Role of CoFeB thickness in electric field controlled sub-100 nm sized magnetic tunnel junctions

Abstract

We report a comprehensive study on the role of the free layer thickness (tF) in electric-field controlled nanoscale perpendicular magnetic tunnel junctions (MTJs), comprising of free layer structure Ta/Co40Fe40B20/MgO, by using dc magnetoresistance and ultra-short magnetization switching measurements. Focusing on MTJs that exhibits positive effective device anisotropy (Keff), we observe that both the voltage-controlled magnetic anisotropy (ξ) and voltage modulation of coercivity show strong dependence on tF. We found that ξ varies dramatically and unexpectedly from ∼−3 fJ/V-m to ∼−41 fJ/V-m with increasing tF. We discuss the possibilities of electric-field tuning of the effective surface anisotropy term, KS as well as an additional interfacial magnetoelastic anisotropy term, K3 that scales with 1/tF2. Voltage pulse induced 180° magnetization reversal is also demonstrated in our MTJs. Unipolar switching and oscillatory function of switching probability vs. pulse duration can be observed at higher tF, and agrees well with the two key device parameters — Keff and ξ.

Emergent Dynamics of Artificial Spin-Ice Lattice Based on an Ultrathin Ferromagnet

“…We have also considered a simplistic way to look into the static magnetic state distribution for ASIs by assuming them an ensemble of weakly interacting single domain particles. , Systems similar to the W/CoFeB/MgO structure are expected to have domain wall width ∼140 nm , and so individual nanostructures can be assumed as single domain systems in their relaxed state. However, because our ensemble of nanostructures is fairly widely spaced and the magnetic layer is also ultrathin, there will be negligible dipolar interactions between them.…”

Multi‐State Magnetic Tunnel Junction Programmable by Nanosecond Spin‐Orbit Torque Pulse Sequence

“…[ 51 ] On the other hand, for perpendicular SOT switching, the transition point is similar at ≈1 ns. [ 52 ] While sub‐ns switching has been reported before using STT in IP‐MTJs [ 53,54 ] or electric‐field in p MTJs, [ 55 ] the write‐voltage‐margin or the write‐error‐rate is significantly compromised at lower pulse widths. [ 56 ] Hence, for the practical implementation of MTJs on an array level‐chip, the pulse width transition point is more important than reducing the absolute value of switching time at any pulse sweep cycle.…”

Thickness and Ferroelectric Polarization Influence on Film Magnetic Anisotropy across a Multiferroic Material Interface

“…On the one hand, a state of strong perpendicular magnetocrystalline anisotropy (PMA) (i.e., where perpendicular magnetization with respect to the film surface is highly stabilized) of the free magnetic layer increases the thermal stability of the device and results in longer data retention times . On the other hand, a state of weaker PMA of the free layer decreases the critical switching current and therefore the overall energy expenditure of device operations. , Since both PMA states are considered advantageous in different stages of device operation, VCMA, which facilitates the transitioning from one state to the other, has increasingly become the focus of much enthusiastic scientific investigation, , both in theoretical − and experimental studies. − …”