A First Principle Study of the Massive TMR in Magnetic Tunnel Junction Using Fe3Al Heusler Alloy Electrodes and MgO Barrier (original) (raw)
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Scientific reports, 2018
Recently magnetic tunnel junctions using two-dimensional MoS as nonmagnetic spacer have been fabricated, although their magnetoresistance has been reported to be quite low. This may be attributed to the use of permalloy electrodes, injecting current with a relatively small spin polarization. Here we evaluate the performance of MoS-based tunnel junctions using FeSi Heusler alloy electrodes. Density functional theory and the non-equilibrium Green's function method are used to investigate the spin injection efficiency (SIE) and the magnetoresistance (MR) ratio as a function of the MoS thickness. We find a maximum MR of ~300% with a SIE of about 80% for spacers comprising between 3 and 5 MoS monolayers. Most importantly, both the SIE and the MR remain robust at finite bias, namely MR > 100% and SIE > 50% at 0.7 V. Our proposed materials stack thus demonstrates the possibility of developing a new generation of performing magnetic tunnel junctions with layered two-dimensional co...
Computational Materials Science, 2022
In this work, employing density functional theory based electronic structure calculations, we search for an alternative to MgO as a spacer layer in a magnetic tunneling junction(MTJ), with half-metallic(HM) Co 2 MnSb as an electrode. First, we demonstrate the possibility of designing an all-Heusler alloy based MTJ with semiconducting(SC) TiCoSb alloy as the spacer material. We probe the robustness of the HM properties of the Mn-Sb/Co interface and show that the HM property is preserved, even with various disorders and defects. The spin-dependent transport behavior indicates that these properties depend sensitively on the heterojunction interfaces and thickness of the spacer material. Further, we study the transport properties of the heterojunctions of Co 2 MnSb alloy with the well-studied insulator MgO as well as the less-explored systems like, NaCl and AlN. In these three insulating materials, the smallest complex band decay coefficient is associated with 1 symmetry, unlike TiCoSb. This feature enables more desirable symmetry-based spin-filtering properties at the point in the 2D Brillouin zone. We further calculate the resistance area (RA) product for all the heterojunctions, important for the realization of highly sensitive magnetic sensors and it is found that the other spacer layers yield a RA product, several orders less in magnitude compared to that of TiCoSb. Our results indicate that NaCl and AlN may be promising as an alternative to MgO as a spacer material. With the chemical compatibilities resulting into minimal interface buckling and an ultra-low RA product, TiCoSb may also be a promising new material for a MTJ with Co 2 MnSb as electrode, specifically in relation to overcoming the variability and current-injection challenges.
Magnetic tunnel junctions with an equiatomic quaternary CoFeMnSi Heusler alloy electrode
Applied Physics Letters, 2018
Tunnel magnetoresistance (TMR) in MgO-based magnetic tunnel junctions (MTJs) with equiatomic quaternary CoFeMnSi Heusler and CoFe alloy electrodes is studied. The epitaxial MTJ stacking structures were prepared using ultrahigh-vacuum magnetron sputtering, where the CoFeMnSi electrode has a full B2 and partial L21 ordering crystal structure. Maximum TMR ratios of 101% and 521% were observed at room temperature and 10 K, respectively, for the MTJs. The large bias voltage dependence of the TMR ratio was also observed at low temperature (LT), as similarly observed in Co2MnSi Heusler alloy-based MTJs in the past. The physical origins of this relatively large TMR ratio at LT were discussed in terms of the half-metallicity of CoFeMnSi.
Scientific Reports, 2018
Recently magnetic tunnel junctions using two-dimensional MoS 2 as nonmagnetic spacer have been fabricated, although their magnetoresistance has been reported to be quite low. This may be attributed to the use of permalloy electrodes, injecting current with a relatively small spin polarization. Here we evaluate the performance of MoS 2-based tunnel junctions using Fe 3 Si Heusler alloy electrodes. Density functional theory and the non-equilibrium Green's function method are used to investigate the spin injection efficiency (SIE) and the magnetoresistance (MR) ratio as a function of the MoS 2 thickness. We find a maximum MR of ~300% with a SIE of about 80% for spacers comprising between 3 and 5 MoS 2 monolayers. Most importantly, both the SIE and the MR remain robust at finite bias, namely MR > 100% and SIE > 50% at 0.7 V. Our proposed materials stack thus demonstrates the possibility of developing a new generation of performing magnetic tunnel junctions with layered two-dimensional compounds as spacers.
IEEE Transactions on Magnetics, 2000
Transport, as well as chemical and magnetic interface properties of two kinds of magnetic tunnel junctions (MTJs) with Co 2 FeSi electrode, Al-O barrier, and Co-Fe counter electrode, are investigated. For junctions with Co 2 FeSi single-layer electrodes, a tunnel magnetoresistance of up to 52% is found after optimal annealing for an optimal Al thickness of 1.5 nm, whereas the room temperature bulk magnetization of the Co 2 FeSi film reaches only 75% of the expected value. By using a [Co 2 MnSi/Co 2 FeSi] 10 multilayer electrode, the magnetoresistance can be increased to 114%, corresponding to a large spin polarization of 0.74, and the full bulk magnetization is reached. For Al thickness smaller than 1 nm, the TMR of both kinds of MTJs decreases rapidly to zero. On the other hand, for 2-to 3-nm-thick Al, the TMR decreases only slowly. The Al thickness dependence of the TMR is directly correlated to the element-specific magnetic moments of Fe and Co at the Co 2 FeSi/Al-O interface for all Al thickness. Especially, for optimal Al thickness and annealing, the interfacial Fe moment of the single-layer electrode is about 20% smaller than for the multilayer electrode, indicating smaller atomic disorder at the barrier interface for the latter MTJ.
Magnetic tunnel junctions with a B2 -ordered CoFeCrAl equiatomic Heusler alloy
Physical Review Materials, 2019
The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for spin-gapless semiconductors (SGSs). However, to date, there have been no experimental attempts at fabricating 3 a junction device. This paper reports a fully epitaxial (001)-oriented MgO barrier magnetic tunnel 4 junction (MTJ) with CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction 5 measurements show that the (001) CoFeCrAl electrode films with atomically flat surfaces have a 6 B2-ordered phase. The saturation magnetization is 380 emu/cm 3 , almost the same as the value 7 given by the Slater-Pauling-like rule, and the maximum tunnel magnetoresistance ratios at 300 8 K and 10 K are 87% and 165%, respectively. Cross-sectional electron diffraction analysis shows 9 that the MTJs have MgO interfaces with fewer dislocations. The temperature-and bias-voltagedependence of the transport measurements indicates magnon-induced inelastic electron tunneling overlapping with the coherent electron tunneling. X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic arrangement of the Co and Fe magnetic moments of B2ordered CoFeCrAl, in contrast to the ferrimagnetic arrangement predicted for the Y-ordered state possessing SGS characteristics. Ab-initio calculations taking account of the Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect of the Cr-Fe swap disorder on the ability for electronic states to allow coherent electron tunneling is discussed. I. INTRODUCTION A spin-gapless semiconductor (SGS) is a material in which the Fermi level is located at a zero-energy gap state for a majority spin band and at an energy gap for a minority spin band.[1-3] SGSs belong to the class of half-metals that have fully spin-polarized carriers at the Fermi level, so they exhibit a huge magnetoresistance (MR) and low spin relaxation (the so-called Gilbert damping). These physical properties are ideally suited to solid-state spintronic devices, and are commonly observed in half-metals.[4-10] In addition to such physical properties, SGSs could be used to realize devices with new functionalities, such as reconfigurable magnetic tunnel diodes and transistors,[11] which use their gapless electronic characteristics. Therefore, it is of fundamental and technological importance to investigate