Spin-½

About: Spin-½ is a research topic. Over the lifetime, 40423 publications have been published within this topic receiving 796639 citations.

Spin-Torque Switching with the Giant Spin Hall Effect

Abstract: Giant Spin Hall One of the primary challenges in the field of spin-electronics, which exploits the electron's spin rather than its charge, is to create strong currents of electrons with polarized spins. One way to do this is to use a ferromagnet as a polarizer, a principle used in magnetic tunnel junctions; however, these devices suffer from reliability problems. An alternative is the spin Hall effect, where running a charge current through a material generates a spin current in the transverse direction, but the efficiency of this process tends to be small. Liu et al. (p. 555) now show that the spin Hall effect in Tantalum in its high-resistance β phase generates spin currents strong enough to induce switching of the magnetization of an adjacent ferromagnet; at the same time, Ta does not cause energy dissipation in the ferromagnet. These properties allowed efficient and reliable operation of a prototype three-terminal device. Tantalum is found to generate strong spin currents that can induce switching of ferromagnets efficiently and reliably. Spin currents can apply useful torques in spintronic devices. The spin Hall effect has been proposed as a source of spin current, but its modest strength has limited its usefulness. We report a giant spin Hall effect (SHE) in β-tantalum that generates spin currents intense enough to induce efficient spin-torque switching of ferromagnets at room temperature. We quantify this SHE by three independent methods and demonstrate spin-torque switching of both out-of-plane and in-plane magnetized layers. We furthermore implement a three-terminal device that uses current passing through a tantalum-ferromagnet bilayer to switch a nanomagnet, with a magnetic tunnel junction for read-out. This simple, reliable, and efficient design may eliminate the main obstacles to the development of magnetic memory and nonvolatile spin logic technologies.

Quantum ferromagnetism and phase transitions in double-layer quantum Hall systems

Abstract: Double-layer quantum Hall systems have interesting properties associated with interlayer correlations. At \ensuremath{ u}=1/m where m is an odd integer they exhibit spontaneous symmetry breaking equivalent to that of spin 1/2 easy-plane ferromagents, with the layer degree of freedom playing the role of spin. We explore the rich variety of quantum and finite temperature phase transitions in these systems. In particular, we show that a magnetic field oriented parallel to the layers induces a highly collective commensurate-incommensurate phase transition in the magnetic order.

Origin of the spin Seebeck effect in compensated ferrimagnets

Abstract: Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE.

Controlling correlated tunneling and superexchange interactions with ac-driven optical lattices.

Abstract: The dynamical control of tunneling processes of single particles plays a major role in science ranging from Shapiro steps in Josephson junctions to the control of chemical reactions via light in molecules. Here we show how such control can be extended to the regime of correlated tunneling of strongly interacting particles. Through a periodic modulation of a biased tunnel contact, we have been able to coherently control single-particle and correlated two-particle hopping processes. We have furthermore been able to extend this control to superexchange spin interactions in the presence of a magnetic-field gradient. Such photon-assisted superexchange processes constitute a novel approach to realize arbitrary $XXZ$ spin models in ultracold quantum gases, where transverse and Ising-type spin couplings can be fully controlled in magnitude and sign.

Pure spin currents and the associated electrical voltage.

Abstract: We present a generalized Landauer-Buttiker transport theory for multiterminal spin transport in the presence of spin-orbit interaction. Using this theory we point out that there exists equilibrium spin currents and nonequilibrium pure spin currents, without any magnetic element in the system. Quantitative results are presented for a Y-shaped conductor. It is shown that pure spin currents cause a voltage drop and, hence, can be measured.