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Jisu Kim,Seyeop Jeong,Donghyeon Lee,Taekhyeon Lee,Suhyeok An,Kab-Jin Kim,Ki-Seung Lee,Chun-Yeol You,Sanghoon Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Ferrimagnet is a material whose magnetic moments are aligned in opposite directions like antiferromagnets with non-zero net moment. In a class of ferrimagnets composed of rare earth (RE)-transition metal (TM), the magnitude of each magnetic moment can be adjusted by changing the ratio of the RE-TM or the measurement temperature. Since the temperature dependence of the magnetization of each element is different, the magnetic moments cancel each other at the magnetization compensation temperature T<sub>M</sub>. In this study, He<sup>+</sup> ions were accelerated with 20 keV energy to a 15-nm-thick Gd<sub>36</sub>Co<sub>64</sub> film with perpendicular magnetic anisotropy. We observe that the T<sub>M</sub> decreases after He<sup>+</sup> irradiation. We also succeed in a local modulation of T<sub>M</sub> using He<sup>+</sup> ion beam. In addition, we will present that magnetic switching properties by current or external field can be modulated by the He<sup>+</sup> irradiation.
Field free switching of ferrimagnetic GdCo with artificially broken symmetry
Jisu Kim,Seyeop Jeong,Taekhyeon Lee,Suhyeok An,Kab-Jin Kim,Ki-Seung Lee,Chun-Yeol You,Soogil Lee,Byong-Guk Park,Sanghoon Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
During the last decade, current-induced magnetization switching by spin-orbit torque (SOT) is of great importance to nanoelectronics due to energy-efficient control of spintronic memory and logic devices. However, it has a problem that an external magnetic field is required to switch magnetization of a device when magnetic layers are perpendicularly magnetized. This implies that there should be limitation of scalability and low energy efficiency because of necessity to use the external magnetic field. Therefore, field-free switching of a magnetization should be achieved for realization of the energy efficient and ultra-fast SOT-driven devices. Here, we report field-free SOT switching of ferrimagnetic GdCo thin films with a He ion microscope (HIM) technique. The Pt(5)/Gd36Co64(5)/Ta(3) structure is irradiated by He ions with the dose range from 5 to 50 ions/nm². We find that magnetic properties of the GdCo layer such as coercivity (HC) and magnetization compensation temperature (TM) strongly depend on ion dose of a He irradiation. Based on the idea that ferrimagnetic properties can be controlled using He ion irradiation method, we introduced a lateral gradient of magnetization by the HIM to form a broken mirror symmetry in the device. The mirror symmetry breaking was observed after the local modulation; TM and perpendicular magnetic anisotropy (PMA) properties were locally modulated by He ion irradiation. As the magnetic mirror symmetry is broken, we observed the field-free SOT switching behavior. The Sz component of the spin current generated by the broken mirror symmetry was also observed. We will discuss details about structural change in the ferrimagnetic GdCo by the He ion irradiation.