Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy∕MgO∕CoFe junctions (original) (raw)
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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.
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.
Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl
arXiv (Cornell University), 2022
Heusler alloys based magnetic tunnel junctions can potentially provide high magnetoresistance, small damping and fast switching. Here junctions with Co2FeAl as a ferromagnetic electrode are fabricated by room temperature sputtering on Si/SiO2 substrates. The doping of Boron in Co2FeAl is found to have a large positive impact on the structural, magnetic and transport properties of the junctions, with a reduced interfacial roughness and substantial improved tunneling magnetoresistance. A two-level magnetoresistance is also observed in samples annealed at low temperature, which is believed to be related to the memristive effect of the tunnel barrier with impurities.
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.
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.
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.
Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers
AIP Advances, 2015
We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co2FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier wit...
Magnetic microstructure of candidates for epitaxial dual Heusler magnetic tunnel junctions
Journal of Magnetism and Magnetic Materials, 2009
Heusler alloys are considered as interesting ferromagnetic electrode materials for magnetic tunnel junctions, because of their high spin polarization. We therefore investigated the micromagnetic properties in a prototypical thin film system comprising two different Heusler phases Co2MnSi (CMS) and Co2FeSi (CFS) separated by a MgO barrier. The magnetic microstructure was investigated by x-ray photoemission microscopy (XPEEM). We find a strong influence of the Heusler phase formation process on the magnetic domain patterns. SiO2/V/CMS/MgO/CFS and SiO2/V/CFS/MgO/CMS trilayer structures exhibit a strikingly different magnetic behavior, which is due to pinhole coupling through the MgO barrier and a strong thickness dependence of the magnetic ordering in Co2MnSi.
Large inverse tunneling magnetoresistance in Co2Cr0.6Fe0.4Al∕MgO∕Co80Fe20 magnetic tunnel junctions
Applied Physics Letters, 2007
Magnetic tunnel junctions with the layer sequence Co2Cr0.6Fe0.4Al∕MgO∕Co80Fe20 were fabricated by magnetron sputtering at room temperature (RT). The samples exhibit a large inverse tunneling magnetoresistance (TMR) effect of up to −66% at RT. The largest value of −84% at 20K reflects a rather weak influence of temperature. The dependence on the voltage drop shows an unusual behavior with two almost symmetric peaks at ±600mV with large inverse TMR ratios and small positive values around zero bias.