http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Various approaches for the more effective spin-orbit torque switching
Suhyeok An,Eunchong Baek,Yeh-Ri Kim,Dongryul Kim,Jin-A Kim,Hyeongjoo Seo,Chun-Yeol You 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
Spin orbit torque (SOT) induced magnetization switching is promising technique for the logic-in-memory applications. SOT switching has many advantages compare to the spin transfer torque switching: separated read/write current paths, faster switching speed, independent switching behavior on the free layer damping constant, and less energy consumption. Despite many advantages, there are still unresolved issues in SOT switching. We studied various technique to improve the efficiency of SOT switching. First, we will discuss about the effect of the He+ ion irradiation on the SOT switching, He+ ion irradiation leads not only the magnetic anisotropy, but also the spin Hall angle variations. We will also introduce several approaches in order to achieve field-free SOT switching by introducing lateral in-plane symmetry breaking.
Asymmetry of Spin-Orbit Torque induced Magnetization Switching by Local Helium Ion Irradiation
Suhyeok An,Jin-A Kim,Hyeong Joo Seo,Chun-Yeol You 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
The spin-orbit torque (SOT) induced magnetization switching based memory devices with perpendicular magnetic anisotropy (PMA) has a perspective as replacement of spin transfer torque (STT). However, magnetization switching using SOT, unlike STT, requires in-plane magnetization symmetry breaking, thus the applying an in-plane external magnetic field is essential. Therefore, several methods have been proposed to break the in-plane magnetization symmetry without the application of an external magnetic field. Among them, there is a few reports that magnetization switching caused by in-plane non-uniformity of PMA creates deterministic SOT-based magnetic field-free switching, but the discussion on how the magnetization reversal starts is still insufficient. In this report, we prepared the sample having in-plane non-uniformity of PMA by locally irradiated He<SUP>+</SUP> ion in Pt(5)/Co(0.8)/MgO(2) structure. And the asymmetry of SOT induced magnetization switching current is observed according to magnetization initial status (+z or -z direction). By local irradiation of He<SUP>+</SUP> ion, the sample is divided two (irradiated and non-irradiated) regions. The PMA energies of two regions are districted and its differences between them increase gradually with higher dose irradiation. The results show different critical switching current according to initial direction of magnetization and this asymmetry reaches ~ 12.3% at dose amount of 45 ions/nm². The domain patterns measured by magneto-optical Kerr microscopy display lower switching current when the domain starts to nucleation at PMA boundary, and it implies that SOT switching can be assisted by internally-formed effective field caused by PMA energy gradient.
Improved Spin-Orbit Torque Switching Efficiency by He<SUP>+</SUP> Ion Irradiation
Suhyeok An,Eunchong Baek,Jin-A Kim,Ki-Seung Lee,Chun-Yeol You 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
The magnetic thin films with inversion symmetry breaking have been investigated because of its great potential for application of magnetic random access memory (MRAM) devices and scientific interests about spin-orbit coupling (SOC) phenomena. Especially because Heavy-metal (HM) / Ferromagnet (FM) / Oxide (MgO) structure has strong SOC at the HM/FM interface and inversion symmetry breaking system, resulting in strong perpendicular magnetic anisotropy (PMA) [1], spin-orbit torque (SOT) [2] and Dzyaloshinskii-Moriya interaction (DMI) [3,4]. Among them, the SOT driven magnetization switching is a perspective phenomenon because of its application to the spintronic devices. For more efficient SOT based spin devices, many researchers try to reduce critical switching current by HM layer modulation [5], interface modifying [6, 7], and ion irradiation [8, 9]. Here, we report that local magnetic properties are modulated by He<sup>+</sup> ion irradiation in Pt/Co/MgO structure. The Pt(5)/Co(0.8)/MgO(2) structure is irradiated by He<sup>+</sup> ion with the dose range from 0 to 30 ions/nm<sup>2</sup>, then the reduction of switching current is shown about ~ 30% at dose amount of 30 ions/nm<sup>2</sup> under external magnetic field of 3 kOe. The reduction of switching current is related with effective PMA field and spin Hall angle (SHA), we analyze each phenomenon using generalized Sucksmith-Thompson method and harmonic Hall analysis, respectively. The result show the decrease of PMA field from 13.7 kOe to 8.5 kOe (~ 38%) and increase of SHA from 0.096 to 0.132 (~ 27%). And then, for understanding the reason of improvement of SHA, we conduct the resistivity measurement with temperature variation from 5 K to 225 K in 5 nm thickness single Platinum layer. The results show gradual increasing tendency in resistivity and decreasing tendency in residual-resistivity ratio (ρ<sub>300K</sub>/ρ<sub>5K</sub>) at higher dose amount. These imply that the He<sup>+</sup> ion irradiation makes extra scattering sources in HM layer and result in increasement of resistivity and SHA.