Magnetic tunnel junctions with metastable bcc Co₃Mn electrodes

Abstract

We studied magnetic tunnel junctions (MTJs) with a MgO(001) barrier and metastable bcc Co3Mn(001) disordered alloy electrodes. A tunnel magnetoresistance (TMR) ratio was approximately 200%–250% observed at room temperature. We successfully observed the TMR ratio greater than 600% at 10 K which was higher than the past reported value of MgO-based MTJs with ultrathin bcc Co(001) electrodes. However, our experimental value was still much lower than the past theoretical prediction in bcc Co/MgO/Co(001) MTJs. We discuss some differences in the bulk band structure affecting the TMR effect for bcc Co and bcc Co3Mn.

Lattice Softening in Metastable bcc CoxMn100−x (001) Ferromagnetic Layers for a Strain-Free Magnetic Tunnel Junction

“…From this analysis, we obtained P0 of 0.87 and A of 1.7 x10 -5 K -3/2 . A is found to be twice as large as that observed in Fe/MgO/Fe MTJs at (7)(8)(9) ´ 10 -6 K -3/2 [27]. Ghop are also plotted in the figure, which is relatively large at RT.…”

“…The TMR ratios measured at 10 K and 300 K show almost square curves for -6 -the lower Co concentration of x = 75 and 66 as seen in Figs. 1(a) and 1(b) [22][23], while the curves for the higher Co concentration of x = 86 and 83 at 10K and 300K contain stronger components of magnetisation rotation [see Figs. 1(a) and 1(b)].…”

“…MTJ samples were prepared using conventional magnetron sputtering with a base pressure of 2 ´ 10 -7 Pa. MgO(001) single crystal substrates were used for the deposition of MTJ consisting of Cr (40)/CoxMn100-x (10)/MgO (2.4 and 20)/CoxMn100-x (4)/Co3Fe(1.5)/IrMn (10)/Ru (5) (thickness in nm) with a Ti and Au top electrode as illustrated in the inset of Fig. 1(a) [22] [23]. Two different thicknesses of the MgO layers were used for MTJs with 2.4 nm and reference samples with 20 nm.…”

“…However, the detailed mechanism of the crystallisation process and the corresponding interfacial strain as well as their resulting advantages of MgO over the other epitaxial barriers have yet to be understood conclusively. Recently we reported a high TMR ratio over 600% -4 -(200%) at 10K (RT) in metastable bcc CoxMn100-x (CoMn)/MgO/CoMn MTJs and discussed the relationship between their magnetism and TMR effect [22] [23]. However, the relationship between their TMR ratios and their crystalline structures is not yet clear.…”

IrCrMnZ (Z=Al, Ga, Si, Ge) Heusler alloys as electrode materials for MgO-based magnetic tunneling junctions: A first-principles study

“…Misfit dislocation resulting from lattice mismatch between electrode and barrier material, is also regarded as another source of reduction of TMR ratio. [12][13][14] Lattice mismatch results in a misfit dislocation at the interface, and could affect coherent tunneling through the barrier. This lattice mismatch is significantly large in case of Co 2 MnSi/MgO (001) MTJ, which is about 5%.…”