Optical investigation of HoFeO3

The absorption spectra of HoFeO₃ were investigated in the near infrared spectral region at temperatures of 1.2, 4.2, 20 and 77 °K respectively. At every temperatureT≦20 °K all the absorption lines show the same splitting which is attributed to the groundstate; this splitting is (7.2±0.5) cm^?1 at 20 °K and decreases to (4.9±0.8) cm^?1 extrapolated to 0 °K. From these splittings the holmium-iron and the holmiumholmium interactions can be deduced. Measurements with an external magnetic field yield a magnetic moment ofμ=(7.6±0.7)μ _B per holmium ion. The moments are directed at angles of ?28° and ?152° with respect to theb-axis.     

Optical investigation of ErFeO3

The absorption spectrum of single crystals of ErFeO₃ has been investigated in the red and near infrared spectral region in the temperature range between 1.2 °K and 4.2 °K and at 20 °K and 77 °K. Between 77 °K and 4.2 °K a constant splitting of the absorption lines is observed. Below the Néel-temperature of the erbium sublattice at 4.5 °K the splitting of the absorption lines increases; the saturation value extrapolated to 0 °K of the splitting of the lowest crystal field level of the⁴ I _15/2 groundterm is (6.08±0.30) cm^?1. By measuring the Zeeman effect the groundstate magnetic moment is determined asμ=(6.6±0.2)μ _B. The measured temperature dependence of the splitting of the lowest crystalfield level of the⁴I_15/2 groundterm is compared with that calculated by a Monte Carlo method.     

Optical investigation of DyFeO3

Optical absorption spectra of DyFeO₃ have been investigated at 1.2≦T≦4.2 °K, andT=77 °K From the temperature dependent lineshift a Néel temperature ofT _N=(3.8±0.5) °K is deduced for the dysprosium sublattices. The groundstate splitting due to the iron-dysprosium interactions is about 1.5 cm^?1 and due to the dysprosiumdysprosium interactions (5.0±1.4) cm^?1. Zeeman studies give the magnetic moment of the dysprosium ions asμ=(9.2±1.0)μ _B.     

Specific Features of the Faraday Effect in Rare-Earth Orthoaluminate DyAlO3

Optics and Spectroscopy - The magnetic susceptibility and the Faraday effect in DyAlO3 single crystal samples are studied in the temperature range of 78–300 K along the easy-magnetization...     

Faraday rotation and optical investigation of the metamagnetic phase transition in dysprosium phosphate

The metamagnetic phase transition in dysprosium phosphate has been studied by optical methods. A theoretical expression for the Faraday rotation in this substance is derived, and experimental results are reported for a long needle-shaped specimen. Observations of domains indicate that in DyPO₄ with magnetic field parallel to the crystallographic c-axis a mixed phase exists up to a tri-critical temperature T_t = 1.95 K.     

Visual investigation of the intermediate state in the region of metamagnetic phase transition in ErFeO3

We carried out the first observation of the intermediate state (IS) in the region of metamagnetic phase transition (MPT) in ErFeO₃: an external magnetic field H∥c (H=0–4 kOe), the temperature range 2.15–1.6 K. The ranges of the IS existence and the domain structure (DS) features were determined. Likely mechanisms of the IS thermodynamic stabilization and conditions for its visualization in ErFeO₃-plates with various crystallographic orientations were analyzed. The thermodynamic model of IS was offered: the intermediate state was stabilized by the mechanical stress that accompanies MPT. Excellent agreement with experiment was achieved.     

Optical investigation of strain-balanced superlattices

A series of strain-balanced GaInAs/AlInAs superlattices were investigated using optical spectroscopy. Three sets of excitonic Landau levels could be resolved in magneto-absorption spectra enabling estimates to be made for the reduced effective masses of the first and second electron to heavy hole (0.040±0.001m_eand 0.034 ± 0.002m_e) and the first electron to light hole (0.053 ±  0.002m_e) excitons. Enhancement in the light hole in-plane effective mass, relative to the heavy hole, is shown to result from the tensile strain in the quantum wells. Temperature-dependent photoluminescence measurements of these samples show evidence of thermal excitation of carriers between the first light and heavy hole states. The activation energy of this process compares well with the separation of the first heavy and light holes confined levels found from low-temperature absorption measurements in two structures with energy splitting of ∼40 meV and <10 meV respectively.     

Magnetization anomaly in metamagnetic superconductors

The magnetization in the tetragonal c-plane was measured below T_N using a single crystal of bct ErRh₄B₄. The magnetization decreases with increasing magnetic field in a field range just below the metamagnetic transition. This magnetization anomaly is explained by the fact that the entrance of the vortices is suppressed by an increase of the vortex core energy due to the precursor metamagnetic transition in the core around metamagnetic transition field.     

Optical investigation of PbTe doping superlattices

We report on a study of the optical properties of HWE-grown PbTe doping superlattices using infrared photoluminescence and -cathodoluminescence. Below-bulk-bandgap luminescence has been observed and is interpreted in the framework of a model giving the excitation dependence of the superlattice potential. Cathodoluminescence is used to investigate the properties of nipi layers.     

Landau expansion for a metamagnetic model

We performed a detailed Landau expansion of the free energy for a metamagnetic model considering terms up to twelfth order. We obtained explicit expressions for the coefficients as a function of the temperature and the ratio between ferro- and antiferromagnetic interactions. We showed that a naive analysis based on the signs of these coefficients cannot always give us sufficient guarantee about the correctness of the phase diagram of the model. In these cases it is necessary to resort to the full expression of the free energy in order to characterize the nature of the phase transition. Received 28 November 2001     

Phase separation in the itinerant metamagnetic transition of Sr4Ru3O10

We have investigated the electronic transport properties of the triple-layered ruthenate Sr4Ru3O10. We observed surprising anomalous features near its itinerant metamagnetic transition, including ultrasharp magnetoresistivity steps, a nonmetallic temperature dependence in resistivity for upward field sweeps, and a resistivity drop in temperature dependence for downward field sweeps. These features suggest that the metamagnetic transition of Sr4Ru3O10 occurs via an electronic phase separation process with magnetic domain formation.     

Effects of spin fluctuations on the paramagnetic susceptibility and metamagnetic transition in UPt3

The paramagnetic susceptibility for UPt₃ is calculated in the static gaussian statistics of spin fluctuations by using a realistic itinerant electron model. The magnetic field dependence of the magnetisation is also calculated and it is shown that the metamagnetic transition occurs at about 140 T.     

A simple model for metamagnetic percolation

An Ising model with both antiferromagnetic and randomly diluted, infinitely strong ferromagnetic interactions is studied on a Bethe lattice. The results are used to interpret recent experimental data on the phase diagram of Fe_xMg_1-xCl₂.     

Optical investigation of dysprosiumaluminumgarnet (DyAlG)

The absorption spectrum of the transitions⁶ H _15/2→⁶ F _3/2,⁶ F _5/2 in Dysprosiumaluminumgarnet (DyAlG) is investigated. In the antiferromagnetic state (T _N =2,49°K) a splitting of the crystal field levels by an internal magnetic field is observed. The splitting of the lowest crystal field level I of the groundterm in the internal field is (5,2±0,5) cm^?1, extrapolated to 0°K.     

Optical investigation of topological semimetal SrMnSb_2

We investigate the temperature-dependent infrared spectroscopy of SrMnSb_2, which is a semimetal with multiple Fermi surfaces. A notable blue shift of the plasma minimum in reflectivity upon cooling indicates that the carrier density varies with temperature. In the real part of the optical conductivity σ_1(ω), a linearly-increased component which extrapolates to zero conductivity at finite frequency has been identified, which suggests dispersion of gapped Dirac band structures near the Fermi level. A two-Drude model, representing two different types of carriers, is introduced to describe the real part of optical conductivity. We separate the contributions of two-Drude model in dc conductivity, and demonstrate that the transport properties of SrMnSb_2 are mainly affected by the narrow-Drude quasiparticles. Compared with the similar phenomena observed in CaMnSb_2 and SrMnBi_2, we can infer that the two-Drude model is an appropriate approach to investigate the multiband materials in AMnSb_2 and AMnBi_2 families.     

Optical method for investigation of acoustic gyrotropy

A photoelastic method for evaluation of components of acoustic gyrotropy preudotensors from acoustic-gyrotropy-induced changes in diffraction curves in elastograms of light diffraction on ultrasound waves propagating along acoustic axes in symmetry planes of elastic properties is developed. It is found that in m, 3m, 2mm, 4mm, and 6mm planal class and and inversion class crystals acoustic gyrotropy does not manifest itself in parameters of waves propagating in symmetry planes. It is shown that 222 class crystals and crystals of six other higher symmetry classes may have a sufficient number of acoustic axes in coordinate planes to ensure evaluation of all components of gyrotropy tensors by the photoelastic method. It is ensure out that evaluation of components of the inherent gyrotropy pseudotensor in 6/m or 4/m class crystals makes it possible to verify the validity of symmetry conditions, due to which only 15 components are left in this tensor in the general case. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 78–83, January–February, 1999.     

Temperature-induced metamagnetic transition in ErCo3: influence of Fe and Ni substitutions for Co

The phenomenon of a temperature-induced itinerant metamagnetism in ErCo₃ (at 65 K) was investigated with respect to small substitutions of Fe and Ni for Co. Five percent of Fe or Ni substitutions change the transition temperature to 170 or 25 K, respectively. The transition is accompanied by a large magneto-volume effect, ΔV/V reaches ∼0.5%, which allowed to relate the thermal expansion data with the magnetic state of the d-electrons. The change of the magnetic characteristics with substitutions is mainly ascribed to the shift of the position of the Fermi level in the hybridised d-electron energy band.     

de Haas-van Alphen effect across the metamagnetic transition in Sr3Ru2O7

We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant metamagnet Sr3Ru2O7. Extremely high sample purity allows the observation of dHvA oscillations both above and below the metamagnetic transition field of 7.9 T. The quasiparticle masses are fairly large away from the transition, and are enhanced by up to an extra factor of 3 as the transition is approached, but the Fermi surface topography change is quite small. The results are qualitatively consistent with a field-induced Stoner transition in which the mass enhancement is the result of critical fluctuations.