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A nonreciprocal polarization converter compatible with InP-based photonic integrated circuits is described, where the device consists of an asymmetric InGaAsP waveguide combined with a ferromagnetic cerium-substituted yttrium iron garnet layer. The nonreciprocal conversion of the polarization state is used in the waveguide and a nonreciprocal TE-TM conversion efficiency of 93% is obtained with a device length of 0.27 nm.

Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide [Fe.sub.3][O.sub.4] on GaAs(100) and the unit cell of the [Fe.sub.3][O.sub.4] was found to be rotated by 45[degrees] to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films are controlled by uniaxial magnetic anisotropy. The dynamic response of the sample shows a heavily damped precessional response to the applied field pulses. In the Heusler alloy system of [Co.sub.2] MnGa on GaAs, we found that the magnetic moment was reduced for thicknesses down to 10 nm, which may account for the lower than expected spin-injection efficiency from the spin-light-emitting diode structures. Using the element-specific technique of X-ray magnetic circular dichroism (XMCD), the reduced spin moments were found to originate from the Mn rather than the Co atoms, and the improvement of the interface is thus needed to increase the spin injection efficiency in this system. Further studies of the I--Vcharacteristics of [Fe.sub.3][O.sub.4]/GaAs(100) and [Fe.sub.3][O.sub.4]MgO/GaAs(100) show that the [Fe.sub.3][O.sub.4]-based spintronic structures have a well-defined Schottky or tunneling barrier of moderate barrier height, which is encouraging for high-efficient spin injection. Index Terms--Gallium arsenide (GaAs), Heusler alloys, magnetic oxides, magnetite, molecular-beam epitaxy, spintronics, ultra-thin films.

Amorphous and crystalline thin films of Mn-doped (0.5%-10%) GaAs and crystalline thin films of [Zn.sub.1-x][Co.sub.x]O(x = 3%-20%) were investigated by means of magnetic susceptibility and electron spin resonance (ESR). For the Mn-doped GaAs samples, our results show the absence of ferromagnetic ordering for the amorphous films in the 300 > T > 2 K temperature range, in contrast to the ferromagnetism found in crystalline films for [T.sub.c] < 110 K. A single ESR line with a temperature independent g-value (g ~ 2) is observed for the amorphous films, and the behavior of this ESR linewidth depends on the level of crystallinity of the film. For the Mn-doped GaAs crystalline films, only a ferromagnetic mode is observed for T < [T.sub.c] when the film is ferromagnetic. Turning now the [Zn.sub.1-x][Co.sub.x]O films, ferromagnetic loops were observed at room temperature for these films. The magnetization data show an increasing of the saturation magnetization [M.sub.s] as a function of x reaching a maximum value for x [approximately equal to] 10%. ESR experiments at T = 300 K in the same films show a strong anisotropic ferromagnetic mode (FMR) for x = 0.10. Index Terms--Dilute ferromagnetic semiconductors, electron spin resonance, magnetization curves.

Holographic transmission electron microscopy showed that magnetic flux does not diverge from the top of an Fe-coated W tip indicating the in-plane magnetization at the apex of successful spin-polarized tips. A dependence of differential conductivities of GaAs with Fe-coated W tips on the helicity of illuminating laser light was confirmed at negative sample bias where partially spin-polarized electrons in the conduction band of p-GaAs tunnel into spin-dependent Fe empty states while no dependence of those with nonmagnetic W tips. Index Terms--Magnetic field measurement, optical pumping, spectroscopy, tunneling.

Magnetically tunable wideband microwave bandstop and bandpass filters using ferromagnetic resonance absorption in yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs) layer structures are reported. The measured characteristics of the bandstop filter, with nonuniform bias magnetic field distribution along the YIG/GGG film, shows a large absorption bandwidth of 1900 MHz at the stopband center frequency of 11.0 GHz, average peak absorption of 13 dB, and an out-of-stopband insertion loss of 1.5 dB. The measured characteristics of the bandpass filter at the passband center frequency of 7.1 GHz demonstrates a 3-dB bandwidth of 1450 MHz, out-of-band rejection of 33 dB, and an insertion loss of 1.5 dB. A good agreement between the experimental results and the simulation results based on a lumped element equivalent circuit modeling of YIG bandstop filters has been achieved. Index Terms--Ferromagnetic resonance (FMR) absorption, tunable bandstop and bandpass filters, YIG filters.

We report the evolution of Fe oxide nanostructures on GaAs(100) upon pre- and post-growth annealing conditions. GaAs nanoscale pyramids were formed on the GaAs surface due to wet etching and thermal annealing. An 8.0-nm epitaxial Fe film was grown, oxidized, and annealed using a gradient temperature method. During the process the nanostripes were formed, and the evolution has been demonstrated using transmission and reflection high energy electron diffraction, and scanning electron microscopy. These nanostripes exhibited uniaxial magnetic anisotropy. The formation of these nanostructures is attributed to surface anisotropy, which in addition could explain the observed uniaxial magnetic anisotropy. Index Terms--Annealing, magnetic Fe oxide, magnetic uniaxial anisotropy, nanostructures.

The magnetic moments of ultrathin Fe films on three different III-V semiconductor substrates, namely GaAs, InAs and [In.sub.0.2][Ga.sub.0.8] As have been measured with X-ray magnetic circular dichroism at room temperature to assess their relative merits as combinations suitable for next-generation spintronic devices. The results revealed rather similar spin moments and orbital moments for the three systems, suggesting the relationship between film and semiconductor lattice parameters to be less critical to magnetic moments than magnetic anisotropy. Index Terms--Fe/InGaAs, interface magnetism, spin electronics, ultrathin films.

Ultrathin Fe oxide films of various thicknesses prepared by post-growth oxidation on GaAs(100) surface have been investigated with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). The XPS confirms that the surfaces of the oxide are [Fe.sub.3][O.sub.4] rather than [Fe.sub.2][O.sub.3]. XAS and XMCD measurements indicate the presence of insulating Fe divalent oxide phases (FeO) beneath the surface [Fe.sub.3][O.sub.4] layer with the sample thickness above 4 nm. This FeO might act as a barrier for the spin injection into the GaAs. Index Terms--Half-metallic [Fe.sub.3][O.sub.4], post-growth oxidation, spintronics, XMCD.

A low transmission barrier is a crucial factor for the efficient spin injection, and an oxide barrier is commonly used for the insulator between the ferromagnet and the semiconductor. After heat treatment at the furnace, an AlAs layer was converted to an aluminum oxide layer, and arsenic gas was evaporated. This new method of forming spin injection barrier on the two-dimensional electron gas (2-DEG) system is very efficient to obtain tunneling behavior. Index Terms--A1As, aluminum oxide, furnace, low transmission barrier, spin injection.