The extensive experimental and computational search for multifunctional materials has resulted in the development of semiconductor and oxide systems, such as (Ga,Mn)N, (Zn,Cr)Te and HfO(2), which exhibit surprisingly stable ferromagnetic signatures despite having a small or nominally zero concentration of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and the associated magnetooptical and magnetotransport functionalities, are dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these nanocrystals can be controlled by manipulating the charge state of the Cr ions during the epitaxy. The findings provide insight into the origin of ferromagnetism in a broad range of semiconductors and oxides, and indicate possible functionalities of these composite systems. Furthermore, they demonstrate a bottom-up method for self-organized nanostructure fabrication that is applicable to any system in which the charge state of a constituent depends on the Fermi-level position in the host semiconductor.

We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spinpolarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation. There are two small schemes in the tested spin-LEDs: first, the stripe-laser-like structure that helps intensify the EL light at the cleaved side walls below the spin injector Fe slab, and second, the crystalline AlO x spin-tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density (J) region, whereas it increases steeply and reaches close to the pure CP when J > 100 A/cm 2 . There, either right-or left-handed CP component is significantly suppressed depending on the direction of magnetization of the spin injector. Spin-dependent reabsorption, spin-induced birefringence, and optical spin-axis conversion are suggested to account for the observed experimental results.A s well represented by the giant magnetoresistance, tunneling magnetoresistance, and spin-transfer-torque magnetic random access memory, spintronics research based on spin transport in magnetic metals has been contributing significantly in the progress of electronics through the advancement in recording bit density and low-power memory retention (1, 2). Proposal of the spin-current modulation with an electric field (3) and invention of diluted magnetic III-V semiconductors (4) have opened the opportunity of introducing spin degree of freedom in semiconductor technology (5). After those works, light-induced magnetism (6), electric-field-controlled magnetism (7), spin qubits in semiconductors (8, 9), spin-polarized light-emitting diodes (spinLEDs) (10, 11), and spin-metal-oxide-semiconductor field-effect transistor (12) were either demonstrated or proposed, which have caused an impact on the metal-based spintronics and applied physics that is not small. However, works that assure the roomtemperature (RT) operation of those semiconductor-based devices have not been accomplished to date.Concerning spin-LEDs, studies on a spin injector consisting of a ferromagnetic metal (FmM) and a tunnel barrier (TB) (13-15) succeeded those using semiconductor-based spin injectors (10, 11). The idea of the FmM-TB injector is to take advantage of spin-polarized carriers at RT with FmM and to simultaneously suppress with the TB the backward flow of unpolarized carriers that is unavoidable in the diffusive transport (16, 17). Many works have been carried out with the FmM-TB injector since then. Among those, the highest circular polarization (CP) value,) and I(σ − ) the intensity of right-and left-handed EL component, respectively, was P CP ∼ 0.3 ∼ 0.35 at RT in the external magnetic flux of B = 0.8 T, which was achieved in the context of studying the spinfiltering effect of the MgO TB (18,19). Most of the past works regarding spin-LED were carried out under the vertical arrangement with low J ranging from 0.1 to 1 A/cm 2 and forcing spins aligned vertically by applying out-of-pla...

Electric and magnetic properties were investigated on p-type Zn1−xCrxTe doped with nitrogen (N) as an acceptor. Thin films of p-Zn1−xCrxTe(x≦0.09) were grown by molecular-beam epitaxy with the supply of N2 gas excited by rf plasma. With the increase of Cr composition x at an almost fixed N concentration of the order of 1020cm−3, the temperature dependence of resistivity changed from metallic behavior to an insulating one, accompanied with a significant decrease of the hole concentration. The magnetization measurements revealed that ferromagnetic behaviors observed in undoped Zn1−xCrxTe were suppressed due to the nitrogen doping; with N concentrations of the order of 1020cm−3, hysteresis loops in the magnetization curve disappeared, the magnitude of magnetization decreased, and the ferromagnetic transition were not observed down to 2 K according to the Arrott plot analysis. These experimental findings are discussed on the basis of the ferromagnetic double exchange interaction which is considered to work on the Cr 3d impurity level formed in the band gap of ZnTe.

The effect of additional doping of charge impurities was investigated in a ferromagnetic semiconductor Zn1-xCrxTe. It was found that the doping of iodine, which is expected to act as an n-type dopant in ZnTe, brought about a drastic enhancement of the ferromagnetism in Zn1-xCrxTe, while the grown films remained electrically insulating. In particular, at a fixed Cr composition of x=0.05, the ferromagnetic transition temperature TC increased up to 300 K at maximum due to the iodine doping from TC=30 K of the undoped counterpart, while the ferromagnetism disappeared due to the doping of nitrogen as a p-type dopant. The observed systematic correlation of ferromagnetism with the doping of charge impurities of both the p and n type, suggesting a key role of the position of Fermi level within the impurity d state, is discussed on the basis of the double-exchange interaction as a mechanism of ferromagnetism in this material.

The circular polarization of light scattered by biological tissues provides valuable information and has been considered as a powerful tool for the diagnosis of tumor tissue. We propose a non-staining, non-invasive and in-vivo cancer diagnosis technique using an endoscope equipped with circularly polarized light-emitting diodes (spin-LEDs). We studied the scattering process of the circularly polarized light against cell nuclei in pseudo-healthy and cancerous tissues using the existing Monte Carlo method. The calculation results indicate that the resultant circular polarizations of light scattered in pseudo tissues shows clear difference in a wide range of detection angle, and the sampling depth depends on those detection angles. The structure of the endoscope probe comprising spin-LEDs is designed based on the calculation results, providing structural and depth information regarding biological tissues simultaneously.Template for JJAP Regular Papers (Jan. 2014) 2