metal (Pt, Ta, etc.) and/or the Rashba effect from the inversion asymmetry of HM/FM and FM/oxide interfaces both contribute to the spin-orbit torque and the effective switching fi eld. [16][17][18][19] Half a decade has already passed since the fi rst report of SOT in perpendicularly magnetized heterostructures. [ 20 ] Efforts are increasingly shifting not only to explore SOT in different systems, but also to its manipulation in practical devices. [21][22][23][24] At the same time, electric fi eld control of magnetization is of great interest in the area of spintronics for its rich physics and potential use in information technology due to its low energy consumption and compatibility with classic electronics. [25][26][27] Following the effective manipulation of magnetic order by electrical means in different systems, Liu et al. [ 28 ] proposed the concept of electrical control of SOT in Pt/Co/Al 2 O 3 heterostructures, but the efficiency is in a quite limited scale. Very recently, Fan et al. [ 29 ] utilized the Cr-doped topological insulator and successfully modulated the SOT by a factor of four using a gate voltage ( V G ) of 10 V at 1.9 K taking the ultralow Curie temperature ( T C ) of the magnetic topological insulator into account. Now the research interest is whether an elegant approach could significantly modulate the SOT in a nonvolatile manner at a practical temperature ( T ). We experimentally demonstrated the strong electrical control of SOT in perpendicularly magnetized Pt/Co/ HfO x heterostructures. Positive and negative V G enhance and reduce the critical current for magnetization switching respectively with the assistance of ionic liquid gating mainly through the modulation of damping-like spin-orbit effective fi elds and the concomitant effective spin Hall angle of Pt/Co. Results and DiscussionIn our Ta(2)/Pt(4)/Co(0.3)/HfO x (4) (unit in nanometers) heterostructures ( Figure 1 a), the bottom Ta layer acts as a seed layer to form a better Pt(111) orientation, and consequently induces a strong perpendicular magnetic anisotropy (PMA). Despite its high spin Hall angle, [ 9,30 ] the contribution of spin current from Ta to Co is negligible due to the short spin diffusion length of Pt and opposite sign of the spin Hall angle of Ta and Pt. [ 8,31 ] The capping HfO x layer, with a large permittivity, also enhances the PMA and protects the metal layers from erosion by ionic Electrical control of current-induced spin-orbit effects in magnets is supposed to reduce the power consumption in high-density memories to the utmost extent, but the effi cient control in metallic magnets at a practical temperature remains elusive. Here, the electrical manipulation of spin-orbit torque is investigated in perpendicularly magnetized Pt/Co/HfO x heterostructures in a nonvolatile manner using an ionic liquid gate. The switching current of magnetization can be reversibly tuned by a factor of two within a small gate voltage range of 1.5 V. The modulation of effective spin Hall angle and the corresponding damping-like torque...

We studied the spin-to-charge and charge-to-spin conversion at room temperature in sputteredWTe2-x (x=0.8)(t)/Co20Fe60B20(6 nm) heterostructures. Spin pumping measurements were used to characterize the spin-to-charge efficiency and the spin efficiency was calculated to be larger than ~0.035. Second harmonic Hall measurements were carried out to estimate the charge-to-spin conversion ratio. We found that the system exhibits a large field-like-torque (spin torque efficiency ~ 0.1) and small damping-like-torque (spin torque efficiency ~0.001) compared to that reported for heavy metals. High-resolution transmission electron microscopy images show that the WTe2-x layer is amorphous, which may enhance the spin swapping effect by inducing large interfacial spin orbit scattering, thus contributing to a large field like torque.

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We investigated temperature dependent current driven spin-orbit torques in magnetron sputtered Ru2Sn3 (4 and 10 nm) /Co20Fe60B20 (5 nm) layered structures with in-plane magnetic anisotropy.The room temperature damping-like and field-like spin torque efficiencies of the amorphous Ru2Sn3 films were extracted to be as large as 0.14 ± 0.008 and -0.2 ± 0.009, respectively, by utilizing the second harmonic Hall technique. The large field-like torque in the relatively thicker Ru2Sn3 (10 nm) thin film is unique compared to the traditional spin Hall materials interfaced with thick magnetic layers with in-plane magnetic anisotropy which typically have negligible field-like torques. Additionally, the observed room temperature field-like torque efficiency in Ru2Sn3 (10 nm)/CoFeB (5 nm) is up to three times larger than the damping-like torque (-0.20 ± 0.009 and 0.07 ± 0.012, respectively) and thirty times larger at 50 K (-0.29 ± 0.014 and 0.009 ± 0.017, respectively). The temperature dependence of the field-like torques are unique and show dominant contributions from the intrinsic spin Hall effect with intrinsic spin conductivity up to -240 ± 19 ℏ 2𝑒𝑒 ⁄ (Ωcm) -1 while the damping-like torques show dominate contributions from the extrinsic spinHall effects with sum of the skew scattering and side jump up to -175 ± 19 ℏ 2𝑒𝑒 ⁄ (Ωcm) -1 . Through macro-spin calculations, we found that including field-like torques on the order or larger than the damping-like torque can reduce the switching critical current and the switching time for a perpendicular ferromagnetic layer.

Recent advancement in the switching of perpendicular magnetic tunnel junctions with an electric field has been a milestone for realizing ultra-low energy memory and computing devices. To integrate with current spin-transfer torque-magnetic tunnel junction and spin–orbit torque-magnetic tunnel junction devices, the typical linear fJ/V m range voltage controlled magnetic anisotropy (VCMA) needs to be significantly enhanced with approaches that include new materials or stack engineering. A possible bidirectional and 1.1 pJ/V m VCMA effect has been predicted by using heavily electron-depleted Fe/MgO interfaces. To improve upon existing VCMA technology, we have proposed inserting high work function materials underneath the magnetic layer. This will deplete electrons from the magnetic layer biasing the gating window into the electron-depleted regime, where the pJ/V m and bidirectional VCMA effect was predicted. We have demonstrated tunable control of the Ta/Pd(x)/Ta underlayer's work function. By varying the Pd thickness (x) from 0 to 10 nm, we have observed a tunable change in the Ta layer's work function from 4.32 to 4.90 eV. To investigate the extent of the electron depletion as a function of the Pd thickness in the underlayer, we have performed DFT calculations on supercells of Ta/Pd(x)/Ta/CoFe/MgO, which demonstrate that electron depletion will not be fully screened at the CoFe/MgO interface. Gated pillar devices with Hall cross geometries were fabricated and tested to extract the anisotropy change as a function of applied gate voltage for samples with various Pd thicknesses. The electron-depleted Pd samples show three to six times VCMA improvement compared to the electron accumulated Ta control sample.

I. SYSTEM REQUIREMENTS INCREASED levels of radio integration with low external component count are essential for cellular handset manufacturers to achieve low product cost. These demands have led to the popularity of low and zero intermediate frequency ( As a full duplex system, one of the key challenges that CDMA2000 presents is dealing with signal leakage from transmit to receive paths; at the present state of the art, separate transmit and receive chips are the rule to avoid substrate-and package-related signal coupling. For the receiver alone, there is also the requirement to tolerate and indeed to work with legacy narrow-band FM analog systems (AMPS) in the same 880-MHz frequency spectrum [1] (Fig. 1), leading to several severe performance restrictions, in terms of input linearity, local oscillator (LO) leakage, and LO phase noise. In this design, we tackle the first two requirements, and meet the limits with a fully integrated signal path. Other designs employing zero IF (ZIF) for U.S. CDMA have opted to use a separate low-noise amplifier (LNA) to achieve this isolation [5]. A companion transmitter IC [6] also uses a direct conversion scheme to keep total system costs to a minimum. II. ZIF RECEIVER ARCHITECTUREThe overall system architecture is shown in Fig. 2, and the key performance requirements are given in Tables I and II. The worst case interference scenario is presented in Fig. 1, where transmit leakage cross-modulates with a strong adjacent FM carrier. This situation tends to dictate the linearity performance specifications. In practical designs, the attenuation afforded at the input by commercial duplexer blocks is typically around 55 dB, which is insufficient to keep the power in the transmit spectrum present at the receiver input low enough to eliminate this cross-modulation problems associated with FM carriers. To minimize the impact of cross-modulation without employing a sharper, more lossy (and costly) filter at this point, the LNA must have very high linearity (IIP3 of 9 dBm). Note that even with this demanding performance, it is necessary to employ an additional bandpass SAW filter in the receive path between the LNA and the mixer to provide additional attenuation of transmit band leakage (typically 40 dB) and thus ease the mixer linearity requirements.An external oscillator module running at double the required frequency provides the drive to the LO quadrature generator. The signal path is split into in-phase (I) and quadrature (Q) paths in the mixer switching core and passed to low-pass channelselection filters. III. LNA DESIGNThree gain settings are used to achieve the best overall gain and linearity; only high ( 15-dB) and low ( 5-dB) gain settings are shown for clarity. The target here is to achieve 20-dB reverse isolation in all gain modes. To meet the overall leakage requirements, the majority of the required 80-dBm isolation is then achieved in the mixer core and its associated interfaces, and maintained with careful layout and pad assignments.To meet the need for very high reverse ...

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Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin–orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.7 × 10−11 per A/cm2, 50% larger than reported values from heavy metals) in sputtered amorphous PtSn4/CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn4/CoFeB bilayers. The observation of a large USMR value in an amorphous spin–orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices.