Nguyen Hy Hau

High field magnetization step in Zn1−xMnxTe

Abstract Low temperature and high field magnetization experiments (H ⩽ 19 T) were carried out in diluted Zn1−xMnxTe alloys (x = 0.03). At 1.3 K, the first magnetization step, corresponding to the level crossing for pairs of nearest-neighbours (NN) is observed around H ⋍ 15 T . Magnetization data are analyzed including, within the molecular field approximation (MFA), interactions between Mn ions distributed in small clusters (singles, pairs, triangles) with more distant neighbours than NN. Both the saturation value observed at H ⋍ 10 T and the magnitude of the step agree with a random Mn distribution. Theoretical fits of the magnetization step provide a determination of the NN exchange constant J k = −9.25 ± 0.3 K .

In situ optical study of H2SO4-graphite intercalation compounds

Abstract Optical reflectance experiments were performed on H2SO4-graphite during electrochemical synthesis. The stage formation was studied from the evolution of intervalence transitions. Quantitative analysis of the plasma reflectance spectra of pure stage compounds led to the determination of the Fermi energy as a function of the electrochemically controlled charge. The results prove the validity of the 2D band structure model and provide the first determination of the band parameter γ0 in acceptor compounds.

Optical determination of the charge transfer in AsF5-graphite intercalation compounds

Abstract Optical reflectance experiments are performed on well-characterized compounds C8nAsF5 (n = 1, 2), in the temperature range 10–300 K. The theoretical analysis of the reflectivity spectra within the 2-D model of graphite independent subsystems [1] provides an optical determination of EF and the charge transfer coefficient which is found independent of temperature.

Intervalence transitions in graphite acceptor compounds

Abstract Optical reflectance experiments were performed on several GAC (Br 2 , AlCl 3 , SbCl 5 -graphite) of well-defined stage ( n = 2,3,4). We observed i.r. reflectivity structures whose energies are characteristic of the stage, but depend slightly on the intercalate species. These stage-specific structures are well understood, within the framework of the model of “Graphite Independent Subsystems”, as evidence of the predicted intervalence transitions. With a charge transfer coefficient comparable with the value obtained for the lowest stages of GAC, the expected energies of the intervalence transitions are in good agreement with the experimental positions of the reflectance structures.

Magnetic-optical studies of acceptor states in HgTe

Abstract Transitions from Γ 6 magnetic levels to acceptor states in HgTe have been observed in magnetotransmission experiments on p-type samples at 4.2 K. Experimental data indicate the existence of localized states with 0.7 and 2.2 meV ionization energies.

Crystal field effects in terbium iron garnet

Abstract The infra-red absorption spectrum of terbium iron garnet, (TbIG), has been recorded at liquid helium temperature. The energy level scheme was reduced and simulated within the frame of crystal field (cf) theory. The cf parameters of TbIG are not significantly different from those of terbium aluminum garnet, (TbAlG).

High Field Magnetization Step in Zn 1−x Mn x Te

High field magnetization experiments are reported for dilute Zn 1−x Mn x Te alloys (x≃0.03) at T=1.3K. The first magnetization step is analyzed including effects of internal field due to the interactions of Mn-Mn pairs with the remaining spins. An accurate estimate of the nearest neighbor (NN) exchange constant is obtained which agrees quite well recent neutron scattering experiments.

Infrared absorption spectra and crystal‐field effect of TbIG (abstract)

Rare‐earth iron garnets (RIG) are well known for their numerous interesting magnetic properties, but few works have been done on their optical behavior, especially at low temperatures. This paper studies the optical properties of TbIG, one of the most anisotropic RIG at low temperatures, showing large magnetic and magneto‐optical effects, in relation with its magnetic properties. For this purpose, polarized and unpolarized spectra of oriented single crystal of TbIG have been recorded at low temperatures (77, 4.2, and 2 °K) and in external magnetic fields up to 5 T, applied along the principal axis of a (110) plane. Transitions were observed from the ground level 7F6 to other states of the 7FJ multiplets of Tb3+ ions (between 2000 and 5500 cm−1). From the derived energy‐level scheme, a set of crystal‐field parameters was derived, within the D2 point symmetry. These parameters as well as the energy levels show no noticeable difference with those of Tb3+ ions in paramagnetic TbAlG. Correlations between polar...