E. Schuster

Electron spin injection into GaAs from ferromagnetic contacts in remanence

We demonstrate electrical spin injection into a (GaIn)As∕GaAs light-emitting diode from the remanent state of ferromagnetic contacts in perpendicular geometry. Using a Fe∕Tb multilayer structure with perpendicular magnetic anisotropy and a reverse-biased Schottky contact, we achieve a circular polarization degree of the emitted light of 0.75% at 90K.

Electrical detection of photoinduced spins both at room temperature and in remanence

We demonstrate a photodetector with ferromagnetic contacts which can electrically detect the polarization degree of incoming light using spin filtering of photoinduced spin-polarized electron currents. Our structure is a pin diode with a single GaAs quantum well as active region and a Fe∕Tb multilayer on top of a MgO tunnel barrier as n-contact where the spin-polarized electron current is filtered. The photocurrent depends on the magnetization of the contacts and on the polarization of the injected light. We prove that even in remanence and at room temperature the degree of circular polarization of the incident light can be unambiguously determined by the photocurrent intensity.

Room temperature electrical spin injection in remanence

We demonstrate electrical spin injection from ferromagnetic Fe/Tb multilayer structures with remanent perpendicular magnetization into GaAs-based light-emitting diodes at room temperature. Using a reverse-biased Schottky contact and a MgO tunnel contact, respectively, we achieve spin injection at remanence. The maximum degree of circular polarization of the emitted light is 3% at room temperature.

Spin injection light-emitting diode with vertically magnetized ferromagnetic metal contacts

We analyze the electrical injection of spin-polarized electrons into a (GaIn)As∕GaAs light-emitting diode. Using an Fe∕Tb multilayer structure with perpendicular magnetic anisotropy and a reverse-biased Schottky contact, we demonstrate spin injection even in remanence between 90 and 260K. The maximum degree of circular polarization of the emitted light is 0.75% at 90K.

Local spin manipulation in ferromagnet-semiconductor hybrids

The authors demonstrate the usage of magnetic fringe fields from nanoscale ferromagnets to locally control the spin degree of freedom in a semiconductor. Fringe fields stemming from Fe∕Tb multilayer ferromagnets induce a local, remanent out-of-plane magnetization in a ZnCdMnSe dilute magnetic semiconductor quantum well, which in turn aligns the spin of photogenerated carriers via sp-d exchange interaction. The authors achieve a local exciton spin polarization of up to ±12% at 4K without the need of an external magnetic field. The spin polarization can be controlled in sign and magnitude via the magnetization of the ferromagnet and is observable up to T=80K.

Epitaxial growth and interfacial magnetism of spin aligner for remanent spin injection: [Fe/Tb]n/Fe/MgO/GaAs-light emitting diode as a prototype system

We have successfully grown and characterized [Fe/Tb]10/Fe(001)/F57e(001)/MgO(001) multilayer contacts on a GaAs-based light emitting diode. Using F57e conversion-electron Mossbauer spectroscopy at room temperature (RT) and at 4.2 K, we provide atomistic proof of large perpendicular Fe spin components in zero external field at and below RT at the F57e(001)/MgO(001) interface. Further, indirect evidence of large interfacial Fe atomic moments is provided. Our contacts serve as a prototype spin aligner for remanent electrical spin injection at RT.

Laser-induced erasure and reversal of the permanent magnetization in a ferromagnet-dilute magnetic semiconductor hybrid structure

Manipulation of the magnetizations via laser pulse heating is studied for a hybrid structure, where the fringe field of a metallic ferromagnet controls remotely the carrier and magnetic ion spins in a diluted magnetic semiconductor quantum well. A single nanosecond pulse with an energy density of 160 pJ/μm2 is found to be sufficient to erase the ferromagnet magnetization. Applying a reversed external bias field about five times below the ferromagnet coercive field, a complete reversal of the magnetization via optical excitation is demonstrated.

Electronic transport and atomic vibrational properties of semiconducting Mg Sn thin film

A polycrystalline Mg2Sn thin film has been prepared by thermal co-evaporation in ultrahigh vacuum of Mg and Sn onto a naturally oxidized Si(100) substrate at  −140°C. The structure of the sample was characterized by X-ray diffraction (XRD) and 119Sn conversion electron Mössbauer spectroscopy (CEMS). The semiconducting property of the Mg2Sn thin film was confirmed by electrical resistance, magnetoresistance, Hall-effect and infrared spectroscopy measurements, and a value of ∼0.2 eV was found for the electronic gap energy. The 119Sn-projected partial vibrational density of states (VDOS), g(E), has been measured by nuclear resonant inelastic X-ray scattering (NRIXS) of 23.878 keV synchrotron radiation. Together with g(E), other thermodynamic quantities such as the probability of recoilless absorption (f-factor), the average kinetic energy per Sn atom, the average force constant, and the vibrational entropy per Sn atom are obtained. The partial VDOS of both elements (Mg and Sn) has been calculated theoretically and reasonable agreement with the measured 119Sn-projected VDOS is observed. g(E) is characterized by a phonon energy gap ranging from ∼17 to ∼21 meV.

Room-temperature spin-controlled optoelectronic devices

We present three spin-dependent optoelectronic devices for spin controlled photonics working at room temperature. A spin controlled light emitting diode is demonstrated which exhibits spin injection through Fe/Tb-multilayers at room temperature and in remanence. Furthermore, we show that a classical vertical resonator laser can amplify spin information even at room temperature due to its nonlinearity at threshold. Accordingly, in combination with the injectors mentioned above it can be used as a spin-controlled emitter, allowing efficient spin-controlled polarization switching of its optical output. Due to the stability of light polarization in comparison to the spin orientation in a semiconductor, spin information can thus be transmitted over long distances and at room temperature with such devices. For detection of such spin information, we present a spin detector. It consists of a pin-diode with Fe/Tb-multilayer contacts and we show that it can create a polarization dependent spin-current also at room temperature and without applied magnetic fields.

Local Control of Carrier Spin States in a Semiconductor by Microscale Ferromagnetic Wires

Employing fringe fields from microscale Fe/Tb multilayer ferromagnets (FMs) with remanent out‐of‐plane magnetization, we are able to define a local, remanent carrier spin polarization in an underlying ZnCdMnSe dilute magnetic semiconductor quantum well (DMS QW). The fringe fields of the FMs “imprint” a locally varying magnetization into the DMS QW by orienting the magnetic moment of the incorporated Mn2+ ions. Optically excited charge carriers align their spin along the local DMS magnetization due to the s‐pd exchange interaction. Using polarization resolved, magnetic field dependent photoluminescence (PL) spectroscopy we demonstrate a remanent DMS carrier spin polarization of 5 % in the vicinity of ferromagnetic Fe/Tb wire structures.