Spin waves in an Invar alloy (Fe0.65Ni0.35)

The spin wave dispersion relation in an Invar alloy Fe_0.65Ni_0.35 has been measured at 4.2 K in the [111] direction by neutron inelastic scattering.Well defined magnon groups have been observed up to an energy transfer of about 80 meV. The spin wave dispersion is well described by ?ω=Dq²(1?βq²) with $\text{D=143}\text{meV}\text{A}\text{?}$ and $\text{β=0.12}\text{A}\text{?}{}^2$. The value of D is in accord with the value extrapolated from other neutron scattering results at higher contents of Ni and disagrees with spin wave resonance results.No trace of γ-iron type antiferromagnetic order could be detected at 4.2 K in this alloy by elastic neutron scattering measurements.     

Critical behaviour of a uniaxial ferromagnet,ErCl3·6H2O with predominant dipolar interactions

The parallel magnetic susceptibility χ of a uniaxial ferromagnet ErCl₃·6H₂O has been measured between 0.3 and 4.2K and specially near T_c = 0.353 K. The predominant contribution to the Curie-Weiss temperature is due to the dipolar interactions. χ is proportional to ?^?γ with $\text{? =}\text{T}\text{T}{}_{\mathrm{c}}\text{?1}$ in the range 10^?3 < ? < 5 × 10^?2. The γ value, γ = 1.01 ±0.03 is consistent with the theoretical prediction for a uniaxial dipolar ferromagnet.     

Spin-wave scattering from A γ-Fe47Mn53alloy

Spin waves in the antiferromagnetic alloy γ-Fe_0.5Mn_0.5 have been studied at $\text{295° K(}\text{T}\text{T}{}_{\mathrm{N}}\text{= 0.63)}$ by the inelastic neutron scattering technique. We observed an isotropic dispersion and obtained a value for the spin-wave velocity of 255 ± 30 meV Å (3.88 ± 0.50 × 10⁶ cm/sec), which is the order of the spin-wave velocity in Cr (a typical itinerant antiferromagnet). The energy gap at q = 0 was found to be 7.0 ± 0.5 meV. These results suggest the existence of a long-range spin ordering in the conduction electrons of this alloy.     

Study on vacancy motion in Y2O3-doped CeO2 by 17O NMR technique

The ¹⁷O NMR measurement was made to elucidate the microscopic nature of vacancy motion in Y₂O₃-doped CeO₂. Spin-lattice relaxation rate, T^?1₁, spin-spin relaxation rate, T^?1₂, and resonance intensity were measured at v₀ = 8.13 MHz as a function of temperature [385 < T (K) < 1110] and composition [$\text{0.06 <}\text{Y}{}_2\text{O}{}_3\text{(}\text{m}\text{o}\text{) < 6}$]. The static electric field gradient associated with lattice defects resulted in the composition dependences of the line width and the intensity. In low dopant concentrations, doubly peaked temperature dependence of T^?1₁ was found, while a single and asymmetric peak was observed in high concentrations. T^?1₁ of 4.0 and 6.0 $\text{m}\text{o}$ doped samples were analyzed using a barrier height distribution model for the oxygen vacancy jump. The mean value of the activation energy was found to increase with the Y₂O₃ concentration.     

Intrinsic V- and Vo centers in single crystal SrO

The intrinsic V^- center (a positive hole trapped at a cation vacancy) has been observed in single crystals of SrO following x-irradiation at 77 K. The ESR spectrum corresponds to a spin-$\text{1}\text{2}$ defect having <100> axial symmetry with g₆ = 2.0012(3) and g_⊥ = 2.0703(3). The concentration of V^- centers was enhanced significantly by heating crystals in oxygen at 1000°C and rapidly quenching. V^o centers (two holes trapped at a cation vacancy) were also observed after x-irradiation at low temperature, with g₆ = 2.0011(3), g_⊥ =2.0751(3), and D = 380.4(5) MHz.     

Specific heat of (C6H11NH3) CuCl3 (CHAC), a system of ferromagnetic chains

The heat capacity of (C₆H₁₁NH₃) CuCl₃ (CHAC) has been measured for 0.45 < T < 60 K. Three-dimensional ordering is observed at T = 2.214 K. The data in the paramagnetic region can be described by a ferromagnetic $\text{S =}\text{1}\text{2}$ Heisenberg linear chain model system with J/k = +45 ± 5K.     

Shallow acceptor bound exciton and free exciton states in high-purity zinc telluride

We investigated excitons bound to shallow acceptors in high-purity ZnTe and measured excitation spectra of two-hole luminescence lines at 1.6 K using a tunable dye-laser. The electron-hole coupling in the bound exciton (BE) states appears to be very different for the various acceptors even for almost identical exciton localisation energies. Three different types of BE are reported. For the Li-acceptor BE we observe three sub-components separated by 0.22 and 0.17 meV and interpreted as J = $\text{1}\text{2}$, $\text{3}\text{2}$, $\text{5}\text{2}$ states. The Ag-acceptor BE exhibits a strong ground state and a weak excited state at 1.3 meV higher energy. For the as yet unidentified k-acceptor we observe a single BE level, degenerate with the Ag-acceptor BE ground state. Dips in the excitation spectra due to absorption into free exciton 1S, 2S, and 3S states yield an exciton Rydberg R₀ = 12.8±0.3 meV and a free exciton binding energy FE(1S) = 13.2±0.3 meV.     

Evidence for assignment of 14.0 MeV state in 11B from 10B(n,n)10B

The differential cross section and polarization for neutrons scattered from ¹⁰B have been measured at E_n = 2.63 MeV (E_x = 13.85 MeV). The results of this experiment and other available neutron scattering data in the range 1 < E_n < 4 MeV are interpreted through a single-level R-matrix calculation over the region 12 < E_x < 15 MeV. Based on this analysis the most probable J^π assignment for the 14.0 MeV level in ¹¹B is $\text{11}\text{2}{}^{\mathrm{+}}$. The anomaly near E_x = 13.1 MeV can only be explained in terms of two overlapping levels having assignments of ($\text{5}\text{2}$, $\text{7}\text{2}$)^? and ($\text{3}\text{2}$, $\text{5}\text{2}$, $\text{7}\text{2}$)⁺.     

Excited states of Ag and Cu acceptors in CdTe

We report on resonantly excited luminescence (REL) at 1.8 K and infrared absorption (IRA) between 6–12 K of CdTe doped with Ag and Cu impurities. The luminescence was excited with a tunable dye laser. Two hole transitions up to $\text{6}\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ state have been observed, the bound exciton lines have been identified. $\text{2}\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ states have been observed in IRA measurements. The binding energies as deduced from REL experiments are 107.5 meV for Ag and 146 meV for Cu. The fitted values of the valence band parameters are Ro = 27 ± 3 meV μ = 0.73 ± 0.03 and δ = 0.12 ± 0.01.     

Isomers in the N = 83 nucleus 149Dy

Energy levels in the N = 83 nucleus ¹⁴⁹Dy were studied by the reaction ¹⁵²Gd(α, 7n) at 106 MeV bombarding energy using in-beam γ-ray spectroscopy methods. The measurements identified three isomers in this nucleus, at 1073 keV (13 ± 3 ns), at 2700±150keV (5 μs < T_{$\text{1}\text{2}$} < 0.5 s), and above 3.5 MeV (50 ± 15 ns). The low-lying isomer is interpreted as i_{$\text{13}\text{2}$}. The configuration $\text{27}\text{2}$^?(πh_{$\text{11}\text{2}$}²)₁₀₊ ×vf_{$\text{7}\text{2}$} is suggested for the state at 2.7 MeV.     

Origins of very shallow photoconduction in Ge:Sb

Three new effects in the very shallow photoconduction spectrum ($\text{h}\text{?}$ω < 5 meV, T ～ 0.4K) of Ge:Sb have been observed: the spectrum is found to depend strongly on electric-field, background excitation spectrum, and on the spectrometer chopping frequency. These effects are interpreted as evidence that the spectra are the consequence of two distinct trapping centers whose spectra overlap; they thus do not support the interpretation of this photoconduction as due entirely to a D^? band.     

Halleffekt und anisotropie der beweglichkeit der elektronen in ZnO

Hallconstant, conductivity and Hall mobility of ZnO crystals were measured as function of temperature (4 °K < T < 370 °K) and orientation. Value and anisotropy of mobility can be explained (50 °K < T < 370 °K) by polar optical scattering, deformation potential sc., piezoelectric sc. and sc. by ionized impurities. The anisotropy of mobility is caused only by piezoelectric sc. Maximum values of μ_H are reached for μ_H ⊥ c, with 2400 cm²/V sec at 40 °K and for μ_H ¦ c with 1350cm²/Vsec at 60 °. Below 50 °K Hallconstant, conductivity and Hall mobility are influenced by impurity band conduction processes. The crystals have impurity concentration in the 10¹⁶ cm^?3 range, but they show different donor activation energies depending on growth conditions: Type I: 38,4 meV (50 °K < T < 100 °K) and Type II: 20,3 meV (50 °K < T < 100 °K) and 6 meV (25 °K < T < 50 °K).     

Non-cubic Mn2+-centers in BaF2

The EPR spectra of thermally treated BaF₂: Mn samples is reported. After thermal annealing at 900 K a trigonal Mn²⁺ center with g=2.000±0.005, |D|=2725±40MHz, |A|=265±10MHz, $\text{D}\text{A}\text{>0}$, is observed. Annealing at 1200 K produces an orthorhombic Mn²⁺ center with g=2.00±0.01, |D|=2430±40MHz, |E|=570±20MHz, |A|=265±10MHz, $\text{D}\text{A}\text{<0}$. The superhyperfine (SHF) structures due to interactions with the neighbouring fluorines indicates that the trigonal manganese interacts with four fluorines, three of them equivalent. The orthorhombic Mn²⁺ shows interaction with four equivalent fluorine nuclei.     

High-spin states in 40K investigated with the 26MG + 16O reaction

Yrast levels in ⁴⁰K and ⁴⁰Ar have been investigated with the ²⁶Mg(¹⁶O, pnγ)⁴⁰K and ²⁶Mg(¹⁶O, 2pγ)⁴⁰Ar reactions at a beam energy of 34 MeV. Gamma-ray angular distribution and γ-γ coincidence measurements have been performed with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. Gamma-ray linear polarizations have been measured with a three-crystal Ge(Li) Compton polarimeter. The ⁴⁰K decay scheme involves new high-spin levels at E_tx = 4365.6±0.3, 4875.6±0.4 and 6227.0±0.5 keV with lifetime limits of < 1, < 1 and < 2ps, respectively. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}\text{, 6}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 9}{}^{\mathrm{+}}\text{and}\text{(8, 10)}{}^{\mathrm{?}}$ to the ⁴⁰K levels at E_x = 0.89, 2.88, 4.37, 4.88 and 6.23 and of $\text{J}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{+}}\text{and}\text{6}{}^{\mathrm{+}}\text{to the}{}^{40}\text{Ar}$ levels at E_x = 2.89 and 3.46 MeV, respectively, have been obtained. Branching ratios and multipole mixing ratios are reported.     

Hopping conductance in electron irradiated n-type GaAs

A.c. conductivity is studied in n-type electron irradiated GaAs at helium temperatures. For T < 25 K variable range hopping $\text{[σ∝exp(-b/T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{)]}$ is observed. The experimentally observed low values of $\text{b(K}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{)}$ are discussed. At T > 30 K the conductivity exhibits an activation energy of 0.5 meV which is attributed to excitation into an upper band. The frequency dependence of hopping conductance is σ ∝ ω^S with S=1.8 and S=0.9 depending on the degree of radiation induced damage.     

Exchange energy for conduction electrons in (ZnMn)Se derived from spin-flip Raman scattering and magnetization

Spin-flip Raman scattering, magnetization, and susceptibility data for Zn_0.97Mn_0.03Se are reported. The exchange energy N_oα = 243 ± 10 meV for the conduction electrons is obtained from an analysis of the Raman and magnetization data. At large magnetic fields (H > 60 kOe), the spin-flip energy ΔE saturates at 14 meV. At low fields ΔE does not extrapolate to zero as H → 0, which is characteristic of scattering from donor-bound electrons. The low temperature magnetization curves are fit to a modified Brillouin function. The fit gives $\text{x}\text{?}\text{/x}\text{= 0.67}$ as the fraction of active magnetic ions, and an effective temperature T_eff = T + T_o with T_o = 1.1 K. The magnetic susceptibility follows a Curie-Weiss law between T = 150 and 280 K with a Curie-Weiss temperature θ = ?33 K.     

Stress-induced crossover phenomena in nickel above its Curie point

The temperature dependence of the anisotropic critical scattering of neutrons from a nickel single crystal was observed under the influence of elastic uniaxial mechanical stress of 140 g/mm². The temperature was varied between 10^-4 < τ = [T ? T_c(Δ)]/T_c(0) < 10^-2, and the momentum transfer between 1.4 × 10^-3 < $\text{q = (2π/λ) sin θ < 6.6 × 10}{}^{-3}\text{A}\text{?}{}^{\mathrm{-I}}$. The expected crossover from isotropic (Heisenberg) to anisotropic (XY) behaviour should occur between 10^-5 < τ < 10^-3, in good agreement with the experimental result.     

Cation self-diffusion and the isotope effect in Mn1−δO

Diffusion of ⁵⁴Mn in Mn_1?δO single crystals has been measured by a serial sectioning technique as a function of temperature (1000–1500°C) and deviation from stoichiometry (0.00003 < δ < 0.12). The value of m in the expression varies from about 6 at low Po₂ at all temperatures to a value approacing 2 at high Po₂ and high temperatures, thus suggesting that diffusion occurs by doubly charged vacancies at low Po₂ with increasing contributions from singly charged and neutral vacancies as Po₂ (and vacancy concentration) increases. For δ near 0.1, the values of D fall below the values extrapolated from smaller defect concentrations. The isotope effect for cation self-diffusion was measured by simultaneous diffusion of ⁵²Mn and ⁵⁴Mn in Mn_1?δO (0.0004 < δ < 0.116) at 1300 and 1500°C. The measured values of fΔK are independent of temperature within experimental error, and decrease from a value of 0.70 at low defect concentrations to 0.37 for large values of δ. The isotope-effect results suggest that diffusion occurs by single non-interacting vacancies at low defect concentrations; defect-defect interactions become important for δ ? 0.01. The defect-defect interactions may involve essentially individual defects or may result in defect clusters; the similarity between the present isotope-effect results and those for Fe_1?δ0 suggests that defect clustering plays a significant role in mass transport in Mn_1?δO at large values of δ.     

Longitudinal magnetoresistance in zero-gap CdxHg1−xTe at low temperatures

The longitudinal magnetoresistance Δ?₆(H)/?₀ is studied experimentally in gapless solid solutions Cd_xHg_1?xTe (0 < x < 0.15) for temperatures 1.3–15 K and the electron concentrations n ～ 10¹⁵ cm^?3. The temperature and the magnetic field dependences of the observed negative longitudinal magnetoresistance are explained by the resonant nature of electron scattering by an acceptor level. The quantitative analysis of the $\text{Δ?6(H)}\text{?}{}_0$ field dependence for weak magnetic fields under strong carrier degeneracy makes it possible to evaluate parameters of the acceptor level involved.     

On the possibility of finding light uncolored supersymmetric partners at present and future machines

Supersymmetric models allow the possibility of finding new light $\text{spin}\text{-}\text{1}\text{2}$ fermions (m <m_w, and perhaps m < 10–15 GeV, charged or neutral) that are (apart from mixing effects) the supersymmetric partners of W, Z⁰, and Higgs bosons. We provide a detailed analysis of their expected properties, production mechanisms, and signatures, with emphasis on detection at e⁺e^- colliders. Although the charged, $\text{spin}\text{-}\text{1}\text{2}$ particles resemble sequential leptons, it turns out that their properties differ enough that they might have been missed in the standard searches with normal cuts, and they still might be found with m < 18 GeV. A neutral, $\text{spin}\text{-}\text{1}\text{2}$ particle with m below about 30 GeV could exist with a clear decay signature and be singly produced at detectable rates at present machines (picobarn cross sections).