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A 3-dimensional control of exchange bias by spin orbit torque in Pt/Co/IrMn heterostructure
Eunchong Baek,Suhyeok An,Woo-Yeong Kim,Ki-Seung Lee,Chun-Yeol You 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Spin orbit torque (SOT) driven magnetization switching has opened up a new field of spintronics. It has been reported that SOT can switch a ferromagnet (FM) layer without the second ferromagnetic layer by spin current from the adjacent heavy metal (HM) layer<sup>1,2,3</sup>. The injection of spin current by SOT can also switch the antiferromagnet (AFM) Neel vector<sup>4,5,6</sup> which have been difficult to manipulate with other means such as a magnetic field. Furthermore, the exchange bias (EB) state in FM/AFM bilayer system was manipulated through SOT while the underlying mechanism is unrevealed yet<sup>7-,8,9,10</sup>. To understand how the SOT modulate EB state, related experiments are needed to provide the clues for the interfacial spin dynamics due to SOT, because the interfacial spin ordering at the interface will govern the EB state. Here we observe SOT driven three-dimensional (3-D) control of the EB state in a Pt/Co/IrMn tri-layer. We control EB field directions with out-of-plane (OOP) and/or in-plane (IP) external magnetic fields with SOT. Similar to the field cooling methods, the magnetization of FM layer is imprinted into the EB field by SOT. Furthermore, manipulated in-plane EB field through SOT enables field-free switching of perpendicular magnetized FM without field-cooling. In order to support the experimental findings, we perform macro-spin simulations which suggest that the SOT induced EB manipulation is the result of SOT driven THz oscillation of interfacial AFM spins. In SOT induced EB manipulation, SOT has the similar role as heat in traditional field cooling, exciting the AFM spins to deviate from the local energy minimum state so that when the current is turned off, the EB is switched along the FM direction. Our work reveals the underlying mechanism of SOT driven EB manipulation and motivates to design novel spintronic devices.
최은총(Eunchong Choi),박영웅(Youngwoong Park),윤수빈(Subin Yun),백소담(Sodam Baek),이진(Jin Lee),이다희(Dahee Lee),주혜련(Hyeryeon Ju),강민주(Minju Kang),이상운(Sangun Lee) 한국방송·미디어공학회 2021 한국방송공학회 학술발표대회 논문집 Vol.2021 No.11
기존의 중계 시스템은 유선 기반으로 방송 중계차와 케이블 등이 필요하여 시간과 비용, 장소의 제약과 같은 여러 한계점을 가지고 있었다. 하지만 무선 중계 기술의 발전으로 무선 카메라만 있으면 긴급재난 현장이나 중계차가 들어갈 수 없는 지역에서도 중계가 가능하게 되면서 중계방송의 제한 범위가 좁아지고 있다. 따라서 본 논문에서는 시간과 장소의 제약 없이 방송을 송출할 수 있는 5G 무선 중계 시스템을 분석한다. 분석한 시스템은 5G 모뎀이 장착된 MNG 장비를 이용해 UHD와 4K 신호를 무선으로 처리하여 초저지연·초고화질로 송출한다. 또한 현존하는 멀티뷰 기술을 접목시켜 시청자들이 원하는 서비스를 제공한다.
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.
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.