Modulation of spin-torque ferromagnetic resonance with a nanometer-thick platinum by ionic gating

The spin Hall effect (SHE) and inverse spin Hall effect (ISHE) have played central roles in modern condensed matter physics especially in spintronics and spin-orbitronics, and much effort has been paid to fundamental and application-oriented research towards the discovery of novel spin–orbit physics and the creation of novel spintronic devices. However, studies on gate-tunability of such spintronics devices have been limited, because most of them are made of metallic materials, where the high bulk carrier densities hinder the tuning of physical properties by gating. Here, we show an experimental demonstration of the gate-tunable spin–orbit torque in Pt/Ni₈₀Fe₂₀ (Py) devices by controlling the SHE using nanometer-thick Pt with low carrier densities and ionic gating. The Gilbert damping parameter of Py and the spin-memory loss at the Pt/Py interface were modulated by ionic gating to Pt, which are compelling results for the successful tuning of spin–orbit interaction in Pt

Modulation of Hanle magnetoresistance in an ultrathin platinum film by ionic gating

Hanle magnetoresistance (HMR) is a type of magnetoresistance where interplay of the spin Hall effect, Hanle-type spin precession, and spin-dependent scattering at the top/bottom surfaces in a heavy metal controls the effect. In this study, we modulate HMR in ultrathin Pt by ionic gating, where the surface Rashba field created by a strong electric field at the interface between the ionic gate and Pt plays the dominant role in the modulation. This finding can facilitate investigations of gate-tunable, spin-related effects and fabrication of spin devices.Comment: 10 pages, 3 figures (To appear in Applied Physics Express

Precise estimation of spin drift velocity and spin mobility in the absence of synthetic Rashba spin-orbit field in a Si metal-oxide-semiconductor

The discovery of built-in and synthetic Rashba fields in Si spin channels [S. Lee et al., Nat. Mater. 20, 1228 (2021)] challenged the conventional understanding of spin transport physics in semiconducting materials and forced researchers to reconsider the procedures used for estimating spin drift velocity and spin mobility. A conventional procedure for the estimation involves the detection of the Hanle-type spin precession under the application of an external magnetic field perpendicular to the plane; however, the in-plane effective magnetic fields due to the built-in Rashba fields hamper precise estimation because of the additional spin precession. In this work, we establish a precise method to estimate spin drift velocity and spin mobility, in addition to the spin lifetime and spin diffusion constant, by appropriately tuning the Rashba fields. Beyond the emblematic case of Si, the established method can be applied to other semiconductors, such as Ge and GaAs

Anomalous sign inversion of spin-orbit torque in ferromagnetic/nonmagnetic bilayer systems due to self-induced spin-orbit torque

Self-induced spin-orbit torques (SI-SOTs) in ferromagnetic (FM) layers have been overlooked when estimating the spin Hall angle (SHA) of adjacent nonmagnetic (NM) layers. In this work, we observe anomalous sign inversion of the total SOT in the spin-torque ferromagnetic resonance due to the enhanced SI-SOT, and successfully rationalize the sign inversion through a theoretical calculation considering the SHE in both the NM and FM layers. The findings show that using an FM layer whose SHA sign is the same as that of the NM achieves efficient SOT-magnetization switching with the assistance of the SI-SOT. The contribution of the SI-SOT becomes salient for a weakly conductive NM layer, and conventional analyses that do not consider the SI-SOT can overestimate the SHA of the NM layer by a factor of more than 150.Comment: 9 pages, 4 figure

Optimization temperature sensitivity using the optically detected magnetic resonance spectrum of a nitrogen-vacancy center ensemble

Temperature sensing with nitrogen vacancy (NV) centers using quantum techniques is very promising and further development is expected. Recently, the optically detected magnetic resonance (ODMR) spectrum of a high-density ensemble of the NV centers was reproduced with noise parameters [inhomogeneous magnetic field, inhomogeneous strain (electric field) distribution, and homogeneous broadening] of the NV center ensemble. In this study, we use ODMR to estimate the noise parameters of the NV centers in several diamonds. These parameters strongly depend on the spin concentration. This knowledge is then applied to theoretically predict the temperature sensitivity. Using the diffraction-limited volume of 0.1 micron^3, which is the typical limit in confocal microscopy, the optimal sensitivity is estimated to be around 0.76 mK/Hz^(1/2) with an NV center concentration of 5.0e10^17/cm^3. This sensitivity is much higher than previously reported sensitivities, demonstrating the excellent potential of temperature sensing with NV centers.Comment: 17 pages, 4 figures, 1 tabl

Significant suppression of two-magnon scattering in ultrathin Co by controlling the surface magnetic anisotropy at the Co/nonmagnet interfaces

To enable suppression of two-magnon scattering (TMS) in nanometer-thick Co (ultrathin Co) layers and realize low-magnon damping in such layers, the magnon damping in ultrathin Co layers grown on various nonmagnetic seed layers with different surface magnetic anisotropy (SMA) energies are investigated. We verify the significantly weak magnon damping realized by varying the seeding layer species used. Although TMS is enhanced in ultrathin Co on Cu and Al seeding layers, the insertion of a Ti seeding layer below the ultrathin Co greatly suppresses the TMS, which is attributed to suppression of the SMA at the interface between Co and Ti. The Gilbert damping constant of the ultrathin Co layer on Ti (3 nm), 0.020, is comparable to the value for bulk Co, although the Co layer thickness here is only 2 nm. Realization of such weak magnon damping can open the door to tunable magnon excitation, thus enabling coupling of magnons with other quanta such as photons, given that the magnetization of ultrathin ferromagnets can be tuned using an external electric field