The doping effect of Al 2 O 3 on the high-frequency electrical and magnetic properties of CoFeB soft magnetic thin films
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The doping effect of Al2O3 on the high-frequency electrical and magnetic properties of CoFeB soft magnetic thin films deposited on Si substrates using RF magnetron sputtering technique Muhammad Arif1 · Xiang Zhang1 · Muhammad Amir1 · Ghulam Muhammad Mustafa2 · Er Liu1 · Feng Xu1 Received: 24 April 2020 / Accepted: 28 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Soft magnetic thin films have drawn tremendous interests in high-frequency spintronics applications. Here we demonstrate the doping effect of Al2O3 on the high-frequency electrical and magnetic properties of CoFeB soft magnetic thin films by systematically investigating the dependences of exchange constant A, saturation magnetization Ms and damping constant α on the A l2O3 doping concentration. In contrast to the decreased exchange constant due to the non-magnetic doping, the electrical resistivity of CoFeB thin films is found to be increased by the doping of Al2O3, indicating the suppression of eddy current loss in high-frequency application. Moreover, we found that the product of Ms and α which determines the critical switching current density of CoFeB thin films first increases and then decreases with the increasing doping concentration of Al2O3. The presented results demonstrated that high doping concentration of Al2O3 in CoFeB thin films is beneficial for the high-frequency spintronics applications.
1 Introduction Soft magnetic thin films have received considerable attentions in high-frequency applications such as soft magnetic underlayers for perpendicular media, high density magnetic recording write heads operating in gigahertz (GHz) frequency range as well as thin-film wireless inductor cores [1–8]. Of specific interest is CoFeB thin films being intensively utilized in high-frequency spintronics devices due to their high spin polarization and low magnetic damping [9]. For instance, CoFeB thin film is employed in the magnetic random access memories (STT-MRAM) technology as the free layer to realize current-induced magnetic switching, in which the switching current Jc is determined by the product * Er Liu [email protected] * Feng Xu [email protected] 1
MIIT Key Laboratory of Advanced Metallic and Intermetallic Materials Technology, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, People’s Republic of China
Centre of Excellence in Solid State Physics, University of the Punjab, Lahore, Pakistan
2
of damping constant α and saturation magnetization Ms of the free layer ( Jc ∼ 𝛼Msn , n = 1 for out-of-plane magnetized system and n = 2 for in-plane magnetized system) [10, 11]. As such, tailoring α and Ms in CoFeB is crucial for the reduction of switching current and power consumption in STT-MRAM devices, which has been intensively studied and can be achieved by various strategies such as doping of metallic element in the CoFeB thin films [12]. However, the metallic doping on the other hand decreases the resistivity of CoFeB thereby in
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