Giant tunnel magnetoresistance in polycrystalline magnetic tunnel junctions with highly textured MgAl2O4(001) based barriers

Abstract

Although single-crystalline spinel (MgAl2O4)-based magnetic tunnel junctions (MTJs) are known to show a good bias voltage dependence of a tunnel magnetoresistance (TMR) ratio over MgO-based MTJs, no polycrystalline MgAl2O4-based MTJs exhibiting large TMR ratios have been grown previously due to the lack of crystallinity of the MgAl2O4 barrier. In this work, we demonstrate the growth of polycrystalline-based MTJs with large TMR ratios exceeding 240% and an improved bias voltage dependence compared to that of MgO-based MTJs. An ultra-thin CoFe/MgO seed layer on the amorphous CoFeB layer induced the growth of a highly (001)-textured MgAl2O4 barrier, which worked as a template layer for the solid epitaxy of CoFe grains during the crystallization of the CoFeB layers. High resolution scanning transmission electron microscopy shows lattice-matched epitaxy between the (001)-textured MgAl2O4 barrier and CoFe grains. This study demonstrates the industrial viability of MgAl2O4-based polycrystalline MTJs with an improved bias voltage dependence.

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

“…For example, zero-bias TMR of 377% and 89% are observed in MgO- and AlO-based MTJs using Co 70 Fe 30 FM layers, and it decreases to 75% and 20%, respectively, at a bias voltage of 0.5 V 21 . The improvement of bias-reduced TMR has been reported in MTJs with a small lattice mismatch (a few percent) between the FM and the insulating layers 22 – 27 . Zero-bias TMR is 92% in fully epitaxial Fe/MgO/GaO x /Fe MTJs, and the half biasing voltage V 1/2 , where the TMR is halved, can be raised to 0.5 V 22 .…”

“…Further improvement has been reported. TMR is 240% near zero bias, and it keeps a large value of 180% at 0.5 V in MgAl 2 O 4 -based MTJs 27 . Nevertheless, a bias voltage always reduces TMR, which remains an essential problem in the applications of MTJs.…”

Large Magnetoresistance in Scandium Nitride Magnetic Tunnel Junctions Using First Principles

“…There is ongoing research in developing barrier materials with large 𝑇𝑀𝑅 ratios to try to compete with MgO, largely in the class of Mg oxide alloys [23][24][25] . In one simulation study, ZnO 26 with rock salt structure, bandgap 2.132 eV at the Γ point, and indirect gap of 0.913 eV showed 𝑇𝑀𝑅 = 446% and 𝑅𝐴 = 0.0468 Ω-µ𝑚 2 .…”

“…There is ongoing research in developing barrier materials with large ratios to try to compete with MgO, largely in the class of Mg oxide alloys. [ 21,22 ] In one simulation study, ZnO [ 23 ] with rock salt structure, bandgap 2.132 eV at the Γ point, and indirect gap of 0.913 eV showed = 446% and = 0.0468 Ω‐ There is also recent interest in exploring alternate electrode materials for higher spin polarization; one such example is the use of Heusler compounds for both electrodes and barrier materials. A recent work on NiMnSb‐MgO junctions [ 24 ] predicted high > 10 4 .…”

Tunneling anisotropic magnetoresistance in fully epitaxial magnetic tunnel junctions with different barriers

“…Recently, the MgAlO x oxide with the spinel structure has been investigated as a promising candidate for the MTJ barrier due to its smaller lattice mismatch with a usual ferromagnetic electrode. [19][20][21][22][23][24] An improved bias dependence of TMR 19,25 and enhanced quantum well states 26 in MgAlO x barrier based MTJs have been realized owing to the high quality of the MgAlO x /ferromagnet interfaces. The IRSs, which impact the TAMR effect, should be modified in MTJs with different barriers.…”