Dynamic Nuclear Polarization by Electrical Spin Injection in Ferromagnet-Semiconductor Heterostructures

Abstract

Electrical spin injection from Fe into AlxGa1−xAs quantum well heterostructures is demonstrated in small (< 500 Oe) in-plane magnetic fields. The measurement is sensitive only to the component of the spin that precesses about the internal magnetic field in the semiconductor. This field is much larger than the applied field and depends strongly on the injection current density. Details of the observed hysteresis in the spin injection signal are reproduced in a model that incorporates the magnetocrystalline anisotropy of the epitaxial Fe film, spin relaxation in the semiconductor, and the dynamical polarization of nuclei by the injected spins.PACS numbers: 72.25. Hg, 72.25.Rb, 76.60.Jx The injection of spin from a conventional ferromagnetic metal into a semiconductor is a prerequisite for several proposed magneto-electronic devices [1]. Although spin transport across the ferromagnet-semiconductor (FM-S) interface has recently been demonstrated [2,3,4,5], most injection experiments on metallic FM-S systems have required relatively large magnetic fields, in excess of several kilogauss, to produce a spin component perpendicular to the FM-S interface. The most useful properties of typical ferromagnetic thin films, however, such as low-field switching and hysteresis, can be exploited only by coupling to the in-plane component of the magnetization [6]. In the case of metallic FM-S structures, in-plane coupling has been observed only as a small change in transport properties [2] or using optically pumped carriers [7,8].In this Letter we report a demonstration of electrical spin injection in FM-S heterostructures using small (< 500 Oe) in-plane magnetic fields. We measure only the component of the spin that precesses after injection into the semiconductor using electroluminescence polarization (ELP) as a detection technique [6,9]. The effective magnetic field inducing the precession depends strongly on the electrical bias conditions and is dramatically enhanced at the highest injection current densities. The origin of the hysteresis in the spin polarization signal is magnetization reversal in the ferromagnet, but the magnitude and shape of the observed loops depend on the effective field in the semiconductor. Modeling based on the results of optical pumping experiments demonstrates that the origin of the large effective field is dynamical nuclear polarization due to the spin-polarized current injected from the ferromagnet [10]. This approach to dynamical nuclear polarization in semiconductors is a simple alternative to the use of optical pumping or high magnetic fields as sources of spin-polarized electrons [11,12].We report results from two heterostructures with different quantum well (QW) spin detectors. The samples are grown by molecular beam epitaxy on p + GaAs (100) substrates and consist of p-Al x Ga 1−x As/QW/n-

Spintronics: Fundamentals and applications

“…21 Supporting the findings of Clark and Feher (1963), Aronov calculated that the electrical spin injection would polarize nuclei and lead to a measurable effect in the electron spin resonance. Several decades later related experiments on spin injection are also examining other implications of dynamical nuclear polarization (Johnson, 2000;Strand et al, 2003). alized as the balance between spins added by the magnetization current and spins removed by spin relaxation.…”

Antiferromagnetic dipolar ordering in[Co2MnGe∕V]Nmultilayers

“…To date, efficient electrical spin injection into semiconductors has been demonstrated only from magnetic semiconductors [76,77] and conventional ferromagnetic metals [78,79]. Fully spin polarized Heusler alloys are in principle ideal candidates for epitaxial contacts.…”

Electron spin dynamics and hyperfine interactions inFe∕Al0.1Ga0.9As∕GaAsStrand1, Lou2, Adelmann3 et al. 2005Phys. Rev. BSelf Cite312440View full textAdd to dashboardCite

“…Recent experiments have demonstrated the electrical injection of spin-polarized electrons using a metallic ferromagnet as a contact and a band-engineered Schottky tunnel barrier. 4,5,6,7,8,9,10,11,12,13,14 The question naturally arises whether the electrically injected population of spin-polarized carriers interacts with lattice nuclei in a manner similar to optically injected spin-polarized carriers. In this paper we present a series of experiments in which a current of spin-polarized electrons electrically injected from an Fe contact dynamically polarizes lattice nuclei in a Al 0.1 Ga 0.9 As/GaAs quantum well (QW).…”