The detection and manipulation of the spin configurations in layered magnetic semiconductors hold significant interest for developing spintronic devices in two-dimensional limit. In this letter, we report a systematical study on the photoluminescence (PL) from the high energy excitons in few-layer CrSBr and its application on detecting the spin configurations. Besides the broad excitonic emission peak (Xl) at around 1.34 eV, we also observed another strong excitonic emission peak (Xh) at around 1.37 eV in hBN encapsulated 2L sample, which splits into two peaks in 3L and 4L samples. With help of the first principles calculations, we conclude that the Xh peak is associated with the transition between the top valence band and the second lowest conduction band, which is forbidden by the inversion symmetry in 1L CrSBr. Furthermore, the position and intensity of the Xh peak are strongly dependent on the interlayer magnetic order of the CrSBr samples, which provides an efficient way to probe their spin configurations. In addition, when the magnetic field is applied at the easy axis direction, we resolve an intermediate magnetic state besides the antiferromagnetic and ferromagnetic states in 3L and 4L samples. Our results reveal few-layer CrSBr as an ideal platform to study the interaction between the excitons and magnetism.

Disordered topological insulator (TI) films have gained intense interest by benefiting from both the TI's exotic transport properties and the advantage of mass production by sputtering. Here, we report on the clear evidence of spin-charge conversion (SCC) in amorphous Gd-alloyed BixSe1-x (BSG)/CoFeB bilayers fabricated by sputtering, which could be related to the amorphous TI surface states. Two methods have been employed to study SCC in BSG (tBSG = 6-16 nm)/CoFeB(5 nm) bilayers with different BSG thicknesses. First, spin pumping is used to generate a spin current in CoFeB and detect SCC by the inverse Edelstein effect (IEE). The maximum SCC efficiency (SCE) is measured to be as large as 0.035 nm (IEE length λIEE) in a 6 nm thick BSG sample, which shows a strong decay when tBSG increases due to the increase of BSG surface roughness. The second method is THz time-domain spectroscopy, which reveals a small tBSG dependence of SCE, validating the occurrence of a pure interface state-related SCC. Furthermore, our angle-resolved photoemission spectroscopy data show dispersive two-dimensional surface states that cross the bulk gap until the Fermi level, strengthening the possibility of SCC due to the amorphous TI states. Our studies provide a new experimental direction toward the search for topological systems in amorphous solids.

Magnetic nanowires (MNWs) were explored as potential magnetic tags for cell detection with giant magnetoresistance (GMR) biosensors based on a handheld system. Due to size, shape anisotropy and higher moment materials, the signal detected from a single MNW was 2500 times larger than that from a single magnetic iron oxide nanobead, which is important for ultra-low concentration cell detection. A model was used to determine how the MNW orientation with respect to the GMR sensor impacts detection performance, and the results aligned well with the experimental results. As a proof of concept OSCA-8 cells tagged with Ni MNWs were also detected using the same handheld system. The limit of detection (LOD) in aqueous solution appeared to be 133 cells, and single-cell detection can be realized if the cell is in direct contact with the sensor surface. Since MNWs are already employed in magnetic separation of cells, directly using MNWs as tags in cell detection eliminates the need of additional functionalization with other labels. This largely simplifies the detection process and reduces the risk of contamination during sample preparation.

In this study, we extend the analyses done on sputtered BixSe1-x based accumulation mode FETs. Previously, we studied the basic electrical and leakage properties of these FET devices. We extend our analyses to obtain key parameters of the BixSe1-x (x = 0.44) film at various gate voltages. We start by extracting the sheet carrier density and bulk mobility for different gate voltages, using the Drude model with the previously obtained semi-empirical relationship between carrier concentration and bulk mobility for BixSe1-x. The change in sheet carrier density is a result of accumulation or depletion or majority carriers from the BixSe1-x/SiO2 interface, which show hysteretic behavior. This allows us to calculate the surface sheet carrier density and the quasi-static capacitance at various gate voltages. We use a simple capacitive model to separate the capacitance originating from the gate and the film bulk. The capacitance from the film bulk is due to the surface charge thickness and is directly dependent on the Debye length. From the change of capacitance, with respect to gate voltage, we were able to identify the characteristics of the conduction band edge and the bulk band gap/Dirac cone.

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 measured to be 0.14 +- 0.008 (0.07 +- 0.012) and -0.03 +- 0.006 (-0.20 +- 0.009), for the 4 (10 nm) films 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 dominant damping-like and 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 show dominant contributions from the intrinsic spin Hall effect while the damping-like torques show dominate contributions from the extrinsic spin Hall effects, skew scattering and side jump. 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 decrease magnetization procession for a perpendicular ferromagnetic layer.

We studied the spin-to-charge and charge-to-spin conversion at room temperature in sputtered WTe2−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 those 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.

Topological materials have attracted a lot of attention in the field of beyond Complementary Metal Oxide Semiconductor (CMOS) devices. Topological Insulators (TI) have been proposed for future high electron mobility field effect transistor (FET) devices that make the physics of operation and especially the oxide-film interface extremely crucial to understand. The effects of the gate voltage on the charge trapping in TI-based FET devices are reported in this work. Sputtered BixSe1-x was chosen as the TI material. The interfacial chemistry was characterized using X-ray photoelectron spectroscopy (XPS), which shows a presence of Mg2+ and oxygen impurities. A unique hysteresis behavior was found for the gate transfer characteristics, with respect to the gate voltage. This was attributed to the charge trapping in the gate oxide and across the SiO2/BixSe1-x interface. We simulated the effects of charge fluctuations on the resistivity of the film. These devices operate under accumulation mode rather inversion mode. Application of positive gate voltage results in accumulation of electrons in the “n-type” BixSe1-x layer resulting in an increase of conductivity. In order to explain the drain current-gate voltage behavior, we used a simple polynomial model to describe the change in the device characteristics due to charge traps. The model was fitted with our experimental results. We further analyzed the gate leakage current, which showed a good match with trap-assisted tunneling (TAT) process that was used to derive trap parameters. The obtained trap parameters show the presence of ultra-deep charge traps contributing to the hysteretic behavior.

Weak magnetic field detection is always a challenging topic and sensing systems face a great challenge to be very sensitive in response to magnetic field, in the meantime, to maintain very low overall system noise. Some external auxiliary system could provide significant enhancement to overall signal-to-noise ratio (SNR) such as a magnetic flux concentrator made with soft magnetic material. In this paper, we have systematically studied and built an integrated magnetic tunnel junction (MTJ) sensing system to meet these challenges. MTJ sensor design is optimized to achieve high zero-field sensitivity of 5% MR/Oe, which is defined by the slope of the device's transfer loops at zero field, equivalent to 20 mV/Oe with 10 mA driving current. Both deposition conditions and fabrication techniques are optimized for magnetic flux concentrator (MFC) made of soft magnetic material to achieve a magnetic susceptibility of chi = 30,800 and a gain of 4 for a 100 nm thick prototype.

Disordered topological insulator (TI) films have gained intense interest because of their possibility for spintronic applications by befitting from TI's exotic transport properties. Here, we have fabricated disordered Gd-alloyed BixSe1-x (BSG) TI films by sputtering methods and have investigated their magneto-transport and spin-torque properties. Structural characterizations show a mainly amorphous feature for the 8 nm thick BSG film, while Bi rich crystallites are developed inside the 16 nm thick BSG film. The bulk resistivity of BSG film is found to be relatively high, up to 6 x 10^4 this http URL, with respect to the resistivity of the polycrystalline BixSe1-x film. Temperature dependent resistivity measurements display the evident character of a variable range hopping transport from 80K to 300K. Second harmonic transport characterizations have been performed on the BSG (t)/ CFB (5 nm) bilayer structures with different thicknesses (t = 6, 8, 12, 16 nm). The effective spin Hall angle deduced form the damping-like torque shows a maximum value of 3.74 corresponding to 8 nm thick BSG at room temperature, which is one order of magnitude higher than that of heavy metals. The possible various origins of suck enhancement are discussed. Our study provides a new experimental direction, beyond crystalline solids, to search for topological systems in amorphous solids and other engineered random systems.

We investigated spin-to-charge current conversion in sputtered Y3Fe5O12 (YIG)/granular bismuth selenide (GBS) bi-layers at room temperature. The spin current is pumped to the GBS layer by the precession of magnetization at ferromagnetic resonance in the YIG layer. The spin-mixing conductance is determined to be as large as (13.64 ± 1.32) × 1018 m−2, which is larger than that of YIG/Pt and comparable or better than that of YIG/crystalline bismuth selenide indicating that GBS is a good spin-sink. The figure of merit of spin-to-charge conversion, the inverse Edelstein effect length (λIEE), is estimated to be as large as (0.11 ± 0.03) nm. λIEE shows GBS film thickness dependence, and its value is three times as large as in crystalline bismuth selenide. The λIEE value larger than that of crystalline bismuth selenide and other topological insulators indicates that the spin-to-charge conversion is due to the spin-momentum locking. As the thickness of GBS increases, λIEE decreases, which means the figure-of-merit of spin-to-charge conversion is influenced by grain size.

Disordered spin-orbit channel films have gained intense interest because of their possibility for spintronics applications by benefiting from other exotic transport properties. Here, we have fabricated disordered Gd-alloyed BixSe1−x (BSG) thin films by magnetron sputtering methods and have investigated their magneto-transport and spin-torque properties. Structural characterizations show a mainly amorphous feature for the 8nm thick BSG film, while Bi rich crystallites are developed inside the 16nm thick BSG film. The bulk resistivity of BSG film is found to be relatively high, up to 6×10μΩ·cm, with respect to the resistivity of the polycrystalline BixSe1−x film. Temperature dependent resistivity measurements display the evident character of a variable range hopping transport from 80K to 300K. Spin pumping transport characterizations have been performed on the BSG(t)/CoFeB(5 nm) bilayer structures with different thickness of BSG (t= 6, 8, 12, 16 nm). The possible various origins of the spinto-charge conversion are related to extrinsic effects. Our study provides a new experimental direction, beyond crystalline solids, to the search for strong SOC systems in amorphous solids and other engineered random systems.

We investigated spin-to-charge conversion in sputtered Bi43Se57/Co20Fe60B20 heterostructures with in-plane magnetization at room temperature. High spin-to-charge conversion voltage signals have been observed at room temperature. The transmission electron microscope images show that the sputtered bismuth selenide thin films are nanogranular in structure. The spin-pumping voltage decreases with an increase in the size of the grains. The inverse Edelstein effect length (λIEE) is estimated to be as large as 0.32 nm. The large λIEE is due to the spin-momentum locking and is further enhanced by quantum confinement in the nanosized grains of the sputtered bismuth selenide films. We also investigated the effect on spin-pumping voltage due to the insertion of layers of MgO and Ag. The MgO insertion layer has almost completely suppressed the spin-pumping voltage, whereas the Ag insertion layer has enhanced the λIEE by 43%.

600 mV magneto-electric switching in 30 nm La-doped BiFeO 3 multiferroic oxide and a proof of concept 7 μV spin-orbit signal output in Pt / CoFe local spin injection device with 100 μA supply current were experimentally demonstrated at room temperature for the 1 st time. Also demonstrated was a path towards 70 mV spin orbit output using Bi 2 Se 3 in a local spin injection device. These are key accomplishments for WRITE and READ building blocks, respectively, toward realization of a magneto-electric spin-orbit (MESO) energy-efficient logic device. Moreover, the 1 st generation of a MESO logic device with a functional READ unit is demonstrated.

We studied the tunnel magnetoresistance (TMR) of L10-FePd perpendicular magnetic tunnel junctions (p-MTJs) with an FePd free layer and an inserted diffusion barrier. The diffusion barriers studied here (Ta and W) were shown to enhance the TMR ratio of the p-MTJs formed using high-temperature annealing, which are necessary for the formation of high quality L10-FePd films and MgO barriers. The L10-FePd p-MTJ stack was developed with an FePd free layer with a stack of FePd/X/Co20Fe60B20, where X is the diffusion barrier, and patterned into micron-sized MTJ pillars. The addition of the diffusion barrier was found to greatly enhance the magneto-transport behavior of the L10-FePd p-MTJ pillars such that those without a diffusion barrier exhibited negligible TMR ratios (<1.0%), whereas those with a Ta (W) diffusion barrier exhibited TMR ratios of 8.0% (7.0%) at room temperature and 35.0% (46.0%) at 10 K after post-annealing at 350 °C. These results indicate that diffusion barriers could play a crucial role in realizing high TMR ratios in bulk p-MTJs such as those based on FePd and Mn-based perpendicular magnetic anisotropy materials for spintronic applications.

We present two types of opto-spintronic devices. In the first device, single optical pulses can directly switch the free layer in a magnetic tunnel junction (MTJ) on a sub-picosecond time scale. In the second device, the TM optical mode of a waveguide generates a directional, spin-polarized surface current in a topological insulator.

Magnetic materials that possess large bulk perpendicular magnetic anisotropy (PMA) are essential for the development of magnetic tunnel junctions (MTJs) used in future spintronic memory and logic devices. The addition of an antiferromagnetic layer to these MTJs was recently predicted to facilitate ultra-fast magnetization switching. Here, we report a demonstration of a bulk perpendicular synthetic antiferromagnetic (P-SAFM) structure comprised of a (001) textured FePd/Ru/FePd trilayer with a face-centered-cubic (fcc) phase Ru spacer. The L10 FePd P-SAFM structure shows a large bulk PMA (~10.2 Merg/cc) and strong antiferromagnetic coupling (~2.60 erg/cm2). Full perpendicular magnetic tunnel junctions (P-MTJs) with a L10 FePd P-SAFM layer are then fabricated. Tunneling magnetoresistance ratios of up to ~25% (~60%) are observed at room temperature (5K) after post-annealing at 350 C. Exhibiting high thermal stabilities and large Ku, the bulk P-MTJs with an L10 FePd P-SAFM layer could pave a way for next-generation ultrahigh-density and ultra-low-energy spintronic applications.