Optically detected magnetic resonance of the zinc vacancy in ZnS

Optical detection of magnetic resonance (ODMR) is reported for the single negative charge state, V_Zn^?, of the isolated zinc vacancy in ZnS. Produced by 2.5 MeV electron irradiation, it is detected in a distant donor-acceptor (DA) pair luminescent band at 570 nm in which the vacancy acts as the acceptor. Excitation and emission spectral dependences of the V_Zn^? ODMR signals are analyzed in terms of a configurational coordinate model. We conclude that the double acceptor level (V_Zn⁼/V_Zn^?) is located ～1.1 eV from the valence band edge and that the trigonal Jahn-Teller relaxation energy for the V_Zn^? state is ～0.5 eV.     

Optical detection of magnetic resonance wiggles

The observation of the wiggles phenomenon of nuclear magnetic resonance in an optically pumped system is reported. A rapid passage double-resonance experiment on the ground state of rubidium vapour is used to demonstrate the effect.     

Role of magnetic circular dichroism in all-optical magnetic recording

Using magneto-optical microscopy in combination with ellipsometry measurements, we show that all-optical switching with polarized femtosecond laser pulses in ferrimagnetic GdFeCo is subjected to a threshold fluence absorbed in the magnetic layer, independent of either the excitation wavelength or the polarization of the laser pulse. Furthermore, we present a quantitative explanation of the intensity window in which all-optical helicity-dependent switching (AO-HDS) occurs, based on magnetic circular dichroism. This explanation is consistent with all the experimental findings on AO-HDS so far, varying from single- to multiple-shot experiments. The presented results give a solid understanding of the origin of AO-HDS, and give novel insights into the physics of ultrafast, laser controlled magnetism.     

X-ray magnetic circular dichroism involving valence states

Accepted: 6 March 1997     

Spin-polarization and x-ray magnetic circular dichroism in GaAs

The combination of angular spin momentum with electronics is a promising successor to charge-based electronics. The conduction bands in GaAs may become spin-polarized via optical spin pumping, doping with magnetic ions, or induction of a moment with an external magnetic field. We investigated the spin populations in GaAs with x-ray magnetic circular dichroism for each of these three cases. We find strong anti-symmetric lineshapes at the Ga L₃ edge indicating conduction band spin splitting, with differences in line width and amplitude depending on the source of spin polarization.     

Soft X-ray magnetic circular dichroism of Cr-doped GaN

Soft X-ray magnetic circular dichroism (XMCD) have been measured for the Ga_0.97Cr_0.03N film grown by NH₃-assisted molecular beam epitaxy. Temperature dependence of the XMCD intensity was well described by the Curie–Weiss law. Although the sample showed ferromagnetic behavior at least up to room temperature, the ferromagnetic component could not be detected by the XMCD measurement.     

The magnetic circular dichroism spectra of matrix-isolated benzene

The magnetic circular dichroism (MCD) spectra of the ¹ B _2u ←¹ A _1g transition of benzene in nitrogen and argon matrices at 20 K have been measured in order to obtain a spectrum devoid of hot bands and complicating rotational structure. The spectrum is dominated by three progressions of B terms, two of positive sign and one of negative. One positive progression and the negative one can be definitely assigned to the e_2g modes v ₆ and v ₉ respectively, whilst the other positive progression may be the e _2g mode v ₈. This is in marked contrast with the absorption spectra of the same matrices which reveal only a single progression built upon v ₆. The MCD spectra are nicely accounted for in terms of a magnetic mixing between the ¹ B _1u and ¹ B _2u states, the electric dipole intensity arising from the mixing in of a ¹ E _1u state via e _2g vibrational modes.     

Optical detection of magnetic resonance on anion antisites in indium phosphide

The paper describes the application of optically detected magnetic resonance (ODMR) methods to the identification of antisite defects in the III–V semiconductor InP. In III–V semiconductors the high abundance of nuclei with large nuclear spins greatly limits the resolution of magnetic resonance techniques. In particular, ODMR signals characteristic of the P_In antisite in InP with slightly differentg-values and hyperfine splitting have been observed. The corresponding centres cannot be distinguished with confidence without the higher resolution of electron-nuclear double resonance (ENDOR). Magnetic resonance signals of the antisite in InP are too weak to allow such measurements in the conventional detection mode, but using optically detected ENDOR (ODENDOR) in absorption as well as in emission, the isolated P_In antisite and at least one other antisite defect were identified. Moreover, the energy position of the P _In ⁺ /P _In ⁺⁺ level in the bandgap was determined from the optical transitions involved.     

X-ray circular magnetic dichroism in the presence of strong spin fluctuations

The use of X-ray magnetic circular dichroism (XMCD) spectra for determininghe t magnitude of atomic magnetic moments in compounds of rare-earth and transition elements is discussed. The standard sum rule approach often yields a magnitude of moments that is often smaller than values obtained from magnetic measurements. We attribute this to strong spin fluctuations in the surface layers in which XMCD signals form. A way of determining the values of local magnetic moments in the presence of strong fluctuations is proposed and tested.     

X-ray magnetic circular dichroism imaging with hard X-rays

X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4 microns. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10 eV above the cobalt K-absorption edge (7709 eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32 eV above the cobalt K-absorption edge.     

Transmission X-ray microscopy using X-ray magnetic circular dichroism

X-ray magnetic circular dichroism (X-MCD) was used as a large, element-specific and quantitative magnetic contrast mechanism in the soft X-ray microscopes at BESSY I (Berlin) and the ALS (Berkeley). The present state and potential of magnetic transmission X-ray microscopy (MTXM) is outlined. The possibility to record images in varying magnetic fields and the high spatial resolution down to 25 nm were used to image out-of-plane magnetized (4 ?Fe / 4 ?Gd)×75 systems. Magnetic domains could be studied in arrays of circular and square dots with lateral dimensions down to 180 nm. Hysteresis loops of individual dots were deduced using the direct proportionality of the X-MCD contrast to the sample magnetization. Images of a 3 nmCr / 50 nmFe / 6 nmCr film demonstrate for the first time that MTXM is also able to observe in-plane magnetized domains. In the future the possible applications of MTXM will be extended with regard to the strength of the external field, the available energy range and the sample conditions by building a dedicated transmission X-ray microscope for magnetic imaging at BESSY II. Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Linear dichroism and magnetic circular dichroism of acenaphth[1,2-a]acenaphthylene

Ultraviolet-visible polarized absorption spectra of acenaphth[1,2-a]acenaphthylene have been determined from low-temperature measurements of linear dichroism in stretched polyethylene. The magnetic circular dichroic spectrum has been measured in solution. Transition energies, polarizations, and relative intensities, as well as the absolute signs of B terms of low-energy transitions are in good agreement with results of π-electron calculations and with simple qualitative arguments, which also account for the close similarity to the known spectra of acenaphthylene.