Enhanced half-metallicity of off-stoichiometric quaternary Heusler alloy 
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 investigated through saturation magnetization and tunneling magnetoresistanc

Moges, Kidist; Honda, Yuichi; Liu, Hong Xi; Uemura, Tetsuya; Yamamoto, Mikio; Miura, Yoshio; Shirai, Masamitsu

doi:10.1103/physrevb.93.134403

Cited by 53 publications

(31 citation statements)

References 59 publications

(98 reference statements)

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“…Thus, the P deduced from Eq. (1) is the value determined by ρ M and ρ m arising from the electronic states contributing to coherent tunneling [12,17]. In this sense, the deduced P should be called the tunneling spin polarization, although we will still refer to it as the tunneling spin polarization or spin polarization without distinguishing the meanings.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Half-metallic ferromagnets (HMFs) are one of the most suitable spin source materials because of their complete spin polarization at the Fermi level (E F ) arising from an energy gap for one spin direction (mostly the minority-spin band) [3]. Co-based Heusler alloys (Co 2 Y Z, where Y is usually a transition metal and Z is a main group element) [4] are among the most extensively applied to spintronic devices, including magnetic tunnel junctions (MTJs) [5][6][7][8][9][10][11][12][13][14][15][16][17] and giant magnetoresistance (GMR) devices [18][19][20][21][22], and for spin injection into semiconductors [23][24][25][26][27]. This is because of the HMF nature theoretically predicted for many of these alloys [28][29][30][31] and because of their high Curie temperatures, which are well above room temperature [32].…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, it was shown that harmful Co Mn antisites can be suppressed and half-metallicity enhanced by preparing CMS thin films with a Mn-rich composition [9][10][11][12]. It was also shown that (Mn + Fe)-rich compositions are critical to suppressing these harmful antisites and to retaining the half-metallic electronic states for Co 2 (Mn,Fe)Si (CMFS) quaternary alloys [16,17]. Given these findings, we demonstrated giant TMR ratios of up to 1995% at 4.2 K and up to 354% at 290 K for CMS/MgO/CMS MTJs (CMS MTJs) having Mn-rich CMS electrodes [11] and up to 2610% at 4.2 K and 429% at 290 K for CMFS/MgO/CMFS MTJs (CMFS MTJs) with Mn-rich, lightly Fe-doped CMFS electrodes [16].…”

Section: Introductionmentioning

confidence: 99%

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Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

Moges

Honda

et al. 2016

Phys. Rev. B

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In order to elucidate the origin of the temperature (T ) dependence of spin-dependent tunneling conductance (G) of magnetic tunnel junctions (MTJs), we experimentally investigated the T dependence of G for the parallel and antiparallel magnetization alignments, G P and G AP , of high-quality Co 2 MnSi (CMS)/MgO/CMS MTJs having systematically varied spin polarizations (P ) at 4.2 K by varying the Mn composition α in Co 2 Mn α Si electrodes that exhibited giant tunneling magnetoresistance ratios. Results showed that G P normalized by its value at 4.2 K exhibited a notable, nonmonotonic T dependence although its variation with T was significantly smaller than that of G AP normalized by its value at 4.2 K, indicating that an analysis of the experimental G P (T ) is critical to revealing the origin of the T dependence of G. By analyzing the experimental G P (T ), we clarified that both spin-flip inelastic tunneling via a thermally excited magnon and spin-conserving elastic tunneling in which P decays with increasing T play key roles. The experimental G AP (T ), including its stronger T dependence for higher P at 4.2 K, was also consistently explained with this model. Our findings provide a unified picture for understanding the origin of the T dependence of G of MTJs with a wide range of P , including MTJs with high P close to a half-metallic value.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

Moges

Honda

et al. 2016

Phys. Rev. B

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“…Highly spin-polarized current source is essential for spintronic devices [1][2][3][4][5][6]. For magnetic tunnel junctions (MTJs), highly spin-polarized ferromagnetic electrodes can achieve large tunneling magnetoresistance (TMR) [7].…”

Section: Introductionmentioning

confidence: 99%

Magnetic tunnel junctions consisting of a periodic grating barrier and two half-metallic electrodes

et al. 2019

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We have developed a spintronic theory for magnetic tunnel junctions consisting of a single-crystal barrier and two half-metallic ferromagnetic electrodes. Radically different from the conventional theories, the barrier is now regarded as an optical diffraction grating, and treated by the traditional optical scattering method, i.e. Bethe theory and two-beam approximation. After tunneling, the electrons can thus possess high coherence. In the case that the electrodes are both half-metallic, the conventional theories give an infinite tunneling magnetoresistance (TMR). By contrast, in the Bethe theory and two-beam approximation, there can exist the scattering channels of nonconservation of energy. Therefore, the TMR can still be far away from infinity, which is in accordance with experiments. Also, we find that, due to the half-metallicity of the electrodes, the parallel conductance oscillates with temperature whereas the antiparallel conductance will increase other than oscillate with temperature. That is in agreement with experiments, too. Finally, two applications of the present theory are discussed with regard to the material design and engineering: one is how to choose appropriate materials for the barrier to realize infinite TMR; the other is a criterion for judging whether a material is half-metallic or not.

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“…A Co-based Heusler alloy is an excellent ferromagnetic candidate for spintronic devices, including magnetic tunnel junctions (MTJs) [26][27][28][29][30][31][32][33][34][35], giant magnetoresistance devices [36][37][38][39][40][41][42], and for spin injection into semiconductors [43][44][45][46][47][48], due to its complete spin polarization at the Fermi level [49][50][51]. We recently reported high tunneling magnetoresistance ratios of up to 1995% at 4.2 K and up to 354% at 290 K in MTJs having Mn-rich Co 2 MnSi (CMS) electrodes [32], and found ratios of 2610% at 4.2 K and 429% at 290 K in Mn-rich Co 2 (Mn,Fe)Si MTJs [33,34], demonstrating a high spin polarization of CMS and CMFS. Moreover, we achieved highly efficient spin injection into a GaAs channel by using Mn-rich CMS as a spin source [23,46].…”

Section: Introductionmentioning

confidence: 99%

Systematic investigations of transient response of nuclear spins in the presence of polarized electrons

2017

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We electrically probed the transient response of nuclear spins in an n-GaAs channel by performing Hanle signal and spin-valve signal measurements on an all-electrical spin-injection device having a half-metallic spin source of Co 2 MnSi. Furthermore, we simulated the Hanle and spin-valve signals by using the time evolution of nuclear-spin polarization under the presence of polarized electron spins by taking both T 1e and T 1 into consideration, where T −1 1e is the polarization rate of nuclear spins through the transfer of angular momentum from polarized electron spins and T −1 1 is the depolarization rate of nuclear spins through the interaction with the lattice. The simulation results reproduced our experimental results on all the nuclear-spin-related phenomena appearing in the Hanle and spin-valve signals at different measurement conditions, providing quantitative explanation for the transient response of nuclear spins in GaAs to a change in magnetic fields and an estimate of the time scales of T 1e and T 1 . These experimental and simulated results will deepen the understanding of nuclear-spin dynamics in semiconductors.

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Enhanced half-metallicity of off-stoichiometric quaternary Heusler alloy Co2(Mn,Fe)Si investigated through saturation magnetization and tunneling magnetoresistanc

Cited by 53 publications

References 59 publications

Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

Magnetic tunnel junctions consisting of a periodic grating barrier and two half-metallic electrodes

Systematic investigations of transient response of nuclear spins in the presence of polarized electrons

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