Xiaopeng Duan

Electrically controlled magnetization in ferromagnet-topological insulator heterostructures

An approach to the electrostatic control of

Electrical switching of antiferromagnets via strongly spin-orbit coupled materials

90^{\circ}

Spin logic via controlled correlation in a topological insulator-nanomagnet hybrid structure

magnetization rotation in the hybrid structures composed of topological insulators (TIs) and adjacent ferromagnetic insulators (FMI) is proposed and studied. The concept is based on TI electron energy variation with in-plane to put-of plane FMI magnetization turn. The calculations explicitly expose the effect of free energy variability in the form of the electrically controlled uniaxial magnetic anisotropy, which depends on proximate exchange interaction and TI surface electron density. Combining with inherent anisotropy, the magnetization rotation from in-plane to out-of-plane direction is shown to be realizable for 1.7~2.7 ns under the electrical variation of TI chemical potential in the range

Quasi-optical electron transport across a magnetically induced junction on a topological insulator surface

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Magnetic domain wall transfer via graphene mediated electrostatic control

100 meV around Dirac point. When bias is withdrawn a small signal current can target the out-of-plane magnetization instable state to the desirable direction of in-plane easy axis, thus the structure can lay the foundation for low energy nonvolatile memory prototype.

Electrically controlled switching of antiferromagnets via proximity interaction induced by topological insulator

Electrically controlled ultra-fast switching of an antiferromagnet (AFM) is shown to be realizable by interfacing it with a material of strong spin-orbit coupling. The proximity interaction between the sublattice magnetic moments of a layered AFM and the spin-polarized free electrons at the interface offers an efficient way to manipulate antiferromagnetic states. A quantitative analysis, using the combination with a topological insulator as an example, demonstrates highly reliable 90° and 180° rotations of AFM magnetic states under two different mechanisms of effective torque generation at the interface. The estimated switching speed and energy requirement are in the ps and aJ ranges, respectively, which are about two-three orders of magnitude better than the ferromagnetic counterparts. The observed differences in the magnetization dynamics may explain the disparate characteristic responses. Unlike the usual precessional/chiral motions in the ferromagnets, those of the AFMs can essentially be described as...

Highly efficient conductance control in a topological insulator based magnetoelectric transistor

A magnetic switching device implemented with a majority-gate logic structure is explored as a potential candidate for beyond-CMOS technology. Specifically, a novel switching mechanism is envisioned that relies on the unique magneto-electric properties of a hybrid structure consisting of topological insulator (TI), insulating ferromagnet (FM) and graphene (Gr) in the Bennett clocking operation scheme (Fig. 1A). A circuit layout is proposed and the logic operation demonstrated in a 1-bit adder.

Proposal of a topological insulator based magnetoelectric transistor

Quasi-optical Dirac electron transport is theoretically analyzed at the magnetic boundaries on a topological insulator (TI) surface. The electronic band mismatch induced by the spatially varying magnetization profile can form an effective junction akin to the electrostatic potential step. The transmission/reflection characteristics show a direct dependence on electron energy and incident angle with highly asymmetric patterns. The investigation also illustrates a nontrivial anomalous Hall current along the boundary which is further shown by a numerical simulation based on the finite-difference time-domain method. The results provide key design guidelines for prospective quasi-optical devices based on the TI-magnet heterostructures.

Electric field driven domain wall transfer in hybrid structures

A mechanism that enables electrically controlled magnetic domain wall transfer in a ferromagnetic insulator (FMI) is investigated theoretically by utilizing graphene as a crucial mediating material. The concept is grounded on the variability of the exchange interaction energy between a ferromagnetic insulator and a proximate graphene layer with an inhomogeneous carrier density. A memory device prototype is proposed based on the effect that does not require an active current for its intrinsic function. Our analysis illustrates the highly efficient device operation, with an estimated switching energy of 10−16 J for one binary bit of nonvolatile information.

Voltage-driven magnetic bifurcations in nanomagnet–topological insulator heterostructures

Here, we propose an electrical control of antiferromagnet (AFM) by utilizing the proximity interaction between a topological insulator (TI) and an AFM. Following the Bennett clocking scheme, this mechanism shows much faster switching speed and higher logic reliabilities compared to its ferromagnetic counterpart according to micro-magnetic simulations. Consequently, both switching period and power consumption are reduced by 2-3 orders of magnitude making the TI-AFM system a better candidate for spintronic applications.