Electrical control of Co/Ni magnetism adjacent to gate oxides with low oxygen ion mobility

Abstract

We investigate the electrical manipulation of Co/Ni magnetization through a combination of ionic liquid and oxide gating, where HfO2 with a low O2− ion mobility is employed. A limited oxidation-reduction process at the metal/HfO2 interface can be induced by large electric field, which can greatly affect the saturated magnetization and Curie temperature of Co/Ni bilayer. Besides the oxidation/reduction process, first-principles calculations show that the variation of d electrons is also responsible for the magnetization variation. Our work discloses the role of gate oxides with a relatively low O2− ion mobility in electrical control of magnetism, and might pave the way for the magneto-ionic memory with low power consumption and high endurance performance.

Recent progress in voltage control of magnetism: Materials, mechanisms, and performance

“…Particularly, the MAE can be modified by approximately 0.7 erg/cm 2 under a voltage of several volts [43] and it was confirmed very recently that magneto-ionic motion can reach beyond the interface limit [288]. In FET-type devices where the electrolyte offers a large electric field, a moderate redox reaction can be induced at the interface with a small gate voltage in similar structures with PMA like HfO 2 /Ni/Co heterostructures [22,62]. The electrochemical effect in a metal/oxide system allows for nonvolatile operation of magnetism and a significant reduction of the energy consumption.…”

“…Thus, through many attempts, various performance behaviors of magnetic metals have been successfully modulated by electric fields, with the breakthrough in the short screening length limitation. By immersing the device in an electrolyte, magnetocrystalline anisotropy and coercivity in ultrathin FePt and FePd of 2 nm is modulated by an electric field [18] [70], HfO 2 /Ni/Co/Pt [22], and HfO 2 /[Co/Ni] n /Pt [62] heterostructures with PMA, where the magnetic properties were modified, including magnetic moments, T C , coercivity, magnetic anisotropy, and exchange bias. In addition, an electric field could also be directly applied on the oxide-capping layer to gain an effective manipulation of the magnetism.…”

“…In contrast, electron beam deposition with a high background vacuum and the largest energy density of 10 9 W/cm 2 , demonstrates a superiority in the deposition of highly pure metals and binary oxide films [92]. It is noteworthy that with the advances in sputtering and electron beam deposition technology, preparation of magnetic metals with PMA has been realized, including a number of ultrathin FM metal alloys, such as 0 1 L -ordered (Co,Fe)-Pt alloys, Co/(Pd,Pt) or Co/Ni multilayers, and CoFeB/MgO [10,22,93,94]. The realization of VCM in most of these systems brings the promise of a bright future for a new generation high-density nonvolatile information storage and logic devices, where a fine thermostability and a low critical current are in demand for current-induced magnetization switching.…”

“…In general, the droplet of ionic liquid is placed directly on the magnetic oxides to obtain a significant manipulatory effect for oxygen ions or vacancies [121,169,178]. Nevertheless, in some situations, the insertion of an oxide layer between the FM metals and the ionic liquids is adopted to avoid an irreversible chemical reaction due to the direct contact [22,61,70]. Interestingly, in light of the high freezing temperature, a frozen ionic liquid is sometimes used to deliberately fix the ion positions and the corresponding electric field of the EDL at low temperature, promising a long-term electric field effect and a nonvolatile VCM.…”

“…For instance, it is reported that positive gate voltage enhances the perpendicular magnetic anisotropy [22,24], whereas it does the opposite in other works [23]. Thus, there is a pressing need to sort out electrical modulation at the category level to address the question of how the magnetic medium and dielectric gating affect VCM.…”