Electric field induced modulation of magnetic anisotropy and switching current for spintronic memory = 전계에 의한 자기이방성 제어 및 스핀 메모리 소자의 자화 반전 전류 감소에 대한 연구

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In recent years, spintronic memory device, which based on the magnetization reversal of magnetic memory using spin polarized currents via spin transfer torque (STT) effect has been introduced in order to achieve low power operation. As device size shrinkage, however, the decrease of effective volume leads to not only the lowering of thermal stability but also the increase of total switching current. Many studies have been introduced to overcome technical issues by addressing development of efficient magnetization control methods based on material, adopting non-collinear magnetic configuration and electrical manipulation. However, each feature is insufficient method of settlement when utilized individually. Therefore, it requires to be complementary to each other to establish the most promising model by merging above advantages. In this study, it is proposed the combination candidates such as electric field effect with cone state or spin orbit torque devices in order to maximize synergy effect each other using perpendicular MTJ. The origin of electric field with MTJ structural parameters and its application of spintronic devices are mainly investigated. The coercivity and perpendicular magnetic anisotropy of all samples strongly depend on oxidation time with non-volatile and reversible way. The magnitude and sign of the magnetoelectric coefficient mainly depends on the slop and initial Hk corresponding to the FM-O hybridization status. Given that the polarity of electric field effect is associated with oxygen ion driven FM-O hybridization, it demonstrate that the origin of electric field effect strongly depends on the oxygen migration effect rather than charge transfer effect due to 3d orbital redistribution. By combination of electric field with cone state, the magnetic anisotropy constants, $K_{1eff}$, and K2 can be controlled by an electric field, resulting in the modulation of the cone angle in a non-volatile and reversible manner, which attributed to the electric modification of the interfacial oxidation state via field-induced ion migration. For the another approaching method of electrical modulation by utilization of spin orbit torque induce switching, It is clearly indicated that the FM-O hybridization status determines the sign of change for Hc and Hk as well as Jc regarding to the polarity of electric field. Thus electric field can modify the switching current which depending on the anisotropy field resulting from the hybridization of FM-O status and also can sequentially control the thermal stability by tuning of anisotropy energy in non-volatile and reversible manner. Therefore, it can provide the proper solution of trade-off relationship between thermal stability and switching current density, as well as electric field induced modulation of cone state. These results open a new pathway to achieve voltage-controlled spintronic devices by directly manipulating the magnetism, rather than only the magnetic anisotropy, of 3d transitional FMs and it allows approaching a commercialization and the development of STT-MRAM in advance. Furthermore, electromagnetic effect can provide key factors that spintronic device realizes a future universal memory device replacing embedded technologies and provides new functionality at 20nm and beyond including automotive application due to high speed and lower power consumption than Flash and denser than SRAM.
Park, Byong Gukresearcher박병국researcher
한국과학기술원 :신소재공학과,
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학위논문(박사) - 한국과학기술원 : 신소재공학과, 2017.8,[xii, 104 p. :]


spintronics▼aelectricfield▼amagnetocrystalline andisotropy▼acone state▼aspin orbit torque▼aSTT-MRAM▼acurrent induced switching▼aion migration; 스핀트로닉스▼a전계▼a자기 이방성▼a콘 스테이트▼a스핀오빗토크

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