Daichi Hirobe

One-dimensional spinon spin currents

Eiji Saitoh† Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan Spin Quantum Rectification Project, ERATO, Japan Science and Technology Agency, Sendai 980-8577, Japan The Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan and WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Dated: September 26, 2016)

Magnetic thermal conductivity far above the Néel temperature in the Kitaev-magnet candidate α−RuCl3

The Kitaev quantum spin liquid on a honeycomb lattice has received much interest in magnetism, mainly because of the possibility of emergence of novel excitations called Majorana quasiparticles. The quest is under way to realize this exotic state in actual materials. One of the promising materials is the layered honeycomb material RuCl

Effect of spin Hall magnetoresistance on spin pumping measurements in insulating magnet/metal systems

{}_{3}

Generation of spin currents in the skyrmion phase of a helimagnetic insulator Cu2OSeO3

, for which the signatures of the Majorana quasiparticles have been reported. Here, the authors investigate the magnetic thermal conductivity of RuCl

Generation of spin currents from one-dimensional quantum spin liquid

{}_{3}

Generation of megahertz-band spin currents using nonlinear spin pumping

along with bulk thermodynamic measurements. They find that in the temperature range on the order of the Kitaev-coupling strength anomalous heat conduction takes place, which correlates with the growth of the magnetic specific heat. The result is consistent with the propagation of magnetic excitations, likely itinerant Majorana quasiparticles, driven by Kitaev coupling.

Spin pumping from nuclear spin waves

We investigate a dc rectification effect of magnetization dynamics based on spin Hall magnetoresistance (SMR) in an insulating magnet/metal system on spin pumping measurements. We theoretically find that the rectification effect by SMR has different in-plane magnetization angle dependence from that of the inverse spin Hall effect on the spin pumping. The negligible contribution from the rectification effect is experimentally confirmed in a cavity measurement.

Observation of spinon spin currents in one-dimensional spin liquid

We report spin-current generation related to skyrmion dynamics resonantly excited by a microwave in a helimagnetic insulator Cu2OSeO3. A Pt layer was fabricated on Cu2OSeO3 and voltage in the Pt layer was measured upon magnetic upon magnetic resonance of Cu2OSeO3 to electrically detect injected spin currents via the inverse spin Hall effect (ISHE) in Pt. We found that ISHE-induced electromotive forces appear in the skyrmion phase of Cu2OSeO3 as well as in the ferrimagnetic phase, which shows that magnetic skyrmions can contribute to the spin pumping effect.

Generation of spin current by spin pumping under nonlinear magnetization dynamics

Spin-Seebeck effects (SSEs) in a one-dimensional quantum spin liquid (QSL) system have been investigated in a Sr2CuO3/Pt hybrid structure. Sr2CuO3 contains one-dimensional spin- 1 2 chains in which typical spinons in QSL have been confirmed. Heat-induced voltage measured in a clean Pt/Sr2CuO3 exhibits anomalous sign reversal with decreasing temperature, the negative component of which can be attributed to the spinon-induced SSE. However, the SSE was found to be critically decreased upon the exposure of Sr2CuO3 to air, which can be associated with the chemical degradation of the interface of Sr2CuO3. Despite the drastic change in the SSE signals, properties of the one-dimensional QSL are little changed in the spin susceptibility as well as the thermal conductivity of Sr2CuO3. The SSE signal is also sensitive to the purity of Sr2CuO3; it is suppressed with a decrease in the purity of the primary compounds of the Sr2CuO3. The result indicates that the spinon-induced SSE in Sr2CuO3 is sensitive to the bulk co...

Enhancement of Spin Pumping in

Spin pumping enables the generation of d.c. and gigahertz-band (GHz-band) voltages from an applied microwave via magnetization dynamics when combined with inverse spin Hall effects. However, generating such voltages in the in-between frequency region, or the megahertz (MHz) band, has been difficult since ferromagnetic resonance usually occurs in the GHz band. Here we show that in spite of GHz-band microwaves applied, MHz-band voltages can be generated by spin pumping with use of nonlinear magnetization dynamics in Y3Fe5O12. The mechanism is ascribed to the MHz-band oscillation of the amplitude of the magnetization precession, which is projected onto a rectified voltage component via spin pumping. The present finding could be useful for frequency down-conversion thanks to the simple and durable structure, continuous-wave operation, and the tunability of an output frequency with low magnetic fields.