Tran Khanh Vien

Bio: Tran Khanh Vien is an academic researcher. The author has contributed to research in topics: Absorption spectroscopy & Crystal field theory. The author has an hindex of 4, co-authored 5 publications receiving 40 citations.

Crystal Field Splitting in Octahedral and Tetrahedral Symmetry for Fe3+ Ions in Y3Fe5012

Abstract: The crystal field splitting of the energy levels of Fe3+ ions in octahedral and tetrahedral sites of Y3Fe5O12 have been computed between 10000 and 32000 cm−1. The calculation is performed using, first, the cubic field approximation, then the effect of a trigonal distortion, and finally the spin-orbit interaction in the two magnetic sites. It is shown that the contributionof thetrigonal distortion to the absorption spectrum can be neglected. Thespin-orbit coupling does not disturb the value of the calculated level energies but induces a coupling between some multiplets. With the use of the spin-orbit coupling a very good fit between the computed and theexperimental spectra is obtained leading to an assignment of the observed absorption lines which is slightly different from that obtained without the spin-orbit coupling effects.

Magnetooptical and magnetic properties of terbium iron garnet at low temperatures

Abstract: The specific circular φF and linear φCM magnetic birefringences of Tb3 Fe5 O12 single‐crystal are reported as a function of the d.c. field Ha and from liquid helium temperature to room temperature. The sign, amplitude and slope of the Cotton‐Mouton effect are strongly dependent on T, Ha and on the direction of this field with respect to the crystal axis. Well defined maxima of % % the slope ΔφF/ΔHa and ΔφCM/ΔHa, observed near T=45 °K, are discussed both from the paramagnetic evolution of the Tb3+ ions in the anisotropic exchange and crystal fields which induce a noncolinear magnetic structure.

Interactions magnéto-optiques linéaires et quadratiques induites par les transitions dipolaires électriques et magnétiques dans les cristaux ferromagnétiques

Abstract: L'analyse en seconde quantification des interactions magneto-optiques dans un cristal ferromagnetique montre que les effets statiques (effets Faraday et Cotton-Mouton) et dynamiques (Raman a 1 et 2 magnons) apparaissent comme des diffusions spin-photon elastiques et inelastiques respectivement. Les relations physiques et analytiques entre ces differents effets dispersifs induits par les transitions dipolaires electriques et magnetiques sont precisees. On montre que les susceptibilites Raman a 1 et 2 magnons sont proportionnelles au carre des birefringences magnetiques specifiques circulaire et lineaire respectivement. Enfin les anomalies importantes de diffusion Raman a 1 magnon que nous avons observees recemment sont interpretees a partir de l'influence des interactions magneto-optiques du second ordre sur les diffusions inelastiques du premier ordre.

On the absorption spectra of complex ions. II

Abstract: The secular determinants obtained in the previous paper are solved for the energy levels which are important in the absorption spectra of the normal complex ions, leaving the crystalline field strength as a parameter. The values of B and C (Racah's parameters) there needed are determined from the observed spectra of free ions or in some cases by extrapolation. The f -values of the transitions which connect the energy levels calculated are estimated and compared with the observed intensities. The difference of the spectral width among absorption bands and lines is also considered using the energy diagram obtained. Following the assignments determined by the above considerations, the calculated positions of lines and bands are rather in good agreement with the experimental data in divalent ions [MX 6 ] 2+ (M=Cr, Mn, Fe, Co, Ni), when we adjust the crystalline field parameter D q suitably. In trivalent ions [MX 6 ] 3+ (M=Ti, V, Cr, Mn, Fe), it is necessary besides the adjustment of D q to use smaller values ...

Second-harmonic generation as a tool for studying electronic and magnetic structures of crystals: review

Abstract: Second-harmonic generation (SHG) in magnetically ordered crystals is reviewed. The symmetry of such crystals is determined by the arrangement of both the charges and the spins, so their contributions to the crystallographic and the magnetic structures, respectively, must be distinguished. Magnetic SHG is introduced as a probe for magnetic structures and sublattice interactions. The specific degrees of optical experiments - including spectral, spatial, and temporal resolution - lead to the observation of novel physical effects that cannot be revealed by other techniques of probing magnetism. These include local or hidden phase transitions, interacting magnetized and polarized sublattices and domain walls, and magnetic interfaces. SHG in various centrosymmetric and noncentrosymmetric crystal classes of antiferromagnetic oxides such as Cr2O3, hexagonal RMnO3(R=Sc,Y,In,Ho-Lu), magnetic garnet films, CuB2O4, CoO, and NiO, is discussed.

Linear optical birefringence of magnetic crystals

Abstract: The study of changes in the refractive indices (with consequent changes of birefringence) of a transparent magnetic crystal which accompany changes in the magnetic order is becoming more popular. The authors review why this is. The first reason is that birefringence can be measured very accurately: the different experimental arrangements are reviewed. The second reason is because a birefringence measurement is an integrational spectroscopic technique and therefore it is studied both experimentally and theoretically as a branch of magneto-optics and hence gives information on the detailed energy level structure of the solid. The third reason is that in a number of interesting systems the birefringence is proportional to the magnetic energy over a wide temperature range and it is often a more convenient method of obtaining the magnetic specific heat than direct specific heat measurements; this is particularly true in magnetic crystals which show low dimensional ordering. The last reason is that in all magnetic crystals the birefringence change should vary like one of the thermodynamic critical exponents near to the phase transition. They review in detail the reasons why birefringence studies have become so successful for measuring critical exponents in pure and particularly mixed crystals.

Phonon and magnon scattering of antiferromagnetic Bi 2 Fe 4 O 9

Abstract: The phonon structure of antiferromagnetic ${\text{Bi}}_{2}{\text{Fe}}_{4}{\text{O}}_{9}$ (space group $Pbnm$ No. 55, ${T}_{N}\ensuremath{\approx}240\text{ }\text{K}$) was studied theoretically by calculations of lattice dynamics and experimentally between 10 and 300 K by polarized Raman spectroscopy. Most of the $12{A}_{g}+12{B}_{1g}+9{B}_{2g}+9{B}_{3g}$ Raman modes were unambiguously identified. Strong second-order scattering was observed for $ab$-plane-confined incident and scattered light polarizations. In addition to the phonon-scattering, broad Raman bands with typical characteristics of magnon scattering appear below ${T}_{N}$. The magnon bands are analyzed on the basis of magnetic structure of ${\text{Bi}}_{2}{\text{Fe}}_{4}{\text{O}}_{9}$ and attributed to two-magnon excitations.

Superposition model analysis of Fe3+ and Mn2+ spin-Hamiltonian parameters

Abstract: Recent work has shown it possible to derive single-ligand contributions from the observed spin-Hamiltonian parameters for the 8S7/2 ground state of f7 lanthanide ions using the superposition model Here the authors apply this model to the 6S5/2 ground state of Mn2+ and Fe3+ and show it to give a consistent description of experimentally determined parameters in several systems The significance of this result is understanding the splitting of the 6S5/2 ground state is discussed