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Register a new userDetection of the Orbital Hall Effect by the Orbital-Spin Conversion
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The intrinsic orbital Hall effect (OHE), the orbital counterpart of the spin Hall effect, was predicted and studied theoretically for more than one decade, yet to be observed in experiments. Here we propose a strategy to convert the orbital current in OHE to the spin current via the spin-orbit coupling from the contact. Furthermore, we find that OHE can induce large nonreciprocal magnetoresistance when employing magnetic contact. Both the generated spin current and the orbital Hall magnetoresistance can be applied to probe the OHE in experiments and design orbitronic devices.
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Spin Hall effect, an electric generation of spin current, allows for efficient control of magnetization. Recent theory revealed that orbital Hall effect creates orbital current, which can be much larger than spin Hall-induced spin current. However, orbital current cannot directly exert a torque on a ferromagnet, requiring a conversion process from orbital current to spin current. Here, we report two effective methods of the conversion through spin-orbit coupling engineering, which allows us to unambiguously demonstrate orbital-current-induced spin torque, or orbital Hall torque. We find that orbital Hall torque is greatly enhanced by introducing either a rare-earth ferromagnet Gd or a Pt interfacial layer with strong spin-orbit coupling in Cr/ferromagnet structures, indicating that the orbital current generated in Cr is efficiently converted into spin current in the Gd or Pt layer. Furthermore, we show that the orbital Hall torque can facilitate the reduction of switching current of perpendicular magnetization in spin-orbit-torque-based spintronic devices.
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Carrying information using generation and detection of the orbital current, instead of the spin current, is an emerging field of research, where the orbital Hall effect (OHE) is an important ingredient. Here, we propose a new mechanism of the OHE that occurs in {it non-}centrosymmetric materials. We show that the broken inversion symmetry in the 2D transition metal dichalcogenides (TMDCs) causes a robust orbital moment, which flow in different directions due to the opposite Berry curvatures under an applied electric field, leading to a large OHE. This is in complete contrast to the inversion-symmetric systems, where the orbital moment is induced only by the external electric field. We show that the valley-orbital locking as well as the OHE both appear even in the absence of the spin-orbit coupling. The non-zero spin-orbit coupling leads to the well-known valley-spin locking and the spin Hall effect, which we find to be weak, making the TMDCs particularly suitable for direct observation of the OHE, with potential application in {it orbitronics}.
We use symmetry analysis and first principles calculations to show that the linear magnetoelectric effect can originate from the response of orbital magnetic moments to the polar distortions induced by an applied electric field. Using LiFePO4 as a model compound we show that spin-orbit coupling partially lifts the quenching of the 3d orbitals and causes small orbital magnetic moments ($mu_{(L)}approx 0.3 mu_B$) parallel to the spins of the Fe$^{2+}$ ions. An applied electric field $mathbf{E}$ modifies the size of these orbital magnetic moments inducing a net magnetization linear in $mathbf{E}$.
We report electronic structure calculations of an iron impurity in gold host. The spin, orbital and dipole magnetic moments were investigated using the LDA+$U$ correlated band theory. We show that the {em around-mean-field}-LDA+$U$ reproduces the XMCD experimental data well and does not lead to formation of a large orbital moment on the Fe atom. Furthermore, exact diagonalization of the multi-orbital Anderson impurity model with the full Coulomb interaction matrix and the spin-orbit coupling is performed in order to estimate the spin Hall angle. The obtained value $gamma_S approx 0.025$ suggests that there is no giant extrinsic spin Hall effect due to scattering on iron impurities in gold.
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