Magnetic microstructure of candidates for epitaxial dual Heusler magnetic tunnel junctions (original) (raw)
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Thin Solid Films, 2014
High resolution transmission electron microscopy, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co 2 MnGe(13 nm)/ Al 2 O 3 (3 nm)/Co(13 nm) tunnel magnetic junctions (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al 2 O 3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co 2 MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co 2 MnGe film. The large Co concentration in the Al 2 O 3 interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates.
Co 2 MnSi as full Heusler alloy ferromagnetic electrode in magnetic tunneling junctions
physica status solidi c, 2006
The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunneling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunneling resistance, where a strong dependence of the tunneling current on an external magnetic field can be found. In order to obtain large magnetoresistance effects, materials with strongly spin polarized electron gas around the Fermi level have to be found. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co 2 MnSi. First, experimental aspects of the integration of this alloy in magnetic tunneling junctions will be addressed. With these junctions, we obtain up to 100% TMR at low temperature. The current status of this research will then be summarized with special regard to the complex diffusion mechanisms occurring in these devices and to the properties of the interfaces between the Heusler material and the insulator.
Tunnel magnetoresistance of disordered, low-moment Co[sub 2]MnSi Heusler alloy thin films
Journal of Applied Physics, 2005
Thin films of Co ͑1−x−y͒ Mn x Si y ͑x = 0.18-0.26 and y = 0.23-0.29͒ were deposited from elemental targets onto thermal-oxidized Si substrates at room temperature using dc magnetron cosputtering. The as-deposited films appear to be amorphous showing no distinguishable peaks in x-ray diffraction, and the magnetic moment at room temperature is nearly zero. Despite of its low magnetic moment ͑less than 0.001 B per formula͒, the disordered Heusler magnetic tunnel junctions show tunnel magnetoresistance ratios as large as 10% at room temperature. The dependence of the tunnel magnetoresistance ratio on compositions x and y is also reported.
Journal of Applied Physics, 2007
Growth and magnetic characterization of thin films of Co2Cr0.6Fe0.4Al and Co2MnSi full-Heusler compounds are investigated. Thin films were deposited by magnetron sputtering at room temperature directly onto oxidized Si wafers. These Heusler films are magnetically very soft and ferromagnetic with Curie temperatures well above room temperature. Polycrystalline Co2Cr0.6Fe0.4Al Heusler films combined with MgO barriers and CoFe counter electrodes are structured to magnetic tunnel junctions and yield almost 50% magnetoresistance at room temperature. The magnetoresistance shows a strong bias dependence with the maximum occurring at a voltage drop well above 1V. This special feature is accompanied by only a moderate temperature dependence of the tunnel magnetoresistance.
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.
Two series of Co2MnAl CMA and Co2MnAlO CMAO thin films deposited on Si 100 coated with thermo-SiO2 by using two CoMnAl targets were studied. One target is oxygen-free and the other one contains 0.8% oxygen. The properties of the two series CMA O films strongly depend on deposition conditions and seed layers. The oxygen impurity is a key factor to influence the properties. It would obviously increase the thickness of magnetic dead layer, weaken the magnetic anisotropy, and significantly decrease the spin polarization in CMA film. The magnetoresistance ratios of IrMn pinned top-type magnetic tunnel junctions by utilizing CMAO/CMA as the bottom ferromagnetic electrode were 19% and 68%, respectively.
Journal of Applied Physics, 2009
Two series of Co 2 MnAl ͑CMA͒ and Co 2 MnAlO ͑CMAO͒ thin films deposited on Si ͑100͒ coated with thermo-SiO 2 by using two CoMnAl targets were studied. One target is oxygen-free and the other one contains 0.8% oxygen. The properties of the two series CMA ͑O͒ films strongly depend on deposition conditions and seed layers. The oxygen impurity is a key factor to influence the properties. It would obviously increase the thickness of magnetic dead layer, weaken the magnetic anisotropy, and significantly decrease the spin polarization in CMA film. The magnetoresistance ratios of IrMn pinned top-type magnetic tunnel junctions by utilizing CMAO/CMA as the bottom ferromagnetic electrode were 19% and 68%, respectively.
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.
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.