No abstract

The nuclear-spin dephasing of the noble gas Kr" has been observed, A nonexponential decay signal, which is a function of the orientation of the experimental cell in the apparatus, has been measured. The spin decay characteristics of K. r" have been explained in terms of an interaction of the nuclear quadrupole moment of Kr" with the electric field gradients present at the nucleus during a collision of the Kr atom with the walls of the experimental cell. Qualitative agreement only is shown, since a complete quantitative analysis of the experiment is not available at the present time.

The generation of spin currents and their application to the manipulation of magnetic states is fundamental to spintronics. Of particular interest are chiral antiferromagnets that exhibit properties typical of ferromagnetic materials even though they have negligible magnetization. Here, we report the generation of a robust spin current with both in-plane and out-of-plane spin polarization in epitaxial thin films of the chiral antiferromagnet Mn3Sn in proximity to permalloy thin layers. By employing temperature-dependent spin-torque ferromagnetic resonance, we find that the chiral antiferromagnetic structure of Mn3Sn is responsible for an in-plane polarized spin current that is generated from the interior of the Mn3Sn layer and whose temperature dependence follows that of this layer’s antiferromagnetic order. On the other hand, the out-of-plane polarized spin current is unrelated to the chiral antiferromagnetic structure and is instead the result of scattering from the Mn3Sn/permalloy interface. We substantiate the later conclusion by performing studies with several other non-magnetic metals all of which are found to exhibit out-of-plane polarized spin currents arising from the spin swapping effect.

As spintronic devices become more and more prevalent, the desire to find Pt-free materials with large spin Hall effects is increasing. Previously it was shown that β-W, the metastable A15 structured variant of pure W, has charge-spin conversion efficiencies on par with Pt, and it was predicted that β-W/Ta alloys should be even more efficient. Here we demonstrate the enhancement of the spin Hall ratio (SHR) in A15-phase β-W films doped with Ta (W4-xTax where 0.28 <= x <= 0.4) deposited at room temperature using DC magnetron co-sputtering. In close agreement with theoretical predictions, we find that the SHR of the doped films was ~9% larger than pure -W films. We also found that the SHR's in devices with Co2Fe6B2 were nearly twice as large as the SHR's in devices with Co4Fe4B2. This work shows that by optimizing deposition parameters and substrates, the fabrication of the optimum W3Ta alloy should be feasible, opening the door to commercially viable, Pt-free, spintronic devices. Introduction/Background:Recently, the spin Hall effect (SHE) has received a great deal of attention not only from a fundamental physics perspective but also for technological applications in the area of memories, logic and sensors[1][2]. The SHE is the conversion of a longitudinal current density into a transverse spin current density, which is characterized by the spin Hall ratio (SHR), θSH=JS/JC and materials with large SHRs are desired for spintronic applications. Note that SHR and SHA (spin Hall angle) have been used interchangeably in literature, however the SHA is rigorously defined as the tan -1 (JS/JC). Previous studies have demonstrated only a handful of materials that can be sputter-deposited and which exhibit large SHRs at room temperature: these include Pt/doped Pt [3], β-Ta [4], β-W [5] and oxygen doped β-W [6]. There is a technological desire towards Pt-free spintronics and among these candidates, β-W and oxygen doped β-W, have the highest resistance (resulting in larger power requirements) but also show the largest SHR, which is approximately -0.35 and -0.5, respectively [5][6][7] [8]. β-W is a metastable phase of W that exhibits the cubic A15 structure (SG# 223, Pm-3n) which has two distinct crystallographic sites with two atoms located on each face of the cubic cell. The α-W phase, on the other hand, is the most stable form of W that crystallizes in body centered cubic structure, while exhibiting a smaller SHE

The spin Hall effect appears in nature in two forms. Its intrinsic form is highly dependent on the crystal symmetry while its extrinsic form stems from impurity scattering. Its efficiency is defined by the spin Hall angle, [Formula: see text], and has profound impact on spintronic technologies. However, an accurate measurement of [Formula: see text] is not straightforward nor the identification of its origin. In this work, we apply a spin-torque driven ferromagnetic resonance method that is probed in two different ways, optically and electrically, to study the dependence of [Formula: see text] in the crystallographic direction in epitaxial Al2O3/Pt (111), MgO(110)/Pt (110), and MgO(001)/Pt (001) films. We show that the electrical technique is limited in its ability to accurately quantify [Formula: see text] at high current densities, and in some cases, it may even result in erroneous [Formula: see text] values. Such cases include films that exhibit a large inhomogeneous broadening. We find that [Formula: see text] is strongly affected by the crystallographic direction. Our study extends the understanding of one of the most commonly used methods for the exploration of the spin Hall effect.