99 research outputs found
Large Tunneling Anisotropic Magneto-Seebeck Effect in a CoPt|MgO|Pt Tunnel Junction
We theoretically investigate the Tunneling Anisotropic Magneto-Seebeck effect
in a realistically-modeled CoPt|MgO|Pt tunnel junction using coherent transport
calculations. For comparison we study the tunneling magneto-Seebeck effect in
CoPt|MgO|CoPt as well. We find that the magneto-Seebeck ratio of CoPt|MgO|Pt
exceeds that of CoPt|MgO|CoPt for small barrier thicknesses, reaching 175% at
room temperature. This result provides a sharp contrast to the
magnetoresistance, which behaves oppositely for all barrier thicknesses and
differs by one order of magnitude between devices. Here the magnetoresistance
results from differences in transmission brought upon by changing the tunnel
junction's magnetization configuration. The magneto-Seebeck effect results from
variations in asymmetry of the energy-dependent transmission instead. We report
that this difference in origin allows for CoPt|MgO|Pt to possess strong thermal
magnetic-transport anisotropy.Comment: 6 pages, 6 figure
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Spin Hall effect emerging from a noncollinear magnetic lattice without spin-orbit coupling
The spin Hall effect (SHE), which converts a charge current into a transverse spin current, has long been believed to be a phenomenon induced by spin-orbit coupling. Here, we identify an alternative mechanism to realize the intrinsic SHE through a noncollinear magnetic structure that breaks the spin rotation symmetry. No spin-orbit coupling is needed even when the scalar spin chirality vanishes, different from the case of the topological Hall effect and topological SHE reported previously. In known noncollinear antiferromagnetic compounds Mn3X (X = Ga, Ge, and Sn), for example, we indeed obtain large spin Hall conductivities based on ab initio calculations
Recommended from our members
Spin Hall effect emerging from a noncollinear magnetic lattice without spin-orbit coupling
The spin Hall effect (SHE), which converts a charge current into a transverse spin current, has long been believed to be a phenomenon induced by spin-orbit coupling. Here, we identify an alternative mechanism to realize the intrinsic SHE through a noncollinear magnetic structure that breaks the spin rotation symmetry. No spin-orbit coupling is needed even when the scalar spin chirality vanishes, different from the case of the topological Hall effect and topological SHE reported previously. In known noncollinear antiferromagnetic compounds Mn3X (X = Ga, Ge, and Sn), for example, we indeed obtain large spin Hall conductivities based on ab initio calculations
Spin-orbit torques in locally and globally non-centrosymmetric crystals: antiferromagnets and ferromagnets
One of the main obstacles that prevents practical applications of antiferromagnets is the dfficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný et al., PRL 113, 157201 (2014)], the electrical switching of magnetic moments in an antiferromagnet has been demonstrated [P. Wadley et al., Science 351, 587 (2016)]. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a non-equilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally non-centrosymmetric crystals. We study when the symmetry allows or a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be effcient for manipulating antiferromagnetic moments
On the similarity of Sturm-Liouville operators with non-Hermitian boundary conditions to self-adjoint and normal operators
We consider one-dimensional Schroedinger-type operators in a bounded interval
with non-self-adjoint Robin-type boundary conditions. It is well known that
such operators are generically conjugate to normal operators via a similarity
transformation. Motivated by recent interests in quasi-Hermitian Hamiltonians
in quantum mechanics, we study properties of the transformations in detail. We
show that they can be expressed as the sum of the identity and an integral
Hilbert-Schmidt operator. In the case of parity and time reversal boundary
conditions, we establish closed integral-type formulae for the similarity
transformations, derive the similar self-adjoint operator and also find the
associated "charge conjugation" operator, which plays the role of fundamental
symmetry in a Krein-space reformulation of the problem.Comment: 27 page
Electric control of Dirac quasiparticles by spin-orbit torque in an antiferromagnet
Spin orbitronics and Dirac quasiparticles are two fields of condensed matter physics initiated independently about a decade ago. Here we predict that Dirac quasiparticles can be controlled by the spin-orbit torque reorientation of the Néel vector in an antiferromagnet. Using CuMnAs as an example, we formulate symmetry criteria allowing for the coexistence of topological Dirac quasiparticles and Néel spin-orbit torques. We identify the nonsymmorphic crystal symmetry protection of Dirac band crossings whose on and off switching is mediated by the Néel vector reorientation. We predict that this concept verified by minimal model and density functional calculations in the CuMnAs semimetal antiferromagnet can lead to a topological metal-insulator transition driven by the Néel vector and to the topological anisotropic magnetoresistance
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