Electric Control Of Exchange Bias Research Articles

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

The fluctuation of switching parameters is unavoidable in conductive filaments (CFs)-type resistive switching (RS) devices, which restricts the application in resistive random-access memory. Here, we employed an uninsulated antiferromagnetic (AFM) NiO layer adhered to a well-insulating HfO2 layer to effectively suppress the RS fluctuation by achieving forming-free, narrower set voltage distribution, a more stable on/off ratio, and better endurance in comparison with single-HfO2-layer based RS devices. The conduction scaling behavior indicates that the NiO/HfO2 bilayer has a smaller scale parameter S0 (lateral dimension of the bottleneck for the CFs). Besides this, considering some preexisting conductive paths in the NiO layer, the electric fields and the formation/rupture of CFs can be highly localized, leading to reduced switching fluctuation and improved RS performance in the NiO/HfO2-based RS devices. Moreover, asymmetric I-V curves measured in a high resistance state (HRS) in positively and negatively biased regions and the electric modulation of exchange bias (EB) arising from the Co-NiO interfacial coupling are favorable for revealing the inherent mechanism for RS. The coexistence of RS and EB is also useful to the design of novel multifunctional memory devices.

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

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/SiO2/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 aberration-corrected 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.

Electrically Enhanced Exchange Bias via Solid-State Magneto-ionics

Electrically induced ionic motion offers a new way to realize voltage-controlled magnetism, opening the door to a new generation of logic, sensor, and data storage technologies. Here, we demonstrate an effective approach to magneto-ionically and electrically tune the exchange bias in Gd/Ni1-xCoxO thin films (x = 0.50 and 0.67), where neither of the layers alone is ferromagnetic at room temperature. The Gd capping layer deposited onto antiferromagnetic Ni1-xCoxO initiates a solid-state redox reaction that reduces an interfacial region of the oxide to ferromagnetic NiCo. An exchange bias is established after field cooling (FC), which can be enhanced by up to 35% after a voltage conditioning and subsequently reset with a second FC. These effects are caused by the presence of an interfacial ferromagnetic NiCo layer, which further alloys with the Gd layer upon FC and voltage application, as confirmed by electron microscopy and polarized neutron reflectometry studies. These results highlight the viability of the solid-state magneto-ionic approach to achieve electric control of exchange bias, with potential for energy-efficient magneto-ionic devices.

Electric control of exchange bias in Co/FeOx bilayer by resistive switching

Two types of electric control of exchange bias (EB) by resistive switching (RS), i.e. conductive-filament-RS (type I) and interface-barrier-RS (type II) were observed in the Si/SiO2Ti/Pt/FeOx/Co/ITO multilayer devices, which were fabricated by magnetron sputtering. It is difficult for the type I device to control EB, which may be due to that the quantity of conductive filaments is not enough to modify the antiferromagnetic structure of FeOx near the Co/FeOx interface. However, the electric control of EB can be accomplished in the type II device. Compared with low-resistance-state (LRS), the exchange bias field (HE) increases a little but the coercivity (HC) increases significantly at high-resistance-state (HRS). We consider that the migration of the oxygen vacancies under different voltages is able to mediate the interfacial barrier height, leading to the bipolar RS effect and the change of EB as well. This provides a way for designing new types of spintronic devices based on electric control.

Nonvolatile Electric Control of Exchange Bias by a Redox Transformation of the Ferromagnetic Layer

AbstractElectric manipulation of exchange bias (EB) systems is highly attractive for the development of modern spintronic and magnetophoretic devices. To date, electric control of the EB has mainly been based on multiferroic or resistive switching behavior in specific antiferromagnets, which limits the material choice and accessible EB states. In addition, the effects are mostly volatile, requiring constant voltage application. The continuous and nonvolatile tuning of the EB via electrochemical manipulation of the ferromagnetic layer is presented. In FeOx/Fe/IrMn systems, large changes in the EB field of fully shifted magnetization curves are achieved at low voltage (<1 V) and room temperature. A ferromagnetic‐layer thickness change resulting from the electrochemical reduction of iron oxide to iron is proposed as the underlying mechanism and is consistent with a simple model for the EB and surface analysis. Nonvolatility is achieved as the reduction proceeds at the buried FeOx/Fe interface, leaving the remaining oxide as a protective layer. A lateral voltage‐controlled patterning of the EB fields and magnetic domain state is demonstrated. This versatile redox‐based electric control of the EB paves a new route for the design of EB systems in general and for the development of future electrically controlled EB devices.

Full Electric Control of Exchange Bias at Room Temperature by Resistive Switching.

Electric control of exchange bias (EB) is of vital importance in energy-efficient spintronics. Although many attempts have been made during the past decade, each has its own limitations for operation and thus falls short of full direct and reversible electrical control of EB at room temperature. Here, a novel approach is proposed by virtue of unipolar resistive switching to accomplish this task in a Si/SiO2 /Pt/Co/NiO/Pt device. By applying certain voltages, the device displays obvious EB in the high-resistance-state while negligible EB in the low-resistance state. Conductive filaments forming in the NiO layer and rupturing near the Co-NiO interface are considered to play dominant roles in determining the combined resistive switching and EB phenomena. This work paves a new way for designing multifunctional and nonvolatile magnetoelectric random access memory devices.

Electrical control of exchange bias via oxygen migration across CoO-ZnO nanocomposite barrier

We proposed a nanocomposite barrier CoO-ZnO for magnetism manipulation in Co/CoO-ZnO/Ag heterojunctions. Both electrical control of magnetism and resistive switching were realized in this junction. An electrical tunable exchange bias of CoO1-v (v denotes O vacancies) on Co films was realized using voltages below 1 volt. The magnetism modulation associated with resistive switching can be attributed to the oxygen ions migration between the insulating CoO1-v layer and the semiconductive ZnO1-v layer, which can cause both ferromagnetic phase and resistance switching of CoO1-v layer.

Full Electric Control of Exchange Bias

We report the creation of a multiferroic field effect device with a BiFeO(3) (BFO) (antiferromagnetic-ferroelectric) gate dielectric and a La(0.7)Sr(0.3)MnO(3) (LSMO) (ferromagnetic) conducting channel that exhibits direct, bipolar electrical control of exchange bias. We show that exchange bias is reversibly switched between two stable states with opposite exchange bias polarities upon ferroelectric poling of the BFO. No field cooling, temperature cycling, or additional applied magnetic or electric field beyond the initial BFO polarization is needed for this bipolar modulation effect. Based on these results and the current understanding of exchange bias, we propose a model to explain the control of exchange bias. In this model the coupled antiferromagnetic-ferroelectric order in BFO along with the modulation of interfacial exchange interactions due to ionic displacement of Fe(3+) in BFO relative to Mn(3+/4+) in LSMO cause bipolar modulation.

Reversible electric control of exchange bias in a multiferroic field-effect device

Electric-field control of magnetization has many potential applications in magnetic memory storage, sensors and spintronics. One approach to obtain this control is through multiferroic materials. Instead of using direct coupling between ferroelectric and ferromagnetic order parameters in a single-phase multiferroic material, which only shows a weak magnetoelectric effect, a unique method using indirect coupling through an intermediate antiferromagnetic order parameter can be used. In this article, we demonstrate electrical control of exchange bias using a field-effect device employing multiferroic (ferroelectric/antiferromagnetic) BiFeO(3) as the dielectric and ferromagnetic La(0.7)Sr(0.3)MnO(3) as the conducting channel; we can reversibly switch between two distinct exchange-bias states by switching the ferroelectric polarization of BiFeO(3). This is an important step towards controlling magnetization with electric fields, which may enable a new class of electrically controllable spintronic devices and provide a new basis for producing electrically controllable spin-polarized currents.

Robust isothermal electric control of exchange bias at room temperature

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr(2)O(3) has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr(2)O(3) single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

Electrical Control of Exchange Bias Mediated by Graphene

The role of graphene in mediating the exchange interaction is theoretically investigated when placed between two ferromagnetic dielectric materials. The calculation based on a tight-binding model illustrates that the magnetic interactions at the interfaces affect not only the graphene band structure but also the thermodynamic potential of the system, leading to an effective exchange bias between magnetic layers. The analysis indicates a strong dependence of the exchange bias on the properties of the mediating layer, revealing an efficient mechanism of electrical control even at room temperature.