The forced magnetostriction of nickel at 4.2 K

The forced volume magnetostriction of polycrystalline nickel at 4.2 K has been determined with a relative accuracy of 2 × 10^?2. Combining our result with previous data on the forced magnetostriction, we derive for the forced magnetostriction constants: h'₀ = (40 ± 1) × 10^?8T^?1, h'₁ = (-95 ± 2) × 10^?8T^?1, h'₂ = (-19 ± 2) × 10 ^?8T^?1.     

Supertransferred hyperfine structure in EPR of V4+ ion in Ca3In2Ge3O12 garnet

Interaction of an unpaired electron of the tetrahedral V⁴⁺ ion in Ca₃In₂Ge₃O₁₂ garnet with the four nearest In nuclei gives rise to clearly resolved structure of EPR spectra. We report the observation and analysis of these spectra at three frequencies and at temperature 77 K. The temperature dependence between liquid helium and the room temperatures was also studied. Parameters of the spin Hamiltonian are g_∥=1·8735; g_⊥=1·9825; ∣ ¦A∥|=150·4×10^?4cm^?1; ¦ A_⊥¦ = 36·7 × 10^?4 cm^?1. The supertransferred hyperfine interaction was found to be isotropic, absolute value of the corresponding parameter a is 22·1 × 10^?4 cm^?1.     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.     

Optical band-gap of Zn3As2

Absorption measurements of single Zn₃As₂ crystals were made at temperatures 5, 80 and 300 K. Free-carrier absorption is interpreted in the simple classical model. Interband absorption shows contributions from Urbach-like excitations. The direct optical gap has been estimated as 0.99 eV at 300 K, 1.09 eV at 80 K and 1.11 eV at 5 K. The linear dependence of band-gap on temperature was found in the range 80–300 K with dE_g/dT = ? 4.55 × 10^?4eVK^?1.     

Measurement of magnetostriction and anisotropy of Mg-ferrite

The magnetostriction constants λ₁₀₀ and λ₁₁₁ and the anisotropy constant K₁ of Mg-ferrites [Mg_η;Fe_1?η][Mg_1?ηFe_1+η]O₄, (η = 0·101, 0·154, 0·184, 0·219) at room temperature, liquid N₂ temperature and liquid He temperature were observed by ferrimagnetic resonance techniques at 9·5 GHz.The signs of the magnetostriction constants λ₁₀₀ and λ₁₁₁ are always negative and positive, respectively and the magnitudes of these constants increase with decreasing temperature. These constants λ₁₀₀ and λ₁₁₁ at liquid He temperature are found to be ? 14·4 × 10^?6 and 2·4 × 10^?6 respectively, when η is 0·101, and then the magnitudes of those constants decrease linearly with increasing η.     

Giant magnetocaloric effect near the curie temperature in the Sm0.6Sr0.4MnO3 manganite

A method is proposed for the calculation of the magnetocaloric effect from simultaneous measurements of thermal expansion and magnetostriction made in different regimes (adiabatic and isothermal). The magnitude of the magnetocaloric effect for Sm_0.6Sr_0.4MnO₃ is estimated. It is found that near the Curie temperature T _C it passes through a maximum to reach a giant value ΔT=4.6 K for ΔB=0.84 T. In addition, in the neighborhood of T _C, we observed colossal magnetoresistance Δρ/ρ = [ρ(H) ? ρ(0)]/ρ(0) = 72% in a weak magnetic field of 0.84 T, a giant negative volume magnetostriction ω=?5×10^?4 in a field of the same strength, and a large change in the sample volume ΔV/V ≈ 0.1%.     

Giant volume magnetostriction and colossal magnetoresistance in La0.7Ba0.3MnO3 at room temperature

In single-crystal La_0.7Ba_0.3MnO₃, giant volume magnetostriction was observed for the first time to reach 2.54 × 10^?4 at room temperature and a still larger level of 4 × 10^?4 at the Curie point T _C = 310 K in a magnetic field of 8.2 kOe. At the same temperatures and magnetic field, this effect is complemented by a colossal magnetoresistance of 15.2 and 22.7%, respectively. The volume magnetostriction ω and magnetoresistance Δρ/ρ follow similar patterns in the proximity of T _C; namely, ω and Δρ/ρ are negative, maxima are observed in the |ω|(T) and |Δρ/ρ|(T) curves, and the ω and Δρ/ρ isotherms do not saturate in the highest fields applied. These phenomena are assigned to the fact that, in the above composition, there exists a two-phase magnetic (ferromagnetic-antiferromagnetic) state induced by strong s–d exchange.     

Electron paramagnetic resonance of Dy3+ in cubic ZnSe and Tm3+ in hexagonal CdS single crystals

Electron paramagnetic resonance has been observed for Dy³⁺ in ZnSe and Tm³⁺ in CdS. For Dy³⁺ doped ZnSe, an isotropic spectrum was observed having well resolved hyperfine lines due to ¹⁶¹Dy and ¹⁶³Dy. The g value obtained was 6.577 ± 0.002 and ¹⁶¹A was 191 ± 1 × 10⁴ cm^?1 and ¹⁶³A was 265 ± 3 × 10^?4 cm^?1. The agreement of the observed g value to g(τ₆) = 6.667 and the point-charge calculations suggest that Dy³⁺ occupies an interstitial (II) site with no local charge compensation. For Tm³⁺ doped in hexagonal CdS, an axial spectrum consistent with g_⊥ = 0, g_∥ = 10.722 ± 0.007, D = 2.57 GHz (crystal field splitting) and ¹⁶⁹A = 1207 ± 5 × 10^?4cm^?1. The large g_∥ value indicates that the Tm ion exits in the trivalent state. This is in reasonable agreement with previous reports of the non-Kramer's state of Tm³⁺.     

Hopping conductivity of carbynes modified under high pressures and temperatures: Galvanomagnetic and thermoelectric properties

The conductivity, thermopower, and magnetoresistance of carbynes structurally modified by heating under a high pressure are investigated in the temperature range 1.8–300 K in a magnetic field up to 70 kOe. It is shown that an increase in the synthesis temperature under pressure leads to a transition from 1D hopping conductivity to 2D and then to 3D hopping conductivity. An analysis of transport data at T ≤ 40 K makes it possible to determine the localization radius a ～ (56?140) Å of the wave function and to estimate the density of localized states _g(E _F) for various dimensions d of space: _g(E _F) ≈ 5.8 × 10⁷ eV^?1 cm^?1 (d=1), _g(E _F) ≈5×10¹⁴ eV^?1 cm ^?2 (d=2), and _g(E _F)≈1.1×10²¹ eV^?1 cm_?3 (d=3). A model for hopping conductivity and structure of carbynes is proposed on the basis of clusterization of sp ² bonds in the carbyne matrix on the nanometer scale.     

Magnetic and ESR studies of Er3+ in lanthanum dihydride LaH2

Er³⁺ electron spin resonance ESR and magnetic susceptibility have been studied in metallic lanthanum dihydride host. The ESR spectrum contains a single asymmetrical line with g-factor g = 6.68 ± 0.05 close to that expected for Γ₇ as ground state. The experimental magnetic susceptibility was interpreted on the base of LLW cubic crystal field Hamiltonian. The best fit of the experimental data has been obtained for the following B₄ and B₆ crystal field parameters: B₄ = ?5.2 × 10^?3 K; B₆ = 3.8 × 10^?5 K which support the anionic-like character hydridic model of hydrogen atoms in this hydride.     

Magnetic field effects on the hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol as studied by a picosecond laser flash photolysis technique

The hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol at 265 K has been studied with a newly developed picosecond laser flash photolysis apparatus under magnetic fields of 0–1.7 T. The decay rate constant of the radical pair generated was found to increase from 3.42 × 10⁹ s^?1 to 4.15 × 10⁹ s^?1 with increasing the magnetic field from 0 to 1.7 T. The observed magnetic field effects can be explained by the Δg mechanism. Using the simple kinetics model with the Δg mechanism, the rate constant of the escape process from the pair (k _esc) and two rate constants for the T-S spin conversion process (k _T-S) at 0 and 1.7 T were found to be 1.97 × 10⁹ s^?1, 1.45 × 10⁹ s^?1, and 2.12 × 10⁹ s^?1, respectively. From the magnetic field dependence on k _T-S, the difference in the g values of the 4-methoxybenzophenone ketyl and phenylthiyl radicals was estimated to be 0.0087.     

The exciton absorption in deformed germanium

Absorption spectra at 77° K near the direct (κ = 0) exciton transition are reported for deformed and undeformed single-crystal films of n-type Ge oriented on (111); Elliott's theory is applied. The optical width of the forbidden band for this transition is found as E_{g 0} = (0.8821 ±±0.0002) eV, while the exciton binding energy is found as E_ex(0) = = (0.0016±0.0003) eV for undeformed Ge at 77 ° K. The mean temperature coefficient of E_g for κ = 0 in the range 77 °–297 ° K is (dE_g/ /dT)_p =?3.50 · 10^?4 eV/deg. The effects of thermoelastic deformation on the exciton spectrum give (dE_g/dT)_d = (?1.5±0.1) · 10^?4 eV/deg. The half-width σ ≈ 5 · 10^?4 eV of the exciton peak gives the exciton lifetime as gt ≥ 10^?12 sec.     

钙钛矿（La1-yTby)0.67Sr0.33MnO3的磁致伸缩效应

采用固相反应烧结法制备了（La_1-yTb_y)_0.67Sr_0.33MnO₃系列样品（y=0,0.05,0.15,0.20,0.25,0.33,0.40,0.50,0.60,1.00).X射线衍射表明,随着y值增大钙钛矿型晶体结构从菱面对称性向正交对称性转变.180K时,μ₀H=7T条件下,在y=0.40样品的巨磁电阻可达900％.μ₀H=1.7T时,y=0.20样品的室温磁致伸缩为-50×10^-6.210K时,y=0.33样品的磁致伸缩可达-130×10^-6. 关键词：     

Thermodynamic properties of the CeSn3 mixed valence compound

We have measured on the CeSn₃ compound, the expansion coefficient between 80 and 800 K at normal pressure, the isothermal compressibility in the 0–8 GPa pressure range at room temperature and the heat capacity at constant pressure in the 60–300 K temperature range. The experimental data were compared with those previously found for the isomorphous LaSn₃ phase, assumed as a proper reference material for the study of the intermediate valency states in CeSn₃. Both the thermal expansion (3α) and the isothermal compressibility (k) of CeSn₃ show behaviours quite different from those of LaSn₃: for instance, in the standard conditions, 3α is 55 × 10^?6K^?1for CeSn₃ and 38 × 10^?6K^?1for LaSn₃; k is 15 × 10^?12 Pa^?1 and 12 × 10^?12 Pa^?1 respectively for CeSn₃ and LaSn₃. The thermal behaviour of the molar specific heat at constant pressure of CeSn₃ is similar to that of LaSn₃ for temperatures lower than 50 K. In the 70–300 K temperature range, the heat capacity of CeSn₃ is clearly higher than that of LaSn₃, ΔC_p being maximum near 150 K. The analysis of the calorimetric data show that the electronic coefficient γ of CeSn₃ is temperature dependent: its value varies from 53 mJ K^?2 mole^?1 at low temperature 24 mJ K^?2 mole^?1 at 300 K.     

A high-resolution study of the 14.4-μm infrared band of deuterofluoroform

The FT-IR spectrum of the ν₃ parallel band of deuterofluoroform has been recorded at a resolution of 0.0045 cm^?1. Nine independent spectral parameters were determined which reproduce some 650 observed wavenumbers with a standard error of 3 × 10^?4 cm^?1. The constants derived for the ν₃ band are (in cm^?1): ν₀ = 694.2822(3); B₀ = 0.3309321(9); B₃ = 0.3302464(11); α^B = 6.859(10) × 10^?4; α^C = 1.429 × 10^?4; D₃^J = 3.168(3) × 10^?7; D₀^J = 3.188(3) × 10^?7; D_JK³ = 4.766 × 10^?7; D_JK⁰ = 4.864 × 10^?7; and D_K⁰ ? D_K³ = 2 × 10^?10.     

Hyperfine and nuclear quadrupole interactions in copper-doped cadmium oxalate trihydrate single crystals

Electron spin resonance experiments on Cu²⁺ doped in a single crystal of cadmium oxalate trihydrate grown by a slow diffusion technique have been carried out at 77 K. The major features of the ESR spectra can be attributed to divalent copper (3d⁹) in substitutional Cd²⁺ sites. Information has been gained about the hyperfine and quadrupole interactions concerning the ion. The spin-Hamiltonian parameters in the $\text{S =}\text{1}\text{2}$, $\text{I =}\text{3}\text{2}$ manifold are: g_x = 2.0211; g_y = 2.2249; g_z = 2.4536; A_x = +84.5 × 10^?4cm^?1; A_y = +16.8 × 10^?4cm^?1; $\text{A}{}_{\mathrm{z}}\text{= ?40.8 × 10 ×}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$; P_x = ?7.4 × 10^?4cm^?1; P_y = ?0.4 × 10^?4cm^?1; and P_z = +7.8 × 10^?4cm^?1. An evaluation of the asymmetry and quadrupole coupling parameters revealed that the ground state of the guest ion in Cd(COO)₂ · 3H₂O is 0.97|x² ?y₂ > +0.24 |3z² ? r² >.     

Triplet-Triplet fluorescence of 9,10-dibromanthracene in hexane

The temperature dependence of the triplet-triplet fluorescence (TTF) spectrum of 9,10-dibromanthracene in hexane is studied in the near infrared region between 800 and 1050 nm in the temperature range from 200 to 320 K. The TTF spectrum exhibits two distinct bands at 842 and 949 nm at 293 K. Upon cooling from 293 to 200 K, the intensity of the 842-nm band decreases and that of the 949-nm band increases. The different behavior of the band intensities is explained by the overlap of the emission at 950 nm, which can be related to a photoproduct. The 842-nm band is assigned to the 0-0 T ₂(³ B _1g →T ₁(³ B _2u transition. The quantum yield of TTF at 293 K measured within the 842-nm band is 8.3×10^?7 (±20%)), and for emission in the region from 800 to 1050 nm it is equal to 1.4×10^?6 (after subtraction of the contribution from the S ₁→S ₀ singlet-singlet fluorescence). The effect of the intersystem crossing and internal conversion on the temperature dependence of TTF is discussed.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

Electron paramagnetic resonance of Dy3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Dy³⁺ ions in lead thiogallate PbGa₂S₄ single crystals have been presented. It has been shown that the ground state of these ions corresponds to the lowest Stark sublevel Γ₆ of the term ⁶ H _15/2. The spectra are well described by the axially symmetric spin Hamiltonian with the effective spin S = 1/2 with the factors g _‖ = 15.06 and g _⊥ = 2.47. The Dy³⁺ ions substitute Pb²⁺ ions in the crystal lattice of PbGa₂S₄. The observed hyperfine structure has allowed to unambiguously interpret the EPR spectra. The hyperfine interaction constants of two odd isotopes of dysprosium in lead thiogallate single crystals have been found to be A _‖ = 675 × 10^?4 cm^?1 and A _⊥ = 111 × 10^?4 cm^?1 for ¹⁶³Dy and A _‖ = 472 × 10^?4 cm^?1 and A _⊥ = 77 × 10^?4 cm^?1 for ¹⁶¹Dy.     

The anomalous magnetic moment of positive and negative muons

The anomalous g-factor a ≡ (g?2)/2 has been measured for muons of both charges in the Muon Storage Ring at CERN. The two results, a_μ⁺ = 1165910(12) × 10^?9 and a_μ^? = 1165936(12) × 10^?9, are in good agreement with each other, and combine to give a mean a_μ = 1165922(9) × 10^?9, which is very close to the most recent theoretical prediction 1165921(10) × 10^?9. For the experimental results, the total statistical and systematic error is given. The measurements thus confirm the remarkable QED calculation plus hadronic contribution, and serve as a precise verification of the CPT theorem for muons.