Working with epitaxial films of Fe, we succeeded in independent control of different scattering processes in the anomalous Hall effect. The result appropriately accounted for the role of phonons, thereby clearly exposing the fundamental flaws of the standard plot of the anomalous Hall resistivity versus longitudinal resistivity. A new scaling has been thus established that allows an unambiguous identification of the intrinsic Berry curvature mechanism as well as the extrinsic skew scattering and side-jump mechanisms of the anomalous Hall effect.PACS numbers: 75.47.Np;72.15.Eb;73.50.Jt Shortly after the discovery of the Hall effect, in 1880 Edwin Hall further observed in ferromagnetic metals an additional large contribution besides the ordinary one, which is now called the anomalous Hall effect (AHE) -one of the most prominent phenomena existing in magnetic materials [1]. While the ordinary Hall effect has been well understood as a result of the Lorentz force deflecting the charge carriers, the mechanism of the AHE has remained controversial despite the long history of research, because its rich phenomenology defies the standard classification methodology, prompting conflicting reports claiming the dominance of various processes [2][3][4][5][6][7][8][9][10][11][12]. Recently it again attracts great attention because of its natural connection to the spin Hall effect and quantum spin Hall effect [13,14].In ferromagnets, the transverse resistivity has two contributions: one is ordinary and is proportional to the applied magnetic field; the other is anomalous and is normally proportional to the magnetization [8,9]. It is often written aswhere r 0 and r a are coefficients that characterize the strength of the ordinary and anomalous Hall resistivity ρ h and ρ ah , respectively.

Magnetotransport properties have been investigated for epitaxial thin films of B20-type MnSi grown on Si(111) substrates. Lorentz transmission electron microscopy images clearly point to the robust formation of Skyrmions over a wide temperature-magnetic field region. New features distinct from those reported previously for MnSi are observed for epitaxial films: a shorter (nearly half) period of the spin helix and Skyrmions, and a topological Hall effect anomaly consisting in ∼2.2 times enhancement of the amplitude and in the opposite sign with respect to bulk samples.

Valley pseudospin, the quantum degree of freedom characterizing the degenerate valleys in energy bands 1 , is a distinct feature of two-dimensional Dirac materials [1][2][3][4][5] . Similar to spin, the valley pseudospin is spanned by a time reversal pair of states, though the two valley pseudospin states transform to each other under spatial inversion. The breaking of inversion symmetry induces various valley-contrasted physical properties; for instance, valley-dependent topological transport is of both scientific and technological interests [2][3][4][5] . Bilayer graphene (BLG) is a unique system whose intrinsic inversion symmetry can be controllably broken by a perpendicular electric field, offering a rare possibility for continuously tunable valley-topological transport. Here, we used a perpendicular gate electric field to break the inversion symmetry in BLG, and a giant nonlocal response was observed as a result of the topological transport of the valley pseudospin. We further showed that the valley transport is fully tunable by external gates, and that the nonlocal signal persists up to room temperature and over long distances. These observations challenge contemporary understanding of topological transport in a gapped system, and the robust topological transport may lead to future valleytronic applications.In crystalline solids, a topological current can be induced by the Berry phase of the electronic wave function 6 . Examples include the quantum Hall current in a magnetic field, and the spin Hall current arising from spin-orbit coupling. Such topological transport is robust against impurities and defects in materials -a feature that is much sought after in potential electronic applications. In such applications, the ability to switch and to continuously tune the topological transport is crucial. The topological current is in principle dictated by the crystal symmetry, which is difficult to change in Page 3 of 16 bulk materials. Bilayer graphene, however, offer new opportunities in which inversion symmetry can be controllably broken by an external electric field in the perpendicular direction.The topological current controlled by the inversion symmetry breaking is associated with carriers' valley pseudospin, which characterises the two-fold degenerate band-edges located at the corners of the hexagonal Brillouin zone. The topological Hall current, odd under time-reversal but even under inversion, is strictly zero in pristine mono-and bi-layer graphene which respect both symmetries. When the inversion symmetry is broken, however, time-reversal symmetry requires the Hall currents to have opposite signs and equal magnitudes in the two valleys (i.e., a valley The nonlocal transport persists up to room temperature and over long distances (up to 10 m). Our results represent major progress in the quest for a robust, tunable valley pseudospin system among various alternatives [3][4][5]11,12 , and indicate the possibility of using the nonlocal topological transport in practical applications under ambient conditio...

This Letter provides evidence for intrinsic longitudinal spin Seebeck effects (LSSEs) that are free from the anomalous Nernst effect (ANE) caused by an extrinsic proximity effect. We report the observation of LSSEs in Au/Y(3)Fe(5)O(12) (YIG) and Pt/Cu/YIG systems, showing that the LSSE appears even when the mechanism of the proximity ANE is clearly removed. In the conventional Pt/YIG structure, furthermore, we separate the LSSE from the ANE by comparing the voltages in different magnetization and temperature-gradient configurations; the ANE contamination was found to be negligibly small even in the Pt/YIG structure.

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We report a large and nonvolatile bipolar-electric-field-controlled magnetization at room temperature in a Co(40)Fe(40)B(20)/Pb(Mg(1/3)Nb(2/3))(0.7)Ti(0.3)O(3) structure, which exhibits an electric-field-controlled looplike magnetization. Investigations on the ferroelectric domains and crystal structures with in situ electric fields reveal that the effect is related to the combined action of 109° ferroelastic domain switching and the absence of magnetocrystalline anisotropy in Co(40)Fe(40)B(20). This work provides a route to realize large and nonvolatile magnetoelectric coupling at room temperature and is significant for applications.

The four α-cobalt hydroxides (green or blue) with different intercalated anions were synthesized by a chemical precipitation route in which polyethylene glycol was used as the structure-directing reagent for application in the electrode materials of electrochemical capacitors. Every one among the four samples displays an interesting and distinctive morphology although the synthesis conditions were the same except for the anions. The intercalated anions have a critical effect on the basal plane spacing, morphologies, and capacitive properties of the products. Structural and morphological characterizations were performed by using power X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The component and thermal stability of the sample were respectively measured by FT-IR and thermal analyses, including thermogravimetry (TG) and differential thermogravimetry (DTG). The electrochemical behaviors were measured by cyclic voltammogram and galvanostatic charge−discharge. The specific capacitance is up to 697 F g−1 at a charge−discharge current density of 1 A g−1 for the sample with intercalated chlorine. But the sample with intercalated sulfate, which has small crystalline size, more disordered structure, and almost perfect alveolate nanostructure with a large surface area, exhibits relatively poor specific capacitance (420 F g−1). The exceptive phenomena caused by intercalated anions were explained by hydrogen bonding and electrostatic forces. Moreover, the relationships between the specific capacitance, basal plane spacing, as well as the content of the interlayer water were discussed in detail for the four as-synthesized samples.

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