Spin injection and detection up to room temperature in Heusler alloy/n-GaAs spin valves

Abstract

We have measured the spin injection efficiency and spin lifetime in Co2FeSi/n-GaAs lateral nonlocal spin valves from 20 to 300 K. We observe large (∼40 µV) spin valve signals at room temperature and injector currents of 10 3 A/cm 2 , facilitated by fabricating spin valve separations smaller than the 1 µm spin diffusion length and applying a forward bias to the detector contact. The spin transport parameters are measured by comparing the injector-detector contact separation dependence of the spin valve signal with a numerical model accounting for spin drift and diffusion. The apparent suppression of the spin injection efficiency at the lowest temperatures reflects a breakdown of the ordinary drift-diffusion model in the regime of large spin accumulation. A theoretical calculation of the D'yakonov-Perel spin lifetime agrees well with the measured n-GaAs spin lifetime over the entire temperature range. arXiv:1610.03797v1 [cond-mat.mes-hall]

Nonlinear Electrical Spin Conversion in a Biased Ferromagnetic Tunnel Contact

“…Because the differential equations for spin-diffusion in a non-magnetic material are linear in the spin accumulation, the spin accumulations from different sources (injector and detector) are simply superimposed. Moreover, as pointed out before 43 , in such a nonlocal measurement with a biased detector, the nonlocal spin-valve signal is not affected by the extra spin accumulation ∆µ det that is induced in the channel by the detector current, because it produces a spin voltage that is proportional to P det (∆µ det /2 e) at the detector interface and that does not depend on the relative magnetization alignment of injector and detector. Hence, the spin-valve signal is still given by P det (∆µ inj /2 e), as in the conventional nonlocal measurement, but now the spin accumulation ∆µ inj induced by the injector current is kept constant and P det changes as a function of the bias across the detector.…”

“…For instance, in two-terminal magnetoresistance devices having two ferromagnetic contacts on a nonmagnetic channel, the current is applied between the two ferromagnetic contacts and the spin signal is obtained from the two-terminal voltage between the two contacts. Importantly, for devices in which the spin detector contact is biased, the observed spin signals are surprising and puzzling [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] , and no suitable explanation for the peculiar behavior is available. Moreover, when existing (linear) transport theories are applied to devices with a biased detector, the conclusions are inconsistent with those obtained from analysis of nonlocal spin transport devices, even if the same structure is used for the different measurement configurations.…”

“…The deviation from linear transport is surprisingly strong and already appears at small bias for which charge transport is still linear. It is also demonstrated that nonlinear spin detection is the common origin of the various puzzling and inexplicable spin signals in devices with a biased detector [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] . In fact, taking the nonlinearity of spin detection into account (i) explains these puzzling results qualitatively and quantitatively, and (ii) provides a unified description of electrical spin signals in devices with and without biased detector, in which the spin signals and spin transport parameters obtained from devices with a biased detector are consistent with those extracted from nonlocal spin-transport measurements.…”

Room-temperature spin transport in n-Ge probed by four-terminal nonlocal measurements

“…[36][37][38][39] To obtain even higher spin signals at room temperature in Ge-based LSVs, we should further improve the quality of the Co-based Heusler alloys on Ge.…”

Systematic investigations of transient response of nuclear spins in the presence of polarized electrons

“…In such a system, a highly efficient spin source is essential for an effective DNP. A Co-based Heusler alloy is an excellent ferromagnetic candidate for spintronic devices, including magnetic tunnel junctions (MTJs) [26][27][28][29][30][31][32][33][34][35], giant magnetoresistance devices [36][37][38][39][40][41][42], and for spin injection into semiconductors [43][44][45][46][47][48], due to its complete spin polarization at the Fermi level [49][50][51]. We recently reported high tunneling magnetoresistance ratios of up to 1995% at 4.2 K and up to 354% at 290 K in MTJs having Mn-rich Co 2 MnSi (CMS) electrodes [32], and found ratios of 2610% at 4.2 K and 429% at 290 K in Mn-rich Co 2 (Mn,Fe)Si MTJs [33,34], demonstrating a high spin polarization of CMS and CMFS.…”