Observation and theoretical calculations of voltage-induced large magnetocapacitance beyond 330% in MgO-based magnetic tunnel junctions

Abstract

Magnetic tunnel junctions (MTJs) in the field of spintronics have received enormous attention owing to their fascinating spin phenomena for fundamental physics and potential applications. MTJs exhibit a large tunnel magnetoresistance (TMR) at room temperature. However, TMR depends strongly on the bias voltage, which reduces the magnitude of TMR. On the other hand, tunnel magnetocapacitance (TMC), which has also been observed in MTJs, can be increased when subjecting to a biasing voltage, thus exhibiting one of the most interesting spin phenomena. Here we report a large voltage-induced TMC beyond 330% in MgO-based MTJs, which is the largest value ever reported for MTJs. The voltage dependence and frequency characteristics of TMC can be explained by the newly proposed Debye-Fröhlich model using Zhang-sigmoid theory, parabolic barrier approximation, and spin-dependent drift diffusion model. Moreover, we predict that the voltage-induced TMC ratio could reach over 3000% in MTJs. It is a reality now that MTJs can be used as capacitors that are small in size, broadly ranged in frequencies and controllable by a voltage. Our theoretical and experimental findings provide a deeper understanding on the exact mechanism of voltage-induced AC spin transports in spintronic devices. Our research may open new avenues to the development of spintronics applications, such as highly sensitive magnetic sensors, high performance non-volatile memories, multi-functional spin logic devices, voltage controlled electronic components, and energy storage devices.

Large magnetocapacitance beyond 420% in epitaxial magnetic tunnel junctions with an MgAl2O4 barrier

“…The TMC ratio increases with increasing the frequency in the low frequency region, and it reaches 227% (223%) at 140 Hz for sample A (B). The TMC of 227% (223%) is larger than the conventional value of 172%, which is observed in MgO-based MTJs 27 . As increasing the frequency, the TMC decreases to 10.5% (10.3%) at 40 kHz, and it slightly increases to 13.2% (16.1%) for sample A (B).…”

“…6 a). Although the method to control the threshold bias V th is not clear at the present stage, it could depend on materials; V th = ~ 100 mV for CoFe/MgO/CoFe MTJs 27 and V th = ~ 300 mV for Fe/MAO/Fe MTJs in this study. The threshold bias could be controlled by changing materials, thicknesses and crystal structures of MTJ layers.…”

“…The sigmoid function under the application of bias voltage can be expressed by where α P(AP) is the broadening of the contributing rate of dynamic capacitance to the overall capacitance in the P (AP) configuration and V 0,P(AP) is the voltage for spin flipping. Thus, the Zhang-sigmoid formula gives the bias voltage dependence of the relaxation time 27 . Based on the SDD model for the static case, the spin capacitance can be given by where S is a junction area, λ is a characteristic screening length and en 0,P(AP) is a screening charge density at the interface.…”

“…TMC’s unique properties include a relative larger TMC (measured in percentage) over TMR at some specific frequencies 4 , good thermal stability in TMC 19 , and robustness of TMC against a bias voltage as opposed to a bias-induced TMR drop 8 . Recently, by optimizing appropriate frequencies and bias voltages, a large TMC of 332% was achieved in MgO-based MTJs at room temperature 27 . The core structure of MTJs is Co 40 Fe 40 B 20 /MgO/Co 40 Fe 40 B 20 , leading to a textured CoFe/MgO/CoFe(001) interfacial structure promoted by an annealing process.…”

Multistate Compound Magnetic Tunnel Junction Synapses for Digital Recognition

“…[24][25][26]28,30 The spin-current-driven sigmoid function of MTJs is commonly utilized for implementing deep spiking and ANN to perform complex recognition tasks with high accuracy. 46−48 To understand the sigmoid relationship with varying V, the P s plots (Figure 2d and S4) are fitted using the slogistic sigmoid relation: 49 = +…”