Metal-organic chemical vapor deposition （MOCVD） grown ferromagnetic GaMnN films are investigated by photo- luminescence （PL） measurement with a mid-gap excitation wavelength of 405 nm. A sharp PL peak at 1.8 eV is found and the PL intensity successively decreases with the addition of Mn, in which the Mn concentration of sample A is below 1% （[Mn]A =0.75%） but its PL intensity is stronger than other samples＇. The 1.8-eV PL peak is attributed to the recombination of electrons in the t2 state of the neutral Mn3＋ acceptor with holes in the valence band. With Mn concentration increasing, the intensity of the PL peak decreases and the magnetic increment reduces in our samples. The correlation between the PL peak intensity and ferromagnetism of the samples is discussed in combination with the experimental results.
Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.
Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.
A compact high precision eight-axis automatism and two-axis manual soft-ray polarimeter with a multi- layer has been designed, constructed, and installed in 3WlB at the Beijing Synchrotron Radiation Facility （BSRF）. Four operational modes in the same device, which are double-reflection, double-transmission, front-reflection-behind- transmission and front-transmission-behind-reflection, have been realized. It can be used for the polarization analysis of synchrotron radiation. It also can be used to characterize the polarization properties of the optical elements in the soft X-ray energy range. Some experiments with Mo/Si and Cr/C multilayers have been performed by using this polarimeter with good results obtained.
To improve the performance of Beamline 3WIB at the Beijing Synchrotron Radiation Facility for the soft X-ray magnetic linear dichroism research at transition metals L2,3 edges, a new monochromator was designed and built to replace the original one. After the assemblage, alignment and adjustment of the monochromator system, the first commissioning results were obtained. The photon energy range is from 50 to 1000 eV with spectral resolutions of 1600 at 250 eV and 1000 at 870 eV. The photon flux is of the order of 10s-109 photons/s/200 mA/0.1%BW. In the electron＇s orbital plane the linear polarization degree of the light is higher than 99% at 704 eV. The beamline has satisfied the basic experimental requirements.
Role of vacancy-type（N vacancy（VN） and Ga vacancy（VGa）） defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic state of a system.The VNcan induce antiferromagnetic state and the VGaindirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN.The transfer of electrons between the vacancy defects and Mn ions results in converting Mn3＋（d4） into Mn2＋（d5）.The introduced VNand the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing,as well as the coexistence of Mn3＋（d4） and Mn2＋（d5） are found in GaMnN films grown by metal–organic chemical vapor deposition.The analysis suggests that a big proportion of Mn3＋changing into Mn2＋will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material.
