Voltage-induced coercivity change in Co film grown on Cr 2 O 3 barrier

Tamaru

Konoto

et al. 2021

Sci Rep

Self Cite

There is urgent need for spintronics materials exhibiting a large voltage modulation effect to fulfill the great demand for high-speed, low-power-consumption information processing systems. Fcc-Co (111)-based systems are a promising option for research on the voltage effect, on account of their large perpendicular magnetic anisotropy (PMA) and high degree of freedom in structure. Aiming to observe a large voltage effect in a fcc-Co (111)-based system at room temperature, we investigated the voltage-induced coercivity (Hc) change of perpendicularly magnetized Pt/heavy metal/Co/CoO/amorphous TiOx structures. The thin CoO layer in the structure was the result of the surface oxidation of Co. We observed a large voltage-induced Hc change of 20.2 mT by applying 2 V (0.32 V/nm) to a sample without heavy metal insertion, and an Hc change of 15.4 mT by applying 1.8 V (0.29 V/nm) to an Ir-inserted sample. The relative thick Co thickness, Co surface oxidation, and large dielectric constant of TiOx layer could be related to the large voltage-induced Hc change. Furthermore, we demonstrated the separate adjustment of Hc and a voltage-induced Hc change by utilizing both upper and lower interfaces of Co.

Section: Methodsmentioning

confidence: 98%

mentioning

confidence: 99%

Large voltage-induced coercivity change in Pt/Co/CoO/amorphous TiOx structure and heavy metal insertion effect

Tamaru

Konoto

et al. 2021

Sci Rep

Self Cite

“…[13][14][15] To apply an extremely strong electric field on the surface, studies on the VCMA effect using an ionic liquid have also been conducted. [16][17][18] Although many experimental studies on the VCMA effect have been conducted, the sign of the VCMA effect in most materials is negative (see Figure 1), [2] and only a few materials exhibit a positive VCMA effect at room temperature; L1 0 -ordered FePd alloys [10,19] and Co/oxide structures such as Co/CoO x /HfO 2 , [20] Co/SrTiO 3 , [21,22] Co/Cr 2 O 3 , [23] and Co/CoO x /TiO x junctions. [24] A positive VCMA has also been reported for Co(0.4 nm)/MgO/ HfO 2 [25] and Ru/CoFeB/MgO structures with sputter-deposited MgO barrier.…”

mentioning

confidence: 99%

Strong Impact of Underlayers on the Voltage‐Controlled Magnetic Anisotropy in Interface Engineered Co/MgO Junctions with Heavy Metals

Nakayama

et al. 2023

Adv Materials Inter

Self Cite

The VCMA effect is a phenomenon that induces a magnetic anisotropy change for the ferromagnet with applying an electric field through the insulator. Since application of an electric current is not necessary to manipulate spins, the VCMA effect has potential advantage toward the spintronic devices with ultra-low power consumption. In addition, the purely electronic VCMA effect enables spin manipulation free from chemical reactions or ionic displacements, which results in high-speed operation and high writing endurance. [3,4] As the origin of the purely electronic VCMA effect, electric-field modulation of the electronic occupation states, [5][6][7] the Rashba spin-orbit anisotropy, [8] and the magnetic dipole moment [9] have been proposed to describe phenomena at the junction between homogeneous ferromagnets and insulators.Since the first report of VCMA in 2007, [10] the effect has been studied for a wide range of materials. In the early stages of the study, however, it was challenging to observe voltage-induced phenomena in ferromagnetic metals because of the extremely small Thomas-Fermi screening length of metals. [5,10,11] Therefore, a combination of ultrathin metallic films and liquid electrolyte were required for the first demonstration of the VCMA effect. [10] A year later, the VCMA effect in all-solid structure was first reported for a ferromagnetic semiconductor at low temperature. [12] Subsequently, the VCMA effect in all-solid structures at room temperature was achieved in ultrathin 3d transition metals. [13][14][15] To apply an extremely strong electric field on the surface, studies on the VCMA effect using an ionic liquid have also been conducted. [16][17][18] Although many experimental studies on the VCMA effect have been conducted, the sign of the VCMA effect in most materials is negative (see Figure 1), [2] and only a few materials exhibit a positive VCMA effect at room temperature; L1 0 -ordered FePd alloys [10,19] and Co/oxide structures such as Co/CoO x /HfO 2 , [20] Co/SrTiO 3 , [21,22] Co/Cr 2 O 3 , [23] and Co/CoO x /TiO x junctions. [24] A positive VCMA has also been reported for Co(0.4 nm)/MgO/ HfO 2 [25] and Ru/CoFeB/MgO structures with sputter-deposited MgO barrier. [26] For the case using sputter-deposited MgO barrier, however, it is also reported that the sign reversal of the VCMA effect occurs due to the subtle changes in the oxidation state at the junction interface. [27] The magnitude of the The voltage-controlled magnetic anisotropy (VCMA) effect in ferromagnets is of crucial interest for next-generation non-volatile magnetic memory technologies since it enables spin manipulation with low power consumption in addition to high-speed operation and high writing endurance. Although intense efforts are made in the past decade to increase the efficiency of the purely electronic VCMA effect, the physical origin of this phenomenon is still elusive, particularly for interface-engineered ferromagnetic materials. Here, a pathway is proposed to tune the VCMA effect by exploiting a combination of ...

“…While MgO (111) single dielectric layer 17,18 and MgO (111)/amorphous HfO x bilayer dielectric layers [19][20][21][22][23][24] have been sometimes used for the voltage effect study, the large mismatch between MgO (111) and Co (111) and the natural polar plane of MgO make the realization of a high-quality interface difficult. Other crystal dielectric layers, such as Cr 2 O 3 25 and SrTiO 3 , 26 with less lattice mismatch, are difficult to grow on Co without degradation. An amorphous dielectric layer is another option, which can be used without concerning the lattice mismatch.…”

mentioning

confidence: 99%

“…After backfilling with SiO 2 , the Cr/Au top electrode was formed. The micro-fabrication process is identical to that in our previous report 25. After the microfabrication, the samples were post annealed at up to 400 ℃ in a vacuum furnace.…”

mentioning

confidence: 99%

Large Voltage-Induced Coercivity Change in Pt/Co/CoO/Amorphous TiOx Structure and Heavy Metal Insertion Effect

Tamaru

Konoto

et al. 2021

Preprint

Self Cite

There is urgent need for spintronics materials exhibiting a large voltage modulation effect to fulfill the great demand for high-speed, low-power-consumption information processing systems. Fcc-Co (111)-based systems are a promising option for research on the voltage effect, on account of their large perpendicular magnetic anisotropy (PMA) and high degree of freedom in structure. Aiming to observe a large voltage effect in a fcc-Co (111)-based system at room temperature, we investigated the voltage-induced coercivity (Hc) change of a perpendicularly magnetized Pt/heavy metal/Co/CoO/amorphous TiOx structure. The thin CoO layer in the structure was the result of the surface oxidation of Co. We observed a large voltage-induced Hc change of 20.2 mT by applying 2 V (0.32 V/nm) to a sample without heavy metal insertion, and an Hc change of 15.4 mT by applying 1.8 V (0.29 V/nm) to an Ir-inserted sample. The relative thick Co thickness, Co surface oxidation, and large dielectric constant of TiOx layer could be related to the large voltage-induced Hc change. Furthermore, we demonstrated the separate adjustment of Hc and a voltage-induced Hc change by utilizing both upper and lower interfaces of Co.