Yufan Li

Topological charge analysis of ultrafast single skyrmion creation

Magnetic skyrmions are topologically nontrivial spin textures of potential interest for future information storage applications, and for such purposes, the control and understanding of single skyrmion creation is required. A scheme is analyzed to create single Neel-type and Bloch-type skyrmions in helimagnetic thin films utilizing the dynamical excitations induced by the Oersted field and the spin transfer torque given by a vertically injected spin-polarized current. A topological charge analysis using a lattice version of the topological charge provides insight into the locally triggered transition from a trivial to a nontrivial topological spin texture of the Neel or Bloch type skyrmion. The topological protection of the magnetic skyrmion is determined by the symmetric Heisenberg exchange energy. The critical switching current density is

Separation of spin Seebeck effect and anomalous Nernst effect in Co/Cu/YIG

ensuremath{sim}{10}^{7}phantom{rule{4pt}{0ex}}{mathrm{A}/mathrm{cm}}^{2}

Large magneto-optical Kerr effect and imaging of magnetic octupole domains in an antiferromagnetic metal

, which decreases with the easy-plane type uniaxial anisotropy and thermal fluctuations. The in-plane spin polarization of the injected current performs better than out-of-plane polarization, and it provides ultrafast switching times (within 100 ps) and reliable switching outcomes.

Electrical Detection of the Helical Spin Texture in a p-type Topological Insulator Sb2Te3.

The spin Seebeck effect (SSE) and Anomalous Nernst effect (ANE) have been observed in Co/Cu/YIG (yttrium iron garnet) multi-layer structure, where the ferromagnetic insulator YIG acts as the pure spin injector and the ferromagnetic metal Co layer acts as the spin current detector. With the insertion of 5u2009nm Cu layer, the two ferromagnetic layers are decoupled, thus allowing unambiguous separation of the SSE and ANE contributions under the same experimental conditions in the same sample.

Manipulation of pure spin current in ferromagnetic metals independent of magnetization

The magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of ferro- and ferrimagnetic materials as a powerful probe for electronic and magnetic properties1–3 and for magneto-optical technologies4. The MOKE can be additionally useful for the investigation of the antiferromagnetic (AF) state, although thus far limited to insulators5–9. Here, we report the first observation of the MOKE in an AF metal. In particular, we find that the non-collinear AF metal Mn3Sn (ref. 10) exhibits a large zero-field Kerr rotation angle of 20 mdeg at room temperature, comparable to ferromagnetic metals. Our first-principles calculations clarify that ferroic ordering of magnetic octupoles11 produces a large MOKE even in its fully compensated AF state. This large MOKE further allows imaging of the magnetic octupole domains and their reversal. The observation of a large MOKE in an AF metal will open new avenues for the study of domain dynamics as well as spintronics using antiferromagnets12–16.The magneto-optical Kerr effect is demonstrated in an antiferromagnetic metal. Large rotation angles, magnetic octupole domain imaging was enabled.

Topological Charge Analysis of Single Skyrmion Creation with a Nanosecond Current Pulse

The surface states of 3D topological insulators (TIs) exhibit a helical spin texture with spin locked at right angles with momentum. The chirality of this spin texture is expected to invert crossing the Dirac point, a property that has been experimentally observed by optical probes. Here, we directly determine the chirality below the Dirac point by electrically detecting spin-momentum locking in surface states of a p-type TI, Sb2Te3. A current flowing in the Sb2Te3 surface states generates a net spin polarization due to spin-momentum locking, which is electrically detected as a voltage on an Fe/Al2O3 tunnel barrier detector. Measurements of this voltage as a function of current direction and detector magnetization indicate that hole spin-momentum locking follows the right-hand rule, opposite that of electron, providing direct confirmation that the chirality is indeed inverted below Dirac point. The spin signal is linear with current, and exhibits a temperature dependence consistent with the semiconducting nature of the TI film and freeze-out of bulk conduction below 100u2009K. Our results demonstrate that the chirality of the helical spin texture of TI surface states can be determined electrically, an enabling step in the electrical manipulation of spins in next generation TI-based quantum devices.