Search

Normal microwave (MW) electromagnetic field detectors convert microwave power into voltages, which results in the loss of the vector characteristics of the microwave field. In this work, we developed a MW magnetic field (h-field) vector detector based on the nonresonant spin rectification effect. By measuring and analyzing the angle dependence of the rectification voltages under nonresonant conditions, we can extract the three components of the h-field. As an initial test of this method, we obtained the h-field distributions at 5.4 GHz generated by a coplanar waveguide with sub-wavelength resolution. Compared to methods using ferromagnetic resonance, this technique offers a faster and more convenient way to determine the spatial distribution of the h-field, which can be used for MW integrated circuit optimization and fault diagnosis.

In order to understand the anti-site disorder effect on the anisotropic magnetoresistance (AMR) effect in alloys, $\rm{Fe}_{50}Co_{50}$ alloys were studied in this work using the fully relativistic spin-polarized screened (KKR) method. The anti-site effect was modeled by interchanging Fe and Co atoms and treated by the coherent potential approximation (CPA). We find that the anti-site disorder broadens the spectral function and decreases the conductivity. Our work emphasizes that the absolute variations of resistivity under magnetic moment rotation are less affected by atomic disorders. The annealing procedure improves the AMR by reduction of the total resistivity. At the same time, we also find that the fourth-order term in the angular dependent resistivity becomes weaker when the disorder increases, resulting from increased scattering of the states around the band-crossing., Comment: 12pages, 7 figures

In this work, a scanning inverse spin Hall effect measurement system based on a shorted coaxial resonator has been built, which provides a high throughput method to characterize spin transport properties. The spin diffusion length of Ta at room temperature is determined via automatic measurements of Py/Ta bilayer strips with different thicknesses of Ta. The results show that the spin diffusion length is about 4 nm with a conductivity of about 7.5E5 {\Omega}-1m-1, which leads to the conclusion that the intrinsic mechanism of spin relaxation of Ta is the Elliott-Yafet interactions. The setup developed in this work provides a convenient, efficient, and non-destructive way to obtain the spin and electron transportation characteristics of the spintronic materials, which will fertilize this community by developing new materials and figuring out their mechanism.

The spin Hall conductivity (SHC) and anomalous Hall conductivity (AHC) in more than 120 full Heusler compounds are calculated using density functional theory in a high-throughtput way. The electronic structures are mapped to the Wannier basis and the linear response theory is used to get the conductivity. Our results show that the mechanism under the SHC or AHC cannot be simply related to the valence electron numbers or atomic weights, is related to the very details of the electronic structure, which can only be obtained by calculations. A high throughput calculation is efficient to screen out the desired materials. According to our present results, Cu2CoSn, as well as Co2MnAl and Co2MnGa are candidates in spintronic materials regarding to their high SHC and AHC values, which can benefit the spin-torque-driven nanodevices.

Hyperdoping Si with chalcogens is a topic of great interest due to the strong sub-bandgap absorption exhibited by the resulting material, which can be exploited to develop broadband room-temperature infrared photodetectors using fully Si-compatible technology. Here, we report on the critical behavior of the impurity-driven insulator-to-metal transition in Te-hyperdoped Si layers fabricated via ion implantation followed by nanosecond pulsed-laser melting. Electrical transport measurements reveal an insulator-to-metal transition, which is also confirmed and understood by density functional theory calculations. We demonstrate that the metallic phase is governed by a power law dependence of the conductivity at temperatures below 25 K, whereas the conductivity in the insulating phase is well described by a variable-range hopping mechanism with a Coulomb gap at temperatures in the range of 2-50 K. These results show that the electron wave-function in the vicinity of the transition is strongly affected by the disorder and the electron-electron interaction., Comment: 19 pages, 6 figures

We measured the spin rectify effect and the inverse spin Hall effect in Nb-doped SrTiO$_3$ by injecting the spins from ferromagnetic thin films to SrTiO$_3$ using spin pumping. It was shown that the spin injection is increased when the doping level is increased. However, the spin Hall angle decreases when Nb occupies more than $\sim$2\% of the Ti sites, which is due to that beyond this concentration, the electron contributed the spin Hall effect is from the $d-$orbitals of Nb instead those from the Ti. Our work points to the importance of orbital occupations in the (inverse) spin Hall effect. We may explore controllable spin and charge interconversion in oxide spintronics., Comment: 6 pages,7 figures

Controlling charge-spin current conversion by electric fields is crucial in spintronic devices, which can be realized in diatom ferroelectric semiconductor GeTe where it is established that ferroelectricity can change the spin texture. We demonstrated that the spin Hall conductivity (SHC) can be further tuned by ferroelectricity based on the density functional theory calculations. The spin texture variation driven by the electric fields was elucidated from the symmetry point of view, highlighting the interlocked spin and orbital degrees of freedom. We observed that the origin of SHC can be attributed to the Rashba effect and the intrinsic spin-orbit coupling. The magnitude of one component of SHC {\sigma}_xy^z can reach as large as 100 {\hbar}/e/({\Omega}cm) in the vicinity of the band edge, which is promising for engineering spintronic devices. Our work on tunable spin transport properties via the ferroelectric polarization brings novel assets into the field of spintronics., Comment: 6 figures

The anisotropic magnetoresistance (AMR) in thin permalloy strips was calculated at each steps during magnetization by the finite element method. The magnetization at equilibrium under different external fields was obtained by micromagnetic simulations, while the resistance with different magnetization was obtained by solving the Poisson equations iteratively until self-consistence. We find that the relation between magnetization and AMR deviates from the Stoner-Wohlfarth prediction when the magnetization is reduced from saturation. The reason is that the demagnetization is not necessarily from coherent rotation of the magnetic moment. We conclude that it is necessary to use numeric simulations to optimize the responses of AMR sensors.

Conversion of spin to charge current was observed in SrTiO3 doped with Nd (Nd:STO), which exhibited a metallic behavior even with low concentration doping. The obvious variation of DC voltages for Py/Nd:STO, obtained by inverting the spin diffusion direction, demonstrated that the detected signals contained the contribution from the inverse spin Hall effect (ISHE) induced by the spin dependent scattering from Nd impurities with strong spin-orbit interaction. The DC voltages of the ISHE for Nd:STO were measured at different microwave frequency and power, which revealed that spin currents were successfully injected into doped STO layer by spin pumping. The linear relation between the ISHE resistivity and the resistivity induced by impurities implied that the skew scattering was the dominant contribution in this case, and the spin Hall angle was estimated to be 0.17%. This work demonstrated that extrinsic spin dependent scattering in oxides can be used in spintroics besides that in heavy elements doped metals.

The (001) surface of SrTiO3 were transformed from insulating to conducting after Ar+ irradiation, producing a quasi two-dimensional electron gas (2DEG). This conducting surface layer can introduce Rashba spin orbital coupling due to the broken inversion symmetry normal to the plane. The spin splitting of such a surface has recently been demonstrated by magneto-resistance and angular resolved photoemission spectra measurements. Here we present experiments evidencing a large spin-charge conversion at the surface. We use spin pumping to inject a spin current from NiFe film into the surface, and measure the resulting charge current. The results indicate that the Rashba effect at the surface can be used for efficient charge-spin conversion, and the large efficiency is due to the multi-d-orbitals and surface corrugation. It holds great promise in oxide spintronics., Comment: 11 pages, 5 figures