Temperature dependence of giant tunnel magnetoresistance in epitaxial Fe/MgO/Fe magnetic tunnel junctions

Abstract

The temperature dependence of giant tunnel magnetoresistance ͑TMR͒ in epitaxial Fe/MgO/Fe magnetic tunnel junctions has been investigated. The resistance in the parallel configuration between the bottom ͑free͒ Fe layer and the top Fe layer, exchange biased by an IrMn antiferromagnetic layer, is nearly independent of the temperature. In contrast, in the antiparallel configuration the resistance increases with decreasing temperature, resulting in an increase in the TMR ratio from 170% at room temperature to 318% at 10 K. The dynamic conductance ͑GЈ = dI / dV͒ in the parallel configuration shows flat bias voltage dependence in the range Ϯ0.4 V, but in the antiparallel configuration it shows typical parabolic behavior as a function of bias voltage. A model, based on the temperature dependence of magnetic disorder in the two electrodes and its effect on the spin-dependent tunneling, is proposed to describe the temperature dependence of the TMR ratio and the resistance, in good agreement with our experimental data.

Structural characterization of interfaces in epitaxial Fe/MgO/Fe magnetic tunnel junctions by transmission electron microscopy

“…[12][13][14][15][16][17][18][19][20] In this work, we report on a detailed structural characterization of epitaxial Fe/MgO/Fe layers, which when fabricated to a MTJ, achieved a TMR value of 170% at room temperature. 6,16 Although fully epitaxial structures will probably not be used in commercial devices, they are model systems to compare experimental results and theoretical calculations and to study spin-polarized coherent tunneling. [4][5][6][7] In particular, the aim of this work is to characterize the interface structure of epitaxial Fe/MgO/Fe multilayers, which when fabricated into MTJ devices, demonstrate among the highest TMR ratios to date.…”

“…[3][4][5][6][7][8] Significant progress has been since achieved with sputter-deposited CoFeB/MgO/CoFeB magnetic tunnel junctions ͑MTJs͒ in which the CoFeB ferromagnetic electrode is amorphous. [9][10][11] For these MTJ, TMR ratios of 604% at room temperature have been reported, 9 which is of interest for technological applications such as in magnetic random access memory and magnetic sensors.…”

Evidence for magnon excitation contribution to the magnetoresistance behavior during thermal annealing in CoFeB/MgO/CoFeB magnetic tunnel junctions

“…This departure increases the AP conductance, leading to a lower MR ratio. 5,26 Second, Mn diffusion can cause the deterioration of the crystal structure of the CoFeB layers, which plays a negative role in spin-dependent tunneling across the MgO barrier. Third, the diffused Mn atoms are located at CoFeB/MgO interfaces or inside the MgO barrier as magnetic impurities, together with a change of the interfacial structure, which enhances the spin flipping scattering, leading to a lower MR ratio.…”

“…MgO-based magnetic tunnel junctions (MTJs) have been investigated widely due to their interesting fundamental physics and potential applications. [1][2][3][4][5][6][7][8] Thermal annealing is a critical process for sputtered CoFeB/MgO/CoFeB junctions because the tunnel magnetoresistance (TMR) ratio of junctions annealed at an appropriate temperature increases dramatically. [9][10][11][12][13] Annealing greatly improves the crystallinity of the MgO barrier and ferromagnetic (FM) CoFeB electrodes as well as the interfaces between the MgO and CoFeB layers, 10,12 which enhances spin-dependent tunneling across the MgO barrier.…”

Structure of epitaxial L1-FePt/MgO perpendicular magnetic tunnel junctions

“…Detailed information regarding growth and MTJ fabrication was reported previously. 21,22 The overall crystallographic structure of the MTJs was determined by conventional high-resolution transmission electron microscopy (phase-contrast, HR-TEM), and selected area electron diffraction (SAED), using a JEOL JEM-2100F. Cscorrected high-angle annular dark-field (HAADF) STEM was chosen to characterize the structure of the L1 0 -FePt/MgO interface.…”