Magnetoelastic effects in terbium

The variation of the elastic modulus C₃₃ of terbium has been investigated as a function of temperature in the range 200–230 K, which includes the whole of the antiferromagnetic phase, and as a function of magnetic field applied along the easy magnetic direction, the b axis. Hysteresis in C₃₃ in the antiferromagnetic phase is interpreted in terms of spiral spin domains. The magnetic phase changes are reflected in anomalies in the elastic constant and these are used to produce a magnetic phase diagram of terbium. The final phase diagram has been compared with earlier measurements of magnetisation and magnetostriction.     

Field induced phase transitions on NdRhIn5 and Nd2RhIn8 antiferromagnetic compounds

In this work, we have investigated the low temperature magnetic phase diagram of the tetragonal NdRhIn₅ and Nd₂RhIn₈ single crystals by means of temperature and field dependent heat capacity and magnetic susceptibility measurements. These compounds order antiferromagnetically with a Néel temperature (T_N) of 11 and 10.7 K for NdRhIn₅ and Nd₂RhIn₈, respectively. The constructed magnetic phase of both compounds are anisotropic and show, as expected, a decrease of T_N as a function of the magnetic field for c crystallographic direction. However when the magnetic field is applied along of the c-axis, which is the magnetic easy axis, first-order-like field induced transitions are observed within the antiferromagnetic state. We compare the phase diagrams obtained for NdRhIn₅ and Nd₂RhIn₈ with those for their cubic relative NdIn₃.     

Effect of natural and magnetic convections on the structure of electrodeposited zinc-nickel alloy

The effects of a magnetic field applied in a direction parallel or perpendicular to the cathode substrate plane, during electrodeposition process of Zn-Ni alloy have been investigated by means of chronoamperometric measurements, X-ray diffraction and EDX analysis. The modification of crystal orientation of the alloy by the superimposition of a high magnetic field is discussed for alloys with a content of nickel range 6-13 at%. Whatever the phase composition obtained without magnetic field, either γ-Ni₅Zn₂₁ or a mixture of the γ and zinc phases, which depends on the concentration of Ni²⁺ in the electrolyte bath, the preferential orientation (1 0 1) of the zinc phase is always favoured with perpendicular and parallel magnetic field. There is no saturation of this effect with amplitude of B up to 8 T. A study of different geometric configurations of the cathode, which induce more or less natural convection, consolidates these results. The structural modifications of Zn-Ni alloy electrodeposits are thus probably due to a magnetohydrodynamic effect. An additional phenomenon is observed in presence of a perpendicular applied magnetic field since the (3 3 0) preferential orientation of the γ-Ni₅Zn₂₁ disappears with high values of B.     

Magnetic cluster developement in In1−x Mn x Sb semiconductor alloys

X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and magnetic measurements as a function of applied magnetic field and temperature for In_1?x Mn _x Sb (0.05≤x≤0.2) system are reported. Magnetic measurements performed at high and small magnetic field in ZFC and FC indicate the coexistence of ferromagnetic In_1?x Mn _x Sb solid solution and two types of magnetic cluster: ferromagnetic MnSb and ferrimagnetic Mn₂Sb. XPS valence band and Mn 2p core level spectra have confirmed the presence of MnSb and Mn₂Sb phases. TEM images show some manganese antimonide phase microinclusions with dimension between (30–40) nm.     

Crystal field measurement for Tb3+ in gold

The crystal field parameters for 0.01 at.% Tb³⁺ in gold have been determined by gamma-ray anisotropy measurements as a function of magnetic field. The values of the parameters are X = 0.90 ± 0.01 and W = -0.19 ± 0.002 K.     

Propagation of high power helicons in n-indium antimonide crystal

The propagation of high power helicon in n-InSb has been analysed taking into account the heating of the carriers by the electric field of the wave. The momentum and energy transfer of the electrons have been taken to be due to acoustic phonons and polar optical phonons scattering at 77°K respectively. The sample is assumed to be finite and the wave is incident on the semiconductor-free space interface. Calculations have been made for phase constant, attenuation constant, reflection coefficient and the electron temperature as function of the magnetic field and the wave amplitude. The theoretical results are found to be in qualitative agreement with the experimental observations of Laurinavichyus and Pozhela[14].     

Anomalous electrical properties of Si/Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> heterostructures with an electron transport channel in Si layers

The electrical properties of elastically stressed FET-like Si/Si_{1 ? x} Ge _x layered heterostructures (x < 0.2) with a modulated dopant concentration are studied. It is presumed that the amplitude of a narrow (～6-nm-thick) potential well in the Si layer corresponds to the amplitude of a fluctuation potential giving rise to nanoscale inhomogeneities in the Si channel. The structures in question undergo a phase transition from the insulating to metallic behavior as the electron density in the Si channel is varied. In a magnetic field, the structures with metallic conductivity have negative magnetoresistance (NMR) for both the longitudinal and transverse directions of the applied magnetic field with respect to the transport current passing through the structure. Investigating the dependence of NMR on the magnetic field strength showed that the main contribution to NMR is due to weak localization. Peculiar properties are also found in electrical measurements of the diode characteristics of the structures in question. In particular, the capacitance-voltage characteristics of these structures show well-defined resonance features, possibly related to one-and quasi-zero-dimensional inclusions existing in addition to two-dimensional charge carriers in the inhomogeneous two-dimensional film.     

Magnetic phase diagram for HO-50%tb from anomalies in ultrasonic propagation

Measurements of the elastic constant c₃₃ for Tb-50% Ho, as a function of temperature and magnetic field, have been used to determine the magnetic phase diagram of the alloy. Evidence for the four phases:paramagnetic, spiral spin antiferromagnetic, fan and ferromagnetic are presented. The true ferromagnetic phase is only found below 100 K even in fields of up to 7 Tesla.     

Magnetic ordering of interstitial iron in Fe1+xSb alloys

Mössbauer and magnetization measurements have been used to observe the magnetic ordering of interstitial iron atoms in the Fe_1+xSb phase in seven Fe:FeSb alloys. Short range magnetic ordering of the interstitials occurs only at temperatures well below the FeSb lattice Néel temperature. Magnetization measurements show that the interstitials form magnetic clusters which freeze in typical mictomagnetic fashion around 30 K. Field cooled alloys show an irreversible magnetization better described as classical superparamagnetism. Variations in the cluster freezing temperature with applied field are observed.     

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100?50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient α _B has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in α _B and this decrease can be several orders of magnitude.     

Level crossing in hyperfine interactions studied by perturbed γ-γ angular correlations

The technique of differential γ-γ angular correlation measurements has been applied to an investigation of the hyperfine interactions in the 482 keV level of¹⁸¹Ta. The activity was embedded in the lattice of a hafnium single crystal. The investigation of the quadrupole interaction gave for the electric interaction frequencyω ₀=(313±4) MHz. The electric field gradient was found to be axially symmetric, the asymmetry parameter beingη<0.1. Furthermore the combined collinear magnetic dipole and electric quadrupole interaction was studied. The angular correlation was investigated as a function of the strength of the external magnetic field by integral as well as time differential measurements. The integral anisotropy as function of the magnetic field has the shape of a resonance curve. The maximum was observed at a magnetic field ofB _res=(24.2±0.5)kG.     

Observation of Microwave-Induced Magnetoresistance Oscillations in a ZnO/Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O Heterojunction

Microwave-induced magnetoresistance and magnetoconductance oscillations in the two-dimensional electron system have been detected in a ZnO/Mg _x Zn_1–x O heterojunction. The structure has a high electron density of n = 6.5 × 10¹¹ cm^–2 and a very low mobility of 10⁵ cm² V^–1 s^–1. This clearly indicates that the mobility of two-dimensional electrons is not a critical parameter for the observation of microwave-induced oscillations. The samples were both Hall bars and Corbino disks. At least four oscillations have been resolved. Their amplitude increases with the magnetic field and all oscillations with numbers >1 have the same phase of 0.25. It has been shown that the microwave-induced photoelectromotive force is also a periodically oscillating function of the inverse magnetic field.     

Study of combined magnetic and electric hyperfine interactions for cadmium in Dysprosium by time differential perturbed angular correlations

The combined magnetic and electric hyperfine interaction at the site of a¹¹¹Cd impurity in magnetically ordered Dysprosium has been investigated as a function of temperature by time differential perturbed angular correlation measurements. Three different phases have been found in metallic Dy with transition temperatures of 85 and 179 °K in agreement with the results of bulk material measurements. In the paramagnetic phase above 179 °K a pure electric quadrupole interaction has been observed. The various contributions to the electric fieldgradient are analyzed and it is shown, that the dominant contribution comes from the conduction electrons. In the ferromagnetic phase which extends from 0 to 85 °K the magnetic hyperfine field at the site of¹¹¹Cd has the same temperature dependence as the spontaneous magnetization. The value of the hyperfine field at 4.2 °K is ¦H _eff¦=(221 ± 4) kG. At 85 °K a transition to the antiferromagnetic phase of Dy occurs, which shows a hysteresis of the transition temperature. In the antiferromagnetic phase the temperature dependence of the hyperfine field deviates considerably from the magnetization curve. It is suggested that this deviation might be due to a temperature dependence of thes-f exchange interaction.     

Field dependence of the thermal conductivity of K2CuCl4 · 2H2O near its ferromagnetic Curie temperature

The thermal conductivity of the ferromagnetic insulator K₂CuCl₄ · 2H₂O has been measured near its Curie temperature T_c. The measurements were made as a function of temperature in constant external magnetic field and as a function of field along isotherms. The results indicate a relaxation rate for magnetic critical scattering of phonons varies as H^?1/2.     

Structural characterization and magnetic properties of NiMg3x/2Cr0.9Fe1.1 − x O4

Magnesium-substituted nickel–chrome ferrites have been studied using X-ray diffraction and Mössbauer spectroscopy. A single cubic spinel phase was obtained in the range 0.0?≤?x?≤?0.4. The lattice parameter was found to decrease with the increase of Mg concentration. The Mössbauer spectra measured at 295 and 78 K of all samples showed magnetic patterns interpreted in term of the tetrahedral and octahedral sites occupancies. The magnetic hyperfine field of both sites decrease with the increase of the Mg concentration. The magnetic properties as a function of the Mg concentration have been explained on the basis of the cation distribution among the two crystallographic sites driven from the Mössbauer measurements.     

An experimental check of the electron distribution function in a current carrying plasma

The local current density obtained by means of Thomson scattering measurements (with a component of the scattering vector k along the current direction) [1] has been compared with the local current density obtained by means of magnetic field measurements made using a magnetic probe inserted in the plasma. A better agreement has been found between the two kinds of measurements when the scattered signals have been treated on the assumption of the Spitzer-Härm electron distribution function than on the assumption of the displaced Maxwellian one for the current carrying plasma.     

Real-space renormalization group study of a two-dimensional nonlinear massless field

The magnetic susceptibility of CuF₂·2H₂O has been measured as a function of magnetic field from 1.5 to 10 K. The spin-flop transition was observed and its value extrapolated to zero temperature is H_SF(0) = 30.5 kOe. This critical field is in very good agreement with data obtained from zero field measurements.     

Production of spin polarized 12N through heavy ion reactions

The structural and magnetic properties of Ho substituted BiFeO₃ (BHFO) have been investigated using ⁵⁷Fe Mössbauer spectroscopy and X-Ray diffraction (XRD) as a function of temperature. The Mössbauer spectrum obtained at room temperature for the as-synthesized BHFO sample exhibits broadened features due to the hyperfine field distributions related to the local variation of the neighbourhood of Fe and the magnetic hyperfine splitting patterns are indicative of magnetic ordering, mostly probably screwed or slightly antiferromagnetic. The spectrum was fitted with two superimposed asymmetric sextets, with similar hyperfine magnetic fields of B_hf1 = 48.0(1) T and B_hf2 = 49.0(1) T, corresponding to rhombohedral BFO. The hyperfine fields of the magnetic components decreased systematically with increasing temperature to a ‘field distribution’ just below the Néel temperature, T_N ~ 600 K. At temperatures above 600 K, the spectral line associated with the Bi₂₅FeO₄₀ impurity phase dominates the spectra. This phase is confirmed by XRD measurements. From the temperature dependence of the site populations of the spectral components an average Debye temperature of θ _D = 240(80) K has been estimated.     

Oscillations of echo amplitude in glasses in a magnetic field induced by nuclear dipole-dipole interaction

The influence of a magnetic field on the dipole echo amplitude in glasses (at temperatures of about 10 mK) induced by the dipole-dipole interaction of nuclear spins has been theoretically studied. It has been shown that a change in the mutual position of nuclear spins at tunneling and the Zeeman energy E _H of their interaction with the external magnetic field lead to a nonmonotonic magnetic-field dependence of the dipole echo amplitude. The approximation that the nuclear dipole-dipole interaction energy E _d is much smaller than the Zeeman energy has been found to be valid in the experimentally important cases. It has been shown that the dipole echo amplitude in this approximation may be described by a simple universal analytic function independent of the microscopic structure of the two-level systems. An excellent agreement of the theory with the experimental data has been obtained without fitting parameters (except for the unknown echo amplitude).     

Suitability of water based magnetic fluid with CoFe2O4 particles in hyperthermia

Magnetic susceptibility of the magnetic fluid with CoFe₂O₄ particles was measured in the low-frequency range in order to determine mean values of the magnetic grain size and the saturation magnetisation. The volume concentration of the solid phase (CoFe₂O₄) was also found. Results of the calorimetric measurements, in the range from 70 kHz to 1.7 MHz, confirmed the suitability of use of the medium studied in magnetic fluid hyperthermia, especially in the frequency region 600–800 kHz. The H²–law-type dependence of the specific absorption rate on the square amplitude of the magnetic field testified to the presence of superparamagnetic particles in the magnetic fluid. The minimum magnetic field intensity needed for successful hyperthermal treatment was experimentally determined.