Yasuo Oka

Magneto‐optical properties of Cd1−xMnxSe microcrystallites in SiO2 glass prepared by rf sputtering

Cd1−xMnxSe microcrystallites have been successfully prepared by rf sputtering in SiO2 matrix glass. Optical absorption edge shows high energy shifts of 20–550 meV to the high energy as compared to its position in bulk crystals; these shifts are interpreted as evidence for exciton confinement in the microcrystallites. Annealing of the Cd1−xMnxSe microcrystallites at 450–650u2009°C for 0.5–5 h increases the size of the microcrystallites from 20 to 250 A. In an external magnetic field of 7 T the absorption edge shifts by 40 meV towards the low energy side due to the exchange coupling of the excitons with the d electrons of Mn2+ ions in the Cd1−xMnxSe microcrystallites. The spectral red shifts of the exciton luminescence in the Cd1−xMnxSe microcrystallites are also observed in the presence of magnetic fields. The corresponding effective g value varied from 138 at 1 T to 99 at 7 T.

Brillouin study of spin waves in sputtered CoNiPt alloy films

Sputtered CoNiPt films prepared for high‐density magnetic recording media have been studied by Brillouin scattering. The spin‐wave spectra in the film are remarkably broadened with width 13 GHz (full width at half maximum), which is much larger than the width of 3 GHz in a film prepared by vapor deposition. Observation by a transmission electron microscope has clarified that the sputtered film consists of Co crystallites with a diameter of 50–100 A, which are separated from each other. The remarkable damping of the spin waves in the sputtered CoNiPt film is caused by the film structure. The film is, however, elastically homogeneous, which is known from the undamped surface acoustic wave spectra. The result shows the segregation of the nonmagnetic Pt‐related alloys takes place between the Co crystallites. The exchange stiffness constant was determined as 2.4×10−9 Oeu2009cm2 in the sputtered film, which is 1/1.7 that in the vapor‐deposited films.

Interlayer exchange coupling in Co/Cr/Co double-layered recording films studied by spin-wave Brillouin scattering

Exchange coupling between Co layers through a Cr interlayer in sputtered Co/Cr/Co films has been studied by Brillouin scattering of spin waves by changing the thickness of the Cr interlayer up to 50 AA. The Brillouin spectrum consists of two spin-wave modes due to the Co double-layered structure which depends on the Cr-layer thickness. From the frequencies of the spin-wave modes, the interlayer exchange coupling A/sub 12/ varying with the Cr layer is determined by using Hillebrands theory. The exchange coupling through the nonmagnetic layer decreases with increase of the Cr thickness and becomes negligible for the Cr layer thicker than 20 AA. The result is compared with the media noise in double-layered CoCrPt alloy films with a Cr interlayer. >

Magneto-Optical Studies on Cd1-xMnxSe Quantum Dots

Magneto-optical effects of Cd1-xMnxSe quantum dots (QDs) embedded in quartz glass have been investigated in magnetic fields up to 7T. The photoluminescence shows large Zeeman shifts from a few meV up to 30meV depending on the size and Mn mole fraction. The exciton luminescence measured by selective excitation spectroscopy in an applied magnetic field shows the excitonic magnetic polaron (EMP) effect in the Cd1-xMnxSe QDs with the EMP formation energy above 20meV. The transient emission of the QD exciton has also been examined in the picosecond time domain. The lifetime of the QD excitons at the emission peak decreases from 900ps to 400ps in the presence of a magnetic field of 5T.

Brillouin spectroscopy of spin waves in sputtered CoPt alloy films and Co/Pt/Co multilayered films

Sputtered Co1−xPtx (x=0–0.14) alloy films have been studied by Brillouin scattering of spin waves and compared with results on Co/Pt/Co multilayered films. Brillouin spectra of the surface spin waves in the sputtered alloy films are remarkably broadened as an increase of the Pt content. The in‐plane coercivity of the films also increases as the increase of the Pt content, which indicates larger and better oriented grains with proper separations that result from higher Pt content. The broadening of the spin‐wave spectra is caused by the magnetic inhomogeneity due to the grains in the film. The exchange stiffness constant of the CoPt alloy films is determined from the magnetic field dependence of the frequency shifts of the surface and standing spin waves. To investigate the exchange interaction in the inhomogeneous alloy films, Co/Pt/Co multilayered films with the Pt interlayer of thickness of 0–40 A have been fabricated as a model material. From the analysis of the frequency shifts of the spin waves, the ...

Photogeneration of Solitons and Polarons in MX Chains

Abstract The effects of the electron-lattice (e-1) coupling and the interchain interaction on the gap states in the one-dimensional Peierls-Hubbard system have been investigated by the photo-induced absorption (PA) measurements of the halogen-bridged metal complexes (the MX chains; M=Pt and X=Cl, Br or I). In the complexes having small amplitude of CDW, three PA bands named a1 , a2 and b are observed. The PA bands a1 and a2 , which are insensitive to the interchain interaction, are assigned to polarons. The decrease of the interchain coupling of CDW leads to a midgap band b, which is attributable to charged-solitons. While, in the complexes having large amplitude of CDW, there are observed the two PA bands A and B having the long life time. Spectral shapes and excitation profiles of these PA bands are considerably different from those of the a1 , a2 and b bands. These results suggest that generation processes and stabilization energies of the gap states are strongly dependent on the magnitude of e-1 inter...

Magneto-optical properties of low-dimensional excitons in microcrystals and superlattices of Cd1-xMnxTe

Abstract Studies have been made on low-dimensional excitons in microcrystals and superlattices of Cd 1− txMnx Te fabricated by RF sputtering and hot-wall epitaxy. Properties of confined excitons in quantum boxes and in quantum wells, which are interacting with the Mn ions, are discussed from the results of the magneto-optical and transient spectroscopies.

Stimulated Emission Processes in Zn1-xCdxSe/ZnSe Multiquantum Wells

A stimulated emission effect has been studied in Zn1-xCdxSe/ZnSe (x=0.3) multiquantum wells (MQWs) with the well width of 7 to 70 A. The luminescence spectrum of the quantum well (QW) exciton at 4.2 K is shifted from the absorption spectrum by 10-12 meV to the lower-energy side. The deviation of the peak energy of the luminescence shows that the excitons in the MQW are inhomogeneously broadened by the monolayer fluctuation of the QW width. Stimulated emission is observed in the low-energy shoulder of the exciton luminescence band, which shifts to lower energies with increasing excitation intensity. The gain process is explained by the exciton-exciton scattering in the MQWs.

Spin correlation and dynamics of excitons in Cd1−xMnxTe, Cd1−xMnxSe and Cd1−xCoxSe

Abstract By time resolved and optical spin orientation spectroscopies of band-edge luminescences, an exchange interaction of excitons with magnetic ions was studied in semimagnetic semiconductors. The exchange interaction gives rise to a marked increase of the exciton luminescence intensity in magnetic fields as well as a dynamical formation process of the excitonic magnetic polaron. These effects are discussed in semimagnetic semiconductor compounds containing Mn, Co and Fe.

Far-infrared electron spin resonance in Cd1-xMnxSe and Cd1-xCoxSe

The ESR of Cd1-xTxSe (T = Mn, Co, Fe) has been investigated in the far-infrared region in pulsed high magnetic fields. In Cd1-xMnxSe with high Mn concentrations, resonance fields decreased with decreasing temperature. The ESR spectrum in Cd0.97Co0.03Se was observed for the first time and the g factor was determined to be 2.30.