Tunneling anomalous Hall effect in nanogranular CoFe-B-Al-O films near the metal-insulator transition

Rylkov, V. V.; Николаев, С. Н.; Chernoglazov, K. Yu.; Демин, В. А.; Ситников, А. В.; Presnyakov, M. Yu.; Vasiliev, A. L.; Перов, Н. С.; Веденеев, А. С.; Kalinin, Yu. E.; Тугушев, В. В.; Granovsky, A. B.

doi:10.1103/physrevb.95.144202

Cited by 47 publications

(18 citation statements)

References 50 publications

(70 reference statements)

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“…The field and temperature dependencies of magnetization for studied samples (Fig.1 [3]. The saturation field for in-plane geometry is less than that for out-ofplane case, increases gradually when x decreases from 57 to 47 at.%, and does not exceed 0.6-0.7 T. This behavior can be easily understood taking into account demagnetization effects.…”

Section: Magnetizationmentioning

confidence: 76%

“…The nanocomposites (Co84Nb14Ta2)x(Al-O)1-x with x=47-57 at.% were obtained by the ion-beam sputtering of targets, which consisted of a metal base of the Co84Nb14Ta2 alloy with several Al2O3 plates on its surface. Details of this method are presented in [3,5]. The thickness of samples was about d=2.7µm.…”

Section: Methodsmentioning

confidence: 99%

“…Recent discovery of memristor effect in metalinsulator nanostructures, in particular in those based on non-stoichiometric oxides AlOz (z<1.5) [1,2], triggered renewed interest to structural, magnetic and magnetotransport properties of magnetic nanocomposites [3,4]. In the case of (CoFeB)x (Al-O)1-x nanogranular thin films with metal content x=49-56 at.% it was found a large number of Co, Fe and B atoms dispersed in Al-O matrix [3], logarithmic temperature dependence of conductivity [3,4] and tunnel anomalous Hall effect [3]. These observations raised numerous questions on dominant transport mechanisms in nanocomposites.…”

Section: Introductionmentioning

confidence: 99%

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High field magnetoresistance of nanocomposites (Co₈₄Nb₁₄Ta₂)X(Al₂O₃)_100-X near the percolation threshold

et al. 2018

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We present results of experimental studies of magnetic properties, resistivity and magnetoresistance (MR) of (Co84Nb14Ta2)x(Al2O3)100-x films deposited onto a glass-ceramic substrate by the ion-beam sputtering, focusing on MR in high magnetic fields for compositions close to the percolation threshold (x=47-57 at.%). The samples consist on Co-Nb-Ta metallic nanogranules size of 2-5 nm which are embedded into the non-stoichiometric Al-O matrix. Magnetization was measured by SQUID magnetometer at T=4.2-350 K. MR was studied in the pulsed magnetic fields μ0H up to 20 T at T=70-300 K in three geometries: magnetic field in plane parallel and perpendicular to current, magnetic field perpendicular to plane. The pulse duration was 11-12 ms. For the sample with x=57 at.% the temperature dependence of conductivity follows the lnT behavior that matches a strong tunnel coupling between nanogranules. With decreasing metal volume fraction lnT behavior gradually changes to the T1/2 dependence at 47 at.%. For all samples MR is small (<1%) and negative. For x<57 at.% it is slightly anisotropic at μ0H<1.0 T and almost saturates with increasing magnetic field. There is an evidence of small positive contribution to MR at μ0H=20T. Accordingly to structural and magnetic data a large amount of metallic atoms are located between magnetic nanogranules that diminish the tunnel barrier height and make tunnel MR small and weakly dependent on temperature.

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Section: Magnetizationmentioning

confidence: 76%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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High field magnetoresistance of nanocomposites (Co₈₄Nb₁₄Ta₂)X(Al₂O₃)_100-X near the percolation threshold

et al. 2018

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“…The unique scaling of the associated TAHE conductances could make the effect a fundamental tool for identifying and characterizing interfacial SOC, thus providing the input for tailoring systems that could, e.g., host Majoranas. Although first experiments on granular junctions [48] confirmed the predictions, the extremely small TAHE conductances remain one of the main obstacles. Sizable TAHE conductances require either interfacial barriers with large SOC, such as ferroelectric semiconductors (SCs) [47], or different junction compositions.…”

mentioning

confidence: 94%

Skew Andreev reflection in ferromagnet/superconductor junctions

2019

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Andreev reflection (AR) in ferromagnet/superconductor junctions is an indispensable spectroscopic tool for measuring spin polarization. We study theoretically how the presence of a thin semiconducting interface in such junctions, inducing Rashba and Dresselhaus spin-orbit coupling, modifies AR processes. The interface gives rise to a momentum-and spin-dependent scattering potential, making the AR probability strongly asymmetric with respect to the sign of the incident electrons' transverse momenta. This skew AR creates spatial charge carrier imbalances and transverse Hall currents in the ferromagnet. We show that the effect is giant, compared to the normal regime. We provide a quantitative analysis and a qualitative picture of this phenomenon, and finally show that skew AR also leads to a widely tunable transverse supercurrent response in the superconductor. strate that, analogously to the tunneling picture in the normalconducting case, skew reflection [49] of spin-polarized carriers at the barrier leads to TAHEs in the F. Due to the presence of a S electrode, we distinguish two skew reflection processes: skew specular reflection (SR) and skew Andreev reflection (AR). By formulating a qualitative physical picture including both processes, we assert that skew SR and skew AR can act together and significantly enhance the TAHE compared to all previously studied (normal) systems. Special attention must be paid to skew AR, which transfers Cooper pairs across the barrier into the S. The electrons forming one Cooper pair are thereby also subject to the proposed skew reflection mechanism. We discuss that the result is a transverse supercurrent response, initially deduced from a phenomenological Ginzburg-Landau treatment [50], with widely tunable characteristics. Both findings, relatively giant TAHE conductances in the F and transverse supercurrents in the S, are distinct fingerprints to experimentally detect skew AR and characterize the junctions' interfacial SOC.We consider a biased ballistic F/SC/S junction grown along theẑ-direction, in which the two semi-infinite F and S regions are separated by an ultrathin SC barrier [see Fig. 1(a)]. The barrier may be composed of a thin layer of zincblende materials (e.g., GaAs or InAs) and introduces potential scattering, as well as strong interfacial Rashba [16] and Dresselhaus [17] SOC [18,19].The system can be modeled by means of the stationary Bogoljubov-de Gennes (BdG) Hamiltonian [51],SCσ0 δ(z)+Ĥ SOC SC δ(z) represents the single-electron Hamiltonian andĤ h = −σ yĤ * eσy its holelike counterpart (σ 0 andσ i indicate the 2 × 2 identity and the ith Pauli matrix; σ = [σ x ,σ y ,σ z ] is the vector of Pauli matrices). The F is described within the Stoner model with exchange energy ∆ XC and magnetization directionm = [cos Φ, sin Φ, 0] , where Φ is measured with respect to thex-axis. Following earlier studies [52-56], the ultrathin SC layer is included into our model as a δ-like barrier with height V SC and width d SC ; its SOC enters the Hamiltonian [18, 19]Ĥ SOC SC = α (k yσx ...

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“…Those spin-currents become essential in view to control the magnetization state of a nanomagnet, via the spin-Hall effect of heavy material either semiconductor [1][2][3][4][5] or metals [6,[12][13][14][15]. The interplay between particle spin and orbital motion is currently at the basis of a new family of effects like the Anomalous Tunnel Hall effect described by the generation of a charge current transverse to a tunneling spin-current [7][8][9][10] or the spin-galvanic effects [11]. SOI at an interface with broken inversion symmetry may lead to the observation of Rashba-split states [16,17] which may be used to convert a flow of spin-current into a transverse charge current by inverse Edelstein effect (IEE) [18,19].…”

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confidence: 99%

Theory of the anomalous tunnel hall effect at ferromagnet-semiconductor junctions

Dang

Erina

et al. 2018

Journal of Magnetism and Magnetic Materials

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We report on theoretical investigations of carrier scattering asymmetry at ferromagnet-semiconductor junctions. By an analytical 2 × 2 spin model, we show that, when Dresselhaus interactions is included in the conduction band of III-V T d symmetry group semiconductors, the electrons may undergo a difference of transmission vs. the sign of their incident parallel wavevector normal to the in-plane magnetization. This asymmetry is universally scaled by a unique function independent of the spin-orbit strength. This particular feature is reproduced by a multiband k · p tunneling transport model. Astonishingly, the asymmetry of transmission persists in the valence band of semiconductors owing to the inner atomic spin-orbit strength and free of asymmetric potentials . We present multiband 14 × 14 and 30 × 30 k · p tunneling models together with tunneling transport perturbation calculations corroborating these results. Those demonstrate that a tunnel spin-current normal to the interface can generate a surface transverse charge current, the so-called Anomalous Tunnel Hall Effect. PACS numbers: 72.25.Mk, 75.70.Tj, 75.76.+j I -INTRODUCTIONSpinorbitronics is a science that uses the spin degree of freedom together with the spin-orbit interactions (SOI) to generate spin-currents without the need of a ferromagnetic material. Those spin-currents become essential in view to control the magnetization state of a nanomagnet, via the spin-Hall effect of heavy material either semiconductor [1][2][3][4][5] or metals [6,[12][13][14][15]. The interplay between particle spin and orbital motion is currently at the basis of a new family of effects like the Anomalous Tunnel Hall effect described by the generation of a charge current transverse to a tunneling spin-current [7][8][9][10] or the spin-galvanic effects [11]. SOI at an interface with broken inversion symmetry may lead to the observation of Rashba-split states [16,17] which may be used to convert a flow of spin-current into a transverse charge current by inverse Edelstein effect (IEE) [18,19]. Recent magnetoresistance (MR) measurements with an unidirectional character (UMR) have been evidenced in metallic [20] and semiconductor bilayers [21] as well as with topological insulator (TI) [22]. It was ascribed to the asymmetric scattering of electrons by magnons absorption-emission processes at ferromagnet-TI interfaces. It clearly reveals a novel symmetry in the field of MR explained by a certain carrier scattering asymmetry incorporated in the Boltzmann transport equation developed at the second order. An anisotropy of electronic diffusion on the Fermi surface along the current direction leads to a supplementary non-linear contribution of M R proportional to the current.In this article, as an extension to our previous work [9], we study unconventional quantum effects resulting in a giant transport asymmetry of carriers in semiconductor heterostructures, interfaces, tunnel barriers or quantum wells. Those are composed of ferromagnets and spin-orbit split electrodes made of semicond...

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Tunneling anomalous Hall effect in nanogranular CoFe-B-Al-O films near the metal-insulator transition

Cited by 47 publications

References 50 publications

High field magnetoresistance of nanocomposites (Co₈₄Nb₁₄Ta₂)X(Al₂O₃)_100-X near the percolation threshold

High field magnetoresistance of nanocomposites (Co₈₄Nb₁₄Ta₂)X(Al₂O₃)_100-X near the percolation threshold

Skew Andreev reflection in ferromagnet/superconductor junctions

Theory of the anomalous tunnel hall effect at ferromagnet-semiconductor junctions

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Tunneling anomalous Hall effect in nanogranular CoFe-B-Al-O films near the metal-insulator transition

Cited by 47 publications

References 50 publications

High field magnetoresistance of nanocomposites (Co84Nb14Ta2)X(Al2O3)100-X near the percolation threshold

High field magnetoresistance of nanocomposites (Co84Nb14Ta2)X(Al2O3)100-X near the percolation threshold

Skew Andreev reflection in ferromagnet/superconductor junctions

Theory of the anomalous tunnel hall effect at ferromagnet-semiconductor junctions

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Product

Resources

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High field magnetoresistance of nanocomposites (Co₈₄Nb₁₄Ta₂)X(Al₂O₃)_100-X near the percolation threshold

High field magnetoresistance of nanocomposites (Co₈₄Nb₁₄Ta₂)X(Al₂O₃)_100-X near the percolation threshold