Magnetization dynamics at finite temperature in CoFeB–MgO based MTJs

Abstract

The discovery of magnetization switching via spin transfer torque (STT) in PMA-based MTJs has led to the development of next-generation magnetic memory technology with high operating speed, low power consumption and high scalability. In this work, we theoretically investigate the influence of finite size and temperature on the mechanism of magnetization switching in CoFeB–MgO based MTJ to get better understanding of STT-MRAM fundamentals and design. An atomistic model coupled with simultaneous solution of the spin accumulation is employed. The results reveal that the incoherent switching process in MTJ strongly depends on the system size and temperature. At 0 K, the coherent switching mode can only be observed in MTJs with the diameter less than 20 nm. However, at any finite temperature, incoherent magnetization switching is thermally excited. Furthermore, increasing temperature results in decreasing switching time of the magnetization. We conclude that temperature dependent properties and thermally driven reversal are important considerations for the design and development of advanced MRAM systems.

Thermodynamic properties and switching dynamics of perpendicular shape anisotropy MRAM

“…where the terms on the RHS from left to right are the isotropic exchange energy, the magnetic anisotropy, the applied magnetic field from the zeeman interaction, and the demagnetising term [4]. The two constants, k u and µ s , are the uniaxial anisotropy constant per atom and the atomic spin moment respectively.…”

“…where γ is the gyro-magnetic ratio, λ is the microscopic damping moment and B eff = − 1 µs ∂H ∂Si is the effective field acting on the local spin [4,30]. Thus, the LLG equation describes how an atomistic spin moment interacts with an effective field.…”

“…These features are often predicted to make MRAM the universal memory of the future, replacing both DRAM and SRAM on the market. However, for this to be a reality, MRAM needs to be scaled down to a sub-20 nm dimension to compete with the density of DRAM while maintaining a compromise of sufficiently high thermal stability for data retention and a low writing current [2][3][4][5].…”

“…Since this study focuses on cylindrical shape PSA-MRAM, the demagnetisation field is a particularly essential addition to the effective field. The LLG equation is then integrated using the Heun predictor-corrector integration algorithm which is well suited to the stochastic nature with larger time-steps for computational efficiency [4,22,25]. Now that we have discussed the mathematical models used in vampire, we now outline the atomistic details of the PSA-MRAM tower structures.…”

Dimensional scaling effects on critical current density and magnetization switching in CoFeB-based magnetic tunnel junction

“…been opened up by the discovery of the STT phenomenon [1,2]. The magnetic tunnel junction (MTJ) consisting of two ferromagnets (FMs) separated by a thin insulator is a crucial component of the reading and writing processes in magnetic data storage systems [3,4]. STT-MRAM is a novel type of non-volatile memory that utilizes magnetic characteristics and magnetization direction to store data in the form of binary bits [5].…”