Spin-optoelectronics is a novel research area at the crossroads between the fundamental physics of quantum-mechanical spin, optoelectronics, and nanotechnology. [ 1 ] Spin-and light-polarization effects in nanostructures, possibly involving the confi nement of both charges and photons, are very appealing for the implementation of innovative optoelectronic systems. In particular, the coupling between the photon helicity and the spin angular momentum of electrons can be used for the magnetically controlled generation and detection of circularly polarized light, to be employed in systems exploiting the additional degree of freedom connected to the light polarization. [ 2 ] Multiple-statelogic and novel communication protocols can be implemented based on the capability of manipulating and detecting the different polarization states of light pulses (linear, circularly left and right) in integrated platforms without the use of external optical elements. In this framework, novel devices such as optical interconnects, optical switches, and modulators [ 3 , 4 ] can be realized with reconfi gurable functionality depending on the confi guration of the magnetic electrodes embedded in the emitters and detectors of the polarized light.Providing that the integrated emitters and detectors of polarized light have enough sensitivity to operate on single photons, the information, ultimately carried out by the spin of electrons and photons, can be encoded in the confi ned spin state, manipulated at the nanoscale and redelivered in the form of polarized photons. Major future applications of such a novel approach comprise the areas of quantum computing and data-transmission cryptography based on the coherent interaction between qubits via photon-polarization effects. [ 5 ] During the last decade, there have been many attempts to implement the integrated electrical detection of light helicity. The spin voltaic effect in graded p-n junctions has been recently employed, [ 6 ] but most work has essentially used spin-LEDs operating in the reverse way. [ 7 ] In these pieces of work, the spin fi ltering of photogenerated carriers in a semiconductor (SC) during their motion towards a ferromagnetic (FM) electrode is exploited to convert the electron spin polarization into a modulation of the photocurrent. For this reason, in analogy with spin-LEDs, these devices are usually referred as "spin-photodiodes" (spin-PDs). Direct FM/SC interfaces with Schottky barriers, [ 8 ] complex structures involving insulating tunneling barriers [ 9 , 10 ] and p-i-n photodiodes with an embedded quantum well, [ 11 ] have been investigated. However, all of the previous work has employed a III-V semiconductor as the optically active layer, and, up to now, there has been no clear demonstration of Ge-based spin-PDs that present a sizable spin fi ltering at room temperature.Although for many years GaAs has been the unquestioned reference material for semiconductor spintronics, recently considerable attention has been devoted to Ge. Spin manipulation, [ 12 ] electric...

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We present a device concept based on controlled micromagnetic configurations in a corner-shaped permalloy nanostructure terminated with two circular disks, specifically designed for the capture and detection of a small number of magnetic beads in suspension. A transverse head-to-head domain wall (TDW) placed at the corner of the structure plays the role of an attracting pole for magnetic beads. The TDW is annihilated in the terminating disks by applying an appropriate magnetic field, whose value is affected by the presence of beads chemically bound to the surface. In the case where the beads are not chemically bound to the surface, the annihilation of the TDW causes their release into the suspension. The variation of the voltage drop across the corner, due to the anisotropic magnetoresistance (AMR) while sweeping the magnetic field, is used to detect the presence of a chemically bound bead. The device response has been characterized by using both synthetic antiferromagnetic nanoparticles (disks of 70 nm diameter and 20 nm height) and magnetic nanobeads, for different thicknesses of the protective capping layer. We demonstrate the detection down to a single nanoparticle, therefore the device holds the potential for the localization and detection of small numbers of molecules immobilized on the particle's functionalized surface.