Abstract
One of the most important achievements in the field of spintronics is the development of magnetic tunnel junctions (MTJs). MTJs exhibit a large tunneling magnetoresistance (TMR). However, TMR is strongly dependent on biasing voltage, generally, decreasing with applying bias. The rapid decay of TMR was a major deficiency of MTJs. Here we report a new phenomenon at room temperature, in which the tunneling magnetocapacitance (TMC) increases with biasing voltage in an MTJ system based on Co40Fe40B20/MgO/Co40Fe40B20. We have observed a maximum TMC value of 102% under appropriate biasing, which is the largest voltage-induced TMC effect ever reported for MTJs. We have found excellent agreement between theory and experiment for the bipolar biasing regions using Debye-Fröhlich model combined with quartic barrier approximation and spin-dependent drift-diffusion model. Based on our calculation, we predict that the voltage-induced TMC ratio could reach 1100% in MTJs with a corresponding TMR value of 604%. Our work has provided a new understanding on the voltage-induced AC spin-dependent transport in MTJs. The results reported here may open a novel pathway for spintronics applications, e.g., non-volatile memories and spin logic circuits.
Highlights
A new class of electronic devices based on the spin degrees of freedom has been extensively studied and it has given rise to the field of spintronics[1,2,3,4,5,6,7]
In this work we report a new phenomenon at room temperature in which the tunneling magnetocapacitance (TMC) increases with applying biasing voltage in an magnetic tunnel junctions (MTJs) system based on Co40Fe40B20/MgO/Co40Fe40B20
We have patterned the multilayer MTJ stacks into a junction area of 1800 μm[2] with an elliptical shape with Ar ion-milling and SiO2 insulation overlayer
Summary
Device structure and TMR and TMC under no bias voltage. Figure 1a shows the device structure prepared by a magnetron sputtering system with a base pressure of 2 × 10−8 Torr, with the following layer sequence: SiO2/Ta(5)/Co50Fe50(2)/IrMn(15)/Co50Fe50(2)/Ru(0.8)/Co40Fe40B20(3)/MgO(2)/Co40Fe40B20(3)/contact layer (thickness in nm). The capacitance CAP increases at around zero bias and it decreases at higher voltages This behavior is in good agreement with the results calculated by Eqs (4)−(6) with parameters of C∞,AP = 1.5 nF, C0,AP = 590 nF, βAP = 0.977, τP = 0.0075 s, PTMC = 0.46, f = 60 Hz, κ = 0.1, S = 1800 μm[2] and λ = 0.1 nm. The enhancement of TMC is attributed to the emergence of the spin capacitance in the AP configuration of MTJs. The voltage-induced TMC increases to 102%, which is the largest value ever reported for MTJs. We found the voltage-induced TMC can be well explained by a newly proposed theoretical calculation using DF model combined with QBA and SDD model. The large TMC effect and the associated robustness against biasing may open up new avenues for spintronics applications and electrical modeling
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