This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON MAGNETICS 1 Annealing Temperature Effects on Spin Hall Magnetoresistance in Perpendicularly Magnetized W/CoFeB Bilayers Thomas J. Peterson 1 , Protyush Sahu 1 , Delin Zhang 2 , Mahendra DC 1 , and Jian-Ping Wang 1, 2 1 School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 USA 2 Department of Electrical Engineering, University of Minnesota, Minneapolis, MN 55455 USA In this paper, we studied the annealing temperature effects on the spin Hall magnetoresistance (SMR) in W/CoFeB metallic bilayer systems. The bilayers were deposited using dc magnetron sputtering. The angle-dependent magnetoresistance was performed in a field of 8 T. The sample was rotated in the yz plane to isolate the SMR signal from the anisotropic magnetoresistance present in metallic systems. For annealing temperatures above 350 ◦ C, we found the SMR signal reduces with an increase in annealing temperature. By measuring the SMR for samples with a varying W layer thickness we were able to find that the spin Hall angle decreases as annealing temperature increases and the spin diffusion length for W remains almost constant with annealing temperature. Index Terms—Annealed W/CoFeB, annealing effects, spin Hall angle (SHA), spin Hall magnetoresistance (SMR). I. I NTRODUCTION D EVICES designed with spin Hall materials have been considerably studied as candidates for developing ultrahigh-density and ultralow-energy spin memory and logic devices, such as spin-orbit torques magnetic random access memory (SOT-MRAM) [1]. SOT devices typically consist of a thin ferromagnetic (FM) layer (e.g., CoFeB) sandwiched between a nonmagnetic heavy metal (NM) layer (e.g., W) and an oxide layer (e.g., MgO). The NM layer interface with the FM layer is responsible for the spin Hall effect (SHE), which is favorable for SOT necessary for SOT-MRAM. To decrease the power consumption of SOT-MRAM requires materials large spin Hall angle (SHA) and large effective anisotropy. In addi- tion, for the integration with the existing CMOS technology, spintronic devices are required to sustain operation reliability for processing temperatures as high as 400 °C [2]. The spin Hall magnetoresistance (SMR) can be used to electrically measure the magnetization direction of an FM and provides a method to non-invasively access fundamental spin transport parameters such as the SHA and spin diffusion length in NM and FM bilayers [3]. II. SPIN HALL MAGNETORESISTANCE SMR originates from the simultaneous action of two effects, the SHE and the inverse SHE (ISHE). The SHE causes a conversion of charge current in a pure spin current without any magnetic field, while the ISHE converts a pure spin current into a charge current. Both the SHE and the ISHE derive from spin-orbit coupling (SOC) in the NM [3]. The spin-orbit force that generates the SHE was first observed in FM materials where it generates the intrinsic anomalous Hall effect. Since the ferromagnet induces a spin Manuscript received June 4, 2018; revised August 14, 2018; accepted September 6, 2018. Corresponding author: T. J. Peterson (e-mail: Pete9290@ umn.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2018.2869472 polarization on the electrons the spin-dependent transverse velocity results in an easily measurable charge current [4]. However, in a nonmagnet material, the SOC acts on a com- pletely unpolarized charge current resulting in a pure spin current, this is known as the intrinsic spin Hall effect. Reflected spins, from the NM/FM interface, undergo the ISHE and convert back to charge current. The SHE and ISHE can be described by * j SHE si = θ SH ˆ ix * j c (1) * j I SHE c = θ SH ˆ ix * j si (2) where θ SH is the SHA and x represents the vector cross prod- uct [5]. Here, * j SHE si /| * j SHE si | is the direction vector of an SHE spin current density polarized along ˆ i with modulus * | j SHE si |. It is driven by the applied charge current density * J c and proportional to the SHA. * j I SHE c is the charge current driven by an ˆ i -polarized spin current in * J si / * | J si direction. For metallic ferromagnets, a model for SMR in the FM insulator/NM bilayers [6] has to be extended to include the longitudinal spin current absorption from the metallic FM layer 1ρ 1 ρ ≈-θ 2 SH λ N t N tanh 2 (d /2λ N ) 1 + ξ ×  g R 1 + g R coth (t N /λ N ) - g F 1 + g F coth (t N /λ N )  g R ≡ 2ρ N λ N G r g F ≡ ( 1 - P 2 ) ρ N λ N ρ F λ F coth (t F /λ F ) (3) where ρ N represents the resistivity of the NM layer [7]. t F ,ρ F ,λ F , and P represent the thickness, resistivity, spin dif- fusion length, and the current spin polarization of the magnetic layer, respectively. ξ ≡ (ρ N t F /ρ F t N ) describes the current shunting effect into the magnetic layer. When considering a metallic ferromagnet, one must include resistance terms from anisotropic magnetoresistance (AMR), a phenomenon that the 0018-9464 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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