High magnetic field behavior of iron impurities in chromium

Mössbauer measurements in ⁵⁷Fe in dilute FeCr alloys in external magnetic fields up to 140 kOe are presented. The magnetic hyperfine interactions are compared with results obtained by Herbert, Clark and Wilson and are discussed in terms of a model due to Housley and Dash.     

On the magnetic anisotropy of chromium

Magnetization and susceptibility measurements have been performed on a single crystal of chromium for field orientations parallel to the symmetry directions [100], [110] and [111] of the cubic unit cell. Particular emphasis is given to the weak temperature-orientation-and field-dependent contributions to the longitudinal (field parallel) susceptibility. For the high-temperature antiferromagnetic phase with transversally polarized spin-density wave (TSDW) the magnetic easy direction is along [100] and the magnetic hard one along [110]. In the low-temperature phase with longitudinal spin density waves (LSDW) the significance of these directions has reversed. The magnetization is not strictly a linear function of the field and shows a weak minimum atB ₀1.8 T in the TSDW phase. This minimum does shift discontinuously at the spin-flip transition (T _sf=132 K) to a value of 4.6 T in the LSDW phase. TheJ/B ₀-minimum is considered as due to the field induced change from the orientationally degenerated multidomain state into a state with only polarization directions perpendicular to the magnetic field.On leave from Academy of Mining and Metallurgy, Department of Solid State Physics, PL-30-059 Krakow, Poland     

Fluorescence of SO2 in a magnetic field in cooled ultrasound molecular beams

Reported to the All-Union Conference on Luminescence, devoted to the 100th anniversary of the birth of Academician S. I. Vavilov (26–28 March, 1991, Moscow).     

快冷Fe71Al29合金中的两个内耗峰

用一个计算机控制的倒扭摆研究了快冷Fe71Al29合金中的两个内耗峰.在快冷的Fe71Al29样品中分别在180℃(P1)，340 ℃(P2)和510℃(P3)出现了内耗峰，而在慢冷的Fe71Al29样品中只发现了P3峰.快冷样品中的P1和P2峰在从650℃冷却下来的测量过程中或在350℃经过较长时间的时效后消失，其峰高随时效时间的增加 而下降，直至消失.P1和P2峰都有弛豫特征，它们的激活能分别为：H1=1．03±0．08eV(P1峰)；H2=1．64±0．05eV(P2峰).P1峰被认为是无序合金中Al原子在四面体点阵内的最近邻运动所引起，P2峰则是无序合金中Al原子在四面体点阵内的次近邻运动所引起. 关键词： Fe-Al合金 内耗     

Levitation of a rapidly oscillating magnetic dipole above a metallic sheet

We show that such a magnetic dipole suspended at a height h above a conducting sheet experiences a lift force proportional to $1/h^2$. This represents an order of magnitude improvement over the $1/h^4$ lift obtained in the quasistatic limit.     

Features of the magnetic and dielectric behavior of mesophases of chromium (III) complexes with azacyclic ligands

Two paramagnetic (1, 2) chromium metallomesogens were studied by the EPR, magnetic-susceptibility, and dielectric-spectroscopy methods. These mesogens possess columnar liquid-crystal phase polymorphism. For mesogen 1 in the columnar Col_xd phase, an irreversible structural phase transition was detected by the EPR method. An anomalous nonlinear temperature dependence of the resonance fields of the EPR line positions and of the fine-structure parameter D in the mesophases of compound 1 was observed. It was shown that this anomaly is associated with the soft mode of crystal lattice. The dielectric spectroscopy data provide support for the existence of the soft mode, which is probably due to the transition of the system from a paraelectric to a dipole-ordered state. The structure of the hexagonal columnar plastic phase of mesogen 2 is formed by a single type of paramagnetic monomer chromium center and does not exhibit any specific features.     

Glass formation and local structure evolution in rapidly cooled PdNi alloy melt under high pressure

Using molecular-dynamics simulation, investigations of the local structure under high pressure and the glass formation in the PdNi alloy melt under high pressure are performed. The critical cooling rates for glass formation are reduced apparently with pressure. With increasing of pressure, a more compacted local structure with more ideal icosahedra than defected icosahedra is obtained, which may be one of the main factors for the contribution of the high pressure to the glass formation.     

Spectroscopic studies of the two-dimensional magnetic insulators chromium trichloride and chromium tribromide—I

The general aspects of the crystal field spectra of the two-dimensional magnetic insulators CrCl₃ and CrBr₃ are considered in detail, with special emphasis on the broad, spin-allowed ⁴T₂ and ⁴T₁ bands. A fit of the point-charge model Hamiltonian to the spectra is presented, with attention to the magnitude of the trigonal field effects. The temperature dependence of the ⁴T₂ and ⁴T₁ dipole strengths in the range 4.2< T < 300°K is analyzed in terms of single-ion (odd-parity trigonal field and odd-parity vibronic) and exchange mechanisms. A moment analysis of the M.C.D. spectra is performed, which (together with dipole strength temperature dependence data) yields a reasonable interpretation of the spin-allowed transition mechanism. The odd-parity crystal field is found to be the most important parity-breaking mechanism in both the ⁴T₂ and ⁴T₁ bands. Both also receive some contribution from the vibronic mechanism. This process is more significant for the ⁴T₂ state than for the ⁴T₁, and may involve a slightly anharmonic low-energy vibration. Evidence for a small exchange contribution is found in the ⁴T₂ band of both systems. Factors influencing the bandshapes are examined quantitatively. The antiresonance formalism of Sturge et al. is applied to the anomalous lineshapes of certain transitions in absorption and M.C.D. and one particularly complex bandshape (that for ⁴A₂ → ⁴T₂ - ²E - ²T₁ in CrCl₃) is analyzed through a computation.     

Anomalous behavior of textures in a magnetic field

It is shown that a qualitatively new type of transition to a nonlinear phase is possible in two-dimensional two-phase textures in a magnetic field. The anomalous growth of the effective response (higher-order correlation functions of the current) near the critical magnetic field is studied. The dependence of the critical magnetic field on the angles of microinclusions is calculated. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 115–119 (25 July 1997)     

Anomalies in the magnetic properties of copper impurity clusters in barium fluoride crystals

Copper impurity trimers with antiferromagnetic coupling between Cu²⁺ ions are synthesized in BaF₂ crystals. In some of the BaF₂: Cu crystals thus prepared, the concentration of copper stable trimers turns out to be higher than that of copper dimers and copper single centers. The BaF₂: Cu crystals are studied using electron paramagnetic resonance (EPR) spectroscopy at frequencies of 9.3, 23.0, and 37.0 GHz in the temperature range 4.2–77 K. It is found that the components of the effective tensor g for copper trimers depend strongly on the external magnetic field and temperature. A static model of the molecular structure of the copper trimer is proposed on the basis of the experimental data obtained.     

Magnetism and magnetic isomers in free chromium clusters

We have used the Stern-Gerlach deflection technique to study magnetism in chromium clusters of 20-133 atoms at temperatures between 60 and 100 K. We observe that these clusters have large magnetic moments and respond superparamagnetically to applied magnetic fields. Using superparamagnetic theory, we have determined the moment per atom for each cluster size and find that it often far exceeds the moment per atom present anywhere in the bulk antiferromagnetic lattice. Remarkably, our cluster beam contains two magnetically distinguishable forms of each cluster size with > or =34 atoms. We attribute this observation to structural isomers.     

Microwave absorption behavior of a polyaniline magnetic composite in the X-band

The development of nanosized materials is a subject of considerable interest both for understanding of the fundamental properties of magnetic materials for new technological applications. Polyaniline, composites Fe₃O₄/(PANI) with conducting, magnetic and electromagnetic properties with different amounts of Fe₃O₄ were successfully prepared. The samples were structurally characterized by scanning electron microscopy (SEM), X-ray diffraction and transmission electron microscopy (TEM) and magnetically, with a superconducting quantum interference device (SQUID) magnetometer. In order to explore microwave-absorbing properties in X-band, the composite nanoparticles were mixed with an epoxy resin to be converted into a microwave-absorbing composite. Microwave behavior with different Fe₃O₄/(PANI)-epoxy resin ratio was studied using a microwave vector network analyzer (VNA) in the range 7.5 to 13 GHz. For a constant thickness of 1.5 mm, absorption increases with the magnetite contents in the composites and in the oriented samples by the application of a magnetic field.     

Possible anomalous behavior of the sound velocity in a magnetic crystal

It is shown that spin-phonon interactions that arise from the strain modulation of the exchange interaction between localized spins can, under certain circumstances, cause an anomaly to appear in the temperature dependence of the sound velocity at a temperature T_sbelow the magnetic phase transition temperature of the ordered system. An interpretation of some recent measurements on uranium mononitride is attempted.     

Nonohmic behavior of semiconductors in a quantizing magnetic field

We have investigated the nonohmic resistivity of a nondegenerate semiconductor in quantizing magnetic fields for the case where acoustic phonons are the dominant scattering mechanism. The type of I-V characteristics found depends upon which of three mechanism are dominant. The three mechanisms are due to collisional broadening, inelasticities due to the finite phonon energy and phonon drag. When collistion broadening is important, the nonlinearities in the current voltage characteristic arise only from electron heating, while when the inelasticities are dominant, there is also an intrinsic nonlinearity in the characteristic. Finally, when phonon drag is dominant, high frequency acoustoelectric amplification will occur when the Hall velocity exceeds the sound velocity, i.e. V_H > S.For the case where inelasticities dominate, a region of negative differential resistance is obtained that should persist even when there is considerable optical phonon scattering.