force microscopy (AFM) measurements were used to analyse changes in the interface structure during annealing.

Investigation of Cap and Buffer Layer Effect in Co/Ni Thin Films by Ferromagnetic Resonance Technique

“…Various experimental studies for multilayer magnetic nanostructures have also been done in the literature such as PMA in magnetic thin film with optimal Mo buffer layer (Saravanan et al, 2018), influence of anisotropy on magnetoresistance in magnetic multilayer structures (Prudnikov et al, 2019), biomedical applications (Peixoto et al, 2020), Skyrmions at zero magnetic field (Ho et al, 2019), Ta buffer layer effect in Pt/Co/Pt trilayers (Mukhopadhyay et al, 2020), magnetic nanowires applications (Piraux, 2020), magnetic anisotropy and thermal stability (Wang et al 2013), giant magnetoresistance effect (Kalayci 2022; Lee et al 2018;Milyaev et al 2019), CoFeB-MgO structures with different buffer layers (Shi et al, 2018), Co/Ni multilayers with different sublayer thicknesses (You et al, 2012).…”

Perpendicular Magnetic Anisotropy and Hydrogenation-Induced Magnetic Change of Ta/Pd/CoFeMnSi/MgO/Pd Multilayers

“…On the other hand, Pd as a noble metal is commonly used for realizing the perpendicular magnetic anisotropy (PMA) owing to the d - d electron orbital hybridization at the interfaces of Pd/ferromagnetic layer. This critical interfacial effect of electron orbital hybridization is very sensitive to the interfacial strain or stress [ 8 ], which could be brought in through the volume evolution of noble metal. Therefore, high sensitivity of hydrogen-induced magnetic change could be expected from the PMA film with Pd layer by making use of the strong interfacial dependences of perpendicular magnetic anisotropy.…”

Skyrmions Under Control—FIB Irradiation as a Versatile Tool for Skyrmion Circuits

“…However, not only the materials but also annealing, ion and electron beam irradiation can drastically alter the magnetic properties of thin-film systems. [17][18][19][20][21][22][23] Irradiation has already been successfully employed to localize skyrmion appearance in magnetic media. [24,25] Irradiation techniques enable the patterning of magnetic media on the nanometer scale and thus circumvent the highly complex physical structuring in this size range.…”