Abstract: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 a junction device. This paper reports a fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction measurements show that the (001) CoFeCrAl electrode films with atomically flat surfaces have a B2-ordered phase. The saturation magnetiz… Show more
“…The first-generation spintronic devices are based on magnetoresistive (MR) junctions, which have been used very widely [ 3 , 4 ], e.g ., a read head in a hard disk drive (HDD) [ 5 ] and a cell in a magnetic random access memory (MRAM) [ 6 ]. The critical measure of efficient magnetic transport in these devices is an MR ratio, which is defined by 152 170 183 289 359 360 361 367 367 384 382 383 348 349 …”
Section: Introductionmentioning
confidence: 99%
“… Figure 13. Four possible energy band structures for spin gapless semiconductors with parabolic dispersion energy against momentum [ 382 ] …”
Heusler alloys are theoretically predicted to become half-metals at room temperature (RT). The advantages of using these alloys are good lattice matching with major substrates, high Curie temperature above RT and intermetallic controllability for spin density of states at the Fermi energy level. The alloys are categorised into half- and full-Heusler alloys depending upon the crystalline structures, each being discussed both experimentally and theoretically. Fundamental properties of ferromagnetic Heusler alloys are described. Both structural and magnetic characterisations on an atomic scale are typically carried out in order to prove the half-metallicity at RT. Atomic ordering in the films is directly observed by X-ray diffraction and is also indirectly probed via the temperature dependence of electrical resistivity. Element specific magnetic moments and spin polarisation of the Heusler alloy films are directly measured using X-ray magnetic circular dichroism and Andreev reflection, respectively. By employing these ferromagnetic alloy films in a spintronic device, efficient spin injection into a non-magnetic material and large magnetoresistance are also discussed. Fundamental properties of antiferromagnetic Heusler alloys are then described. Both structural and magnetic characterisations on an atomic scale are shown. Atomic ordering in the Heusler alloy films is indirectly measured by the temperature dependence of electrical resistivity. Antiferromagnetic configurations are directly imaged by X-ray magnetic linear dichroism and polarised neutron reflection. The applications of the antiferromagnetic Heusler alloy films are also explained. The other non-magnetic Heusler alloys are listed. A brief summary is provided at the end of this review.
“…The first-generation spintronic devices are based on magnetoresistive (MR) junctions, which have been used very widely [ 3 , 4 ], e.g ., a read head in a hard disk drive (HDD) [ 5 ] and a cell in a magnetic random access memory (MRAM) [ 6 ]. The critical measure of efficient magnetic transport in these devices is an MR ratio, which is defined by 152 170 183 289 359 360 361 367 367 384 382 383 348 349 …”
Section: Introductionmentioning
confidence: 99%
“… Figure 13. Four possible energy band structures for spin gapless semiconductors with parabolic dispersion energy against momentum [ 382 ] …”
Heusler alloys are theoretically predicted to become half-metals at room temperature (RT). The advantages of using these alloys are good lattice matching with major substrates, high Curie temperature above RT and intermetallic controllability for spin density of states at the Fermi energy level. The alloys are categorised into half- and full-Heusler alloys depending upon the crystalline structures, each being discussed both experimentally and theoretically. Fundamental properties of ferromagnetic Heusler alloys are described. Both structural and magnetic characterisations on an atomic scale are typically carried out in order to prove the half-metallicity at RT. Atomic ordering in the films is directly observed by X-ray diffraction and is also indirectly probed via the temperature dependence of electrical resistivity. Element specific magnetic moments and spin polarisation of the Heusler alloy films are directly measured using X-ray magnetic circular dichroism and Andreev reflection, respectively. By employing these ferromagnetic alloy films in a spintronic device, efficient spin injection into a non-magnetic material and large magnetoresistance are also discussed. Fundamental properties of antiferromagnetic Heusler alloys are then described. Both structural and magnetic characterisations on an atomic scale are shown. Atomic ordering in the Heusler alloy films is indirectly measured by the temperature dependence of electrical resistivity. Antiferromagnetic configurations are directly imaged by X-ray magnetic linear dichroism and polarised neutron reflection. The applications of the antiferromagnetic Heusler alloy films are also explained. The other non-magnetic Heusler alloys are listed. A brief summary is provided at the end of this review.
“…Co-based Heusler alloys have attracted prime attention of the researchers, because of their suitability in terms of highly spin-polarized conduction electrons, and high Curie temperature (T C ), which are the crucial prerequisites for spintronics application to obtain spin-polarized current at room temperature. [1][2][3][4][5][6][7] The most studied Heusler alloy as the electrode material of MgO-based magnetic tunnel junctions (MTJs) is Co 2 MnSi. [1,8] It is a long-standing challenge for the researchers to obtain large tunneling magnetoresistance (TMR) ratio at room temperature.…”
We study IrCrMnZ (Z=Al, Ga, Si, Ge) systems using first-principles calculations from the perspective of their application as the electrode materials of MgO-based MTJs. These materials have highly spin-polarized conduction electrons with partially occupied ∆ 1 band, which is important for coherent tunneling in parallel magnetization configuration. The Curie temperatures of IrCrMnAl and IrCrMnGa are very high (above 1300 K) as predicted from mean-field-approximation. The stability of ordered phase against various antisite disorders has been investigated. We discuss here the effect of "spin-orbit-coupling" on the electronic structure around Fermi level. Further, we investigate the electronic structure of IrCrMnZ/MgO heterojunction along (001) direction. Ir-CrMnAl/MgO and IrCrMnGa/MgO maintain half-metallicity even at the MgO interface, with no interfacial states at/around Fermi level in the minority-spin channel. Large majority-spin conductance of IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa is reported from the calculation of ballistic spin-transport property for parallel magnetization configuration. We propose IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa as promising MTJs with a weaker temperature dependence of tunneling magnetoresistance ratio, owing to their very high Curie temperatures.
“…High tunnelling magnetoresistance (TMR) ratios of > 600% were obtained at room temperature (RT) [4] [5][6] [7]. Recently, the other ferromagnetic alloys such as half-metallic ferromagnetic Heusler alloys and metastable ferromagnets, e.g., Co75Mn25, have been employed as electrodes in MTJ [8][9] [10]. However, the corresponding TMR ratios measured experimentally are still far below from theoretical predictions of > 1,000% at RT [11] [12].…”
In spintronics, one of the long standing questions is why the MgO-based magnetic tunnel junction (MTJ) is almost the only option to achieve a large tunnelling magnetoresistance (TMR) ratio at room temperature (RT) but not as large as the theoretical prediction. This study focuses on the development of an almost strain-free MTJ using metastable bcc CoxMn100-x ferromagnetic films. We have investigated the degree of crystallisation in MTJ consisting of CoxMn100-x/MgO/CoxMn100-x (x = 66, 75, 83 and 86) in relation to their TMR ratios. Cross-sectional high resolution transmission electron microscopy (HRTEM) reveals that almost consistent lattice constants of these layers for 66 ≤ x ≤ 83 with maintaining large TMR ratios of 229% at RT, confirming the soft nature of the CoxMn100-x layer with some dislocations at the MgO/Co75Mn25 interfaces. For x = 86, on the other hand, the TMR ratio is found to be reduced to 142% at RT, which is partially attributed to the increased number of the dislocations at the MgO/Co86Mn14 interfaces and amorphous grains identified in the MgO -2 -barrier. Ab-initio calculations confirm the crystalline deformation stability across a broad compositional range in CoMn, proving the advantage of a strain-free interface for much larger TMR ratios.
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