Electric Control of Exchange Bias at Room Temperature by Resistive Switching via Electrochemical Metallization

Abstract

Electric field control of exchange bias (EB) plays an important role in spintronics due to its attractive merit of lower energy consumption. Here, we propose a novel method for electrically tunable EB at room temperature in a device with the stack of Si/SiO 2 /Ta/Pt/Ag/Mn-doped ZnO (MZO)/Pt/FeMn/ Co/ITO by resistive switching (RS) via electrochemical metallization (ECM). The device shows enhanced and weakened EB when set at high-resistance state (HRS) and low-resistance state (LRS), respectively. For the device at LRS, the aberrationcorrected scanning transmission electron microscopy (STEM) characterizations unambiguously reveal that the Ag filaments grow initially from the Ag anode and then elongate toward the ITO cathode. It is inferred that at LRS, a small portion of Ag filaments have passed through the MZO and the intervening thin Pt layer and extended into the FeMn layer. After applying reverse voltage, these Ag filaments are electrochemically dissolved and ruptured near the MZO/Pt interface. This is considered to be the main mechanism responsible for RS and switchable EB as well. This work presents a new strategy for designing low-power, nonvolatile magnetoelectric random access memory devices.

Improved resistive switching performance and realized electric control of exchange bias in a NiO/HfO2 bilayer structure

“…The direction of H is the same as that during the sample fabrication and negative exchange bias (EB) can be observed. The variation of EB field (H E ) for the initial three cycles are summarized in Fig.S11(b) (ESI †), exhibiting a quasiperiodic variation of H E against the cycle number with a larger (smaller) value at HRS/OS (LRS) in the same cycle, similar to those modulations of EB via RS reported previously 44,[48][49][50]. Here,H E = À(H C1 + H C2 )/2 and H C = (H C2 À H C1 )/2, where H C1 and H C2 denote the coercive field for the descending and ascending branch of the M-H loop, respectively.…”

“…S11(b) (ESI†), exhibiting a quasiperiodic variation of H E against the cycle number with a larger (smaller) value at HRS/OS (LRS) in the same cycle, similar to those modulations of EB via RS reported previously. 44,48–50 Here, H E = −( H C1 + H C2 )/2 and H C = ( H C2 − H C1 )/2, where H C1 and H C2 denote the coercive field for the descending and ascending branch of the M – H loop, respectively. To explain the electric modulation of H E in the present work, a series of Co/NiO bilayer samples with various oxygen concentrations in the NiO layer were made with a fixed (varied) flow rate of Ar (O 2 ) during sputtering deposition of the NiO layer.…”

“…The multilayer films with the stack of Ta(5)/Pt(30)/Co(6)/ NiO(15)/HfO 2 (25)/Pt(30) (thickness in unit nm) were deposited by magnetron sputtering at room temperature on commercial surface oxidized Si (100) substrates with an area of 5 Â 5 mm 2 . Note that the top layer of Pt (30) was replaced by a bilayer of Pt(5)/ITO (50) for M-H loop measurements. The targets (Ta, Pt, Co, NiO, HfO 2 and ITO) used for sputtering were all purchased commercially and their purities are all larger than 99.99%.…”

“…47 Recently, reversible electric control of EB based on RS has attracted much interest because EB can be reversibly modulated as the device is switched between the high resistance state (HRS) and LRS back and forth. 44,[48][49][50] Moreover, the coexistence of EB and RS exhibits a promising prospect in the design of multifunctional memory devices. On the other hand, electric control of EB can provide an alternative way to help us reveal the underlying mechanism for RS since the characterization of oxygen vacancies is usually difficult.…”

Resistive Memristor Coupled with Multilevel Perpendicular Magnetic States

“…As a result, the resistance of the LRS device decreases with increasing compliance current, enhancing the ability to influence the Co-NiO exchange coupling. These findings disclose an important message that multilevel exchange coupling exists in our Pt/Co/NiO device, contrary to the previous understanding of |H EB | as having a binary on/off behavior only; 23,27,28,50 moreover, it is controllable with the CFs.…”