Magneto-circular Dichroism Spectra Research Articles

Plasmonic enhancement of the magneto-optical response of MnP nanoclusters embedded in GaP epilayers

We report on the magneto-optical activity of MnP nanoclusters embedded in GaP epilayers and MnP thin film as a function of temperature, magnetic field, and wavelength in the near infrared and visible. The measured Faraday rotation originates from the ferromagnetic magnetization of the metallic MnP phase and exhibits a hysteretic behavior as a function of an externally applied magnetic field closely matching that of the magnetization. The Faraday rotation spectrum of MnP shows a magnetoplasmonic resonance whose energy depends on the MnP filling factor and surrounding matrix permittivity. At resonance, the measured rotary power for the epilayer systems increases by a factor of 2 compared to that of the MnP film in terms of degrees of rotation per MnP thickness for an applied magnetic field of 410 mT. We propose an effective medium model, which qualitatively reproduces the Faraday rotation and the magnetocircular dichroism spectra, quantitatively determines the spectral shift induced by variations in the MnP volume fraction, and demonstrates the influence of the shape and orientation distributions of ellipsoidal MnP nanoclusters on the magneto-optical activity and absorption spectra.

Polar Kerr effect studies ofGa1−xMnxAsepitaxial films

The ferromagnetic state of thin ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ layers ($d=300\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$; $x=0.014$, $p=6.7\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, ${T}_{C}=40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, easy axis in plane; $x=0.03$, $p=9.5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, ${T}_{C}=60\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, easy axis out of plane) on GaAs substrates is investigated by polar magneto-optical Kerr effect (MOKE) and reflectance magnetocircular dichroism (MCD) studies in the temperature range between $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, in magnetic fields normal to the layer plane ranging from $\ensuremath{-}5\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}+5\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$. A magnetic field of $70\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ is applied in those cases when truly saturated magnetization has to be determined. A parabolic interband dielectric function model that includes the relevant (heavy-hole, light-hole, and split-off) valence bands, as well as the finite Moss-Burstein shift, was developed for analyzing both the MOKE and MCD. The occupation of the spin-split valence bands is taken into account by explicitly including the Fermi level for holes in analytic form. The samples were sufficiently different in their Curie temperatures, easy axis directions, magnetic ion contents, and hole concentrations to demonstrate experimentally the versatility of the proposed model. Superconducting quantum interference device measurements carried out on the samples demonstrated the validity of the dilute-magnetic-semiconductor (DMS) mean-field approach for the contact exchange interaction between manganese spins and hole carriers, reflected by a more or less fixed conduction-band exchange parameter ${N}_{0}\ensuremath{\alpha}=0.22--0.29\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and a hole exchange parameter ${N}_{0}\ensuremath{\beta}$ varying between 0.9 and $2.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, depending on the hole concentration and on the Mn content. Note that the magnitudes are close to those familiar from II-VI DMS's, but the sign of ${N}_{0}\ensuremath{\beta}$ is reversed from the II-VI case---i.e., from antiferromagnetic to ferromagnetic local exchange. The quantitative wavelength-dependent $(\ensuremath{\lambda}=550--950\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ analysis of MOKE and MCD spectra for both samples and the imposed requirement that the band parameters should not deviate significantly from the GaAs-related band alignment and from exchange-induced spin multiplicities lead us to the introduction of a dispersionless level superimposed in the conduction band of GaMnAs (fitted energy gaps $1.50--1.57\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$). The physical nature of such a level could not be identified by our simplified model, but we note that a high-density-of-states level in the conduction band of GaMnAs has been predicted recently by Sandratskii and Bruno [Phys. Rev. B 66, 134435 (2002)]. The hysteresis measurements are presented without deeper analysis. The hole concentration fitted to MOKE and MCD spectra deviates for the $x=0.014$ sample by a factor of 0.8 from the data obtained by anomalous Hall effect measurements, but this inconsistency should probably be viewed as a result of the difficulty in interpreting experimental magnetotransport measurements, rather than a shortcoming of our theoretical treatment.

Magneto-Optical Effects and Electrical Resistivity of La0.8-xBixSr0.2MnO3 Films

In La0.8-X Bi x Sr0.2MnO 3 films(x=0∼0.3) prepared by a laser deposition technique, Magneto-Circular Dichroism (MCD) spectra between 1.5 to 6 eV and temperature dependence of resistivity were investigated. In the films without Bi, three optical transitions between 3 and 5 eV in MCD spectra are confirmed by the fitting. The Bi-doping makes shift these three transitions to higher energy and induces a new transition which shifts to lower energy by increasing of doping content. These transitions are ascribed to the charge transfer transitions from O2p to Mndγ (eg).

Characterization of Below-Gap Absorption in Semi-Insulating GaAs:Cr by Magneto-Circular Dichroism Spectrum

Magneto-circular dichroism (MCD) spectra in semi-insulating (SI) single crystals of GaAs:Cr have been measured between 0.7 and 1.4 eV with a magnetic field of about 106 A/m (13 kOe) at temperatures above 20 K. Relatively strong MCD signals were observed in the below-gap energy region where a strong photoionization absorption band appears. Assuming that this strong absorption is caused by the charge transfer transition from the top of the valence band to the Cr-related deep state, we have analyzed the observed data by a theoretical calculation using a model adopted by Martinez et al., from which the Cr-related state was located 0.89 eV above the top of the valence band. The spin-orbit parameter used for the fitting is much smaller than that expected from the splitting in the top of the valence band. Modification of the theory used in this analysis is required.

Reflectance magnetocircular-dichroism spectra and electronic structures of CdCr2Se4

Reflectance magnetocircular-dichroism spectra of a ferromagnetic semiconductor CdCr2Se4 were measured for temperatures between 4.2 K and 157 K. Off-diagonal elements of the dielectric tensor were calculated from the measured spectra. A number of fine structures was resolved, the energy position of which was plotted against temperature. It is found that there are two red-shifting structures: one at 1.1 eV (the well-known absorption edge) and the other at 1.9 eV. Other structures show slight blue-shift. These energy positions were compared with the band structure calculated by means of the self-consistentDV-Xα technique.

Observation of a Strong Infrared Magneto-Optical Effect in a Pyrite Type Ferromagnet CoS2

Reflectance magneto-circular dichroism spectra and Kerr rotation spectra have been measured for the first time on a pyrite type ferromagnet CoS 2 , for photon energies between 0.5 and 3.5 eV below the Curie temperature. There have been observed three major structures around 0.8, 1.5 and 2.8 eV, among which the most prominent is the one at 0.8 eV; the Kerr rotation reaches the value of 1.1° at the peak. Real and imaginary parts of the off-diagonal element of the dielectric tensor have been calculated from the observed spectra. Theoretical study has revealed that the line shape of the 0.8 eV structure can be explained in terms of the localized many-electron excitation associated with the d e -dγ absorption edge of this compound. This corresponds to the narrow-band nature of the pyrite type compound.